Bellicum Pharmaceuticals (BLCM) 10-K 24 Mar 22 2021 FY Annual report Financial data

Cover

Cover - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 21, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-36783
Entity Registrant Name	Bellicum Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-1450200
Entity Address, Address Line One	3730 Kirby Drive, Suite 1200
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77098
City Area Code	281
Local Phone Number	454-3424
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	BLCM
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
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 26,796,617
Entity Common Stock, Shares Outstanding (in shares)		8,552,207
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to its 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K. Such Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days following the Registrant’s fiscal year ended December 31, 2021.
Entity Central Index Key	0001358403
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Auditor Information [Abstract]
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Houston, Texas

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 46,156	$ 35,495
Restricted cash	1,501	1,501
Accounts receivable, interest and other receivables	205	2
Prepaid expenses and other current assets	1,269	802
Assets held for sale	0	1,643
Total current assets	49,131	39,443
Operating lease right-of-use assets	0	645
Property and equipment, net	12	189
Other assets	0	307
Total assets	49,143	40,584
Current liabilities:
Accounts payable	90	891
Accrued expenses and other current liabilities	3,849	4,165
Warrant derivative liability	2,773	10,345
Private placement option liability	0	7,803
Current portion of lease liabilities	0	825
Liabilities held for sale	0	672
Total current liabilities	6,712	24,701
Long-term lease liabilities	0	344
Total liabilities	6,712	25,045
Commitments and contingencies
Redeemable Preferred stock: $0.01 par value; 10,000,000 shares authorized series 1 redeemable convertible preferred stock, $0.01 par value, 1,517,500 shares authorized at December 31, 2021 and December 31, 2020, 452,000 shares issued and outstanding at December 31, 2021 and December 31, 2020	18,036	18,036
Stockholders’ equity (deficit):
Common stock, $0.01 par value; 80,000,000 shares authorized at December 31, 2021 and December 31, 2020, respectively; 8,497,025 shares issued and 8,429,279 shares outstanding at December 31, 2021; 8,385,650 shares issued and 8,317,904 shares outstanding at December 31, 2020	85	84
Treasury stock: 67,746 shares held at December 31, 2021 and December 31, 2020	(5,056)	(5,056)
Additional paid-in capital	580,156	543,561
Accumulated other comprehensive loss	(338)	(339)
Accumulated deficit	(550,452)	(540,747)
Total stockholders’ equity (deficit)	24,395	(2,497)
Total liabilities, redeemable preferred stock and stockholders’ equity (deficit)	$ 49,143	$ 40,584

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	80,000,000	80,000,000
Common stock, issued (in shares)	8,497,025	8,385,650
Common stock, outstanding (in shares)	8,429,279	8,317,904
Treasury stock (in shares)	67,746	67,746
Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	1,517,500	1,517,500
Preferred stock, issued (in shares)	452,000	452,000
Preferred stock, outstanding (in shares)	452,000	452,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses
Research and development	$ 23,578	$ 39,052
General and administrative	7,010	15,531
Total operating expenses	30,588	54,583
Other operating income (expense)
Impairment of property and equipment	0	(1,265)
(Loss) Gain on dispositions, net	(478)	3,656
Total other operating income (expense)	(478)	2,391
Loss from operations	(24,866)	(51,692)
Other income (expense):
Interest income	32	387
Interest expense	(4)	(2,659)
Change in fair value of warrant and private placement option liabilities	15,126	46,130
Gain on extinguishment of debt	0	112
Other income	7	0
Total other income	15,161	43,970
Net loss	$ (9,705)	$ (7,722)
Net loss per common share attributable to common shareholders, basic (in dollars per share)	$ (0.84)	$ (1.34)
Net loss per common share attributable to common shareholders, diluted (in dollars per share)	$ (0.84)	$ (1.34)
Weighted-average shares outstanding-basic (in shares)	11,504,294	5,760,159
Weighted-average shares outstanding- diluted (in shares)	11,504,294	5,760,159
Net loss	$ (9,705)	$ (7,722)
Other comprehensive income (loss):
Foreign currency translation adjustment	1	(12)
Comprehensive loss	(9,704)	(7,734)
Supply Agreement And License Revenue
Revenues
Revenues	6,200	500
Supply agreement
Revenues
Revenues	700	0
License revenue
Revenues
Revenues	$ 5,500	$ 500

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Series 1 Preferred	Series 1 PreferredPreferred Stock
Preferred stock, beginning balance (in shares) at Dec. 31, 2019								538,000
Preferred stock, beginning balance at Dec. 31, 2019								$ 21,468
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock into common stock (in shares)		(860,000)					(86,000)	(86,000)
Conversion of redeemable convertible preferred stock into common stock	$ 3,432	$ 9		$ 3,423				$ (3,432)
Preferred stock, ending balance (in shares) at Dec. 31, 2020								452,000
Preferred stock, ending balance at Dec. 31, 2020	18,036							$ 18,036
Balance, beginning of period (in shares) at Dec. 31, 2019		5,076,593	67,746
Balance, beginning of period at Dec. 31, 2019	(26,217)	$ 507	$ (5,056)	511,684	$ (533,025)	$ (327)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	5,031			5,031
1-for-10 Reverse Stock Split	0	$ (457)		457
Issuance of common stock - Employee Stock Purchase Plan (in shares)		14,975
Issuance of common stock - Employee Stock Purchase Plan	78			78
Issuance of common stock upon vesting of restricted stock units (in shares)		1,406
Issuance of common stock and pre-funded warrants exercise, net of issuance costs (in shares)		2,432,676
Issuance of common stock and pre-funded warrants exercise, net of issuance costs	22,913	$ 25		22,888
Conversion of redeemable convertible preferred stock into common stock (in shares)		860,000					86,000	86,000
Conversion of redeemable convertible preferred stock into common stock	3,432	$ 9		3,423				$ (3,432)
Comprehensive loss	(7,734)				(7,722)	(12)
Balance, end of period (in shares) at Dec. 31, 2020		8,385,650	67,746
Balance, end of period at Dec. 31, 2020	(2,497)	$ 84	$ (5,056)	543,561	(540,747)	(339)
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock into common stock (in shares)							0
Preferred stock, ending balance (in shares) at Dec. 31, 2021								452,000
Preferred stock, ending balance at Dec. 31, 2021	18,036							$ 18,036
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,439			3,439
Issuance of common stock upon vesting of restricted stock units (in shares)		111,375
Issuance of common stock upon vesting of restricted stock units	0	$ 1		(1)
Issuance of common stock and pre-funded warrants exercise, net of issuance costs	32,908			32,908
Conversion of redeemable convertible preferred stock into common stock (in shares)							0
Extinguishment of private option liability	249			249
Comprehensive loss	(9,704)				(9,705)	1
Balance, end of period (in shares) at Dec. 31, 2021		8,497,025	67,746
Balance, end of period at Dec. 31, 2021	$ 24,395	$ 85	$ (5,056)	$ 580,156	$ (550,452)	$ (338)

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ (Deficit) Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2020
Common Stock
Reverse stock split ratio	0.01

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (9,705,000)	$ (7,722,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	3,439,000	5,031,000
Depreciation and amortization expense	105,000	1,472,000
Change in fair value of warrant and private placement derivative liabilities	(15,126,000)	(46,130,000)
(Gain) loss on dispositions, net	478,000	(3,656,000)
Amortization of right-of-use assets	33,000	402,000
Accretion of lease liability	23,000	414,000
Impairment of property and equipment	0	1,265,000
Amortization of deferred issuance costs	0	550,000
Gain on debt extinguishment	0	(112,000)
Changes in operating assets and liabilities:
Accounts receivable, interest and other receivables	170,000	301,000
Prepaid expenses and other assets	(462,000)	563,000
Accounts payable	(801,000)	(1,917,000)
Accrued liabilities and other	(1,260,000)	(7,111,000)
Net cash used in operating activities	(23,106,000)	(56,650,000)
Cash flows from investing activities:
Proceeds from sale of property and equipment	900,000	14,705,000
Purchases of property and equipment	(7,000)	(625,000)
Cash provided by investing activities	893,000	14,080,000
Cash flows from financing activities:
Payment on debt	0	(37,155,000)
Proceeds from exercise of stock options	0	12,000
Proceeds from issuance of stock from employee stock purchase plan	0	78,000
Proceeds from issuance of pre-funded warrants, net	32,908,000	22,901,000
Payment on financing lease obligations	(35,000)	(74,000)
Net cash provided by (used in) financing activities	32,873,000	(14,238,000)
Effect of exchange rate changes on cash	1,000	(12,000)
Net change in cash, cash equivalents and restricted cash	10,661,000	(56,820,000)
Cash, cash equivalents and restricted cash at beginning of period	36,996,000	93,816,000
Cash, cash equivalents and restricted cash at end of period	47,657,000	36,996,000
Supplemental cash flow information:
Cash paid during the period for interest	0	2,340,000
Non-cash investing and financing activities:
Conversion of redeemable preferred stock into common stock	0	3,432,000
Reclassification of property and equipment, net to assets held for sale	0	2,300,000
Leasehold improvements paid by landlord	$ 0	$ 113,000

