Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2019	Oct. 31, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	Bellicum Pharmaceuticals, Inc.
Entity Central Index Key	0001358403
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		49,616,316
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Shell Company	false
Entity Current Reporting Status	Yes

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 99,151	$ 43,695
Investment securities, available for sale - short-term	4,152	49,304
Accounts receivable, interest and other receivables	328	909
Prepaid expenses and other current assets	1,234	1,387
Total current assets	104,865	95,295
Right-of-use assets	6,234	0
Property and equipment, net	16,204	20,878
Restricted cash	3,603	4,973
Other assets	3,026	355
TOTAL ASSETS	133,932	121,501
Current liabilities:
Accounts payable	1,300	3,774
Accrued expenses and other current liabilities	14,363	8,589
Warrant derivative liability	37,842	0
Private placement option liability	12,094	0
Current portion of long-term debt	8,000	0
Current portion of lease liabilities	1,866	40
Current portion of deferred revenue	973	2,983
Current portion of deferred rent	0	418
Total current liabilities	76,438	15,804
Long-term liabilities:
Long-term debt, net of deferred financing costs	28,494	35,832
Long-term lease liabilities	6,163	91
Deferred rent	0	1,296
TOTAL LIABILITIES	111,095	53,023
Commitments and contingencies: (Note 17)
Preferred stock: $0.01 par value; 10,000,000 shares authorized	21,608	0
Stockholders’ equity:
Common stock, $0.01 par value; 200,000,000 shares authorized at September 30, 2019 and December 31, 2018, 50,290,029 shares issued and 49,612,566 shares outstanding at September 30, 2019; 44,242,059 shares issued and 43,564,596 shares outstanding at December 31, 2018	503	442
Treasury stock: 677,463 shares held at September 30, 2019 and December 31, 2018	(5,056)	(5,056)
Additional paid-in capital	509,963	493,784
Accumulated other comprehensive loss	(137)	(144)
Accumulated deficit	(504,044)	(420,548)
Total stockholders’ equity	1,229	68,478
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	133,932	$ 121,501
Series 1 Preferred Stock
Long-term liabilities:
Preferred stock: $0.01 par value; 10,000,000 shares authorized	$ 21,608

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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)	200,000,000	200,000,000
Common stock, issued (in shares)	50,290,029	44,242,059
Common stock, outstanding (in shares)	49,612,566	43,564,596
Treasury stock, shares (in shares)	677,463	677,463
Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, authorized (in shares)	1,517,500
Preferred stock, shares issued (in shares)	541,500
Preferred stock, outstanding (in shares)	541,500

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
REVENUES
Revenues	$ 103	$ 292	$ 2,010	$ 808
OPERATING EXPENSES
Research and development	14,331	16,413	51,008	51,361
License fees	0	139	203	319
General and administrative	9,209	6,968	24,263	18,027
Total operating expenses	23,540	23,520	75,474	69,707
Loss from operations	(23,437)	(23,228)	(73,464)	(68,899)
OTHER INCOME (EXPENSE):
Interest income	323	492	1,044	1,196
Interest expense	(1,079)	(1,065)	(3,237)	(3,113)
Change in fair value of warrant liability	(4,850)	0	(4,850)	0
Other expense	(2,989)	0	(2,989)	0
Total other income (expense)	(8,595)	(573)	(10,032)	(1,917)
NET LOSS	$ (32,032)	$ (23,801)	$ (83,496)	$ (70,816)
Net loss per common share attributable to common shareholders, basic and diluted (in dollars per share)	$ (0.68)	$ (0.55)	$ (1.82)	$ (1.81)
Weighted-average shares outstanding, basic and diluted (in shares)	47,208,958	43,334,727	45,845,928	39,168,559
Other comprehensive income (loss):
Unrealized gain (loss) on investment securities	$ (8)	$ 33	$ 48	$ 11
Foreign currency translation adjustment	(23)	0	(41)	0
Comprehensive loss	(32,063)	(23,768)	(83,489)	(70,805)
CPRIT \| Grants
REVENUES
Revenues	$ 103	$ 292	$ 2,010	$ 808

Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Series 1 Preferred Stock
Balance, beginning of period (in shares) at Dec. 31, 2017		(33,962,640)	(677,463)
Balance, beginning of period at Dec. 31, 2017	$ 84,648	$ 340	$ (5,056)	$ 411,922	$ (322,512)	$ (46)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,605			3,605
Exercise of stock options (in shares)		313,258
Exercise of stock options	828	$ 3		825
Issuance of common stock upon vesting of restricted stock units (in shares)		12,658
Comprehensive loss	(22,898)				(22,840)	(58)
Balance, end of period (in shares) at Mar. 31, 2018		(34,288,556)	(677,463)
Balance, end of period at Mar. 31, 2018	66,183	$ 343	$ (5,056)	416,352	(345,352)	(104)
Balance, beginning of period (in shares) at Dec. 31, 2017		(33,962,640)	(677,463)
Balance, beginning of period at Dec. 31, 2017	84,648	$ 340	$ (5,056)	411,922	(322,512)	(46)
Increase (Decrease) in Stockholders' Equity
Comprehensive loss	(70,805)
Balance, end of period (in shares) at Sep. 30, 2018		(44,028,622)	(677,463)
Balance, end of period at Sep. 30, 2018	92,457	$ 440	$ (5,056)	490,436	(393,328)	(35)
Balance, beginning of period (in shares) at Mar. 31, 2018		(34,288,556)	(677,463)
Balance, beginning of period at Mar. 31, 2018	66,183	$ 343	$ (5,056)	416,352	(345,352)	(104)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,572			3,572
Exercise of stock options (in shares)		521,348
Exercise of stock options	2,158	$ 5		2,153
Issuance of common stock - Employee Stock Purchase Plan (in shares)		13,779
Issuance of common stock - Employee Stock Purchase Plan	99			99
Issuance of common stock in open market transactions, net of issuance costs (in shares)		9,200,000
Issuance of common stock in open market transactions, net of issuance costs	64,665	$ 92		64,573
Comprehensive loss	(24,139)				(24,175)	36
Balance, end of period (in shares) at Jun. 30, 2018		(44,023,683)	(677,463)
Balance, end of period at Jun. 30, 2018	112,538	$ 440	$ (5,056)	486,749	(369,527)	(68)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,677			3,677
Exercise of stock options (in shares)		2,786
Exercise of stock options	10			10
Issuance of common stock upon vesting of restricted stock units (in shares)		2,153
Comprehensive loss	(23,768)				(23,801)	33
Balance, end of period (in shares) at Sep. 30, 2018		(44,028,622)	(677,463)
Balance, end of period at Sep. 30, 2018	92,457	$ 440	$ (5,056)	490,436	(393,328)	(35)
Preferred stock, beginning balance at Dec. 31, 2018	0
Balance, beginning of period (in shares) at Dec. 31, 2018		(44,242,059)	(677,463)
Balance, beginning of period at Dec. 31, 2018	68,478	$ 442	$ (5,056)	493,784	(420,548)	(144)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	2,136			2,136
Exercise of stock options (in shares)		27,647
Exercise of stock options	70			70
Issuance of common stock upon vesting of restricted stock units (in shares)		22,702
Issuance of common stock in open market transactions, net of issuance costs (in shares)		1,350,652
Issuance of common stock in open market transactions, net of issuance costs	4,625	$ 14		4,611
Comprehensive loss	(24,449)				(24,528)	79
Balance, end of period (in shares) at Mar. 31, 2019		(45,643,060)	(677,463.000)
Balance, end of period at Mar. 31, 2019	50,860	$ 456	$ (5,056)	500,601	(445,076)	(65)
Preferred stock, beginning balance at Dec. 31, 2018	0
Preferred stock, ending balance (in shares) at Sep. 30, 2019							541,500
Preferred stock, ending balance at Sep. 30, 2019	21,608						$ 21,608
Balance, beginning of period (in shares) at Dec. 31, 2018		(44,242,059)	(677,463)
Balance, beginning of period at Dec. 31, 2018	68,478	$ 442	$ (5,056)	493,784	(420,548)	(144)
Increase (Decrease) in Stockholders' Equity
Comprehensive loss	(83,489)
Balance, end of period (in shares) at Sep. 30, 2019		(50,290,029)	(677,463)
Balance, end of period at Sep. 30, 2019	1,229	$ 503	$ (5,056)	509,963	(504,044)	(137)
Preferred stock, ending balance (in shares) at Jun. 30, 2019							0
Preferred stock, ending balance at Jun. 30, 2019							$ 0
Balance, beginning of period (in shares) at Mar. 31, 2019		(45,643,060)	(677,463.000)
Balance, beginning of period at Mar. 31, 2019	50,860	$ 456	$ (5,056)	500,601	(445,076)	(65)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,996			1,996
Exercise of stock options (in shares)		2,206
Exercise of stock options	6			6
Issuance of common stock - Employee Stock Purchase Plan (in shares)		40,000
Issuance of common stock - Employee Stock Purchase Plan	71	$ 1		70
Issuance of common stock upon vesting of restricted stock units (in shares)		5,857
Issuance of common stock in open market transactions, net of issuance costs (in shares)		1,240,503
Issuance of common stock in open market transactions, net of issuance costs	4,352	$ 12		4,340
Comprehensive loss	(26,977)				(26,936)	(41)
Balance, end of period (in shares) at Jun. 30, 2019		(46,931,626)	(677,463.000)
Balance, end of period at Jun. 30, 2019	30,308	$ 469	$ (5,056)	507,013	(472,012)	(106)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable preferred stock in public offering, net (in shares)							575,000
Issuance of redeemable preferred stock in public offering, net	0						$ 22,944
Conversion of redeemable preferred stock into common stock (in shares)		3,350,000					33,500
Conversion of redeemable preferred stock into common stock	(1,336)	$ (34)		(1,302)			$ 1,336
Preferred stock, ending balance (in shares) at Sep. 30, 2019							541,500
Preferred stock, ending balance at Sep. 30, 2019	21,608						$ 21,608
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,648			1,648
Issuance of common stock upon vesting of restricted stock units (in shares)		8,403
Issuance of redeemable convertible preferred stock in public offering, net	0						$ 22,944
Conversion of redeemable preferred stock into common stock (in shares)		3,350,000					33,500
Conversion of redeemable convertible preferred stock into common stock	1,336	$ 34		1,302			$ (1,336)
Comprehensive loss	(32,063)				(32,032)	(31)
Balance, end of period (in shares) at Sep. 30, 2019		(50,290,029)	(677,463)
Balance, end of period at Sep. 30, 2019	$ 1,229	$ 503	$ (5,056)	$ 509,963	$ (504,044)	$ (137)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (83,496)	$ (70,816)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	5,762	10,854
Depreciation and amortization expense	5,479	4,916
Change in fair value of warrant derivative liability	4,850	0
Amortization of (discount) premium on investment securities, net	(29)	118
Amortization of right-of-use assets	996	0
Accretion of lease liability	590	(198)
Amortization of deferred financing costs	662	663
Loss on disposition of fixed assets	4	0
Expense of issuance costs on warrants and private placement option	3,047	0
Changes in operating assets and liabilities:
Accounts receivable, interest and other receivables	581	(218)
Prepaid expenses and other assets	(1,524)	162
Accounts payable	(2,474)	(1,444)
Accrued liabilities and other	2,727	2,390
Deferred revenue	(2,010)	(808)
NET CASH USED IN OPERATING ACTIVITIES	(64,835)	(54,381)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities	0	(50,641)
Proceeds from sale of investment securities	45,229	52,239
Purchases of property and equipment	(554)	(1,321)
NET CASH PROVIDED BY INVESTING ACTIVITIES	44,675	277
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock in a public offering, net	8,977	64,665
Proceeds from issuance of redeemable convertible preferred stock in a public offering, net	22,944	0
Proceeds from issuance of warrants in a public offering, net	30,995	0
Proceeds received from private placement option, net	11,254	0
Proceeds from exercise of stock options	76	2,996
Proceeds from issuance of stock from employee stock purchase plan	71	99
Payment on financing lease obligations	(30)	(23)
NET CASH PROVIDED BY FINANCING ACTIVITIES	74,287	67,737
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(41)	0
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	54,086	13,633
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	48,668	45,029
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	102,754	58,662
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	2,611	2,451
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment in accounts payables and accrued liabilities	0	55
Accrued issuance costs for public offering	210	0
Conversion of redeemable preferred stock into common stock	1,336	0
Financing leases incurred for equipment	$ 167	$ 0

