View Filing Data

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 23, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	UNUM THERAPEUTICS INC.
Entity Central Index Key	0001622229
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		30,614,600
Entity Public Float			$ 40.2
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity File Number	001-38443
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5308248
Entity Address, Address Line One	200 Cambridge Park Drive
Entity Address, Address Line Two	Suite 3100
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02140
City Area Code	(617)
Local Phone Number	945-5576
Title of 12(b) Security	Common Stock, $0.001 Par Value
Trading Symbol	UMRX
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Portions of the registrant’s Proxy Statement for its 2020 Annual Meeting of Stockholders, which the registrant intends to file with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2019, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 37,424	$ 55,671
Marketable securities		22,923
Accounts receivable	2,000	1,668
Prepaid expenses and other current assets	1,167	740
Total current assets	40,591	81,002
Operating lease, right-of-use asset	5,285
Property and equipment, net	1,865	3,251
Restricted cash	1,255	1,255
Other assets	427	419
Total assets	49,423	85,927
Current liabilities:
Accounts payable	3,183	1,519
Accrued expenses and other current liabilities	7,131	5,477
Operating lease liability	1,619
Deferred revenue	1,315	17,949
Total current liabilities	13,248	24,945
Deferred rent		748
Operating lease liability, net of current portion	4,413
Total liabilities	17,661	25,693
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 150,000,000 shares authorized; 30,663,054 shares and 30,057,970 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	30	30
Additional paid-in capital	155,624	152,275
Accumulated other comprehensive loss		(12)
Accumulated deficit	(123,892)	(92,059)
Total stockholders’ equity	31,762	60,234
Total liabilities and stockholders' equity	$ 49,423	$ 85,927

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, Par value	$ 0.001	$ 0.001
Common stock, Shares authorized	150,000,000	150,000,000
Common stock, Shares issued	30,663,054	30,057,970
Common stock, Shares outstanding	30,663,054	30,057,970

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 22,499	$ 9,734
Operating expenses:
Research and development	43,709	38,285
General and administrative	10,968	7,454
Total operating expenses	54,677	45,739
Loss from operations	(32,178)	(36,005)
Other income (expense):
Interest income	267	1,153
Other income, net	78	320
Total other income, net	345	1,473
Net loss	(31,833)	(34,532)
Accretion of redeemable convertible preferred stock to redemption value		(16)
Net loss attributable to common stockholders	$ (31,833)	$ (34,548)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.04)	$ (1.39)
Weighted average common shares outstanding, basic and diluted	30,480,330	24,895,670
Comprehensive loss:
Net loss	$ (31,833)	$ (34,532)
Other comprehensive income (loss):
Unrealized gains on marketable securities, net of tax of $0	12	4
Total other comprehensive income	12	4
Comprehensive loss	$ (31,821)	$ (34,528)

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Unrealized gains (losses) on marketable securities, tax	$ 0	$ 0

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	IPO [Member]	Private Placement [Member]	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Common Stock [Member] Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPO [Member]	Additional Paid-in Capital [Member] Private Placement [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2017	$ (48,846)			$ 77,151	$ 10			$ 2,499			$ (16)	$ (51,339)
Beginning Balances, Shares at Dec. 31, 2017				20,771,850	10,201,690
Accretion of redeemable convertible preferred stock to redemption value				$ 16
Accretion of redeemable convertible preferred stock to redemption value	(16)							(16)
Conversion of redeemable convertible preferred stock to common stock	77,167			$ (77,167)	$ 13			77,154
Conversion of redeemable convertible preferred stock to common stock, Shares				(20,771,850)	13,229,362
Issuance of common stock sold in initial public offering, net of underwriting discounts, commissions and offering costs		$ 63,948	$ 5,000			$ 6	$ 1		$ 63,942	$ 4,999
Issuance of common stock sold in initial public offering, net of underwriting discounts, commissions and offering costs, Shares						5,985,000	416,666
Issuance of common stock upon exercise of stock options	609							609
Issuance of common stock upon exercise of stock options, Shares					225,252
Stock-based compensation expense	3,088							3,088
Unrealized gains on marketable securities	4										4
Net loss	(34,532)											(34,532)
Ending Balances at Dec. 31, 2018	60,234				$ 30			152,275			(12)	(92,059)
Ending Balances, Shares at Dec. 31, 2018					30,057,970
Adjustment to retained earnings for change in accounting policy	(6,188)											(6,188)
Issuance of common stock upon exercise of stock options	108							108
Issuance of common stock upon exercise of stock options, Shares					605,084
Stock-based compensation expense	3,241							3,241
Unrealized gains on marketable securities	12										$ 12
Net loss	(31,833)											(31,833)
Ending Balances at Dec. 31, 2019	$ 31,762				$ 30			$ 155,624				$ (123,892)
Ending Balances, Shares at Dec. 31, 2019					30,663,054

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (31,833)	$ (34,532)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,241	3,088
Depreciation and amortization expense	1,293	1,321
Net amortization (accretion) of premiums (discounts) on marketable securities	(53)	(246)
(Gain)/loss on disposal of fixed assets	(78)	10
Non-cash interest expense		23
Changes in operating assets and liabilities:
Accounts receivable	(332)	(838)
Prepaid expenses and other current assets	(8)	(250)
Operating lease, right-of-use asset	1,365
Other assets	(427)	(419)
Accounts payable	1,664	367
Accrued expenses and other current liabilities	1,760	2,883
Deferred rent		(52)
Operating lease liability	(1,472)
Deferred revenue	(16,634)	(3,844)
Net cash used in operating activities	(41,514)	(32,489)
Cash flows from investing activities:
Purchases of property and equipment	(33)	(549)
Proceeds from sale of property and equipment	204
Purchases of marketable securities		(47,682)
Maturities and sales of marketable securities	22,988	37,700
Net cash provided by (used in) investing activities	23,159	(10,531)
Cash flows from financing activities:
Proceeds from initial public offering, net of underwriting discounts and commissions		66,793
Proceeds from private placement concurrent with initial public offering		5,000
Proceeds from issuance of common stock upon stock option exercises	108	609
Payments of initial public offering costs		(2,056)
Net cash provided by financing activities	108	70,346
Net increase (decrease) in cash, cash equivalents and restricted cash	(18,247)	27,326
Cash, cash equivalents and restricted cash at beginning of period	56,926	29,600
Cash, cash equivalents and restricted cash at end of period	$ 38,679	56,926
Supplemental disclosure of noncash investing and financing information:
Conversion of convertible redeemable preferred stock into common stock		77,154
Accretion of redeemable convertible preferred stock to redemption value		$ 16

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Unum Therapeutics, Inc. (“Unum” or “the Company”) is a biopharmaceutical company focused on developing curative cell therapies for solid tumors. Unum’s novel proprietary technology includes Bolt-On Chimeric Receptor (BOXR), designed to improve the functionality of engineered T cells by incorporating a “bolt-on” transgene to overcome resistance of the solid tumor microenvironment (TME) to T cell attack. Unum also developed product candidates using its novel proprietary technology, Antibody-Coupled T cell Receptor (ACTR), an autologous engineered T-cell therapy that combines the cell-killing ability of T cells and the tumor-targeting ability of co-administered antibodies to exert potent antitumor immune responses. Unum was incorporated in March 2014 under the laws of the State of Delaware.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

On April 3, 2018, the Company completed an initial public offering (“IPO”) of its common stock and issued and sold 5,770,000 shares of common stock at a public offering price of $12.00 per share, resulting in net proceeds of $61.5 million after deducting underwriting discounts and commissions and other offering costs. In addition, Seattle Genetics, Inc. (“Seattle Genetics”) purchased from the Company, concurrently with the IPO in a private placement, $5.0 million of shares of common stock at a price per share equal to the initial public offering price, or 416,666 shares (the “concurrent private placement”). Upon closing of the IPO, the Company’s outstanding redeemable convertible preferred stock automatically converted into shares of common stock. On April 25, 2018, the Company issued and sold an additional 215,000 shares of its common stock at the IPO price of $12.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $2.4 million after deducting underwriting discounts and commissions.

On April 1, 2019, the Company filed a shelf registration statement on Form S-3 with the SEC. The shelf registration statement allows the Company to sell from time-to-time up to $150 million of common stock, preferred stock, debt securities, warrants, or units comprised of any combination of these securities, for its own account in one or more offerings. The terms of any offering under the shelf registration statement will be established at the time of such offering and will be described in a prospectus supplement filed with the SEC prior to the completion of any such offering.

Additionally, on April 1, 2019 and pursuant to the Form S-3, the Company entered into a Sales Agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $50.0 million through Cowen as the sales agent. As of December 31, 2019, no shares have been sold under this Sales Agreement.

As announced on March 2, 2020, the Company initiated a reduction in force that is intended to result in the termination of approximately 60% of the Company’s employee workforce, or approximately 43 employees. These reductions are expected to be substantially completed by the end of first quarter of 2020. The reduction in force was approved in connection with the Company’s restructuring plans to prioritize resources towards advancing its preclinical program, BOXR1030, for the treatment of solid tumor cancers.

In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued.

The Company’s financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. We believe that our existing cash and cash equivalents of $37.4 million as of December 31, 2019 will enable us to fund our operating expenses and capital expenditure requirements into mid-2021. Based on our available cash resources, recurring losses and cash outflows from operations, since our inception, an expectation of continuing operating losses and cash outflows from operations for the foreseeable future, and the removal of revenues generated under the Collaboration Agreement with Seattle Genetics as a result of the termination of that Agreement, we have concluded that there is substantial doubt about our ability to continue as a going concern. The financial statements do not include any adjustments that might result from the outcome of this uncertainty.

On December 31, 2019, the Company received a deficiency letter from the Listing Qualifications Department of the Nasdaq Stock Market notifying it that, for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued inclusion on the Nasdaq Global Select Market (“Minimum Bid Price Requirement”). In accordance with Nasdaq Listing Rules, the Company has an initial period of 180 calendar days to regain compliance with the minimum bid price rule. If we do not regain compliance with the Minimum Bid Price Requirement by June 29, 2020, then, under Nasdaq Listing Rules, we may transfer to The Nasdaq Capital Market, provided that we meet the continued listing requirement for the market value of publicly held shares and all other initial listing standards for The Nasdaq Capital Market, except for the Minimum Bid Price Requirement, and we would need to provide written notice to Nasdaq of our intention to cure the deficiency during the additional compliance period. Following a transfer to The Nasdaq Capital Market, under Nasdaq Listing Rules, we may be eligible for an additional 180 calendar day compliance period. The Company is actively monitoring its stock price and will consider any and all options available to the Company to regain compliance. The alternatives to trading on the Nasdaq Stock Market or another national securities exchange are generally considered to be less efficient and less broad-based than the national securities exchanges and the liquidity of the Company’s common stock will likely be reduced if we fail to regain compliance with the Minimum Bid Price Requirement.

The Company expects that it will continue to incur significant expenses in connection with its ongoing business activities. The Company will need to seek additional funding through equity offerings, debt financings, collaborations, licensing arrangements and other marketing and distribution arrangements, partnerships, joint ventures, combinations or divestitures of one or more of its businesses. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborative arrangements or divest its assets. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or product candidates. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations.

