0001104659-21-043161 | 10-K | XBRL Viewer

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2020	Mar. 22, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	Celldex Therapeutics, Inc.
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		39,614,638
Entity Central Index Key	0000744218
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Security Exchange Name	NASDAQ
Amendment Flag	false
Trading Symbol	CLDX
Title of 12(b) Security	Common Stock, par value $.001
Document Annual Report	true
Document Transition Report	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 507

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 43,836	$ 11,232
Marketable securities	150,586	53,151
Accounts and other receivables	1,802	1,015
Prepaid and other current assets	1,619	1,300
Total current assets	197,843	66,698
Property and equipment, net	3,815	4,031
Operating lease right-of-use assets, net	3,449	3,473
Intangible assets, net	30,690	48,690
Other assets	41	41
Total assets	235,838	122,933
Current liabilities:
Accounts payable	1,048	1,174
Accrued expenses	8,459	6,499
Current portion of operating lease liabilities	1,327	1,944
Current portion of long-term liabilities	3,372	2,026
Total current liabilities	14,206	11,643
Long-term portion of operating lease liabilities	2,154	1,713
Other long-term liabilities	10,121	15,551
Total liabilities	26,481	28,907
Commitments and contingent liabilities (Note 14)
Stockholders' equity:
Convertible preferred stock, $.01 par value; 3,000,000 shares authorized; no shares issued and outstanding at December 31, 2020 and 2019
Common stock, $.001 par value; 297,000,000 shares authorized; 39,603,771 and 16,972,077 shares issued and outstanding at December 31, 2020 and 2019, respectively	40	17
Additional paid-in capital	1,279,824	1,104,706
Accumulated other comprehensive income	2,589	2,619
Accumulated deficit	(1,073,096)	(1,013,316)
Total stockholders' equity	209,357	94,026
Total liabilities and stockholders' equity	$ 235,838	$ 122,933

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED BALANCE SHEETS
Convertible Preferred Stock, Par Value (in dollars per share)	$ 0.01	$ 0.01
Convertible Preferred Stock, Shares Authorized	3,000,000	3,000,000
Convertible Preferred Stock, Shares Issued	0	0
Convertible Preferred Stock, Shares Outstanding	0	0
Common Stock, Par Value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	297,000,000	297,000,000
Common Stock, Shares Issued	39,603,771	16,972,077
Common Stock, Shares Outstanding	39,603,771	16,972,077

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 7,418	$ 3,573	$ 9,538
Operating expenses:
Research and development	42,534	42,672	66,449
General and administrative	14,456	15,426	19,269
Goodwill impairment			90,976
Intangible asset impairment	18,000		18,677
Other asset impairment		1,800
Gain on fair value remeasurement of contingent consideration	(4,218)	(1,294)	(29,621)
Amortization of acquired intangible assets	0	0	224
Total operating expenses	70,772	58,604	165,974
Operating loss	(63,354)	(55,031)	(156,436)
Investment and other income, net	2,407	4,153	4,487
Net loss before income tax benefit	(60,947)	(50,878)	(151,949)
Income tax benefit	1,167		765
Net loss	$ (59,780)	$ (50,878)	$ (151,184)
Basic and diluted net loss per common share	$ (2.02)	$ (3.51)	$ (14.48)
Shares used in calculating basic and diluted net loss per share	29,640	14,507	10,442
Comprehensive loss:
Net loss	$ (59,780)	$ (50,878)	$ (151,184)
Other comprehensive income (loss):
Unrealized (loss) gain on marketable securities	(30)	36	19
Comprehensive loss	(59,810)	(50,842)	(151,165)
Product development and licensing agreements
Revenues:
Total revenues	2,301	473	3,341
Contracts and grants
Revenues:
Total revenues	$ 5,117	$ 3,100	$ 6,197

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Period Start Balance at Dec. 31, 2017	$ 9	$ 1,046,313	$ 2,564	$ (812,517)	$ 236,369
Balance (in shares) at Dec. 31, 2017	9,234,693
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		419			419
Shares issued under stock option and employee stock purchase plans (in shares)	16,047
Shares issued in connection with at the market agreement	$ 3	29,019			29,022
Shares issued in connection with at the market agreement (in shares)	2,702,660
Shares issued in connection with Kolltan severance		71			71
Shares issued in connection with Kolltan severance (in shares)	4,235
Stock-based compensation		8,081			8,081
Unrealized gain on marketable securities			19		19
Net loss				(151,184)	(151,184)
Period End Balance (ASC 606) at Dec. 31, 2018				1,263	1,263
Period End Balance at Dec. 31, 2018	$ 12	1,083,903	2,583	(962,438)	124,060
Balance (in shares) at Dec. 31, 2018	11,957,635
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		9			9
Shares issued under stock option and employee stock purchase plans (in shares)	3,285
Shares issued in connection with at the market agreement	$ 5	16,243			16,248
Shares issued in connection with at the market agreement (in shares)	5,011,157
Stock-based compensation		4,551			4,551
Unrealized gain on marketable securities			36		36
Net loss				(50,878)	(50,878)
Period End Balance at Dec. 31, 2019	$ 17	1,104,706	2,619	(1,013,316)	$ 94,026
Balance (in shares) at Dec. 31, 2019	16,972,077				16,972,077
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		434			$ 434
Shares issued under stock option and employee stock purchase plans (in shares)	122,076
Shares issued in connection with at the market agreement	$ 8	29,423			29,431
Shares issued in connection with at the market agreement (in shares)	7,125,004
Shares issued in underwritten public offering	$ 15	141,346			141,361
Shares issued in underwritten public offering (in shares)	15,384,614
Stock-based compensation		3,915			3,915
Unrealized gain on marketable securities			(30)		(30)
Net loss				(59,780)	(59,780)
Period End Balance at Dec. 31, 2020	$ 40	$ 1,279,824	$ 2,589	$ (1,073,096)	$ 209,357
Balance (in shares) at Dec. 31, 2020	39,603,771				39,603,771

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (59,780)	$ (50,878)	$ (151,184)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,929	4,858	3,577
Amortization of intangible assets	0	0	224
Amortization and premium of marketable securities, net	(729)	(1,140)	(1,048)
(Gain) loss on sale or disposal of assets	(55)	11	1,220
Goodwill impairment			90,976
Intangible asset impairment	18,000		18,677
Other asset impairment		1,800
Gain on fair value remeasurement of contingent consideration	(4,218)	(1,294)	(29,621)
Non-cash income tax benefit	(1,167)		(765)
Stock-based compensation expense	3,915	4,551	8,081
Changes in operating assets and liabilities:
Accounts and other receivables	(787)	2,274	(777)
Prepaid and other current assets	(334)	362	1,783
Other assets		(39)
Accounts payable and accrued expenses	1,638	(321)	(13,110)
Other liabilities	(816)	(6,599)	(3,268)
Net cash used in operating activities	(40,404)	(46,415)	(75,235)
Cash flows from investing activities:
Sales and maturities of marketable securities	123,600	113,173	201,469
Purchases of marketable securities	(220,321)	(95,382)	(171,182)
Acquisition of property and equipment	(1,552)	(731)	(813)
Proceeds from sale or disposal of assets	55	20	342
Net cash (used in) provided by investing activities	(98,218)	17,080	29,816
Cash flows from financing activities:
Net proceeds from stock issuances	170,792	16,248	29,022
Proceeds from issuance of stock from employee benefit plans	434	9	419
Issuance of term loan	2,962
Payment of term loan	(2,962)
Net cash provided by financing activities	171,226	16,257	29,441
Net increase (decrease) in cash and cash equivalents	32,604	(13,078)	(15,978)
Cash and cash equivalents at beginning of period	11,232	24,310	40,288
Cash and cash equivalents at end of period	43,836	11,232	24,310
Non-cash investing activities
Accrued construction in progress	$ 221	$ 25	107
Non-cash supplemental disclosure
Shares issued to former Kolltan executive for settlement of severance			$ 71

Nature of Business and Overview	12 Months Ended
Nature of Business and Overview	Dec. 31, 2020
Nature of Business and Overview
Nature of Business and Overview	(1) Nature of Business and Overview Celldex Therapeutics, Inc. (the “Company” or “Celldex”) is a biopharmaceutical company dedicated to developing therapeutic monoclonal and bispecific antibodies that address diseases for which available treatments are inadequate. The Company is primarily focusing its efforts and resources on the continued research and development of CDX-0159, CDX-1140 and CDX-527. The Board of Directors of the Company approved a one for fifteen reverse stock split of the Company’s outstanding common stock, which was effected on February 8, 2019. All share and per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to additional paid-in capital. At December 31, 2020, the Company had cash, cash equivalents and marketable securities of $194.4 million. The Company has had recurring losses and incurred a loss of $59.8 million for the year ended December 31, 2020. Net cash used in operations for the year ended December 31, 2020 was $40.4 million. The Company believes that the cash, cash equivalents and marketable securities at the filing date of this Form 10-K will be sufficient to meet estimated working capital requirements and fund planned operations for at least the next twelve months from the date of issuance of these financial statements. During the next twelve months and beyond, the Company may take further steps to raise additional capital to meet its long-term liquidity needs including, but not limited to, one or more of the following: the licensing of drug candidates with existing or new collaborative partners, possible business combinations, issuance of debt, or the issuance of common stock or other securities via private placements or public offerings. Although the Company has been successful in raising capital in the past, there can be no assurance that additional financing will be available on acceptable terms, if at all, and the Company’s negotiating position in capital-raising efforts may worsen as existing resources are used. There is also no assurance that the Company will be able to enter into further collaborative relationships. Additional equity financings may be dilutive to the Company’s stockholders; debt financing, if available, may involve significant cash payment obligations and covenants that restrict the Company’s ability to operate as a business; and licensing or strategic collaborations may result in royalties or other terms which reduce the Company’s economic potential from products under development. The Company’s ability to continue funding its planned operations into and beyond twelve months from the issuance date is also dependent on the timing and manner of payment of contingent milestones from the Kolltan acquisition, in the event that the Company achieves the drug candidate milestones related to those payments. The Company, at its option, may decide to pay those milestone payments in cash, shares of its common stock or a combination thereof. If the Company is unable to raise the funds necessary to meet its long-term liquidity needs, it may have to delay or discontinue the development of one or more programs, discontinue or delay ongoing or anticipated clinical trials, license out programs earlier than expected, raise funds at a significant discount or on other unfavorable terms, if at all, or sell all or a part of the Company. 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 hundreds of 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. In an effort to halt the outbreak of COVID-19, various states, including New Jersey, Massachusetts and Connecticut, where the Company has office, research and manufacturing facilities, have placed significant restrictions on travel and many businesses have announced extended closures which could adversely impact our operations. To date, the Company has not experienced significant delays or disruptions in planned and ongoing preclinical and clinical trials, manufacturing or shipping. Potential impacts to our business include delays in planned and ongoing preclinical and clinical trials including enrollment of patients, disruptions in time and resources provided by independent clinical investigators, contract research organizations, other third-party service providers, temporary closures of our facilities, disruptions or restrictions on our employees’ ability to travel, and delays in manufacturing and/or shipments to and from third party suppliers and contract manufacturers for APIs and drug product. Any prolonged negative impacts to our business could materially impact our operating results and could lead to impairments of our Intangible (IPR&D) assets with a carrying value of $30.7 million at December 31, 2020.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

(2) Summary of Significant Accounting Policies

Basis of Presentation

The balance sheets and statements of operations and comprehensive loss, stockholders’ equity, and cash flows, are consolidated for the years ended December 31, 2020, 2019 and 2018. These consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company operates in one segment, which is the business of development, manufacturing and commercialization of novel therapeutics for human health care.

