Bellicum Pharmaceuticals (BLCM) 10-Q 7 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 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	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		46,009,066
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 42,274	$ 43,695
Investment securities, available for sale - short-term	31,210	49,304
Accounts receivable, interest and other receivables	947	909
Prepaid expenses and other current assets	2,254	1,387
Total current assets	76,685	95,295
Right-of-use assets	4,655	0
Property and equipment, net	19,189	20,878
Restricted cash	4,585	4,973
Other assets	3,054	355
TOTAL ASSETS	108,168	121,501
Current liabilities:
Accounts payable	2,027	3,774
Accrued expenses and other current liabilities	10,389	8,589
Current portion of lease liability	1,282	40
Current portion of deferred revenue	2,467	2,983
Current portion of deferred rent	0	418
Total current liabilities	16,165	15,804
Long-term liabilities:
Long-term debt, net of deferred financing costs	36,050	35,832
Long-term lease liability	5,093	91
Deferred rent	0	1,296
TOTAL LIABILITIES	57,308	53,023
Commitments and contingencies: (Note 14)
Stockholders’ equity:
Preferred stock: $0.01 par value; 10,000,000 shares authorized: no shares issued and outstanding	0	0
Common stock, $0.01 par value; 200,000,000 shares authorized at March 31, 2019 and December 31, 2018, 45,643,060 shares issued and 44,965,597 shares outstanding at March 31, 2019; 44,242,059 shares issued and 43,564,596 shares outstanding at December 31, 2018	456	442
Treasury stock: 677,463 shares held at March 31, 2019 and December 31, 2018	(5,056)	(5,056)
Additional paid-in capital	500,601	493,784
Accumulated other comprehensive loss	(65)	(144)
Accumulated deficit	(445,076)	(420,548)
Total stockholders’ equity	50,860	68,478
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 108,168	$ 121,501

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
REVENUES
Revenues	$ 516	$ 154
OPERATING EXPENSES
Research and development	16,818	16,536
License fees	30	30
General and administrative	7,536	5,692
Total operating expenses	24,384	22,258
Loss from operations	(23,868)	(22,104)
OTHER INCOME (EXPENSE):
Interest income	410	267
Interest expense	(1,070)	(1,003)
Total other expense	(660)	(736)
NET LOSS	$ (24,528)	$ (22,840)
Net loss per common share attributable to common shareholders, basic and diluted (in dollars per share)	$ (0.55)	$ (0.68)
Weighted-average shares outstanding, basic and diluted (in shares)	44,243,896	33,456,446
Other comprehensive income (loss):
Unrealized gain (loss) on investment securities	$ 51	$ (58)
Foreign currency translation adjustment	28
Comprehensive loss	$ (24,449)	$ (22,898)

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
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)	45,643,060	44,242,059
Common stock, outstanding (in shares)	44,965,597	43,564,596
Treasury stock, shares (in shares)	677,463	677,463

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance, beginning of period (in shares) at Dec. 31, 2017		33,962,640	(677,463,000)
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	(677,463,000)
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, 2018		44,242,059	(677,463,000)
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)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (24,528)	$ (22,840)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	2,136	3,605
Depreciation expense	1,787	1,426
Amortization of (discount) premium on investment securities, net	(18)	91
Amortization of right-of-use assets	312	0
Accretion of lease liability	133	(58)
Amortization of deferred financing costs	218	219
Changes in operating assets and liabilities:
Receivables	(38)	(101)
Prepaid expenses and other assets	(1,322)	71
Accounts payable	(1,752)	(1,271)
Accrued liabilities and other	(968)	340
Deferred revenue	(516)	(154)
NET CASH USED IN OPERATING ACTIVITIES	(24,556)	(18,672)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities	0	(6,312)
Proceeds from sale of investment securities	18,163	17,275
Purchases of property and equipment	(131)	(416)
NET CASH PROVIDED BY INVESTING ACTIVITIES	18,032	10,547
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock offering, net of offering costs	4,625	0
Proceeds from exercise of stock options	70	828
Payment on financing lease obligations	(8)	(7)
NET CASH PROVIDED BY FINANCING ACTIVITIES	4,687	821
EFFECT OF EXCHANGE RATE CHANGES ON CASH	28	0
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(1,809)	(7,304)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	48,668	45,029
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	46,859	37,725
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	857	784
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment in accounts payables and accrued liabilities	$ 5	$ 219