ORGANIZATION AND BUSINESS DESCRIPTION	9 Months Ended
ORGANIZATION AND BUSINESS DESCRIPTION	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION AND BUSINESS DESCRIPTION	ORGANIZATION AND BUSINESS DESCRIPTION Bellicum Pharmaceuticals, Inc., or Bellicum, was incorporated in Delaware in July 2004 and is based in Houston, Texas. Bellicum is a clinical stage biopharmaceutical company focused on discovering and developing novel cellular immunotherapies for various forms of cancer, including both hematological cancers and solid tumors. Bellicum is devoting substantially all of its present efforts to developing next-generation product candidates in some of the most important areas of cellular immunotherapy, including CAR-T therapy. 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”. Bellicum Europe GmbH, a dormant Swiss subsidiary, was liquidated in the third quarter of 2019. The Company has determined that it has one operating and reporting segment as it allocates resources and assesses financial performance on a consolidated basis.

BASIS OF PRESENTATION	9 Months Ended
BASIS OF PRESENTATION	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, and follow the requirements of the U.S. Securities and Exchange Commission, or the SEC, for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been omitted. In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and its cash flows for the periods presented. All such adjustments are normal and recurring in nature. These statements should be read in conjunction with the Company's Annual Report on Form 10-K filed for the fiscal year ended December 31, 2018, or the Annual Report. A copy of the Annual Report is available on the SEC’s website, www.sec.gov, under the Company’s ticker symbol “BLCM” or on Bellicum’s website, www.bellicum.com. The results for the interim periods are not necessarily indicative of the results expected for the full fiscal year or any other interim period. Any reference in these footnotes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or the FASB. The Company considered its going concern disclosure requirements in accordance with ASC 205-40-50. The Company concluded that its accumulated deficit since inception and its non-generation of revenue from operations are conditions that raised substantial doubt about the Company’s ability to continue as a going concern. Without a successful plan in place from management, these conditions could negatively impact the Company’s ability to meets its financial obligations over the next year. In response, the Company has raised capital during the 3rd quarter of 2019 (see Note 11) to alleviate such substantial concern. As a result, following this plan, substantial doubt about the Company’s ability to continue as a going concern for the 12 months from the date of issuance of these financial statements is alleviated. 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.

CASH, CASH EQUIVALENTS AND RESTRICTED CASH

9 Months Ended

Sep. 30, 2019

Cash and Cash Equivalents [Abstract]

CASH, CASH EQUIVALENTS AND RESTRICTED CASH

As of September 30, 2019, and December 31, 2018, respectively, the Company maintained $3.6 million and $5.0 million as restricted cash.

During 2017, $4.2 million was received from the Cancer Prevention and Research Institute of Texas, or “CPRIT”, and the unreleased balance is being held in a separate account to be used for costs solely related to the CPRIT grant. Release of the CPRIT funds are subject to the terms of the grant agreement and requirements therein and require the authorization of CPRIT. To-date, CPRIT authorized the release of $1.7 million of restricted funds from the CPRIT account, leaving a balance of $2.5 million at September 30, 2019. For more information about the CPRIT grant, see Note 10.

The remaining $1.1 million of restricted cash as of September 30, 2019 is held in escrow to cover specific construction of manufacturing improvement costs related to the facility lease. The release of the escrowed funds is subject to the terms of the escrow agreement and requirements therein including approval by both the Company and the landlord based on authorized completion of certain aspects of the manufacturing improvements.

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.



	September 30, 2019		December 31, 2018
	(in thousands)
Cash and cash equivalents ⁽¹⁾	$	99,151	$	43,695
Restricted cash, noncurrent	3,603		4,973
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	102,754	$	48,668

⁽¹⁾As of September 30, 2019, and December 31, 2018, the Company invested approximately $87.6 million and $25.0 million, respectively, in cash equivalent instruments.

SIGNIFICANT ACCOUNTING POLICIES

9 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates

The preparation of the interim condensed consolidated financial statements in accordance with GAAP requires management to make certain estimates and judgments that affect the reported amounts of assets, liabilities, and expenses. Actual results could differ from those estimates.

Consolidation

All financial information presented includes the accounts of Bellicum and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.

Revenue Recognition

The Company has not yet generated any revenue from product sales. The Company’s source of revenue for the three and nine months ended September 30, 2019 and 2018 has been from grants. When grant funds are received after costs have been incurred, the Company accrues revenue and records a grant receivable. Cash received from grants in advance of incurring qualifying costs is recorded as deferred revenue and recognized as revenue when qualifying costs are incurred.

Cash and Cash Equivalents

The Company considers all short-term, highly liquid investments with maturity of three months or less from the date of purchase to be cash equivalents.

Investment Securities

Consistent with its investment policy, the Company invests its cash allocated to fund its short-term liquidity requirements with prominent financial institutions in bank depository accounts and institutional money market funds. The Company invests the remainder of its cash in corporate debt securities and municipal bonds rated at least A quality or equivalent, U.S. Treasury notes and bonds and U.S. and state government agency-backed securities.

The Company determines the appropriate classification of investment securities based on whether they represent the investment of funds available for current operations. The Company reevaluates its classification as of each balance sheet date. All investment securities owned are classified as available-for-sale. The cost of securities sold is based on the specific identification method. Investment securities are recorded as of each balance sheet date at fair value, with unrealized gains and, to the extent deemed temporary, unrealized losses reported as accumulated other comprehensive gain (loss), a separate component of stockholders' equity. Interest and dividend income on investment securities, accretion of discounts and amortization of premiums and realized gains and losses are included in interest income in the statements of operations and comprehensive income (loss).

Property and Equipment

Leasehold improvements, 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 three to five years. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term.

Intangible Assets

Non-refundable upfront payments related to a supply agreement with future benefits have been capitalized as an intangible asset, presented in other assets on the balance sheet and amortized over the term of the agreement. The amortization of the intangible asset is included in operating expenses.

Debt Issuance Costs

Costs related to debt issuance are presented in the balance sheet as a direct deduction from the carrying amount of the debt liability, consistent with debt discounts and are amortized using the effective interest method. Amortization of debt issuance costs are included in interest expense.

Warrant Derivatives

Freestanding warrants exercisable for multiple instruments are classified as liabilities. The Company accounts for these warrants in accordance with ASC Topic 815, Accounting for Derivative Instruments and Hedging Activities (“ASC 815”). In accordance with this standard, a derivative instrument is recognized as either an asset or liability in the balance sheet and are measured at fair values with gains or losses recognized in earnings at the end of each reporting period.

Offering expenses arising from the issuance of warrants were expensed as incurred.

Private Placement Option

The Company has entered into the Security Purchase Agreement which contains a call option on shares that are puttable outside the control of the Company. The Company treats the option as a liability under ASC Topic 480, Distinguishing Liabilities from Equity (“ASC 480”) and measures the fair value of the option at the time of issuance and records changes in fair value as a charge to current earnings at each reporting period.

The Company uses the binomial model, adjusted for the effect of dilution, because it embodies all of the requisite assumptions (including trading volatility, estimated terms, dilution and risk-free rates) necessary to determine the fair value of this instrument. Estimating fair values of derivative financial instruments requires the development of significant and subjective estimates that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors. In addition, option-based techniques are highly volatile and sensitive to changes in the trading market price of our common stock. Since derivative financial instruments are initially and subsequently carried at fair values, our income (expense) going forward will reflect the volatility in these estimates and assumption changes. Under the terms of this accounting standard, increases in the trading price of the Company’s common stock and increases in fair value during a given financial period result in the application of non-cash derivative expense. Conversely, decreases in the trading price of the Company’s common stock and decreases in trading fair value during a given financial period result in the application of non-cash derivative income.

Offering expenses arising from the issuance of the private placement option were expensed as incurred.

Preferred Stock

The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity.

Operating Leases

Operating leases are recognized as right-of-use, or ROU, assets and operating lease liabilities on the balance sheet. 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.

Fair Value of Financial Instruments

Accounting standards include disclosure requirements around fair values used for certain financial instruments and establish a fair value hierarchy. The three-tier hierarchy prioritizes valuation inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market, as described further in Note 5.

The Company believes the recorded values of its financial instruments, including cash and cash equivalents, accounts payable and accrued liabilities 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, investment securities, 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. The costs related to preferred and common stock 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.

Clinical Trials

The Company estimates its clinical trial expense accrual for a given period based on the number of patients enrolled at each site, estimated cost per patient, and the length of time each patient has been in the trial, less amounts previously billed. These accruals are recorded in accrued expenses and other current liabilities, and the related expense is recorded in research and development expense.

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 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. When contingent milestone payments are due to third parties under research and development arrangements, the milestone payment obligations are expensed when the milestone events are achieved.

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. 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 its share-based compensation in accordance with ASC 718, Compensation - Stock Compensation, which requires the measurement and recognition of compensation expense for all share-based payment awards made to employees and directors to be recognized in the financial statements, based on their fair value. The Company measures share-based compensation to consultants in accordance with ASC 505-50, Equity-Based Payments to Non-Employees, and recognizes the fair value of the award over the period the services are rendered.

The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock option awards. The fair value is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award on a straight-line basis.

Comprehensive Loss

Comprehensive income (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 comprehensive income (loss) includes, among other items, unrealized gains and losses on the changes in fair value of investments. These components are added, net of their related tax effect, to the reported net income (loss) to arrive at comprehensive income (loss). The components of accumulated other comprehensive loss at September 30, 2019 and December 31, 2018, on the Company’s balance sheet was comprised of the net unrealized holding gains and losses on the Company’s investment securities and unrealized gains or losses arising from fluctuations in foreign currency exchange rates related to foreign operations. See Note 5 for further detail of the unrealized holding gains and losses on the Company’s investment securities.