The Company’s consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Principles of Consolidation

The accompanying consolidated financial statements include those of the Company and its wholly-owned subsidiary, Mono, Inc. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions.

Risks and Uncertainties

Impact of the COVID-19 Coronavirus

In December 2019, a novel strain of coronavirus, now referred to as COVID-19, surfaced in Wuhan, China. The virus continues to spread globally, has been declared a pandemic by the World Health Organization and has spread to over 100 countries, including the United States. The impact of this pandemic has been and will likely continue to be extensive in many aspects of society, which has resulted in and will likely continue to result in significant disruptions to the global economy, as well as businesses and capital markets around the world.

Potential impacts to our business include temporary closures of our facilities or those of our vendors, disruptions or restrictions on our employees’ ability to travel, disruptions to or delays in ongoing laboratory experiments and operations and the potential diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, and our ability to raise capital.

Concentrations of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains most of its cash and cash equivalents at three accredited financial institutions. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party vendors for its product candidates. In particular, the Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and process its product candidates for its development programs. These programs could be adversely affected by a significant interruption in the manufacturing process.

Debt Issuance Costs

The Company capitalizes certain legal and other third-party fees that are directly associated with obtaining access to capital under credit facilities. Debt issuance costs incurred in connection with obtaining access to capital are recorded in prepaid expenses and other current assets and are amortized over the availability period or term of the credit facility. Debt issuance costs related to a recognized debt liability are recorded as a direct reduction of the carrying amount of the debt liability.

Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

Restricted cash consists of security deposits in separate restricted bank accounts as required under the terms of the Company’s lease agreement for its Corporate Office in Cambridge, Massachusetts.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:

		Estimated Useful Life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of life of lease or 10 years

Costs for capital assets not yet placed into service are capitalized as construction-in-progress and depreciated in accordance with the above guidelines once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2019 or 2018.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities.

Marketable Securities

The Company’s marketable securities, consisting of debt securities, are classified as available-for-sale and are reported at fair value. Unrealized gains and losses on available-for-sale debt securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity (deficit). Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss. The Company classifies its marketable securities with maturities beyond one year as short-term, based on their highly liquid nature and because such marketable securities are available for current operations.

The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Classification and Accretion of Redeemable Convertible Preferred Stock

The Company classified redeemable convertible preferred stock outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company. The carrying values of the redeemable convertible preferred stock were accreted to their respective redemption values from the date of issuance through the earliest date of redemption.

Segment Information

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is the development and commercialization of immunotherapy products for cancer. All of the Company’s tangible assets are held in the United States.

Leases

The Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the assets’ economic benefits. The Company determines the initial classification and measurement of its operating right-of-use assets and operating lease liabilities at the lease commencement date, and thereafter if modified. The lease term includes any renewal options that the Company is reasonably assured to exercise. The Company’s policy is to not record leases with an original term of twelve months or less on its consolidated balance sheets. The Company’s only existing lease is for office space.

The right-of-use asset represents the right to use the leased asset for the lease term. The lease liability represents the present value of the lease payments under the lease. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term.

Lease payments included in the measurement of the lease liability consist of the following: the fixed noncancelable lease payments, payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and payments for early termination options unless it is reasonably certain the lease will not be terminated early.

Leases may contain rent escalation clauses and variable lease payments that require additional rental payments in later years of the term, including payments based on an index or inflation rate. Payments based on the change in an index or inflation rate, or payments based on a change in the Company’s portion of the operating expenses, including real estate taxes and insurance, are not included in the initial lease liability and are recorded as a period expense when incurred. The operating leases may include an option to renew the lease term for various renewal periods and/or to terminate the leases early. These options to exercise the renewal or early termination clauses in the Company’s operating leases were not reasonably certain of exercise as of the date of adoption and these have not been included in the determination of the initial lease liability or operating lease expense.

Rent expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments and is included in operating expense in the consolidated statements of operations and comprehensive loss. For finance leases, any interest expense is recognized using the effective interest method and is included within interest expense. The Company has no financing leases.

Revenue Recognition

On January 1, 2018, the Company adopted Accounting Standards Codification (ASC) Topic 606, Revenue from Contracts with Customers (ASC 606), which amended revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. ASC 606 provides a five-step framework whereby revenue is recognized when control of promised goods or services is transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation. The Company only applies the five-step model to contracts when collectability of the consideration to which the Company is entitled in exchange for the goods or services transferred to the customer is determined to be probable.

At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses whether the goods or services promised within each contract are distinct and, therefore, represent a separate performance obligation. Goods and services that are determined not to be distinct are combined with other promised goods and services until a distinct bundle is identified. In determining whether goods or services are distinct, management evaluates certain criteria, including whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (capable of being distinct) and (ii) the good or service is separately identifiable from other goods or services in the contract (distinct in the context of the contract).

At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation.

The Company then determines the transaction price, which is the amount of consideration expected to be received from a customer in exchange for the promised goods or services. The Company’s estimate of the transaction price for each contract includes all fixed and variable consideration to which it expects to be entitled. Variable consideration includes payments in the form of collaboration payments, regulatory milestone payments, commercial milestone payments, and royalty payments. For collaboration, regulatory milestone, and commercial milestone payments, the Company evaluates whether it is probable that the consideration associated with each milestone will not be subject to a significant reversal in the cumulative amount of revenue recognized. Amounts that meet this threshold are included in the transaction price using the most likely amount method, whereas amounts that do not meet this threshold are considered constrained and excluded from the transaction price until they meet this threshold. At the end of each subsequent reporting period, the Company re-evaluates the probability of a significant reversal of the cumulative revenue recognized for its milestones, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis. The Company excludes sales-based royalties until the sale occurs.

ASC 606 requires the Company to allocate the arrangement consideration on a relative standalone selling price basis for each performance obligation after determining the transaction price of the contract and identifying the performance obligations to which that amount should be allocated. The relative standalone selling price is defined as the price at which an entity would sell a promised good or service separately to a customer. If other observable transactions in which the Company has sold the same performance obligation separately are not available, the Company is required to estimate the standalone selling price of each performance obligation. Key assumptions to determine the standalone selling price may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it.

For performance obligations consisting of licenses and other promises (combined performance obligations), the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company recognizes revenue using the cost-to-cost method, which it believes best depicts the transfer of control to the customer. Under the cost-to-cost method, the extent of progress towards completion is measured based on the ratio of actual costs incurred to the total estimated costs expected upon satisfying the identified performance obligation. Under this method, revenue will be recorded as a percentage of the estimated transaction price based on the extent of progress towards completion. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement. The estimate of the measure of progress and estimate of variable consideration to be included in the transaction price will be updated at each reporting date as a change in estimate. The amount of transaction price allocated to the satisfied portion of the performance obligation, based on the Company’s measure of progress, will be recognized immediately on a cumulative catch-up basis, resulting in an adjustment to revenue in the period of change. The amount related to the unsatisfied portion will be recognized as that portion is satisfied over time.

If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license.

Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company recognizes deferred revenue by first allocating from the beginning deferred revenue balance to the extent that the beginning deferred revenue balance exceeds the revenue to be recognized. Billings during the period are added to the deferred revenue balance to be recognized in future periods. To the extent that the beginning deferred revenue balance is less than revenue to be recognized during the period, billings during the period are allocated to revenue. In the event that a collaboration agreement was to be terminated and the Company had no further performance obligations, the Company would recognize as revenue any portion of the upfront payment and other payments that had not previously been recorded as revenue and were classified as deferred revenue at the date of such termination.

Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. The Company expenses incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that the Company would have recognized is one year or less or the amount is immaterial. The Company has not capitalized any costs to obtain its contract.

Collaborative Arrangements

The Company records the elements of collaboration agreements that represent joint operating activities in accordance with ASC Topic 808, Collaborative Arrangements (ASC 808). Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities, are recorded as collaborative arrangements. The Company considers the guidance in ASC Topic 606 in determining the appropriate treatment for the transactions between the Company and its collaborative partners and the transactions between the Company and third parties. Generally, the classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. To the extent revenue is generated from a collaboration, the Company will recognize its share of the net sales on a gross basis if it is deemed to be the principal in the transactions with customers, or on a net basis if the Company is instead deemed to be the agent in the transactions with customers, consistent with the guidance in Topic 606. When the Company has concluded that it has a customer relationship with one of its collaborators, such as that with Seattle Genetics, the Company follows the guidance in ASC 606.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs and laboratory supplies, depreciation, manufacturing expenses and external costs of outside vendors engaged to conduct preclinical development activities and clinical trials as well as the cost of licensing technology. Research and development costs include costs for the development of product candidates that the Company is jointly developing with Seattle Genetics and for which it receives reimbursement as specified in the agreement.

Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Stock-Based Compensation

The Company measures stock options and other stock-based awards granted to employees, non-employees and directors based on their fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions and applies the graded-vesting method to all awards with performance-based vesting conditions or to awards with both service-based and performance-based vesting conditions.

For performance-based stock options, we begin to recognize expense when we determine that the achievement of such performance conditions is deemed probable. This determination requires significant judgment by management. At the probable date, we record a cumulative expense catch-up, with remaining expense amortized over the remaining service period.

The Company estimates the fair value of stock-based awards to employees and non-employees using the Black-Scholes option-pricing model, which requires the input of highly subjective assumptions, including (a) the expected volatility of its stock, (b) the expected term of the award, (c) the risk-free interest rate, and (d) expected dividends. Due to the lack of a public market for the trading of the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based the estimate of expected volatility on the historical volatility of a group of companies in the pharmaceutical and biotechnology industries in a similar stage of development and that are publicly traded. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company has estimated the expected life of employee stock options using the "simplified" method, whereby, the expected life equals the average of the vesting term and the original contractual term of the option. The risk-free interest rates for periods within the expected life of the option are based on the U.S. Treasury yield curve in effect during the period the options were granted.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2019 and 2018, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities.

Net Income (Loss) per Share

Prior to the closing of its IPO, the Company followed the two-class method when computing net income (loss) per share, as the Company had issued shares that met the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred stock contractually entitled the holders of such shares to participate in dividends but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reported a net loss, such losses were not allocated to such participating securities, and as a result, basic and diluted net loss per share were the same.

Subsequent to the closing of its IPO, basic net income (loss) per common share is computed by dividing the net income (loss) by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per common share is computed by dividing net income (loss) by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options. Accordingly, in periods in which the Company reported a net loss, dilutive common shares were not assumed to have been issued as their affect was anti-dilutive, and as a result, diluted net loss per common share was the same as basic net loss per common share.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. The guidance is effective for public entities for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years, and early adoption is permitted. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842), which added an optional transition method under which financial statements may be prepared under the revised guidance for the year of adoption, but not for prior years. Under the latter method, entities will recognize a cumulative catch-up adjustment to the opening balance of retained earnings in the period of adoption. The Company has adopted the new leasing standard on January 1, 2019, using a modified retrospective transition approach to be applied to leases existing as of, or entered into after, January 1, 2019. The Company has applied the “package of practical expedients”, which permits the Company not to reassess under the new standards for prior conclusions about lease identification, lease classification and initial direct costs.

Upon adoption of the new leasing standards, the Company recognized a lease liability of $7.5 million and a related right-of-use asset of $6.7 million on its consolidated balance sheet with the difference being due to the elimination of previously reported deferred rent. The adoption of the standard did not have a material impact on the results of operations or cash flows.