ORGANIZATION AND BUSINESS DESCR

ORGANIZATION AND BUSINESS DESCRIPTION	3 Months Ended
	Mar. 31, 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, as well as orphan inherited blood disorders. 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 and hematopoietic stem cell transplantation. In 2017, Bellicum formed two wholly-owned subsidiaries, Bellicum Pharma Limited, a private limited company organized under the laws of the United Kingdom, and Bellicum Europe GmbH, a private limited liability company organized under Swiss law. In 2018, Bellicum formed Bellicum Pharma GmbH, a wholly-owned private limited liability company organized under German law. All were formed for the purpose of developing product candidates in Europe. Bellicum, Bellicum Pharma Limited, Bellicum Europe GmbH and Bellicum Pharma GmbH are collectively referred to herein as the “Company”.

BASIS OF PRESENTATION

BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION	BASIS OF PRESENTATION The interim condensed consolidated financial statements have been prepared on a going concern basis, which assumes the Company will continue to realize its assets and discharge its liabilities in the normal course of business. The continuation of the Company as a going concern is dependent upon the ability of the Company to obtain necessary funding to continue operations. As of March 31, 2019, the Company has incurred an accumulated deficit of $445.1 million since inception and has not yet generated any revenue from operations. Additionally, the Company continues to expend cash to continue its research and development efforts. Management anticipates that its cash on hand as of March 31, 2019, grants and other cash inflows will be insufficient to fund its operations within one year from the financial statement issuance date and therefore, substantial doubt about the entity’s ability to continue as a going concern exists. These consolidated financial statements do not include any adjustments to the recoverability and classification of recorded asset amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company may seek additional funding through a combination of equity offerings, debt financings, government or other third-party funding, commercialization, marketing and distribution arrangements, other collaborations, strategic alliances and licensing arrangements and delay planned cash outlays or a combination thereof. Management cannot be certain that such events or a combination thereof can be achieved. 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 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.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	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 the Company 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 months ended March 31, 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, as defined in ASC 210-10-45-1 and ASC 210-10-45-2. 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). An investment security is considered to be impaired when a decline in fair value below its cost basis is determined to be other than temporary. The Company evaluates whether a decline in fair value of an investment security is below its cost basis is other than temporary using available evidence. In the event that the cost basis of the investment security exceeds its fair value, the Company evaluates, among other factors, the amount and duration of the period that the fair value is less than the cost basis, the financial health of and business outlook for the issuer, including industry and sector performance, and operational and financing cash flow factors, overall market conditions and trends, the Company’s intent to sell the investment security and whether it is more likely than not the Company would be required to sell the investment security before its anticipated recovery. If a decline in fair value is determined to be other than temporary, the Company records an impairment charge in the statement of operations and comprehensive loss and establishes a new cost basis in the investment. 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 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. 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. These costs have been netted against the proceeds of the equity issuances. Licenses and Patents Licenses and patent costs for technologies that are utilized in research and development and have no alternative future use are expensed as incurred. Costs related to the license of patents from third parties and internally developed patents are classified as research and development expenses. Legal costs related to patent applications and maintenance are classified as general and administrative expenses. 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. Where 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 March 31, 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. 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. 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 March 31, 2019 2018 Common Stock Equivalents: Number of shares Options to purchase common stock 6,780,896 5,662,800 Unvested shares of restricted stock units 222,187 217,186 Unvested shares of restricted stock — 29,413 Total common stock equivalents 7,003,083 5,909,399 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 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. Upon adoption, the Company recognized operating lease liabilities of $6.7 million and corresponding operating lease ROU assets, net of deferred rent and tenant allowances, of $5.0 million . See Note 7 - Leases for additional information.

CASH, CASH EQUIVALENTS AND REST

CASH, CASH EQUIVALENTS AND RESTRICTED CASH	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
CASH, CASH EQUIVALENTS AND RESTRICTED CASH	CASH, CASH EQUIVALENTS AND RESTRICTED CASH As of March 31, 2019, and December 31, 2018, respectively, the Company maintained $ 4.6 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 $1.1 million of restricted funds from the CPRIT account, leaving a balance of $3.1 million at March 31, 2019. For more information about the CPRIT grant, see Note 10. The remaining $ 1.5 million of restricted cash as of March 31, 2019 and the $1.6 million in 2018 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. March 31, 2019 December 31, 2018 (in thousands) Cash and cash equivalents (1) $ 42,274 $ 43,695 Restricted cash, noncurrent 4,585 4,973 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 46,859 $ 48,668 (1) As of March 31, 2019, and December 31, 2018, the Company invested approximately $31.2 million and $25.0 million , respectively, in cash equivalent instruments.