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 net loss per common share is computed by dividing the net loss applicable to common shareholders by the diluted weighted-average number of common shares outstanding during the period calculated by applying the more dilutive of the if-converted method and the two class method for the Series 1 preferred stock, and the more dilutive of the treasury stock method and the two class method for the Public Warrants. In periods in which the Company reports a net loss, all common share equivalents are deemed anti-dilutive such that basic net loss per common share and diluted net loss per common share are equivalent. Potentially dilutive common shares have been excluded from the diluted net loss per common share computations in all periods presented because such securities have an anti-dilutive effect on net loss per common share due to the Company’s net loss. There are no reconciling items used to calculate the weighted-average number of total common shares outstanding for basic and diluted net loss per common share data

The following outstanding shares of common stock equivalents were excluded from the computations of diluted net loss per share of common stock attributable to common stockholders for the periods presented, as the effect of including such securities would be anti-dilutive.




	As of September 30,
	2019	2018
Common Stock Equivalents:	Number of Shares
Redeemable convertible Series 1 Preferred Stock	54,150,000	—
Warrants to purchase common stock	57,500,000	—
Options to purchase common stock	7,010,200	5,868,433
Unvested shares of restricted stock units	166,093	205,155
Unvested shares of restricted stock	—	14,707
Total common stock equivalents	118,826,293	6,088,295

Application of New Accounting Standards

In the first quarter of 2019, the Company adopted ASU 2016-02, “Leases (Topic 842),” (“ASC 842”) which requires companies that lease assets to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. ASC 842 provides for a modified retrospective transition approach requiring lessees to recognize and measure leases on the balance sheet at the beginning of either the earliest period presented or as of the beginning of the period of adoption with the option to elect certain practical expedients. The Company has elected to apply ASC 842 as of the beginning of the period of adoption (January 1, 2019) and has not restated comparative periods. The adoption of the new standard did not materially impact the Company's consolidated results of operations and cash flows and did not have an impact on the Company's beginning accumulated deficit balance.

The Company has elected the ‘package of practical expedients’, which permit it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company did not elect the use of hindsight practical expedient. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected the short-term lease recognition exemption for all leases that qualify.

FAIR VALUE MEASUREMENTS

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

Fair Value Measurement

The Company follows ASC, Topic 820, Fair Value Measurements and Disclosures, or ASC 820, for application to financial assets and liabilities. ASC 820 defines fair value, provides a consistent framework for measuring fair value under GAAP and requires fair value financial statement disclosures. ASC 820 applies only to the measurement and disclosure of financial assets and liabilities that are required or permitted to be measured and reported at fair value under other ASC topics (except for standards that relate to share-based payments such as ASC Topic 718, Compensation - Stock Compensation).

The valuation techniques required by ASC 820 may be based on either observable or unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, and unobservable inputs reflect the Company’s market assumptions.

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.

Investment Securities

The following tables present the Company’s investment securities (including, if applicable, those classified on the Company’s balance sheet as cash equivalents) that are measured at fair value on a recurring basis as of September 30, 2019 and December 31, 2018:



			Fair Value Measurements at Reporting Date Using
	Balance at September 30, 2019		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
Cash Equivalents:
Money market funds and treasury bills	$	87,645	$	87,645	$	—	$	—
Total Cash Equivalents	$	87,645	$	87,645	$	—	$	—
Investment Securities:
U.S. government agency-backed securities	$	2,002	$	—	$	2,002	$	—
Corporate debt securities	2,150		—		2,150		—
Total Investment Securities	$	4,152	$	—	$	4,152	$	—



			Fair Value Measurements at Reporting Date Using
	Balance at December 31, 2018		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
Cash Equivalents:
Money market funds	$	24,953	$	24,953	$	—	$	—
Total Cash Equivalents	$	24,953	$	24,953	$	—	$	—

Investment Securities:
U.S. government agency-backed securities	$	7,383	$	—	$	7,383	$	—
Corporate debt securities	41,921		—		41,921		—
Total Investment Securities	$	49,304	$	—	$	49,304	$	—

U.S. Treasury, U.S. government agency-backed securities and corporate debt securities are valued based on various observable inputs such as benchmark yields, reported trades, broker/dealer quotes, benchmark securities and bids.

Investment securities, all classified as available-for-sale, consisted of the following as of September 30, 2019 and December 31, 2018:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Aggregate Estimated Fair Value
September 30, 2019	(in thousands)
Investment Securities:
U.S. government agency-backed securities	$	2,000	$	2	$	—	$	2,002
Corporate debt securities	2,150		—		—		2,150
Total Investment Securities	$	4,150	$	2	$	—	$	4,152



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Estimated Fair Value
December 31, 2018	(in thousands)
Investment Securities:
U.S. government agency-backed securities	$	7,382	$	2	$	(1	)	$	7,383
Corporate debt securities	41,968		—		(47		)	41,921
Total	$	49,350	$	2	$	(48	)	$	49,304

The Company's investment securities as of September 30, 2019, will reach maturity between October 2019 and November 2019, with a weighted-average maturity date in October 2019.

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 discussed in Notes 12 and 13, respectively. In the accompanying interim condensed consolidated financial statements as of September 30, 2019, the fair values of the warrant derivative liability and the private placement option liability are classified as current liabilities. 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.

The following table provides the warrant derivative and private placement option reported at fair value and measured on a recurring basis at September 30, 2019:



			Fair Value Measurements at Reporting Date Using
	September 30, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Warrant derivative liability	$	37,842	$	—	$	—	$	37,842
Private placement option liability	12,094		—		—		12,094
	$	49,936	$	—	$	—	$	49,936

The table below (in thousands) of Level 3 liabilities begins with the valuation as of the beginning of the third quarter of 2019 and then is adjusted for any issuances and exercises that occurred during the third quarter of 2019 and adjusts the balances for changes in fair value that occurred during the current quarter. The ending balance of the Level 3 financial instrument presented above represents our best estimates and may not be substantiated by comparison to independent markets and, in many cases, could not be realized in immediate settlement of the instruments.



Three months ended September 30, 2019	Warrant Derivative Liability		Private Placement Option Liability		Total
Balance, June 30, 2019	$	—	$	—	$	—
Issuance of warrants	32,992		—		32,992
Receipt of option fee	—		12,094		12,094
Change in fair value	4,850		—		4,850
Balance, September 30, 2019	$	37,842	$	12,094	$	49,936

There were no warrant derivative or private placement option liabilities at December 31, 2018.

- Definition

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

+ References + Details

PROPERTY AND EQUIPMENT

9 Months Ended

Sep. 30, 2019

Property, Plant and Equipment [Abstract]

PROPERTY AND EQUIPMENT



Property and equipment consist of the following:
					September 30, 2019			December 31, 2018
	Estimated Useful Lives				(in thousands)
Leasehold improvements			5	Years	$	21,633		$	21,633
Lab equipment			5	Years	8,855			8,471
Office furniture			5	Years	1,704			1,704
Manufacturing equipment			5	Years	1,891			1,890
Computer and office equipment	3	to	5	Years	1,693			1,606
Equipment held under financing leases			5	Years	270			204
Software			5	Years	393			361
Total					36,439			35,869
Less: accumulated depreciation					(20,235		)	(14,991		)
Property and equipment, net					$	16,204		$	20,878

During the nine months ended September 30, 2019 and 2018, the Company recorded $5.4 million and $4.9 million of depreciation expense, respectively. Leasehold improvements as of September 30, 2019 and December 31, 2018 includes $2.5 million related to costs incurred by the landlord.

LEASES

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

LEASES

The Company determines whether an arrangement is a lease at its inception. Operating leases relate primarily to office space and manufacturing facilities with remaining lease terms of one year to seven years, some of which include options to extend the lease term for up to five years. Management considered the options in determining the lease term used to establish the Company's ROU assets and lease liabilities.

The Company entered into a lease agreement for office space and equipment in South San Francisco, California commencing in April 2019 and expiring in 2022. The Company recorded right-of-use assets of $1.2 million and leased assets of $0.2 million for the real estate and equipment components of the lease, respectively, and a corresponding lease liability of $1.4 million upon lease commencement.

In July 2019, the Company exercised the first of its renewal options to extend its lease of office and laboratory space at its Houston, Texas facility for an additional year, commencing February 1, 2020. As a result of the lease renewal, the Company recorded an incremental ROU asset and lease liability of $1.0 million upon exercising the option.

As most of the Company's leases do not provide an implicit rate, the Company's incremental borrowing rate based on the information available at lease commencement date was used to determine the present value of lease payments. Components of lease cost are as follows:



	Three months ended September 30, 2019		Nine months ended September 30, 2019
	(in thousands)
Operating lease cost⁽¹⁾	$	594	$	1,587
Short-term lease cost	$	—	$	47

(1) Includes right-of-use asset amortization of $359,000 and $996,000 for the three and nine months ended September 30, 2019, respectively.

Supplemental cash flow information and non-cash activity related to the Company's operating leases are as follows:



	Nine months ended September 30, 2019
	(in thousands)
Operating cash flow information:
Cash paid for amounts included in the measurement of lease liabilities	$	1,741
Non-cash activity:
Right-of-use assets obtained in exchange for lease obligations	$	2,263

Weighted-average remaining lease term and discount rate for operating leases are as follows:



	September 30, 2019
Weighted-average remaining lease term	5.3 years
Weighted-average discount rate	12.1	%

Maturities of lease liabilities by year for leases are as follows (in thousands):



		Operating Leases				Financing Leases
2019⁽¹⁾			$	655		$	24
2020			2,663			96
2021			1,673			90
2022			1,418			39
2023			1,143			—
2024 and beyond			3,250			—
Total lease payments			10,802			249
Less: Imputed interest			(2,982		)	(40		)
Present value of lease liabilities			$	7,820		$	209

(1)	Excluding the 9 months ended September 30, 2019.

As of December 31, 2018, minimum lease payments under non-cancelable leases by period were expected to be as follows:



Year	Operating Leases		Capital Leases
	(in thousands)
2019	$	2,087	$	68
2020	1,112		68
2021	1,055		43
2022	1,094		—
2023	1,133		—
Thereafter	3,222		—
Total minimum rentals	$	9,703	179

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES

9 Months Ended

Sep. 30, 2019

Payables and Accruals [Abstract]

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES

Accrued expenses and other liabilities consist of the following:



	September 30, 2019		December 31, 2018
	(in thousands)
Accrued construction costs	$	—	457
Accrued payroll ⁽¹⁾	5,007		3,430
Accrued patient treatment and monitoring costs	2,083		2,053
Accrued manufacturing costs	2,104		546
Accrued professional services	1,820		235
Accrued obligations under material supply agreements	1,091		—
Accrued other	2,258		1,868
Total accrued expenses and other current liabilities	$	14,363	8,589

(1) In the third quarter of 2019, the Company implemented a reduction in force to reduce costs and focus on strategic initiatives. As such approximately 19% of the consolidated headcount was reduced resulting in severance costs of approximately $3.7 million, of which approximately $3.3 million is included in accrued payroll.

