Aceragen (ACGN) 10-K 31 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 31, 2022	Jun. 30, 2021
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2021
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-31918
Entity Registrant Name	IDERA PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3072298
Entity Address, Address Line One	505 Eagleview Blvd., Suite 212
Entity Address, City or Town	Exton
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19341
City Area Code	484
Local Phone Number	348-1600
Title of 12(b) Security	Common Stock, $.001 par value
Trading Symbol	IDRA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
ICFR Auditor Attestation Flag	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		52,924,870
Entity Public Float			$ 63.8
Entity Central Index Key	0000861838
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Auditor Firm ID	42
Auditor Name	ERNST & YOUNG LLP
Auditor Location	Philadelphia, Pennsylvania

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 32,545	$ 33,229
Short-term investments		4,499
Prepaid expenses and other current assets	1,493	3,627
Total current assets	34,038	41,355
Property and equipment, net	22	44
Operating lease right-of-use assets	734	930
Other assets	70	70
Total assets	34,864	42,399
Current liabilities:
Accounts payable	565	329
Accrued expenses	4,088	6,072
Operating lease liability	209	191
Other current liability	0	435
Total current liabilities	4,862	7,027
Warrant liability, long-term		6,983
Future tranche right liability, long-term		118,803
Operating lease liability, net of current portion	549	758
Total liabilities	5,411	133,571
Commitments and contingencies (Note 12)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 52,818 and 38,291 at December 31, 2021 and December 31, 2020, respectively	53	38
Additional paid-in capital	764,861	742,342
Accumulated deficit	(735,461)	(833,552)
Total stockholders' deficit	29,453	(91,172)
Total liabilities and stockholders' deficit	34,864	42,399
Series B1 Redeemable Convertible Preferred Stock
TEMPORARY EQUITY
Preferred stock
Series A Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	140,000,000	140,000,000
Common stock, shares issued	52,818,000	38,291,000
Common stock, shares outstanding	52,818,000	38,291,000
Series B1 Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	277,921	278,000
Preferred stock, shares issued	0	24,000
Preferred stock, shares outstanding	0	24,000
Common stock, shares outstanding		24,000
Series A Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	1,500,000	1,500,000
Preferred stock, shares issued	1,000	1,000
Preferred stock, shares outstanding	655	655

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
STATEMENTS OF OPERATIONS
Alliance revenue			$ 1,448
Revenue, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Operating expenses:
Research and development	$ 16,375	$ 24,772	$ 34,853
General and administrative	9,976	11,915	12,481
Restructuring costs	1,322		181
Total operating expenses	27,673	36,687	47,515
Loss from operations	(27,673)	(36,687)	(46,067)
Other income (expense):
Interest income	9	165	1,150
Interest expense	(7)	(3)
Warrant revaluation gain (loss)	6,983	(3,742)	(598)
Future tranche right revaluation gain (loss)	118,803	(72,367)	(10,964)
Foreign currency exchange loss	(24)	(28)	(36)
Net income / (loss)	98,091	(112,662)	(56,515)
Deemed dividend on preferred stock related to December 2019 Private Placement (see Note 7)			(28,043)
Undistributed earnings to preferred stockholders	(1,150)
Net income (loss) applicable to common stockholders	96,941	(112,662)	(84,558)
Net income (loss) applicable to common stockholders (Note 16)
Net income (loss)	96,941	(112,662)	(84,558)
Diluted	$ (28,845)	$ (112,662)	$ (84,558)
Net income (loss) per share applicable to common stockholders (Note 16)
Basic	$ 1.97	$ (3.33)	$ (2.96)
Diluted	$ (0.58)	$ (3.33)	$ (2.96)
Weighted-average number of common shares used in computing net income (loss) per share applicable to common stockholders
Basic	49,203	33,821	28,545
Diluted	50,127	33,821	28,545

STATEMENTS OF REDEEMABLE PREFER

STATEMENTS OF REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Series B1 Redeemable Convertible Preferred Stock	Total
Beginning balance at Dec. 31, 2018	$ 27	$ 728,342	$ (664,375)		$ 63,994
Beginning balance (in shares) at Dec. 31, 2018	27,188,000
Sale of redeemable convertible preferred stock				24,000
Sale of common stock, net of issuance costs	$ 3	5,295			5,298
Sale of common stock, net of issuance costs (in shares)	2,068,000
Deemed dividend related to December 2019 Private Placement (Note 7)		(28,043)			(28,043)
Issuance of commitment shares (in shares)	270,000
Issuance of common stock under employee stock purchase plan		121			121
Issuance of common stock under employee stock purchase plan (in shares)	61,000
Issuance of common stock upon exercise of common stock options and warrants		3			3
Issuance of common stock upon exercise of common stock options and warrants (in shares)	38,000
Issuance of common stock for services rendered		129			129
Issuance of common stock for services rendered (in shares)	47,000
Stock-based compensation expense		3,845			3,845
Net income (loss)			(56,515)		(56,515)
Ending balance at Dec. 31, 2019	$ 30	709,692	(720,890)		(11,168)
Ending balance (in shares) at Dec. 31, 2019	29,672,000			24,000
Sale of common stock, net of issuance costs	$ 8	28,638			28,646
Sale of common stock, net of issuance costs (in shares)	8,218,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)	177,000
Issuance of common stock under employee stock purchase plan		113			113
Issuance of common stock under employee stock purchase plan (in shares)	76,000
Issuance of common stock upon exercise of common stock options and warrants		15			15
Issuance of common stock upon exercise of common stock options and warrants (in shares)	5,000
Issuance of common stock for services rendered		243			243
Issuance of common stock for services rendered (in shares)	143,000
Stock-based compensation expense		3,641			3,641
Net income (loss)			(112,662)		(112,662)
Ending balance at Dec. 31, 2020	$ 38	742,342	(833,552)		$ (91,172)
Ending balance (in shares) at Dec. 31, 2020	38,291,000			24,000	38,291,000
Sale of common stock, net of issuance costs	$ 6	19,509			$ 19,515
Sale of common stock, net of issuance costs (in shares)	5,918,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)	237,000
Issuance of common stock under employee stock purchase plan		59			59
Issuance of common stock under employee stock purchase plan (in shares)	49,000
Issuance of common stock upon exercise of common stock options and warrants	$ 7	264			271
Issuance of common stock upon exercise of common stock options and warrants (in shares)	5,871,000
Issuance of common stock for services rendered		152			152
Issuance of common stock for services rendered (in shares)	84,000
Stock-based compensation expense		2,537			2,537
Conversion of Series B1 preferred stock	$ 2	(2)
Conversion of Series B1 preferred stock (in shares)	2,368,000			(23,684)
Net income (loss)			98,091		98,091
Ending balance at Dec. 31, 2021	$ 53	$ 764,861	$ (735,461)		$ 29,453
Ending balance (in shares) at Dec. 31, 2021	52,818,000				52,818,000

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities:
Net income (loss)	$ 98,091	$ (112,662)	$ (56,515)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation	2,537	3,641	3,845
Warrant liability revaluation loss (gain)	(6,983)	3,742	598
Future tranche right liability revaluation (gain) loss	(118,803)	72,367	10,964
Issuance of common stock for services rendered	152	243	129
Accretion of discounts on short-term investments	(1)	(46)	(372)
Depreciation and amortization expense	22	61	120
(Gain) loss on disposal of property and equipment			(10)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	2,134	500	(2,160)
Accounts payable, accrued expenses, and other liabilities	(1,751)	(1,629)	(1,105)
Other	5	11	8
Net cash used in operating activities	(24,597)	(33,772)	(44,498)
Cash Flows from Investing Activities:
Purchases of available-for-sale securities		(12,178)	(44,502)
Proceeds from maturity of available-for-sale securities	4,500	10,499	42,100
Proceeds from the sale of property and equipment			11
Purchases of property and equipment		(8)	(11)
Net cash (used in) provided by investing activities	4,500	(1,687)	(2,402)
Cash Flows from Financing Activities:
Proceeds from private placement			10,072
Proceeds from common stock financings, net	19,518	28,758	5,298
Proceeds from employee stock purchases	59	113	121
Proceeds from exercise of common stock options and warrants	271	15	3
Payments on note payable and seller-financed purchases	(435)	(217)
Other			(6)
Net cash provided by financing activities	19,413	28,669	15,488
Net decrease in cash and cash equivalents	(684)	(6,790)	(31,412)
Cash and cash equivalent, beginning of period	33,229	40,019	71,431
Cash and cash equivalents, end of period	32,545	33,229	40,019
Supplemental disclosure of cash flow information:
Cash paid for interest	5	3
Increase to operating lease right-of-use asset upon adoption of ASC 842			1,236
Increase to operating lease right-of-use assets upon acquisition		54
Increase to operating lease liability upon adoption of ASC 842			1,236
Increase to operating lease liability upon acquisition		54
Supplemental disclosure of non-cash financing and investing activities:
Offering costs in accounts payable and accrued expenses	$ 3	112	$ 165
Non-cash seller-financed purchases		$ 652

Business and Organization

Business and Organization	12 Months Ended
	Dec. 31, 2021
Business and Organization
Business and Organization	Note 1. Business and Organization ​ Business Overview ​ Idera Pharmaceuticals, Inc. (“Idera” or the “Company”), a Delaware corporation, is a biopharmaceutical company with a business strategy focused on the clinical development, and ultimately the commercialization, of drug candidates for rare disease indications characterized by small, well-defined patient populations with serious unmet medical needs. The Company’s current focus is to identify and potentially acquire rights to novel development or commercial stage rare disease programs, through new business development opportunities, including additional strategic alternatives. The Company has in the past and may in the future explore collaborative alliances to support development and commercialization of any of our drug candidates. ​ Until May 2021, the Company was developing tilsotolimod, via intratumoral injection, for the treatment of anti-PD1 refractory metastatic melanoma in combination with ipilimumab, an anti-CTLA4 antibody marketed as Yervoy® by Bristol Myers Squibb Company (“BMS”) in a Phase 3 registration trial. During the first quarter of 2021, the Company announced that ILLUMINATE-301, its pivotal registration trial of tilsotolimod in combination with ipilimumab versus ipilimumab alone in patients with anti-PD-1 refractory advanced melanoma, did not meet its primary endpoint of Objective Response Rate (“ORR”). Based on subsequent evaluation of the full data set, in May 2021, the Company announced that it would not continue the trial to its Overall Survival (“OS”) primary endpoint. ​ Through December 2021, the Company was also evaluating intratumoral tilsotolimod in combination with nivolumab, an anti-PD1 antibody marketed as Opdivo® by BMS, and ipilimumab for the treatment of multiple solid tumors in a multicohort Phase 2 trial. In December 2021, the Company announced that preliminary data from the second 10 patients dosed in the safety cohort of ILLUMINATE-206 showed a safety profile consistent with the first 10 patients in ILLUMINATE-206 and with prior studies. No further enrollment in ILLUMINATE-206 is planned at this time. ​ The Company believes that while the clinical trials with tilsotolimod have not yet translated into a new treatment alternative for patients, data supporting tilsotolimod’s mechanism of action and encouraging safety profile from across the array of pre-clinical and clinical work to date, together with its intellectual property protection, are noteworthy. As a result, in December 2021, the Company announced that it will consider an out-licensing arrangement so that tilsotolimid’s full potential may continue to be explored on behalf of patients who do not respond to traditional immunotherapy. ​ Reduction-in-Force ​ In April 2021, following the announcement that the Company’s ILLUMINATE-301 trial did not meet its primary endpoint of ORR, the Company implemented a reduction-in-force which affected approximately 50% of its workforce through September 30, 2021. The Company eliminated 17 positions primarily in the area of research and development. The decision was made in order to align the Company’s workforce with its needs in light of the outcome of ILLUMINATE-301’s ORR endpoint, its ongoing ILLUMINATE development program and other business development activities focused on identifying new portfolio opportunities. ​ In connection with these actions, the Company incurred and paid termination costs for the reduction in workforce, which includes severance, benefits and related costs, of approximately $1.3 million during the year ended December 31, 2021. ​ Note 1. Business and Organization (Continued) ​ Nasdaq Compliance As previously disclosed, on November 26, 2021, we received a deficiency letter (the “Nasdaq Letter”) from the Nasdaq Listing Qualifications Department, notifying us that the Company is not in compliance with Nasdaq Listing Rule 5550(a)(2), which requires the Company to maintain a minimum bid price of at least $1 per share for continued listing on The Nasdaq Capital Market (the “Minimum Bid Requirement”). The Company’s failure to comply with the Minimum Bid Requirement was based on the Company’s common stock per share price being below the $1 threshold for a period of 30 consecutive business days. In accordance with Nasdaq Listing Rule 5810(c)(3)(A) (the “Compliance Period Rule”), the Company has been provided an initial period of 180 calendar days (the “Compliance Date”), to regain compliance with the Minimum Bid Requirement. If, at any time before the Compliance Date, the bid price for the Company’s common stock closes at $1.00 or more per share for a minimum of 10 consecutive business days, as required under Nasdaq requirements, the Staff will provide written notification to the Company that it complies with the Minimum Bid Requirement, unless the Staff exercises its discretion to extend this 10-day period pursuant to Nasdaq Listing Rule 5810(c)(3)(H). If the Company does not regain compliance with the Minimum Bid Requirement by the Compliance Date, the Company may be eligible for an additional 180 calendar day compliance period (the “Second Compliance Period”). To qualify, the Company would need to meet the continued listing requirement for the market value of publicly held shares and all other initial listing standards of the Nasdaq Capital Market, with the exception of the Minimum Bid Requirement, and provide written notice to the Staff of its intention to cure the deficiency during the Second Compliance Period. Neither the Nasdaq Letter nor the Company’s noncompliance with the Minimum Bid Requirement have an immediate effect on the listing or trading of the Company’s common stock, which continue to trade on The Nasdaq Capital Market under the symbol “IDRA.” Liquidity and Financial Condition ​ As of December 31, 2021, the Company had an accumulated deficit of $735.5 million and a cash and cash equivalents balance of $32.5 million. The Company expects to incur substantial operating losses in future periods and will require additional capital as it seeks to advance any future drug candidates through development to commercialization. The Company does not expect to generate product revenue, sales-based milestones, or royalties until the Company successfully completes development of and obtains marketing approval for any future drug candidates, either alone or in collaboration with third parties, which the Company expects will take a number of years, if at all. To commercialize any future drug candidates, the Company needs to complete clinical development and comply with comprehensive regulatory requirements. The Company is subject to a number of risks and uncertainties similar to those of other companies of the same size within the biotechnology industry, such as uncertainty of clinical trial outcomes, uncertainty of additional funding, and history of operating losses. ​ The Company follows the provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 205-40, Presentation of Financial Statements—Going Concern