ORGANIZATION, BASIS OF PRESENTA

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization Bellicum Pharmaceuticals, Inc. (“Bellicum”) is a clinical stage biopharmaceutical company focused on discovering and developing novel cellular immunotherapies for various forms of cancer. Bellicum is devoting substantially all of its present efforts to developing next-generation CAR-T product candidates in cellular immunotherapy. Bellicum has two wholly-owned subsidiaries, Bellicum Pharma Limited, a private limited company organized under the laws of the United Kingdom, and Bellicum Pharma GmbH, a private limited liability company organized under German law. Both were formed for the purpose of developing product candidates in Europe. Bellicum, Bellicum Pharma Limited and Bellicum Pharma GmbH are collectively referred to herein as the “Company.” All intercompany balances and transactions among the consolidated entities have been eliminated in consolidation. Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker. The Company has determined that it has one operating and reporting segment as it allocates resources and assesses financial performance on a consolidated basis. The Company’s chief operating decision maker is its Chief Executive Officer who manages operations and reviews the financial information as a single operating segment for purposes of allocating resources and evaluating its financial performance. Reverse Stock Split On February 5, 2020, the Company filed a Certificate of Amendment of the Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware to (i) effect a reverse stock split of all issued and outstanding shares of the Company’s common stock at a ratio of 1-for-10 and (ii) reduce the number of authorized shares of the Company’s common stock from 200,000,000 to 40,000,000. The accompanying consolidated financial statements and notes to the consolidated financial statements gives retroactive effect to the reverse stock split for all periods presented. On June 15, 2020, the Company filed with the Secretary of State of the State of Delaware a Second Certificate of Amendment to the Company’s Amended and Restated Certificate of Incorporation to increase the authorized number of shares of the Company’s common stock from 40,000,000 shares to 80,000,000 shares. Basis of Presentation The accompanying financial statements have been prepared in conformity with the authoritative U.S. generally accepted accounting principles (“GAAP”). The accompanying financial statements have been prepared on a basis that assumes that the Company will continue as a going concern, and do not include any adjustments that may result from the outcome of this uncertainty. This basis of accounting contemplates the recovery of the Company’s assets and the satisfaction of the Company’s liabilities and commitments in the normal course of business and does not include any adjustments to reflect the possible future effects of the recoverability and classification of recorded asset amounts or amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company has experienced net losses since its inception and if the Company does not successfully obtain regulatory approval and commercialize any of its product candidates, the Company will not be able to achieve profitability. As of December 31, 2021, the Company has an accumulated deficit of $550.5 million. The Company is subject to risks common to companies in the biotechnology industry and the future success of the Company is dependent on its ability to successfully complete the development of, and obtain regulatory approval for, its product candidates, manage the growth of the organization, obtain additional financing necessary in order to develop, launch and commercialize its product candidates, and compete successfully with other companies in its industry. The Company believes that its current capital resources, which consist of cash and cash equivalents, are sufficient to fund operations through at least the next twelve months from the date the accompanying financial statements are issued based on the expected cash burn rate. The Company may be required to raise additional capital to fund future operations through the sale of additional equity, incurrence of debt, the entry into licensing or collaboration agreements with partners, grants or other sources of financing. Sufficient funds may not be available to the Company at all or on attractive terms when needed from equity or debt financings. If the Company is unable to obtain additional funding from these or other sources when needed, or to the extent needed, it may be necessary to significantly reduce its controllable and variable expenditures and current rate of spending through reductions in staff and delaying, scaling back, or suspending certain research and development, sales and marketing programs and other operational goals. Use of Estimates The preparation of the financial statements in accordance with GAAP requires management to make certain estimates and judgments that affect the reported amounts of assets, liabilities, revenue recognition, and expenses. Actual results could differ materially from those estimates. Revenue Recognition The Company’s sources of revenue in 2021 were from its supply agreement with Takeda Development Center Americas, Inc. ("Takeda") and from its licensing agreements with The University of Texas MD Anderson Cancer Center (“MD Anderson”). The Company has generated revenue from its licensing agreements since 2019. Prior to 2019, the Company's only source of revenue was from grants. Supply of Product The promised product in the supply agreement with Takeda consists of rimiducid including any components, drug substance, raw materials and/or excipients to be supplied by the Company. Revenue is generally recognized upon the transfer of control of promised goods to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods. On May 4, 2021, the Company entered a multi-year supply agreement with Takeda. The Company will supply Takeda with rimiducid for potential use in clinical trials of TAK-007 (CD19 CAR-NK cell therapy). The Company generated revenue of $0.7 million in the second quarter of 2021, with the possibility of additional revenue from future sales. Licenses of Intellectual Property If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, revenue is recognized from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company uses judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over a period of time or at a point in time. If over a period of time, the Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. On January 22, 2019, the Company entered into a licensing and commercialization agreement with MD Anderson (the “2019 MD Anderson License Agreement”). Under the 2019 MD Anderson License Agreement, the Company granted MD Anderson non-exclusive rights in certain Caspase-9 and related technologies and use of a small molecule known as rimiducid in a certain cell therapy program. During the fourth quarter of 2019, and under the terms of the 2019 MD Anderson License Agreement, MD Anderson exercised an option to grant a non-exclusive sublicense of the rights licensed by the Company to MD Anderson. MD Anderson, as a result of this exercise, granted a sublicense that entitled the Company to receive as consideration an upfront license fee as well as additional future annual maintenance fees, milestone payments related to the achievement of pre-specified development, regulatory, and commercialization events, and royalties on net sales of licensed products. On August 31, 2021, the Company entered into a second licensing and commercialization agreement with MD Anderson (the “2021 MD Anderson Option and License Agreement”). Under the 2021 MD Anderson Option and License Agreement, MD Anderson has certain rights to the use of CaspaCIDe and rimiducid in product candidates nominated under the agreement, and receives options to non-exclusive licenses to the technology in these candidates. These options were evaluated and were not determined to be material rights. Upon sublicense of the product candidates nominated under the agreement, or upon exercise of an option and sublicense of a product candidate to a third party, the Company is entitled to a sublicense execution fee, a percentage of certain consideration received by MD Anderson for the sublicense, an annual maintenance fee, and a percentage royalty on net sales of licensed products. During the third quarter of 2021, the Company received an upfront payment of $5.0 million, which was recognized as revenue upon execution of the agreement, and granted licenses for two nominated programs. Milestone Payments At the inception of each arrangement that includes developmental, regulatory or commercial milestone payments, the Company evaluates whether achieving the milestones is considered probable and estimate the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone is included in the transaction price. Milestone payments that are not within the Company's control, such as approvals from regulators or where attainment of the specified event is dependent on the development activities of a third party, are not considered probable of being achieved until those approvals are received or the specified event occurs. Revenue is recognized from the satisfaction of performance obligations when such obligations have been fulfilled. Royalty Revenues For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, no royalties have been received. Cash, Cash Equivalents, and Restricted Cash The Company considers all short-term, highly liquid investments with a maturity of three months or less from the date of purchase and that can be liquidated without prior notice or penalty, to be cash equivalents. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same such amounts shown in the statements of cash flows. (in thousands) December 31, 2021 December 31, 2020 Cash and cash equivalents $ 46,156 $ 35,495 Restricted cash 1,501 1,501 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 47,657 $ 36,996 In connection with the closing of the Asset Purchase Agreement with M.D. Anderson on April 14, 2020, $1.5 million of the cash proceeds received are subject to certain escrow provisions and recorded as restricted cash. The funds are required to be held until any claims against the escrow are resolved. Disposition of Assets and Liabilities Held for Sale and Held for Use In the fourth quarter of 2020, in connection with the Company’s restructuring plan, Management elected to seek an exit to its leased manufacturing facility in Houston, Texas. As a result of this decision, the Company reclassified the assets and liabilities associated with the leased facility as held for sale. The reclassified assets and liabilities included a right-of-use asset of $0.5 million, property and equipment of $2.3 million and the related lease liability of $0.7 million. Based on the cost to exit the lease and the net realizable value of the related assets, the Company recognized an impairment charge of $1.3 million in the fourth quarter of 2020. The disposal of the assets and liabilities associated with the Houston facility was completed on February 26, 2021. Under the terms of the agreement, a third party assumed the lease for the facility. In addition, the third party paid $1.1 million to the Company for substantially all of the property and equipment associated with the location. The consideration included $0.9 million in cash and an unsecured promissory note for $0.2 million. On March 15, 2021, the Company entered an agreement to terminate its sub-lease of the South San Francisco office space contingent upon consent of the prime lessor. Under the terms of the agreement, the company agreed to pay a lease termination fee of $0.9 million while the security deposit of $0.2 million was returned to the Company in June 2021. The decision to exit this lease reflects the ability of the Company to carry on its administrative function remotely. On March 26, 2021, the Company met all of the conditions of the agreement and disposed of substantially all of the assets and liabilities associated with the lease including the right-of-use asset of $0.6 million, leased equipment with a net book value less than $0.1 million, and the related lease liability of $1.0 million. The Company recognized a loss on termination of $0.5 million during the first quarter of 2021. Property and Equipment Furniture, equipment and software are recorded at cost and are depreciated using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 5 years. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term. Property and equipment consisted of the following: (in thousands, except useful lives) Estimated Useful Lives December 31, 2021 December 31, 2020 Leasehold improvements 5 Years $ — $ 167 Lab equipment 5 Years 530 530 Manufacturing equipment 5 Years 138 138 Computer and office equipment 3 to 5 Years 841 834 Software 3 Years 94 94 Total 1,603 1,763 Less: accumulated depreciation (1,591) (1,574) Property and equipment, net $ 12 $ 189 During the years ended December 31, 2021 and 2020, the Company recorded $0.1 million and $1.5 million of depreciation expense, respectively. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment when events or changes in business conditions indicate that their carrying value may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset. Accrued Expenses and Other Current Liabilities Accrued expenses and other liabilities consist of the following: December 31, 2021 December 31, 2020 Accrued payroll $ 320 $ 1,071 Accrued patient treatment costs 2,086 899 Accrued clinical research costs 479 1,562 Accrued manufacturing costs 328 41 Accrued professional services 305 279 Accrued other 331 313 Total accrued expenses and other current liabilities $ 3,849 $ 4,165 Certain prior year amounts have been reclassified to conform to the 2021 presentation. Expenses related to clinical studies totaling $1.5 million were reclassified from Accrued Other to Accrued Clinical Research Costs. Another $0.1 million for expenses related to drug manufacture and professional consulting services were reclassified from Accrued Other to Accrued Manufacturing Costs and Accrued Professional Services. Warrant Derivatives In an underwritten public offering (the “2019 Offering”), the Company issued Series 1 Redeemable Convertible Non-Voting Preferred Stock (the “Series 1 Preferred Stock”) and warrants (the “2019 Public Warrants”) to purchase its common stock. These 2019 Public Warrants are classified as liabilities in the accompanying consolidated balance sheets, because the public warrants embody a conditional or unconditional obligation to repurchase the Company’s shares. The Company accounted for these warrants at fair value on the date of issuance and they are subject to re-measurement to fair value at each balance sheet date. Any change in fair value is recognized as a component of other income (expense) on the accompanying consolidated statements of operations and comprehensive loss. The Company estimates the fair value of these liabilities using the Black-Scholes valuation technique, which utilizes assumptions including (i) the fair value of the underlying stock at the valuation measurement date, (ii) volatility of the price of the underlying stock, (iii) the expected term, and (iv) risk-free interest rates. The Company will continue to adjust the liability for changes in fair value until the earlier of the exercise or expiration of the warrants or a change in control, as defined. The warrants are freely exercisable at any time from the issuance date until the expiration date, provided exercise does not cause a warrant holder to exceed a pre-determined beneficial ownership limit. See Note 5 - Public Offering and Private Placement for discussions of the 2019 Public Warrants. In November 2020 and December 2021, the Company issued prefunded warrants and accompanying warrants (the “2020 Pre-funded Warrants” and “2020 Common Warrants”, the “2021 Pre-funded Warrants” and “2021 Common Warrants”, respectively). These pre-funded warrants and common warrants are classified as equity. The pre-funded warrants and common warrants neither embody a conditional or unconditional obligation, nor are they indexed to an obligation, to repurchase the Company’s shares by transferring assets. Furthermore, the monetary value of the pre-funded warrants and accompanying warrants, at inception, is not solely or predominately based on (a) a fixed monetary amount, (b) variations in something other than the fair value of the Company’s shares, or (c) variations inversely related to the fair value of the Company’s own shares. Therefore, the pre-funded warrants and common warrants do not meet the criteria requiring liability classification. See Note 5 - Public Offering and Private Placement for discussions of the 2020 Pre-funded and Common Warrants and 2021 Pre-funded and Common Warrants. Private Placement Option Besides the 2019 Offering, the Company completed a private placement and entered into the 2019 Securities Purchase Agreement that contained a call option on preferred shares that are puttable outside the control of the Company. Prior to the fourth quarter of 2021, the Company recorded the option as a liability and measured the option at fair value. The Company re-measured the option to fair value at each balance sheet date and recorded changes in fair value in other income (expense) in the accompanying consolidated statement of operations and comprehensive loss at each reporting period. Offering expenses arising from the issuance of the private placement option were expensed as incurred. The Company estimated the fair value of these liabilities using a binomial lattice model, which utilized assumptions including (i) the fair value of the underlying stock at the valuation measurement date, (ii) volatility of the price of the underlying stock, (iii) the expected term, and (iv) risk-free interest rates. In 2021, the Company entered into the 2021 Securities Purchase Agreement, pursuant to which certain of the purchasers irrevocably waived the right to cause the Company to conduct the “First Closing” and “Second Closing” under the private placement option contained in the 2019 Securities Purchase Agreement (each term as defined in the 2019 Securities Purchase Agreement), which releases the Company of potential obligations. The Company has therefore derecognized the option liability at its balance sheet date ended on December 31, 2021. Preferred Stock Preferred shares issued by the Company that are subject to mandatory redemption are classified as liability instruments in the accompanying consolidated balance sheets and are measured at fair value at the date of issuance. 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 within mezzanine equity in the accompanying consolidated balance sheets. At all other times, preferred shares are classified within stockholders’ deficit. Operating Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. If both criteria are met, upon lease commencement, the Company records a lease liability which represents the Company’s obligation to make lease payments arising from the lease, and a corresponding right-of-use (“ROU”) asset which represents the Company’s right to use an underlying asset during the lease term. Operating leases are recognized as ROU assets and operating lease liabilities on the balance sheet at the commencement date based on the present value of the future minimum lease payments over the lease term calculated using the Company’s incremental borrowing rate applicable to the underlying asset unless the implicit rate is readily determinable. Any lease incentives received are deferred and recorded as a reduction of the ROU asset and amortized over the term of the lease. Rent expense, comprised of amortization of the ROU asset and the implicit interest accreted on the operating lease liability, is recognized on a straight-line basis over the lease term. The Company determines the lease term as the noncancellable period of the lease and may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. Leases with a term of 12 months or less are not recognized on the balance sheets. Fair Value of Financial Instruments Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a fair value hierarchy has been established that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). These inputs are classified into the following hierarchy: Level 1 Inputs - quoted prices (unadjusted) in active markets for identical assets that the reporting entity has the ability to access at the measurement date; Level 2 Inputs - inputs other than quoted prices included within Level 1 that are observable for the asset, either directly or indirectly; and Level 3 Inputs - unobservable inputs for the assets. The categorization of a financial instrument within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company believes the recorded values of its financial instruments, including cash and cash equivalents, accounts payable, accrued liabilities, and debt approximate their fair values due to the short-term nature of these instruments. Financial Instruments and Credit Risks Financial instruments that potentially subject the Company to credit risk include cash and cash equivalents and accounts receivable. Cash is deposited in demand accounts in federally insured domestic institutions to minimize risk. Insurance is provided through the Federal Deposit Insurance Corporation and Security Investor Protection Corporation. Although the balances in these accounts exceed the federally insured limit from time to time, the Company has not incurred losses related to these deposits. Equity Issuance Costs Equity issuance costs represent costs paid to third parties in order to obtain equity financing. These costs have been netted against the proceeds of the equity issuances. Licenses and Patents Licenses and patent costs for technologies that are utilized in research and development and have no alternative future use are expensed as incurred. Costs related to the license of patents from third parties and internally developed patents are classified as research and development expenses. Legal costs related to patent applications and maintenance are classified as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss. Research and Development Research and development expenses consist of expenses incurred in performing research and development activities, including compensation and benefits for research and development employees and consultants, facilities expenses, overhead expenses, cost of laboratory supplies, manufacturing expenses, fees paid to third parties and other outside expenses. Research and development costs are expensed as incurred. Clinical trial and other development costs incurred by third parties are expensed as the contracted work is performed. The Company accrues for costs incurred as the services are being provided by monitoring the status of the clinical trial or project and the invoices received from its external service providers. The Company ’ s estimates depend on the timeliness and accuracy of the data provided by the vendors regarding the status of each project and total project spending. The Company adjusts its accrual as actual costs become known. Collaboration Agreements The Company enters into collaboration agreements that include varying arrangements regarding which parties perform and bear the costs of research and development activities. The Company may share the costs of research and development activities with a collaborator, or the Company may be reimbursed for all or a significant portion of the costs of the Company ’ s research and development activities. The Company records its internal and third-party development costs associated with these collaborations as research and development expenses. When the Company is entitled to reimbursement of all or a portion of the research and development expenses that it incurs under a collaboration, the Company records those reimbursable amounts as a deduction to the research and development expenses. If the collaboration is a cost-sharing arrangement in which both the Company and its collaborator perform development work and share costs, the Company also recognizes, as research and development expenses in the period when its collaborator incurs development expenses, the portion of the collaborator's development expenses that the Company is obligated to reimburse. Contract Manufacturing Services Contract manufacturing services are expensed as incurred. Prepaid expenses are capitalized and amortized as services are performed. Share-Based Compensation The Company accounts for share-based compensation based on the measurement and recognition of compensation expense for all share-based payment awards made to employees, directors and consultants to be recognized in the financial statements, based on their fair value. The Company calculates the fair value of stock options on the date of grant using the Black-Scholes pricing model, which requires a number of estimates, including the expected life of awards, interest rates, stock volatility and other assumptions. Restricted stock is measured based on the fair market value of the underlying stock on the date of grant. If the awards are classified as liability awards, the fair value is remeasured at each reporting date and the compensation expense is adjusted accordingly. Additionally, the Company applies a forfeiture rate to estimate the number of grants that will ultimately vest, as applicable, and adjusts the expense as these awards vest. All of the Company’s current equity awards are service based awards and the share-based compensation cost is being recognized over the requisite service period of the awards on a straight-line basis. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. This method also requires the recognition of future tax benefits such as net operating loss and tax credit carry forwards, to the extent that realization of such benefits is more likely than not. A valuation allowance is recorded when the realization of future tax benefits is uncertain. The Company records a valuation allowance for the full amount of deferred tax assets, which would otherwise be recorded for tax benefits relating to the operating loss and tax credit carryforwards, as realization of such deferred tax assets cannot be determined to be more likely than not. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. As of December 31, 2021, the Company had recorded a full valuation allowance on its net U.S. and foreign deferred tax assets because the Company expects that it is more likely than not that its deferred tax assets will not be realized in the foreseeable future. Should the actual amounts differ from our estimates, the amount of the valuation allowance could be materially impacted. The Company accounts for uncertain tax positions in accordance with the provisions of the Accounting Standards Codification (ASC) 740 , Income Taxes . When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2021 and 2020, the Company had no uncertain tax positions and no interest or penalties have been charged for the years ended December 31, 2021 and 2020. The Company is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The tax years 2005 through 2021 remain open to examination by the U.S. Internal Revenue Service. Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period, from transactions, and other events and circumstances from non-owner sources. Components of other comprehensive loss includes, among other items, unrealized gains and losses on the changes in fair value of investments and unrealized gains and losses on the change in foreign currency exchange rates. These components are added, net of their related tax effect, to the reported net loss to arrive at comprehensive loss. Net Loss and Net Loss per Share of Common Stock Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period without consideration for common stock equivalents. Diluted earnings per share is based on the more dilutive method between the two-class method and the treasury stock method and includes the effect from potential issuance of ordinary shares, such as shares issuable