Use of Estimates

The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP) requires management to make estimates and use assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consist principally of money market funds and debt securities.

Marketable Securities

The Company invests its excess cash balances in marketable securities, including municipal bond securities, U.S. government agency securities, and highly rated corporate bonds. The Company classifies all of its marketable securities as current assets on the balance sheets because they are available-for-sale and available to fund current operations. Marketable securities are stated at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity, until such gains and losses are realized. If a decline in the fair value is considered other-than-temporary, based on available evidence, the unrealized loss is reclassified from accumulated other comprehensive income (loss) to the statements of operations. Realized gains and losses are determined on the specific identification method and are included in investment and other income, net.

Concentration of Credit Risk and of Significant Customers and Suppliers

Financial instruments that potentially subject the Company to concentrations of credit risk primarily consist of cash, cash equivalents, marketable securities and accounts receivable. The Company invests its cash, cash equivalents and marketable securities in debt instruments and interest-bearing accounts at major financial institutions in excess of insured limits. The Company mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality. The Company has not historically experienced credit losses from its accounts receivable and therefore has not established an allowance for doubtful accounts.

Revenue from Rockefeller University and Gilead Sciences represented 85% of total Company revenue for the year ended December 31, 2020. Combined revenue from Rockefeller University and Duke University represented 74% of total Company revenue for the year ended December 31, 2019 and combined revenue from BMS, Rockefeller University and International AIDS Vaccine Initiative represented 86% of total Company revenue for the year ended December 31, 2018.

The Company relies on contract manufacturing organizations (CMO) to manufacture drug substance and drug product as well as for future commercial supplies. The Company also relies on CMOs for supply of raw materials as well as filling, packaging, storing and shipping our drug products. The Company relies on third‑party collaborators to develop companion diagnostic tests.

Fair Value Measurements

The Company has certain assets and liabilities that are measured at fair value in the financial statements. The Company seeks to maximize the use of observable inputs (market data obtained from sources independent from the Company) and to minimize the use of unobservable inputs (the Company’s assumptions about how market participants would price assets and liabilities) when measuring the fair value of its assets and liabilities. These assets and liabilities are classified into one of three levels of the following fair value hierarchy as defined by U.S. GAAP:

Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2: Observable inputs other than Level 1 prices, such as quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active.

Level 3: Unobservable inputs based on the Company’s assessment of the assumptions that market participants would use in pricing the asset or liability.

Property and Equipment

Property and equipment is stated at cost and depreciated over the estimated useful lives of the related assets using the straight‑line method. Laboratory equipment and office furniture and equipment are depreciated over five years, and computer equipment is depreciated over three years. Manufacturing equipment is depreciated over seven to ten years. Leasehold improvements are amortized over the shorter of the estimated useful life or the non‑cancelable term of the related lease, including any renewals that are reasonably assured of occurring. Property and equipment under construction is classified as construction in progress and is depreciated or amortized only after the asset is placed in service. Expenditures for maintenance and repairs are charged to expense whereas the costs of significant improvements which extend the life of the underlying asset are capitalized. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are eliminated and any resulting gain or loss is reflected in the Company’s statements of operations and comprehensive loss.

The treatment of costs to construct property and equipment depends on the nature of the costs and the stage of construction. Costs incurred in the project planning, design, construction and installation phases are capitalized as part of the cost of the asset. The Company stops capitalizing these costs when the asset is substantially complete and ready for its intended use. For manufacturing property and equipment, the Company also capitalizes the cost of validating these assets for the underlying manufacturing process. The Company completes the capitalization of validation costs when the asset is substantially complete and ready for its intended use. Costs capitalized include incremental labor and fringe benefits, and direct consultancy services.

Leases

On January 1, 2019, the Company adopted a new U.S. GAAP accounting standard which requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements (ASC 842). The new standard was adopted using the modified retrospective transition method, which requires the Company to apply the standard as of the effective date and does not require restatement of prior periods. The Company elected to apply the package of practical expedients, which allowed the Company to not reassess: (i) whether expired or existing contracts contain leases; (ii) lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. Adoption of this standard did not have a material impact on the Company's Consolidated Statement of Operations and Comprehensive Loss or Statement of Cash Flow, however, upon adoption, the Company recorded right-of-use assets of $3.8 million and lease liabilities of $4.7 million on its Consolidated Balance Sheet related to the Company's operating leases.

The Company has operating leases of office, manufacturing and laboratory space, which have remaining lease terms of one to five years and may include one or more options to renew or terminate early.

The Company determines if an arrangement contains a lease at inception. Operating lease right-of-use assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. Certain adjustments to the right-of-use asset may be required for items such as prepaid or accrued lease payments, initial direct costs paid or incentives received. The Company's leases do not contain an implicit rate, and therefore the Company uses an estimated incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Options to extend or terminate the lease are reflected in the calculation when it is reasonably certain that the option will be exercised. The Company has elected to account for lease and non-lease components as a single lease component, however non-lease components that are variable, such as common area maintenance and utilities, are generally paid separately from rent based on actual costs incurred and therefore are not included in the right-of-use asset and operating lease liability and are reflected as an expense in the period incurred. Leases with an initial term of 12 months or less are not recorded on the balance sheet.

Other Assets

Other assets included a $1.8 million non-controlling investment in a privately-held company that was accounted for under the cost method of accounting as of December 31, 2018. Based on information received in April 2019, it was determined that there was a deterioration of the private company’s financial condition due to a working capital deficiency and an inability to secure additional funding. Therefore, the Company concluded that the investment was impaired, and a non-cash impairment charge of $1.8 million was recorded during the first quarter of 2019.

Contingent Consideration

The Company records contingent consideration resulting from a business combination at its fair value on the acquisition date. The Company determines the fair value of the contingent consideration based primarily on the (i) timing and probability of success of clinical events or regulatory approvals; (ii) timing and probability of success of meeting clinical and commercial milestones; and (iii) discount rates. The Company’s contingent consideration liabilities arose in connection with its acquisition of Kolltan. On a quarterly basis, the Company revalues these obligations and records increases or decreases in their fair value as an adjustment to operating earnings. Changes to contingent consideration obligations can result from adjustments to discount rates, accretion of the discount rates due to the passage of time, changes in the Company’s estimates of the likelihood or timing of achieving development or commercial milestones, changes in the probability of certain clinical events or changes in the assumed probability associated with regulatory approval. The assumptions related to determining the value of contingent consideration include a significant amount of judgment, and any changes in the underlying estimates could have a material impact on the amount of contingent consideration adjustment recorded in any given period.

Intangible Assets

IPR&D assets acquired in a business combination initially are recorded at fair value and accounted for as indefinite-lived intangible assets. The valuation model used to measure the fair value of the Company’s IPR&D assets was primarily a discounted cash flow approach. The assumptions used in determining the fair value of the Company’s IPR&D assets include (i) probability of success; (ii) probability of partnership; (iii) partnership milestones; and (iv) discount rate. These assets are capitalized on the Company’s balance sheets until either the project underlying them is completed or the assets become impaired. If a project is completed, the carrying value of the related intangible asset is amortized over the remaining estimated life of the asset beginning in the period in which the project is completed. If a project becomes impaired or is abandoned, the carrying value of the related intangible asset is written down to its fair value and an impairment charge is taken in the period in which the impairment occurs.

Each IPR&D asset is assessed for impairment at least annually or when impairment indicators are present. The Company has the option to assess qualitative factors to determine if it is more likely than not that the IPR&D asset is impaired and whether it is necessary to perform a quantitative impairment test.

Intangible assets acquired in a business combination with a finite life are recorded at fair value and amortized over the greater of economic consumption or on a straight‑line basis over their estimated useful life.

Goodwill

The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination is allocated to goodwill. Goodwill is evaluated for impairment on an annual basis or when impairment indicators are present. The Company has the option to assess qualitative factors to determine if it is more likely than not that goodwill is impaired and whether it is necessary to perform a quantitative single-step goodwill impairment test. As a result of the discontinuation of the Glemba program, the Company evaluated goodwill for potential impairment in the first quarter of 2018. It was determined that the goodwill asset was fully impaired and an impairment charge of $91.0 million was recorded.

Impairment of Intangible and Long‑Lived Assets

The Company evaluates the recoverability of its long‑lived assets, including property and equipment, right-of-use assets, and intangible assets when circumstances indicate that an event of impairment may have occurred. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written‑down to their estimated fair values.

Revenue Recognition

On January 1, 2018, the Company adopted a new revenue accounting standard, “Revenue from Contracts with Customers” (ASC 606). Upon adoption using the modified retrospective application, the Company recognized a $1.3 million decrease to accumulated deficit, a $0.8 million decrease in deferred revenue and $0.5 million increase in accounts receivable due to the cumulative impact of adopting ASC 606. This impact was driven by the acceleration of revenue using a percentage-of-completion method of accounting under ASC 606 for an open contract that had previously been accounted for using the Contingency Adjusted Performance Model (“CAPM”) under previous guidance. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606. There were no significant changes to the Company’s business processes, systems or internal controls as a result of adopting the new standard. Revenue recognition remained largely unchanged under the new standard.

Revenues are recognized when performance obligations under agreements or contracts are satisfied, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services.

The Company determines revenue recognition through the following steps:

Identification of the contract, or contracts, with a customer;

Identification of the performance obligations in the contract;

Determination of the transaction price;

Allocation of the transaction price to the performance obligations in the contract; and

Recognition of revenue when, or as, the Company satisfies a performance obligation.

Revenue for the Company has historically been derived from biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic drug candidates. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties on any product sales derived from collaborations. The Company assesses the multiple obligations typically within product development contracts to determine the distinct performance obligations and how to allocate the arrangement consideration to each distinct performance obligation.

Under product development agreements, revenue is generally recognized using a cost-to-cost measure of progress. Revenue is recognized based on the costs incurred to date as a percentage of the total estimated costs to fulfill the contract. Incurred cost represents work performed, which corresponds with, and thereby best depicts, the transfer of control to the customer. Due to the nature of the work performed in these arrangements, the estimation of cost at completion is complex, subject to many variables, such as expected clinical trial costs, and requires significant judgements. Circumstances can arise that change original estimates of costs or progress toward completion. Any revisions to estimates are reflected in revenue on a cumulative catch-up basis in the period in which the change in circumstances became known.

Revenue for the Company is also derived from manufacturing and research and development arrangements. The Company owns and operates a cGMP manufacturing facility in Fall River, Massachusetts, to produce drug substance for its current and planned early-stage clinical trials. In order to utilize excess capacity, the Company has, from time to time, entered into contract manufacturing and research and development arrangements in which services are provided on a time-and-material basis or at a negotiated fixed-price. Revenue from time-and-material contracts is generally recognized on an output basis as labor hours and/or direct expenses are incurred. Under fixed-price contracts, revenue is generally recognized on an output basis as progress is made toward completion of the performance obligations using surveys of performance completed to date.