FAIR VALUE MEASUREMENTS AND INV

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES	FAI R VALU E MEASUREMENTS AND INVESTMENT SECURITIES Fair Value Measurement The Company follows ASC, Topic 820, Fair Value Measurements and Disclosures , or ASC 820, for application to financial assets. 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 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. 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 March 31, 2019 and December 31, 2018 : Fair Value Measurements at Reporting Date Using Balance at 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 $ 31,249 $ 31,249 $ — $ — Total Cash Equivalents $ 31,249 $ 31,249 $ — $ — Investment Securities: U.S. government agency-backed securities $ 4,745 $ — $ 4,745 $ — Corporate debt securities 26,465 — 26,465 — Total Investment Securities $ 31,210 $ — $ 31,210 $ — Fair Value Measurements at Reporting Date Using Balance at 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 March 31, 2019 and December 31, 2018: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value March 31, 2019 (in thousands) Investment Securities: U.S. government agency-backed securities $ 4,739 $ 6 $ — $ 4,745 Corporate debt securities 26,465 7 (7 ) 26,465 Total Investment Securities $ 31,204 $ 13 $ (7 ) $ 31,210 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value December 31, 2018 (in thousands) 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 March 31, 2019 , will reach maturity between April 2019 and November 2019 , with a weighted-average maturity date in June 2019.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERT Y AND EQUIPMENT Property and equipment consists of the following: March 31, 2019 December 31, 2018 Estimated Useful Lives (in thousands) Leasehold improvements 5 Years $ 21,633 $ 21,633 Lab equipment 5 Years 8,511 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 1,698 1,606 Equipment held under financing leases 5 Years 103 204 Software 3 Years 362 361 Total 35,902 35,869 Less: accumulated depreciation (16,713 ) (14,991 ) Property and equipment, net $ 19,189 $ 20,878 During the three months ended March 31, 2019 and 2018, the Company recorded $1.8 million and $1.4 million of depreciation expense, respectively. Leasehold improvements as of March 31, 2019 and December 31, 2018 includes $2.5 million related to costs incurred by the landlord.

LEASES

LEASES	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
LEASES	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. 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 March 31, 2019 (in thousands) Operating lease cost (1) $ 446 Short-term lease cost $ 35 Operating cash flow information: Cash paid for amounts included in the measurement of lease liabilities $ 530 (1) Includes right-of-use asset amortization of $312. Weighted-average remaining lease term and discount rate for operating leases are as follows: Three months ended March 31, 2019 Weighted-average remaining lease term 6.5 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) $ 1,596 $ 24 2020 1,147 31 2021 1,091 24 2022 1,124 — 2023 1,133 — 2024 and beyond 3,222 — Total lease payments 9,313 79 Less: Imputed interest (3,001 ) (16 ) Present value of lease liabilities $ 6,312 $ 63 (1) Excluding the 3 months ended March 31, 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 CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	3 Months Ended
	Mar. 31, 2019
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other liabilities consist of the following: March 31, 2019 December 31, 2018 (in thousands) Accrued construction costs $ 457 $ 457 Accrued payroll 1,943 3,430 Accrued patient treatment costs 1,967 2,053 Accrued manufacturing costs 204 546 Accrued professional services 1,227 235 Accrued obligations under material supply agreements 2,243 — Accrued other 2,348 1,868 Total accrued expenses and other current liabilities $ 10,389 $ 8,589

DEBT

DEBT	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
DEBT	DEBT Oxford Loan 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 March 31, 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

GRANT REVENUE	3 Months Ended
	Mar. 31, 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-month period ended March 31, 2019 and 2018, the Company recognized expenses and accrued revenue of $0.5 million and $0.2 million , respectively, for work performed under the CPRIT grant.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY On April 20, 2018 , the Company completed an underwritten public offering of 9,200,000 shares of its 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 with Jefferies LLC, or Jefferies, as sales agent, or the Jefferies Agreement, pursuant to which the Company may offer and sell, from time to time, through Jefferies, shares of the Company’s common stock having an aggregate offering price of up to $60.0 million . The shares will be offered and sold pursuant to the Company’s shelf registration statement on Form S-3. During the three months ended March 31, 2019, the Company received $4.6 million in proceeds, net of discounts and offering expenses totaling $0.2 million , and issued 1,350,652 shares of common stock pursuant to the Jefferies Agreement.