DEBT	9 Months Ended
DEBT	Sep. 30, 2019
Debt Disclosure [Abstract]
DEBT	DEBT On December 21, 2017, or the Oxford Closing Date, the Company entered into a loan and security agreement, or the Oxford Loan Agreement, with Oxford Finance LLC, as the collateral agent and a lender, pursuant to which the Company borrowed $35.0 million in a single term loan, or the Oxford Loan on the Oxford Closing Date. For additional information about the Oxford Loan Agreement, see Note 8 to the audited financial statements contained in the Annual Report. 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, have been recorded as deferred financing costs, and are included in long-term debt on the Company's balance sheet. The deferred financing costs are being amortized over the term of the loan as interest expense. Interest expenses included amortization of deferred financing costs of $0.2 million during each of the three-month periods ended September 30, 2019 and 2018 and $0.7 million during each of the nine-month periods ended September 30, 2019 and 2018. Management believes that the carrying value of the debt facility approximates its fair value, as the Company's debt facility bears interest at a rate that approximates prevailing market rates for instruments with similar characteristics. The fair value of the Company's debt facility is determined under Level 2 in the fair value hierarchy.

GRANT REVENUE	9 Months Ended
GRANT REVENUE	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
GRANT REVENUE	GRANT REVENUE Cancer Research Grant Contract On August 9, 2017, the Company entered into a Cancer Research Grant Contract with CPRIT, pursuant to which CPRIT awarded a grant of approximately $16.9 million to the Company to fund development of rivo-cel for hematologic cancer, or the CPRIT Award. The CPRIT Award is contingent upon funds being available during the term of the grant agreement and subject to CPRIT’s ability to perform its obligations under the grant agreement. For additional information about the grant agreement, see Note 9 to the audited financial statements in the Annual Report. During the three and nine-month periods ended September 30, 2019, the Company recognized expenses and accrued revenue of $0.1 million and $2.0 million, respectively, for work performed under the CPRIT grant. During the three and nine-month period ended September 30, 2018, the Company recognized expenses and accrued revenue of $0.3 million and $0.8 million, respectively for work performed under the CPRIT grant.

AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT (Notes)	9 Months Ended
	Sep. 30, 2019
Statement of Stockholders' Equity [Abstract]
AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT	AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT 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 “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 “Public Warrants”) to purchase up to 57,500,000 shares of its common stock. Each share of Series 1 Preferred Stock was being sold together with a warrant to purchase 100 shares of common stock at a combined price to the public of $100.00. Under certain circumstances, each warrant to purchase 100 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 $53.9 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company, and excluding any proceeds that the Company may receive upon exercise of the Public Warrants. All of the Public Warrants sold in the Offering have an exercise price of $1.30 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 Public Warrants will be immediately exercisable upon issuance, provided that the holder will be 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. Private Placement On August 16, 2019, the Company entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with certain institutional investors named therein (the “Purchasers”), pursuant to which the Company has 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 (the “Private Warrants”) to purchase up to 28,000,000 shares of common stock at an exercise price of $1.00 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 (also, “Private Warrants”) to purchase up to 8,750,000 shares of common stock at an exercise price of $1.40 per share. The purchase and sale of the securities issuable under the private placement agreement may occur in two or more separate closings, each to be conducted at the Purchasers’ discretion within five days’ notice to the Company, and is subject to the Company’s obtaining stockholder approval for additional authorized shares of Common Stock or a reverse stock split (the “Required Stockholder Approval”), and the right of the Purchasers to purchase such securities will expire two and a half years after the Required Stockholder Approval, with respect to the Series 2 Preferred Stock, and three years after such stockholder approval, with respect to the Series 3 Preferred Stock, if not exercised prior to that date. The Company received $11.3 million in option proceeds, net of offering costs, upon the execution of the Securities Purchase Agreement. Total offering costs incurred by the Company related to the Public Warrants, Private Warrants and options amounted to $3.0 million, which are presented as other expense on the accompanying condensed consolidated statements of operations and comprehensive loss. STOCKHOLDERS' EQUITY On April 20, 2018, the Company completed an underwritten public offering of 9,200,000 shares of its common stock, or Common Stock, at a price of $7.50 per share, for an aggregate offering size of $69.0 million, pursuant to a registration statement on Form S-3. The net proceeds to the Company, after deducting underwriting discounts, and commissions and offering expenses was approximately $64.7 million. On October 5, 2018, the Company entered into an Open Market Sale Agreement^SM, or the Sale Agreement, with Jefferies LLC, as sales agent, pursuant to which the Company may offer and sell, from time to time, through Jefferies, shares of our common stock having an aggregate offering price of up to $60.0 million. The shares will be offered and sold pursuant to our shelf registration statement on Form S-3. During the nine months ended September 30, 2019, the Company received $9.0 million in net proceeds from the sale of 2,591,155 shares of its common stock in the open market. On August 16, 2019, in connection with the Public Offering, the Company delivered written notice to Jefferies LLC that the Company was suspending and terminating the prospectus supplement related to the shares of its common stock issuable pursuant to the Sale Agreement. The Company will not make any sales of its securities pursuant to the Sales Agreement, unless and until a new prospectus supplement is filed. Other than the termination of the ATM Prospectus Supplement, the Sale Agreement remains in full force and effect.

WARRANT DERIVATIVE LIABILITY

9 Months Ended

Sep. 30, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Warrant Derivative Liability

WARRANT DERIVATIVE LIABILITY

In connection with the Company’s August 2019 Public Offering of the Series 1 redeemable convertible preferred stock (see Note 11), the Company issued immediately exercisable warrants ("Series 1 warrants") to purchase up to 57,500,000 shares of common stock and, under certain circumstances, each warrant to purchase 100 shares of common stock will be exercisable, at the irrevocable election of the holder, for one share of Series 1 Preferred Stock (see Note 11). The Company recorded the Series 1 warrants as a derivative liability under ASC 815, Derivatives and Hedging.

The Company determined the fair value of the Series 1 warrants on the date of issuance to be $33.0 million, as determined using the binomial model. The Company revalued the Public Warrants at September 30, 2019 using a binomial model, and the fair value of the Public Warrants were estimated to be $37.8 million as at September 30, 2019. The Company recorded $4.9 million as a non-cash loss on warrant derivative liability as current period expense during the quarter ended September 30, 2019.

Inputs used to determine estimated fair value (Level 3) include the estimated fair value of the warrants, as determined by 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, risk-free interest rates and expected dividends.

The fair value of the warrants has been estimated with the following weighted-average assumptions:



	August 21, 2019		September 30, 2019
Risk-free interest rate	1.54	%	1.62	%
Volatility	69.72	%	70.89	%
Expected life (years)	7.00		6.89
Expected dividend yield	—		—

PRIVATE PLACEMENT OPTION LIABILITY	9 Months Ended
PRIVATE PLACEMENT OPTION LIABILITY	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
PRIVATE PLACEMENT OPTION LIABILITY	PRIVATE PLACEMENT OPTION LIABILITY In August 2019, the Company executed the Securities Purchase Agreement in relation to the August 2019 private placement (see Note 11), and received net option fee proceeds of approximately $11.3 million (the “Option Fee”). Pursuant to the Securities Purchase Agreement, the Company agreed to issue, in multiple private placements, Series 2 and 3 Preferred Stock and Private Warrants upon the request of the Purchasers, provided that the Company obtains stockholder approval for additional authorized shares or a reverse stock split to cover all the common shares underlying the Series 2 and 3 Preferred Stock and Private Warrants issuable for the Option Fee. The right of the Purchasers to purchase such securities will expire two and a half years after the obtaining stockholder approval for additional authorized shares or a reverse stock split, with respect to the Series 2 Preferred Stock, and three years after such stockholder approval or such reverse stock split, with respect to the Series 3 Preferred Stock, if not exercised prior to that date. The Company determined that the Option Fee is a liability under ASC 480 because it can be exercised for Series 2 and 3 Preferred Stock that are puttable outside the control of the Company. The Company recorded the net proceeds of the Option Fee as a liability which approximates the fair value at September 30, 2019. The Company will mark-to-market the Option Fee and record the change in fair value as a non-cash charge to current period earnings at each reporting period.

REDEEMABLE CONVERTIBLE PREFERRED STOCK

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

REDEEMABLE CONVERTIBLE PREFERRED STOCK

In August 2019, the Company sold Series 1 Preferred Stock pursuant to an underwritten public offering (see Note 11). 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 541,500 shares of Series 1 preferred stock issued and outstanding as of September 30, 2019. There were no shares of Series 2 or 3 preferred stock issued and outstanding as of September 30, 2019. There were no preferred shares issued and outstanding at December 31, 2018. 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 100 shares of common stock. During the three months ended September 30, 2019, 33,500 shares of Series 1 preferred stock were converted to common stock.

As of September 30, 2019, the Company classified the Series 1 Preferred Stock as temporary equity, under ASC 480, 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 in temporary 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 100 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 and Series 2 Preferred Stock) and $140.00 per share (for Series 3 Preferred Stock). The “Transition Date” means:



			With respect to the Series 1 preferred stock, the first date following August 21, 2021, on which each of the Conditions (as defined below) is met (the “Series 1 Transition Date”);



			With respect to the Series 2 preferred stock, the first date following the six-month anniversary of the Series 1 Transition Date on which each of the Conditions is met (the “Series 2 Transition Date”); and



			With respect to the Series 3 preferred stock, the first date following the six-month anniversary of the Series 2 Transition Date on which each of the Conditions is met.

The “Conditions” mean: (1) the closing price of the Company’s common stock has been equal to or exceeded $2.50 per share for 180 calendar days (for determining if the Conditions are met for the Series 1 preferred stock and Series 2 preferred stock) and $3.50 per share (for the Series 3 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 500,000 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

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

SHARE-BASED COMPENSATION

The Company has five share-based compensation plans, including the 2019 Equity Incentive Plan which was adopted in June 2019. Each plan authorizes the granting of shares of common stock and 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 four years, and have a term of up to 10 years. Unexercised stock options terminate on the expiration date of the grant. The Company recognizes the share-based compensation expense over the requisite service period of the individual grantees, which generally equals the vesting period.

For a description of each of the plans in existence as of December 31, 2018, or the Prior Plans, refer to Note 11 to the audited financial statements included the Annual Report.

2019 Equity Incentive Plan

The 2019 Equity Incentive Plan, or the 2019 Plan, is designed to secure and retain the services of the Company’s employees and directors, provide incentives for employees and directors to exert maximum efforts for the success of the Company and its affiliates, and provide a means by which employees and directors may be given an opportunity to benefit from increases in the value of the Company’s common stock. The 2019 Plan is successor to and continuation of the 2014 Equity Incentive Plan, as amended, or 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, or the Share Reserve, will not exceed the sum of (i) 2,500,000 new shares and (ii) the Prior Plans’ Returning Shares, as defined in the 2019 Plan documents, in an amount not to exceed 6,005,401 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 was approved by the Company's stockholders, as such shares become available from time to time.