FAIR VALUE OF MEASUREMENTS AND

FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES	FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES Investment Securities The following tables present the Company’s investment securities (including those classified on the Company’s balance sheet as cash equivalents) that are measured at fair value on a recurring basis as of December 31, 2021 and 2020: Fair Value at December 31, 2021 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Cash Equivalents: Money market funds and treasury bills $ 42,487 $ — $ — $ 27,463 $ — $ — Total Cash Equivalents $ 42,487 $ — $ — $ 27,463 $ — $ — Additionally, the $1.5 million of restricted cash on the Company's balance sheet is held in a money market fund as of December 31, 2021. Money market funds and U.S. Treasury bills are valued based on various observable inputs such as benchmark yields, reported trades, broker/dealer quotes, benchmark securities and bids. Warrant Derivative Liability and Private Placement Option Liability The Company’s financial liabilities recorded at fair value on a recurring basis include the fair values of the warrant derivative liability and the private placement option liability prior to its derecognition in December 2021. Inputs used to determine estimated fair value (Level 3) of the warrants include the fair value of the underlying stock relative to the warrant exercise price at the valuation measurement date, volatility of the price of the underlying stock, the expected term of the warrants, and risk-free interest rates. The fair values of the warrant derivative liability and the private placement option liability, prior to its derecognition in December 2021, are classified as current liabilities in the accompanying consolidated balance sheets. These liabilities will be shown as current liabilities on the balance sheet when it is deemed more probable than not by management to be exercised within one year. On December 4, 2021, the Company entered into the 2021 Securities Purchase Agreement, pursuant to which certain of the investors irrevocably waived the right to cause the Company to conduct the “First Closing” and “Second Closing” under the private placement option contained in the 2019 Securities Purchase Agreement (each term as defined in the 2019 Securities Purchase Agreement). The Company derecognized the private placement option liability and recorded a gain on change in the fair value for the year ended December 31, 2021 of $2.8 million in the accompanying statements of operations and comprehensive loss. The fair value of the warrants has been estimated with the following weighted-average assumptions, including the most sensitive input, volatility: December 31, 2021 December 31, 2020 Risk-free interest rate 1.22 % 0.46 % Volatility 94 % 90 % Expected life (years) 4.64 5.64 The following table provides the warrant derivative and private placement option liabilities reported at fair value and measured on a recurring basis: Fair Value at December 31, 2021 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Warrant derivative liability $ — $ — $ 2,773 $ — $ — $ 10,345 Private placement option liability — — — — — 7,803 Total fair value $ — $ — $ 2,773 $ — $ — $ 18,148 The ending balance of the Level 3 financial instruments presented above represents the Company’s best estimate of valuation and may not be substantiated by comparison to independent markets and, in many cases, could not be realized in immediate settlement of the instruments.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
LEASES	LEASES The Company entered into a lease agreement for office and laboratory space in Houston, Texas commencing in July 2020 and expiring in 2023. The Company recorded ROU assets of $0.5 million and a corresponding lease liability of $0.6 million upon lease commencement. In October 2020, in connection with the Company’s restructuring plan, Management elected to seek an exit to its leased office and laboratory space in Houston, Texas. As a result of this decision, the Company reclassified the assets and liabilities associated with the leased facility as held for sale. The reclassified assets included a right-of-use asset of $0.5 million, property and equipment of $2.3 million, and related lease liability of $0.7 million. Based on the cost to exit the lease and the net realizable value of the related assets, the Company recognized an impairment charge of $1.3 million in 2020. The disposal of the assets and liabilities associated with the facility was completed on February 26, 2021. Under the terms of the agreement a third party assumed the lease for the facility. In addition, the third party paid $1.1 million to the Company for substantially all of the property, and equipment associated with the location. The consideration included $0.9 million in cash and an unsecured promissory note for $0.2 million. On March 15, 2021, the Company entered an agreement to terminate its sub-lease of the South San Francisco office space contingent upon consent of the prime lessor. Under the terms of the agreement, the company agreed to pay a lease termination fee of $0.9 million while the security deposit of $0.2 million was returned to the Company. On March 26, 2021, the Company met all of the conditions of the agreement and disposed of substantially all of the assets and liabilities associated with the lease including the right-of-use asset of $0.6 million, leased equipment with net book value less than $0.1 million, and the related lease liability of $1.0 million. The Company recognized a loss on termination of $0.5 million during the year ended December 31, 2021. Components of lease cost are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Finance lease cost: Amortization of leased assets $ 16 $ 74 Interest on lease liabilities 5 21 Operating lease cost 56 814 Short-term lease cost 53 582 Total lease cost $ 130 $ 1,491 Weighted-average remaining lease term: Operating leases 0.0 years 1.7 years Finance leases 0.0 years 1.4 years Weighted-average discount rate: Operating leases — % 11.47 % Finance leases — % 13.05 % Supplemental cash flow information and non-cash activity related to the Company’s operating and finance leases are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 71 $ 950 Operating cash flows from finance leases 5 21 Financing cash flows from finance leases 35 74
LEASES	LEASES The Company entered into a lease agreement for office and laboratory space in Houston, Texas commencing in July 2020 and expiring in 2023. The Company recorded ROU assets of $0.5 million and a corresponding lease liability of $0.6 million upon lease commencement. In October 2020, in connection with the Company’s restructuring plan, Management elected to seek an exit to its leased office and laboratory space in Houston, Texas. As a result of this decision, the Company reclassified the assets and liabilities associated with the leased facility as held for sale. The reclassified assets included a right-of-use asset of $0.5 million, property and equipment of $2.3 million, and related lease liability of $0.7 million. Based on the cost to exit the lease and the net realizable value of the related assets, the Company recognized an impairment charge of $1.3 million in 2020. The disposal of the assets and liabilities associated with the facility was completed on February 26, 2021. Under the terms of the agreement a third party assumed the lease for the facility. In addition, the third party paid $1.1 million to the Company for substantially all of the property, and equipment associated with the location. The consideration included $0.9 million in cash and an unsecured promissory note for $0.2 million. On March 15, 2021, the Company entered an agreement to terminate its sub-lease of the South San Francisco office space contingent upon consent of the prime lessor. Under the terms of the agreement, the company agreed to pay a lease termination fee of $0.9 million while the security deposit of $0.2 million was returned to the Company. On March 26, 2021, the Company met all of the conditions of the agreement and disposed of substantially all of the assets and liabilities associated with the lease including the right-of-use asset of $0.6 million, leased equipment with net book value less than $0.1 million, and the related lease liability of $1.0 million. The Company recognized a loss on termination of $0.5 million during the year ended December 31, 2021. Components of lease cost are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Finance lease cost: Amortization of leased assets $ 16 $ 74 Interest on lease liabilities 5 21 Operating lease cost 56 814 Short-term lease cost 53 582 Total lease cost $ 130 $ 1,491 Weighted-average remaining lease term: Operating leases 0.0 years 1.7 years Finance leases 0.0 years 1.4 years Weighted-average discount rate: Operating leases — % 11.47 % Finance leases — % 13.05 % Supplemental cash flow information and non-cash activity related to the Company’s operating and finance leases are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 71 $ 950 Operating cash flows from finance leases 5 21 Financing cash flows from finance leases 35 74

DEBT

DEBT	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
DEBT	DEBT Oxford Loan On December 21, 2017 (the “Oxford Closing Date”), the Company entered into a loan and security agreement (the “Oxford Loan Agreement”) with Oxford Finance LLC, pursuant to which the Company borrowed $35.0 million in a single term loan (the “Oxford Loan”). On the Oxford Closing Date, the Company used approximately $32.9 million of the proceeds from the Oxford Loan to repay its indebtedness to a previous lender. The Company paid expenses related to the Oxford Loan Agreement of $0.1 million, which, along with the final facility charge of $3.0 million, were recorded as deferred issuance costs, which offset long-term debt on the Company’s consolidated balance sheet. The deferred issuance costs were being amortized over the term of the loan as interest expense using the effective interest method. During the year ended December 31, 2020, interest expense included $0.6 million of amortized deferred issuance costs. During November 2020, the Company entered into an agreement for the early settlement of all debt obligations under the Oxford Loan Agreement. During the same month, the Company remitted payment of $27.4 million, which included full repayment of the outstanding principal balance, the Oxford Final Payment Fee, and accrued interest. As of December 31, 2020, the Company recorded a gain on extinguishment of $0.1 million in the accompanying statements of operations and comprehensive loss.

PUBLIC OFFERING AND PRIVATE PLA

PUBLIC OFFERING AND PRIVATE PLACEMENT	12 Months Ended
	Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]
PUBLIC OFFERING AND PRIVATE PLACEMENT	PUBLIC OFFERING AND PRIVATE PLACEMENT December 2021 Private Placement On December 4, 2021, the Company entered into a Securities Purchase Agreement (the “2021 Securities Purchase Agreement”) with certain institutional investors (the “Purchasers”), pursuant to which the Company agreed to issue to the Purchasers 2021 pre-funded warrants to purchase an aggregate of 20,559,210 shares of its common stock and accompanying 2021 common warrants to purchase an aggregate of 2,055,920 shares of common stock. Each pre-funded warrant to purchase one share of common stock will be sold together with a warrant to purchase one-tenth of one share of common stock at a combined unit price of $1.7024. The pre-funded warrants will be immediately exercisable at an exercise price of $0.0001 per share of common stock. The accompanying common warrants will be immediately exercisable at an exercise price of $1.69 per share of common stock and will expire seven years from the date of issuance. The gross proceeds to the Company from the private placement were approximately $35.0 million before deducting placement agent commissions and offering expenses payable by the Company, excluding any proceeds that may be received upon exercise of the accompanying warrants. In addition, pursuant to the 2021 Securities Purchase Agreement, certain of the Purchasers irrevocably waived the right to cause the Company to conduct the “First Closing” and “Second Closing” under the 2019 Securities Purchase Agreement (each term as defined in the 2019 Securities Purchase Agreement), which releases the Company of potential cash or equity obligations. The representations, warranties and covenants contained in the 2021 Securities Purchase Agreement were made only for purposes of such agreement and as of specific dates, were solely for the benefit of the parties to such agreement and may be subject to limitations agreed upon by the contracting parties. November 2020 Underwritten Offering On November 2, 2020, the Company closed an underwritten offering of 1,040,000 shares of its common stock, 2020 pre-funded warrants to purchase 3,109,378 shares of its common stock, and accompanying 2020 common warrants to purchase up to an aggregate of 4,149,378 shares of its common stock. Each share of common stock and pre-funded warrant to purchase one share of common stock was sold together with a common warrant to purchase one share of common stock. The public offering price of each share of common stock and accompanying common warrant was $6.025 and $6.024 for each pre-funded warrant. The pre-funded warrants were immediately exercisable at a price of $0.001 per share of common stock. The common warrants were immediately exercisable at an exercise price of $6.50 per share of common stock and will expire five years from the date of issuance. The shares of common stock and pre-funded warrants, and the accompanying common warrants, were issued separately and were immediately separable upon issuance. The gross proceeds to the Company were approximately $25.0 million before deducting underwriting discounts and commissions and other offering expenses. August 2019 Public Offering On August 16, 2019, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Jefferies LLC and Wells Fargo Securities, LLC, as representatives of the several underwriters named therein (the “Underwriters”), relating to an underwritten public offering (the “2019 Offering”) of 575,000 shares of the Series 1 Redeemable Convertible Non-Voting Preferred Stock of the Company (the “Series 1 Preferred Stock”) and warrants (the “2019 Public Warrants”) to purchase up to 5,750,000 shares of its common stock. Each share of Series 1 Preferred Stock was sold together with a warrant to purchase 10 shares of common stock at a combined price to the public of $100.00. Under certain circumstances, each warrant to purchase 10 shares of common stock will be exercisable, at the irrevocable election of the holder, for one share of Series 1 Preferred Stock. The offering closed on August 21, 2019, and the net proceeds to the Company from the Offering was approximately $53.8 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company, and excluding any proceeds that the Company may receive upon exercise of the Public Warrants. All of the 2019 Public Warrants sold in the 2019 Offering have an exercise price of $13.00 per share of common stock or, in certain circumstances, for $130.00 per share of Series 1 Preferred Stock, subject to proportional adjustments in the event of stock splits or combinations or similar events. The 2019 Public Warrants were immediately exercisable upon issuance, provided that the holder is prohibited, subject to certain exceptions, from exercising a warrant for shares of common stock to the extent that immediately prior to or after giving effect to such exercise, the holder, together with its affiliates and other attribution parties, would own more than 9.99% of the total number of shares of common stock then issued and outstanding, which percentage may be changed at the holder’s election to a lower percentage at any time or to a higher percentage not to exceed 19.99% upon 61 days’ notice to the Company. The Public Warrants will expire on August 21, 2026, unless exercised prior to that date The following table reflects the fair value roll forward reconciliation of the 2019 Public Warrants liabilities for the period ended December 31, 2021: (in thousands) Warrant Derivative Liability Balance, December 31, 2020 $ 10,345 Change in fair value (7,572) Balance, December 31, 2021 $ 2,773 Private Placement On August 16, 2019, the Company entered into a securities purchase agreement (the “2019 Securities Purchase Agreement”) with certain institutional investors named therein (the “Purchasers”), pursuant to which the Company agreed to issue in a private placement (i) 350,000 shares of its Series 2 Redeemable Convertible Non-Voting Preferred Stock (the “Series 2 Preferred Stock”), at a purchase price of $100.00 per share, and related warrants to purchase up to 2,800,000 shares of common stock at an exercise price of $10.00 per share, and (ii) 250,000 shares of its Series 3 Redeemable Convertible Non-Voting Preferred Stock (the “Series 3 Preferred Stock” and, together with the Series 1 Preferred Stock and Series 2 Preferred Stock, the “Preferred Stock”), at a purchase price of $140.00 per share, and related warrants to purchase up to 875,000 shares of common stock at an exercise price of $14.00 per share. The right of the Purchasers to purchase such securities was waived, effective as of December 4, 2021, pursuant to the 2021 Purchase Agreement. The Company received $11.2 million in net option fee proceeds, net of offering costs, upon the execution of the 2019 Securities Purchase Agreement. Pursuant to the 2021 Securities Purchase Agreement entered into on December 4, 2021, the Company derecognized the private placement option liability, and the Company is no longer obligated to issue the Series 2 Preferred Stock, Series 3 Preferred Stock, or any associated Private Warrants. A summary of warrants outstanding and exercisable as of December 31, 2021 is as follows: Warrants Outstanding Warrants Exercisable Year Issued Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price (in years) (per share) (per share) 2019 5,750,000 4.64 $ 13.00 5,750,000 $ 13.00 2020 4,149,378 3.84 $ 6.50 4,149,378 $ 6.50 2020 1 1,716,702 — $ — 1,716,702 $ — 2021 2,055,920 6.94 $ 1.69 2,055,920 $ 1.69 2021 2 20,559,210 — $ — 20,559,210 $ — 34,231,210 34,231,210