Contract Assets and Liabilities

The Company classifies the right to consideration in exchange for products or services transferred to a client as either a receivable or a contract asset. A receivable is a right to consideration that is unconditional as compared to a contract asset which is a right to consideration that is conditional upon factors other than the passage of time.

The Company’s contract liabilities result from arrangements where the Company has received payment in advance of performance under the contract. These amounts are included as deferred revenue within current portion of long-term liabilities on the condensed consolidated balance sheets.

Research and Development Expenses

Research and development costs, including internal and contract research costs, are expensed as incurred. Research and development expenses consist mainly of clinical trial costs, manufacturing of clinical material, toxicology and other preclinical studies, personnel costs, depreciation, license fees and funding of outside contracted research.

Clinical trial expenses include expenses associated with clinical research organization, or CRO, services. Contract manufacturing expenses include expenses associated with contract manufacturing organization, or CMO, services. The invoicing from CROs and CMOs for services rendered can lag several months. The Company accrues the cost of services rendered in connection with CRO and CMO activities based on our estimate of costs incurred. The Company maintains regular communication with our CROs and CMOs to assess the reasonableness of its estimates. Differences between actual expenses and estimated expenses recorded have not been material and are adjusted for in the period in which they become known.

Patent Costs

Patent costs are expensed to general and administrative expense as incurred. Certain patent costs are reimbursed by the Company’s product development and licensing partners. Any reimbursed patent costs are recorded as product development and licensing agreement revenues in the Company’s financial statements.

Stock‑Based Compensation

The Company records stock-based compensation expense for all stock-based awards made to employees, directors and non-employees based on the estimated fair values of the stock-based awards expected to vest at the grant date and adjusts, if necessary, to reflect actual forfeitures. Compensation expense for all stock-based awards is recognized using the straight-line method over the term of vesting or performance.

Foreign Currency Translation

Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income. At December 31, 2020 and 2019, accumulated other comprehensive income includes a net unrealized gain related to foreign currency translation of $2.6 million.

Income Taxes

The Company uses the asset and liability method to account for income taxes, including the recognition of deferred tax assets and deferred tax liabilities for the anticipated future tax consequences attributable to differences between financial statement amounts and their respective tax basis. Quarterly, the Company reviews its deferred tax assets for recovery. A valuation allowance is established when the Company believes that it is more likely than not that its deferred tax assets will not be realized. Changes in valuation allowances from period to period are included in the Company’s tax provision in the period of change.

The Company records uncertain tax positions in the financial statements only if it is more likely than not that the uncertain tax position will be sustained upon examination by the taxing authorities. The Company records interest and penalties related to uncertain tax positions in income tax expense.

Comprehensive Loss

Comprehensive loss is comprised of net loss and certain changes in stockholders’ equity that are excluded from net loss. The Company includes foreign currency translation adjustments and unrealized gains and losses on marketable securities in other comprehensive loss. The statements of operations and comprehensive loss reflect total comprehensive loss for the years ended December 31, 2020, 2019 and 2018.

Net Loss Per Share

Basic net loss per common share is based upon the weighted‑average number of common shares outstanding during the period, excluding restricted stock that has been issued but is not yet vested. Diluted net loss per common share is based upon the weighted‑average number of common shares outstanding during the period plus additional weighted-average potentially dilutive common shares outstanding during the period when the effect is dilutive. In periods in which the Company reports a net loss, there is no difference between basic and diluted net loss per share because dilutive shares of common stock are not assumed to have been issued as their effect is anti-dilutive. The potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive are as follows:


	Year Ended December 31,
	2020	2019	2018
Stock options	3,042,229	1,699,202	866,132
Restricted stock	—	1,110	3,552
	3,042,229	1,700,312	869,684

Newly-Adopted Accounting Pronouncements

On January 1, 2020, the Company adopted a new accounting standard that modifies certain disclosure requirements for fair value measurements. For instance, the Company is required to disclose weighted average information for significant unobservable inputs for all Level 3 fair value measurements. The adoption of this new guidance did not have a material impact on the Company’s consolidated financial statements and related disclosures. Refer to Note 4 for the disclosures related to the Company’s level 3 fair value measurements.

On January 1, 2020, the Company adopted a new accounting standard that clarifies the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The amendments clarify that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606, when the collaborative arrangement participant is a customer in the context of a unit of account. The adoption of this standard did not have a material impact on our consolidated financial statements, as we have no arrangements within the scope of ASC 808.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption.

In June 2016, the FASB issued guidance on the Measurement of Credit Losses on Financial Instruments. The guidance requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, the standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This standard will be effective for the Company on January 1, 2023. We are currently evaluating the potential impact that this standard may have on the Company's consolidated financial statements and related disclosures.

Accumulated Other Comprehensive Income

12 Months Ended

Dec. 31, 2020

Accumulated Other Comprehensive Income

Accumulated Other Comprehensive Income

(3) Accumulated Other Comprehensive Income

The changes in accumulated other comprehensive income, which is reported as a component of stockholders’ equity, for the year ended December 31, 2020 are summarized below:


	Unrealized
	Gain (Loss) on
	Marketable		Foreign
	Securities		Currency Items		Total
	(In thousands)
Balance at December 31, 2019	$	23	$	2,596	$	2,619
Other comprehensive loss		(30)		—		(30)
Balance at December 31, 2020	$	(7)	$	2,596	$	2,589

No amounts were reclassified out of accumulated other comprehensive income during the years ended December 31, 2020, 2019 and 2018.

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Measurements

Fair Value Measurements

(4) Fair Value Measurements

The following tables set forth the Company’s financial assets and liabilities subject to fair value measurements:


	As of
	December 31, 2020		Level 1	Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	35,066	—	$	35,066		—
Marketable securities		150,586	—		150,586		—
	$	185,652	—	$	185,652		—
Liabilities:
Kolltan acquisition contingent consideration	$	8,267	—		—	$	8,267
	$	8,267	—		—	$	8,267


	As of
	December 31, 2019		Level 1	Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	4,024	—	$	4,024		—
Marketable securities		53,151	—		53,151		—
	$	57,175	—	$	57,175		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,485	—		—	$	12,485
	$	12,485	—		—	$	12,485

The Company’s financial assets consist mainly of cash and cash equivalents and marketable securities and are classified as Level 2 within the valuation hierarchy. The Company values its marketable securities utilizing independent pricing services which normally derive security prices from recently reported trades for identical or similar securities, making adjustments based on significant observable transactions. At each balance sheet date, observable market inputs may include trade information, broker or dealer quotes, bids, offers or a combination of these data sources.

The following table reflects the activity for the Company’s contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2020 (in thousands):


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		(4,218)
Balance at December 31, 2020	$	8,267

The valuation technique used to measure fair value of the Company’s Level 3 liabilities, which consist of contingent consideration related to the acquisition of Kolltan in 2016 (Note 17), was primarily an income approach. The significant unobservable inputs used in the fair value measurement of the contingent consideration are estimates, including probability of success, discount rates and amount of time until the conditions of the milestone payments are met. As of December 31, 2020, the weighted average discount rate used in calculating the fair value of contingent consideration was 8.1% (with a range of 8.0% to 9.0%) and the weighted average amount of time until the conditions of the milestone payments are met was 4 years.

During the year ended December 31, 2020, the Company recorded a $4.2 million gain on fair value remeasurement of contingent consideration, primarily due to updated assumptions for CDX-3379 related milestones due to the discontinuation of the CDX-3379 program partially offset by changes in discount rates and the passage of time. The assumptions related to determining the value of contingent consideration include a significant amount of judgment, and any changes in the underlying estimates could have a material impact on the amount of contingent consideration adjustment recorded in any given period.

The Company did not have any transfers of assets or liabilities between the fair value measurement classifications during the years ended December 31, 2020 and 2019.

- 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

Marketable Securities

12 Months Ended

Dec. 31, 2020

Marketable Securities

Marketable Securities

(5) Marketable Securities

The following is a summary of marketable debt securities, classified as available-for-sale:


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(In thousands)
December 31, 2020
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	40,328	$	3	$	(2)	$	40,329
Maturing after one year through three years		—		—		—		—
Total U.S. government and municipal obligations	$	40,328	$	3	$	(2)	$	40,329
Corporate debt securities
Maturing in one year or less	$	110,265	$	2	$	(10)	$	110,257
Maturing after one year through three years		—		—		—		—
Total corporate debt securities	$	110,265	$	2	$	(10)	$	110,257
Total marketable securities	$	150,593	$	5	$	(12)	$	150,586
December 31, 2019
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	18,509	$	13	$	—	$	18,522
Maturing after one year through three years		—		—		—		—
Total U.S. government and municipal obligations	$	18,509	$	13	$	—	$	18,522
Corporate debt securities
Maturing in one year or less	$	34,619	$	13	$	(3)	$	34,629
Maturing after one year through three years		—		—		—		—
Total corporate debt securities	$	34,619	$	13	$	(3)	$	34,629
Total marketable securities	$	53,128	$	26	$	(3)	$	53,151

The Company holds investment grade marketable securities, and none were considered to be other‑than‑temporarily impaired as of December 31, 2020. Marketable securities include $0.2 million in accrued interest at December 31, 2020 and December 31, 2019.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2020

Property and Equipment, Net

Property and Equipment, Net

(6) Property and Equipment, Net

Property and Equipment, Net includes the following:


	December 31,		December 31,
	2020		2019
	(In thousands)
Laboratory equipment	$	8,566	$	8,622
Manufacturing equipment		2,630		2,510
Office furniture and equipment		3,409		3,873
Leasehold improvements		10,103		17,238
Construction in progress		344		191
Total property and equipment		25,052		32,434
Less: accumulated depreciation and amortization		(21,237)		(28,403)
Property and equipment, net	$	3,815	$	4,031

Depreciation and amortization expense related to property and equipment was $2.0 million, $2.7 million and $3.6 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Leases

12 Months Ended

Dec. 31, 2020

Leases

Leases

(7) Leases

The Company has operating leases of office, manufacturing and laboratory space, which have remaining lease terms of one to five years and may include one or more options to renew or terminate early.

During the year ended December 31, 2020, the Company recorded right of use assets and lease liabilities of $1.9 million related to new leases and lease extensions. During the first quarter of 2019, the Company amended its Hampton, New Jersey lease to eliminate 16,200 square feet of space and extend the remaining 33,400 square feet of space for an additional five-year term with an early termination option after three years. This resulted in an increase to the Company’s right-of-use assets and lease liabilities of $1.4 million during the first quarter of 2019 for the initial 3 years related to the amendment.

Operating lease expense was $2.3 million and $2.5 million for years ended December 31, 2020 and 2019, respectively. Variable lease expense was $1.2 million and $1.5 million for years ended December 31, 2020 and 2019, respectively. Under the prior lease accounting guidance, the Company recorded total operating lease expense and variable lease expense of $4.0 million for the year ended December 31, 2018. Cash paid for amounts included in the measurement of operating lease liabilities was $2.4 million and $3.3 million for the years ended December 31, 2020 and 2019, respectively. As of December 31, 2020, the weighted-average remaining lease term was 2 years and the weighted-average discount rate was 10.4%, compared to a weighted-average remaining lease term of 2 years and weighted average discount rate of 11% as of December 31, 2019.