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED COMPENSATION PLANS	SHARE-BASED COMPENSATION PLANS The Company has four share-based compensation plans, which authorize 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. 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 plan, refer to Note 11 to the audited financial statements included the Annual Report. The following table summarizes the stock option activity for all stock plans during the three months ended March 31, 2019: Options and Inducement awards Outstanding at December 31, 2018 5,759,246 Granted 1,325,125 Exercised — Forfeited (303,475 ) Outstanding at March 31, 2019 6,780,896 Exercisable at March 31, 2019 2,865,439 The following table summarizes the stock award activity for all stock plans during the three months ended March 31, 2019: Restricted Stock Awards and Units Outstanding at December 31, 2018 246,155 Granted 30,000 Vested (41,031 ) Forfeited (12,937 ) Outstanding at March 31, 2019 222,187 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. There were no shares purchased by the ESPP in either of the three-month periods ended March 31, 2019 and 2018, respectively. As of March 31, 2019, there were 414,637 shares available for issuance under the ESPP. A summary of activity within the ESPP follows: Three months ended March 31, 2019 2018 (amounts in thousands) Deductions from employees $ 96 $ 49 Share-based compensation expense recognized $ 76 $ 36 Remaining share-based compensation expense $ 493 $ 244 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 implied volatilities from traded stocks of peer companies. 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: Three months ended March 31, 2019 2018 Risk-free interest rate 2.53 % 2.41 % Volatility 72.0 % 71.1 % Expected life (years) 6.08 6.08 Expected dividend yield — % — % Share-based compensation expense by classification for the three months ended March 31, 2019 and 2018 are as follows: Three Months Ended March 31, 2019 2018 (in thousands) Research and development $ 1,065 $ 1,669 General and administrative 1,071 1,936 Total $ 2,136 $ 3,605 At March 31, 2019 , total compensation cost not yet recognized was $15.5 million and the weighted-average period over which this amount is expected to be recognized is 2.63 years.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS Subsequent to March 31, 2019, the Company executed an additional operating lease for office space and expects to record a right -of-use asset and lease liability of approximately $1.4 million when the lease commences in the second quarter of 2019.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 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. 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 derivative cause of action until reinstated on motion of the parties.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 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 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 the Company 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 months ended March 31, 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, as defined in ASC 210-10-45-1 and ASC 210-10-45-2. 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). An investment security is considered to be impaired when a decline in fair value below its cost basis is determined to be other than temporary. The Company evaluates whether a decline in fair value of an investment security is below its cost basis is other than temporary using available evidence. In the event that the cost basis of the investment security exceeds its fair value, the Company evaluates, among other factors, the amount and duration of the period that the fair value is less than the cost basis, the financial health of and business outlook for the issuer, including industry and sector performance, and operational and financing cash flow factors, overall market conditions and trends, the Company’s intent to sell the investment security and whether it is more likely than not the Company would be required to sell the investment security before its anticipated recovery. If a decline in fair value is determined to be other than temporary, the Company records an impairment charge in the statement of operations and comprehensive loss and establishes a new cost basis in the investment.
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
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.
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. These costs 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. Where 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 March 31, 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. 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.
New Accounting Requirements and Disclosures	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 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. Upon adoption, the Company recognized operating lease liabilities of $6.7 million and corresponding operating lease ROU assets, net of deferred rent and tenant allowances, of $5.0 million . See Note 7 - Leases for additional information.

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Earnings Per Share, Potentially Dilutive Securities	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 March 31, 2019 2018 Common Stock Equivalents: Number of shares Options to purchase common stock 6,780,896 5,662,800 Unvested shares of restricted stock units 222,187 217,186 Unvested shares of restricted stock — 29,413 Total common stock equivalents 7,003,083 5,909,399

CASH, CASH EQUIVALENTS AND RE_2

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash, Reconciliation	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. March 31, 2019 December 31, 2018 (in thousands) Cash and cash equivalents (1) $ 42,274 $ 43,695 Restricted cash, noncurrent 4,585 4,973 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 46,859 $ 48,668 (1) As of March 31, 2019, and December 31, 2018, the Company invested approximately $31.2 million and $25.0 million , respectively, in cash equivalent instruments.