The following shares of common stock, or 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 following shares of common stock will not become available again for issuance under the 2019 Plan: (i) any shares that are reacquired or withheld (or not issued) by the Company to satisfy the exercise, strike or purchase price of a stock award granted under the 2019 Plan or any Prior Plan (including any shares subject to such award that are not delivered because such award is exercised through a reduction of shares subject to such award); (ii) any shares that are reacquired or withheld (or not issued) by the Company to satisfy a tax withholding obligation in connection with a stock award granted under the 2019 Plan or any Prior Plan; (iii) any shares repurchased by the Company on the open market with the proceeds of the exercise, strike or purchase price of a stock award granted under the 2019 Plan or any Prior Plan; and (iv) in the event that a stock appreciation right granted under the 2019 Plan or any Prior Plan is settled in shares, the gross number of shares subject to such award.

The number of shares of common stock available for issuance under the 2019 Plan will be reduced by: (i) one share for each share issued pursuant to a stock option or stock appreciation right with an exercise price that is at least 100% of the fair market value of common stock on the date of grant, or an Appreciation Award granted under the 2019 Plan; and (ii) 1.25 shares for each share issued pursuant to a stock award that is not an Appreciation Award, or a Full Value Award, granted under the 2019 Plan.

The number of shares of common stock available for issuance under the 2019 Plan will be increased by: (i) one share for each Prior Plans’ Returning Share or 2019 Plan Returning Share subject to an Appreciation Award; and (ii) 1.25 shares for each Prior Plans’ Returning Share or 2019 Plan Returning Share subject to a Full Value Award.

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.

The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2019:



	Options and Inducement Awards
Outstanding at December 31, 2018	5,759,246
Granted	2,756,305
Exercised	(2,206	)
Forfeited	(1,503,145	)
Outstanding at September 30, 2019	7,010,200
Exercisable at September 30, 2019	2,911,752

The following table summarizes the stock award activity for all stock plans during the nine months ended September 30, 2019:



	Restricted Stock Awards and Units
Outstanding at December 31, 2018	246,155
Granted	30,000
Vested	(61,031	)
Forfeited	(49,031	)
Outstanding at September 30, 2019	166,093

2014 Employee Stock Purchase Plan

The 2014 Employee Stock Purchase Plan, or 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 550,000 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. During the nine-month periods ended September 30, 2019 and 2018, there were 40,000 and 13,779 shares purchased by the ESPP, respectively. As of September 30, 2019, there were 374,637 shares available for issuance under the ESPP.



A summary of activity within the ESPP follows:	Nine months ended September 30,
	2019		2018
	(amounts in thousands)
Deductions from employees	$	113	$	168
Share-based compensation expense recognized	75		111
Remaining share-based compensation expense	116		285

Share-Based Compensation Expense

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:



	Nine months ended September 30,
	2019		2018
Risk-free interest rate	2.24	%	2.63	%
Volatility	72.1	%	72.1	%
Expected life (years)	6.04		6.08
Expected dividend yield	—		—

Share-based compensation expense by classification for the three and nine months ended September 30, 2019 and 2018 are as follows:



	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
	(in thousands)				(in thousands)
Research and development	$	761	$	1,606	$	2,784	$	4,898
General and administrative	873		2,070		2,978		5,956
Total	$	1,634	$	3,676	$	5,762	$	10,854

At September 30, 2019, total compensation cost not yet recognized was $11.3 million and the weighted-average period over which this amount is expected to be recognized is 2.3 years.

STOCKHOLDERS' EQUITY	9 Months Ended
STOCKHOLDERS' EQUITY	Sep. 30, 2019
Equity [Abstract]
STOCKHOLDERS' EQUITY	AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT 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 “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 “Public Warrants”) to purchase up to 57,500,000 shares of its common stock. Each share of Series 1 Preferred Stock was being sold together with a warrant to purchase 100 shares of common stock at a combined price to the public of $100.00. Under certain circumstances, each warrant to purchase 100 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 $53.9 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company, and excluding any proceeds that the Company may receive upon exercise of the Public Warrants. All of the Public Warrants sold in the Offering have an exercise price of $1.30 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 Public Warrants will be immediately exercisable upon issuance, provided that the holder will be 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. Private Placement On August 16, 2019, the Company entered into a Securities Purchase Agreement (the “Securities Purchase Agreement”) with certain institutional investors named therein (the “Purchasers”), pursuant to which the Company has 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 (the “Private Warrants”) to purchase up to 28,000,000 shares of common stock at an exercise price of $1.00 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 (also, “Private Warrants”) to purchase up to 8,750,000 shares of common stock at an exercise price of $1.40 per share. The purchase and sale of the securities issuable under the private placement agreement may occur in two or more separate closings, each to be conducted at the Purchasers’ discretion within five days’ notice to the Company, and is subject to the Company’s obtaining stockholder approval for additional authorized shares of Common Stock or a reverse stock split (the “Required Stockholder Approval”), and the right of the Purchasers to purchase such securities will expire two and a half years after the Required Stockholder Approval, with respect to the Series 2 Preferred Stock, and three years after such stockholder approval, with respect to the Series 3 Preferred Stock, if not exercised prior to that date. The Company received $11.3 million in option proceeds, net of offering costs, upon the execution of the Securities Purchase Agreement. Total offering costs incurred by the Company related to the Public Warrants, Private Warrants and options amounted to $3.0 million, which are presented as other expense on the accompanying condensed consolidated statements of operations and comprehensive loss. STOCKHOLDERS' EQUITY On April 20, 2018, the Company completed an underwritten public offering of 9,200,000 shares of its common stock, or Common Stock, at a price of $7.50 per share, for an aggregate offering size of $69.0 million, pursuant to a registration statement on Form S-3. The net proceeds to the Company, after deducting underwriting discounts, and commissions and offering expenses was approximately $64.7 million. On October 5, 2018, the Company entered into an Open Market Sale Agreement^SM, or the Sale Agreement, with Jefferies LLC, as sales agent, pursuant to which the Company may offer and sell, from time to time, through Jefferies, shares of our common stock having an aggregate offering price of up to $60.0 million. The shares will be offered and sold pursuant to our shelf registration statement on Form S-3. During the nine months ended September 30, 2019, the Company received $9.0 million in net proceeds from the sale of 2,591,155 shares of its common stock in the open market. On August 16, 2019, in connection with the Public Offering, the Company delivered written notice to Jefferies LLC that the Company was suspending and terminating the prospectus supplement related to the shares of its common stock issuable pursuant to the Sale Agreement. The Company will not make any sales of its securities pursuant to the Sales Agreement, unless and until a new prospectus supplement is filed. Other than the termination of the ATM Prospectus Supplement, the Sale Agreement remains in full force and effect.

COMMITMENTS AND CONTINGENCIES	9 Months Ended
COMMITMENTS AND CONTINGENCIES	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Miltenyi Supply Agreement On March 27, 2019, Bellicum entered into a strategic, long-term supply agreement with Miltenyi Biotec GmbH, or Miltenyi, for the supply of Miltenyi’s CliniMACS tubing set, reagents and disposables for the manufacture of Bellicum’s programmed T cell therapies for preclinical and clinical use and, if approved, for commercial use, as well as support services. Under the supply agreement, Bellicum is required to make non-refundable upfront payments totaling €2,000,000, which have been capitalized as an intangible asset and will be amortized over the 10-year term of the agreement. The annual amortization will be approximately $0.2 million for each of the next five years. Under the supply agreement, Bellicum will provide Miltenyi with regularly scheduled rolling forecasts of anticipated purchase requirements on a product-by-product and country-by-country basis. Within the rolling forecasts, there is a period of time referred to as the “Firm Zone” in which Bellicum is obligated to purchase, and Miltenyi has agreed to provide, the number of products Bellicum has specified for that period, subject to specified conditions and limitations. Litigation On February 6, 2018, a purported securities class action complaint captioned Nipun Kakkar v. Bellicum Pharmaceuticals, Inc., Rick Fair and Alan Musso was filed against the Company, and certain of its officers in the U.S. District Court for the Southern District of Texas, Houston Division. A second substantially similar class action was filed on March 14, 2018 by plaintiff Frances Rudy against the same defendants in the same court. The lawsuits purport to assert class action claims on behalf of purchasers of the Company's securities during the period from May 8, 2017 through January 30, 2018. The complaints allege that the defendants violated the Securities Exchange Act of 1934, as amended, or the Exchange Act, by making materially false and misleading statements concerning the Company's clinical trials being conducted in the U.S. to assess rivo-cel (rivogenlecleucel, formerly known as BPX-501) as an adjunct T-cell therapy administered after allogeneic hematopoietic stem cell transplantation. The complaints purport to assert claims for violations of Sections 10(b) and 20(a) of the Exchange Act and Rule 10b-5 promulgated thereunder. The complaints seek, on behalf of the purported class, an unspecified amount of monetary damages, interest, fees and expenses of attorneys and experts, and other relief. On April 9, 2018, the District Court consolidated the two lawsuits under the Kakkar action. On March 26, 2019, the court appointed lead plaintiffs to represent the putative class and on May 15, 2019, plaintiffs filed an amended class action complaint. On July 5, 2019, defendants filed a motion to dismiss the amended complaint. Plaintiffs filed an opposition to the motion to dismiss on August 26, 2019 and the Company filed its reply to the opposition on September 22, 2019. On July 19, 2018, a purported shareholder derivative complaint captioned Seung Paik v. Richard A. Fair, et al. was filed against the Company’s directors and certain of the Company’s officers in the U.S. District Court for the Southern District of Texas, Houston Division. The lawsuit purports to seek damages on behalf of the Company against the individual defendants for breach of fiduciary duty, waste, unjust enrichment and violations of Section 14(a) of the Exchange Act. The complaint alleges that the defendants caused or allowed the Company to disseminate misstatements regarding the clinical trials for rivo-cel and to make false or misleading statements in the proxy materials for the Company’s 2017 annual meeting of stockholders. On October 3, 2018, the District Court granted the Company’s motion to stay the Paik derivative cause of action until reinstated on motion of the parties. On July 8, 2019, another purported shareholder derivative complaint captioned Scott Ludovissy and Ann Gordon Trammell v. Richard A. Fair, et al. was filed against the same defendants in the same court. The Ludovissy complaint includes substantially similar factual allegations as the class action case and seeks to hold the defendants liable for allegedly causing the Company to make material misstatements. 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, a third amended complaint was filed, which alleges 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. Plaintiffs are seeking unspecified monetary damages including punitive damages. In response to the third amended complaint, Bellicum filed a demurrer and a motion to strike portions of the third amended complaint, both of which are set for hearing on November 26, 2019. Written discovery and depositions are proceeding in the litigation. The Company intends to vigorously defend itself in these proceedings. An adverse finding could materially affect our business and results of operations.

SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
SIGNIFICANT ACCOUNTING POLICIES (Policies)	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, and follow the requirements of the U.S. Securities and Exchange Commission, or the SEC, for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP have been omitted. In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and its cash flows for the periods presented. All such adjustments are normal and recurring in nature. These statements should be read in conjunction with the Company's Annual Report on Form 10-K filed for the fiscal year ended December 31, 2018, or the Annual Report. A copy of the Annual Report is available on the SEC’s website, www.sec.gov, under the Company’s ticker symbol “BLCM” or on Bellicum’s website, www.bellicum.com. The results for the interim periods are not necessarily indicative of the results expected for the full fiscal year or any other interim period. Any reference in these footnotes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or the FASB. The Company considered its going concern disclosure requirements in accordance with ASC 205-40-50. The Company concluded that its accumulated deficit since inception and its non-generation of revenue from operations are conditions that raised substantial doubt about the Company’s ability to continue as a going concern. Without a successful plan in place from management, these conditions could negatively impact the Company’s ability to meets its financial obligations over the next year. In response, the Company has raised capital during the 3rd quarter of 2019 (see Note 11) to alleviate such substantial concern. As a result, following this plan, substantial doubt about the Company’s ability to continue as a going concern for the 12 months from the date of issuance of these financial statements is alleviated. 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.
Use of Estimates	Use of Estimates The preparation of the interim condensed consolidated financial statements in accordance with GAAP requires management to make certain estimates and judgments that affect the reported amounts of assets, liabilities, and expenses. Actual results could differ from those estimates.
Consolidation	Consolidation All financial information presented includes the accounts of Bellicum and its wholly-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Revenue Recognition	Revenue Recognition The Company has not yet generated any revenue from product sales. The Company’s source of revenue for the three and nine months ended September 30, 2019 and 2018 has been from grants. When grant funds are received after costs have been incurred, the Company accrues revenue and records a grant receivable. Cash received from grants in advance of incurring qualifying costs is recorded as deferred revenue and recognized as revenue when qualifying costs are incurred.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all short-term, highly liquid investments with maturity of three months or less from the date of purchase to be cash equivalents.
Investment Securities	Investment Securities Consistent with its investment policy, the Company invests its cash allocated to fund its short-term liquidity requirements with prominent financial institutions in bank depository accounts and institutional money market funds. The Company invests the remainder of its cash in corporate debt securities and municipal bonds rated at least A quality or equivalent, U.S. Treasury notes and bonds and U.S. and state government agency-backed securities. The Company determines the appropriate classification of investment securities based on whether they represent the investment of funds available for current operations. The Company reevaluates its classification as of each balance sheet date. All investment securities owned are classified as available-for-sale. The cost of securities sold is based on the specific identification method. Investment securities are recorded as of each balance sheet date at fair value, with unrealized gains and, to the extent deemed temporary, unrealized losses reported as accumulated other comprehensive gain (loss), a separate component of stockholders' equity. Interest and dividend income on investment securities, accretion of discounts and amortization of premiums and realized gains and losses are included in interest income in the statements of operations and comprehensive income (loss).
Property and Equipment	Property and Equipment Leasehold improvements, 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 three to five years. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term.
Intangible Assets	Intangible Assets Non-refundable upfront payments related to a supply agreement with future benefits have been capitalized as an intangible asset, presented in other assets on the balance sheet and amortized over the term of the agreement. The amortization of the intangible asset is included in operating expenses.
Debt Issuance Costs	Debt Issuance Costs Costs related to debt issuance are presented in the balance sheet as a direct deduction from the carrying amount of the debt liability, consistent with debt discounts and are amortized using the effective interest method. Amortization of debt issuance costs are included in interest expense.
Derivatives Warrants	Warrant Derivatives Freestanding warrants exercisable for multiple instruments are classified as liabilities. The Company accounts for these warrants in accordance with ASC Topic 815, Accounting for Derivative Instruments and Hedging Activities (“ASC 815”). In accordance with this standard, a derivative instrument is recognized as either an asset or liability in the balance sheet and are measured at fair values with gains or losses recognized in earnings at the end of each reporting period. Offering expenses arising from the issuance of warrants were expensed as incurred.
Private Placement Option	Private Placement Option The Company has entered into the Security Purchase Agreement which contains a call option on shares that are puttable outside the control of the Company. The Company treats the option as a liability under ASC Topic 480, Distinguishing Liabilities from Equity (“ASC 480”) and measures the fair value of the option at the time of issuance and records changes in fair value as a charge to current earnings at each reporting period. The Company uses the binomial model, adjusted for the effect of dilution, because it embodies all of the requisite assumptions (including trading volatility, estimated terms, dilution and risk-free rates) necessary to determine the fair value of this instrument. Estimating fair values of derivative financial instruments requires the development of significant and subjective estimates that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors. In addition, option-based techniques are highly volatile and sensitive to changes in the trading market price of our common stock. Since derivative financial instruments are initially and subsequently carried at fair values, our income (expense) going forward will reflect the volatility in these estimates and assumption changes. Under the terms of this accounting standard, increases in the trading price of the Company’s common stock and increases in fair value during a given financial period result in the application of non-cash derivative expense. Conversely, decreases in the trading price of the Company’s common stock and decreases in trading fair value during a given financial period result in the application of non-cash derivative income. Offering expenses arising from the issuance of the private placement option were expensed as incurred.
Preferred Stock	Preferred Stock The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity.
Operating Leases	Operating Leases Operating leases are recognized as right-of-use, or ROU, assets and operating lease liabilities on the balance sheet. 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.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Accounting standards include disclosure requirements around fair values used for certain financial instruments and establish a fair value hierarchy. The three-tier hierarchy prioritizes valuation inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market, as described further in Note 5. The Company believes the recorded values of its financial instruments, including cash and cash equivalents, accounts payable and accrued liabilities 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, investment securities, 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. The costs related to preferred and common stock have been netted against the proceeds of the equity issuances.
Research and Development	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 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. When contingent milestone payments are due to third parties under research and development arrangements, the milestone payment obligations are expensed when the milestone events are achieved. 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.
Clinical Trials	Clinical Trials The Company estimates its clinical trial expense accrual for a given period based on the number of patients enrolled at each site, estimated cost per patient, and the length of time each patient has been in the trial, less amounts previously billed. These accruals are recorded in accrued expenses and other current liabilities, and the related expense is recorded in research and development expense.
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. 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 its share-based compensation in accordance with ASC 718, Compensation - Stock Compensation, which requires the measurement and recognition of compensation expense for all share-based payment awards made to employees and directors to be recognized in the financial statements, based on their fair value. The Company measures share-based compensation to consultants in accordance with ASC 505-50, Equity-Based Payments to Non-Employees, and recognizes the fair value of the award over the period the services are rendered. The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock option awards. The fair value is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award on a straight-line basis.
Comprehensive Loss	Comprehensive Loss Comprehensive income (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 comprehensive income (loss) includes, among other items, unrealized gains and losses on the changes in fair value of investments. These components are added, net of their related tax effect, to the reported net income (loss) to arrive at comprehensive income (loss). The components of accumulated other comprehensive loss at September 30, 2019 and December 31, 2018, on the Company’s balance sheet was comprised of the net unrealized holding gains and losses on the Company’s investment securities and unrealized gains or losses arising from fluctuations in foreign currency exchange rates related to foreign operations. See Note 5 for further detail of the unrealized holding gains and losses on the Company’s investment securities.
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 net loss per common share is computed by dividing the net loss applicable to common shareholders by the diluted weighted-average number of common shares outstanding during the period calculated by applying the more dilutive of the if-converted method and the two class method for the Series 1 preferred stock, and the more dilutive of the treasury stock method and the two class method for the Public Warrants. In periods in which the Company reports a net loss, all common share equivalents are deemed anti-dilutive such that basic net loss per common share and diluted net loss per common share are equivalent. Potentially dilutive common shares have been excluded from the diluted net loss per common share computations in all periods presented because such securities have an anti-dilutive effect on net loss per common share due to the Company’s net loss. There are no reconciling items used to calculate the weighted-average number of total common shares outstanding for basic and diluted net loss per common share data
Application of New Accounting Standards	Application of New Accounting Standards In the first quarter of 2019, the Company adopted ASU 2016-02, “Leases (Topic 842),” (“ASC 842”) which requires companies that lease assets to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in its balance sheet. ASC 842 provides for a modified retrospective transition approach requiring lessees to recognize and measure leases on the balance sheet at the beginning of either the earliest period presented or as of the beginning of the period of adoption with the option to elect certain practical expedients. The Company has elected to apply ASC 842 as of the beginning of the period of adoption (January 1, 2019) and has not restated comparative periods. The adoption of the new standard did not materially impact the Company's consolidated results of operations and cash flows and did not have an impact on the Company's beginning accumulated deficit balance. The Company has elected the ‘package of practical expedients’, which permit it not to reassess under the new standard its prior conclusions about lease identification, lease classification and initial direct costs. The Company did not elect the use of hindsight practical expedient. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected the short-term lease recognition exemption for all leases that qualify.

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)

9 Months Ended

Sep. 30, 2019

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents and Restricted Cash, Reconciliation



	September 30, 2019		December 31, 2018
	(in thousands)
Cash and cash equivalents ⁽¹⁾	$	99,151	$	43,695
Restricted cash, noncurrent	3,603		4,973
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$	102,754	$	48,668

⁽¹⁾As of September 30, 2019, and December 31, 2018, the Company invested approximately $87.6 million and $25.0 million, respectively, in cash equivalent instruments.