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies ​ Basis of Presentation ​ The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). ​ Use of Estimates ​ The preparation of financial statements in conformity with GAAP requires management to make estimates, judgements, and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosure of contingencies in the accompanying financial statements and these notes. In addition, management’s assessment of the Company’s ability to continue as a going concern involves the estimation of the amount and timing of future cash inflows and outflows. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. Actual results could differ materially from those estimates. ​ Segment Information ​ Operating segments are defined as components of an enterprise in which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and assessing performance. The Company views its operations and manages its business as one operating segment, which is the business of developing novel therapeutics for rare diseases and oncology. ​ Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of December 31, 2021, the Company’s financial instruments consisted of cash and cash equivalents. As of December 31, 2020, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2021 and 2020. As of December 31, 2021, the Company did not have any other derivatives, hedging instruments or other similar financial instruments. ​ Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2021, all of the Company’s cash and cash equivalents were held at two financial institutions. ​ Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2021 consisted of cash and money market funds. Cash and cash equivalents at December 31, 2020 consisted of cash and cash equivalents and short-term investments. ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Property and Equipment ​ Property and equipment are carried at acquisition cost less accumulated depreciation, subject to review for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable as described further under the heading "Impairment of Long-Lived Assets" below. The cost of normal, recurring, or periodic repairs and maintenance activities related to property and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits. ​ Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter. Equipment and other long-lived assets are depreciated over three ​ When an asset is disposed of, the associated cost and accumulated depreciation is removed from the related accounts on the Company's balance sheet with any resulting gain or loss included in the Company's statement of operations. ​ Operating Lease Right-of-use Asset and Lease Liability ​ The Company accounts for leases under ASC 842, Leases Property, Plant, and Equipment ​ As of December 31, 2021 and 2020, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, Pennsylvania facility operating lease, which expires on May 31, 2025. ​ Impairment of Long-Lived Assets ​ In accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Other Current Liability ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. The aggregate amount financed under this agreement was ​ Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC 480, Distinguishing Liabilities from Equity Derivatives and Hedging ​ Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (the “Purchasers”), an existing stockholder and related party (see Note 15). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contained call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represent freestanding financial instruments and accounts for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation (Loss) Gain in the Company’s statements of operations. ​ As of December 31, 2020, the Future Tranche Right Liability was classified as a long-term liability in the Company’s balance sheet as settlement is in the form of the applicable Series B convertible preferred stock and warrants exercisable for shares of either Series B1 Preferred Stock or the Company’s common stock. During the three months ended March 31, 2021, the liability-classified call options provided for under the December 2019 Securities Purchase Agreement terminated and, accordingly, the liability balance was derecognized. For additional discussion on the Future Tranche Right Liability, see Note 7. ​ Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is being accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption or until the redeemable convertible preferred stock ceases to be outstanding. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Redeemable Preferred Stock Issued with Other Freestanding Instruments ​ The Company considers guidance within ASC 470-20, Debt ​ Revenue Recognition ​ The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. ​ The Company only applies the five-step model to contracts when it determines that it is probable it will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. ​ Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. ​ Alliance Revenues The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable, up-front license fees; research, development and commercial milestone payments; and other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statements of operations. ​ See Note 10, “Collaboration and License Agreements” for additional details regarding the Company’s collaboration and out-licensing arrangements. Note 2. Summary of Significant Accounting Policies (Continued) ​ Research and Development Prepayments, Accruals and Related Expenses ​ All research and development expenses are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, research collaborations, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. The Company is required to estimate our accrued and prepared expenses for research and development activities performed by third parties, including Clinical Research Organizations (“CRO’s”) and clinical investigators. These estimates are made as of the reporting date of the work completed over the life of the individual study in accordance with agreements established with CRO’s and other clinical sites. Some CRO’s invoice the Company on a monthly basis, while others invoice upon the achievement of milestones. The Company determines the estimates of research and development activities incurred at the end of each reporting period through discussion with internal personnel, outside service providers, and research collaboration partners as to the progress or stage of completion of trials or services, as of the end of the reporting period, pursuant to contracts with clinical trial centers or CRO’s and the agreed upon fee to be paid for such services. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2021 and 2020, the Company recorded approximately ​ Stock-Based Compensation ​ The Company accounts for stock-based compensation using ASC 718, Compensation – Stock Compensation Equity – Equity Based Payments to Non-Employees ​ The Company recognizes all share-based payments to employees and directors as expense in the statements of operations based on their fair values. The Company records compensation expense on a straight-line basis over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. Vesting for time-based options and restricted stock units is generally four years for employees and one year for directors. The Company uses a Black-Scholes option-pricing model to determine the fair value of each option grant as of the date of grant for expense incurred. The Black-Scholes option pricing model requires inputs for risk-free interest rate, dividend yield, expected stock price volatility and expected term of the options. Forfeitures are accounted for as they occur. See Note 11, “Stock-based Compensation” for additional details. ​ Income Taxes ​ An asset and liability approach is used for financial accounting and reporting for income taxes. Deferred income taxes arise from temporary differences between income tax and financial reporting and principally relate to recognition of revenue and expenses in different periods for financial and tax accounting purposes and are measured using currently enacted tax rates and laws. In addition, a deferred tax asset can be generated by a net operating loss carryover. If it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is recognized. ​ In the event the Company is charged interest or penalties related to income tax matters, the Company would record such interest as interest expense and would record such penalties as other expense in the Statements of Operations. No such charges have been incurred by the Company. For each of the years ended December 31, 2021, 2020 and 2019, the Company had no uncertain tax positions. See Note 13, “Income Taxes” for additional details. ​ ​ ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) Net Income (Loss) per Common Share applicable to Common Stockholders ​ The Company uses the two-class method to compute net income per common share during periods the Company realizes net income and has securities outstanding (e.g. redeemable convertible preferred stock) that entitle the holder to participate in dividends and earnings of the Company. In addition, the Company analyzes the potential dilutive effect of outstanding redeemable convertible preferred stock under the "if-converted" method when calculating diluted earnings per share and reports the more dilutive of the approaches (two class or "if-converted"). The two-class method is not applicable during periods with a net loss, as the holders of the redeemable convertible preferred stock have no obligation to fund losses. The Company also analyzes the potential dilutive effect of outstanding stock options, unvested restricted stock units, warrants and shares underlying future tranche rights under the treasury stock method (as applicable), during periods of income, or during periods in which income is recognized related to changes in fair value of its liability-classified securities. ​ New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In June 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-13, Financial Instruments Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ​ In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework Changes to the Disclosure Requirements for Fair Value Measurement Fair Value Measurement ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The Company adopted ASU 2020-06 in the first quarter of 2021. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ COVID-19 While the Company is not aware of a material impact from the continuation of the coronavirus ("COVID-19") pandemic through December 31, 2021, the full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations, and financial condition, depends on future developments.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Measurements
Fair Value Measurements	Note 3. Fair Value Measurements ​ Assets and Liabilities Measured at Fair Value on a Recurring Basis ​ The Company applies the guidance in ASC 820, Fair Value Measurement ​ The Company uses a fair value hierarchy, which distinguishes between assumptions based on market data (observable inputs) and an entity's own assumptions (unobservable inputs). The guidance requires that fair value measurements be classified and disclosed in one of the following three categories: ​ ● Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; ● Level 2: Quoted prices in markets that are not active or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability; and ● Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). ​ Determining which category an asset or liability falls within the hierarchy requires significant judgment. The Company evaluates its hierarchy disclosures each reporting period. There were no transfers between Level 1 2, 3 year ended December 31 2021 ​ The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at December 31, 2021 and 2020 categorized by the level of inputs used in the valuation of each asset and liability. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,295 ​ ​ 32,295 ​ ​ — ​ ​ — ​ Total assets ​ $ 32,545 ​ $ 32,545 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 3,499 ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​ ​ The Level 1 assets consist of money market funds, which are actively traded daily. The Level 2 assets consist of commercial paper and US treasury bills whose fair value may not represent actual transactions of identical securities. The fair value of commercial paper is generally determined based on the relationship between the investment’s discount rate and the discount rates of the same issuer’s commercial paper available in the market which may not be actively traded daily. Since these fair values may not be based upon actual transactions of identical securities, they are classified as Level 2. Note 3. Fair Value Measurements (Continued) ​ Changes in Level 3 Liabilities Measured at Fair Value on a Recurring Basis ​ Warrant Liability and Future Tranche Right Liability ​ The reconciliation of the Company's warrant and future tranche right liability measured at fair value on a recurring basis using unobservable inputs (Level 3) is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2019 $ 3,241 ​ $ 46,436 Change in the fair value of liability 3,742 ​ 72,367 Balance, December 31, 2020 $ 6,983 ​ $ 118,803 Change in the fair value of liability (1) (6,983) ​ (118,803) Balance, December 31, 2021 $ — ​ $ — (1) During the year ended December 31, 2021, the Company’s liability-classified warrants and future tranche rights terminated, and accordingly, the liabilities were derecognized. See Notes 7 and 8. ​ Assumptions Used in Determining Fair Value of Liability-Classified Warrants ​ The Company utilizes an option pricing model to value its liability-classified warrants. Inherent in the valuation model are assumptions related to volatility, risk-free interest rate, expected term, dividend rate, and other scenarios (i.e. probability of complex features of the warrants being triggered). ​ The fair value of the warrants has been estimated with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.50% ​ ​ 1.79% Expected dividend yield ​ — ​ ​ — Expected term (years) ​ 5.98 ​ ​ 6.98 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) $ 1.52 ​ $ 1.52 ​ Assumptions Used in Determining Fair Value of Future Tranche Rights ​ Th e Company utilizes a lattice model to value the Series B2 and B3 future tranche rights and a Monte Carlo simulation to value the Series B4 future tranche rights. The Company selected these models as it believes they are reflective of all significant assumptions that market participants would likely consider in negotiating the transfer of the Future Tranche Rights (as defined in Note 7). Such assumptions include, among other inputs, stock price volatility, risk-free rates, and expected terms inclusive of early exercise and cancellation assumptions . ​ The estimated fair value of the Future Tranche Rights is determined using Level 2 and Level 3 inputs. Significant inputs and assumptions used in the valuation models are as follows: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.64% - 0.73% ​ ​ 1.84% - 1.88% Expected dividend yield ​ — ​ ​ — Expected term (years) of call options on preferred stock ​ 0.25 - 1.12 ​ ​ 1.16 - 2.16 Expected term (years) of warrants ​ 7.25 - 8.12 ​ ​ 8.16 - 9.16 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) for common stock equivalent for preferred stock and warrant $ 1.52 - 1.82 ​ $ 1.52 - 1.82 ​ ​

Investments

Investments	12 Months Ended
	Dec. 31, 2021
Investments
Investments	Note 4. Investments The Company had no available-for-sale investments at December 31, 2021. The Company’s available-for-sale investments at fair value consisted of the following at December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ — ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​ ​ The Company had no realized gains or losses from the sale of investments in available-for-sale securities during each of the years ended December 31, 2021 and 2020. In accordance with ASU 2016-13, if the fair value of the Company’s investments in available-for-sale debt securities is less than the amortized cost, the Company records (i) an allowance for credit losses with a corresponding charge to net income (loss) for any credit-related impairment, with subsequent improvements in expected credit losses recognized as a reversal of the allowance, and/or (ii) any non-credit impairment loss to other comprehensive income (loss). ​ As of December 31, 2020, the Company had no allowance for credit losses pertaining to the Company’s investments in available-for-sale debt securities. Additionally, there were no impairment charges or recoveries recorded during each of the years ended December 31, 2021 and 2020.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2021
Property and Equipment
Property and Equipment	Note 5. Property and Equipment ​ At December 31, 2021 and 2020, net property and equipment at cost consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ (In thousands) 2021 2020 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 712 ​ 770 ​ Total property and equipment, at cost ​ $ 819 ​ $ 877 ​ Less: Accumulated depreciation and amortization ​ 797 ​ 833 ​ Property and equipment, net ​ $ 22 ​ $ 44 ​ ​ Depreciation and amortization expense on property and equipment was approximately $0.1 million for each of the years ended December 31, 2021, 2020, and 2019.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Accrued Expenses	Note 6. Accrued Expenses ​ At December 31, 2021 and 2020, accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, (In thousands) ​ 2021 2020 Payroll and related costs ​ $ 477 ​ $ 2,133 ​ Clinical and nonclinical trial expenses ​ 2,909 ​ 3,229 ​ Professional and consulting fees ​ 591 ​ 584 ​ Other ​ 111 ​ 126 ​ Total accrued expenses ​ $ 4,088 ​ $ 6,072 ​ ​