In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent with the accounting for employee share-based compensation. ASU 2018-07 is required to be adopted for annual periods beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company early adopted ASU 2018-07 on January 1, 2018. The adoption of this guidance did not have a material impact on its consolidated financial statements.

Recently Issued Accounting Pronouncements

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018-13”). The new standard removes certain disclosures, modifies certain disclosures and adds additional disclosures related to fair value measurement. The new standard will be effective beginning January 1, 2020 and early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2018-13 will have on its consolidated financial statements.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (“ASU 2018-18”). The main provisions of ASU 2018-18 include: (i) clarifying that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and (ii) precluding the presentation of transactions with collaborative arrangement participants that are not directly related to sales to third parties together with revenue. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The guidance per ASU 2018-18 is to be adopted retrospectively to the date of initial application of Topic 606. The Company is currently evaluating the impact that the adoption of ASU 2018-18 will have on its consolidated financial statements.

Marketable Securities and Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Marketable Securities and Fair Value Measurements

3. Marketable Securities and Fair Value Measurements

Marketable securities by security type consisted of the following (in thousands):

December 31, 2019

Amortized

Cost

Gross

Unrealized

Gains

Gross

Unrealized

Losses

Fair

Value

U.S. Treasury bills and notes (due within one year)

—

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury bills and notes (due within one year)	$	22,935	$	—	$	(12	)	$	22,923
	$	22,935	$	—	$	(12	)	$	22,923

The following tables present the Company’s fair value hierarchy for its cash equivalents and marketable securities, which are measured at fair value on a recurring basis (in thousands):

	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	485	$	—	$	485
Marketable securities:
U.S. Treasury bills and notes		—		—		—		—
	$	—	$	485	$	—	$	485

	Fair Value Measurements at December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	52,100	$	—	$	52,100
Marketable securities:
U.S. Treasury bills and notes		22,923		—		—		22,923
	$	22,923	$	52,100	$	—	$	75,023

U.S. Treasury bills and notes were valued based on Level 1 inputs. Money market funds were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

During the years ended December 31, 2019 and 2018, there were no transfers between Level 1, Level 2 and Level 3.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

	December 31,
	2019			2018
Laboratory equipment	$	5,529		$	5,801
Computer equipment and software		224			203
Furniture and fixtures		317			317
Leasehold improvements		426			426
Total property and equipment		6,496			6,747
Accumulated depreciation and amortization		(4,631	)		(3,496	)
Property and equipment, net	$	1,865		$	3,251

Depreciation and amortization expense was $1.3 million for each of the years ended December 31, 2019 and 2018.

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

5. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	December 31,
	2019		2018
Accrued employee compensation and benefits	$	2,500	$	1,599
Accrued external research and development expense		2,987		1,799
Accrued external manufacturing costs		750		1,015
Other		894		1,064
	$	7,131	$	5,477

Collaboration Agreement

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Collaboration Agreement

6. Collaboration Agreement

In June 2015, the Company entered into a Collaboration Agreement with Seattle Genetics (the “Collaboration Agreement”). Pursuant to the terms of the Collaboration Agreement, the Company and Seattle Genetics agreed to jointly develop two product candidates incorporating our ACTR platform and Seattle Genetics’ antibodies. Under the Collaboration Agreement, we conduct preclinical research and clinical development activities related to the two specified product candidates through Phase 1 clinical development, and Seattle Genetics provides the funding for those activities. Seattle Genetics will continue development activities of the two specified product candidates in collaboration with the Company unless it exercises one of its two options to opt-out from further development and commercialization activities for each of the two product candidates during specified periods subsequent to Phase 1 clinical development. In addition, the Company has an option to opt-out from further development and commercialization activities for each of the two product candidates, exercisable during a specified period subsequent to Phase 2 clinical development. If neither party exercises its options to opt-out from further development and commercialization activities for each product candidate, the parties will work together to co-develop and fund each product candidate after Phase 1 clinical development and Seattle Genetics will pay the Company specified collaboration and milestone payments upon the occurrence of specified events related to each product candidate of up to an aggregate of $400.0 million across the two active product candidates, consisting of $100.0 million of aggregate collaboration payments, $100.0 million of aggregate regulatory milestone payments and $200.0 million of aggregate commercial milestone payments. The individual collaboration payments are payable upon the occurrence of specified clinical development events and range up to $30.0 million per product candidate. The individual regulatory milestone payments are payable upon the first regulatory approval of each product in the United States and the first regulatory approval of each product in specified territories outside the United States and range up to $35.0 million per product. The individual commercial milestone payments are payable upon the achievement of specified aggregate annual net sales for each product and range up to $60.0 million per product. Through December 31, 2019, no milestones had been achieved or paid.

In the event that a party exercises its option to opt-out from further development and commercialization of a product candidate, the parties will negotiate in good faith the payment obligations of the continuing party to the opt-out party for that product candidate. Unless either party exercises its right to opt-out from further development and commercialization activities, the Company and Seattle Genetics will co-commercialize and share profits and losses equally on any co-developed products in the United States. Seattle Genetics will retain exclusive commercial rights outside of the United States and is obligated to pay the Company tiered royalties ranging in the high single-digit to mid-teens percentages based on net sales outside of the United States. The royalties are payable on a product-by-product basis and may be reduced in specified circumstances. Seattle Genetics will purchase ACTR T cells from the Company on a cost-plus basis for its commercial supply outside of the United States.

Unless earlier terminated, the Collaboration Agreement will expire on a product-by-product basis in the United States on the date on which neither party is researching, developing or commercializing such product. Outside of the United States, the Collaboration Agreement will expire on a product-by-product and country-by-country basis at the end of the applicable royalty term for such product in such country. The royalty term will be in effect beginning at the first commercial sale of a product and ending upon the later to incur of (i) expiration of the last valid claim within any patent right that the Company or Seattle Genetics has that would be infringed by the manufacture, use, sale, offer for sale, or importation of such product in such country, (ii) the end of any regulatory exclusivity periods that apply to the manufacture, use, sale, offer for sale, or importation of such product in such country, or (iii) ten years from the first commercial sale of such product in such country.

The Company evaluated whether the performance obligations under this agreement, including the license, research and development services, steering committee participation, and manufacturing services should be accounted for as a single unit or multiple units of accounting. Because of the risk associated with obtaining approval for commercial sale in the Seattle Genetics territories, manufacturing services associated with commercial supply were considered a contingent deliverable and will be accounted for if and when performed. The Company accounts for the license, research and development services, and steering committee services under ASC 606 as a single performance obligation under the Collaboration Agreement.

At the inception of the arrangement, the Company evaluated the separate options held by Seattle Genetics (i) to expand the collaboration to include a third product candidate upon payment of an additional fee and (ii) to continue development activities beyond Phase 1 clinical development activities and determined that each option was substantive. Each option represents a separate buying decision by Seattle Genetics, is not essential to the functionality of the current deliverables, and was not offered at a substantially discounted price. As each option was deemed to be substantive, the item underlying the option was not considered to be a deliverable at the inception of the arrangement and the incremental fees associated with each option were not included in the initial arrangement consideration. These options will be accounted for as separate units of accounting when, and if, such options are exercised by Seattle Genetics.

The Company determined that the transaction price includes the $25.0 million upfront payment and the total payments to be earned for preclinical research and clinical development activities. The total transaction price is being recognized as revenue over the performance period using the cost-to-cost method, which the Company believes best depicts the transfer of control to the customer. As payments from Seattle Genetics are earned related to the Company’s preclinical research and clinical development activities through Phase 1 clinical development, the Company recognizes as revenue the portion of the payments equal to the percentage of the cost of completed research and development activities to the cost of the total estimated research and development activities. Any future milestone payments, if any, will be recognized, along with the other arrangement consideration, over the remaining estimated period of performance, if any, beginning at the time a milestone payment is earned, with a cumulative catch up being recognized for the completed portion of the estimated research costs.

On January 16, 2020, the Company and Seattle Genetics announced that they have entered into an agreement to terminate the Collaboration Agreement (the “Termination Agreement”) effective as of January 16, 2020 (the “Termination Effective Date”), pursuant to which the Parties will cease all research, development, manufacturing and other exploitations of any and all research candidates and development candidates under the Collaboration Agreement, including, without limitation, the development candidate ACTR-BCMA and a research candidate.

Pursuant to terms of the Termination Agreement, among other things, (i) Seattle Genetics paid the Company $5.75 million, (ii) Seattle Genetics surrendered, assigned and transferred to the Company all of its right, title and interest in the 831,847 shares of the Company’s common stock owned by Seattle Genetics, (iii) the Company will continue to pay all expenses for the wind-down of the ACTR-BCMA trial and (iv) Seattle Genetics paid all research and development costs incurred through the Termination Effective Date. In addition, the exclusivity provisions in the Collaboration Agreement terminate and each party will be free to research, develop and commercialize its individual intellectual property either by themselves or with third parties, subject to the intellectual property rights of the other party.

In considering all facts known prior to December 31, 2019, including the suspension of the ATTCK-17-01 clinical trial as announced in November 2019 and the intention of the parties to terminate the Collaboration Agreement, the Company has adjusted the estimated transaction price to be the $25.0 million upfront payment and the total payments to be earned for preclinical research and clinical development activities through the Termination Date. The Company has also adjusted the costs to complete the remaining performance obligations to represent our best estimate as of December 31, 2019. The Termination Payment of $5.75 million and return of the 831,847 common shares will be accounted for in 2020 after the Termination Effective Date as these are contingent upon execution of the Termination Agreement.

The Company recorded a cumulative adjustment to revenue as a result of the change in the estimated transaction price and the estimated costs to complete the remaining performance obligations in the fourth quarter of 2019. Under the Collaboration Agreement, the Company recognized revenue of $22.5 million and $9.7 million for the years ended December 31, 2019 and 2018, respectively. As of December 31, 2019 and 2018, deferred revenue of $1.3 million and $17.9 million, respectively, was recorded related to this agreement. All revenue recognized in 2019 is from the deferred balance as of December 31, 2018 plus additional amounts received as reimbursement of research and development costs from Seattle Genetics. As of December 31, 2019, the aggregate amount of the transaction price allocated to the remaining performance obligation for preclinical research and clinical development activities related to the two specified product candidates through Phase 1 is estimated to be approximately $1 million, which is expected to be recognized as revenue through December 31, 2020.

Loan and Security Agreement

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Loan and Security Agreement

7. Loan and Security Agreement

The Company has a loan and security agreement (the “Loan Agreement”) with Pacific Western Bank (“PWB”), entered into in 2017, which provided for term loan borrowings of up to $15.0 million through January 19, 2019. Borrowings under the Loan Agreement bear interest at a variable annual rate equal to the greater of (i) the prime rate plus 0.25% or (ii) 3.75%, and were payable over an interest-only period until January 19, 2019, followed by a 24-month period of equal monthly payments of principal and interest. All amounts outstanding as of the maturity date of January 19, 2021 become immediately due and payable. In January 2019, the Company amended the Loan Agreement to extend the available date for borrowings from January 19, 2019 to June 30, 2019 and extend the interest only period from January 19, 2019 to June 30, 2020, with the possibility of further extension to March 31, 2021 if certain equity financing considerations are met. As of December 31, 2019, these equity financing considerations have not been met. Additionally, the loan repayment period will be over a 24-month period following the end of the interest-only period. In June 2019, the Company further amended the Loan Agreement to extend the available date for borrowings from June 30, 2019 to June 30, 2020. On July 31, 2019, the Company amended the Loan Agreement to provide for changes to the primary depository requirements with PWB.