FAIR VALUE MEASUREMENTS (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Available-For-Sale Securities

Investment securities, all classified as available-for-sale, consisted of the following as of September 30, 2019 and December 31, 2018:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Aggregate Estimated Fair Value
September 30, 2019	(in thousands)
Investment Securities:
U.S. government agency-backed securities	$	2,000	$	2	$	—	$	2,002
Corporate debt securities	2,150		—		—		2,150
Total Investment Securities	$	4,150	$	2	$	—	$	4,152



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Estimated Fair Value
December 31, 2018	(in thousands)
Investment Securities:
U.S. government agency-backed securities	$	7,382	$	2	$	(1	)	$	7,383
Corporate debt securities	41,968		—		(47		)	41,921
Total	$	49,350	$	2	$	(48	)	$	49,304

Investment Securities Measured at Fair Value on a Recurring Basis



			Fair Value Measurements at Reporting Date Using
	Balance at September 30, 2019		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
Cash Equivalents:
Money market funds and treasury bills	$	87,645	$	87,645	$	—	$	—
Total Cash Equivalents	$	87,645	$	87,645	$	—	$	—
Investment Securities:
U.S. government agency-backed securities	$	2,002	$	—	$	2,002	$	—
Corporate debt securities	2,150		—		2,150		—
Total Investment Securities	$	4,152	$	—	$	4,152	$	—



			Fair Value Measurements at Reporting Date Using
	Balance at December 31, 2018		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
Cash Equivalents:
Money market funds	$	24,953	$	24,953	$	—	$	—
Total Cash Equivalents	$	24,953	$	24,953	$	—	$	—

Investment Securities:
U.S. government agency-backed securities	$	7,383	$	—	$	7,383	$	—
Corporate debt securities	41,921		—		41,921		—
Total Investment Securities	$	49,304	$	—	$	49,304	$	—



Three months ended September 30, 2019	Warrant Derivative Liability		Private Placement Option Liability		Total
Balance, June 30, 2019	$	—	$	—	$	—
Issuance of warrants	32,992		—		32,992
Receipt of option fee	—		12,094		12,094
Change in fair value	4,850		—		4,850
Balance, September 30, 2019	$	37,842	$	12,094	$	49,936

The following table provides the warrant derivative and private placement option reported at fair value and measured on a recurring basis at September 30, 2019:



			Fair Value Measurements at Reporting Date Using
	September 30, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Warrant derivative liability	$	37,842	$	—	$	—	$	37,842
Private placement option liability	12,094		—		—		12,094
	$	49,936	$	—	$	—	$	49,936

PROPERTY AND EQUIPMENT (Tables)

9 Months Ended

Sep. 30, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment



Property and equipment consist of the following:
					September 30, 2019			December 31, 2018
	Estimated Useful Lives				(in thousands)
Leasehold improvements			5	Years	$	21,633		$	21,633
Lab equipment			5	Years	8,855			8,471
Office furniture			5	Years	1,704			1,704
Manufacturing equipment			5	Years	1,891			1,890
Computer and office equipment	3	to	5	Years	1,693			1,606
Equipment held under financing leases			5	Years	270			204
Software			5	Years	393			361
Total					36,439			35,869
Less: accumulated depreciation					(20,235		)	(14,991		)
Property and equipment, net					$	16,204		$	20,878

LEASES (Tables)

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Components of Lease Cost

Components of lease cost are as follows:



	Three months ended September 30, 2019		Nine months ended September 30, 2019
	(in thousands)
Operating lease cost⁽¹⁾	$	594	$	1,587
Short-term lease cost	$	—	$	47

(1) Includes right-of-use asset amortization of $359,000 and $996,000 for the three and nine months ended September 30, 2019, respectively.

Supplemental cash flow information and non-cash activity related to the Company's operating leases are as follows:



	Nine months ended September 30, 2019
	(in thousands)
Operating cash flow information:
Cash paid for amounts included in the measurement of lease liabilities	$	1,741
Non-cash activity:
Right-of-use assets obtained in exchange for lease obligations	$	2,263

Weighted-average remaining lease term and discount rate for operating leases are as follows:



	September 30, 2019
Weighted-average remaining lease term	5.3 years
Weighted-average discount rate	12.1	%

Maturity of Finance Lease Liabilities

Maturities of lease liabilities by year for leases are as follows (in thousands):



		Operating Leases				Financing Leases
2019⁽¹⁾			$	655		$	24
2020			2,663			96
2021			1,673			90
2022			1,418			39
2023			1,143			—
2024 and beyond			3,250			—
Total lease payments			10,802			249
Less: Imputed interest			(2,982		)	(40		)
Present value of lease liabilities			$	7,820		$	209

(1)	Excluding the 9 months ended September 30, 2019.

Maturity of Operating Lease Liabilities

Maturities of lease liabilities by year for leases are as follows (in thousands):



		Operating Leases				Financing Leases
2019⁽¹⁾			$	655		$	24
2020			2,663			96
2021			1,673			90
2022			1,418			39
2023			1,143			—
2024 and beyond			3,250			—
Total lease payments			10,802			249
Less: Imputed interest			(2,982		)	(40		)
Present value of lease liabilities			$	7,820		$	209

(1)	Excluding the 9 months ended September 30, 2019.

Minimum Rental Payments for Operating Leases

As of December 31, 2018, minimum lease payments under non-cancelable leases by period were expected to be as follows:



Year	Operating Leases		Capital Leases
	(in thousands)
2019	$	2,087	$	68
2020	1,112		68
2021	1,055		43
2022	1,094		—
2023	1,133		—
Thereafter	3,222		—
Total minimum rentals	$	9,703	179

Minimum Lease Payments, Capital Leases

As of December 31, 2018, minimum lease payments under non-cancelable leases by period were expected to be as follows:



Year	Operating Leases		Capital Leases
	(in thousands)
2019	$	2,087	$	68
2020	1,112		68
2021	1,055		43
2022	1,094		—
2023	1,133		—
Thereafter	3,222		—
Total minimum rentals	$	9,703	179

SHARE-BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

Stock Option Activity

The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2019:



	Options and Inducement Awards
Outstanding at December 31, 2018	5,759,246
Granted	2,756,305
Exercised	(2,206	)
Forfeited	(1,503,145	)
Outstanding at September 30, 2019	7,010,200
Exercisable at September 30, 2019	2,911,752

Stock Award Activity For All Stock Plans

The following table summarizes the stock award activity for all stock plans during the nine months ended September 30, 2019:



	Restricted Stock Awards and Units
Outstanding at December 31, 2018	246,155
Granted	30,000
Vested	(61,031	)
Forfeited	(49,031	)
Outstanding at September 30, 2019	166,093

ESPP Activity



A summary of activity within the ESPP follows:	Nine months ended September 30,
	2019		2018
	(amounts in thousands)
Deductions from employees	$	113	$	168
Share-based compensation expense recognized	75		111
Remaining share-based compensation expense	116		285

Valuation Assumptions

The fair value of the option grants has been estimated, with the following weighted-average assumptions:



	Nine months ended September 30,
	2019		2018
Risk-free interest rate	2.24	%	2.63	%
Volatility	72.1	%	72.1	%
Expected life (years)	6.04		6.08
Expected dividend yield	—		—

Share-Based Compensation Expense by Classification

Share-based compensation expense by classification for the three and nine months ended September 30, 2019 and 2018 are as follows:



	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
	(in thousands)				(in thousands)
Research and development	$	761	$	1,606	$	2,784	$	4,898
General and administrative	873		2,070		2,978		5,956
Total	$	1,634	$	3,676	$	5,762	$	10,854

ORGANIZATION AND BUSINESS DESCRIPTION (Details)	9 Months Ended
ORGANIZATION AND BUSINESS DESCRIPTION (Details)	Sep. 30, 2019 segment subsidiary
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of wholly-owned subsidiaries formed \| subsidiary	2
Number of reportable segments	1
Number of operating segments	1

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 3,603	$ 4,973
Grant from CPRIT
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	2,500		$ 4,200
Release of restricted cash	1,700
Held in escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 1,100

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Reconciliation (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 99,151	$ 43,695
Restricted cash, noncurrent	3,603	4,973
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	102,754	48,668	$ 58,662	$ 45,029
Cash equivalent instruments	$ 87,600	$ 25,000

SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share, Potentially Dilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	118,826,293	6,088,295
Redeemable convertible Series 1 Preferred Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	54,150,000	0
Warrants to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	57,500,000	0
Options to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	7,010,200	5,868,433
Unvested shares of restricted stock units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	166,093	205,155
Unvested shares of restricted stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	0	14,707

FAIR VALUE MEASUREMENTS - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	$ 87,645,000	$ 24,953,000
Total Investment Securities	4,152,000	49,304,000
U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	2,002,000	7,383,000
Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	2,150,000	41,921,000
Money market funds and treasury bills
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	87,645,000	24,953,000
Quoted prices in active markets for identical assets (Level 1)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	87,645,000	24,953,000
Total Investment Securities	0	0
Quoted prices in active markets for identical assets (Level 1) \| U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Quoted prices in active markets for identical assets (Level 1) \| Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Quoted prices in active markets for identical assets (Level 1) \| Money market funds and treasury bills
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	87,645,000	24,953,000
Significant other observable inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Total Investment Securities	4,152,000	49,304,000
Significant other observable inputs (Level 2) \| U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	2,002,000	7,383,000
Significant other observable inputs (Level 2) \| Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	2,150,000	41,921,000
Significant other observable inputs (Level 2) \| Money market funds and treasury bills
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Significant unobservable inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Total Investment Securities	0	0
Significant unobservable inputs (Level 3) \| U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Significant unobservable inputs (Level 3) \| Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Significant unobservable inputs (Level 3) \| Money market funds and treasury bills
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,150	$ 49,350
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	(48)
Aggregate Estimated Fair Value	4,152	49,304
U.S. government agency-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,000	7,382
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	(1)
Aggregate Estimated Fair Value	2,002	7,383
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,150	41,968
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(47)
Aggregate Estimated Fair Value	$ 2,150	$ 41,921

FAIR VALUE MEASUREMENTS - Derivative Liabilities Reported at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	$ 37,842	$ 0
Private placement option derivative liability	12,094	$ 0
Total derivative liabilities	49,936
Quoted prices in active markets for identical assets (Level 1)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	0
Private placement option derivative liability	0
Total derivative liabilities	0
Significant other observable inputs (Level 2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	0
Private placement option derivative liability	0
Total derivative liabilities	0
Significant unobservable inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant derivative liability	37,842
Private placement option derivative liability	12,094
Total derivative liabilities	$ 49,936

FAIR VALUE MEASUREMENTS - Level 3 Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value at date of issuance	$ 503	$ 442
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance	0
Issuance of warrants	32,992
Private placement option derivative liability	12,094
Change in fair value	4,850
Ending balance	49,936
Warrant Derivative Liability \| Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance	0
Issuance of warrants	32,992
Change in fair value	4,850
Ending balance	37,842
Private Placement Option Liability \| Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance	0
Private placement option derivative liability	12,094
Change in fair value	0
Ending balance	$ 12,094

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	9 Months Ended
PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018	Jul. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Right-of-use assets	$ 6,234			$ 0
Total	36,439			35,869
Less: accumulated depreciation	(20,235)			(14,991)
Property and equipment, net	16,204			20,878
Depreciation and amortization expense	5,400	$ 4,900
Leasehold improvements	2,500			2,500
Office and Laboratory Space
Property, Plant and Equipment [Line Items]
Right-of-use assets			$ 1,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total	$ 21,633			21,633
Estimated Useful Lives	5 years
Lab equipment
Property, Plant and Equipment [Line Items]
Total	$ 8,855			8,471
Estimated Useful Lives	5 years
Office furniture
Property, Plant and Equipment [Line Items]
Total	$ 1,704			1,704
Estimated Useful Lives	5 years
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,891			1,890
Estimated Useful Lives	5 years
Computer and office equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,693			1,606
Equipment held under financing leases
Property, Plant and Equipment [Line Items]
Total	$ 270			204
Estimated Useful Lives	5 years
Software
Property, Plant and Equipment [Line Items]
Total	$ 393			$ 361
Estimated Useful Lives	3 years
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

LEASES - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jul. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Leas term option to extend	5 years
Right-of-use assets	$ 6,234		$ 0
Lease liability	7,820	$ 1,000
South San Francisco, California \| Office space
Lessee, Lease, Description [Line Items]
Right-of-use assets	1,200
South San Francisco, California \| Office equipment
Lessee, Lease, Description [Line Items]
Right-of-use assets	200
South San Francisco, California \| Office space and equipment
Lessee, Lease, Description [Line Items]
Lease liability	$ 1,400
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	7 years