FAIR VALUE MEASUREMENTS AND I_2

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Investment Securities Measured at Fair Value on a Recurring Basis	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 March 31, 2019 and December 31, 2018 : Fair Value Measurements at Reporting Date Using Balance at 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 $ 31,249 $ 31,249 $ — $ — Total Cash Equivalents $ 31,249 $ 31,249 $ — $ — Investment Securities: U.S. government agency-backed securities $ 4,745 $ — $ 4,745 $ — Corporate debt securities 26,465 — 26,465 — Total Investment Securities $ 31,210 $ — $ 31,210 $ — Fair Value Measurements at Reporting Date Using Balance at 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 $ —
Available-For-Sale Securities	Investment securities, all classified as available-for-sale, consisted of the following as of March 31, 2019 and December 31, 2018: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value March 31, 2019 (in thousands) Investment Securities: U.S. government agency-backed securities $ 4,739 $ 6 $ — $ 4,745 Corporate debt securities 26,465 7 (7 ) 26,465 Total Investment Securities $ 31,204 $ 13 $ (7 ) $ 31,210 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value December 31, 2018 (in thousands) 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

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and equipment consists of the following: March 31, 2019 December 31, 2018 Estimated Useful Lives (in thousands) Leasehold improvements 5 Years $ 21,633 $ 21,633 Lab equipment 5 Years 8,511 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 1,698 1,606 Equipment held under financing leases 5 Years 103 204 Software 3 Years 362 361 Total 35,902 35,869 Less: accumulated depreciation (16,713 ) (14,991 ) Property and equipment, net $ 19,189 $ 20,878

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Components of Lease Cost	Components of lease cost are as follows: Three months ended March 31, 2019 (in thousands) Operating lease cost (1) $ 446 Short-term lease cost $ 35 Operating cash flow information: Cash paid for amounts included in the measurement of lease liabilities $ 530 (1) Includes right-of-use asset amortization of $312. Weighted-average remaining lease term and discount rate for operating leases are as follows: Three months ended March 31, 2019 Weighted-average remaining lease term 6.5 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) $ 1,596 $ 24 2020 1,147 31 2021 1,091 24 2022 1,124 — 2023 1,133 — 2024 and beyond 3,222 — Total lease payments 9,313 79 Less: Imputed interest (3,001 ) (16 ) Present value of lease liabilities $ 6,312 $ 63 (1) Excluding the 3 months ended March 31, 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) $ 1,596 $ 24 2020 1,147 31 2021 1,091 24 2022 1,124 — 2023 1,133 — 2024 and beyond 3,222 — Total lease payments 9,313 79 Less: Imputed interest (3,001 ) (16 ) Present value of lease liabilities $ 6,312 $ 63 (1) Excluding the 3 months ended March 31, 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

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	3 Months Ended
	Mar. 31, 2019
Payables and Accruals [Abstract]
Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consist of the following: March 31, 2019 December 31, 2018 (in thousands) Accrued construction costs $ 457 $ 457 Accrued payroll 1,943 3,430 Accrued patient treatment costs 1,967 2,053 Accrued manufacturing costs 204 546 Accrued professional services 1,227 235 Accrued obligations under material supply agreements 2,243 — Accrued other 2,348 1,868 Total accrued expenses and other current liabilities $ 10,389 $ 8,589

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option Activity	The following table summarizes the stock option activity for all stock plans during the three months ended March 31, 2019: Options and Inducement awards Outstanding at December 31, 2018 5,759,246 Granted 1,325,125 Exercised — Forfeited (303,475 ) Outstanding at March 31, 2019 6,780,896 Exercisable at March 31, 2019 2,865,439
Stock Award Activity For All Stock Plans	The following table summarizes the stock award activity for all stock plans during the three months ended March 31, 2019: Restricted Stock Awards and Units Outstanding at December 31, 2018 246,155 Granted 30,000 Vested (41,031 ) Forfeited (12,937 ) Outstanding at March 31, 2019 222,187
ESPP Activity	A summary of activity within the ESPP follows: Three months ended March 31, 2019 2018 (amounts in thousands) Deductions from employees $ 96 $ 49 Share-based compensation expense recognized $ 76 $ 36 Remaining share-based compensation expense $ 493 $ 244
Valuation Assumptions	The fair value of the option grants has been estimated, with the following weighted-average assumptions: Three months ended March 31, 2019 2018 Risk-free interest rate 2.53 % 2.41 % Volatility 72.0 % 71.1 % Expected life (years) 6.08 6.08 Expected dividend yield — % — %
Share-Based Compensation Expense by Classification	Share-based compensation expense by classification for the three months ended March 31, 2019 and 2018 are as follows: Three Months Ended March 31, 2019 2018 (in thousands) Research and development $ 1,065 $ 1,669 General and administrative 1,071 1,936 Total $ 2,136 $ 3,605