REDEEMABLE CONVERTIBLE PREFERRE

REDEEMABLE CONVERTIBLE PREFERRED STOCK	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
REDEEMABLE CONVERTIBLE PREFERRED STOCK	REDEEMABLE CONVERTIBLE PREFERRED STOCK In August 2019, the Company sold Series 1 Preferred Stock pursuant to the 2019 Offering. The Company has 10,000,000 authorized shares of preferred stock with a par value of $0.01, of which the Company has designated 1,517,500 shares as Series 1 redeemable convertible non-voting preferred stock, 350,000 shares as Series 2 redeemable convertible non-voting preferred stock and 250,000 shares as Series 3 redeemable convertible non-voting preferred stock. There were 452,000 shares of Series 1 Preferred Stock issued and outstanding as of both December 31, 2021 and 2020. There were no shares of Series 2 or 3 Preferred Stock issued or outstanding as of December 31, 2020, and the Series 2 and 3 Preferred Stock were cancelled during 2021 pursuant to the 2021 Securities Purchase Agreement. The Series 1 Preferred Stock was issued together with warrants for a combined purchase price of $100.00 per share of Series 1 Preferred Stock and one warrant to purchase 10 shares of common stock. There were 86,000 shares of Series 1 Preferred Stock converted to common stock as of December 31, 2020, while no shares were converted during 2021. As of December 31, 2021 and 2020, the Company classified the Series 1 preferred stock within mezzanine equity, as the Series 1 preferred stock is redeemable at the option of the holders upon passage of time, which is outside of the Company’s control to prevent. The Series 1 Preferred Stock is not currently redeemable and is only redeemable upon a fundamental change at a redemption price. The Company does not believe a fundamental change is considered probable until it occurs. Subsequent adjustment of the amount presented within mezzanine equity to its redemption amount is unnecessary if it is not probable that the instrument will become redeemable. As (i) the Series 1 Preferred Stock is only redeemable upon a fundamental change, the occurrence of which is not probable, and (ii) the occurrence of Transition Date (defined below) is probable, the Company did not accrete the Series 1 Preferred Stock to its redemption amount. Optional Conversion Each share of Preferred Stock is initially convertible into 10 shares of Common Stock. The conversion price at which Preferred Stock may be converted into shares of common stock is subject to adjustment in connection with certain specified events. Redemption Until the applicable Transition Date (defined below), at any time on or after the date that is the fifth (5th) anniversary of the initial issue date of the applicable series of preferred stock, all or any portion of the preferred stock is redeemable at the option of the holder at a redemption price of $100.00 per share (for Series 1 Preferred Stock). The “Transition Date” means the first date following August 21, 2021, on which each of the Conditions (as defined below) is met. The “Conditions” mean: (1) the closing price of the Company’s common stock has been equal to or exceeded $25.00 per share for 180 calendar days (for determining if the Conditions are met for the Series 1 Preferred Stock) for 180 calendar days; (2) the 50-day average trading volume of the Company’s common stock on the Nasdaq stock market is greater than 50,000 shares; and (3) a Phase 3 or Phase 2 pivotal clinical trial for one of the Company’s CAR-T product candidates has been initiated, meaning that at least one clinical trial site has been activated. Dividends Shares of Preferred Stock will be entitled to receive dividends equal to (on an as-if-converted-to-common stock basis), and in the same form and manner as, dividends actually paid on shares of common stock. Liquidation Until the applicable Transition Date, in the event of a liquidation, dissolution, winding up or deemed liquidation, holders of the Preferred Stock will receive a payment equal to the applicable per share purchase price of their Preferred Stock before any proceeds are distributed to the holders of Common Stock. The liquidation preferences, protective voting provisions and redemption rights of the Preferred Stock will terminate upon the occurrence of certain events. Voting Shares of Preferred Stock will generally have no voting rights, except to the extent expressly provided in the Company’s certificate of incorporation or as otherwise required by law.

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
SHARE-BASED COMPENSATION PLANS	SHARE-BASED COMPENSATION PLANS The Company has five share-based compensation plans, including the 2019 Equity Incentive Plan the (“2019 Plan”) which was adopted in June 2019. Each plan authorizes the granting of shares of common stock and/or options to purchase common stock to employees and directors of the Company, as well as non-employee consultants, and allows the holder of the option to purchase common stock at a stated exercise price. The only plan under which the Company may currently grant equity awards is the 2019 Equity Incentive Plan although there remain outstanding awards under the other four plans. Options vest according to the terms of the grant, which may be immediately or based on the passage of time, generally over two 2019 Equity Incentive Plan The 2019 Plan, is designed to secure and retain the services of the Company’s employees and directors. The 2019 Plan is successor to and continuation of the 2014 Equity Incentive Plan, as amended, the (“2014 Plan”), and no additional awards may be issued from the 2014 Plan. Subject to adjustment for certain changes in the Company’s capitalization, the aggregate number of shares of common stock that may be issued under the 2019 Plan (the "Share Reserve") will not exceed the sum of (i) 250,000 new shares, plus (ii) an additional 600,000 shares that were approved at the Company’s Special Meeting of Stockholders in January 2020, plus (iii) an additional 500,000 shares that were approved at the Company’s Annual meeting of Stockholders in June 2020, (iv) an additional 500,000 shares that were approved at the Company’s Annual Meeting of Stockholders in June 2021 and plus (v) the Prior Plans’ Returning Shares, as defined in the 2019 Plan documents, in an amount not to exceed 600,540 shares, including any stock award granted under the 2014 Plan, 2011 Stock Option Plan, as amended, or 2006 Stock Option Plan, as amended, that were outstanding as of the date the 2019 Plan were approved by the Company’s stockholders, as such shares become available from time to time. The following shares of common stock (the “2019 Plan Returning Shares”) will also become available again for issuance under the 2019 Plan: (i) any shares subject to a stock award granted under the 2019 Plan that are not issued because such stock award expires or otherwise terminates without all of the shares covered by such stock award having been issued; (ii) any shares subject to a stock award granted under the 2019 Plan that are not issued because such stock award is settled in cash; and (iii) any shares issued pursuant to a stock award granted under the 2019 Plan that are forfeited back to or repurchased by the Company because of a failure to vest. The 2019 Plan provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, and other stock awards. At December 31, 2021 and 2020, outstanding awards were comprised of the following: December 31, 2021 December 31, 2020 Options 2,074,858 1,425,207 Inducement option awards 65,760 85,761 Restricted stock units 137,004 129,361 Inducement restricted stock units 500 500 Total outstanding awards 2,278,122 1,640,829 Grant Date Fair Value The valuation of the share-based compensation awards is a significant accounting estimate that requires the use of judgments and assumptions that are likely to have a material impact on the financial statements. The fair value of option grants is determined using the Black-Scholes option-pricing model. Expected volatilities utilized in the model are based on historical volatility of the Company’s common stock. Similarly, the dividend yield is based on historical experience and the estimate of future dividend yields. The risk-free interest rate is derived from the U.S. Treasury yield curve in effect at the time of grant. The expected term of the options is based on the average period the stock options are expected to remain outstanding. As the Company does not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior, the expected term is calculated as the midpoint between the weighted-average vesting term and the contractual expiration period also known as the simplified method. The fair value of the option grants has been estimated, with the following weighted-average assumptions: Year Ended December 31, 2021 December 31, 2020 Options granted 1,023,000 1,352,595 Weighted-average exercise price 2.80 7.59 Weighted-average grant date fair value 2.02 5.29 Assumptions: Risk-free interest rate 0.92 % 0.82 % Volatility 90 % 85 % Expected life (years) 5.63 5.83 Expected dividend yield — — Share-Based Compensation Activity The following table summarizes the stock option activity for all stock plans during the year ended December 31, 2021 and 2020 as follows: Options Outstanding Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2019 567,842 $ 76.25 7.82 $ 12 Granted 1,352,595 $ 7.59 Exercised — Forfeited (409,469) $ 29.86 Balance at December 31, 2020 1,510,968 $ 27.36 8.19 $ 379 Granted 1,023,000 $ 2.80 Exercised — Forfeited (393,350) $ 30.66 Balance at December 31, 2021 2,140,618 $ 15.01 8.48 $ — Exercisable at December 31, 2021 718,123 $ 36.42 6.98 $ — There were no options exercised or cash received for the year ended December 31, 2021; the Company received cash of less than $0.1 million upon option exercises for year ended December 31, 2020. The following table summarizes the options outstanding and exercisable at December 31, 2021: Options Outstanding Options Exercisable Exercise Price Total Shares Weighted Average Remaining Contractual Term (in years) Weighted Average Exercise Price Total Shares Weighted Average Remaining Contractual Term (in years) Weighted Average Exercise Price $1.73 to $2.87 215,000 9.89 $ 1.81 — 0.00 $ — $2.88 to $2.93 665,000 9.62 $ 2.88 — 0.00 $ — $2.94 to $3.01 506,000 8.95 $ 2.97 253,000 8.95 $ 2.97 $3.02 to $16.15 475,076 7.32 $ 9.97 207,374 6.15 $ 11.97 $16.16 to $234.70 279,542 5.82 $ 84.39 257,749 5.71 $ 88.94 Total 2,140,618 8.48 $ 15.01 718,123 6.98 $ 36.42 The following table summarizes the stock award activity for all restricted stock units during the year ended December 31, 2021: Awards Outstanding Restricted Stock Awards and Units Weighted-Average Grant Date Fair Value Per Share Outstanding Aggregate Intrinsic Value (in thousands) Total Fair Value of Restricted Awards Vested (in thousands) Balance at December 31, 2019 6,359 $ 92.29 $ 82 Granted 239,023 $ 4.70 Vested (2,309) $ 96.14 $ 30 $ 222 Forfeited (113,212) $ 6.73 Balance at December 31, 2020 129,861 $ 5.59 $ 458 Granted 136,626 $ 3.54 Vested (126,477) $ 5.05 $ 413 $ 659 Forfeited (2,506) $ 4.85 Balance at December 31, 2021 137,504 $ 4.06 $ 205 2014 Employee Stock Purchase Plan The 2014 Employee Stock Purchase Plan, the “ESPP”, provides for eligible Company employees, as defined by the ESPP, to be given an opportunity to purchase the Company’s common stock at a discount, through payroll deductions, with stock purchases being made upon defined purchase dates. The ESPP authorizes the issuance of up to 55,000 shares of the Company’s common stock to participating employees and allows eligible employees to purchase shares of common stock at a 15% discount from the lesser of the grant date or purchase date fair market value. For the year ended December 31, 2020, there were 14,975 shares purchased by employees under the ESPP. The ESPP has been suspended since December 2020. As of December 31, 2021, there were 18,488 shares available for issuance under the ESPP. A summary of activity within the ESPP follows: Year Ended (in thousands except share data) December 31, 2021 December 31, 2020 Deductions from employees $ — $ 56 Share-based compensation expense recognized $ — $ 96 Proceeds received by the Company for ESPP $ — $ 78 Weighted-average purchase price per common share $ — $ 5.21 Share-Based Compensation Expense Share-based compensation expense by classification for December 31, 2021 and 2020 are as follows: Year Ended (in thousands) December 31, 2021 December 31, 2020 General and administrative $ 2,275 $ 3,170 Research and development 1,164 1,861 Total $ 3,439 $ 5,031 At December 31, 2021, total compensation cost not yet recognized was $3.2 million and the weighted-average period over which this amount is expected to be recognized is 1.52 years. The aggregate fair value of options and restricted shares vesting in the years ended December 31, 2021 and 2020 was $4.3 million and $4.8 million, respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Co-Development and Co-Commercialization Agreement - Adaptimmune Therapeutics plc On December 16, 2016, the Company entered into a Co-Development and Co-Commercialization Agreement with and Adaptimmune Therapeutics plc (Adaptimmune) in order to facilitate a staged collaboration to evaluate, develop and commercialize next generation T cell therapies. Under the Agreement, the parties agreed to evaluate the Company’s GoTCR technology (inducible MyD88/CD40 co-stimulation, or iMC) with Adaptimmune’s affinity-optimized SPEAR® T cells for the potential to create enhanced TCR product candidates. Depending on results of the preclinical proof-of-concept phase, the parties expect to progress to a two-target co-development and co-commercialization phase. To the extent necessary, and in furtherance of the parties’ proof-of-concept and co-development efforts, the parties granted each other a royalty-free, non-transferable, non-exclusive license covering their respective technologies for purposes of facilitating such proof-of-concept and co-development efforts. In addition, as to covered therapies developed under the agreement, the parties granted each other a reciprocal exclusive license for the commercialization of such therapies. With respect to any joint commercialization of a covered therapy, the parties agreed to negotiate in good faith the commercially reasonable terms of a co-commercialization agreement. The parties also agreed that any such agreement shall provide for, among other things, equal sharing of the costs of any such joint commercialization and the calculation of profit shares as set forth in the Agreement. The Agreement will expire on a country-by-country basis once the parties cease commercialization of the T cell therapies covered by the Agreement, unless earlier terminated by either party for material breach, non-performance or cessation of development, bankruptcy/insolvency, or failure to progress to co-development phase. License Agreement - Baylor In 2008, 2010, 2014 and 2016, the Company and Baylor College of Medicine (“BCM”) entered into license agreements pursuant to which the Company obtained exclusive rights to certain technologies and patent rights owned by BCM. Under the 2014 license agreement, the Company is required to pay BCM a low annual maintenance fee on each anniversary of the agreement date. The Company is also required to make royalty payments in the low single digits, subject to certain annual minimums, on net sales of products covered by the license and, to the extent the Company enters into a sublicensing agreement relating to a licensed product, the Company is also required to pay BCM a percentage in the low double-digits on all non-royalty income received from sublicensing revenue. During the second quarter of 2021, the Company determined that $0.6 million of sublicense expense was incurred in 2019 through 2020 related to the Company’s obligation to pay BCM a percentage of sublicense revenue earned by the Company under the 2014 license agreement. Management evaluated the impact of the adjustment and determined that the amount was immaterial to the consolidated financial statements for the current year and prior years. As such, the entire amount of $0.6 million was recorded during the second quarter in 2021. During the third quarter of 2021, the Company earned additional sublicense revenue and, therefore, recorded additional sublicense expense of $0.5 million. License Agreement - Agensys, Inc. On December 10, 2015, the Company and Agensys, Inc. (“Agensys”), entered into a license agreement (the “Agensys Agreement”), pursuant to which (i) Agensys granted the Company, within the field of cell and gene therapy of diseases in humans, an exclusive, worldwide license and sublicense to its patent rights directed to prostate stem cell antigen 1 (“PSCA”) and related antibodies, and (ii) the Company granted Agensys a non-exclusive, fully paid license to the Company’s patents directed to inventions that were made by the Company in the course of developing the Company’s licensed products, solely for use with Agensys therapeutic products containing a soluble antibody that binds to PSCA or, to the extent not based upon the Company’s other proprietary technology, to non-therapeutic applications of antibodies not used within the field. As consideration for the rights granted to the Company under the Agreement, the Company agreed to pay to Agensys a non-refundable upfront fee of $3.0 million, which was included in license fee expense. The Company is also required to make aggregate milestone payments to Agensys of up to (i) $5 million upon the first achievement of certain specified clinical milestones for its licensed products, (ii) $50 million upon the achievement of certain specified clinical milestones for each licensed product, and (iii) $75 million upon the achievement of certain sales milestones for each licensed product. The Agreement additionally provides that the Company will pay to Agensys a royalty that ranges from the mid to high single digits based on the level of annual net sales of licensed products by the Company, its affiliates or permitted sublicensees. The royalty payments are subject to reduction under specified circumstances. These milestone and royalty payments will be expensed as incurred. Under the Agreement, Agensys also was granted the option to obtain an exclusive license, on a product-by-product basis, from the Company to commercialize in Japan each licensed product developed under the Agensys Agreement that has completed a phase 2 clinical trial. As to each such licensed product, if Agensys or its affiliate, Astellas Pharma, Inc., exercises the option, the Agensys Agreement provides that the Company will be paid an option exercise fee of $5 million. In addition, the Agensys Agreement provides that the Company will be paid a royalty that ranges from the mid to high single digits based on the level of annual net sales in Japan of each such licensed product. If the option is exercised, the aggregate milestone payments payable by the Company to Agensys, described above with respect to each licensed product, would be reduced by up to an aggregate of $65 million upon the achievement of certain specified clinical and sales milestones. The Agensys Agreement will terminate upon the expiration of the last royalty term for the products covered by the Agensys Agreement, which is the earlier of (i) the date of expiration or abandonment of the last valid claim within the licensed patent rights covering any licensed products under the Agreement, (ii) the expiration of regulatory exclusivity as to a licensed product, and (iii) 10 years after the first commercial sale of a licensed product. Either party may terminate the Agensys Agreement upon a material breach by the other party that remains uncured following 60 days after the date of written notice of such breach (or 30 days if such material breach is related to failure to make payment of amounts due under the Agensys Agreement) or upon certain insolvency events. In addition, Agensys may terminate the Agensys Agreement immediately upon written notice to the Company if the Company or any of its affiliates or permitted sublicensees commences an interference proceeding or challenges the validity or enforceability of any of Agensys’ patent rights. License Agreement - BioVec On June 10, 2015, the Company and BioVec Pharma, Inc. (“BioVec”) entered into a license agreement (the “BioVec Agreement”) pursuant to which BioVec agreed to supply the Company with certain proprietary cell lines and granted to the Company a non-exclusive, worldwide license to certain of its patent rights and related know-how related to such proprietary cell lines. As consideration for the products supplied and rights granted to the Company under the BioVec Agreement, the Company agreed to pay to BioVec an upfront fee of $100,000 within ten ten Litigation On May 29, 2019, Bellicum was served with a second amended complaint indicating that the Company had been added as an additional defendant in an ongoing civil tort lawsuit, captioned Kelly v. Children’s Hospital of Los Angeles et al., filed in the Los Angeles County Superior Court, Case No. BC681477. On July 10, 2019 plaintiffs filed a third amended complaint seeking unspecified monetary damages including punitive damages and alleging claims for wrongful death, negligence, breach of fiduciary duty, fraud, medical battery on decedent, medical battery on individual plaintiffs, products liability - failure to warn, breach of express warranty and products liability design or manufacturing defect. Bellicum filed a demurrer and motion to strike plaintiffs’ third amended