Future minimum lease payments under non-cancellable leases as of December 31, 2020 were as follows:


2021	$	1,620
2022		1,615
2023		698
Total lease payments		3,933
Less imputed interest		(452)
Present value of operating lease liabilities	$	3,481

Intangible Assets and Goodwill	12 Months Ended
Intangible Assets and Goodwill	Dec. 31, 2020
Intangible Assets and Goodwill
Intangible Assets and Goodwill	(8) Intangible Assets and Goodwill Intangible Assets, Net The Company’s finite-lived intangible assets consisted solely of license rights amended under a 2009 agreement with Amgen Fremont related to developing and commercializing Glemba. As a result of the discontinuation of the Glemba program, the Company concluded that the finite-lived intangible asset was fully impaired and a non-cash impairment charge of $6.9 million was recorded in the first quarter of 2018. Amortization expense for finite intangible assets was $0.2 million for the year ended December 31, 2018 and $0.0 million for the years ended December 31, 2020 and 2019. At December 31, 2020 and 2019, the carrying value of the Company’s indefinite-lived intangible assets was $30.7 million and $48.7 million, respectively. At December 31, 2020, indefinite-lived intangible assets consist of acquired in-process research and development (“IPR&D”) related to the development of the anti-KIT program (including CDX-0159) and the TAM program, a broad antibody discovery effort to generate antibodies that modulate the TAM family of RTKs, comprised of Tyro3, AXL and MerTK.CDX-0159 is in Phase 1 development and the TAM program is in preclinical development. As of December 31, 2020, no IPR&D asset had reached technological feasibility nor did any have alternative future uses. Each IPR&D asset is assessed for impairment at least annually, or more frequently if events or changes in circumstances indicate that IPR&D assets may be impaired. During the fourth quarter of 2020, the Company prioritized its preclinical resources towards ILT4 and non-oncology bispecific antibody programs based on recent data supporting their value. The Company also decided that although it had developed promising data for the AxL target within the TAM program, it will focus its efforts on out-licensing opportunities for its TAM program. As a result, the Company evaluated the TAM program IPR&D asset for potential impairment as a result of changes in projected development and regulatory timelines related to the program. As part of this evaluation, the present value of probability adjusted estimated net future cash flows was used to determine the fair value of the program. The Company concluded that the TAM IPR&D asset was partially impaired, and a non-cash impairment charge of $14.5 million was recorded in the fourth quarter of 2020. The Company evaluated the CDX-3379 IPR&D asset for potential impairment as a result of the discontinuation of the CDX-3379 program in the second quarter of 2020. The Company concluded that the CDX-3379 IPR&D asset was fully impaired, and a non-cash impairment charge of $3.5 million was recorded during the second quarter of 2020. In the first quarter of 2018, as a result of the discontinuation of the Glemba program, the Company concluded that the Glemba IPR&D asset was fully impaired and a non-cash impairment charge of $11.8 million was recorded. The Company performed its annual impairment test of the remaining IPR&D assets during the fourth quarter of 2020 and concluded that the IPR&D assets were not impaired. Due to the nature of IPR&D projects, the Company may experience future delays or failures to obtain regulatory approvals to conduct clinical trials, failures of such clinical trials or other failures to achieve a commercially viable product, and as a result, may recognize further impairment losses in the future. Goodwill In the first quarter of 2018, the Company’s goodwill was evaluated for potential impairment due to the discontinuation of the Glemba program and it was determined that the carrying amount of the Company exceeded its fair value by over $91.0 million. As such, the Company concluded that the goodwill asset was fully impaired and a non-cash impairment charge of $91.0 million was recorded during the first quarter of 2018.

Accrued Expenses

12 Months Ended

Dec. 31, 2020

Accrued Expenses

Accrued Expenses

(9) Accrued Expenses

Accrued expenses include the following:


	December 31,		December 31,
	2020		2019
	(In thousands)
Accrued payroll and employee benefits	$	6,113	$	4,575
Accrued research and development contract costs		1,590		1,186
Accrued professional fees		421		400
Other accrued expenses		335		338
	$	8,459	$	6,499

Other Long-Term Liabilities

12 Months Ended

Dec. 31, 2020

Other Long-Term Liabilities

Other Long-Term Liabilities

(10) Other Long‑Term Liabilities

Other long‑term liabilities include the following:


	December 31,		December 31,
	2020		2019
	(In thousands)
Net deferred tax liabilities related to IPR&D (Note 15)	$	1,840	$	3,007
Deferred income from sale of tax benefits		—		1,831
Contingent milestones (Note 4)		8,267		12,485
Deferred revenue (Note 13)		3,386		254
Total		13,493		17,577
Less current portion		(3,372)		(2,026)
Long-term portion	$	10,121	$	15,551

In November 2015, the Company received approval from the New Jersey Economic Development Authority and agreed to sell New Jersey tax benefits of $9.8 million to an independent third party for $9.2 million. Under the agreement, the Company must maintain a base of operations in New Jersey for five years or the tax benefits must be paid back on a pro‑rata basis based on the number of years completed. During the years ended December 31, 2020, 2019 and 2018, the Company recorded $1.8 million, $2.4 million and $2.5 million to other income related to the sale of these tax benefits, respectively.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2020
Stockholders' Equity
Stockholders' Equity	(11) Stockholders’ Equity Common Stock In November 2020, the Company filed an automatic shelf registration statement with the Securities and Exchange Commission to register for sale any combination of the types of securities described in the shelf registration statement. In May 2016, the Company entered into a controlled equity offering sales agreement with Cantor Fitzgerald & Co. (“Cantor”) to allow the Company to issue and sell shares of its common stock from time to time through Cantor, acting as agent. During the years ended December 31, 2020, 2019 and 2018, the Company issued 7.1 million, 5.0 million and 2.7 million shares of its common stock, respectively, under the agreement with Cantor resulting in net proceeds to the Company of $29.4 million, $16.2 million and $29.0 million, respectively, after deducting commission and offering expenses. At December 31, 2020, the Company had $50.0 million remaining in aggregate gross offering price available under the Company’s November 2020 prospectus supplement. In June 2020, the Company issued 15,384,614 shares of its common stock in an underwritten public offering resulting in net proceeds to the Company of $141.4 million, after deducting underwriting fees and offering expenses. Convertible Preferred Stock At December 31, 2020, the Company had authorized 3,000,000 shares of preferred stock all of which have been designated Class C Preferred Stock including 350,000 shares which have been designated Series C‑1 Junior Participating Cumulative Preferred Stock (the “Series C‑1 Preferred Stock”). No shares of Series C-1 Preferred Stock were outstanding at December 31, 2020 or 2019.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Stock-Based Compensation

Stock-Based Compensation

(12) Stock‑Based Compensation

The Company has the following stock-based compensation plans: the 2004 Employee Stock Purchase Plan (the “2004 ESPP Plan”) and the 2008 Stock Option and Incentive Plan (the “2008 Plan”).

Employee Stock Purchase Plan

At December 31, 2020, a total of 276,666 shares of common stock are reserved for issuance under the 2004 ESPP Plan. Under the 2004 ESPP Plan, each participating employee may purchase shares of common stock through payroll deductions at a purchase price equal to 85% of the lower of the fair market value of the common stock at either the beginning of the offering period or the applicable exercise date. During the years ended December 31, 2020, 2019 and 2018, the Company issued 39,817, 3,507 and 9,524 shares under the 2004 ESPP Plan, respectively. At December 31, 2020, 210,342 shares were available for issuance under the 2004 ESPP Plan.

Employee Stock Option and Incentive Plan

The 2008 Plan permits the granting of incentive stock options (intended to qualify as such under Section 422A of the Internal Revenue Code of 1986, as amended), non‑qualified stock options, stock appreciation rights, performance share units, restricted stock and other awards of restricted stock in lieu of cash bonuses to employees, consultants and non‑employee directors.

At December 31, 2020, the 2008 Plan allowed for a maximum of 4,133,333 shares of common stock to be issued for grants of new awards until June 9, 2025 and grants of incentive stock options until April 16, 2025. The Company’s Board of Directors determines the term of each option, option price, and number of shares for which each option is granted and the rate at which each option vests. Options generally vest over a period not to exceed four years. The term of each option cannot exceed ten years (five years for options granted to holders of more than 10% of the voting stock of the Company), and the exercise price of stock options cannot be less than the fair market value of the common stock at the date of grant (110% of fair market value for incentive stock options granted to holders of more than 10% of the voting stock of the Company). Vesting of all employee and non‑employee director stock option awards may accelerate upon a change in control as defined in the 2008 Plan.

A summary of stock option activity for the year ended December 31, 2020 is as follows:


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options outstanding at December 31, 2019	1,699,202	$	44.87	8.0
Granted	1,512,675	$	10.53
Exercised	(78,259)	$	4.57
Canceled	(91,389)	$	41.86
Options outstanding at December 31, 2020	3,042,229	$	28.93	8.2
Options vested and expected to vest at December 31, 2020	2,881,532	$	30.04	8.2
Options exercisable at December 31, 2020	907,982	$	76.39	6.2
Shares available for grant under the 2008 Plan	898,977

The total intrinsic value of stock options exercised during the years ended December 31, 2020, 2019 and 2018 was $0.8 million, $0.0 million and $0.0 million, respectively. The weighted average grant‑date fair value of stock options granted during the years ended December 31, 2020, 2019 and 2018 was $8.08, $2.08 and $6.60, respectively. The total fair value of stock options vested during the years ended December 31, 2020, 2019 and 2018 was $2.4 million, $4.9 million and $8.0 million, respectively.

The aggregate intrinsic value of stock options outstanding at December 31, 2020 was $24.7 million. The aggregate intrinsic value of stock options vested and expected to vest at December 31, 2020 was $23.3 million. As of December 31, 2020, total compensation cost related to non‑vested employee and non‑employee director stock options not yet recognized was approximately $11.3 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 3.0 years.

Restricted Stock

A summary of restricted stock activity under the 2008 Plan for the year ended December 31, 2020 is as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	(per share)
Outstanding and unvested at December 31, 2019	1,110	$	34.83
Granted	—	$	—
Vested	(1,110)	$	34.83
Canceled	—	$	—
Outstanding and unvested at December 31, 2020	—	$	—

Valuation and Expenses Information

Stock‑based compensation expense for the years ended December 31, 2020, 2019 and 2018 was recorded as follows:


	2020		2019		2018
	(In thousands)
Research and development	$	1,933	$	2,053	$	3,874
General and administrative		1,982		2,498		4,207
Total stock-based compensation expense	$	3,915	$	4,551	$	8,081

The fair values of employee and director stock options granted during the years ended December 31, 2020, 2019 and 2018 were valued using the Black‑Scholes option pricing model with the following assumptions:


	2020	2019	2018
Expected stock price volatility	91 - 98%	90 - 91%	73 - 85%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	0.5 - 0.7%	1.6 - 2.5%	2.8 - 3.1%
Expected dividend yield	None	None	None

The Company estimates expected term based on historical exercise patterns. The Company uses its historical stock price volatility consistent with the expected term of grant as the basis for its expected volatility assumption. The risk‑free interest rate is based upon the yield of U.S. Treasury securities consistent with the expected term of the option. The dividend yield assumption is based on the Company’s history of zero dividend payouts and expectation that no dividends will be paid in the foreseeable future.