ORGANIZATION AND BUSINESS DES_2

ORGANIZATION AND BUSINESS DESCRIPTION (Details)	12 Months Ended
	Dec. 31, 2017subsidiary
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of wholly-owned subsidiaries formed	2

BASIS OF PRESENTATION (Details)

BASIS OF PRESENTATION (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 445,076	$ 420,548

SIGNIFICANT ACCOUNTING POLICI_4

SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Operating lease liabilities	$ 6,312
Right-of-use assets	$ 4,655		$ 0
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
Accounting Standards Update 2016-02 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Operating lease liabilities		$ 6,700
Right-of-use assets		$ 5,000

SIGNIFICANT ACCOUNTING POLICI_5

SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share, Potentially Dilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	7,003,083	5,909,399
Options to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	6,780,896	5,662,800
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)	222,187	217,186
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	29,413

CASH, CASH EQUIVALENTS AND RE_3

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 4,585	$ 4,973
Release of restricted cash	1,100
Grant from CPRIT
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	3,100		$ 4,200
Held in escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 1,500	$ 1,600

CASH, CASH EQUIVALENTS AND RE_4

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 42,274	$ 43,695
Restricted cash, noncurrent	4,585	4,973
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	46,859	48,668	$ 37,725	$ 45,029
Cash equivalent instruments	$ 31,200	$ 25,000

FAIR VALUE MEASUREMENTS AND I_3

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	$ 31,249	$ 24,953
Total Investment Securities	31,210	49,304
U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	4,745	7,383
Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	26,465	41,921
Money market funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	31,249	24,953
Quoted prices in active markets for identical assets (Level 1)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	31,249	24,953
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
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	31,249	24,953
Significant other observable inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Total Investment Securities	31,210	49,304
Significant other observable inputs (Level 2) | U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	4,745	7,383
Significant other observable inputs (Level 2) | Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	26,465	41,921
Significant other observable inputs (Level 2) | Money market funds
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
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	$ 0	$ 0

FAIR VALUE MEASUREMENTS AND I_4

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 31,204	$ 49,350
Gross Unrealized Gains	13	2
Gross Unrealized Losses	(7)	(48)
Aggregate Estimated Fair Value	31,210	49,304
U.S. government agency-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,739	7,382
Gross Unrealized Gains	6	2
Gross Unrealized Losses	0	(1)
Aggregate Estimated Fair Value	4,745	7,383
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,465	41,968
Gross Unrealized Gains	7	0
Gross Unrealized Losses	(7)	(47)
Aggregate Estimated Fair Value	$ 26,465	$ 41,921

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total	$ 35,902		$ 35,869
Less: accumulated depreciation	(16,713)		(14,991)
Property and equipment, net	19,189		20,878
Depreciation and amortization expense	1,787	$ 1,426
Leasehold improvements	2,500		2,500
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	$ 8,511		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	$ 1,698		1,606
Equipment held under financing leases
Property, Plant and Equipment [Line Items]
Total	$ 103		204
Estimated Useful Lives	5 years
Software
Property, Plant and Equipment [Line Items]
Total	$ 362		$ 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 - Components of Lease Co

LEASES - Components of Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Operating lease cost	$ 446
Short-term lease cost	35
Operating cash flow information:
Cash paid for amounts included in the measurement of lease liabilities	$ 530
Weighted-average remaining lease term	6 years 6 months
Weighted-average discount rate	12.10%
Amortization of right-of-use assets	$ 312	$ 0

LEASES - Maturity of Operating

LEASES - Maturity of Operating Lease Liabilities (Details) $ in Thousands	Mar. 31, 2019USD ($)
Operating Leases
2019	$ 1,596
2020	1,147
2021	1,091
2022	1,124
2023	1,133
2024 and beyond	3,222
Total lease payments	9,313
Less: Imputed interest	(3,001)
Present value of lease liabilities	6,312
Financing Leases
2019	24
2020	31
2021	24
2022	0
2023	0
2024 and beyond	0
Total lease payments	79
Less: Imputed interest	(16)
Present value of lease liabilities	$ 63