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The reconciliation between federal income taxes at the statutory U.S. federal income tax rate and the Company’s income tax expense for the year is as follows: (in thousands) December 31, 2021 December 31, 2020 Tax benefit at statutory rate $ (2,038) $ (1,658) Other 4 200 Stock based compensation 780 642 Offering issuance costs and changes in fair value of warrants and private placement option (3,176) (9,687) Deferred tax valuation allowances 4,718 11,690 Research and development credit (288) (1,187) Income tax expense $ — $ — Deferred income taxes reflect the net tax effect of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes, and the amounts used for income tax purposes. Significant components of the Company’s deferred taxes as of December 31, 2021 and 2020 are as follows: (in thousands) December 31, 2021 December 31, 2020 Deferred tax assets (liabilities): Net operating loss carryforward $ 100,346 $ 94,132 Stock compensation 3,541 3,539 Intangible assets 7,156 7,682 Research and development credit 18,076 17,787 Operating lease assets — (213) Operating lease liabilities — 354 Other (144) 976 Total deferred tax assets, net of deferred tax liabilities 128,975 124,257 Valuation allowance (128,975) (124,257) Net deferred tax $ — $ — Net operating loss carryforwards and research tax credits as of December 31, 2021 and 2020 are as follows: (in thousands) December 31, 2021 December 31, 2020 U.S. federal income tax net operating loss carryforwards $ 477,839 $ 448,250 U.K. net operating loss carryforwards $ — $ 133 U.S. federal research tax credits $ 12,985 $ 12,535 Texas research tax credits $ 5,091 $ 5,252 The Company has $228.4 million of U.S. federal net operating loss carryovers that have no expiration date and the remaining begin to expire in 2025. The U.S. Federal and state research credits will begin to expire in 2028 and 2034 respectively. No study has been performed on the research and development (R&D) credits and gross R&D credits in the amount of $17.8 million could be limited based on review by the Internal Revenue Service. The Internal Revenue Code Section 382 limits NOL and tax credit carry forwards when an ownership change of more than 50% of the value of the stock in a loss corporation occurs. Accordingly, the ability to utilize remaining NOL and tax credit carryforwards may be significantly restricted. In assessing the realization of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax asset will be realized. The ultimate realization of deferred tax assets is dependent upon the Company attaining future taxable income during periods in which those temporary differences become deductible. Due to the uncertainty surrounding the realization of the benefits of its deferred assets, including NOL carryforwards, the Company has provided a 100% valuation allowance on its net deferred tax assets at December 31, 2021 and 2020. The changes in the valuation allowance was an increase of $4.7 million and an increase of $11.7 million for the years ended December 31, 2021 and 2020, respectively.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSNone.

ORGANIZATION, BASIS OF PRESEN_2

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of PresentationThe accompanying financial statements have been prepared in conformity with the authoritative U.S. generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of Estimates The preparation of the financial statements in accordance with GAAP requires management to make certain estimates and judgments that affect the reported amounts of assets, liabilities, revenue recognition, and expenses. Actual results could differ materially from those estimates.
Revenue Recognition	Revenue Recognition The Company’s sources of revenue in 2021 were from its supply agreement with Takeda Development Center Americas, Inc. ("Takeda") and from its licensing agreements with The University of Texas MD Anderson Cancer Center (“MD Anderson”). The Company has generated revenue from its licensing agreements since 2019. Prior to 2019, the Company's only source of revenue was from grants. Supply of Product The promised product in the supply agreement with Takeda consists of rimiducid including any components, drug substance, raw materials and/or excipients to be supplied by the Company. Revenue is generally recognized upon the transfer of control of promised goods to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods. On May 4, 2021, the Company entered a multi-year supply agreement with Takeda. The Company will supply Takeda with rimiducid for potential use in clinical trials of TAK-007 (CD19 CAR-NK cell therapy). The Company generated revenue of $0.7 million in the second quarter of 2021, with the possibility of additional revenue from future sales. Licenses of Intellectual Property If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, revenue is recognized from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company uses judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over a period of time or at a point in time. If over a period of time, the Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. On January 22, 2019, the Company entered into a licensing and commercialization agreement with MD Anderson (the “2019 MD Anderson License Agreement”). Under the 2019 MD Anderson License Agreement, the Company granted MD Anderson non-exclusive rights in certain Caspase-9 and related technologies and use of a small molecule known as rimiducid in a certain cell therapy program. During the fourth quarter of 2019, and under the terms of the 2019 MD Anderson License Agreement, MD Anderson exercised an option to grant a non-exclusive sublicense of the rights licensed by the Company to MD Anderson. MD Anderson, as a result of this exercise, granted a sublicense that entitled the Company to receive as consideration an upfront license fee as well as additional future annual maintenance fees, milestone payments related to the achievement of pre-specified development, regulatory, and commercialization events, and royalties on net sales of licensed products. On August 31, 2021, the Company entered into a second licensing and commercialization agreement with MD Anderson (the “2021 MD Anderson Option and License Agreement”). Under the 2021 MD Anderson Option and License Agreement, MD Anderson has certain rights to the use of CaspaCIDe and rimiducid in product candidates nominated under the agreement, and receives options to non-exclusive licenses to the technology in these candidates. These options were evaluated and were not determined to be material rights. Upon sublicense of the product candidates nominated under the agreement, or upon exercise of an option and sublicense of a product candidate to a third party, the Company is entitled to a sublicense execution fee, a percentage of certain consideration received by MD Anderson for the sublicense, an annual maintenance fee, and a percentage royalty on net sales of licensed products. During the third quarter of 2021, the Company received an upfront payment of $5.0 million, which was recognized as revenue upon execution of the agreement, and granted licenses for two nominated programs. Milestone Payments At the inception of each arrangement that includes developmental, regulatory or commercial milestone payments, the Company evaluates whether achieving the milestones is considered probable and estimate the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the value of the associated milestone is included in the transaction price. Milestone payments that are not within the Company's control, such as approvals from regulators or where attainment of the specified event is dependent on the development activities of a third party, are not considered probable of being achieved until those approvals are received or the specified event occurs. Revenue is recognized from the satisfaction of performance obligations when such obligations have been fulfilled. Royalty Revenues For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, no royalties have been received.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all short-term, highly liquid investments with a maturity of three months or less from the date of purchase and that can be liquidated without prior notice or penalty, to be cash equivalents.
Property and Equipment	Property and Equipment Furniture, equipment and software are recorded at cost and are depreciated using the straight-line method over the estimated useful lives of the related assets, which range from 3 to 5 years. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment when events or changes in business conditions indicate that their carrying value may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset.
Warrant Derivatives	Warrant Derivatives In an underwritten public offering (the “2019 Offering”), the Company issued Series 1 Redeemable Convertible Non-Voting Preferred Stock (the “Series 1 Preferred Stock”) and warrants (the “2019 Public Warrants”) to purchase its common stock. These 2019 Public Warrants are classified as liabilities in the accompanying consolidated balance sheets, because the public warrants embody a conditional or unconditional obligation to repurchase the Company’s shares. The Company accounted for these warrants at fair value on the date of issuance and they are subject to re-measurement to fair value at each balance sheet date. Any change in fair value is recognized as a component of other income (expense) on the accompanying consolidated statements of operations and comprehensive loss. The Company estimates the fair value of these liabilities using the Black-Scholes valuation technique, which utilizes assumptions including (i) the fair value of the underlying stock at the valuation measurement date, (ii) volatility of the price of the underlying stock, (iii) the expected term, and (iv) risk-free interest rates. The Company will continue to adjust the liability for changes in fair value until the earlier of the exercise or expiration of the warrants or a change in control, as defined. The warrants are freely exercisable at any time from the issuance date until the expiration date, provided exercise does not cause a warrant holder to exceed a pre-determined beneficial ownership limit. See Note 5 - Public Offering and Private Placement for discussions of the 2019 Public Warrants.
Private Placement Option	Private Placement Option Besides the 2019 Offering, the Company completed a private placement and entered into the 2019 Securities Purchase Agreement that contained a call option on preferred shares that are puttable outside the control of the Company. Prior to the fourth quarter of 2021, the Company recorded the option as a liability and measured the option at fair value. The Company re-measured the option to fair value at each balance sheet date and recorded changes in fair value in other income (expense) in the accompanying consolidated statement of operations and comprehensive loss at each reporting period. Offering expenses arising from the issuance of the private placement option were expensed as incurred. The Company estimated the fair value of these liabilities using a binomial lattice model, which utilized assumptions including (i) the fair value of the underlying stock at the valuation measurement date, (ii) volatility of the price of the underlying stock, (iii) the expected term, and (iv) risk-free interest rates.
Preferred stock	Preferred Stock Preferred shares issued by the Company that are subject to mandatory redemption are classified as liability instruments in the accompanying consolidated balance sheets and are measured at fair value at the date of issuance. 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 within mezzanine equity in the accompanying consolidated balance sheets. At all other times, preferred shares are classified within stockholders’ deficit.
Operating Leases	Operating Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. If both criteria are met, upon lease commencement, the Company records a lease liability which represents the Company’s obligation to make lease payments arising from the lease, and a corresponding right-of-use (“ROU”) asset which represents the Company’s right to use an underlying asset during the lease term.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a fair value hierarchy has been established that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). These inputs are classified into the following hierarchy: Level 1 Inputs - quoted prices (unadjusted) in active markets for identical assets that the reporting entity has the ability to access at the measurement date; Level 2 Inputs - inputs other than quoted prices included within Level 1 that are observable for the asset, either directly or indirectly; and Level 3 Inputs - unobservable inputs for the assets. The categorization of a financial instrument within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company believes the recorded values of its financial instruments, including cash and cash equivalents, accounts payable, accrued liabilities, and debt approximate their fair values due to the short-term nature of these instruments.
Financial Instruments and Credit Risks	Financial Instruments and Credit Risks Financial instruments that potentially subject the Company to credit risk include cash and cash equivalents and accounts receivable. Cash is deposited in demand accounts in federally insured domestic institutions to minimize risk. Insurance is provided through the Federal Deposit Insurance Corporation and Security Investor Protection Corporation. Although the balances in these accounts exceed the federally insured limit from time to time, the Company has not incurred losses related to these deposits.
Equity Issuance Costs	Equity Issuance Costs Equity issuance costs represent costs paid to third parties in order to obtain equity financing. These costs have been netted against the proceeds of the equity issuances.
Licenses and Patents, Research and Development	Licenses and Patents Licenses and patent costs for technologies that are utilized in research and development and have no alternative future use are expensed as incurred. Costs related to the license of patents from third parties and internally developed patents are classified as research and development expenses. Research and Development Research and development expenses consist of expenses incurred in performing research and development activities, including compensation and benefits for research and development employees and consultants, facilities expenses, overhead expenses, cost of laboratory supplies, manufacturing expenses, fees paid to third parties and other outside expenses. Research and development costs are expensed as incurred. Clinical trial and other development costs incurred by third parties are expensed as the contracted work is performed. The Company accrues for costs incurred as the services are being provided by monitoring the status of the clinical trial or project and the invoices received from its external service providers. The Company ’ s estimates depend on the timeliness and accuracy of the data provided by the vendors regarding the status of each project and total project spending. The Company adjusts its accrual as actual costs become known.
General and administrative expenses	Legal costs related to patent applications and maintenance are classified as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss.
Collaboration Agreements	Collaboration Agreements The Company enters into collaboration agreements that include varying arrangements regarding which parties perform and bear the costs of research and development activities. The Company may share the costs of research and development activities with a collaborator, or the Company may be reimbursed for all or a significant portion of the costs of the Company ’ s research and development activities. The Company records its internal and third-party development costs associated with these collaborations as research and development expenses. When the Company is entitled to reimbursement of all or a portion of the research and development expenses that it incurs under a collaboration, the Company records those reimbursable amounts as a deduction to the research and development expenses. If the collaboration is a cost-sharing arrangement in which both the Company and its collaborator perform development work and share costs, the Company also recognizes, as research and development expenses in the period when its collaborator incurs development expenses, the portion of the collaborator's development expenses that the Company is obligated to reimburse.
Contract Manufacturing Services	Contract Manufacturing Services Contract manufacturing services are expensed as incurred. Prepaid expenses are capitalized and amortized as services are performed.
Share-Based Compensation	Share-Based Compensation The Company accounts for share-based compensation based on the measurement and recognition of compensation expense for all share-based payment awards made to employees, directors and consultants to be recognized in the financial statements, based on their fair value.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. This method also requires the recognition of future tax benefits such as net operating loss and tax credit carry forwards, to the extent that realization of such benefits is more likely than not. A valuation allowance is recorded when the realization of future tax benefits is uncertain. The Company records a valuation allowance for the full amount of deferred tax assets, which would otherwise be recorded for tax benefits relating to the operating loss and tax credit carryforwards, as realization of such deferred tax assets cannot be determined to be more likely than not. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. As of December 31, 2021, the Company had recorded a full valuation allowance on its net U.S. and foreign deferred tax assets because the Company expects that it is more likely than not that its deferred tax assets will not be realized in the foreseeable future. Should the actual amounts differ from our estimates, the amount of the valuation allowance could be materially impacted. The Company accounts for uncertain tax positions in accordance with the provisions of the Accounting Standards Codification (ASC) 740 , Income Taxes . When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2021 and 2020, the Company had no uncertain tax positions and no interest or penalties have been charged for the years ended December 31, 2021 and 2020. The Company is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The tax years 2005 through 2021 remain open to examination by the U.S. Internal Revenue Service.
Comprehensive Loss	Comprehensive LossComprehensive loss is defined as the change in equity of a business enterprise during a period, from transactions, and other events and circumstances from non-owner sources. Components of other comprehensive loss includes, among other items, unrealized gains and losses on the changes in fair value of investments and unrealized gains and losses on the change in foreign currency exchange rates. These components are added, net of their related tax effect, to the reported net loss to arrive at comprehensive loss.
Net Loss and Net Loss per Share of Common Stock Attributable to Common Stockholders	Net Loss and Net Loss per Share of Common Stock Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period without consideration for common stock equivalents. Diluted earnings per share is based on the more dilutive method between the two-class method and the treasury stock method and includes the effect from potential issuance of ordinary shares, such as shares issuable pursuant to the conversion of preferred stock to common stock, exercise of warrants to purchase common stock, exercise of stock options, and vesting of restricted stock units. For periods of net loss, diluted net loss per share is calculated similarly to basic net loss per share.
New Accounting Requirements and Disclosures	New Accounting Requirements and Disclosures Financial Instruments – Credit Losses In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which requires the measurement of all expected credit losses for financial assets including trade receivables held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. ASU No. 2016-13 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted the standard effective January 1, 2020 with no material effect on its financial statements. Subsequent to the issuance of ASU 2016-13, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments - Credit Losses. This ASU does not change the core principle of the guidance in ASU 2016-13, instead these amendments are intended to clarify and improve operability of certain topics included within the credit losses guidance. The FASB also subsequently issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments—Credit Losses, Derivatives and Hedging (Topic 815), and Financial Instruments (Topic 842), which did not change the core principle of the guidance in ASU 2016-13 but clarified that expected recoveries of amounts previously written off and expected to be written off should be included in the valuation account and should not exceed amounts previously written off and expected to be written off. The guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019 for public business entities, excluding smaller reporting companies. Early adoption is permitted. As a smaller reporting company, the guidance will be effective for the Company during the first quarter of 2023. The Company is in the process of assessing the impact adoption will have on its consolidated financial statements. Investments In January 2020, the FASB issued Accounting Standards Update No. 2020-01, Investments—Equity Securities (Topic 321), Investments—Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815)—Clarifying the Interactions between Topic 321, Topic 323, and Topic 815 (a consensus of the Emerging Issues Task Force), which clarifies the interaction of the accounting for equity securities, investments accounted for under the equity method, and certain forward contracts and purchased options. This update is effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years, and early adoption is permitted. The Company adopted the standard effective January 1, 2021 with no impact on its consolidated financial statements. Convertible Instruments In August 2020, the FASB issued ASU 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) , which reduces the number of accounting models for convertible debt instruments and convertible preferred stock. In addition, the update amends the guidance for the derivatives scope exception for contracts in an entity’s own equity to reduce form-over-substance-based accounting conclusions. Furthermore, this update improves the related EPS guidance. This update is effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years, and early adoption is permitted. The Company adopted the standard effective January 1, 2021 with no impact on its consolidated financial statements.