LEASES - Components of Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Operating lease cost	$ 594	$ 1,587
Short-term lease cost	0	47
Amortization of right-of-use assets	$ 359	$ 996	$ 0

LEASES - Supplemental Cash Flow Information Related to Operating Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Operating cash flow information:
Cash paid for amounts included in the measurement of lease liabilities	$ 1,741
Non-cash activity:
Right-of-use assets obtained in exchange for lease obligations	$ 2,263

LEASES - Weighted Average Remaining Lease Term and Discount Rate (Details)	Sep. 30, 2019
Leases [Abstract]
Weighted-average remaining lease term	5 years 3 months 18 days
Weighted-average discount rate	12.10%

LEASES - Maturity of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jul. 31, 2019
Operating Leases
2019	$ 655
2020	2,663
2021	1,673
2022	1,418
2023	1,143
2024 and beyond	3,250
Total lease payments	10,802
Less: Imputed interest	(2,982)
Present value of lease liabilities	7,820	$ 1,000
Financing Leases
2019	24
2020	96
2021	90
2022	39
2023	0
2024 and beyond	0
Total lease payments	249
Less: Imputed interest	(40)
Present value of lease liabilities	$ 209

LEASES - Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leases
2019	$ 2,087
2020	1,112
2021	1,055
2022	1,094
2023	1,133
Thereafter	3,222
Total minimum rentals	9,703
Financing Leases
2019	68
2020	68
2021	43
2022	0
2023	0
Thereafter	0
Total minimum rentals	$ 179

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued construction costs	$ 0	$ 457
Accrued payroll	5,007	3,430
Accrued patient treatment and monitoring costs	2,083	2,053
Accrued manufacturing costs	2,104	546
Accrued professional services	1,820	235
Accrued obligations under material supply agreements	1,091	0
Accrued other	2,258	1,868
Total accrued expenses and other current liabilities	$ 14,363	$ 8,589
Headcount reduction	19.00%
Severance costs	$ 3,700
Severance costs included in accrued payroll	$ 3,300

DEBT (Details) - USD ($)		3 Months Ended		9 Months Ended
DEBT (Details) - USD ($)	Dec. 21, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Line of Credit Facility [Line Items]
Amortized deferred financing costs				$ 662,000	$ 663,000
Oxford Loan
Line of Credit Facility [Line Items]
Borrowings	$ 35,000,000.0
Expenses related to the loan	100,000
Final facility charge	$ 3,000,000
Amortized deferred financing costs		$ 200,000	$ 200,000	$ 700,000	$ 700,000

GRANT REVENUE (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
GRANT REVENUE (Details) - USD ($) $ in Thousands	Aug. 09, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues		$ 103	$ 292	$ 2,010	$ 808
Grants \| CPRIT
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 16,900	$ 103	$ 292	$ 2,010	$ 808

AUGUST 2019 PUBLIC OFFERING AND PRIVATE PLACEMENT (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 16, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Aug. 31, 2019
Class of Stock [Line Items]
Shares issuable under warrants (in shares)						57,500,000
Proceeds from issuance of redeemable convertible preferred stock in a public offering, net				$ 53,900
Proceeds upon entering into private placement agreement				11,254	$ 0
Total offering costs related to warrants and options		$ 2,989	$ 0	$ 2,989	$ 0
Redeemable convertible Series 1 Preferred Stock
Class of Stock [Line Items]
Shares issuable per warrants (in shares)		100		100
Public Offering
Class of Stock [Line Items]
Shares issuable under warrants (in shares)	57,500,000
Price per share (in dollars per share)	$ 100.00
Public Offering \| Redeemable convertible Series 1 Preferred Stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	575,000
Warrants exercise price (in dollars per share)	$ 130.00
Public Offering \| Common Stock
Class of Stock [Line Items]
Shares issuable per warrants (in shares)	100
Warrants exercise price (in dollars per share)	$ 1.30
Private Placement \| Series 2 Preferred Stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	350,000
Shares issuable under warrants (in shares)	28,000,000
Price per share (in dollars per share)	$ 100.00
Warrants exercise price (in dollars per share)	$ 1.00
Private Placement \| Series 3 Preferred Stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	250,000
Private Placement \| Preferred Stock
Class of Stock [Line Items]
Shares issuable under warrants (in shares)	8,750,000
Price per share (in dollars per share)	$ 140.00
Warrants exercise price (in dollars per share)	$ 1.40
Minimum \| Public Offering \| Common Stock
Class of Stock [Line Items]
Warrants, limitations on ownership after exercise		9.99%		9.99%
Maximum \| Public Offering \| Common Stock
Class of Stock [Line Items]
Warrants, limitations on ownership after exercise		19.99%		19.99%

WARRANT DERIVATIVE LIABILITY - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Aug. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Shares issuable under warrants (in shares)					57,500,000
Warrant derivative liability	$ 37,842		$ 37,842			$ 0
Change in fair value of warrant liability	4,850	$ 0	4,850	$ 0
Significant unobservable inputs (Level 3)
Derivatives, Fair Value [Line Items]
Warrant derivative liability, fair value at date of issuance	32,992		32,992
Warrant derivative liability	37,842		37,842
Significant unobservable inputs (Level 3) \| Warrant Derivative Liability
Derivatives, Fair Value [Line Items]
Warrant derivative liability, fair value at date of issuance	$ 32,992		$ 32,992

WARRANT DERIVATIVE LIABILITY - Fair Value of Warrants (Details)		9 Months Ended
	Aug. 21, 2019	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Risk-free interest rate		2.24%	2.63%
Volatility		72.10%	72.10%
Expected life (years)		6 years 15 days	6 years 29 days
Expected dividend yield		0.00%	0.00%
Warrant Derivative Liability
Derivative [Line Items]
Risk-free interest rate	1.54%	1.62%
Volatility	69.72%	70.89%
Expected life (years)	7 years	6 years 10 months 21 days
Expected dividend yield	0.00%	0.00%

REDEEMABLE CONVERTIBLE PREFERRED STOCK (Details) - $ / shares		3 Months Ended
	Aug. 16, 2019	Sep. 30, 2019	Aug. 31, 2019
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			10,000,000
Preferred stock, par value (in dollars per share)			$ 0.01
50-day trading volume on Nasdaq stock market		500,000
Redeemable convertible Series 1 Preferred Stock
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			1,517,500
Preferred stock, outstanding (in shares)		541,500
Shares issuable per warrants (in shares)		100
Conversion of redeemable preferred stock into common stock (in shares)		33,500
Series 1 and 2 Preferred Stock
Class of Stock [Line Items]
Price per share (in dollars per share)		$ 100.00
Closing price of common stock (in usd per share)		2.50
Series 3 Preferred Stock
Class of Stock [Line Items]
Closing price of common stock (in usd per share)		$ 3.50
Private Placement \| Series 2 Preferred Stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	350,000
Price per share (in dollars per share)	$ 100.00
Private Placement \| Series 3 Preferred Stock
Class of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	250,000
Private Placement \| Preferred Stock
Class of Stock [Line Items]
Price per share (in dollars per share)	$ 140.00

STOCKHOLDERS' EQUITY (Details) - USD ($) $ / shares in Units, $ in Millions			9 Months Ended
	Oct. 05, 2018	Apr. 20, 2018	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Common stock, issued (in shares)				50,290,029	44,242,059
Jefferies LLC
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of stock from employee stock purchase plan	$ 60.0		$ 9.0
Common stock, issued (in shares)				2,591,155
Underwritten public offering
Subsidiary, Sale of Stock [Line Items]
Price per share (in dollars per share)		$ 7.50
Proceeds from issuance of stock from employee stock purchase plan		$ 69.0
Net proceeds from offering		$ 64.7
Common Stock \| Underwritten public offering
Subsidiary, Sale of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)		9,200,000

SHARE-BASED COMPENSATION - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) plan shares	Sep. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans \| plan	5
Compensation cost not yet recognized \| $	$ 11.3
Period for recognition	2 years 3 months 18 days
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	4 years
Expiration period (in years)	10 years
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	550,000
Discount rate from grant date fair market value	15.00%
Issuance of common stock - Employee Stock Purchase Plan (in shares)	40,000	13,779
Capital shares reserved for future issuance (in shares)	374,637
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	2,500,000
2019 Equity Incentive Plan \| Prior Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	6,005,401
2019 Equity Incentive Plan \| Stock appreciation awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction factor for number of shares available for award	1
Increase factor for number of shares available for award	1
2019 Equity Incentive Plan \| Stock not an appreciation award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction factor for number of shares available for award	1.25
Increase factor for number of shares available for award	1.25

SHARE-BASED COMPENSATION - Stock Option Activity (Details) - Employee Stock Options And Inducement Option Awards shares in Thousands	9 Months Ended
	Sep. 30, 2019 shares
Options and Inducement awards
Outstanding at beginning of period (in shares)	5,759,246
Granted (in shares)	2,756,305
Exercised (in shares)	(2,206)
Forfeited (in shares)	(1,503,145)
Outstanding at end of period (in shares)	7,010,200
Exercisable (in shares)	2,911,752

SHARE-BASED COMPENSATION - Stock Award Activity For All Stock Plans (Details) - Restricted Stock Awards and Units shares in Thousands	9 Months Ended
	Sep. 30, 2019 shares
Restricted Stock Awards and Units
Beginning balance (in shares)	246,155
Granted (in shares)	30,000
Vested (in shares)	(61,031)
Forfeited (in shares)	(49,031)
Ending balance (in shares)	166,093

SHARE-BASED COMPENSATION - ESPP Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 1,634	$ 3,676	$ 5,762	$ 10,854
Remaining share-based compensation expense			5,762	10,854
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deductions from employees			113	168
Share-based compensation expense recognized			75	111
Remaining share-based compensation expense			$ 116	$ 285

SHARE-BASED COMPENSATION - Valuation Assumptions (Details)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement [Abstract]
Risk-free interest rate	2.24%	2.63%
Volatility	72.10%	72.10%
Expected life (years)	6 years 15 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

SHARE-BASED COMPENSATION - Expense by Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 1,634	$ 3,676	$ 5,762	$ 10,854
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	761	1,606	2,784	4,898
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 873	$ 2,070	$ 2,978	$ 5,956

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Mar. 27, 2019 USD ($)	Mar. 27, 2019 EUR (€)	Apr. 09, 2018 lawsuit
Nipun Kakkar Action
Loss Contingencies [Line Items]
Lawsuits \| lawsuit			2
Miltenyi
Loss Contingencies [Line Items]
Upfront payments (in EUR) \| €		€ 2,000,000
Term of agreement (in years)	10 years	10 years
Annual amortization \| $	$ 0.2
Remaining amortization period (in years)	5 years	5 years

SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	9 Months Ended
SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	Sep. 30, 2019
Minimum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Property and equipment, useful life	3 years
Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Property and equipment, useful life	5 years