In connection with the loan and security agreement, the Company agreed to enter into warrant agreements with the lender pursuant to which warrants will be issued to purchase a number of shares of the Company’s capital stock equal to 1% of the amount of each term loan borrowing under the loan and security agreement, divided by the applicable exercise price.

No amounts have been borrowed as term loans under the loan and security agreement as of December 31, 2019. Borrowings under the Loan Agreement are collateralized by substantially all of the Company’s assets, except for its intellectual property. Under the Loan Agreement, the Company has agreed to affirmative and negative covenants to which it will remain subject until maturity. These covenants include limitations on the Company’s ability to incur additional indebtedness and engage in certain fundamental business transactions, such as mergers or acquisitions of other businesses. There are no financial covenants associated with the Loan Agreement. Events of default under the Loan Agreement include failure to make payments when due, insolvency events, failure to comply with covenants and material adverse effects with respect to the Company.

Preferred Stock and Common Stock

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Preferred Stock and Common Stock

8. Preferred Stock and Common Stock

Preferred Stock

The Company had issued Series A redeemable convertible preferred stock (the “Series A preferred stock”) and Series B redeemable convertible preferred stock (the “Series B preferred stock”). The Series A preferred stock and the Series B preferred stock are collectively referred to as the “Preferred Stock”. The Preferred Stock converted to shares of common stock on a 1:1.57 basis upon the closing of the IPO on April 3, 2018.

Common Stock

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

On March 16, 2018, the Company effected a one-for-1.57 reverse stock split of its issued and outstanding shares of common stock. Accordingly, all share and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split.

On April 3, 2018, the Company completed an IPO of its common stock and issued and sold 5,770,000 shares of common stock at a public offering price of $12.00 per share, resulting in net proceeds of $61.5 million after deducting underwriting discounts and commissions and other offering costs. In addition, Seattle Genetics purchased from the Company, concurrently with the IPO in a private placement, $5.0 million of shares of common stock at a price per share equal to the initial public offering price, or 416,666 shares. Upon closing of the IPO, the Company’s authorized shares of common stock were increased to 150,000,000 shares. The Company also authorized 10,000,000 shares of undesignated preferred stock.

On April 25, 2018, the Company issued and sold an additional 215,000 shares of its common stock at the IPO price of $12.00 per share pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds of $2.4 million after deducting underwriting discounts and commissions.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

2015 Stock Incentive Plan

The Company’s 2015 Stock Incentive Plan (the “2015 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2015 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The board of directors could also delegate to one or more officers of the Company the power to grant awards to employees and certain officers of the Company. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2015 Plan with service-based vesting conditions generally vest over four years and expire after ten years. The total number of shares of common stock that could have been issued under the 2015 Plan was 4,144,876 shares. Upon effectiveness of the Company’s 2018 Stock Option and Incentive Plan, the (“2018 Plan”) in March 2018, the remaining shares available under the 2015 Plan became available for issuance under the 2018 Plan and no future issuance will be made under the 2015 Plan. Additionally, outstanding options under the 2015 Plan that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future issuance under the 2018 Plan.

The exercise price for stock options granted is not less than the fair value of common shares as determined by the board of directors as of the date of grant. Prior to the Company’s IPO, the Company’s board of directors valued the Company’s common stock, taking into consideration its most recently available valuation of common stock performed by third parties as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant.

2018 Stock Option and Incentive Plan

The Company’s 2018 Stock Option and Incentive Plan, (the “2018 Plan”), which became effective on March 27, 2018 provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights. The number of shares initially reserved for issuance under the 2018 Plan is 2,800,721. Additionally, the shares of common stock that remained available for issuance under the previously outstanding 2015 Stock Incentive Plan (the “2015 Plan”) became available under the 2018 Plan. The number of shares reserved for the 2018 Plan will automatically increase on each January 1 by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or a lesser number of shares determined by the Company’s board of directors. The shares of common stock underlying any awards that are forfeited, canceled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, repurchased or are otherwise terminated by the Company under the 2018 Plan or the 2015 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. The number of authorized shares reserved for issuance under the 2018 Plan was increased by 1,226,500 shares effective as of January 1, 2020. As of December 31, 2019, 2,009,911 shares remained available for future issuance under the 2018 Plan.

2018 Employee Stock Purchase Plan

The Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) became effective on March 28, 2018 at which time a total of 314,000 shares of common stock were reserved for issuance. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on each January 1 through January 1, 2027, by the least of (i) 500,000 shares of common stock, (ii) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or (iii) such lesser number of shares as determined by the ESPP administrator. The number of authorized shares reserved for issuance under the ESPP was increased by 306,600 shares effective as of January 1, 2020. The first six month offering period was initiated on July 1, 2019. As of December 31, 2019, no shares have been issued under the ESPP and 614,580 shares remain available for issuance. In January 2020, 57,011 shares were issued to employees under the ESPP.

Stock Option Valuation

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model. The Company historically had been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock options granted to employees and directors:

	Year Ended December 31,
	2019			2018
Risk-free interest rate		2.15	%		2.64	%
Expected volatility		74.07	%		67.40	%
Expected dividend yield		—			—
Expected life (in years)		5.85			6.07

Stock Option Activity

The following table summarizes the activity of our 2018 Stock Option and Incentive Plan, excluding performance-based stock options:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2018		3,661,982		$	5.92
Granted		2,029,886			2.90
Exercised		(605,084	)		0.18
Forfeited		(924,901	)		7.75
Outstanding as of December 31, 2019		4,161,883		$	4.87		7.9	$	321
Vested and expected to vest as of December 31, 2019		4,161,883		$	4.87		7.9	$	321
Options exercisable as of December 31, 2019		1,799,024		$	4.96		6.5	$	310

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had strike prices lower than the fair value of the Company’s common stock.

The aggregate intrinsic value of options exercised during the years ended December 31, 2019 and 2018 was $2.2 million and $1.6 million, respectively. The weighted average grant-date fair value of awards granted during the years ended December 31, 2019 and 2018 was $1.90 per share and $6.50 per share, respectively.

Performance-based Stock Options

In 2019, the Company granted options to certain employees for the purchase of 635,000 shares of common stock that vest under a combination of performance-based and service-based vesting conditions if certain performance vesting criteria are achieved on or before March 31, 2020. As of December 31, 2019, the Company has not recorded stock-based compensation expense as the performance conditions have not been deemed to be probable of being achieved.

The following table summarizes the activity of our performance-based stock options granted under our 2018 Stock Option and Incentive Plan:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2018		—		$	—
Granted		635,000			3.73
Exercised		—			—
Forfeited		(125,000	)		4.42
Outstanding as of December 31, 2019		510,000		$	3.56		9.3	$	—
Vested and expected to vest as of December 31, 2019		—		$	—		—	$	—
Options exercisable as of December 31, 2019		—		$	—		—	$	—

The weighted average grant-date fair value of awards granted during the years ended December 31, 2019 and 2018 was $2.46 per share and $0 per share, respectively.

Restricted Stock Units

In 2019, the Company granted restricted stock units to employees with service-based vesting conditions. The restricted stock units vest over the 2 year service period. The following table summarizes the activity of our restricted stock units granted under our 2018 Stock Option and Incentive Plan:

	Number of Shares		Weighted Average Grant Date Fair Value per Share
Unvested as of December 31, 2018		—	$	—
Granted		371,161		0.69
Vested		—		—
Forfeited		—		—
Unvested as of December 31, 2019		371,161	$	0.69

Employee Stock Purchase Plan

The weighted-average fair value of stock purchase rights granted as part of 2018 Employee Stock Purchase Plan was $0.85 per share for the year ended December 31, 2019. The fair value was estimated using the Black-Scholes option-pricing model. During the year ended December 31, 2019, we used a weighted-average stock-price volatility of 84 percent, expected option life assumption of six months and a risk-free interest rate of 2.1 percent.

Stock-Based Compensation

The following table summarizes stock-based compensation expense during the two years ended December 31, 2019, in thousands:

	Year Ended December 31,
	2019		2018
Stock-based compensation expense by type of award:
Time-based stock options	$	3,189	$	3,088
Performance-based stock options		—		—
Time-based restricted stock units		15		—
Employee stock purchase plan		37		—
Total	$	3,241	$	3,088

The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended December 31,
	2019		2018
Research and development expenses	$	2,237	$	2,184
General and administrative expenses		1,004		904
Total	$	3,241	$	3,088

As of December 31, 2019, total unrecognized compensation cost related to the unvested stock-based options of $6.2 million to be recognized over a weighted average period of 2.65 years and unrecognized compensation cost related to unvested restricted stock units was $0.2 million, which is expected to be recognized over a weighted average period of 1.88 years.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

2017 U.S. Tax Reform

On December 22, 2017, the Tax Cuts and Jobs Act (the “TCJA”) was signed into United States law. The TCJA includes a number of changes to existing tax law, including, among other things, a permanent reduction in the federal corporate income tax rate from 34% to 21%, effective as of January 1, 2018, as well as limitation of the deduction for net operating losses to 80% of annual taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2017 (though any such net operating losses may be carried forward indefinitely). The tax rate change resulted in (i) a reduction in the gross amount of the Company’s deferred tax assets recorded as of December 31, 2017, without an impact on the net amount of its deferred tax assets, which are recorded with a full valuation allowance, and (ii) no income tax expense or benefit being recognized as of the enactment date of the TCJA. The Company finalized its accounting for the income tax effects of TCJA during 2018, with no adjustment to the provisional amounts previously recorded.

Income Taxes

During the years ended December 31, 2019 and 2018, the Company recorded no current or deferred income tax benefits for the net operating losses or research and development tax credits generated in each year due to its uncertainty of realizing a benefit from those items. The Company had no foreign operating losses.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2019			2018
Federal statutory income tax rate		(21.0	)%		(21.0	)%
State taxes, net of federal benefit		(6.2	)		(6.2	)
Federal and state research and development tax credits		(5.5	)		(4.2	)
Nondeductible items		1.0			0.7
Other Items		1.6			—
Increase in deferred tax asset valuation allowance		30.1			30.7
Effective income tax rate		0.0	%		0.0	%

Net deferred tax assets as of December 31, 2019 and 2018 consisted of the following (in thousands):

	December 31,
	2019			2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	30,055		$	19,189
Research and development and investment tax credits		6,620			4,891
Deferred revenue		—			3,294
Accrued expenses		644			437
Capitalized start-up costs		85			93
Capitalized research and development expense		48			60
Operating lease right-of-use assets		(1,444	)		—
Operating lease liabilities		1,648			—
Other		831			933
Total deferred tax assets		38,487			28,897
Valuation allowance		(38,487	)		(28,897	)
Net deferred tax assets	$	—		$	—

As of December 31, 2019, the Company had U.S. federal and state net operating loss carryforwards of $109.8 million and $110.8 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2035. Of the federal net operating loss carryforwards at December 31, 2019, $79.6 million is available to be carried forward indefinitely but can only offset 80% of taxable income per year. As of December 31, 2019, the Company also had U.S. federal and state research and development tax credit carryforwards of $5.3 million and $1.6 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2034 and 2030, respectively.

Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the federal and state net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed by the Company and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2019 and 2018. Management reevaluates the positive and negative evidence at each reporting period.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2019 and 2018 related primarily to the increase in net operating loss carryforwards and research and development tax credit carryforwards and were as follows (in thousands):

	Year Ended December 31,
	2019		2018
Valuation allowance as of beginning of year	$	28,897	$	16,611
Decreases recorded as benefit to income tax provision		—		—
Increases recorded to income tax provision		9,590		12,286
Valuation allowance as of end of year	$	38,487	$	28,897

As of December 31, 2019 and 2018, the Company had not recorded any amounts for unrecognized tax benefits. The Company files income tax returns in the U.S. and Massachusetts. The statute of limitations for assessment by the Internal Revenue Service and Massachusetts tax authorities remains open for all years since 2016. The Company’s tax attributes related to years prior to 2016 can still be adjusted under audit. No federal or state tax audits are currently in process.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

Operating Leases

The Company leases office and laboratory space under a non-cancelable operating lease that expires in April 2023 with the Company’s option to extend for an additional five-year term. The lessee has the right to terminate the lease in the event of the inability to use the space due to substantial damage while the lessor has the right to terminate the lease for tenant’s default of lease financial obligations. Per the terms of the lease agreement, the Company does not have any residual value guarantees. This extension has not been considered in the determination of the lease liability as the Company is not obligated to exercise their option and it is not reasonably certain that the option will be exercised. The lease payments include fixed lease payments that escalate over the term of the lease on an annual basis. The Company’s real estate lease in Cambridge is a net lease, as the non-lease components (i.e. common area maintenance) are paid separately from rent based on actual costs incurred. Therefore, the non-lease component and related payments are not included in the right-of-use asset and liability and are reflected as an expense in the period incurred. The discount rate used in determining the lease liability represents the Company’s incremental borrowing rate as the rate implicit in the lease could not be readily determined.

The elements of the lease expense were as follows (in thousands):

	Year Ended December 31, 2019
Lease cost
Operating lease cost	$	1,772
Variable lease cost (1)		1,075
Total lease cost	$	2,847

Other information
Cash paid for amounts included in the measurement of lease liabilities	$	2,954
Remaining lease term		3.33
Discount rate		6.25	%

(1)	The variable lease costs for the quarter ended December 31, 2019 include common area maintenance and other operating charges.

Future minimum lease payments under the operating lease as of December 31, 2019 are as follows (in thousands):

Year Ending December 31,
2020		1,933
2021		1,989
2022		2,046
2023		689
Total future minimum lease payments		6,657
Less: imputed interest		625
Total operating lease liability	$	6,032
Included in the consolidated balance sheet:
Current operating lease liability		1,619
Operating lease liability, net of current portion		4,413
Total operating lease liability	$	6,032

As previously disclosed in our 2018 Annual Report on Form 10-K, future minimum lease payments under the operating lease as of December 31, 2018 were as follows (in thousands):

Year Ending December 31,
2019	$	1,878
2020		1,933
2021		1,989
2022		2,046
2023		689
Total future minimum lease payments	$	8,535

Under the terms of the lease, the Company secured a $1.3 million letter of credit as security for its leased facility. The underlying cash securing this letter of credit has been classified as non-current restricted cash in the accompanying consolidated balance sheets. This is a refundable deposit and not a lease payment. This has been excluded from the undiscounted cash flows above.

License Agreement

Under its license agreement with National University of Singapore and St. Jude Children’s Research Hospital, Inc. (collectively the “Licensors”) entered into in 2014, the Company is obligated to pay license maintenance fees on each anniversary of the effective date of the agreement that escalate from less than $0.1 million for each of the first seven years to $0.1 million on the eighth anniversary and each year thereafter. The Company is also obligated to make aggregate milestone payments of up to 5.5 million Singapore dollars (equivalent to approximately $4.1 million as of December 31, 2019) upon the achievement of specified clinical and regulatory milestones and to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis and may be reduced in specified circumstances. Additionally, under certain circumstances, the Company is obligated to pay the Licensors a percentage of amounts received from sublicensees.

The license agreement will expire on a country-by-country basis until the last to expire of the patents and patent applications covering such licensed product or service. The Licensors may terminate the license agreement within 60 days after written notice in the event of a breach of contract. The Licensors may also terminate the agreement upon written notice in the event of the Company’s bankruptcy, liquidation, or insolvency. In addition, the Company has the right to terminate this agreement in its entirety at will upon 90 days’ advance written notice to the Licensors. However, if the Company has commenced the commercialization of licensed products, the Company can only terminate at will if it ceases all development and commercialization of licensed products.

Manufacturing Commitment

As of December 31, 2019, the Company had non-cancelable minimum purchase commitments under contract manufacturing agreements for payments totaling $1.0 million over the following 12 months.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2019 or 2018.

Legal Proceedings

The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Net Loss Per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss Per Share

12. Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts):

	Year Ended December 31,
	2019			2018
Numerator:
Net loss	$	(31,833	)	$	(34,532	)
Accretion of redeemable convertible preferred stock to redemption value		—			(16	)
Net loss attributable to common stockholders	$	(31,833	)	$	(34,548	)
Denominator:
Weighted average common shares outstanding, basic and diluted		30,480,330			24,895,670
Net loss per share attributable to common stockholders, basic and diluted	$	(1.04	)	$	(1.39	)

The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:

	December 31,
	2019		2018
Stock options to purchase common stock		4,671,883		3,661,982
Unvested restricted common stock units		371,161		—
		5,043,044		3,661,982

Retirement Plan

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

Retirement Plan

13. Retirement Plan

The Company has a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pre-tax basis. As currently established, the Company is not required to make and to date has not made any contributions to the 401(k) Plan. The Company did not make any matching contributions during the years ended December 31, 2019 or 2018.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

14. Selected Quarterly Financial Data (Unaudited)

The following information has been derived from unaudited financial statements that, in the opinion of management, include all recurring adjustments necessary for a fair statement of such information (in thousands except per share data):

	Mar 31, 2018			Jun 30, 2018			Sep 30, 2018			Dec 31, 2018			Mar 31, 2019			Jun 30, 2019			Sep 30, 2019			Dec 31, 2019 (1)
Statements of Operations Data:
Revenue	$	2,220		$	1,666		$	2,043		$	3,805		$	3,053		$	3,138		$	1,020		$	15,288
Loss from operations		(6,986	)		(9,439	)		(10,576	)		(9,004	)		(11,841	)		(10,541	)		(12,036	)		2,240
Net loss		(6,735	)		(9,023	)		(10,168	)		(8,606	)		(11,691	)		(10,516	)		(11,923	)		2,297
Net loss attributable to common stockholders		(6,751	)		(9,023	)		(10,168	)		(8,606	)		(11,691	)		(10,516	)		(11,923	)		2,297
Basic net loss attributable to common stockholders per share:	$	(0.66	)	$	(0.31	)	$	(0.34	)	$	(0.29	)	$	(0.39	)	$	(0.34	)	$	(0.39	)	$	0.07
Weighted average common shares outstanding- basic		10,204,591			29,155,790			29,879,476			30,018,342			30,083,006			30,505,773			30,661,125			30,663,054
Diluted net loss attributable to common stockholders per share:	$	(0.66	)	$	(0.31	)	$	(0.34	)	$	(0.29	)	$	(0.39	)	$	(0.34	)	$	(0.39	)	$	0.07
Weighted average common shares outstanding- diluted		10,204,591			29,155,790			29,879,476			30,018,342			30,083,006			30,505,773			30,661,125			31,195,620

(1)	The Q4 2019 results include the impact of the adjustment to the transaction price and the expected costs to complete the remaining performance obligations under the terms of the Collaboration Agreement with Seattle Genetics, as described more fully within Footnote 6, Collaboration Agreement.

Subsequent Events

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent Events

15. Subsequent Events

Termination of the Collaboration Agreement with Seattle Genetics

On January 16, 2020, the Company and Seattle Genetics announced that they have agreed to terminate the Collaboration Agreement effective as of January 16, 2020 (the “Termination Effective Date”), pursuant to which the Parties will cease all research, development, manufacturing and other exploitations of any and all research candidates and development candidates under the Collaboration Agreement, including, without limitation, the development candidate ACTR-BCMA and a research candidate. Refer to Footnote 6 above for additional information regarding this subsequent event.

Option Exchange Program

On January 24, 2020, the compensation committee of the Board of Directors authorized a stock option cancellation and regrant program, or the Option Exchange, that would allow the Company to cancel out-of-the-money stock options, or outstanding stock options that have an exercise price that is less than the market price for Unum’s stock in exchange for the issuance of stock options for the same number of shares and otherwise on the same terms but with lower exercise prices. The Option Exchange is subject to stockholder approval and implementation by our Board of Directors. The Company held its special meeting (the Special Meeting) of stockholders on March 9, 2020. The Option Exchange was submitted to a vote of the Company’s stockholders at the Special Meeting was approved.

Strategic Restructuring to Prioritize Efforts on BOXR1030 for the Treatment of Solid Tumor Cancers

As announced on March 2, 2020, the Company has initiated a reduction in force that is intended to result in the termination of approximately 60% of the Company’s employee workforce, or approximately 43 employees. These reductions are expected to be substantially completed by the end of first quarter of 2020. The reduction in force was approved in connection with the Company’s restructuring plans to prioritize resources towards advancing its preclinical program, BOXR1030, for the treatment of solid tumor cancers.

As a result of the reduction of force, the Company estimates that it will incur aggregate charges of approximately $2.0 million, in one-time severance and employee termination related costs which are all expected to result in cash expenditures.

On March 19, 2020, the Company entered into a Purchase Agreement with Lincoln Park Capital Fund, LLC (“LPC”), pursuant to which the Company may elect to sell to LPC up to $25,000,000 in shares of our common stock, subject to certain limitations and conditions set forth in the Purchase Agreement. Pursuant to the Purchase Agreement, 726,382 shares of Common Stock were issued to LPC as a commitment fee.

On March 26, 2020, the Company announced that they would be exploring strategic alternatives in order to maximize stockholder value and that the Company had engaged Ladenburg Thalmann & Co. Inc. to act as they strategic financial advisor to assist in the strategic review process. Despite undertaking this process, the Company may not be successful in completing a transaction, and, even if a strategic transaction is completed, it ultimately may not deliver the anticipated benefits or enhance stockholder value.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Principles of Consolidation

The accompanying consolidated financial statements include those of the Company and its wholly-owned subsidiary, Mono, Inc. All intercompany balances and transactions have been eliminated.

Use of Estimates

Risks and Uncertainties

Impact of the COVID-19 Coronavirus

Concentrations of Credit Risk and of Significant Suppliers

Debt Issuance Costs

Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

Restricted cash consists of security deposits in separate restricted bank accounts as required under the terms of the Company’s lease agreement for its Corporate Office in Cambridge, Massachusetts.