ORGANIZATION, BASIS OF PRESEN_3

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same such amounts shown in the statements of cash flows. (in thousands) December 31, 2021 December 31, 2020 Cash and cash equivalents $ 46,156 $ 35,495 Restricted cash 1,501 1,501 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 47,657 $ 36,996
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the balance sheets that sum to the total of the same such amounts shown in the statements of cash flows. (in thousands) December 31, 2021 December 31, 2020 Cash and cash equivalents $ 46,156 $ 35,495 Restricted cash 1,501 1,501 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 47,657 $ 36,996
Property and Equipment	Property and equipment consisted of the following: (in thousands, except useful lives) Estimated Useful Lives December 31, 2021 December 31, 2020 Leasehold improvements 5 Years $ — $ 167 Lab equipment 5 Years 530 530 Manufacturing equipment 5 Years 138 138 Computer and office equipment 3 to 5 Years 841 834 Software 3 Years 94 94 Total 1,603 1,763 Less: accumulated depreciation (1,591) (1,574) Property and equipment, net $ 12 $ 189
Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consist of the following: December 31, 2021 December 31, 2020 Accrued payroll $ 320 $ 1,071 Accrued patient treatment costs 2,086 899 Accrued clinical research costs 479 1,562 Accrued manufacturing costs 328 41 Accrued professional services 305 279 Accrued other 331 313 Total accrued expenses and other current liabilities $ 3,849 $ 4,165
Earnings Per Share, Potentially Dilutive Securities	The following outstanding shares of common stock equivalents were excluded from the computations of diluted earnings per share (if in a net income position) of common stock attributable to common stockholders for the periods presented as the effect of including such securities would be anti-dilutive. December 31, 2021 December 31, 2020 Anti-dilutive common stock equivalents: Number of Shares Redeemable convertible series 1 preferred stock 4,520,000 4,520,000 Warrants to purchase common stock 5,750,000 11,616,080 Private placement option — 9,675,000 Options to purchase common stock 2,140,618 1,510,968 Unvested shares of restricted stock units 137,504 129,861 Total anti-dilutive common stock equivalents 12,548,122 27,451,909

FAIR VALUE OF MEASUREMENTS AN_2

FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on a Recurring Basis	The following tables present the Company’s investment securities (including those classified on the Company’s balance sheet as cash equivalents) that are measured at fair value on a recurring basis as of December 31, 2021 and 2020: Fair Value at December 31, 2021 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Cash Equivalents: Money market funds and treasury bills $ 42,487 $ — $ — $ 27,463 $ — $ — Total Cash Equivalents $ 42,487 $ — $ — $ 27,463 $ — $ — The following table provides the warrant derivative and private placement option liabilities reported at fair value and measured on a recurring basis: Fair Value at December 31, 2021 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Warrant derivative liability $ — $ — $ 2,773 $ — $ — $ 10,345 Private placement option liability — — — — — 7,803 Total fair value $ — $ — $ 2,773 $ — $ — $ 18,148
Schedule of Derivative Liabilities at Fair Value	The fair value of the warrants has been estimated with the following weighted-average assumptions, including the most sensitive input, volatility: December 31, 2021 December 31, 2020 Risk-free interest rate 1.22 % 0.46 % Volatility 94 % 90 % Expected life (years) 4.64 5.64 (in thousands) Warrant Derivative Liability Balance, December 31, 2020 $ 10,345 Change in fair value (7,572) Balance, December 31, 2021 $ 2,773

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Components of Lease Cost	Components of lease cost are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Finance lease cost: Amortization of leased assets $ 16 $ 74 Interest on lease liabilities 5 21 Operating lease cost 56 814 Short-term lease cost 53 582 Total lease cost $ 130 $ 1,491 Weighted-average remaining lease term: Operating leases 0.0 years 1.7 years Finance leases 0.0 years 1.4 years Weighted-average discount rate: Operating leases — % 11.47 % Finance leases — % 13.05 % Supplemental cash flow information and non-cash activity related to the Company’s operating and finance leases are as follows: (in thousands) Year Ended December 31, 2021 Year Ended December 31, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 71 $ 950 Operating cash flows from finance leases 5 21 Financing cash flows from finance leases 35 74

PUBLIC OFFERING AND PRIVATE P_2

PUBLIC OFFERING AND PRIVATE PLACEMENT (Tables)	12 Months Ended
	Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]
Schedule of Derivative Liabilities at Fair Value	The fair value of the warrants has been estimated with the following weighted-average assumptions, including the most sensitive input, volatility: December 31, 2021 December 31, 2020 Risk-free interest rate 1.22 % 0.46 % Volatility 94 % 90 % Expected life (years) 4.64 5.64 (in thousands) Warrant Derivative Liability Balance, December 31, 2020 $ 10,345 Change in fair value (7,572) Balance, December 31, 2021 $ 2,773
Summary of Warrants Outstanding and Exercisable	A summary of warrants outstanding and exercisable as of December 31, 2021 is as follows: Warrants Outstanding Warrants Exercisable Year Issued Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price (in years) (per share) (per share) 2019 5,750,000 4.64 $ 13.00 5,750,000 $ 13.00 2020 4,149,378 3.84 $ 6.50 4,149,378 $ 6.50 2020 1 1,716,702 — $ — 1,716,702 $ — 2021 2,055,920 6.94 $ 1.69 2,055,920 $ 1.69 2021 2 20,559,210 — $ — 20,559,210 $ — 34,231,210 34,231,210

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Outstanding Awards	At December 31, 2021 and 2020, outstanding awards were comprised of the following: December 31, 2021 December 31, 2020 Options 2,074,858 1,425,207 Inducement option awards 65,760 85,761 Restricted stock units 137,004 129,361 Inducement restricted stock units 500 500 Total outstanding awards 2,278,122 1,640,829
Weighted-Average Valuation Assumptions	The fair value of the option grants has been estimated, with the following weighted-average assumptions: Year Ended December 31, 2021 December 31, 2020 Options granted 1,023,000 1,352,595 Weighted-average exercise price 2.80 7.59 Weighted-average grant date fair value 2.02 5.29 Assumptions: Risk-free interest rate 0.92 % 0.82 % Volatility 90 % 85 % Expected life (years) 5.63 5.83 Expected dividend yield — —
Schedule of Stock Option Activity	The following table summarizes the stock option activity for all stock plans during the year ended December 31, 2021 and 2020 as follows: Options Outstanding Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Balance at December 31, 2019 567,842 $ 76.25 7.82 $ 12 Granted 1,352,595 $ 7.59 Exercised — Forfeited (409,469) $ 29.86 Balance at December 31, 2020 1,510,968 $ 27.36 8.19 $ 379 Granted 1,023,000 $ 2.80 Exercised — Forfeited (393,350) $ 30.66 Balance at December 31, 2021 2,140,618 $ 15.01 8.48 $ — Exercisable at December 31, 2021 718,123 $ 36.42 6.98 $ —
Summary of Options Outstanding and Exercisable	The following table summarizes the options outstanding and exercisable at December 31, 2021: Options Outstanding Options Exercisable Exercise Price Total Shares Weighted Average Remaining Contractual Term (in years) Weighted Average Exercise Price Total Shares Weighted Average Remaining Contractual Term (in years) Weighted Average Exercise Price $1.73 to $2.87 215,000 9.89 $ 1.81 — 0.00 $ — $2.88 to $2.93 665,000 9.62 $ 2.88 — 0.00 $ — $2.94 to $3.01 506,000 8.95 $ 2.97 253,000 8.95 $ 2.97 $3.02 to $16.15 475,076 7.32 $ 9.97 207,374 6.15 $ 11.97 $16.16 to $234.70 279,542 5.82 $ 84.39 257,749 5.71 $ 88.94 Total 2,140,618 8.48 $ 15.01 718,123 6.98 $ 36.42
Schedule of Restricted Stock Unit Activity	The following table summarizes the stock award activity for all restricted stock units during the year ended December 31, 2021: Awards Outstanding Restricted Stock Awards and Units Weighted-Average Grant Date Fair Value Per Share Outstanding Aggregate Intrinsic Value (in thousands) Total Fair Value of Restricted Awards Vested (in thousands) Balance at December 31, 2019 6,359 $ 92.29 $ 82 Granted 239,023 $ 4.70 Vested (2,309) $ 96.14 $ 30 $ 222 Forfeited (113,212) $ 6.73 Balance at December 31, 2020 129,861 $ 5.59 $ 458 Granted 136,626 $ 3.54 Vested (126,477) $ 5.05 $ 413 $ 659 Forfeited (2,506) $ 4.85 Balance at December 31, 2021 137,504 $ 4.06 $ 205
Summary of ESPP Activity	A summary of activity within the ESPP follows: Year Ended (in thousands except share data) December 31, 2021 December 31, 2020 Deductions from employees $ — $ 56 Share-based compensation expense recognized $ — $ 96 Proceeds received by the Company for ESPP $ — $ 78 Weighted-average purchase price per common share $ — $ 5.21
Schedule Share-based Compensation	Share-based compensation expense by classification for December 31, 2021 and 2020 are as follows: Year Ended (in thousands) December 31, 2021 December 31, 2020 General and administrative $ 2,275 $ 3,170 Research and development 1,164 1,861 Total $ 3,439 $ 5,031