LEASES - Minimum Lease Payments

LEASES - Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
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 CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued construction costs	$ 457	$ 457
Accrued payroll	1,943	3,430
Accrued patient treatment costs	1,967	2,053
Accrued manufacturing costs	204	546
Accrued professional services	1,227	235
Accrued obligations under material supply agreements	2,243	0
Accrued other	2,348	1,868
Total accrued expenses and other current liabilities	$ 10,389	$ 8,589

DEBT (Details)

DEBT (Details) - USD ($)	Dec. 21, 2017	Mar. 31, 2019	Mar. 31, 2018
Line of Credit Facility [Line Items]
Amortized deferred financing costs		$ 218,000	$ 219,000
Oxford Loan
Line of Credit Facility [Line Items]
Borrowings	$ 35,000,000
Expenses related to the loan	100,000
Final facility charge	$ 3,000,000
Amortized deferred financing costs		$ 200,000	$ 200,000

GRANT REVENUE (Details)

GRANT REVENUE (Details) - USD ($) $ in Thousands	Aug. 09, 2017	Mar. 31, 2019	Mar. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues		$ 516	$ 154
Grants | CPRIT
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 16,900	$ 516	$ 154

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 05, 2018	Apr. 20, 2018	Mar. 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Common stock, issued (in shares)			45,643,060	44,242,059
Underwritten public offering
Subsidiary, Sale of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)		9,200,000
Price per share (in dollars per share)		$ 7.50
Aggregate offering size		$ 69
Net proceeds from offering		$ 64.7
Jefferies LLC
Subsidiary, Sale of Stock [Line Items]
Aggregate offering size	$ 60		$ 4.6
Discounts and offering expenses			$ 0.2
Common stock, issued (in shares)			1,350,652

SHARE-BASED COMPENSATION PLAN_2

SHARE-BASED COMPENSATION PLANS - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)planshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans | plan	4
Compensation cost not yet recognized | $	$ 15.5
Period for recognition	2 years 7 months 17 days
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Expiration period	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%
Capital shares reserved for future issuance (in shares)	414,637

SHARE-BASED COMPENSATION PLAN_3

SHARE-BASED COMPENSATION PLANS - Stock Option Activity (Details) - Employee Stock Options And Inducement Option Awards	3 Months Ended
	Mar. 31, 2019shares
Options and Inducement awards
Outstanding at beginning of period (in shares)	5,759,246
Granted (in shares)	1,325,125
Exercised (in shares)	0
Forfeited (in shares)	(303,475)
Outstanding at end of period (in shares)	6,780,896
Exercisable (in shares)	2,865,439

SHARE-BASED COMPENSATION PLAN_4

SHARE-BASED COMPENSATION PLANS - Stock Award Activity For All Stock Plans (Details) - Restricted Stock Awards and Units	3 Months Ended
	Mar. 31, 2019shares
Restricted Stock Awards and Units
Beginning balance (in shares)	246,155
Granted (in shares)	30,000
Vested (in shares)	(41,031)
Forfeited (in shares)	(12,937)
Ending balance (in shares)	222,187

SHARE-BASED COMPENSATION PLAN_5

SHARE-BASED COMPENSATION PLANS - ESPP Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 2,136	$ 3,605
Remaining share-based compensation expense	2,136	3,605
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deductions from employees	96	49
Share-based compensation expense recognized	76	36
Remaining share-based compensation expense	$ 493	$ 244

SHARE-BASED COMPENSATION PLAN_6

SHARE-BASED COMPENSATION PLANS - Valuation Assumptions (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.53%	2.41%
Volatility	72.00%	71.10%
Expected life (years)	6 years 29 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

SHARE-BASED COMPENSATION PLAN_7

SHARE-BASED COMPENSATION PLANS - Expense by Classification (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 2,136	$ 3,605
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	1,065	1,669
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 1,071	$ 1,936

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Operating lease liabilities		$ 6,312
Right-of-use assets		$ 4,655	$ 0
Scenario, Forecast | Subsequent Event
Subsequent Event [Line Items]
Operating lease liabilities	$ 1,400
Right-of-use assets	$ 1,400

COMMITMENTS AND CONTINGENCIES (

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