Property and Equipment

		Estimated Useful Life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of life of lease or 10 years

Impairment of Long-Lived Assets

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Marketable Securities

Classification and Accretion of Redeemable Convertible Preferred Stock

Segment Information

Leases

Revenue Recognition

Collaborative Arrangements

Research and Development Costs

Research Contract Costs and Accruals

Patent Costs

Stock-Based Compensation

Comprehensive Loss

Net Income (Loss) per Share

Income Taxes

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of Estimated Useful Life

		Estimated Useful Life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of life of lease or 10 years

Marketable Securities and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Marketable Securities by Type

Marketable securities by security type consisted of the following (in thousands):

December 31, 2019

Amortized

Cost

Gross

Unrealized

Gains

Gross

Unrealized

Losses

Fair

Value

U.S. Treasury bills and notes (due within one year)

—

	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury bills and notes (due within one year)	$	22,935	$	—	$	(12	)	$	22,923
	$	22,935	$	—	$	(12	)	$	22,923

Schedule of Cash Equivalents and Marketable Securities Measured at Fair Value on Recurring Basis

The following tables present the Company’s fair value hierarchy for its cash equivalents and marketable securities, which are measured at fair value on a recurring basis (in thousands):

	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	485	$	—	$	485
Marketable securities:
U.S. Treasury bills and notes		—		—		—		—
	$	—	$	485	$	—	$	485

	Fair Value Measurements at December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	52,100	$	—	$	52,100
Marketable securities:
U.S. Treasury bills and notes		22,923		—		—		22,923
	$	22,923	$	52,100	$	—	$	75,023

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

	December 31,
	2019			2018
Laboratory equipment	$	5,529		$	5,801
Computer equipment and software		224			203
Furniture and fixtures		317			317
Leasehold improvements		426			426
Total property and equipment		6,496			6,747
Accumulated depreciation and amortization		(4,631	)		(3,496	)
Property and equipment, net	$	1,865		$	3,251

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	December 31,
	2019		2018
Accrued employee compensation and benefits	$	2,500	$	1,599
Accrued external research and development expense		2,987		1,799
Accrued external manufacturing costs		750		1,015
Other		894		1,064
	$	7,131	$	5,477

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Fair Value Option Granted

	Year Ended December 31,
	2019			2018
Risk-free interest rate		2.15	%		2.64	%
Expected volatility		74.07	%		67.40	%
Expected dividend yield		—			—
Expected life (in years)		5.85			6.07

Schedule of Common Stock Option Activity

The following table summarizes the activity of our 2018 Stock Option and Incentive Plan, excluding performance-based stock options:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2018		3,661,982		$	5.92
Granted		2,029,886			2.90
Exercised		(605,084	)		0.18
Forfeited		(924,901	)		7.75
Outstanding as of December 31, 2019		4,161,883		$	4.87		7.9	$	321
Vested and expected to vest as of December 31, 2019		4,161,883		$	4.87		7.9	$	321
Options exercisable as of December 31, 2019		1,799,024		$	4.96		6.5	$	310

Schedule of Performance-based Stock Options Activity

The following table summarizes the activity of our performance-based stock options granted under our 2018 Stock Option and Incentive Plan:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2018		—		$	—
Granted		635,000			3.73
Exercised		—			—
Forfeited		(125,000	)		4.42
Outstanding as of December 31, 2019		510,000		$	3.56		9.3	$	—
Vested and expected to vest as of December 31, 2019		—		$	—		—	$	—
Options exercisable as of December 31, 2019		—		$	—		—	$	—

Schedule of Restricted Stock Units Activity

The following table summarizes the activity of our restricted stock units granted under our 2018 Stock Option and Incentive Plan:

	Number of Shares		Weighted Average Grant Date Fair Value per Share
Unvested as of December 31, 2018		—	$	—
Granted		371,161		0.69
Vested		—		—
Forfeited		—		—
Unvested as of December 31, 2019		371,161	$	0.69

Schedule of Stock-based Compensation Expense by Type of Award

The following table summarizes stock-based compensation expense during the two years ended December 31, 2019, in thousands:

	Year Ended December 31,
	2019		2018
Stock-based compensation expense by type of award:
Time-based stock options	$	3,189	$	3,088
Performance-based stock options		—		—
Time-based restricted stock units		15		—
Employee stock purchase plan		37		—
Total	$	3,241	$	3,088

Schedule of Stock Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended December 31,
	2019		2018
Research and development expenses	$	2,237	$	2,184
General and administrative expenses		1,004		904
Total	$	3,241	$	3,088

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2019			2018
Federal statutory income tax rate		(21.0	)%		(21.0	)%
State taxes, net of federal benefit		(6.2	)		(6.2	)
Federal and state research and development tax credits		(5.5	)		(4.2	)
Nondeductible items		1.0			0.7
Other Items		1.6			—
Increase in deferred tax asset valuation allowance		30.1			30.7
Effective income tax rate		0.0	%		0.0	%

Schedule of Deferred Tax Assets

Net deferred tax assets as of December 31, 2019 and 2018 consisted of the following (in thousands):

	December 31,
	2019			2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	30,055		$	19,189
Research and development and investment tax credits		6,620			4,891
Deferred revenue		—			3,294
Accrued expenses		644			437
Capitalized start-up costs		85			93
Capitalized research and development expense		48			60
Operating lease right-of-use assets		(1,444	)		—
Operating lease liabilities		1,648			—
Other		831			933
Total deferred tax assets		38,487			28,897
Valuation allowance		(38,487	)		(28,897	)
Net deferred tax assets	$	—		$	—

Changes in Valuation Allowance for Deferred Tax Assets

	Year Ended December 31,
	2019		2018
Valuation allowance as of beginning of year	$	28,897	$	16,611
Decreases recorded as benefit to income tax provision		—		—
Increases recorded to income tax provision		9,590		12,286
Valuation allowance as of end of year	$	38,487	$	28,897

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Elements of Lease Expense

The elements of the lease expense were as follows (in thousands):

	Year Ended December 31, 2019
Lease cost
Operating lease cost	$	1,772
Variable lease cost (1)		1,075
Total lease cost	$	2,847

Other information
Cash paid for amounts included in the measurement of lease liabilities	$	2,954
Remaining lease term		3.33
Discount rate		6.25	%

(1)	The variable lease costs for the quarter ended December 31, 2019 include common area maintenance and other operating charges.

Summary of Future Minimum Payments under Operating Lease

Future minimum lease payments under the operating lease as of December 31, 2019 are as follows (in thousands):

Year Ending December 31,
2020		1,933
2021		1,989
2022		2,046
2023		689
Total future minimum lease payments		6,657
Less: imputed interest		625
Total operating lease liability	$	6,032
Included in the consolidated balance sheet:
Current operating lease liability		1,619
Operating lease liability, net of current portion		4,413
Total operating lease liability	$	6,032

Summary of Future Minimum Lease Payments under Operating Lease

As previously disclosed in our 2018 Annual Report on Form 10-K, future minimum lease payments under the operating lease as of December 31, 2018 were as follows (in thousands):

Year Ending December 31,
2019	$	1,878
2020		1,933
2021		1,989
2022		2,046
2023		689
Total future minimum lease payments	$	8,535

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of Earnings Per Share Basic and Diluted

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts):

	Year Ended December 31,
	2019			2018
Numerator:
Net loss	$	(31,833	)	$	(34,532	)
Accretion of redeemable convertible preferred stock to redemption value		—			(16	)
Net loss attributable to common stockholders	$	(31,833	)	$	(34,548	)
Denominator:
Weighted average common shares outstanding, basic and diluted		30,480,330			24,895,670
Net loss per share attributable to common stockholders, basic and diluted	$	(1.04	)	$	(1.39	)

Summary of Potential Dilutive Securities

	December 31,
	2019		2018
Stock options to purchase common stock		4,671,883		3,661,982
Unvested restricted common stock units		371,161		—
		5,043,044		3,661,982

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Financial Data

	Mar 31, 2018			Jun 30, 2018			Sep 30, 2018			Dec 31, 2018			Mar 31, 2019			Jun 30, 2019			Sep 30, 2019			Dec 31, 2019 (1)
Statements of Operations Data:
Revenue	$	2,220		$	1,666		$	2,043		$	3,805		$	3,053		$	3,138		$	1,020		$	15,288
Loss from operations		(6,986	)		(9,439	)		(10,576	)		(9,004	)		(11,841	)		(10,541	)		(12,036	)		2,240
Net loss		(6,735	)		(9,023	)		(10,168	)		(8,606	)		(11,691	)		(10,516	)		(11,923	)		2,297
Net loss attributable to common stockholders		(6,751	)		(9,023	)		(10,168	)		(8,606	)		(11,691	)		(10,516	)		(11,923	)		2,297
Basic net loss attributable to common stockholders per share:	$	(0.66	)	$	(0.31	)	$	(0.34	)	$	(0.29	)	$	(0.39	)	$	(0.34	)	$	(0.39	)	$	0.07
Weighted average common shares outstanding- basic		10,204,591			29,155,790			29,879,476			30,018,342			30,083,006			30,505,773			30,661,125			30,663,054
Diluted net loss attributable to common stockholders per share:	$	(0.66	)	$	(0.31	)	$	(0.34	)	$	(0.29	)	$	(0.39	)	$	(0.34	)	$	(0.39	)	$	0.07
Weighted average common shares outstanding- diluted		10,204,591			29,155,790			29,879,476			30,018,342			30,083,006			30,505,773			30,661,125			31,195,620

(1)	The Q4 2019 results include the impact of the adjustment to the transaction price and the expected costs to complete the remaining performance obligations under the terms of the Collaboration Agreement with Seattle Genetics, as described more fully within Footnote 6, Collaboration Agreement.