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Reconciliation of Income Tax Expense	The reconciliation between federal income taxes at the statutory U.S. federal income tax rate and the Company’s income tax expense for the year is as follows: (in thousands) December 31, 2021 December 31, 2020 Tax benefit at statutory rate $ (2,038) $ (1,658) Other 4 200 Stock based compensation 780 642 Offering issuance costs and changes in fair value of warrants and private placement option (3,176) (9,687) Deferred tax valuation allowances 4,718 11,690 Research and development credit (288) (1,187) Income tax expense $ — $ —
Significant Components of Deferred Taxes	Significant components of the Company’s deferred taxes as of December 31, 2021 and 2020 are as follows: (in thousands) December 31, 2021 December 31, 2020 Deferred tax assets (liabilities): Net operating loss carryforward $ 100,346 $ 94,132 Stock compensation 3,541 3,539 Intangible assets 7,156 7,682 Research and development credit 18,076 17,787 Operating lease assets — (213) Operating lease liabilities — 354 Other (144) 976 Total deferred tax assets, net of deferred tax liabilities 128,975 124,257 Valuation allowance (128,975) (124,257) Net deferred tax $ — $ —
Summary of Net Operating Loss Carryforwards	Net operating loss carryforwards and research tax credits as of December 31, 2021 and 2020 are as follows: (in thousands) December 31, 2021 December 31, 2020 U.S. federal income tax net operating loss carryforwards $ 477,839 $ 448,250 U.K. net operating loss carryforwards $ — $ 133 U.S. federal research tax credits $ 12,985 $ 12,535 Texas research tax credits $ 5,091 $ 5,252

ORGANIZATION, BASIS OF PRESEN_4

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	Mar. 15, 2021USD ($)	Apr. 14, 2020USD ($)	Feb. 05, 2020shares	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)shares	Dec. 31, 2021USD ($)segmentsubsidiaryshares	Dec. 31, 2020USD ($)shares	Mar. 26, 2021USD ($)	Feb. 26, 2021USD ($)	Oct. 31, 2020USD ($)	Jun. 15, 2020shares	Jun. 14, 2020shares	Feb. 04, 2020shares
Class of Stock [Line Items]
Number of wholly-owned subsidiaries formed | subsidiary									2
Number of operating segments | segment									1
Number of reportable segments | segment									1
Reverse stock split ratio			0.1
Common stock, authorized (in shares) | shares			40,000,000					80,000,000	80,000,000	80,000,000				80,000,000	40,000,000	200,000,000
Accumulated deficit								$ (540,747)	$ (550,452)	$ (540,747)
Operating lease right-of-use assets								645	0	645
Property and equipment, net								189	12	189
Depreciation expense									100	1,500
Accrued clinical research costs								1,562	$ 479	1,562
Scenario, Adjustment
Class of Stock [Line Items]
Accrued clinical research costs								1,500		1,500
Accrued manufacturing costs and accrued professional fees, current								100		100
Minimum
Class of Stock [Line Items]
Estimated useful lives									3 years
Maximum
Class of Stock [Line Items]
Estimated useful lives									5 years
Lab equipment
Class of Stock [Line Items]
Estimated useful lives									5 years
2130 W. Holcombe Blvd. Assets
Class of Stock [Line Items]
Cash proceeds subject to escrow provisions		$ 1,500
R&D Facility | Disposal Group, Held-for-sale, Not Discontinued Operations
Class of Stock [Line Items]
Operating lease right-of-use assets								500		500			$ 500
Property and equipment, net								2,300		2,300			2,300
Lease liability								700		700			$ 700
Accretion of lease liability								$ 1,300		$ 1,300
Reed Road, Houston, TX
Class of Stock [Line Items]
Amount paid upon closing of asset sale												$ 1,100
Lease exit agreement, cash receivable												900
Lease exit agreement, note receivable												$ 200
San Francisco Office Space
Class of Stock [Line Items]
Operating lease right-of-use assets											$ 600
Lease liability											1,000
Lease termination fee	$ 900
Security deposits refund	$ 200			$ 200
Loss on termination of lease							$ 500		$ 500
San Francisco Office Space | Lab equipment
Class of Stock [Line Items]
Operating lease right-of-use assets											$ 100
MD Anderson
Class of Stock [Line Items]
Upfront payment received					$ 5,000
Takeda
Class of Stock [Line Items]
Additional revenue from sales						$ 700

ORGANIZATION, BASIS OF PRESEN_5

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash Reconciliation (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 46,156	$ 35,495
Restricted cash	1,501	1,501
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 47,657	$ 36,996	$ 93,816

ORGANIZATION, BASIS OF PRESEN_6

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,603	$ 1,763
Less: accumulated depreciation	(1,591)	(1,574)
Property and equipment, net	$ 12	189
Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Property and equipment, gross	$ 0	167
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Property and equipment, gross	$ 530	530
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Property and equipment, gross	$ 138	138
Computer and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 841	834
Software
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Property and equipment, gross	$ 94	$ 94
Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Minimum | Computer and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum | Computer and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years

ORGANIZATION, BASIS OF PRESEN_7

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued payroll	$ 320	$ 1,071
Accrued patient treatment costs	2,086	899
Accrued clinical research costs	479	1,562
Accrued manufacturing costs	328	41
Accrued professional services	305	279
Accrued other	331	313
Total accrued expenses and other current liabilities	$ 3,849	$ 4,165

ORGANIZATION, BASIS OF PRESEN_8

ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share, Potentially Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	12,548,122	27,451,909
Redeemable convertible series 1 preferred stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	4,520,000	4,520,000
Warrants to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	5,750,000	11,616,080
Private placement option
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	0	9,675,000
Options to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	2,140,618	1,510,968
Unvested shares of restricted stock units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total anti-dilutive common stock equivalents (in shares)	137,504	129,861

FAIR VALUE OF MEASUREMENTS AN_3

FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES - Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash, noncurrent	$ 1,500
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	42,487	$ 27,463
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Money market funds and treasury bills | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	42,487	27,463
Money market funds and treasury bills | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Money market funds and treasury bills | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	$ 0	$ 0

FAIR VALUE OF MEASUREMENTS AN_4

FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES - Fair Value of Warrants (Details) - Warrant Derivative Liability - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Gain on change in the fair value	$ 2.8
Risk-free interest rate	1.22%	0.46%
Volatility	94.00%	90.00%
Expected life (years)	4 years 7 months 20 days	5 years 7 months 20 days

FAIR VALUE OF MEASUREMENTS AN_5

FAIR VALUE OF MEASUREMENTS AND INVESTMENT SECURITIES - Derivative Liabilities Reported at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	$ 2,773	$ 10,345
Private placement option liability	0	7,803
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	0	0
Private placement option liability	0	0
Total fair value	0	0
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	0	0
Private placement option liability	0	0
Total fair value	0	0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	2,773	10,345
Private placement option liability	0	7,803
Total fair value	$ 2,773	$ 18,148

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Thousands	Mar. 15, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Mar. 26, 2021	Feb. 26, 2021	Oct. 31, 2020	Jul. 31, 2020
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				$ 645	$ 0	$ 645
Property and equipment, net				189	12	189
Reed Road, Houston, TX
Lessee, Lease, Description [Line Items]
Amount paid upon closing of asset sale								$ 1,100
Lease exit agreement, cash receivable								900
Lease exit agreement, note receivable								$ 200
San Francisco Office Space
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets							$ 600
Lease liability							1,000
Lease termination fee	$ 900
Security deposits refund	$ 200	$ 200
Loss on termination of lease			$ 500		$ 500
Disposal Group, Held-for-sale, Not Discontinued Operations | R&D Facility
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				500		500			$ 500
Lease liability				700		700			700
Property and equipment, net				2,300		2,300			$ 2,300
Accretion of lease liability				$ 1,300		$ 1,300
Lab equipment | San Francisco Office Space
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets							$ 100
Houston, Texas | Office space
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets										$ 500
Lease liability										$ 600

LEASES - Components of Lease Co

LEASES - Components of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Finance lease cost:
Amortization of leased assets	$ 16	$ 74
Interest on lease liabilities	5	21
Operating lease cost	56	814
Short-term lease cost	53	582
Total lease cost	$ 130	$ 1,491
Weighted-average remaining lease term, operating leases	0 years	1 year 8 months 12 days
Weighted-average remaining lease term, finance leases	0 years	1 year 4 months 24 days
Weighted-average discount rate, operating leases	0.00%	11.47%
Weighted-average discount rate, finance leases	0.00%	13.05%

LEASES - Supplemental Cash Flow

LEASES - Supplemental Cash Flow Information Related to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 71	$ 950
Operating cash flows from finance leases	5	21
Financing cash flows from finance leases	$ 35	$ 74

DEBT - Narrative (Details)

DEBT - Narrative (Details) - USD ($)	Dec. 21, 2017	Nov. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Payment on debt			$ 0	$ 37,155,000
Amortization of deferred issuance costs			0	550,000
Gain on extinguishment of debt			$ 0	112,000
Oxford Loan
Debt Instrument [Line Items]
Face amount borrowed	$ 35,000,000
Payment on debt		$ 27,400,000
Payment of debt issuance costs	100,000
Final facility charge payment	3,000,000
Amortization of deferred issuance costs				$ 600,000
Hercules Loan
Debt Instrument [Line Items]
Payment on debt	$ 32,900,000

PUBLIC OFFERING AND PRIVATE P_3

PUBLIC OFFERING AND PRIVATE PLACEMENT - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 04, 2021	Nov. 02, 2020	Aug. 21, 2019	Aug. 16, 2019	Aug. 31, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock, par value (in dollars per share)							$ 0.01	$ 0.01
Warrant exercise price (in dollars per share)							$ 36.42
Common stock, issued (in shares)							8,497,025	8,385,650
Proceeds from issuance of redeemable convertible preferred stock in a public offering, net			$ 53.8
Proceeds upon entering into private placement agreement						$ 11.2
Series 1 Preferred
Class of Stock [Line Items]
Shares issuable per warrants (in shares)					10		10
Price per share (in dollars per share)							$ 100
December 2021 Private Placement
Class of Stock [Line Items]
Shares issuable per warrants (in shares)	20,559,210
Warrants to purchase aggregate shares of common stock (in shares)	2,055,920
Shares purchased by selling pre-funded warrant (in shares)	0.1
Price per share (in dollars per share)	$ 1.7024
Common stock, par value (in dollars per share)	0.0001
Warrant exercise price (in dollars per share)	$ 1.69
Expiration period	7 years
Proceeds from issuance of common stock	$ 35
December 2021 Private Placement | Pre-Funded Warrant
Class of Stock [Line Items]
Shares purchased by selling pre-funded warrant (in shares)	1
Public Offering
Class of Stock [Line Items]
Price per share (in dollars per share)				$ 100
Shares issuable under warrants (in shares)				5,750,000
Public Offering | Series 1 Preferred
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)				575,000
Weighted Average Exercise Price				$ 130
Public Offering | Common Stock
Class of Stock [Line Items]
Shares issuable per warrants (in shares)				10
Weighted Average Exercise Price				$ 13
Notice period for percentage change				61 days
Public Offering | Common Stock | Minimum
Class of Stock [Line Items]
Warrants, limitations on ownership after exercise				9.99%
Public Offering | Common Stock | Maximum
Class of Stock [Line Items]
Warrants, limitations on ownership after exercise				19.99%
Private placement option | Series 2 redeemable convertible non-voting preferred stock
Class of Stock [Line Items]
Price per share (in dollars per share)				$ 100	$ 100
Number of shares of common stock sold in offering (in shares)				350,000	350,000
Shares issuable under warrants (in shares)				2,800,000
Weighted Average Exercise Price				$ 10
Private placement option | Series 3 redeemable convertible non-voting preferred stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)				250,000	250,000
Private placement option | Preferred Stock
Class of Stock [Line Items]
Price per share (in dollars per share)				$ 140
Shares issuable under warrants (in shares)				875,000
Weighted Average Exercise Price				$ 14
November 2020 Underwritten Offering
Class of Stock [Line Items]
Shares issuable per warrants (in shares)		3,109,378
Warrants to purchase aggregate shares of common stock (in shares)		4,149,378
Shares purchased by selling pre-funded warrant (in shares)		1
Common stock, par value (in dollars per share)		$ 0.001
Warrant exercise price (in dollars per share)		$ 6.50
Expiration period		5 years
Proceeds from issuance of common stock		$ 25
Common stock, issued (in shares)		1,040,000
November 2020 Underwritten Offering | Minimum
Class of Stock [Line Items]
Price of each share of common stock and accompanying common warrant (in dollars per share)		$ 6.024
November 2020 Underwritten Offering | Maximum
Class of Stock [Line Items]
Price of each share of common stock and accompanying common warrant (in dollars per share)		$ 6.025

PUBLIC OFFERING AND PRIVATE P_4

PUBLIC OFFERING AND PRIVATE PLACEMENT - Fair Value of Derivative Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Warrant Derivative Liabilities, Unobservable Input Reconciliation [Roll Forward]
Change in fair value	$ (15,126)	$ (46,130)
Warrant Derivative Liability | Level 3
Fair Value, Warrant Derivative Liabilities, Unobservable Input Reconciliation [Roll Forward]
Fair value of warrants beginning valance	10,345
Change in fair value	(7,572)
Fair value of warrants ending balance	$ 2,773	$ 10,345