Revenue	12 Months Ended
Revenue	Dec. 31, 2020
Revenue
Revenue	(13) Revenue Product Development and Licensing Revenue The Company’s agreement with Rockefeller University, as amended, (the “Rockefeller Agreement”) provides for the Company to perform manufacturing and development services for Rockefeller University for their portfolio of antibodies against HIV. This portfolio was licensed to Gilead Sciences in January 2020 from Rockefeller University (“Rockefeller Transaction”). Pursuant to the Rockefeller Agreement, the Company received an upfront payment of $1.8 million as a result of the Rockefeller Transaction which was recorded to revenue during the first quarter of 2020. The Company is eligible to receive additional payments from Rockefeller University if this portfolio progresses through clinical and commercial development. The Company entered into a clinical collaboration agreement with BMS in 2014 to evaluate the safety, tolerability and preliminary efficacy of varlilumab and Opdivo(R), BMS's PD-1 immune checkpoint inhibitor, in a Phase 1/2 study. Under this agreement, BMS made an upfront payment to Celldex of $5.0 million and provides funding for 50% of the external costs incurred by the Company in connection with the clinical trial. The performance obligations under the collaboration agreement consist of intellectual property licenses and the performance of research and development services. The Company determined that the performance obligations were not separately identifiable and were not distinct (and did not have standalone value) due to the specialized nature of the services to be provided, the dependent relationship between the performance obligations and the Company's proprietary technology that makes them uniquely qualified to perform the R&D services. Therefore, the Company concluded that the collaboration agreement has a single identified or combined performance obligation. As of December 31, 2020, deferred revenue related to the Company's remaining performance obligation under this arrangement was $0.0 million. The Company recorded $0.0 million, $0.2 million and $3.3 million in revenue related to this agreement during the years ended December 31, 2020, 2019 and 2018, respectively. Contract and Grants Revenue The Company has entered into the Rockefeller Agreement and agreements with Gilead Sciences and Duke University pursuant to which the Company performs manufacturing and research and development services on a time-and-materials basis or at a negotiated fixed-price. The Company recognized $4.5 million, $2.6 million and $3.2 million in revenue under these agreements during the years ended December 31, 2020, 2019 and 2018, respectively. During the third quarter of 2020, the Company was awarded a Small Business Innovation Research (“SBIR”) grant from the National Institutes of Health (NIH) to support the Company’s CDX-1140 and CDX-301 programs. The Company recognized $0.4 million in grant revenue under the award during the year ended December 31, 2020. Contract Assets and Liabilities At December 31, 2020 and 2019, the Company’s right to consideration under all contracts was considered unconditional, and as such, there were no recorded contract assets. At December 31, 2020, the Company had $3.4 million in contract liabilities recorded, which is expected to be recognized during the next 12 months as manufacturing and research and development services are performed. At December 31, 2019, the Company had $0.3 million in contract liabilities recorded. Revenue recognized from contract liabilities as of December 31, 2019 during the year ended December 31, 2020 was $0.2 million.

Collaboration Agreements	12 Months Ended
Collaboration Agreements	Dec. 31, 2020
Collaboration Agreements
Collaboration Agreements	(14) Collaboration Agreements The Company has entered into license agreements whereby the Company has received licenses or options to license technology, specified patents and/or patent applications. These license and collaboration agreements generally provide for royalty payments equal to specified percentages of product sales, annual license maintenance fees, continuing patent prosecution costs and potential future milestone payments to third parties upon the achievement of certain development, regulatory and/or commercial milestones. Nonrefundable license fee expense of $0.2 million, $0.1 million and $0.7 million was recorded to research and development expense for the years ended December 31, 2020, 2019 and 2018, respectively. University of Southampton, UK (Southampton) Under a license agreement with Southampton, the Company acquired the rights to develop human antibodies towards CD27, a potentially important target for immunotherapy of various cancers. The Company may be required to pay Southampton milestones of up to approximately $1.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low‑single digits on any net product sales with respect to development and commercialization of CDX-527. Amgen Inc. (Amgen) Under a license agreement with Amgen, the Company acquired the exclusive rights to CDX-301 and CD40 ligand, or CD40L. CDX-301 and CD40L are immune modulating molecules that increase the numbers and activity of immune cells that control immune responses. The Company may be required to pay Amgen milestones of up to $0.9 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low‑single digits on any net product sales with respect to development and commercialization of the technology licensed from Amgen, including CDX‑301. Yale University (Yale) Under a license agreement with Yale, the Company may be required to make a one-time payment to Yale of $3.0 million with respect to each therapeutic or prophylactic RTK royalty-bearing product, including CDX-0159, that achieves a specified commercial milestone. In addition, the Company may be required to pay a low single-digit royalty on annual worldwide net sales of each RTK royalty-bearing product, including CDX-0159. Unless earlier terminated by us or Yale, the Yale license agreement is due to expire no later than May 2038 but may expire earlier on a country by country basis under specified circumstances.

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Taxes

Income Taxes

(15) Income Taxes

The components of income tax benefit (provision) are as follows:


	Year Ended December 31,
	2020		2019		2018
	(In thousands)
Income tax benefit (provision):
Federal	$	16,615	$	13,869	$	22,255
State		5,802		2,170		6,406
Foreign		—		—		913
Expiration of NOLs and R&D credit		(20,294)		(18,966)		—
		2,123		(2,927)		29,574
Deferred tax valuation allowance		(956)		2,927		(28,809)
	$	1,167	$	—	$	765

A reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate is as follows:


	2020		2019		2018
	(In thousands)
Pre-tax loss	$	(60,947)	$	(50,878)	$	(151,949)
Loss at statutory rates		(12,799)		(10,684)		(31,909)
Research and development credits		(1,778)		(1,902)		(2,056)
State taxes		(5,802)		(2,170)		(6,406)
Other		(1,152)		(1,011)		(1,175)
Change in fair value remeasurement of contingent consideration		(886)		(272)		(6,220)
Intangible impairment		—		—		19,105
Impact of pass-through entities		—		—		(913)
Expiration of NOLs and R&D credit		20,294		18,966		—
Change in valuation allowance		956		(2,927)		28,809
Income tax (benefit) provision	$	(1,167)	$	—	$	(765)

Deferred tax assets and liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using future expected enacted rates. The principal components of the deferred tax assets and liabilities at December 31, 2020 and 2019, respectively, are as follows:


	December 31,		December 31,
	2020		2019
	(In thousands)
Gross deferred tax assets
Net operating loss carryforwards	$	174,369	$	172,745
Foreign net operating loss carryforwards		—		—
Tax credit carryforwards		44,936		42,642
Deferred research and development expenses		63,215		70,042
Stock-based compensation		13,196		12,651
Fixed assets		1,303		1,759
Accrued expenses and other		325		328
		297,344		300,167
Gross deferred tax liabilities
IPR&D intangibles		(7,802)		(12,748)
Total deferred tax assets and liabilities		289,542		287,419
Valuation allowance		(291,382)		(290,426)
Net deferred tax liability	$	(1,840)	$	(3,007)

The Company has evaluated the positive and negative evidence bearing upon the realizability of its net deferred tax assets and considered its history of losses, ultimately concluding that it is “more likely than not” that the Company will not recognize the benefits of federal, state and foreign deferred tax assets and, as such, has maintained a full valuation allowance on its deferred tax assets.

In response to COVID-19, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was enacted on March 27, 2020. Among other provisions, the CARES Act included (i) the ability to use net operating losses to offset income without the 80% taxable income limitation enacted as part of the Tax Cuts and Jobs Act (“TCJA”) for net operating losses incurred in the 2018, 2019 or 2020 tax years; and (ii) the ability to claim a current deduction for interest expense up to 50% of adjusted taxable income for the 2019 and 2020 tax years (rather than 30% of adjusted taxable income pursuant to the TCJA). We do not expect that any of the provisions of the CARES Act will result in a material impact to the financial statements.

The net deferred tax liability of $1.8 million and $3.0 million at December 31, 2020 and 2019, respectively, relates to the temporary differences associated with the IPR&D intangible assets acquired in previous business combinations and are not deductible for tax purposes. The Company recorded an income tax benefit of $1.2 million during the year ended December 31, 2020 due to a decrease in deferred tax liabilities resulting from the impairment of the CDX-3379 IPR&D asset in the second quarter of 2020 and the partial impairment of the TAM program IPR&D asset in the fourth quarter of 2020. The Company recorded an income tax benefit of $0.8 million during the year ended December 31, 2018 due to a decrease in deferred tax liabilities resulting from the partial impairment of the anti-KIT program.

As of December 31, 2020, the Company had federal and state net operating loss carryforwards of $611.0 million and $704.8 million, respectively, which may be available to offset certain future income tax liabilities and begin to expire in 2021 and 2028, respectively. Of the federal net operating loss carryforwards of $611.0 million, approximately $214.8 million are from 2018, 2019 and 2020 and have no expiration date. As of December 31, 2020, the Company also had federal and state research and development tax credit carryforwards of $35.1 million and $12.4 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2021 and 2020, respectively.

Utilization of the net operating loss carryforwards and research and credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, or Section 382, due to ownership changes that 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 shareholders or public groups in the stock of a corporation by more than 50% over a three‑year period. The Company has estimated the amounts of net operating loss and research and development tax credit carryforwards which will expire unutilized as a result of its estimated annual limitations under Section 382 and has excluded those amounts from the carryforward amounts disclosed above and in the deferred tax assets and liabilities table included in this footnote. The Company has concluded Section 382 studies through 2015 for Celldex generated NOLs.

Beginning with the 2016 tax returns, the Company elected to classify the Australian entity as a disregarded entity for income tax purposes. The foreign pre-tax losses have been included with the Federal net operating loss carryforwards. In 2019 the Australian Subsidiary was liquidated and $14.9 million of Foreign Net Operating Loss Carryovers related to the foreign subsidiary were written off.

As of December 31, 2020 and 2019, the Company did not have any unrecognized tax benefits.

Massachusetts, New Jersey, New York and Connecticut are the jurisdictions in which the Company primarily operates or has operated and has income tax nexus. The Company is not currently under examination by these or any other jurisdictions for any tax year. Generally, in U.S. federal and state taxing jurisdictions, all years which generated net operating losses and/or tax credit carryforwards remain subject to examination to the extent those carryforwards are utilized in a subsequent period.