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands						12 Months Ended
	Mar. 02, 2020 Employee	Sep. 30, 2019 shares	Apr. 01, 2019 USD ($)	Apr. 25, 2018 USD ($) $ / shares shares	Apr. 03, 2018 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) shares
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from initial public offering							$ 66,793
Cash and cash equivalents						$ 37,424	$ 55,671
Deficiency letter from listing qualifications department notifying period						30 days
Minimum bid price of common stock \| $ / shares						$ 1.00
Initial period to regain compliance with minimum bid price rule						180 days
Additional period to regain compliance with minimum bid price rule						180 days
Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Employee workforce, termination percentage	60.00%
Number of employees expected to be terminated \| Employee	43
Cowen [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares of common stock issued and sold \| shares		0				0
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from issuance of equity and debt financing			$ 150,000
Maximum [Member] \| Cowen [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock offering cost			$ 50,000
Common Stock [Member] \| IPO [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares of common stock issued and sold \| shares				215,000	5,770,000		5,985,000
Public offering price, per share \| $ / shares				$ 12.00	$ 12.00
Net proceeds from initial public offering				$ 2,400	$ 61,500
Common Stock [Member] \| Private Placement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shares of common stock issued and sold \| shares					416,666		416,666
Sale of stock, consideration received on transaction					$ 5,000

Summary of Significant Accounting Policies - Schedule of Estimated Useful Life (Detail)	12 Months Ended
	Dec. 31, 2019
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Computer equipment and software	5 years
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Computer equipment and software	3 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Computer equipment and software	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Leasehold improvements	Shorter of life of lease or 10 years

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Impairment losses on long-lived assets	$ 0	$ 0
Capitalized contract costs	0
Lease liability	6,032,000
Operating lease, right-of-use asset	$ 5,285,000
Accounting Standards Update 2016-02 [Member]
Significant Accounting Policies [Line Items]
Lease liability			$ 7,500,000
Operating lease, right-of-use asset			$ 6,700,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Expenses incremental costs expiration period	1 year
Period of Transfer of promised goods or services to customer	1 year

Marketable Securities and Fair Value Measurements - Schedule of Marketable Securities by Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 0	$ 22,935
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(12)
Fair Value	0	22,923
U.S. Treasury Bills and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	22,935
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(12)
Fair Value	$ 0	$ 22,923

Marketable Securities and Fair Value Measurements - Schedule of Cash Equivalents and Marketable Securities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Measured at Fair Value on Recurring Basis	$ 485	$ 75,023
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Measured at Fair Value on Recurring Basis		22,923
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Measured at Fair Value on Recurring Basis	485	52,100
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents Measured at Fair Value on Recurring Basis	485	52,100
Money Market Funds [Member] \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents Measured at Fair Value on Recurring Basis	$ 485	52,100
Marketable securities [Member] \| U.S. Treasury Bills and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Measured at Fair Value on Recurring Basis		22,923
Marketable securities [Member] \| Level 1 \| U.S. Treasury Bills and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Measured at Fair Value on Recurring Basis		$ 22,923

Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Fair value asset, transfers between Level 1, Level 2 and Level 3, amount	$ 0	$ 0

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 6,496	$ 6,747
Accumulated depreciation and amortization	(4,631)	(3,496)
Property and equipment, net	1,865	3,251
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,529	5,801
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	224	203
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	317	317
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 426	$ 426

Property Plant Equipment Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipments [Abstract]
Depreciation and amortization expense	$ 1,293	$ 1,321

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued employee compensation and benefits	$ 2,500	$ 1,599
Accrued external research and development expense	2,987	1,799
Accrued external manufacturing costs	750	1,015
Other	894	1,064
Total	$ 7,131	$ 5,477

Collaboration Agreement - Additional Information (Detail) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Jan. 16, 2020

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

$ 15,288

^[1]

$ 1,020

$ 3,138

$ 3,053

$ 3,805

$ 2,043

$ 1,666

$ 2,220

$ 22,499

$ 9,734

Seattle Genetics [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

22,500

9,700

Deferred revenue

1,300

$ 17,900

1,300

$ 17,900

Remaining performance obligation related to two product candidates

$ 1,000

1,000

Seattle Genetics [Member] | Subsequent Event [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Collaborative arrangement consideration received upon termination agreement

$ 5,750

Collaborative arrangement common stock surrender

831,847

Preclinical Research And Clinical Development [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Collaborative Arrangement Upfront Payment recognized

25,000

Collaborative Arrangement [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

100,000

Regulatory Milestone Payments [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

100,000

Commercial Milestone Payments [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

200,000

Maximum [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

400,000

Maximum [Member] | Collaborative Arrangement [Member] | Clinical Development Events [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

30,000

Maximum [Member] | Regulatory Milestone Payments [Member] | First Regulatory Approval [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

35,000

Maximum [Member] | Commercial Milestone Payments [Member] | Annual Net Sales Achievement [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Future collaboration and milestone payments

$ 60,000

[1]	The Q4 2019 results include the impact of the adjustment to the transaction price and the expected costs to complete the remaining performance obligations under the terms of the Collaboration Agreement with Seattle Genetics, as described more fully within Footnote 6, Collaboration Agreement.

Loan and Security Agreement - Additional Information (Detail) - Loan and Security Agreement [Member] - Pacific Western Bank [Member]	12 Months Ended
	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Warrant to be issued to purchase number of shares capital stock equal to the amount of each term loan borrowing percentage	1.00%
Term Loan [Member]
Debt Instrument [Line Items]
Maximum term loan borrowings	$ 15,000,000
Interest rate during period	3.75%
Term loan payment terms	The Company has a loan and security agreement (the “Loan Agreement”) with Pacific Western Bank (“PWB”), entered into in 2017, which provided for term loan borrowings of up to $15.0 million through January 19, 2019. Borrowings under the Loan Agreement bear interest at a variable annual rate equal to the greater of (i) the prime rate plus 0.25% or (ii) 3.75%, and were payable over an interest-only period until January 19, 2019, followed by a 24-month period of equal monthly payments of principal and interest. All amounts outstanding as of the maturity date of January 19, 2021 become immediately due and payable. In January 2019, the Company amended the Loan Agreement to extend the available date for borrowings from January 19, 2019 to June 30, 2019 and extend the interest only period from January 19, 2019 to June 30, 2020, with the possibility of further extension to March 31, 2021 if certain equity financing considerations are met. As of December 31, 2019, these equity financing considerations have not been met. Additionally, the loan repayment period will be over a 24-month period following the end of the interest-only period. In June 2019, the Company further amended the Loan Agreement to extend the available date for borrowings from June 30, 2019 to June 30, 2020. On July 31, 2019, the Company amended the Loan Agreement to provide for changes to the primary depository requirements with PWB.
Outstanding amount maturity date	Jan. 19, 2021
Term of loan	24 months
Term loan frequency of periodic payment	monthly
Term loans borrowed	$ 0
Term Loan [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Annual variable interest rate	0.25%

Preferred Stock and Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands						12 Months Ended
	Sep. 30, 2019 shares	Apr. 01, 2019 USD ($)	Apr. 25, 2018 USD ($) $ / shares shares	Apr. 03, 2018 USD ($) $ / shares shares	Mar. 16, 2018	Dec. 31, 2019 shares	Dec. 31, 2018 USD ($) shares
Class of Stock [Line Items]
Net proceeds from initial public offering \| $							$ 66,793
Common stock, Shares authorized						150,000,000	150,000,000
Preferred stock, shares authorized						10,000,000	10,000,000
Cowen [Member]
Class of Stock [Line Items]
Shares of common stock issued and sold	0					0
Maximum [Member]
Class of Stock [Line Items]
Proceeds from issuance of equity and debt financing \| $		$ 150,000
Maximum [Member] \| Cowen [Member]
Class of Stock [Line Items]
Stock offering cost \| $		$ 50,000
Preferred Stock [Member]
Class of Stock [Line Items]
Reverse stock split description				1:1.57 basis upon the closing of the IPO
Reverse stock split ratio				0.63694267
Common Stock [Member]
Class of Stock [Line Items]
Reverse stock split description					one-for-1.57 reverse stock split
Reverse stock split ratio					0.636942
Common stock voting right						Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Common stock, Shares authorized				150,000,000
Preferred stock, shares authorized				10,000,000
Common Stock [Member] \| IPO [Member]
Class of Stock [Line Items]
Shares of common stock issued and sold			215,000	5,770,000			5,985,000
Public offering price, per share \| $ / shares			$ 12.00	$ 12.00
Net proceeds from initial public offering \| $			$ 2,400	$ 61,500
Common Stock [Member] \| Private Placement [Member]
Class of Stock [Line Items]
Shares of common stock issued and sold				416,666			416,666
Sale of stock, consideration received on transaction \| $				$ 5,000

Stock-Based Compensation - Additional Information (Detail) - USD ($)				12 Months Ended
	Jan. 01, 2020	Mar. 28, 2018	Mar. 27, 2018	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock share issued				30,663,054	30,057,970
Aggregate intrinsic value of options exercised				$ 2,200,000	$ 1,600,000
Weighted average grant date fair value				$ 1.90	$ 6.50
Share based compensation expense				$ 3,241,000	$ 3,088,000
Weighted average expected option life				5 years 10 months 6 days	6 years 25 days
Weighted average risk free interest rate				2.15%	2.64%
Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants				635,000
Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value				$ 2.46	$ 0
Share based compensation expense				$ 0
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock option				2 years
Unrecognized compensation expenses, recognition period				1 year 10 months 17 days
Unrecognized compensation cost				$ 200,000
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost				$ 6,200,000
Unrecognized compensation expenses, recognition period				2 years 7 months 24 days
2015 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock option				4 years
Expiration period of stock option				10 years
Number of increases in authorized shares				4,144,876
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of increases in authorized shares			2,800,721
Percentage applied to the outstanding shares as annual increase in the number of shares authorized for issuance			4.00%
Shares available for future issuance				2,009,911
Option grants				2,029,886
2018 Stock Option and Incentive Plan [Member] \| Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants				635,000
2018 Stock Option and Incentive Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased in authorized shares reserved for issuance	1,226,500
2018 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance				614,580
Shares reserved for future issuance		314,000
Common stock share issued				0
Weighted average grant date fair value				$ 0.85
Weighted-average stock-price volatility				84.00%
Weighted average expected option life				6 months
Weighted average risk free interest rate				2.10%
2018 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of increases in authorized shares		500,000
Percentage of shares of common stock available for issuance		1.00%
2018 Employee Stock Purchase Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased in authorized shares reserved for issuance	306,600
Common stock share issued	57,011

Stock-Based Compensation - Schedule of Fair Value Option Granted (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Stock Options/Shares Outstanding, Weighted-Average Exercise Price, and Additional Disclosures [Abstract]
Risk-free interest rate	2.15%	2.64%
Expected volatility	74.07%	67.40%
Expected life (in years)	5 years 10 months 6 days	6 years 25 days

Stock-Based Compensation - Schedule of Common Stock Option Activity (Detail) - 2018 Stock Option and Incentive Plan [Member] $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options Outstanding, Beginning balance \| shares	3,661,982
Number of Options, Granted \| shares	2,029,886
Number of Options, Exercised \| shares	(605,084)
Number of Options, Forfeited \| shares	(924,901)
Number of Options Outstanding, Ending balance \| shares	4,161,883
Number of Options, Vested and expected to vest \| shares	4,161,883
Number of Options, Exercisable \| shares	1,799,024
Weighted Average Exercise Price, Outstanding, Beginning balance \| $ / shares	$ 5.92
Weighted Average Exercise Price, Granted \| $ / shares	2.90
Weighted Average Exercise Price, Exercised \| $ / shares	0.18
Weighted Average Exercise Price, Forfeited \| $ / shares	7.75
Weighted Average Exercise Price, Outstanding, Ending balance \| $ / shares	4.87
Weighted Average Exercise Price, Vested and expected to vest \| $ / shares	4.87
Weighted Average Exercise Price, Exercisable \| $ / shares	$ 4.96
Weighted Average Contractual Term, Outstanding, Ending balance	7 years 10 months 24 days
Weighted Average Contractual Term, Vested and expected to vest	7 years 10 months 24 days
Weighted Average Contractual Term, Exercisable	6 years 6 months
Aggregate Intrinsic Value, Outstanding \| $	$ 321
Aggregate Intrinsic Value, Vested and expected to vest \| $	321
Aggregate Intrinsic Value, Exercisable \| $	$ 310