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2021
Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock	Note 7. Redeemable Convertible Preferred Stock ​ December 2019 Private Placement ​ On December 23, 2019, the Company entered into the December 2019 Securities Purchase Agreement, under which the Company sold 23,684 shares of Series B1 convertible preferred stock (“Series B1 Preferred Stock”) and warrants to purchase 2,368,400 shares of the Company’s common stock at an exercise price of $1.52 per share (or, if the holder elected to exercise the warrants for shares of Series B1 Preferred Stock, 23,684 shares of Series B1 Preferred Stock at an exercise price of $152 per share) for aggregate gross proceeds of $3.9 million (the “Initial Closing”). ​ In addition, the Company agreed to sell to the purchasers, at their option and subject to certain conditions, (i) 98,685 shares of Series B2 convertible preferred stock (“Series B2 Preferred Stock”) and 9,868,500 warrants to purchase common stock at an exercise price of $1.52 per share (or, at the election of the holder, 98,685 shares of Series B2 Preferred Stock at an price of $152 per share), for aggregate gross proceeds of $15 million (the “Series B2 Tranche”), (ii) 82,418 shares of Series B3 convertible preferred stock (“Series B3 Preferred Stock”) and 6,593,440 warrants to purchase common stock at an exercise price of $1.82 per share (or, at the election of the holder, 65,934 shares of Series B3 Preferred Stock at a price of $182 per share), for aggregate gross proceeds of $15 million (the “Series B3 Tranche”), and (iii) 82,418 shares of Series B4 convertible preferred stock (“Series B4 Preferred Stock”) and 6,593,440 warrants to purchase common stock at an exercise price of $1.82 per share (or, at the election of the holder, 65,934 shares of Series B3 Preferred Stock at a price of $182 per share), for aggregate gross proceeds of $15 million (the “Series B4 Tranche”) over a period of up to 21 months following the Company’s 2020 Annual Meeting of Stockholders held on May 12, 2020, where stockholders of the Company voted to approve an amendment to the Company’s Restated Certificate of Incorporation to increase the authorized number of shares of the Company’s common stock to 140,000,000. As consideration for the future tranche rights, the Company received aggregate gross proceeds of $6.2 million in December 2019. ​ The purchase and sale of the securities issuable under the Series B2, B3, and B4 tranches described above were subject to three separate closings, each to be conducted at the purchasers’ discretion. The right of the purchasers to purchase Series B2, Series B3 and Series B4 Preferred Stock was set to expire on the 10th business day following the Company’s ORR Data Announcement as defined in the for its ILLUMINATE-301 study. ​ Accounting Considerations ​ The Company determined that the Series B1 Preferred Stock, the accompanying Series B1 warrants, and each of the future tranche rights represent freestanding financial instruments. The Series B1 warrants and the future tranche rights were classified as liabilities until their termination in March 2021 as the underlying shares were potentially redeemable and such redemption was deemed to be outside of the Company’s control. The $10.1 million in gross proceeds received in December 2019 was allocated to the Series B1 warrants and the Future Tranche Rights based on their estimated fair values of $2.6 million and $35.5 million, respectively. The excess fair value of $28.0 million over the gross proceeds received of $10.1 million was recorded as a deemed dividend to Baker Brothers, an existing significant shareholder. Costs incurred in connection with the December 2019 Securities Purchase Agreement were expensed as incurred. ​ Due to the redeemable nature of the Series B1 Preferred Stock, the Series B1 Preferred Stock was classified as temporary equity and the carrying value was being accreted to its redemption value as of December 31, 2020 and while the Series B1 Preferred Stock was outstanding during 2021. During 2021, all the Company’s 23,684 shares of Series B1 Preferred Stock outstanding were converted into shares of the Company’s common stock. See Note 15 for details. For the years ended December 31, 2021 and 2020, accretion was de minimis.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	Note 8. Stockholders’ Equity (Deficit) ​ Preferred Stock ​ The Restated Certificate of Incorporation, as amended, of the Company permits its Board of Directors to issue up to 5,000,000 shares of preferred stock, par value $0.01 per share, in one or more series, to designate the number of shares constituting such series, and fix by resolution, the powers, privileges, preferences and relative, optional or special rights thereof, including liquidation preferences and dividends, and conversion and redemption rights of each such series. ​ As of December 31, 2020, the Company has designated the following class of preferred stock: ● Series A: 1,500,000 authorized shares of Series A Convertible Preferred Stock ● Series B1: 277,921 authorized shares of Series B1 Redeemable Convertible Preferred Stock ● Series B2: 98,685 authorized shares of Series B2 Redeemable Convertible Preferred Stock ● Series B3: 82,814 authorized shares of Series B3 Redeemable Convertible Preferred Stock ● Series B4: 82,814 authorized shares of Series B4 Redeemable Convertible Preferred Stock ​ Series A Convertible Preferred Stock . ​ Series B Convertible Preferred Stock. ​ Common Stock ​ Common Stock Authorized ​ As of December 31, 2021, the Company had 140,000,000 shares of common stock authorized of which 23,918,172 shares of common stock were reserved for issuance upon the exercise of outstanding warrants and options to purchase common stock, outstanding restricted stock units, the conversion of Series A convertible preferred stock, shares required to be reserved under the LPC Purchase Agreement (defined below), and shares available for grant under the Company’s 2013 Stock Incentive Plan and shares available for purchase under the Company’s 2017 Employee Stock Purchase Plan. ​ The expiration of the LPC Purchase Agreement on March 4, 2022 decreased the reserved shares of the common stock to 14,906,278 shares. ​ ​ ​ ​ ​ Note 8. Stockholders’ Equity (Deficit) (Continued) ​ Put Shares ​ Pursuant to the terms of a unit purchase agreement dated as of May 5, 1998, the Company issued and sold a total of 149,960 shares of common stock (the “Put Shares”) at a price of $128.00 per share. Under the terms of the unit purchase agreement, the initial purchasers (the “Put Holders”) of the Put Shares have the right (the “Put Right”) to require the Company to repurchase the Put Shares. The Put Right may not be exercised by any Put Holder unless: (1) the Company liquidates, dissolves or winds up its affairs pursuant to applicable bankruptcy law, whether voluntarily or involuntarily; (2) all of the Company’s indebtedness and obligations, including without limitation the indebtedness under the Company’s then outstanding notes, has been paid in full; and (3) all rights of the holders of any series or class of capital stock ranking prior and senior to the common stock with respect to liquidation, including without limitation the Series A convertible preferred stock, have been satisfied in full. The Company may terminate the Put Right upon written notice to the Put Holders if the closing sales price of its common stock exceeds $256.00 per share for the twenty ​ As of December 31, 2021, the Company has repurchased or received documentation of the transfer of 49,993 Put Shares and 4,472 of the Put Shares continued to be held in the name of Put Holders. The Company cannot determine at this time what portion of the Put Rights of the remaining 95,494 Put Shares have terminated. ​ Equity Financings ​ April 2020 Private Placement ​ On April 7, 2020, the Company entered into a Securities Purchase Agreement with Pillar Partners Foundation, L.P. (“Pillar Partners”), a related party as more fully described in Note 15, which was amended on December 11, 2020 (as amended to date, the “April 2020 Securities Purchase Agreement”), under which the Company sold 3,039,514 shares of common stock and accompanying warrants to purchase 3,039,514 shares of the Company’s common stock with an exercise price of $2.28 per share, for aggregate gross proceeds of $5.0 million. Each share and the accompanying common warrant had a combined purchase price of $1.645, which included $0.125 for each share of common stock underlying each warrant. The April 2020 Securities Purchase Agreement also provided for the option for Pillar Partners to purchase 2,747,252 shares of the Company’s common stock (or pre-funded warrants to purchase shares of the Company’s common stock at an exercise price of $0.01 in lieu of certain shares to the extent that purchasing such shares will cause Pillar Investment Entities (as defined below) to beneficially own in excess of 19.99% of the total number of shares of common stock outstanding post transaction) and warrants to purchase up to 1,373,626 shares of the Company’s common stock (with an exercise price of $2.71), for aggregate gross proceeds of $5.0 million (the “April 2020 Private Placement Second Closing”). Subsequently, in December 2020, the April 2020 Private Placement Second Closing was consummated. Total net proceeds received pursuant to the April 2020 Securities Purchase Agreement, after deduction of offering expenses, was $9.8 million. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Note 8. Stockholders’ Equity (Deficit) (Continued) ​ July 2020 Private Placement On July 13, 2020, the Company entered into a Securities Purchase Agreement (the “July 2020 Securities Purchase Agreement”) with Pillar Partners, Pillar Pharmaceuticals 6 L.P. (“Pillar 6”), and Pillar Pharmaceuticals 7 L.P. (“Pillar 7” and, together with Pillar Partners and Pillar 6, the “July 2020 Purchasers”), each a related party as more fully described in Note 15, pursuant to which, among other things, provided the July 2020 Purchasers the option to purchase, at their sole discretion, pre-funded warrants to purchase up to 784,615 shares of the Company’s common stock, at an exercise price of $0.01 per share, and warrants to purchase up to 274,615 shares of the Company’s common stock, at an exercise price of $9.75, for aggregate gross proceeds of $5.1 million (the “July 2020 Private Placement Second Closing”). During the three months ended March 31, 2021, the option to purchase securities in the July 2020 Private Placement Second Closing terminated. As a result, the Company is no longer eligible to receive additional proceeds from the sale of additional securities pursuant to the July 2020 Securities Purchase Agreement. However, the July 2020 Purchasers still hold outstanding warrants previously issued under the July 2020 Securities Purchase Agreement, as detailed below under the heading “Common Stock Warrants”. Common Stock Purchase Agreement On March 4, 2019, the Company entered into a Purchase Agreement with Lincoln Park Capital Fund, LLC (“Lincoln Park”), which was amended on September 2, 2020 (as amended to date, the “LPC Purchase Agreement”), pursuant to which, upon the terms and subject to the conditions and limitations set forth therein, Lincoln Park has committed to purchase an aggregate of $35.0 million of shares of Company common stock from time to time at the Company’s sole discretion over a 36-month ​ During the years ended December 31, 2021 and 2020, the Company sold 800,000 and 750,000 shares, respectively, pursuant to the LPC Purchase Agreement, resulting in net proceeds of $4.2 million and $1.7 million, respectively. The 36-month period noted above for expired on March 4, 2022; accordingly, the Company no longer has access to additional capital under the LPC Purchase Agreement subsequent to this date. ​ "At-The-Market" Equity Program In November 2018, the Company entered into an Equity Distribution Agreement (the “ATM Agreement”) with JMP Securities LLC (“JMP”) pursuant to which the Company may issue and sell shares of its common stock having an aggregate offering price of up to $50.0 million (the “Shares”) through JMP as its agent. Subject to the terms and conditions of the ATM Agreement, JMP will use its commercially reasonable efforts to sell the Shares from time to time, based upon the Company’s instructions, by methods deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or if specified by the Company, by any other method permitted by law, including but not limited to in negotiated transactions. The Company has no obligation to sell any of the Shares, and the Company or JMP may at any time suspend sales under the ATM Agreement or terminate the ATM Agreement. JMP is entitled to a fixed commission of 3.0% of the gross proceeds from Shares sold. ​ During the years ended December 31, 2021 and 2020, the Company sold 5,117,357 and 3,608,713 Shares, respectively, pursuant to the ATM Agreement resulting in net proceeds, after deduction of commissions and other offering expenses, of $15.3 million and $12.3 million, respectively. As of March 31, 2022, the Company may sell up to an additional $19.5 million of shares under the ATM Agreement. ​ ​ Note 8. Stockholders’ Equity (Deficit) (Continued) ​ Common Stock Warrants ​ In connection with various financing transactions, the Company has issued warrants to purchase shares of the Company’s common stock and preferred stock. The Company accounts for common stock and preferred stock warrants as equity instruments or liabilities, depending on the specific terms of the warrant agreement. See Note 2 for further details on accounting policies related to the Company’s warrants. ​ The following table summarizes outstanding warrants to purchase shares of the Company’s common stock and/or preferred stock as of December 31, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2021 ​ 2020 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ — ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ — ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 15,437 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 4,096 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 2,171 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ 3,039,514 ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ 1,373,626 ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 1,143,428 ​ 2,677,311 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 389,731 ​ 2,014,234 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ 2,764,227 ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 8,732,230 ​ 14,599,428 ​ ​ ​ ​ ​ ​ Total outstanding 8,732,230 ​ 16,967,828 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants were exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder. However, as more fully disclosed in Note 7, the December 2019 Series B1 warrants were terminated during the three months ended March 31, 2021 contemporaneously with the termination of the future tranche rights. The table below is a summary of the Company's warrant activity for the year ended December 31, 2021. ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 Issued — ​ — Exercised (1) (5,867,198) ​ 0.04 Expired (2,368,400) ​ 1.52 Outstanding at December 31, 2021 8,732,230 ​ $ 2.04 (1) During th e year ended December 31, 2021, certain related parties were issued warrants as more fully described in Note 15.

Alliance Revenue

Alliance Revenue	12 Months Ended
	Dec. 31, 2021
Alliance Revenue
Alliance Revenue	Note 9. Alliance Revenue ​ There were no Alliance revenues for the years ended December 31, 2021 and 2020. Alliance revenue for the years ended December 31, 2019 represents revenue from contracts with customers accounted for in accordance with ASC 606. ​ For the year ended December 31, 2019, the Company recognized Alliance revenues totaling $1.4 million which consistent primarily of revenues recognized under the Licensee Agreement, primarily related to the transfer of the IMO-8400 License and IMO-8400 drug product. See Note 10 for additional details regarding the Company’s collaboration arrangements.