PUBLIC OFFERING AND PRIVATE P_5

PUBLIC OFFERING AND PRIVATE PLACEMENT - Summary of Warrants Outstanding and Exercisable (Details)	Dec. 31, 2021$ / sharesshares
Warrants Outstanding
Number Outstanding	34,231,210
Warrants Exercisable
Number Exercisable	34,231,210
2019
Warrants Outstanding
Number Outstanding	5,750,000
Weighted Average Remaining Contractual Life	4 years 7 months 20 days
Weighted Average Exercise Price | $ / shares	$ 13
Warrants Exercisable
Number Exercisable	5,750,000
Weighted Average Exercise Price | $ / shares	$ 13
2020
Warrants Outstanding
Number Outstanding	4,149,378
Weighted Average Remaining Contractual Life	3 years 10 months 2 days
Weighted Average Exercise Price | $ / shares	$ 6.50
Warrants Exercisable
Number Exercisable	4,149,378
Weighted Average Exercise Price | $ / shares	$ 6.50
Issued On November 2, 2020
Warrants Outstanding
Number Outstanding	1,716,702
Weighted Average Remaining Contractual Life	0 years
Weighted Average Exercise Price | $ / shares	$ 0
Warrants Exercisable
Number Exercisable	1,716,702
Weighted Average Exercise Price | $ / shares	$ 0
2021
Warrants Outstanding
Number Outstanding	2,055,920
Weighted Average Remaining Contractual Life	6 years 11 months 8 days
Weighted Average Exercise Price | $ / shares	$ 1.69
Warrants Exercisable
Number Exercisable	2,055,920
Weighted Average Exercise Price | $ / shares	$ 1.69
Issued On December 7, 2021
Warrants Outstanding
Number Outstanding	20,559,210
Weighted Average Remaining Contractual Life	0 years
Weighted Average Exercise Price | $ / shares	$ 0
Warrants Exercisable
Number Exercisable	20,559,210
Weighted Average Exercise Price | $ / shares	$ 0

REDEEMABLE CONVERTIBLE PREFER_2

REDEEMABLE CONVERTIBLE PREFERRED STOCK - Narrative (Details) - $ / shares	Aug. 16, 2019	Aug. 31, 2019	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Preferred stock, authorized (in shares)		10,000,000
Preferred stock, par value (in dollars per share)		$ 0.01
Closing price of common stock threshold period			180 days
Average trading volume period			50 days
50-day trading volume on Nasdaq stock market (in shares)			50,000
Series 1 Preferred
Class of Stock [Line Items]
Preferred stock, authorized (in shares)		1,517,500
Preferred stock, outstanding (in shares)			452,000	452,000
Preferred stock, issued (in shares)			452,000	452,000
Price per share (in dollars per share)			$ 100
Shares issuable per warrants (in shares)		10	10
Conversion of redeemable convertible preferred stock into common stock (in shares)			0	86,000
Closing price of common stock (in dollars per share)			$ 25
Closing price of common stock threshold period			180 days
Series 2 redeemable convertible non-voting preferred stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)				0
Preferred stock, issued (in shares)				0
Series 2 redeemable convertible non-voting preferred stock | Private placement option
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	350,000	350,000
Price per share (in dollars per share)	$ 100	$ 100
Series 3 redeemable convertible non-voting preferred stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)				0
Preferred stock, issued (in shares)				0
Series 3 redeemable convertible non-voting preferred stock | Private placement option
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	250,000	250,000

SHARE-BASED COMPENSATION PLAN_2

SHARE-BASED COMPENSATION PLANS - Narrative (Details)	1 Months Ended			12 Months Ended
	Jun. 30, 2021shares	Jun. 30, 2020shares	Jan. 31, 2020shares	Dec. 31, 2021USD ($)planshares	Dec. 31, 2020USD ($)shares
Share-based Goods and Nonemployee Services Transaction [Line Items]
Number of share-based compensation plans | plan				5
Proceeds from exercise of stock options | $				$ 0	$ 12,000
Proceeds from exercise of stock options, less than amount | $					100,000
Compensation cost not yet recognized | $				$ 3,200,000
Period of recognition (in years)				1 year 6 months 7 days
Aggregate fair value of options and restricted shares vesting | $				$ 4,300,000	$ 4,800,000
2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Number of shares authorized (in shares)				250,000
Additional authorized shares approved (in shares)	500,000	500,000	600,000
Options
Share-based Goods and Nonemployee Services Transaction [Line Items]
Expiration period				10 years
Employee Stock | 2014 Employee Stock Purchase Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Number of shares authorized (in shares)				55,000
ESPP common stock discount				15.00%
Number of shares purchased by employees under ESPP (in shares)					14,975
Shares available for issuance under ESPP (in shares)				18,488
Minimum | Options
Share-based Goods and Nonemployee Services Transaction [Line Items]
Vesting period				2 years
Maximum | 2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Number of shares authorized (in shares)				600,540
Maximum | Options
Share-based Goods and Nonemployee Services Transaction [Line Items]
Vesting period				4 years

SHARE-BASED COMPENSATION PLAN_3

SHARE-BASED COMPENSATION PLANS - Outstanding Awards (Details) - shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Goods and Nonemployee Services Transaction [Line Items]
Options outstanding (in shares)	2,140,618	1,510,968	567,842
2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Total awards outstanding (in shares)	2,278,122	1,640,829
Options | 2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Options outstanding (in shares)	2,074,858	1,425,207
Inducement option awards | 2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Options outstanding (in shares)	65,760	85,761
Restricted stock units | 2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Awards other than options outstanding (in shares)	137,004	129,361
Inducement restricted stock units | 2019 Equity Incentive Plan
Share-based Goods and Nonemployee Services Transaction [Line Items]
Awards other than options outstanding (in shares)	500	500

SHARE-BASED COMPENSATION PLAN_4

SHARE-BASED COMPENSATION PLANS - Weighted-Average Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	1,023,000	1,352,595
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)	1,023,000	1,352,595
Weighted-average exercise price (in dollars per share)	$ 2.80	$ 7.59
Weighted-average grant date fair value (in dollars per share)	$ 2.02	$ 5.29
Risk-free interest rate	0.92%	0.82%
Volatility	90.00%	85.00%
Expected life (years)	5 years 7 months 17 days	5 years 9 months 29 days
Expected dividend yield	0.00%	0.00%

SHARE-BASED COMPENSATION PLAN_5

SHARE-BASED COMPENSATION PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Outstanding Stock Options
Beginning balance (in shares)	1,510,968	567,842
Granted (in shares)	1,023,000	1,352,595
Exercised (in shares)	0	0
Forfeited (in shares)	(393,350)	(409,469)
Ending balance (in shares)	2,140,618	1,510,968	567,842
Exercisable at end of period (in shares)	718,123
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 27.36	$ 76.25
Granted (in dollars per share)	2.80	7.59
Exercised (in dollars per share)
Forfeited (in dollars per share)	30.66	29.86
Ending balance (in dollars per share)	15.01	$ 27.36	$ 76.25
Exercisable at end of period (in dollars per share)	$ 36.42
Outstanding Stock Options, Other Disclosures
Weighted-average remaining contractual term, outstanding (in years)	8 years 5 months 23 days	8 years 2 months 8 days	7 years 9 months 25 days
Weighted-average remaining contractual term, exercisable (in years)	6 years 11 months 23 days
Aggregate intrinsic value, outstanding	$ 0	$ 379	$ 12
Aggregate intrinsic value, exercisable	$ 0

SHARE-BASED COMPENSATION PLAN_6

SHARE-BASED COMPENSATION PLANS - Stock Options Outstanding and Exercisable (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option outstanding (in shares)	2,140,618
Weighted-average remaining contractual term, option outstanding (in years)	8 years 5 months 23 days	8 years 2 months 8 days	7 years 9 months 25 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 15.01
Option exercisable (in shares)	718,123
Weighted-average remaining contractual term, option exercisable (in years)	6 years 11 months 23 days
Weighted-average exercise price (in dollars per share)	$ 36.42
$1.73 to $2.87
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price - minimum (in dollars per share)	1.73
Exercise Price - maximum (in dollars per share)	$ 2.87
Option outstanding (in shares)	215,000
Weighted-average remaining contractual term, option outstanding (in years)	9 years 10 months 20 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 1.81
Option exercisable (in shares)	0
Weighted-average remaining contractual term, option exercisable (in years)	0 years
Weighted-average exercise price (in dollars per share)	$ 0
$2.88 to $2.93
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price - minimum (in dollars per share)	2.88
Exercise Price - maximum (in dollars per share)	$ 2.93
Option outstanding (in shares)	665,000
Weighted-average remaining contractual term, option outstanding (in years)	9 years 7 months 13 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 2.88
Option exercisable (in shares)	0
Weighted-average remaining contractual term, option exercisable (in years)	0 years
Weighted-average exercise price (in dollars per share)	$ 0
$2.94 to $3.01
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price - minimum (in dollars per share)	2.94
Exercise Price - maximum (in dollars per share)	$ 3.01
Option outstanding (in shares)	506,000
Weighted-average remaining contractual term, option outstanding (in years)	8 years 11 months 12 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 2.97
Option exercisable (in shares)	253,000
Weighted-average remaining contractual term, option exercisable (in years)	8 years 11 months 12 days
Weighted-average exercise price (in dollars per share)	$ 2.97
$3.02 to $16.15
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price - minimum (in dollars per share)	3.02
Exercise Price - maximum (in dollars per share)	$ 16.15
Option outstanding (in shares)	475,076
Weighted-average remaining contractual term, option outstanding (in years)	7 years 3 months 25 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 9.97
Option exercisable (in shares)	207,374
Weighted-average remaining contractual term, option exercisable (in years)	6 years 1 month 24 days
Weighted-average exercise price (in dollars per share)	$ 11.97
$16.16 to $234.70
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise Price - minimum (in dollars per share)	16.16
Exercise Price - maximum (in dollars per share)	$ 234.70
Option outstanding (in shares)	279,542
Weighted-average remaining contractual term, option outstanding (in years)	5 years 9 months 25 days
Weighted-average exercise price, option outstanding (in dollars per share)	$ 84.39
Option exercisable (in shares)	257,749
Weighted-average remaining contractual term, option exercisable (in years)	5 years 8 months 15 days
Weighted-average exercise price (in dollars per share)	$ 88.94

SHARE-BASED COMPENSATION PLAN_7

SHARE-BASED COMPENSATION PLANS - Restricted Stock Award Activity (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Outstanding Restricted Stock Awards and Units
Beginning balance (in shares)	129,861	6,359
Granted (in shares)	136,626	239,023
Vested (in shares)	(126,477)	(2,309)
Forfeited (in shares)	(2,506)	(113,212)
Ending balance (in shares)	137,504	129,861
Weighted-Average Grant Date Fair Value Per Share
Beginning balance (in dollars per share)	$ 5.59	$ 92.29
Granted (in dollars per share)	3.54	4.70
Vested (in dollars per share)	5.05	96.14
Forfeited (in dollars per share)	4.85	6.73
Ending balance (in dollars per share)	$ 4.06	$ 5.59
Outstanding Aggregate Intrinsic Value
Beginning balance	$ 205	$ 458	$ 82
Vested	413	30
Ending balance	205	458
Total Fair Value of Restricted Awards Vested (in thousands)	$ 659	$ 222

SHARE-BASED COMPENSATION PLAN_8

SHARE-BASED COMPENSATION PLANS - ESPP Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 3,439	$ 5,031
Employee Stock | 2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deductions from employees	0	56
Share-based compensation expense recognized	0	96
Proceeds received by the Company for ESPP	$ 0	$ 78
Weighted-average purchase price per common share (in dollars per share)	$ 0	$ 5.21

SHARE-BASED COMPENSATION PLAN_9

SHARE-BASED COMPENSATION PLANS - Expense by Classification (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	$ 3,439	$ 5,031
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	2,275	3,170
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense recognized	$ 1,164	$ 1,861

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - Licensing Agreements	Dec. 10, 2015USD ($)	Jun. 10, 2015USD ($)product	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Dec. 31, 2019USD ($)
Baylor
Long-term Purchase Commitment [Line Items]
Sublicense expense			$ 500,000	$ 600,000	$ 600,000
Agensys
Long-term Purchase Commitment [Line Items]
Nonrefundable upfront fee	$ 3,000,000
Milestone payments upon first achievement of specified clinical milestones	5,000,000
Milestone payments upon achievement of specified clinical milestones for each licensed product	50,000,000
Milestone payments upon achievement of sales milestones	75,000,000
Option exercise fee	5,000,000
Milestone payments reduced upon exercise of option	$ 65,000,000
Termination period, number of years after first commercial sale of licensed product	10 years
Termination period, notice of failure on uncured items	60 days
Period of notice of failure on uncured items, if material breach is related to failure to make payments	30 days
BioVec
Long-term Purchase Commitment [Line Items]
Nonrefundable upfront fee		$ 100,000
Milestone payments upon first achievement of specified clinical milestones		$ 250,000
Termination period, notice of failure on uncured items		60 days
Upfront fee payment period, number of days from effective date		10 days
License costs due upon first release of product		$ 300,000
License costs due upon first release of product, period of payment		10 days
License agreement, annual fee		$ 150,000
License agreement, annual fee period, from first IND filing		30 days
Milestone payments, number of initial products | product		3
License agreement, milestone payments upon receipt of FDA or EMA registration		$ 2,000,000
Termination notice period for any other breach		90 days
Termination period, after insolvency event		30 days

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Tax benefit at statutory rate	$ (2,038)	$ (1,658)
Other	4	200
Stock based compensation	780	642
Offering issuance costs and changes in fair value of warrants and private placement option	(3,176)	(9,687)
Deferred tax valuation allowances	4,718	11,690
Research and development credit	(288)	(1,187)
Income tax expense	$ 0	$ 0

INCOME TAXES - Significant Comp

INCOME TAXES - Significant Components of Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets (liabilities):
Net operating loss carryforward	$ 100,346	$ 94,132
Stock compensation	3,541	3,539
Intangible assets	7,156	7,682
Research and development credit	18,076	17,787
Operating lease assets	0	(213)
Operating lease liabilities	0	354
Other	(144)
Other		976
Total deferred tax assets, net of deferred tax liabilities	128,975	124,257
Valuation allowance	(128,975)	(124,257)
Net deferred tax	$ 0	$ 0

INCOME TAXES - Operating Loss C

INCOME TAXES - Operating Loss Carryforwards and Research Tax Credits (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Research tax credits	$ 18,076	$ 17,787
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	477,839	448,250
Research tax credits	12,985	12,535
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	0	133
Texas
Operating Loss Carryforwards [Line Items]
Research tax credits	$ 5,091	$ 5,252

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforwards, no expiration date	$ 228,400
Research tax credits	$ 18,076	$ 17,787
Deferred tax asset, valuation allowance, percentage	100.00%	100.00%
Increase (decrease) in valuation allowance	$ 4,700	$ 11,700