Stock-Based Compensation - Schedule of Performance-based Stock Options Activity (Detail) - 2018 Stock Option and Incentive Plan [Member] $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options Outstanding, Beginning balance \| shares	3,661,982
Number of Options, Granted \| shares	2,029,886
Number of Options, Exercised \| shares	(605,084)
Number of Options, Forfeited \| shares	(924,901)
Number of Options Outstanding, Ending balance \| shares	4,161,883
Number of Options, Vested and expected to vest \| shares	4,161,883
Number of Options, Exercisable \| shares	1,799,024
Weighted Average Exercise Price, Outstanding, Beginning balance \| $ / shares	$ 5.92
Weighted Average Exercise Price, Granted \| $ / shares	2.90
Weighted Average Exercise Price, Exercised \| $ / shares	0.18
Weighted Average Exercise Price, Forfeited \| $ / shares	7.75
Weighted Average Exercise Price, Outstanding, Ending balance \| $ / shares	4.87
Weighted Average Exercise Price, Vested and expected to vest \| $ / shares	4.87
Weighted Average Exercise Price, Exercisable \| $ / shares	$ 4.96
Weighted Average Contractual Term, Outstanding, Ending balance	7 years 10 months 24 days
Weighted Average Contractual Term, Vested and expected to vest	7 years 10 months 24 days
Weighted Average Contractual Term, Exercisable	6 years 6 months
Aggregate Intrinsic Value, Outstanding \| $	$ 321
Aggregate Intrinsic Value, Vested and expected to vest \| $	321
Aggregate Intrinsic Value, Exercisable \| $	$ 310
Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Granted \| shares	635,000
Number of Options, Forfeited \| shares	(125,000)
Number of Options Outstanding, Ending balance \| shares	510,000
Weighted Average Exercise Price, Granted \| $ / shares	$ 3.73
Weighted Average Exercise Price, Forfeited \| $ / shares	4.42
Weighted Average Exercise Price, Outstanding, Ending balance \| $ / shares	$ 3.56
Weighted Average Contractual Term, Outstanding, Ending balance	9 years 3 months 18 days
Weighted Average Contractual Term, Vested and expected to vest	0 years
Weighted Average Contractual Term, Exercisable	0 years

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Detail) - 2018 Stock Option and Incentive Plan [Member] - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted \| shares	371,161
Number of Shares Unvested, Ending Balance \| shares	371,161
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares	$ 0.69
Weighted Average Grant Date Fair Value per Share Unvested, Ending Balance \| $ / shares	$ 0.69

Stock-Based Compensation - Schedule of Stock-based Compensation Expense by Type of Award (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	$ 3,241,000	$ 3,088,000
Time-based Stock Options [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	3,189,000	$ 3,088,000
Performance Based Stock Options [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	0
Time-based Restricted Stock Units [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	15,000
Employee Stock Purchase Plan [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	$ 37,000

Stock-Based Compensation - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	$ 3,241	$ 3,088
Research and Development Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	2,237	2,184
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation expense	$ 1,004	$ 904

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Federal corporate income tax rate	21.00%	21.00%	34.00%
Percentage of net operating loss carry forward deductible from current year taxable income	80.00%
Income tax expense or benefit recognized	$ 0
Operating losses carried forward, expiration date	2035
Operating loss carryforwards, federal	$ 79,600,000
Uncertain tax position	0
Unrecognized tax benefits	0	$ 0
Current income tax benefits	0	0
Deferred income tax benefits	0	$ 0
U.S. federal [Member]
Income Tax Disclosure [Line Items]
Net operating losses carryforwards	109,800,000
Research and development tax credits carryforwards	$ 5,300,000
Tax credit carryforwards, expiration year	2034
State [Member]
Income Tax Disclosure [Line Items]
Net operating losses carryforwards	$ 110,800,000
Research and development tax credits carryforwards	$ 1,600,000
Tax credit carryforwards, expiration year	2030

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	21.00%	21.00%	34.00%
State taxes, net of federal benefit	6.20%	6.20%
Federal and state research and development tax credits	5.50%	4.20%
Nondeductible items	(1.00%)	(0.70%)
Other Items	(1.60%)
Increase in deferred tax asset valuation allowance	(30.10%)	(30.70%)
Effective income tax rate	(0.00%)	(0.00%)

Income Taxes - Schedule of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 30,055	$ 19,189
Research and development and investment tax credits	6,620	4,891
Deferred revenue		3,294
Accrued expenses	644	437
Capitalized start-up costs	85	93
Capitalized research and development expense	48	60
Operating lease right-of-use assets	(1,444)
Operating lease liabilities	1,648
Other	831	933
Total deferred tax assets	38,487	28,897
Valuation allowance	(38,487)	(28,897)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$ 28,897	$ 16,611
Increases recorded to income tax provision	9,590	12,286
Valuation allowance as of end of year	$ 38,487	$ 28,897

Commitments and Contingencies - Additional Information (Detail) - 12 months ended Dec. 31, 2019	USD ($)	SGD ($)
Commitments And Contingencies Disclosure [Line Items]
Lease expiration date	Apr. 30, 2023
Operating Lease option to extend	The Company’s option to extend for an additional five-year term.
Non-cancelable minimum purchase commitments	$ 1,000,000
License Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
License agreement expiration terms	The license agreement will expire on a country-by-country basis until the last to expire of the patents and patent applications covering such licensed product or service. The Licensors may terminate the license agreement within 60 days after written notice in the event of a breach of contract. The Licensors may also terminate the agreement upon written notice in the event of the Company’s bankruptcy, liquidation, or insolvency. In addition, the Company has the right to terminate this agreement in its entirety at will upon 90 days’ advance written notice to the Licensors. However, if the Company has commenced the commercialization of licensed products, the Company can only terminate at will if it ceases all development and commercialization of licensed products.
Eighth Year Anniversary and Thereafter [Member] \| License Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
License maintenance fees	$ 100,000
Maximum [Member] \| License Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent contractual obligation	4,100,000	$ 5,500,000
Maximum [Member] \| First Seven Year Anniversary [Member] \| License Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
License maintenance fees	100,000
Non-current restricted cash [Member] \| Letter of Credit [Member]
Commitments And Contingencies Disclosure [Line Items]
Lease security	$ 1,300,000

Commitments and Contingencies - Elements of Lease Expense (Detail)
$ in Thousands

12 Months Ended

Dec. 31, 2019

USD ($)

Lease cost

Operating lease cost

$ 1,772

Variable lease cost

1,075

^[1]

Total lease cost

2,847

Other information

Cash paid for amounts included in the measurement of lease liabilities

$ 2,954

Remaining lease term

3 years 3 months 29 days

Discount rate

6.25%

[1]	The variable lease costs for the quarter ended December 31, 2019 include common area maintenance and other operating charges.

Commitments and Contingencies - Summary of Future Minimum Payments under Operating Lease (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2020	$ 1,933
2021	1,989
2022	2,046
2023	689
Total future minimum lease payments	6,657
Less: imputed interest	625
Total operating lease liability	6,032
Current operating lease liability	1,619
Operating lease liability, net of current portion	4,413
Total operating lease liability	$ 6,032

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Operating Lease (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Leases, Operating [Abstract]
2019	$ 1,878
2020	1,933
2021	1,989
2022	2,046
2023	689
Total future minimum lease payments	$ 8,535

Net Loss Per Share - Schedule of Earnings Per Share Basic and Diluted (Detail) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2019

^[1]

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Earnings Per Share [Abstract]

Net loss

$ 2,297

$ (11,923)

$ (10,516)

$ (11,691)

$ (8,606)

$ (10,168)

$ (9,023)

$ (6,735)

$ (31,833)

$ (34,532)

Accretion of redeemable convertible preferred stock to redemption value

(16)

Net loss attributable to common stockholders

$ 2,297

$ (11,923)

$ (10,516)

$ (11,691)

$ (8,606)

$ (10,168)

$ (9,023)

$ (6,751)

$ (31,833)

$ (34,548)

Weighted average common shares outstanding, basic and diluted

30,480,330

24,895,670

Net loss per share attributable to common stockholders, basic and diluted

$ (1.04)

$ (1.39)

[1]	The Q4 2019 results include the impact of the adjustment to the transaction price and the expected costs to complete the remaining performance obligations under the terms of the Collaboration Agreement with Seattle Genetics, as described more fully within Footnote 6, Collaboration Agreement.

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss Per Share - Summary of Potential Dilutive Securities (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	5,043,044	3,661,982
Unvested Restricted Common Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	371,161
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per common share	4,671,883	3,661,982

Retirement Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Defined contribution plan, matching amount	$ 0	$ 0

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2019

^[1]

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Revenue

$ 15,288

$ 1,020

$ 3,138

$ 3,053

$ 3,805

$ 2,043

$ 1,666

$ 2,220

$ 22,499

$ 9,734

Loss from operations

2,240

(12,036)

(10,541)

(11,841)

(9,004)

(10,576)

(9,439)

(6,986)

(32,178)

(36,005)

Net loss

2,297

(11,923)

(10,516)

(11,691)

(8,606)

(10,168)

(9,023)

(6,735)

(31,833)

(34,532)

Net loss attributable to common stockholders

$ 2,297

$ (11,923)

$ (10,516)

$ (11,691)

$ (8,606)

$ (10,168)

$ (9,023)

$ (6,751)

$ (31,833)

$ (34,548)

Basic net loss attributable to common stockholders per share:

$ 0.07

$ (0.39)

$ (0.34)

$ (0.39)

$ (0.29)

$ (0.34)

$ (0.31)

$ (0.66)

Weighted average common shares outstanding- basic

30,663,054

30,661,125

30,505,773

30,083,006

30,018,342

29,879,476

29,155,790

10,204,591

Diluted net loss attributable to common stockholders per share:

$ 0.07

$ (0.39)

$ (0.34)

$ (0.39)

$ (0.29)

$ (0.34)

$ (0.31)

$ (0.66)

Weighted average common shares outstanding- diluted

31,195,620

30,661,125

30,505,773

30,083,006

30,018,342

29,879,476

29,155,790

10,204,591

[1]	The Q4 2019 results include the impact of the adjustment to the transaction price and the expected costs to complete the remaining performance obligations under the terms of the Collaboration Agreement with Seattle Genetics, as described more fully within Footnote 6, Collaboration Agreement.

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1337-109256

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=117327953&loc=d3e4984-109258

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1252-109256

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117326831&loc=SL5780133-109256

+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=117327953&loc=d3e4984-109258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1252-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=117326831&loc=d3e1337-109256

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117326831&loc=SL5780133-109256

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Events - Additional Information (Detail) $ in Millions	Mar. 02, 2020 USD ($) Employee	Jan. 16, 2020	Mar. 19, 2020 shares	Dec. 31, 2019 shares	Dec. 31, 2018 shares
Subsequent Event [Line Items]
Shares available per Purchase Agreement with LPC				150,000,000	150,000,000
Shares issued to LPC as commitment fee				30,663,054	30,057,970
Subsequent Event [Member]
Subsequent Event [Line Items]
Collaboration agreement termination effective date		Jan. 16, 2020
Employee workforce, termination percentage	60.00%
Number of employees expected to be terminated \| Employee	43
Severance and employee termination related costs \| $	$ 2.0
Subsequent Event [Member] \| Lincoln Park Capital Fund [Member]
Subsequent Event [Line Items]
Shares available per Purchase Agreement with LPC			25,000,000
Shares issued to LPC as commitment fee			726,382