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2021
Collaboration and License Agreements
Collaboration and License Agreements	Note 10. Collaboration and License Agreements ​ Option and License Agreement with Licensee In April 2019, the Company entered into an amended and restated option and license agreement with a privately-held biopharmaceutical company (“Licensee”), pursuant to which the Company granted Licensee (i) exclusive worldwide rights to develop and market IMO-8400 for the treatment, palliation and diagnosis of all diseases, conditions or indications in humans (the “IMO-8400 License”), (ii) an exclusive right and license to develop IMO-9200 in accordance with certain IMO-9200 pre-option exercise protocols (the “IMO-9200 Option Period License”), and (iii) an exclusive one-year option, exercisable at Licensee’s discretion, to obtain the exclusive worldwide rights to develop and market IMO-9200 for the treatment, palliation and diagnosis of all diseases, conditions or indications in humans (the “IMO-9200 Option”) (collectively, the “Licensee Agreement”). In connection with the Licensee Agreement, the Company transferred certain drug material to Licensee for Licensee’s use in development activities. Licensee is solely responsible for the development and commercialization of IMO-8400 and, if Licensee exercises the IMO-9200 Option, Licensee would be solely responsible for the development and commercialization of IMO-9200. ​ Under the terms of the Licensee Agreement, the Company received upfront, non-refundable fees totaling approximately $1.4 million and ownership of 10% of Licensee’s outstanding common stock, subject to future adjustment, for granting Licensee the IMO-8400 License, the IMO-9200 Option Period License and transfer of related drug materials. In addition, following expiry of the IMO-9200 Option in 2020, the Company is now only eligible to receive certain development and sales-based milestone payments and royalties on global net sales related to the IMO-8400 Compound and potential future IMO-8400 Products, each as defined in the Licensee Agreement. The Company does not anticipate the receipt of any of the future milestones or royalties in the short term, if ever. ​ The Company accounts for the Licensee Agreement in accordance with ASC 606. As of December 31, 2021, the total transaction price of the contract was $1.4 million, which excluded the Option Fee and all development and sales milestones as all such payments were fully constrained. Additionally, as of December 31, 2021, there were no remaining performance obligations under the Licensee Agreement. The Company re-evaluates its performance obligations and transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. As disclosed above, in connection with the Licensee Agreement, the Company owns 10% of Licensee’s outstanding common stock, subject to future adjustment. The Company evaluated the guidance in ASC 321, Investments-Equity Securities ​ ​ ​ Note 10. Collaboration and License Agreement (Continued) ​ Collaboration Agreement with Scriptr ​ In February 2021, the Company entered into a collaboration and option agreement with Scriptr, pursuant to which (i) Scriptr and Idera will conduct a research collaboration utilizing Scriptr Platform Technology (“SPT”) to identify, research and develop gene therapy candidates (each, a “Collaboration Candidate”) for the treatment, palliation, diagnosis or prevention of (a) myotonic dystrophy type 1 (“DM1 Field”) and (b) Friedreich’s Ataxia (“FA Field”) on a Research Program-by-Research Program basis, as applicable, and (ii) the Company was granted an exclusive option, in its sole discretion, to make effective the Scriptr License Agreement, as defined below, for a given Research Program, as defined below, to make use of Collaboration Candidates and related intellectual property (collectively, the “Scriptr Agreement”). ​ Pursuant to the Scriptr Agreement, Scriptr will use commercially reasonable efforts to carry out research activities set forth in accordance with the applicable DM1 Field and FA Field research plans, including certain pre-clinical proof of concept studies, to identify research Collaboration Candidates utilizing SPT (each, a “Research Program”). Following the completion of activities under a given Research Program, Scriptr will prepare and submit to us a comprehensive data package (each, a “Data Package”) that summarizes, on a Research Program-by-Research Program basis, any Collaboration Candidates researched under the Research Program, including any data and results. Upon receipt of a Data Package, Idera has, in its sole discretion, up to two-hundred seventy ( 270 ​ In partial consideration of the rights granted by Scriptr to Idera under the Scriptr Agreement, the Company made a one-time, non-creditable and non-refundable payment to Scriptr during the first quarter of 2021. In order to fund the Research Programs, Idera will reimburse Scriptr for costs incurred by or on behalf of Scriptr in connection with the conduct of each Research Program during the research term in accordance with the applicable Research Program budget and payment schedule. The Company incurred approximately $2.1 million in research and development expenses under the Scriptr Agreement during the year ended December 31, 2021. ​ ​

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Stock-Based Compensation
Stock-Based Compensation	Note 11. Stock-based Compensation ​ As of December 31, 2021, the only equity compensation plans from which the Company may currently issue new awards are the Company’s 2013 Stock Incentive Plan (as amended to date, the “2013 Plan”) and 2017 Employee Stock Purchase Plan (the “2017 ESPP”), each as more fully described below. ​ Equity Incentive and Employee Stock Purchase Plans ​ 2013 Stock Incentive Plan ​ The Company's board of directors adopted the 2013 Plan, which was approved by the Company’s stockholders effective July 26, 2013. Amendments to the 2013 Plan were approved by the Company’s stockholders in June 2014, June 2015, June 2017 and June 2019. The 2013 Plan is intended to further align the interests of the Company and its stockholders with its employees, including its officers, non-employee directors, consultants and advisers by providing equity-based incentives. The 2013 Plan allows for the issuance of incentive stock options intended to qualify under Section 422 of the Internal Revenue Code, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”), other stock-based awards and performance awards. The total number of shares of common stock authorized for issuance under the 2013 Plan is 5,653,057 shares of the Company’s common stock, plus such additional number of shares of common stock (up to 868,372 shares) as is equal to the number of shares of common stock subject to awards granted under the Company’s 2005 Stock Incentive Plan or 2008 Stock Incentive Plan (the “2008 Plan”), to the extent such awards expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right. ​ As of December 31, 2021, options to purchase a total of 4,721,038 shares of common stock and 575,703 RSUs were outstanding and up to 199,873 shares of common stock remained available for grant under the 2013 Plan. ​ Other Awards and Inducement Grants ​ The Company has not made any awards pursuant to other equity incentive plans, including the 2008 Plan, since the Company’s stockholders approved the 2013 Plan. As of December 31, 2021, options to purchase a total of 155,968 shares of common stock were outstanding under the 2008 Plan. In addition, as of December 31, 2021, non-statutory stock options to purchase an aggregate of 325,000 shares of common stock were outstanding that were issued outside of the 2013 Plan to certain employees in 2017, 2015 and 2014 pursuant to the Nasdaq inducement grant exception as a material component of new hires’ employment compensation. ​ 2017 Employee Stock Purchase Plan ​ The Company’s board of directors adopted the 2017 ESPP which was approved by the Company’s stockholders and became effective June 7, 2017. An amendment to the 2017 ESPP was approved by the Company’s stockholders in June 2019. The 2017 ESPP is intended to qualify as an "employee stock purchase plan" as defined in Section 423 of the Internal Revenue Code, and is intended to encourage our employees to become stockholders of ours, to stimulate increased interest in our affairs and success, to afford employees the opportunity to share in our earnings and growth and to promote systematic savings by them. The total number of shares of common stock authorized for issuance under the 2017 ESPP is 412,500 shares of common stock, subject to adjustment as described in the 2017 ESPP. ​ ​ Note 11. Stock-based Compensation (Continued) ​ Stock Purchase Plan Administration ​ The 2017 ESPP provides for offerings to employees to purchase common stock with offerings beginning on dates determined by the compensation committee of the board of directors or on the first business day thereafter. Each offering begins a “plan period” during which payroll deductions are to be made and held for the purchase of common stock at the end of the plan period. The compensation committee may, at its discretion, choose a plan period of or less for subsequent offerings and/or choose a different commencement date for offerings. During each plan period participating employees may elect to have a portion of their compensation, ranging from ​ For the years ended December 31, 2021, 2020 and 2019, the Company issued 49,117, 75,999, and 60,953, shares of common stock, in each year respectively, under the 2017 ESPP and received proceeds of $0.1 million for each year, as a result of stock purchases. ​ Accounting for Stock-based Compensation ​ The Company recognizes non-cash compensation expense for stock-based awards under the Company’s equity incentive plans and employee stock purchases under the Company’s 2017 ESPP as follows: ● Stock Options: Compensation cost is recognized over an award’s requisite service period, or vesting period, using the straight-line attribution method, based on the grant date fair value determined using the Black-Scholes option-pricing model. ● RSUs: Compensation cost for time-based RSUs, which vest over time based only on continued service, is recognized on a straight-line basis over the requisite service period based on the fair value of the Company’s common stock on the date of grant. Compensation cost for awards that are subject to market considerations is recognized on a straight-line basis over the implied requisite service period, based on the grant date fair value estimated using a Monte Carlo simulation. Compensation cost for awards that are subject to performance conditions is recognized over the period of time commencing when the performance condition is deemed probable of achievement based on the fair value of the Company’s common stock on the date of grant. ● Employee Stock Purchases: Compensation cost is recognized over each plan period based on the fair value of the look-back provision, calculated using the Black-Scholes option-pricing model, considering the 15% discount on shares purchased. Total stock-based compensation expense attributable to stock-based payments made to employees and directors and employee stock purchases included in operating expenses in the Company's statements of operations for the years ended December 31, 2021, 2020 and 2019 was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 2020 2019 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 28 $ 88 $ 36 Equity Incentive Plan ​ ​ 546 ​ 673 ​ 1,312 ​ ​ $ 574 $ 761 $ 1,348 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 3 $ 9 $ 20 Equity Incentive Plan ​ ​ 1,960 ​ 2,871 ​ 2,477 ​ ​ $ 1,963 $ 2,880 $ 2,497 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total stock-based compensation expense ​ $ 2,537 $ 3,641 $ 3,845 ​ Note 11. Stock-based Compensation (Continued) ​ During the years ended December 31, 2021, 2020 and 2019, the weighted average fair market value of stock options granted was $1.54, $1.25, and $1.64, respectively. ​ Assumptions Used in Determining Fair Value of Stock Options ​ Inherent in the Black-Scholes option-pricing model are the following assumptions: Volatility Risk-free interest rate Expected term Dividend rate. Forfeitures ​ The fair value of each option award at the date of grant was estimated using the Black-Scholes option pricing model. All options granted during the three years in the period ended December 31, 2021 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . ​ The following weighted average assumptions apply to the options to purchase 1,356,700, 1,215,382, and 1,279,016 shares of common stock granted to employees and directors during the years ended December 31, 2021, 2020 and 2019, respectively: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ Average risk-free interest rate ​ ​ 0.4% ​ ​ 1.0% ​ ​ 2.1% ​ Expected dividend yield ​ ​ — ​ ​ — ​ ​ — ​ Expected lives (years) ​ ​ 3.6 ​ ​ 3.9 ​ ​ 3.7 ​ Expected volatility ​ ​ 94% ​ ​ 84% ​ ​ 84% ​ Weighted average exercise price (per share) ​ $ 2.68 ​ $ 2.08 ​ $ 2.75 ​ ​ All options granted during the years ended December 31, 2021, 2020 and 2019 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . ​ Stock Option Activity ​ The following table summarizes stock option activity for the year ended December 31, 2021. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock Options ​ Weighted-Average Exercise Price ​ Weighted-Average Remaining Contractual Life (in years) ​ Aggregate Intrinsic Value Outstanding at December 31, 2020 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Granted 1,356,700 ​ 2.68 ​ ​ ​ ​ ​ ​ Exercised (22,500) ​ 2.11 ​ ​ ​ ​ ​ ​ Forfeited (261,426) ​ 4.44 ​ ​ ​ ​ ​ ​ Expired (485,091) ​ 11.52 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2021 (1) 5,202,006 ​ $ 8.06 5.9 ​ $ — ​ Exercisable at December 31, 2021 4,096,875 ​ $ 9.62 5.1 ​ $ — ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition. Note 11. Stock-based Compensation (Continued) ​ In March 2021, the Company accelerated the vesting of 1,535,578 options, which were previously granted from 2019 to 2021. The modification results in an incremental stock based compensation charge that was not significant. As of December 31, 2021, there was $1.2 million of unrecognized compensation cost related to unvested options, which the Company expects to recognize over a weighted average period of 2.1 years. ​ Restricted Stock Activity The following table summarizes restricted stock activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average Grant Date Fair Value ​ Number of Shares ​ Weighted-Average Grant Date Fair Value Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54 Granted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cancelled (48,563) ​ ​ 2.31 ​ ​ (42,290) ​ ​ 1.54 Vested (236,765) ​ ​ 2.25 ​ ​ — ​ ​ — Nonvested shares at December 31, 2021 68,675 ​ $ 2.30 ​ 507,028 ​ $ 1.54 ​ Time-based Restricted Stock Units ​ In December 2020, the Company’s Chief Executive Officer was granted an award of 128,170 RSUs, pursuant to the 2013 Plan, in lieu of salary pursuant to a January 10, 2020 amendment to the officers’ employment agreement. The RSUs were fully vested on the grant date. ​ In March 2021, the Company accelerated the vesting of 137,872 unvested time-based restricted stock units which were previously granted in 2019 and 2020. The modification results in an incremental stock based compensation charge that was not significant. During the year ended December 31, 2021, the Company recognized $0.3 million of compensation expense related to these awards. As of December 31, 2021, there was ​ Market/Performance-based Restricted Stock Units ​ In July 2020, the Company granted RSUs to certain employees, including executive officers, under the 2013 Plan, with vesting that may occur upon a combination of specific performance and/or market conditions. Accordingly, the Company views these RSUs as two separate awards: (i) an award that vests if the market condition is achieved, and (ii) an award that vests whether or not the market condition is achieved, so long as the performance condition is achieved. The Company is currently recognizing compensation expense for these awards over the estimated requisite service period of 2.36 years based on the estimated fair value when considering the market condition of the award, which was determined using a Monte Carlo simulation. During the year ended December 31, 2021, the Company recognized $0.3 million of compensation expense related to these awards. As of December 31, 2021, the remaining unrecognized compensation cost for the market-based component of these awards, which is expected to be recognized over a weighted-average period of 0.9 years, is $0.3 million. In addition, should the performance condition be achieved, the Company would recognize an additional $0.3 million of compensation expense.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies
Commitments and Contingencies	Note 12. Commitments and Contingencies ​ Lease Commitments ​ As of December 31, 2021, the Company’s leased assets primarily consisted of its office headquarters in Exton, Pennsylvania. During 2021, 2020 and 2019, rent expense, including real estate taxes, was $0.3 million, $0.4 million, and $0.3 million, respectively. The leases are classified as operating leases. ​ Future minimum commitments as of December 31, 2021 under the Company’s lease agreements are approximately: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ Operating Leases (in thousands) 2022 ​ 249 ​ 2023 ​ ​ 250 ​ 2024 ​ ​ 240 ​ 2025 ​ ​ 101 ​ ​ ​ $ 840 ​ ​ The Company entered into the Exton, Pennsylvania facility lease on April 1, 2015, which was subsequently amended on September 23, 2015 to include additional space. The Company currently leases approximately 11,000 square feet of office space at our Exton facility. The lease expires on May 31, 2025. ​ Vendor Financing Arrangement ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. As of December 31, 2020, the balance of $0.4 million, was paid in monthly installments through June 2021. Accordingly, as of December 31, 2021, no amounts were outstanding under this agreement.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes
Income Taxes	Note 13. Income Taxes ​ As of December 31, 2021, the Company had cumulative federal and state net operating loss carryforwards (“NOLs”) of approximately $327.5 million and $322.0 million available to reduce federal and state taxable income, respectively. As a result of the Tax Cuts and Jobs Act of 2017, federal net operating losses incurred for taxable years beginning after January 1, 2018 have an unlimited carryforward period, but can only be utilized to offset 80% of taxable income in future taxable periods. Of the $327.5 million of federal NOLs, $130.1 million have an unlimited carryforward and the remaining NOLs are still subject to expiration through 2037. State NOLs are still subject to expiration according to the laws of each respective jurisdiction. The Company files state tax returns in Massachusetts and Pennsylvania ​ Sections 382 and 383 of the Internal Revenue Code prescribe limitations on the amount of NOLs and tax credit carryforwards that may be utilized in any one year. The Company has completed several financings since the effective date of the Tax Reform Act of 1986, which as of December 31, 2021, have resulted in ownership changes that will significantly limit the Company’s ability to utilize its net operating loss and tax credit carryforwards. In December 2017, the Company completed a study which determined that ownership changes had occurred. The federal and state net operating loss and tax credit carryforwards and related deferred tax assets shown in the table below have been adjusted to reflect the limitations that resulted from this study. As no study has been completed subsequent to 2017, additional ownership change limitations may result from ownership changes that have occurred, or may occur in the future. The Company continues to monitor equity activity and potential ownership changes. Note 13. Income Taxes (Continued) ​ As of December 31, 2021 and 2020, the components of the deferred tax assets are approximately as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 2020 Operating loss carryforwards ​ $ 90,550 ​ $ 90,895 ​ Tax credit carryforwards ​ 28,226 ​ 26,550 ​ Stock-based compensation ​ ​ 6,902 ​ ​ 6,820 ​ Capitalized research and development ​ ​ 7,818 ​ ​ — ​ Lease liabilities ​ ​ 220 ​ ​ 276 ​ Other ​ 70 ​ 162 ​ Total deferred tax assets ​ 133,786 ​ 124,703 ​ Right-of-use asset ​ ​ (213) ​ ​ (270) ​ Valuation allowance ​ (133,573) ​ (124,433) ​ Net deferred tax assets ​ $ — ​ $ — ​ ​ ​ The Company has provided a full valuation allowance for its deferred tax asset due to the uncertainty surrounding the ability to realize these assets. ​ The difference between the U.S. federal corporate tax rate and the Company’s effective tax rate for the years ended December 31, 2021, 2020 and 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 ​ 2020 ​ 2019 Expected federal income tax rate (21.0) % ​ (21.0) % ​ (21.0) % Expiring credits and NOLs — ​ ​ — ​ ​ — ​ Change in valuation allowance (9.3) ​ ​ 10.6 ​ ​ 26.2 ​ Federal and state credits 1.7 ​ ​ (3.1) ​ ​ (8.1) ​ State income taxes, net of federal benefit 2.1 ​ ​ (1.9) ​ ​ (4.7) ​ Warrant and future tranche right revaluation loss ​ 26.9 ​ ​ 14.2 ​ ​ 4.3 ​ Stock-based compensation — ​ ​ 0.2 ​ ​ 0.5 ​ Other (0.4) ​ ​ 1.0 ​ ​ 2.8 ​ Effective tax rate 0.0 % ​ 0.0 % ​ 0.0 % ​ The Company applies ASC 740-10, Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740 ​ The Company has not conducted a study of its research and development tax credit carryforwards. Such a study might result in an adjustment to the Company’s research and development credit carryforwards, however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position under ASC 740-10. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact on the statements of operations if an adjustment was required. ​ The Company files income tax returns in the U.S. federal, Massachusetts and Pennsylvania jurisdictions. The Company is no longer subject to tax examinations for years before 2018, except to the extent that it utilizes tax attributes that originated before 2018. The Company does not believe there will be any material changes in its unrecognized tax positions over the next 12 months. The Company has not incurred any interest or penalties. In the event that the Company is assessed interest or penalties at some point in the future, they will be classified in the statements of operations as general and administrative expense.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2021
Employee Benefit Plan
Employee Benefit Plan	Note 14. Employee Benefit Plan ​ The Company has an employee benefit plan under Section 401(k) of the Internal Revenue Code. The plan allows employees to make contributions up to a specified percentage of their compensation. Under the plan, the Company matches up to 5% of employee base salary, by matching 100% of the first 5% of annual base salary contributed by each employee. Approximately ​