Retirement Savings Plan	12 Months Ended
Retirement Savings Plan	Dec. 31, 2020
Retirement Savings Plan
Retirement Savings Plan	(16) Retirement Savings Plan The Company maintains a 401(k) Plan which is available to substantially all employees. Under the terms of the 401(k) Plan, participants may elect to contribute up to 60% of their compensation or the statutory prescribed limits. The Company may make 50% matching contributions on up to 4% of a participant’s annual salary. Benefit expense for the 401(k) Plan was $0.3 million, $0.3 million and $0.4 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Kolltan Acquisition

12 Months Ended

Dec. 31, 2020

Kolltan Acquisition

Kolltan Acquisition

(17) Kolltan Acquisition

On November 29, 2016, the Company acquired all of the share and debt interests of Kolltan Pharmaceuticals, Inc. (“Kolltan”), a clinical-stage biopharmaceutical company, in exchange for 1,217,200 shares of the Company’s common stock plus contingent consideration in the form of development, regulatory approval and sales-based milestones ("Kolltan Milestones") of up to $172.5 million. The Kolltan Milestone payments, if any, may be made, at Celldex's sole election, in cash, in shares of Celldex's common stock or a combination of both, subject to provisions of the Merger Agreement. Certain Kolltan Milestones related to the METRIC clinical study, TAM partnership closing within two years of the acquisition, CDX-3379 and CDX-0158 have been abandoned and, because of this, as of December 31, 2020, the Company believes that the adjusted amount we may be required to pay for future consideration is up to $107.5 million contingent upon the achievement of the Kolltan Milestones.

In October 2019, the Company received a letter from Shareholder Representative Services LLC (“SRS”), the hired representative of the former stockholders of Kolltan, notifying the Company that it objected to the Company’s characterization of the development, regulatory approval and sales-based Kolltan Milestones relating to CDX-0158 as having been abandoned and contending instead that the related milestone payments are due from Celldex to the Kolltan stockholder. The Company disagrees with their objection and believes their objection to be without merit.

On August 18, 2020, Celldex filed a Verified Complaint in the Court of Chancery of the State of Delaware against SRS (acting in its capacity as the representative of the former stockholders of Kolltan pursuant to the Merger Agreement) seeking declaratory relief with respect to the rights and obligations of the parties relating to certain contingent milestone payments under the Merger Agreement relating to the discontinued CDX-0158 program. Specifically, Celldex sought the entry of an order declaring that:

(i)

Celldex’s determination to discontinue the development of CDX-0158 (formerly known as KTN0158) was proper and valid under the Merger Agreement;

(ii)

the Milestone Abandonment Notice dated December 5, 2018 from Celldex was valid and effective under the Merger Agreement and that the “Successful Completion of Phase I Clinical Trial for KTN0158” Milestone has not been achieved and has properly been abandoned; and

(iii)

under the Merger Agreement, the CDX-0159 program is not a program that results in milestone payments under the Merger Agreement.

In SRS’ responsive Answer and Verified Counterclaim, SRS made claims of breach of contract with respect to the Merger Agreement, breach of implied covenant of good faith and fair dealing, declaratory relief, and unjust enrichment regarding abandonment of the CDX-0158 milestones, based in part on SRS’ assertion that the CDX-0159 program is in essence an extension of the CDX-0158 (formerly KTN0158) program. The case remains ongoing and we are currently unable to predict or estimate the outcome of this matter. The case is currently scheduled for trial in 2022.

Following the Company’s discontinuation of the CDX-3379 program, the Company sent a milestone abandonment notice to SRS with respect to Kolltan Milestones related to the CDX-3379 program. In October 2020, the Company received notice that SRS has objected to that notice, seeking further information from the Company.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2020

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

(18) Selected Quarterly Financial Data (Unaudited)


2020	Q1 2020		Q2 2020		Q3 2020		Q4 2020
	(In thousands, except per share amounts)
Total revenue	$	2,728	$	236	$	668	$	3,786
Net loss		(12,625)		(11,031)		(14,224)		(21,900)
Basic and diluted net loss per common share		(0.73)		(0.50)		(0.36)		(0.55)


2019	Q1 2019		Q2 2019		Q3 2019		Q4 2019
	(In thousands, except per share amounts)
Total revenue	$	1,425	$	715	$	546	$	887
Net loss		(17,239)		(11,779)		(11,413)		(10,447)
Basic and diluted net loss per common share		(1.40)		(0.84)		(0.75)		(0.64)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Cash and Cash Equivalents

Marketable Securities

Concentration of Credit Risk and of Significant Customers and Suppliers

Fair Value Measurements

Level 3: Unobservable inputs based on the Company’s assessment of the assumptions that market participants would use in pricing the asset or liability.

Property and Equipment

Leases

The Company has operating leases of office, manufacturing and laboratory space, which have remaining lease terms of one to five years and may include one or more options to renew or terminate early.

Other Assets

Contingent Consideration

Intangible Assets

Goodwill

Impairment of Intangible and Long-Lived Assets

Impairment of Intangible and Long‑Lived Assets

Revenue Recognition

The Company determines revenue recognition through the following steps:

Identification of the contract, or contracts, with a customer;

Identification of the performance obligations in the contract;

Determination of the transaction price;

Allocation of the transaction price to the performance obligations in the contract; and

Recognition of revenue when, or as, the Company satisfies a performance obligation.

Contract Assets and Liabilities

Research and Development Expenses

Patent Costs

Stock-Based Compensation

Stock‑Based Compensation

Foreign Currency Translation

Income Taxes

Comprehensive Loss

Net Loss Per Share


	Year Ended December 31,
	2020	2019	2018
Stock options	3,042,229	1,699,202	866,132
Restricted stock	—	1,110	3,552
	3,042,229	1,700,312	869,684

Newly-Adopted Accounting Pronouncements

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Summary of Significant Accounting Policies

Schedule of potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive


	Year Ended December 31,
	2020	2019	2018
Stock options	3,042,229	1,699,202	866,132
Restricted stock	—	1,110	3,552
	3,042,229	1,700,312	869,684

Accumulated Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2020

Accumulated Other Comprehensive Income

Summary of changes in accumulated other comprehensive income


	Unrealized
	Gain (Loss) on
	Marketable		Foreign
	Securities		Currency Items		Total
	(In thousands)
Balance at December 31, 2019	$	23	$	2,596	$	2,619
Other comprehensive loss		(30)		—		(30)
Balance at December 31, 2020	$	(7)	$	2,596	$	2,589

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Measurements

Schedule of financial assets and liabilities subject to fair value measurements


	As of
	December 31, 2020		Level 1	Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	35,066	—	$	35,066		—
Marketable securities		150,586	—		150,586		—
	$	185,652	—	$	185,652		—
Liabilities:
Kolltan acquisition contingent consideration	$	8,267	—		—	$	8,267
	$	8,267	—		—	$	8,267


	As of
	December 31, 2019		Level 1	Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	4,024	—	$	4,024		—
Marketable securities		53,151	—		53,151		—
	$	57,175	—	$	57,175		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,485	—		—	$	12,485
	$	12,485	—		—	$	12,485

Schedule of the contingent consideration liabilities measured at fair value using Level 3 inputs

The following table reflects the activity for the Company’s contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2020 (in thousands):


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		(4,218)
Balance at December 31, 2020	$	8,267

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

Marketable Securities

Summary of marketable debt securities, classified as available-for-sale


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(In thousands)
December 31, 2020
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	40,328	$	3	$	(2)	$	40,329
Maturing after one year through three years		—		—		—		—
Total U.S. government and municipal obligations	$	40,328	$	3	$	(2)	$	40,329
Corporate debt securities
Maturing in one year or less	$	110,265	$	2	$	(10)	$	110,257
Maturing after one year through three years		—		—		—		—
Total corporate debt securities	$	110,265	$	2	$	(10)	$	110,257
Total marketable securities	$	150,593	$	5	$	(12)	$	150,586
December 31, 2019
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	18,509	$	13	$	—	$	18,522
Maturing after one year through three years		—		—		—		—
Total U.S. government and municipal obligations	$	18,509	$	13	$	—	$	18,522
Corporate debt securities
Maturing in one year or less	$	34,619	$	13	$	(3)	$	34,629
Maturing after one year through three years		—		—		—		—
Total corporate debt securities	$	34,619	$	13	$	(3)	$	34,629
Total marketable securities	$	53,128	$	26	$	(3)	$	53,151

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2020

Property and Equipment, Net

Schedule of property and equipment


	December 31,		December 31,
	2020		2019
	(In thousands)
Laboratory equipment	$	8,566	$	8,622
Manufacturing equipment		2,630		2,510
Office furniture and equipment		3,409		3,873
Leasehold improvements		10,103		17,238
Construction in progress		344		191
Total property and equipment		25,052		32,434
Less: accumulated depreciation and amortization		(21,237)		(28,403)
Property and equipment, net	$	3,815	$	4,031

Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases

Schedule of future minimum lease payments under non-cancellable leases

Future minimum lease payments under non-cancellable leases as of December 31, 2020 were as follows:


2021	$	1,620
2022		1,615
2023		698
Total lease payments		3,933
Less imputed interest		(452)
Present value of operating lease liabilities	$	3,481

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2020

Accrued Expenses

Schedule of accrued expenses


	December 31,		December 31,
	2020		2019
	(In thousands)
Accrued payroll and employee benefits	$	6,113	$	4,575
Accrued research and development contract costs		1,590		1,186
Accrued professional fees		421		400
Other accrued expenses		335		338
	$	8,459	$	6,499

Other Long-Term Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Other Long-Term Liabilities

Schedule of other long-term liabilities


	December 31,		December 31,
	2020		2019
	(In thousands)
Net deferred tax liabilities related to IPR&D (Note 15)	$	1,840	$	3,007
Deferred income from sale of tax benefits		—		1,831
Contingent milestones (Note 4)		8,267		12,485
Deferred revenue (Note 13)		3,386		254
Total		13,493		17,577
Less current portion		(3,372)		(2,026)
Long-term portion	$	10,121	$	15,551

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Stock-Based Compensation

Summary of stock option activity


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options outstanding at December 31, 2019	1,699,202	$	44.87	8.0
Granted	1,512,675	$	10.53
Exercised	(78,259)	$	4.57
Canceled	(91,389)	$	41.86
Options outstanding at December 31, 2020	3,042,229	$	28.93	8.2
Options vested and expected to vest at December 31, 2020	2,881,532	$	30.04	8.2
Options exercisable at December 31, 2020	907,982	$	76.39	6.2
Shares available for grant under the 2008 Plan	898,977

Summary of restricted stock activity


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	(per share)
Outstanding and unvested at December 31, 2019	1,110	$	34.83
Granted	—	$	—
Vested	(1,110)	$	34.83
Canceled	—	$	—
Outstanding and unvested at December 31, 2020	—	$	—

Schedule of stock-based compensation expense


	2020		2019		2018
	(In thousands)
Research and development	$	1,933	$	2,053	$	3,874
General and administrative		1,982		2,498		4,207
Total stock-based compensation expense	$	3,915	$	4,551	$	8,081

Schedule of assumptions used for the fair value of employee stock options granted


	2020	2019	2018
Expected stock price volatility	91 - 98%	90 - 91%	73 - 85%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	0.5 - 0.7%	1.6 - 2.5%	2.8 - 3.1%
Expected dividend yield	None	None	None

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Taxes

Schedule of components of income tax benefit (provision)