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions
Related Party Transactions	Note 15. Related Party Transactions ​ Baker Brothers ​ Julian C. Baker, a member of the Company’s Board of Directors until his resignation in September 2018, is a principal of Baker Bros. Advisors, LP. Additionally, Kelvin M. Neu, a member of Company’s Board until his resignation in June 2019, is an employee of Baker Bros. Advisors, LP. As of December 31, 2021, Baker Bros. Advisors, LP and certain of its affiliated funds (collectively, “Baker Brothers”) held sole voting power with respect to an aggregate of 2,047,180 shares of the Company’s common stock, representing approximately 4% of the Company's outstanding common stock. ​ During 2019, Baker Brothers purchased shares of the Company’s Series B1 Preferred Stock and accompanying warrants to purchase common stock in connection with the December 2019 Private Placement, as more fully described in Note 7. Concurrent with the December 2019 Private Placement, the Company amended the warrants initially issued to Baker Brothers and other holders on May 7, 2013, September 30, 2013 and February 10, 2014 to remove expiration date. Under the terms of the warrants issued to Baker Brothers and the December 2019 Securities Purchase Agreement related to the securities issued in connection with the 2019 Private Placement, Baker Brothers is not permitted to convert or exercise any common stock equivalents to the extent that such conversion or exercise would result in Baker Brothers (and its affiliates) beneficially owning more than 4.99% of the number of shares of our common stock outstanding immediately after giving effect to the issuance of shares of common stock issuable upon conversion or exercise of such securities. Baker Brothers has the right to increase this beneficial ownership limitation in its discretion on 61 days' prior written notice to us, provided that in no event is Baker Brothers permitted to convert or exercise such securities to the extent that such exercise would result in Baker Brothers (and its affiliates) beneficially owning more than 19.99% of the number of shares of our common stock outstanding immediately after giving effect to the issuance of shares of common stock issuable upon conversion or exercise of such securities. ​ During March 2021, Baker Brothers exercised warrants to purchase 2,708,812 shares of the Company’s common stock at an exercise price of $0.08 per share for a total exercise price of approximately $0.2 million. Additionally, ​ Pillar Investment Entities ​ Youssef El Zein, a member of the Company’s Board of Directors until his resignation in October 2017, is a director and controlling stockholder of Pillar Invest Corporation (“Pillar Invest”), which is the general partner of Pillar Pharmaceuticals I, L.P., Pillar Pharmaceuticals II, L.P., Pillar Pharmaceuticals III, L.P., Pillar Pharmaceuticals IV, L.P., Pillar Pharmaceuticals V, L.P., Pillar 6 and Pillar Partners (collectively, the “Pillar Investment Entities”). As of December 31, 2021, the Pillar Investment Entities beneficially owned approximately 19.99% of the Company's common stock. ​ ​ Note 15. Related Party Transactions (Continued) ​ During 2020, the Company sold shares of its common stock, prefunded warrants and common stock warrants to entities affiliated with Pillar Invest Corporation in connection with private placement transactions, as more fully descried in Note 8. ​ During the year ended December 31, 2021, certain of the Pillar Investment Entities exercised warrants to purchase 3,158,386 shares of the Company’s common stock at an exercise price of $0.01 per share for a total exercise price of less than $0.1 million. 19,052 shares were used as cashless shares for the exercise costs. ​ As of December 31, 2021, the Pillar Investment Entities held (i) prefunded warrants to purchase up to 1,533,159 shares of the Company’s common stock at an exercise price of $0.01 per share, (ii) warrants to purchase up to 3,039,514 shares of the Company’s common stock at an exercise price of $2.28 per share, (iii) warrants to purchase up to 2,764,227 shares of the Company’s common stock at an exercise price of $2.58 per share, and (iv) warrants to purchase up to 1,373,626 shares of the Company’s common stock at an exercise price of $2.71 per share. ​ Board Fees Paid in Stock ​ Pursuant to the Company’s director compensation program, in lieu of director board and committee fees of $0.1 million, $0.3 million, and $0.1 million, respectively, incurred during each of the years ended December 31, 2021, 2020 and 2019, respectively, the Company issued 105,691, 145,392, and 53,985 , shares of common stock, respectively, to certain of its directors. Director board and committee fees are paid in arrears and the number of shares issued was calculated based on the market closing price of the Company’s common stock on the issuance date. ​ Officer Salary Paid in Stock ​ In December 2020, the Company’s Chief Executive Officer was granted an award of 128,170 RSUs, pursuant to the 2013 Plan, in lieu of salary of $0.6 million pursuant to a January 10, 2020 amendment to the officers’ employment agreement. The RSUs were fully vested on the grant date. ​ No such RSU awards were granted to any executive officers as compensation in 2021. ​

Net Income (Loss) per Common Sh

Net Income (Loss) per Common Share Applicable to Common Stockholders	12 Months Ended
	Dec. 31, 2021
Net Income (Loss) per Common Share Applicable to Common Stockholders
Net Income (Loss) per Common Share Applicable to Common Stockholders	Note 16. Net Income (Loss) per Common Share Applicable to Common Stockholders ​ Details in the computation of basic and diluted net income (loss) per common share were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ December 31, ($ in thousands except per share data) ​ 2021 ​ ​ 2020 ​ ​ 2019 Net income (loss) applicable to common stockholders — Basic: ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) $ 98,091 ​ $ (112,662) ​ $ (56,515) Less: Deemed dividend on preferred stock ​ — ​ ​ — ​ ​ (28,043) Less: Undistributed earnings to preferred stockholders ​ (1,150) ​ ​ — ​ ​ — Net income (loss) applicable to common stockholders - basic $ 96,941 ​ $ (112,662) ​ $ (84,558) ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator for basic net income (loss) applicable to common stockholders $ 96,941 ​ $ (112,662) ​ $ (84,558) Denominator for basic net income (loss) applicable to common stockholders ​ 49,203 ​ ​ 33,821 ​ ​ 28,545 Net income (loss) applicable to common stockholders - basic $ 1.97 ​ $ (3.33) ​ $ (2.96) ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss applicable to common stockholders — Diluted: ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) $ 96,941 ​ $ (112,662) ​ $ (84,558) Less: Warrant revaluation gain applicable to dilutive liability-classified warrants ​ (6,983) ​ ​ — ​ ​ — Less: Future tranche right revaluation gain applicable to dilutive liability-classified future tranche rights ​ (118,803) ​ ​ — ​ ​ — Numerator for diluted net income (loss) applicable to common stockholders $ (28,845) ​ $ (112,662) ​ $ (84,558) ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator for basic net income (loss) applicable to common stockholders ​ 49,203 ​ ​ 33,821 ​ ​ 28,545 Plus: Incremental shares underlying “in the money” liability-classified warrants outstanding ​ 93 ​ ​ — ​ ​ — Plus: Incremental shares underlying “in the money” liability-classified future tranche rights outstanding ​ 831 ​ ​ — ​ ​ — Denominator for diluted net income (loss) applicable to common stockholders ​ 50,127 ​ ​ 33,821 ​ ​ 28,545 Net income (loss) applicable to common stockholders - diluted $ (0.58) ​ $ (3.33) ​ $ (2.96) ​ T otal antidilutive securities excluded from the calculation of diluted net loss per share for the years ended December 31, , were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 ​ ​ 2020 ​ ​ 2019 Stock options ​ 5,202 ​ ​ 4,614 ​ ​ 4,220 Restricted stock units ​ 576 ​ ​ 903 ​ ​ 194 Common stock warrants ​ 8,732 ​ ​ 16,968 ​ ​ 5,099 Convertible preferred stock ​ — ​ ​ 2,369 ​ ​ 2,369 Future tranche rights ​ — ​ ​ 50,467 ​ ​ 49,407 Total ​ 14,510 ​ ​ 75,321 ​ ​ 61,289 ​ ​

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events
Subsequent Events	Note 17. Subsequent Events ​ The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. ​ ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of Estimates ​ The preparation of financial statements in conformity with GAAP requires management to make estimates, judgements, and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosure of contingencies in the accompanying financial statements and these notes. In addition, management’s assessment of the Company’s ability to continue as a going concern involves the estimation of the amount and timing of future cash inflows and outflows. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. Actual results could differ materially from those estimates.
Segment Information	Segment Information ​ Operating segments are defined as components of an enterprise in which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and assessing performance. The Company views its operations and manages its business as one operating segment, which is the business of developing novel therapeutics for rare diseases and oncology.
Financial Instruments	Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of December 31, 2021, the Company’s financial instruments consisted of cash and cash equivalents. As of December 31, 2020, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2021 and 2020. As of December 31, 2021, the Company did not have any other derivatives, hedging instruments or other similar financial instruments.
Concentration of Credit Risk	Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2021, all of the Company’s cash and cash equivalents were held at two financial institutions. ​
Cash and Cash Equivalents	Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2021 consisted of cash and money market funds. Cash and cash equivalents at December 31, 2020 consisted of cash and cash equivalents and short-term investments.
Property and Equipment	Property and Equipment ​ Property and equipment are carried at acquisition cost less accumulated depreciation, subject to review for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable as described further under the heading "Impairment of Long-Lived Assets" below. The cost of normal, recurring, or periodic repairs and maintenance activities related to property and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits. ​ Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter. Equipment and other long-lived assets are depreciated over three ​ When an asset is disposed of, the associated cost and accumulated depreciation is removed from the related accounts on the Company's balance sheet with any resulting gain or loss included in the Company's statement of operations.
Operating Lease Right-of-use Asset and Lease Liability	Operating Lease Right-of-use Asset and Lease Liability ​ The Company accounts for leases under ASC 842, Leases Property, Plant, and Equipment ​ As of December 31, 2021 and 2020, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, Pennsylvania facility operating lease, which expires on May 31, 2025.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets ​ In accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets
Other Current Liability	Other Current Liability ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. The aggregate amount financed under this agreement was
Warrant Liability	Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC 480, Distinguishing Liabilities from Equity Derivatives and Hedging
Future Tranche Right Liability	Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (the “Purchasers”), an existing stockholder and related party (see Note 15). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contained call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represent freestanding financial instruments and accounts for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation (Loss) Gain in the Company’s statements of operations. ​ As of December 31, 2020, the Future Tranche Right Liability was classified as a long-term liability in the Company’s balance sheet as settlement is in the form of the applicable Series B convertible preferred stock and warrants exercisable for shares of either Series B1 Preferred Stock or the Company’s common stock. During the three months ended March 31, 2021, the liability-classified call options provided for under the December 2019 Securities Purchase Agreement terminated and, accordingly, the liability balance was derecognized. For additional discussion on the Future Tranche Right Liability, see Note 7. ​
Preferred Stock	Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is being accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption or until the redeemable convertible preferred stock ceases to be outstanding.
Redeemable Preferred Stock Issued with Other Freestanding Instruments	Redeemable Preferred Stock Issued with Other Freestanding Instruments ​ The Company considers guidance within ASC 470-20, Debt
Revenue Recognition	Revenue Recognition ​ The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. ​ The Company only applies the five-step model to contracts when it determines that it is probable it will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. ​ Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. ​ Alliance Revenues The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable, up-front license fees; research, development and commercial milestone payments; and other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statements of operations. ​ See Note 10, “Collaboration and License Agreements” for additional details regarding the Company’s collaboration and out-licensing arrangements.
Research and Development Prepayments, Accruals and Related Expenses	Research and Development Prepayments, Accruals and Related Expenses ​ All research and development expenses are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, research collaborations, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. The Company is required to estimate our accrued and prepared expenses for research and development activities performed by third parties, including Clinical Research Organizations (“CRO’s”) and clinical investigators. These estimates are made as of the reporting date of the work completed over the life of the individual study in accordance with agreements established with CRO’s and other clinical sites. Some CRO’s invoice the Company on a monthly basis, while others invoice upon the achievement of milestones. The Company determines the estimates of research and development activities incurred at the end of each reporting period through discussion with internal personnel, outside service providers, and research collaboration partners as to the progress or stage of completion of trials or services, as of the end of the reporting period, pursuant to contracts with clinical trial centers or CRO’s and the agreed upon fee to be paid for such services. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2021 and 2020, the Company recorded approximately
Stock-Based Compensation	Stock-Based Compensation ​ The Company accounts for stock-based compensation using ASC 718, Compensation – Stock Compensation Equity – Equity Based Payments to Non-Employees ​ The Company recognizes all share-based payments to employees and directors as expense in the statements of operations based on their fair values. The Company records compensation expense on a straight-line basis over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. Vesting for time-based options and restricted stock units is generally four years for employees and one year for directors. The Company uses a Black-Scholes option-pricing model to determine the fair value of each option grant as of the date of grant for expense incurred. The Black-Scholes option pricing model requires inputs for risk-free interest rate, dividend yield, expected stock price volatility and expected term of the options. Forfeitures are accounted for as they occur. See Note 11, “Stock-based Compensation” for additional details.
Income Taxes	Income Taxes ​ An asset and liability approach is used for financial accounting and reporting for income taxes. Deferred income taxes arise from temporary differences between income tax and financial reporting and principally relate to recognition of revenue and expenses in different periods for financial and tax accounting purposes and are measured using currently enacted tax rates and laws. In addition, a deferred tax asset can be generated by a net operating loss carryover. If it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is recognized. ​ In the event the Company is charged interest or penalties related to income tax matters, the Company would record such interest as interest expense and would record such penalties as other expense in the Statements of Operations. No such charges have been incurred by the Company. For each of the years ended December 31, 2021, 2020 and 2019, the Company had no uncertain tax positions. See Note 13, “Income Taxes” for additional details.
Net Income (Loss) per Common Share applicable to Common Stockholders	Net Income (Loss) per Common Share applicable to Common Stockholders ​ The Company uses the two-class method to compute net income per common share during periods the Company realizes net income and has securities outstanding (e.g. redeemable convertible preferred stock) that entitle the holder to participate in dividends and earnings of the Company. In addition, the Company analyzes the potential dilutive effect of outstanding redeemable convertible preferred stock under the "if-converted" method when calculating diluted earnings per share and reports the more dilutive of the approaches (two class or "if-converted"). The two-class method is not applicable during periods with a net loss, as the holders of the redeemable convertible preferred stock have no obligation to fund losses. The Company also analyzes the potential dilutive effect of outstanding stock options, unvested restricted stock units, warrants and shares underlying future tranche rights under the treasury stock method (as applicable), during periods of income, or during periods in which income is recognized related to changes in fair value of its liability-classified securities.
New Accounting Pronouncements	New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In June 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-13, Financial Instruments Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ​ In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework Changes to the Disclosure Requirements for Fair Value Measurement Fair Value Measurement ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The Company adopted ASU 2020-06 in the first quarter of 2021. The adoption of this ASU did not have a material effect on the Company’s financial statements.
Accounting for Uncertainty in Income Taxes	The Company applies ASC 740-10, Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740
COVID-19	COVID-19 While the Company is not aware of a material impact from the continuation of the coronavirus ("COVID-19") pandemic through December 31, 2021, the full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations, and financial condition, depends on future developments.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Measurements
Schedule of assets and liabilities measured and recorded in financial statements at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,295 ​ ​ 32,295 ​ ​ — ​ ​ — ​ Total assets ​ $ 32,545 ​ $ 32,545 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 3,499 ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​
Schedule of reconciliation measured at fair value on a recurring basis using unobservable inputs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2019 $ 3,241 ​ $ 46,436 Change in the fair value of liability 3,742 ​ 72,367 Balance, December 31, 2020 $ 6,983 ​ $ 118,803 Change in the fair value of liability (1) (6,983) ​ (118,803) Balance, December 31, 2021 $ — ​ $ — (1) During the year ended December 31, 2021, the Company’s liability-classified warrants and future tranche rights terminated, and accordingly, the liabilities were derecognized. See Notes 7 and 8.
Warrant liability
Fair Value Measurements
Schedule of assumptions used in determining fair value	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.50% ​ ​ 1.79% Expected dividend yield ​ — ​ ​ — Expected term (years) ​ 5.98 ​ ​ 6.98 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) $ 1.52 ​ $ 1.52
Future tranche right liability
Fair Value Measurements
Schedule of assumptions used in determining fair value	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.64% - 0.73% ​ ​ 1.84% - 1.88% Expected dividend yield ​ — ​ ​ — Expected term (years) of call options on preferred stock ​ 0.25 - 1.12 ​ ​ 1.16 - 2.16 Expected term (years) of warrants ​ 7.25 - 8.12 ​ ​ 8.16 - 9.16 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) for common stock equivalent for preferred stock and warrant $ 1.52 - 1.82 ​ $ 1.52 - 1.82

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2021
Investments
Schedule of available-for-sale investments at fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ — ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​ ​

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
Property and Equipment
Schedule of net property and equipment at cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ (In thousands) 2021 2020 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 712 ​ 770 ​ Total property and equipment, at cost ​ $ 819 ​ $ 877 ​ Less: Accumulated depreciation and amortization ​ 797 ​ 833 ​ Property and equipment, net ​ $ 22 ​ $ 44 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Schedule of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, (In thousands) ​ 2021 2020 Payroll and related costs ​ $ 477 ​ $ 2,133 ​ Clinical and nonclinical trial expenses ​ 2,909 ​ 3,229 ​ Professional and consulting fees ​ 591 ​ 584 ​ Other ​ 111 ​ 126 ​ Total accrued expenses ​ $ 4,088 ​ $ 6,072 ​

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity (Deficit)
Schedule of warrants outstanding and exercisable for purchase of common stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2021 ​ 2020 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ — ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ — ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 15,437 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 4,096 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 2,171 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ 3,039,514 ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ 1,373,626 ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 1,143,428 ​ 2,677,311 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 389,731 ​ 2,014,234 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ 2,764,227 ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 8,732,230 ​ 14,599,428 ​ ​ ​ ​ ​ ​ Total outstanding 8,732,230 ​ 16,967,828 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants were exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder. However, as more fully disclosed in Note 7, the December 2019 Series B1 warrants were terminated during the three months ended March 31, 2021 contemporaneously with the termination of the future tranche rights.
Summary of warrant activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 Issued — ​ — Exercised (1) (5,867,198) ​ 0.04 Expired (2,368,400) ​ 1.52 Outstanding at December 31, 2021 8,732,230 ​ $ 2.04 (1) During th e year ended December 31, 2021, certain related parties were issued warrants as more fully described in Note 15.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Stock-Based Compensation
Schedule of stock-based compensation expense attributable to share-based payments made to employees and directors and included in operating expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 2020 2019 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 28 $ 88 $ 36 Equity Incentive Plan ​ ​ 546 ​ 673 ​ 1,312 ​ ​ $ 574 $ 761 $ 1,348 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 3 $ 9 $ 20 Equity Incentive Plan ​ ​ 1,960 ​ 2,871 ​ 2,477 ​ ​ $ 1,963 $ 2,880 $ 2,497 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total stock-based compensation expense ​ $ 2,537 $ 3,641 $ 3,845
Schedule of weighted average assumptions applied to options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ Average risk-free interest rate ​ ​ 0.4% ​ ​ 1.0% ​ ​ 2.1% ​ Expected dividend yield ​ ​ — ​ ​ — ​ ​ — ​ Expected lives (years) ​ ​ 3.6 ​ ​ 3.9 ​ ​ 3.7 ​ Expected volatility ​ ​ 94% ​ ​ 84% ​ ​ 84% ​ Weighted average exercise price (per share) ​ $ 2.68 ​ $ 2.08 ​ $ 2.75 ​
Schedule of information related to outstanding and exercisable options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock Options ​ Weighted-Average Exercise Price ​ Weighted-Average Remaining Contractual Life (in years) ​ Aggregate Intrinsic Value Outstanding at December 31, 2020 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Granted 1,356,700 ​ 2.68 ​ ​ ​ ​ ​ ​ Exercised (22,500) ​ 2.11 ​ ​ ​ ​ ​ ​ Forfeited (261,426) ​ 4.44 ​ ​ ​ ​ ​ ​ Expired (485,091) ​ 11.52 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2021 (1) 5,202,006 ​ $ 8.06 5.9 ​ $ — ​ Exercisable at December 31, 2021 4,096,875 ​ $ 9.62 5.1 ​ $ — ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition.
Schedule of summary of restricted stock activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average Grant Date Fair Value ​ Number of Shares ​ Weighted-Average Grant Date Fair Value Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54 Granted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cancelled (48,563) ​ ​ 2.31 ​ ​ (42,290) ​ ​ 1.54 Vested (236,765) ​ ​ 2.25 ​ ​ — ​ ​ — Nonvested shares at December 31, 2021 68,675 ​ $ 2.30 ​ 507,028 ​ $ 1.54

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ Operating Leases (in thousands) 2022 ​ 249 ​ 2023 ​ ​ 250 ​ 2024 ​ ​ 240 ​ 2025 ​ ​ 101 ​ ​ ​ $ 840 ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Taxes
Schedule of components of deferred tax assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 2020 Operating loss carryforwards ​ $ 90,550 ​ $ 90,895 ​ Tax credit carryforwards ​ 28,226 ​ 26,550 ​ Stock-based compensation ​ ​ 6,902 ​ ​ 6,820 ​ Capitalized research and development ​ ​ 7,818 ​ ​ — ​ Lease liabilities ​ ​ 220 ​ ​ 276 ​ Other ​ 70 ​ 162 ​ Total deferred tax assets ​ 133,786 ​ 124,703 ​ Right-of-use asset ​ ​ (213) ​ ​ (270) ​ Valuation allowance ​ (133,573) ​ (124,433) ​ Net deferred tax assets ​ $ — ​ $ — ​
Schedule of difference between U.S. federal corporate tax rate and Company effective tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 ​ 2020 ​ 2019 Expected federal income tax rate (21.0) % ​ (21.0) % ​ (21.0) % Expiring credits and NOLs — ​ ​ — ​ ​ — ​ Change in valuation allowance (9.3) ​ ​ 10.6 ​ ​ 26.2 ​ Federal and state credits 1.7 ​ ​ (3.1) ​ ​ (8.1) ​ State income taxes, net of federal benefit 2.1 ​ ​ (1.9) ​ ​ (4.7) ​ Warrant and future tranche right revaluation loss ​ 26.9 ​ ​ 14.2 ​ ​ 4.3 ​ Stock-based compensation — ​ ​ 0.2 ​ ​ 0.5 ​ Other (0.4) ​ ​ 1.0 ​ ​ 2.8 ​ Effective tax rate 0.0 % ​ 0.0 % ​ 0.0 %

Net Income (Loss) per Common _2

Net Income (Loss) per Common Share Applicable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2021
Net Income (Loss) per Common Share Applicable to Common Stockholders
Computation of basic and diluted net income (loss) per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ December 31, ($ in thousands except per share data) ​ 2021 ​ ​ 2020 ​ ​ 2019 Net income (loss) applicable to common stockholders — Basic: ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) $ 98,091 ​ $ (112,662) ​ $ (56,515) Less: Deemed dividend on preferred stock ​ — ​ ​ — ​ ​ (28,043) Less: Undistributed earnings to preferred stockholders ​ (1,150) ​ ​ — ​ ​ — Net income (loss) applicable to common stockholders - basic $ 96,941 ​ $ (112,662) ​ $ (84,558) ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator for basic net income (loss) applicable to common stockholders $ 96,941 ​ $ (112,662) ​ $ (84,558) Denominator for basic net income (loss) applicable to common stockholders ​ 49,203 ​ ​ 33,821 ​ ​ 28,545 Net income (loss) applicable to common stockholders - basic $ 1.97 ​ $ (3.33) ​ $ (2.96) ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss applicable to common stockholders — Diluted: ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) $ 96,941 ​ $ (112,662) ​ $ (84,558) Less: Warrant revaluation gain applicable to dilutive liability-classified warrants ​ (6,983) ​ ​ — ​ ​ — Less: Future tranche right revaluation gain applicable to dilutive liability-classified future tranche rights ​ (118,803) ​ ​ — ​ ​ — Numerator for diluted net income (loss) applicable to common stockholders $ (28,845) ​ $ (112,662) ​ $ (84,558) ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator for basic net income (loss) applicable to common stockholders ​ 49,203 ​ ​ 33,821 ​ ​ 28,545 Plus: Incremental shares underlying “in the money” liability-classified warrants outstanding ​ 93 ​ ​ — ​ ​ — Plus: Incremental shares underlying “in the money” liability-classified future tranche rights outstanding ​ 831 ​ ​ — ​ ​ — Denominator for diluted net income (loss) applicable to common stockholders ​ 50,127 ​ ​ 33,821 ​ ​ 28,545 Net income (loss) applicable to common stockholders - diluted $ (0.58) ​ $ (3.33) ​ $ (2.96)
Schedule of potentially dilutive securities excluded from diluted net income (loss) per common share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2021 ​ ​ 2020 ​ ​ 2019 Stock options ​ 5,202 ​ ​ 4,614 ​ ​ 4,220 Restricted stock units ​ 576 ​ ​ 903 ​ ​ 194 Common stock warrants ​ 8,732 ​ ​ 16,968 ​ ​ 5,099 Convertible preferred stock ​ — ​ ​ 2,369 ​ ​ 2,369 Future tranche rights ​ — ​ ​ 50,467 ​ ​ 49,407 Total ​ 14,510 ​ ​ 75,321 ​ ​ 61,289