	Year Ended December 31,
	2020		2019		2018
	(In thousands)
Income tax benefit (provision):
Federal	$	16,615	$	13,869	$	22,255
State		5,802		2,170		6,406
Foreign		—		—		913
Expiration of NOLs and R&D credit		(20,294)		(18,966)		—
		2,123		(2,927)		29,574
Deferred tax valuation allowance		(956)		2,927		(28,809)
	$	1,167	$	—	$	765

Schedule of reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate


	2020		2019		2018
	(In thousands)
Pre-tax loss	$	(60,947)	$	(50,878)	$	(151,949)
Loss at statutory rates		(12,799)		(10,684)		(31,909)
Research and development credits		(1,778)		(1,902)		(2,056)
State taxes		(5,802)		(2,170)		(6,406)
Other		(1,152)		(1,011)		(1,175)
Change in fair value remeasurement of contingent consideration		(886)		(272)		(6,220)
Intangible impairment		—		—		19,105
Impact of pass-through entities		—		—		(913)
Expiration of NOLs and R&D credit		20,294		18,966		—
Change in valuation allowance		956		(2,927)		28,809
Income tax (benefit) provision	$	(1,167)	$	—	$	(765)

Schedule of principal components of the deferred tax assets and liabilities


	December 31,		December 31,
	2020		2019
	(In thousands)
Gross deferred tax assets
Net operating loss carryforwards	$	174,369	$	172,745
Foreign net operating loss carryforwards		—		—
Tax credit carryforwards		44,936		42,642
Deferred research and development expenses		63,215		70,042
Stock-based compensation		13,196		12,651
Fixed assets		1,303		1,759
Accrued expenses and other		325		328
		297,344		300,167
Gross deferred tax liabilities
IPR&D intangibles		(7,802)		(12,748)
Total deferred tax assets and liabilities		289,542		287,419
Valuation allowance		(291,382)		(290,426)
Net deferred tax liability	$	(1,840)	$	(3,007)

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2020

Selected Quarterly Financial Data (Unaudited)

Schedule of selected quarterly financial data (unaudited)


2020	Q1 2020		Q2 2020		Q3 2020		Q4 2020
	(In thousands, except per share amounts)
Total revenue	$	2,728	$	236	$	668	$	3,786
Net loss		(12,625)		(11,031)		(14,224)		(21,900)
Basic and diluted net loss per common share		(0.73)		(0.50)		(0.36)		(0.55)


2019	Q1 2019		Q2 2019		Q3 2019		Q4 2019
	(In thousands, except per share amounts)
Total revenue	$	1,425	$	715	$	546	$	887
Net loss		(17,239)		(11,779)		(11,413)		(10,447)
Basic and diluted net loss per common share		(1.40)		(0.84)		(0.75)		(0.64)

Nature of Business and Overview (Details) $ in Thousands		3 Months Ended								12 Months Ended
Nature of Business and Overview (Details) $ in Thousands	Feb. 08, 2019	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Nature of Business and Overview
Reverse stock split	0.067
Cash, cash equivalents and marketable securities		$ 194,400								$ 194,400
Net loss		(21,900)	$ (14,224)	$ (11,031)	$ (12,625)	$ (10,447)	$ (11,413)	$ (11,779)	$ (17,239)	(59,780)	$ (50,878)	$ (151,184)
Net cash used in operations										(40,404)	(46,415)	$ (75,235)
Gross carrying amount of indefinite-lived		$ 30,700				$ 48,700				$ 30,700	$ 48,700

Summary of Significant Accounting Policies - Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2020 segment
Summary of Significant Accounting Policies
Operating segments (in segments)	1

Summary of Significant Accounting Policies - Concentration of Credit Risk and Significant Customers and Suppliers (Details) - Revenue - Customer concentration	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Combined Rockefeller University and Gilead Sciences
Concentration risk
Concentration risk (as a percent)	85.00%
Combined Rockefeller and Duke University
Concentration risk
Concentration risk (as a percent)		74.00%
Combined BMS, Rockefeller and International AIDS Vaccine Initiative
Concentration risk
Concentration risk (as a percent)			86.00%

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Laboratory equipment
Property and Equipment
Useful lives (in years)	5 years
Office furniture and equipment
Property and Equipment
Useful lives (in years)	5 years
Computer equipment
Property and Equipment
Useful lives (in years)	3 years
Manufacturing equipment \| Minimum
Property and Equipment
Useful lives (in years)	7 years
Manufacturing equipment \| Maximum
Property and Equipment
Useful lives (in years)	10 years

Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Right-of-use assets		$ 3,449	$ 3,473
Lease liabilities		3,481
ASC 842
Lease, Practical Expedients, Package [true false]	true
Right-of-use assets	$ 3,800	1,900		$ 1,400
Lease liabilities	$ 4,700	$ 1,900		$ 1,400
Term of lease (in years)				3 years
Minimum
Term of lease (in years)		1 year
Maximum
Term of lease (in years)		5 years

Summary of Significant Accounting Policies - Other Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Non-controlling investment		$ 1.8
Non-cash impairment charge on investments	$ 1.8

Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018
Goodwill
Non-cash impairment charge of goodwill		$ 90,976
Glemba
Goodwill
Non-cash impairment charge of goodwill	$ 91,000

Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2018
Revenue Recognition
Accumulated deficit	$ (1,073,096)	$ (1,013,316)
Deferred revenue	3,386	254
Accounts receivable	$ 1,802	$ 1,015
ASC 606
Revenue Recognition
Accumulated deficit			$ (1,300)
Deferred revenue			(800)
Accounts receivable			$ 500

Summary of Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies
Unrealized gain related to foreign currency translation included in AOCI	$ 2.6	$ 2.6

- Definition

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

+ References + Details

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	3,042,229	1,700,312	869,684
Stock options
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	3,042,229	1,699,202	866,132
Restricted Stock
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive		1,110	3,552

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income
Period Start Balance	$ 94,026	$ 124,060	$ 236,369
Period End Balance	209,357	94,026	124,060
Amounts reclassified from AOCI	0	0	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	23
Other comprehensive loss	(30)
Period End Balance	(7)	23
Foreign Currency Items
Accumulated Other Comprehensive Income
Period Start Balance	2,596
Period End Balance	2,596	2,596
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income
Period Start Balance	2,619	2,583	2,564
Other comprehensive loss	(30)
Period End Balance	$ 2,589	$ 2,619	$ 2,583

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Liabilities:
Kolltan acquisition contingent consideration	$ 8,267	$ 12,485
Fair value \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Fair Value Measurements. \| Level 2
Assets:
Money market funds and cash equivalents	35,066	4,024
Marketable securities	150,586	53,151
Total financial assets at fair value	185,652	57,175
Fair Value Measurements. \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Total financial liabilities at fair value	8,267	12,485
Fair Value Measurements. \| Fair value
Assets:
Money market funds and cash equivalents	35,066	4,024
Marketable securities	150,586	53,151
Total financial assets at fair value	185,652	57,175
Liabilities:
Kolltan acquisition contingent consideration	8,267	12,485
Total financial liabilities at fair value	$ 8,267	$ 12,485

Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Contingent consideration liabilities measured at fair value
Balance at beginning of period	$ 12,485
Balance at end of period	8,267
Fair value \| Level 3
Contingent consideration liabilities measured at fair value
Balance at beginning of period	12,485
Fair value adjustments included in operating expenses	(4,218)
Balance at end of period	$ 8,267

Fair Value Measurements - Additional information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) Y	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair value measurements
Measurement input \| Y	4
Gain on Fair Value Remeasurement of Contingent Consideration	$ 4,218	$ 1,294	$ 29,621
Discount rate \| Weighted average
Fair value measurements
Measurement input	8.1
Discount rate \| Minimum
Fair value measurements
Measurement input	8.0
Discount rate \| Maximum
Fair value measurements
Measurement input	9.0
Fair value
Fair value measurements
Asset transfer out of level 3	$ 0	0
Asset transfer into level 3	0	0
Liabilities transfers out of level 3	0	0
Liabilities transfers into level 3	0	0
Assets level 1 to level 2 transfers	0	0
Assets level 2 to level 1 transfers	0	0
Liabilities level 1 to level 2 transfers	0	0
Liabilities level 2 to level 1 transfers	$ 0	$ 0

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 150,593	$ 53,128
Gross Unrealized Gains
Gross Unrealized Gains	5	26
Gross Unrealized Losses
Gross Unrealized Losses	(12)	(3)
Fair Value
Fair Value	150,586	53,151
U.S. government and municipal obligations
Amortized Cost
Maturing in one year or less	40,328	18,509
Amortized Cost	40,328	18,509
Gross Unrealized Gains
Maturing in one year or less	3	13
Gross Unrealized Gains	3	13
Gross Unrealized Losses
Maturing in one year or less	(2)
Gross Unrealized Losses	(2)
Fair Value
Maturing in one year or less	40,329	18,522
Fair Value	40,329	18,522
Corporate debt securities
Amortized Cost
Maturing in one year or less	110,265	34,619
Amortized Cost	110,265	34,619
Gross Unrealized Gains
Maturing in one year or less	2	13
Gross Unrealized Gains	2	13
Gross Unrealized Losses
Maturing in one year or less	(10)	(3)
Gross Unrealized Losses	(10)	(3)
Fair Value
Maturing in one year or less	110,257	34,629
Fair Value	$ 110,257	$ 34,629

Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities
Number of investment-grade securities in unrealized loss position over 12 months	$ 0
Accrued interest	$ 200	$ 200

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment
Total property and equipment	$ 25,052	$ 32,434
Less: accumulated depreciation and amortization	(21,237)	(28,403)
Property and equipment, net	3,815	4,031
Depreciation and amortization expense	3,929	4,858	$ 3,577
Laboratory equipment
Property and Equipment
Total property and equipment	8,566	8,622
Manufacturing equipment
Property and Equipment
Total property and equipment	2,630	2,510
Office furniture and equipment
Property and Equipment
Total property and equipment	3,409	3,873
Leasehold improvements
Property and Equipment
Total property and equipment	10,103	17,238
Construction in progress
Property and Equipment
Total property and equipment	344	191
Property and equipment
Property and Equipment
Depreciation and amortization expense	$ 2,000	$ 2,700	$ 3,600

Leases (Details) $ in Thousands	12 Months Ended
Leases (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) ft²	Jan. 01, 2019 USD ($)
Leases
Lease to eliminate square feet \| ft²				16,200
Renewal term (in years)				5 years
Lease, remaining square feet \| ft²				33,400
Lease liabilities	$ 3,481
Right-of-use assets	3,449	$ 3,473
Operating lease expense	2,300	2,500	$ 4,000
Variable lease expense	1,200	1,500	$ 4,000
Operating lease payments	$ 2,400	$ 3,300
Weighted-average remaining lease term	0 years	2 years
Weighted-average discount rate	10.40%	11.00%
Minimum
Leases
Term of lease (in years)	1 year
Maximum
Leases
Term of lease (in years)	5 years
ASC 842
Leases
Term of lease (in years)				3 years
Lease liabilities	$ 1,900			$ 1,400	$ 4,700
Right-of-use assets	$ 1,900			$ 1,400	$ 3,800

Leases - Future minimum lease payments under non-cancellable leases (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Operating lease liabilities, payments due
2021	$ 1,620
2022	1,615
2023	698
Total lease payments	3,933
Less imputed interest	(452)
Present value of operating lease liabilities	$ 3,481