Business and Organization (Deta

Business and Organization (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021person	Dec. 31, 2021USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)
Business and Organization
Percentage of positions eliminated	50.00%
Restructuring and Related Cost, Number of Positions Eliminated | person	17
Restructuring costs		$ 1,322	$ 181
Accumulated deficit		735,461		$ 833,552
Cash, cash equivalents and investments		$ 32,500

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)Institutionsegment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Oct. 31, 2020USD ($)
Accounting Policies
Number of operating segments | segment	1
Number of financial institutions | Institution	2
Short-term financing arrangement				$ 600
Other current liability	$ 0	$ 435
Prepaid expenses research and development	900	2,500
Charges incurred	0	0	$ 0
Uncertain tax positions	$ 0	$ 0	$ 0
Minimum [Member]
Accounting Policies
Equipment depreciation period	3 years
Maximum [Member]
Accounting Policies
Equipment depreciation period	5 years
Employees
Accounting Policies
Stock options, vesting period	4 years
Directors [Member]
Accounting Policies
Stock options, vesting period	1 year

Fair Value Measurements - Trans

Fair Value Measurements - Transfers Between Levels (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Fair Value Measurements
Fair value of assets transfers from level 1 to level 2	$ 0
Fair value of assets transfers from level 2 to level 1	0
Fair value of liabilities transfers from level 1 to level 2	0
Fair value of liabilities transfers from level 2 to level 1	0
Fair value of assets transfers into level 3	0
Fair value of assets transfers out of level 3	0
Fair value of liabilities transfers into level 3	0
Fair value of liabilities transfers out of level 3	$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		$ 4,499
Fair Value, Measurements, Recurring [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	$ 32,545	37,728
Total Liabilities		125,786
Fair Value, Measurements, Recurring [Member] | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		6,983
Fair Value, Measurements, Recurring [Member] | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		118,803
Fair Value, Measurements, Recurring [Member] | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	32,295	32,979
Fair Value, Measurements, Recurring [Member] | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		3,499
Fair Value, Measurements, Recurring [Member] | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		1,000
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	32,545	33,229
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	$ 32,295	32,979
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets		4,499
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		3,499
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		1,000
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		125,786
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		6,983
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		$ 118,803

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities at Fair Value Changes in Level 3 Liabilities (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	$ 6,983
Change in the fair value of liability	(6,983)	$ 3,742	$ 3,241
Ending balance		6,983
Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	118,803
Change in the fair value of liability	$ (118,803)	72,367	$ 46,436
Ending balance		$ 118,803

Fair Value Measurements - Weigh

Fair Value Measurements - Weighted-average assumptions (Details)	Dec. 31, 2021$ / shares	Dec. 31, 2020$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0050	0.0179
Expected term
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0598	0.0698
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.80	0.80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.52	1.52

Fair Value Measurements - Futur

Fair Value Measurements - Future Tranche Rights (Details)	Dec. 31, 2021$ / sharesUSD ($)	Dec. 31, 2020$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0050	0.0179
Risk-free interest rate | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.64
Risk-free interest rate | Future tranche right liability | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.73
Risk-free interest rate | Preferred stock | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.84
Risk-free interest rate | Preferred stock | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.88
Expected dividend yield | Future tranche right liability | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.12
Expected term
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0598	0.0698
Expected term | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.25
Expected term | Future tranche right liability | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	8.12
Expected term | Warrants | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	7.25	8.16
Expected term | Warrants | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		9.16
Expected term | Preferred stock | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.16
Expected term | Preferred stock | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		2.16
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.80	0.80
Expected volatility | Future tranche right liability
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	80	80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input | $ / shares	1.52	1.52
Exercise price | Future tranche right liability | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.52	1.52
Exercise price | Future tranche right liability | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.82	1.82

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Investments at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities
Cost		$ 4,499
Estimated Fair Value	$ 0	4,499
Short-term investments - commercial paper
Schedule of Available-for-sale Securities
Cost		3,499
Estimated Fair Value		3,499
US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities
Cost		1,000
Estimated Fair Value		$ 1,000

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investments
Realized gains or losses	$ 0	$ 0
Allowance for credit losses on available-for-sale debt securities		0
Losses or other-than-temporary declines	$ 0	$ 0

Property and Equipment - Net Pr

Property and Equipment - Net Property and Equipment at Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment
Total property and equipment, at cost	$ 819	$ 877
Less: Accumulated depreciation and amortization	797	833
Property and equipment, net	22	44
Leasehold improvements
Property, Plant and Equipment
Total property and equipment, at cost	107	107
Laboratory equipment and other
Property, Plant and Equipment
Total property and equipment, at cost	$ 712	$ 770

Property and Equipment - Deprec

Property and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property and Equipment
Depreciation and amortization expense on property and equipment	$ 0.1	$ 0.1	$ 0.1

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Expenses
Payroll and related costs	$ 477	$ 2,133
Clinical and nonclinical trial expenses	2,909	3,229
Professional and consulting fees	591	584
Other	111	126
Total accrued expenses	$ 4,088	$ 6,072

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 23, 2019	Mar. 31, 2021	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2019	Dec. 31, 2020
Temporary Equity
Warrant exercised price (per share)				$ 2.04		$ 1.28
Aggregate gross proceeds	$ 3,900				$ 10,072
Gross proceeds			$ 6,200
Common Stock, Shares Authorized			140,000,000	140,000,000	140,000,000	140,000,000
Baker Bros. Advisors LP [Member]
Temporary Equity
Warrant exercised price (per share)		$ 0.08
Deemed Dividend	28,000
Series B1 Warrants
Temporary Equity
Gross proceeds received	10,100
Estimated fair values	2,600
Future Tranche Rights
Temporary Equity
Estimated fair values	$ 35,500
Series B1 Redeemable Convertible Preferred Stock
Temporary Equity
Sale of redeemable convertible preferred stock	23,684				24,000
Conversion of preferred stock to common, shares				23,684
Series B1 Redeemable Convertible Preferred Stock | Baker Bros. Advisors LP [Member]
Temporary Equity
Conversion of preferred stock to common, shares		14,150
Series B1 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	2,368,400
Warrant exercised price (per share)	$ 1.52
Series B1 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	23,684
Warrant exercised price (per share)	$ 152
Series B2 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15,000
Preferred Shares	98,685
Series B2 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	9,868,500
Warrant exercised price (per share)	$ 1.52
Series B2 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	98,685
Warrant exercised price (per share)	$ 152
Series B3 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15,000
Preferred Shares	82,418
Series B3 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	6,593,440
Warrant exercised price (per share)	$ 1.82
Series B3 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	65,934
Warrant exercised price (per share)	$ 182
Series B4 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15,000
Preferred Shares	82,418
Expiration period	21 months
Series B4 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	6,593,440
Warrant exercised price (per share)	$ 1.82
Series B4 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	65,934
Warrant exercised price (per share)	$ 182

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Preferred Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Series A Preferred Stock [Member]
Class of Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares designated	1,500,000	1,500,000
Annual percentage of dividend of preferred stock	1.00%
Preferred stock, shares outstanding	655	655
Series A preferred stock liquidation preference per share	$ 1
Series A Preferred stock conversion price per share	$ 272
Preferred stock, shares issued	1,000	1,000
Series B1 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares designated	277,921	278,000
Preferred stock, shares outstanding	0	24,000
Preferred stock, shares issued	0	24,000
Series B2 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	98,685
Series B3 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	82,814
Series B4 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	82,814
Series B2 Preferred Stock
Class of Stock
Preferred stock, shares outstanding	0	23,684

Stockholders' Equity (Deficit_3

Stockholders' Equity (Deficit) - Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 31, 2022	Jul. 13, 2020	Apr. 07, 2020	Dec. 23, 2019	Mar. 04, 2019	May 05, 1998	Nov. 30, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021	Mar. 04, 2022
Class of Stock
Common stock, shares reserved for future issuance								23,918,172			23,918,172	14,906,278
Par value (per share)								$ 0.001	$ 0.001		$ 0.001
Proceeds from issuance				$ 3,900						$ 10,072
Warrant exercised price (per share)								$ 2.04	$ 1.28		$ 2.04
Directors [Member]
Class of Stock
Ownership percentage								4.00%			4.00%
"At-The-Market" Equity Program
Class of Stock
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 19,500
Stock issued (in shares)								5,117,357	3,608,713
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement							3.00%
Net proceeds from offering of common stock								$ 15,300	$ 12,300
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares which may be sold					$ 35,000
Duration over which common stock purchase agreement may be sold					36 months
Stock issued (in shares)					269,749			800,000	750,000
Stock issued (per share)					$ 2.84
Net proceeds from offering of common stock								$ 4,200	$ 1,700
Common Stock [Member]
Class of Stock
Stock issued (in shares)						149,960		5,918,000	8,218,000	2,068,000
Sale price of common shares subject to the liquidation put						$ 128
Minimum closing sales price of common stock to issue termination notice to put holders								$ 256
Price exceeds on number of days								20 days
Liquidation put shares no longer held by original holders								49,993
Shares held by put holders								4,472
Put Rights outstanding								0
Remaining shares of common stock subject to the liquidation put								95,494
Common Stock [Member] | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock							$ 50,000
April 2020 Private Placement
Class of Stock
Stock issued (in shares)			3,039,514
Shares of common stock that may be purchased upon exercise of warrants			3,039,514
Warrant exercised price (per share)			$ 2.28
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5,000
Combined purchase price (per share)			$ 1.645
Stock price underlying warrants (per share)			$ 0.125
April 2020 Private Placement Second Closing
Class of Stock
Stock issued (in shares)			2,747,252
Ownership percentage			19.99%
Shares of common stock that may be purchased upon exercise of warrants			1,373,626
Warrant exercised price (per share)			$ 2.71
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5,000
Stock price (in dollars per share)			$ 0.01
April 2020 Private Placement and April 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock											$ 9,800
July 2020 Private Placement Second Closing
Class of Stock
Proceeds from issuance		$ 5,100
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		784,615
Stock price (in dollars per share)		$ 0.01
July 2020 Private Placement Second Closing | Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		274,615
Stock price (in dollars per share)		$ 9.75

Stockholders' Equity (Deficit_4

Stockholders' Equity (Deficit) - Reverse Stock Split (Details) - $ / shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stockholders' Equity (Deficit)
Common stock, shares authorized	140,000,000	140,000,000	140,000,000
Common stock, par value	$ 0.001	$ 0.001

Stockholders' Equity (Deficit_5

Stockholders' Equity (Deficit) - Common Stock Warrants (Details) - $ / shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Warrant or Right
Number of Shares	8,732,230	16,967,828
Weighted-Average Exercise Price	$ 2.04	$ 1.28
Warrants
Class of Warrant or Right
Weighted-Average Exercise Price			$ 1.52
Preferred stock
Class of Warrant or Right
Weighted-Average Exercise Price		$ 152
Liability Classified Warrants
Class of Warrant or Right
Number of Shares		2,368,400
December 2019 Series B1 warrants
Class of Warrant or Right
Number of Shares		2,368,400
Weighted-Average Exercise Price	$ 1.52	$ 1.52
Equity Classified Warrants
Class of Warrant or Right
Number of Shares	8,732,230	14,599,428
May 2013 Warrants
Class of Warrant or Right
Number of Shares	15,437	1,949,754
Weighted-Average Exercise Price	$ 0.08	$ 0.08
September 2013 Warrants
Class of Warrant or Right
Number of Shares	4,096	514,756
Weighted-Average Exercise Price	$ 0.08	$ 0.08
February 2014 Warrants
Class of Warrant or Right
Number of Shares	2,171	266,006
Weighted-Average Exercise Price	$ 0.08	$ 0.08
April 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	3,039,514	3,039,514
Weighted-Average Exercise Price	$ 2.28
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Shares	1,373,626	1,373,626
Weighted-Average Exercise Price	$ 2.71
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Shares	1,143,428	2,677,311
Weighted-Average Exercise Price	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	389,731	2,014,234
Weighted-Average Exercise Price	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	2,764,227	2,764,227
Weighted-Average Exercise Price	$ 2.58

Stockholders' Equity (Deficit_6

Stockholders' Equity (Deficit) - Common Stock Warrant Activity (Details)	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Class of Warrant or Right
Outstanding at December 31, 2020 | shares	16,967,828
Exercised | shares	(5,867,198)
Outstanding at December 31, 2021 | shares	8,732,230
Warrant exercise price at December 31,2020 | $ / shares	$ 1.28
Exercised | $ / shares	0.04
Warrant exercise price at December 31,2021 | $ / shares	$ 2.04
Class of Warrant Two [Member]
Class of Warrant or Right
Expired | shares	(2,368,400)
Warrant exercise price per share, expired | $ / shares	1.52

Alliance Revenue (Details)

Alliance Revenue (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Alliance Revenue
Alliance revenue	$ 1,448
Out-license arrangement
Alliance Revenue
Alliance revenue	$ 1,400

Collaboration and License Agr_2

Collaboration and License Agreements (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2021	Apr. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Alliance revenue					$ 1,448
Revenue, Product and Service [Extensible List]			us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development			$ 16,375	$ 24,772	$ 34,853
Option and License Agreement with Licensee
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Transaction price			1,400
Performance obligation			$ 0
Percentage of shares acquired		10.00%	10.00%
Option and License Agreement with Licensee | Other Assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Value of securities without a readily determinable fair value			$ 100
Scriptr Global, Inc. | Research and Development Plans and Designation of Development Candidates [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Research and development			$ 2,100
Scriptr Global, Inc. | Maximum [Member] | Research and Development Plans and Designation of Development Candidates [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue recognition period	270 days
IMO-9200 License | Option and License Agreement with Licensee
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement		$ 1,400