Intangible Assets and Goodwill - Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible assets
Amortization of acquired intangible assets				$ 0	$ 0	$ 224
Indefinite-lived intangible assets	$ 30,700			30,700	$ 48,700
Non-cash impairment charge, indefinite-lived				$ 18,000		$ 18,677
IPR&D
Intangible assets
Non-cash impairment charge, indefinite-lived	$ 14,500	$ 3,500	$ 11,800
License Rights
Intangible assets
Non-cash impairment charge, finite lived			$ 6,900

Intangible Assets and Goodwill - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018
Goodwill
Non-cash impairment charge of goodwill		$ 90,976
Glemba
Goodwill
Amount of carrying amount in excess of fair value amount	$ 91,000
Non-cash impairment charge of goodwill	$ 91,000

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Expenses
Accrued payroll and employee benefits	$ 6,113	$ 4,575
Accrued research and development contract costs	1,590	1,186
Accrued professional fees	421	400
Other accrued expenses	335	338
Accrued expenses	$ 8,459	$ 6,499

Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Other Long-Term Liabilities
Net deferred tax liabilities related to IPR&D (Note 15)	$ 1,840	$ 3,007
Deferred income from sale of tax benefits		1,831
Contingent milestones (Note 4)	8,267	12,485
Deferred revenue	3,386	254
Total	13,493	17,577
Less current portion	(3,372)	(2,026)
Long-term portion	$ 10,121	$ 15,551

Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment and other income		$ 2,407	$ 4,153	$ 4,487
New Jersey tax benefits
Amount of tax benefit	$ 9,800
Proceeds from sale of tax credits	$ 9,200
Base of operations requirement (in years)		5 years
Investment and other income		$ 1,800	$ 2,400	$ 2,500

Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Stockholders' Equity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Preferred stock, shares authorized		3,000,000	3,000,000
Preferred stock, shares outstanding		0	0
Net proceeds from sale of common stock		$ 170,792	$ 16,248	$ 29,022
Series C-1 Preferred Stock
Preferred stock, shares authorized		350,000
Preferred stock, shares outstanding		0	0
Common Stock
Shares issued in connection with at the market agreement (in shares)		7,125,004	5,011,157	2,702,660
Common stock issued (in shares)		15,384,614
Aggregate gross offering price available		$ 50,000
Underwritten Public Offering
Net proceeds from sale of common stock	$ 141,400
Common stock issued (in shares)	15,384,614

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Common stock reserved for issuance (in shares)	276,666
Purchase price of fair value of common stock (in percent)	85.00%
Issued (in shares)	39,817	3,507	9,524
Available for issuance (in shares)	210,342

Stock-Based Compensation - Employee Stock Option and Incentive Plan (Details) - Stock options	12 Months Ended
	Dec. 31, 2020 shares
Stock-Based Compensation
Common stock authorized grants (in shares)	4,133,333
Vesting period (in years)	4 years
Expiration period (in years)	10 years
Principal Owner
Stock-Based Compensation
Expiration period (in years)	5 years
Exercise price as a percentage of fair market value	110.00%

Stock-Based Compensation - Stock Option Activity (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Shares
Options outstanding at beginning of the period (in shares)	1,699,202
Granted (in shares)	1,512,675
Exercised (in shares)	(78,259)
Canceled (in shares)	(91,389)
Options outstanding at the end of the period (in shares)	3,042,229	1,699,202
Options vested and expected to vest at the end of the period (in shares)	2,881,532
Options exercisable at the end of the period (in shares)	907,982
Shares available for grant under the 2008 Plan	898,977
Weighted Average Exercise Price Per Share
Options outstanding at beginning of the period (in dollars per share)	$ 44.87
Granted (in dollars per share)	10.53
Exercised (in dollars per share)	4.57
Canceled (in dollars per share)	41.86
Options outstanding at the end of the period (in dollars per share)	28.93	$ 44.87
Options vested and expected to Vest at the end of the period (in dollars per share)	30.04
Options exercisable at the end of the period (in dollars per share)	$ 76.39
Weighted Average Remaining Contractual Term (In Years)
Options outstanding at the end of the period	0 years	8 years
Options vested and expected to vest at the end of the period	0 years
Options exercisable at the end of the period	0 years

Stock-Based Compensation - Employee Stock Option and Incentive Plan Activity Additional Information (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Additional information
Intrinsic value of options exercised	$ 0.8	$ 0.0	$ 0.0
Weighted average grant-date fair value (in dollars per share)	$ 8.08	$ 2.08	$ 6.60
Fair value of options vested	$ 2.4	$ 4.9	$ 8.0
Intrinsic value of options outstanding	24.7
Intrinsic value of options vested and expected to vest	23.3
Compensation cost not yet recognized	$ 11.3
Weighted average period compensation cost is expected to be recognized (in years)	0 years

Stock-Based Compensation - Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation expense
Stock-based compensation expense	$ 3,915	$ 4,551	$ 8,081
Research and development
Stock-based compensation expense
Stock-based compensation expense	1,933	2,053	3,874
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 1,982	$ 2,498	$ 4,207

Stock-Based Compensation - Restricted Stock (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Shares
Outstanding and unvested at the beginning of the period (in shares) \| shares	1,110
Vested (in shares) \| shares	(1,110)
Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at the beginning of the period (in dollars per share) \| $ / shares	$ 34.83
Vested (in dollars per share) \| $ / shares	$ 34.83

Stock-Based Compensation - Valuation (Details) - Stock options	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Black-Scholes option with following assumptions:
Expected stock price volatility, minimum (as a percent)	91.00%	90.00%	73.00%
Expected stock price volatility, maximum (as a percent)	98.00%	91.00%	85.00%
Expected option term	6 years	6 years	6 years
Risk-free interest rate, minimum (as a percent)	0.50%	1.60%	2.80%
Risk-free interest rate, maximum (as a percent)	0.70%	2.50%	3.10%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2014
Revenue
Contract assets	$ 0								$ 0
Contract liability	3,386				$ 254				3,386	$ 254
Revenue, contract liabilities									200
Revenues	3,786	$ 668	$ 236	$ 2,728	$ 887	$ 546	$ 715	$ 1,425	7,418	3,573	$ 9,538
Product development and licensing agreements
Revenue
Revenues									2,301	473	3,341
Contracts and grants
Revenue
Revenues									5,117	3,100	6,197
Rockefeller \| Product development and licensing agreements
Revenue
Revenue, contract liabilities				$ 1,800
Rockefeller \| Contracts and grants
Revenue
Revenues									4,500	2,600	3,200
Bristol-Myers Squibb Company \| Product development and licensing agreements
Revenue
Revenues									0	$ 200	$ 3,300
Deferred Revenue	$ 0								0			$ 5,000
Reimbursement of external costs (as percent)												50.00%
IAVI & Frontier \| Contracts and grants
Revenue
Revenues									$ 400

Collaboration Agreements (Details) - USD ($) $ in Millions	12 Months Ended
Collaboration Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Collaborative Agreements
License fee expense	$ 0.2	$ 0.1	$ 0.7
Type of cost of goods sold line item	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Southampton
Collaborative Agreements
Potential milestone payment	$ 1.0
Amgen
Collaborative Agreements
Potential milestone payment	0.9
Yale
Collaborative Agreements
Potential milestone payment	$ 3.0

Income Taxes - Benefit (Provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income tax benefit (provision):
Federal	$ 16,615	$ 13,869	$ 22,255
State	5,802	2,170	6,406
Foreign			913
Expiration of NOLs and R&D Credit	(20,294)	(18,966)
Income tax benefit (provision) before valuation allowance	2,123	(2,927)	29,574
Deferred tax valuation allowance	(956)	$ 2,927	(28,809)
Income tax benefit (provision)	$ 1,167		$ 765

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation between the amount of reported income tax and the amount computed using U.S. Statutory rate
Pre-tax loss	$ (60,947)	$ (50,878)	$ (151,949)
Loss at statutory rates	(12,799)	(10,684)	(31,909)
Research and development credits	(1,778)	(1,902)	(2,056)
State taxes	(5,802)	(2,170)	(6,406)
Other	(1,152)	(1,011)	(1,175)
Change in fair value remeasurement of contingent consideration	(886)	(272)	(6,220)
Intangible impairment			19,105
Impact of pass-through entities			(913)
Expiration of NOLs and R&D credit	20,294	18,966
Change in Valuation Allowance	956	$ (2,927)	28,809
Income tax (benefit) provision	$ (1,167)		$ (765)

Income Taxes - Summary of Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019
Gross deferred tax assets
Net operating loss carryforwards	$ 174,369		$ 172,745
Tax credit carryforwards	44,936		42,642
Deferred research and development expenses	63,215		70,042
Stock-based compensation	13,196		12,651
Fixed assets	1,303		1,759
Accrued expenses and other	325		328
Gross deferred tax assets	297,344		300,167
Gross deferred tax liabilities
IPR&D intangibles	7,802		12,748
Total deferred tax assets and liabilities	289,542		287,419
Valuation Allowance	(291,382)		(290,426)
Net deferred tax liability	1,840		$ 3,007
Principal components of the deferred tax assets and liabilities
Income Tax Benefit	$ (1,167)	$ (765)

Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards
Foreign pre-tax loss	$ 0.0	$ 0.0
Federal
Operating Loss Carryforwards
Net operating loss carryforwards	611.0	611.0	$ 611.0
Net operating loss carryforwards with no expiration date		214.8
Federal \| R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	35.1
State
Operating Loss Carryforwards
Net operating loss carryforwards	704.8
State \| R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	$ 12.4
Australian Subsidiary
Operating Loss Carryforwards
Foreign Net Operating Loss written off		$ 14.9

Retirement Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
Retirement Savings Plan (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Savings Plan
Maximum contribution by participants (as a percent)	60.00%
Employer matching contributions (as a percent)	50.00%
Maximum percentage of employees' gross pay subject to employer matching contributions	4.00%
Benefit expense for the 401(k) Plan	$ 0.3	$ 0.3	$ 0.4

Kolltan Acquisition (Details) - USD ($) $ in Millions	Nov. 29, 2016	Dec. 31, 2020
Kolltan Acquisition
Shares issued as part of consideration (in shares)	1,217,200
Kolltan
Kolltan Acquisition
Potential milestone payments	$ 172.5
Kolltan \| Specified development, regulatory approvals or sales-based milestones
Kolltan Acquisition
Potential milestone payments		$ 107.5

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Quarterly Financial Data (Unaudited)
Revenues	$ 3,786	$ 668	$ 236	$ 2,728	$ 887	$ 546	$ 715	$ 1,425	$ 7,418	$ 3,573	$ 9,538
Net loss	$ (21,900)	$ (14,224)	$ (11,031)	$ (12,625)	$ (10,447)	$ (11,413)	$ (11,779)	$ (17,239)	$ (59,780)	$ (50,878)	$ (151,184)
Basic and diluted net loss per common share (in dollars per share)	$ (0.55)	$ (0.36)	$ (0.50)	$ (0.73)	$ (0.64)	$ (0.75)	$ (0.84)	$ (1.40)	$ (2.02)	$ (3.51)	$ (14.48)