Stock-Based Compensation - Equi

Stock-Based Compensation - Equity Incentive Plans (Details) - shares	Jul. 26, 2013	Dec. 31, 2021	Mar. 04, 2022	Dec. 31, 2020
Class of Stock
Common stock, shares reserved for future issuance		23,918,172	14,906,278
Common stock options outstanding		5,202,006		4,614,323
Options outstanding under earlier plans		155,968
Grant of inducement stock option		325,000
2013 Stock Incentive Plan [Member]
Class of Stock
Common shares available for grant	5,653,057	199,873
Maximum number of additional common shares	868,372
Common stock options outstanding		4,721,038
Restricted stock units outstanding		575,703

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 07, 2017
Class of Stock
Proceeds from employee stock purchases	$ 59,000	$ 113,000	$ 121,000
Percentage of share-based compensation expense	15.00%
Weighted average grant date fair value of options granted during the period (per share)	$ 1.54	$ 1.25	$ 1.64
2017 Employee Stock Purchase Plan
Class of Stock
Maximum percentage of total combined voting power or value of the stock of the Company after the grant	5.00%
Common shares available for grant	196,225
Common stock share issued	49,117	75,999	60,953
Employee Stock Purchase Plan [Member]
Class of Stock
Minimum percentage in payroll of deduction base salary to acquire shares of common stock	1.00%
Maximum percentage in payroll of deduction base salary to acquire shares of common stock	10.00%
Percentage of fair market value of common stock for the ESPP option price	85.00%
Annual maximum a participant may purchase under the employee stock purchase plan	$ 25,000
Defined Contribution Plan, Cost	$ 100,000	$ 100,000	$ 100,000
Maximum [Member] | 2017 Employee Stock Purchase Plan
Class of Stock
Common stock shares authorized for issuance under stock purchase plan				412,500
Maximum [Member] | Employee Stock Purchase Plan [Member]
Class of Stock
Subsequent offering period as established by the compensation committee	12 months

Stock-Based Compensation - Acco

Stock-Based Compensation - Accounting for Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 2,537	$ 3,641	$ 3,845
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	574	761	1,348
Research and development | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	28	88	36
Research and development | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	546	673	1,312
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	1,963	2,880	2,497
General and administrative | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	3	9	20
General and administrative | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 1,960	$ 2,871	$ 2,477

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Determining Fair Value of Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-Based Compensation
Options to purchase common stock granted to employees and directors	1,356,700	1,215,382	1,279,016
Average risk free interest rate	0.40%	1.00%	2.10%
Dividend rate	0.00%
Expected lives (years)	3 years 7 months 6 days	3 years 10 months 24 days	3 years 8 months 12 days
Expected volatility	94.00%	84.00%	84.00%
Weighted average exercise price of options granted during the period (per share)	$ 2.68	$ 2.08	$ 2.75

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-Based Compensation
Options, Outstanding, Beginning Balance		4,614,323
Granted		1,356,700
Exercised		(22,500)
Forfeited		(261,426)
Expired		(485,091)
Options, Outstanding, Ending Balance		5,202,006	4,614,323
Exercisable, Ending Balance		4,096,875
Weighted Average Exercise Price, Beginning Balance		$ 9.78
Granted, Weighted Average Exercise Price		2.68	$ 2.08	$ 2.75
Exercised, Weighted Average Exercise Price		2.11
Forfeited, Weighted Average Exercise Price		4.44
Expired, Weighted Average Exercise Price		11.52
Weighted Average Exercise Price, Ending Balance		8.06	$ 9.78
Exercisable, Weighted Average Exercise Price		$ 9.62
Outstanding, Ending balance, Weighted Average Remaining Contractual Term		5 years 10 months 24 days	6 years 9 months 18 days
Exercisable Ending Balance, Weighted Average Remaining Contractual Term		5 years 1 month 6 days
Outstanding, Intrinsic Value, Ending Balance			$ 2,949
Number of shares vested	1,535,578
Unrecognized compensation cost related to nonvested stock-based compensation		$ 1,200
Weighted average remaining period over which unrecognized compensation expense will be recognized		2 years 1 month 6 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Jul. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 26, 2013
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Unrecognized compensation expense				$ 1,200
Weighted average remaining period over which unrecognized compensation expense will be recognized				2 years 1 month 6 days
Share-based compensation				$ 2,537	$ 3,641	$ 3,845
2013 Stock Incentive Plan [Member]
Restricted Stock Activity, Number of Shares
Nonvested shares, Ending Balance				575,703
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				199,873			5,653,057
Restricted stock units
Restricted Stock Activity, Number of Shares
Nonvested shares, Beginning Balance				354,003
Cancelled				(48,563)
Vested				(236,765)
Nonvested shares, Ending Balance		354,003		68,675	354,003
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Nonvested shares, Weighted Average Grant Date Fair Value, Beginning Balance				$ 2.27
Cancelled, Weighted-Average Grant Date Fair Value				2.31
Vested, Weighted-Average Grant Date Fair Value				2.25
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 2.27		$ 2.30	$ 2.27
Accelerated vesting, number of shares	137,872
Recognized compensation expense				$ 300
Unrecognized compensation expense				$ 100
Weighted average remaining period over which unrecognized compensation expense will be recognized				1 year 7 months 6 days
Restricted stock units | 2013 Stock Incentive Plan [Member]
Restricted Stock Activity, Number of Shares
Granted		128,170
Market/Performance-based Awards
Restricted Stock Activity, Number of Shares
Nonvested shares, Beginning Balance				549,318
Cancelled				(42,290)
Nonvested shares, Ending Balance		549,318		507,028	549,318
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Nonvested shares, Weighted Average Grant Date Fair Value, Beginning Balance				$ 1.54
Cancelled, Weighted-Average Grant Date Fair Value				1.54
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 1.54		$ 1.54	$ 1.54
Weighted average remaining period over which unrecognized compensation expense will be recognized				10 months 24 days
Requisite service period (in years)			2 years 4 months 9 days
Share-based compensation				$ 300
Unrecognized compensation expense related to the restricted stock units				300
Additional compensation expense as a result of meeting certain achievements				$ 300

Commitments and Contingencies -

Commitments and Contingencies - Rent Expense and Lease Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)ft²	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Property, Plant and Equipment [Line Items]
Rent expense, including real estate taxes	$ 0.3	$ 0.4
Rent expense, including real estate taxes			$ 0.3
Vendor financing arrangement, outstanding balance	$ 0
Vendor Financing Arrangement
Property, Plant and Equipment [Line Items]
Vendor financing arrangement, outstanding balance		$ 0.4
Exton Facility [Member]
Property, Plant and Equipment [Line Items]
Leased office space | ft²	11,000

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Commitments Under Lease Agreements (Details) $ in Thousands	Dec. 31, 2021USD ($)
Commitments and Contingencies
2022	$ 249
2023	250
2024	240
2025	101
Total future minimum lease commitments	$ 840

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Unrecognized tax benefits from uncertain tax	$ 0	$ 0	$ 0
Period over which material changes in unrecognized tax positions are not expected	12 months
Federal [Member]
Income Taxes
Cumulative net operating loss carryforwards	$ 327,500
Percentage of taxable income that can be used to offset future taxable periods as a result of the TCJA	80.00%
Unlimited carryforward	$ 130,100
Tax credit carryforwards	26,700
State [Member]
Income Taxes
Cumulative net operating loss carryforwards	322,000
Tax credit carryforwards	$ 1,900
State [Member] | Massachusetts
Income Taxes
Carryforward term	20 years
Potential amount that may expire in a future period	$ 23,400
State [Member] | Pennsylvania
Income Taxes
Carryforward term	20 years

Income Taxes - Components of th

Income Taxes - Components of the Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Income Taxes
Operating loss carryforwards	$ 90,550	$ 90,895
Tax credit carryforwards	28,226	26,550
Stock-based compensation	6,902	6,820
Capitalized research and development	7,818
Lease liabilities	220	276
Other	70	162
Total deferred tax assets	133,786	124,703
Right-of-use asset	(213)	(270)
Valuation allowance	$ (133,573)	$ (124,433)

Income Taxes - Difference Betwe

Income Taxes - Difference Between U.S. Federal Corporate Tax Rate and Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Expected federal income tax rate	(21.00%)	(21.00%)	(21.00%)
Change in valuation allowance	(9.30%)	10.60%	26.20%
Federal and state credits	1.70%	(3.10%)	(8.10%)
State income taxes, net of federal benefit	2.10%	(1.90%)	(4.70%)
Warrant and future tranche right revaluation loss	26.90%	14.20%	4.30%
Stock-based compensation		0.20%	0.50%
Other	(0.40%)	1.00%	2.80%
Effective tax rate	0.00%	0.00%	0.00%

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Employee Benefit Plan
Maximum employer match as a percentage of base pay	5.00%
Percentage the employer matches of employee contributions	100.00%
Portion of the employee's base salary that the Company matches	5.00%
Employer matching contributions to the plan	$ 0.3	$ 0.3	$ 0.3

Related Party Transactions - Ov

Related Party Transactions - Overview of Related Parties (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	Apr. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Related Party Transactions
Exercise price of warrants			$ 1.28	$ 1.28	$ 2.04	$ 1.28
Number of Shares			16,967,828	16,967,828	8,732,230	16,967,828
Common stock issued in lieu of board fees					105,691	145,392	53,985
Restricted stock units | 2013 Stock Incentive Plan [Member]
Related Party Transactions
Award granted			128,170
Directors [Member]
Related Party Transactions
Ownership percentage					4.00%
Aggregate common shares					2,047,180
Maximum [Member]
Related Party Transactions
Proceeds from issuance of common stock in lieu of director board and committee fees					$ 0.1	$ 0.3	$ 0.1
Series B1 Redeemable Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares					23,684
Baker Bros. Advisors LP [Member]
Related Party Transactions
Issuance of common stock upon exercise of warrants (in shares)		2,708,812
Exercise price of warrants		$ 0.08
Proceeds from exercise of warrants		$ 0.2
Maximum beneficial ownership percentage holding, after convertible securities converted							4.99%
Prior notice period (in days)							61 days
Baker Bros. Advisors LP [Member] | Maximum [Member]
Related Party Transactions
Maximum beneficial ownership percentage holding, after convertible securities converted							19.99%
Baker Bros. Advisors LP [Member] | Series B1 Redeemable Convertible Preferred Stock
Related Party Transactions
Aggregate common shares	9,534
Conversion of preferred stock to common, shares		14,150
Baker Bros. Advisors LP [Member] | Common stock
Related Party Transactions
Shares issued on exercise of warrants during the period	953,400	1,415,000
Pillar Investment Entities
Related Party Transactions
Ownership percentage					19.99%
Issuance of common stock upon exercise of warrants (in shares)					3,158,386
Exercise price of warrants					$ 0.01
Proceeds from exercise of warrants					$ 0.1
Cashless shares					19,052
Pillar Investment Entities | Pre-funded Warrants
Related Party Transactions
Exercise price of warrants					$ 0.01
Number of Shares					1,533,159
Pillar Investment Entities | Warrant, Tranche One
Related Party Transactions
Exercise price of warrants					$ 2.28
Number of Shares					3,039,514
Pillar Investment Entities | Warrant, Tranche Two
Related Party Transactions
Exercise price of warrants					$ 2.58
Number of Shares					2,764,227
Pillar Investment Entities | Warrant, Tranche Three
Related Party Transactions
Exercise price of warrants					$ 2.71
Number of Shares					1,373,626
Chief Executive Officer | 2013 Stock Incentive Plan [Member]
Related Party Transactions
Award granted				128,170	0
Proceeds from issuance of restricted stock in lieu of salary				$ 0.6

Net Income (Loss) per Common _3

Net Income (Loss) per Common Share Applicable to Common Stockholders -Computation of basic and diluted net income per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (loss) applicable to common stockholders - Basic:
Net income (loss)	$ 98,091	$ (112,662)	$ (56,515)
Less: Deemed dividend on preferred stock			(28,043)
Less: Undistributed earnings to preferred stockholders	(1,150)
Net income (loss) applicable to common stockholders	96,941	(112,662)	(84,558)
Numerator for basic net income (loss) applicable to common stockholders	$ 96,941	$ (112,662)	$ (84,558)
Denominator for basic net income (loss) applicable to common stockholders	49,203	33,821	28,545
Net income (loss) income applicable to common stockholders - basic	$ 1.97	$ (3.33)	$ (2.96)
Net loss applicable to common stockholders - Diluted:
Net income (loss)	$ 96,941	$ (112,662)	$ (84,558)
Less: Warrant revaluation gain applicable to dilutive liability-classified warrants	(6,983)
Less: Future tranche right revaluation gain applicable to dilutive liability-classified future tranche rights	(118,803)
Numerator for diluted net income (loss) applicable to common stockholders	$ (28,845)	$ (112,662)	$ (84,558)
Denominator for basic net income (loss) applicable to common stockholders	49,203	33,821	28,545
Plus: Incremental shares underlying "in the money" warrants outstanding	93
Plus: Incremental shares underlying "in the money" liability-classified future tranche rights outstanding	831
Denominator for diluted net income (loss) applicable to common stockholders	50,127	33,821	28,545
Net income (loss) applicable to common stockholders - diluted	$ (0.58)	$ (3.33)	$ (2.96)

Net Income (Loss) per Common _4

Net Income (Loss) per Common Share Applicable to Common Stockholders - Antidilutive securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive securities
Total antidilutive securities	14,510	75,321	61,289
Stock options
Antidilutive securities
Total antidilutive securities	5,202	4,614	4,220
Restricted stock units
Antidilutive securities
Total antidilutive securities	576	903	194
Common Stock Warrants
Antidilutive securities
Total antidilutive securities	8,732	16,968	5,099
Convertible preferred stock
Antidilutive securities
Total antidilutive securities		2,369	2,369
Future tranche right liability
Antidilutive securities
Total antidilutive securities		50,467	49,407

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Subsequent Events
Sale of common stock, net of issuance costs	$ 19,515	$ 28,646	$ 5,298
"At-The-Market" Equity Program
Subsequent Events
Stock issued (in shares)	5,117,357	3,608,713

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements - Recently Issued
Operating lease right-of-use assets	$ 734	$ 930