Bellicum Pharmaceuticals (BLCM) 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Bellicum Pharmaceuticals, Inc.
Entity Central Index Key	1,358,403
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		43,361,159
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 53,027	$ 38,839
Investment securities, available for sale - short-term	59,720	60,057
Accounts receivable, interest and other receivables	538	320
Prepaid expenses and other current assets	2,254	2,434
Total current assets	115,539	101,650
Investment securities, available for sale - long-term	0	1,368
Property and equipment, net	22,402	25,942
Restricted cash	5,635	6,190
Other assets	396	378
TOTAL ASSETS	143,972	135,528
Current liabilities:
Accounts payable	1,843	3,287
Accrued expenses and other current liabilities	8,837	6,392
Current portion of capital lease obligations	37	31
Current portion of deferred revenue	3,295	2,049
Current portion of deferred rent	411	397
Total current liabilities	14,423	12,156
Long-term liabilities:
Long-term debt, net of deferred financing costs	35,609	34,946
Capital lease obligations	102	131
Deferred revenue	0	2,054
Deferred rent	1,381	1,593
TOTAL LIABILITIES	51,515	50,880
Commitments and contingencies: (Note 12)
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 September 30, 2018 and December 31, 2017, 44,028,622 shares issued and 43,351,159 shares outstanding at September 30, 2018; 33,962,640 shares issued and 33,285,177 shares outstanding at December 31, 2017	440	340
Treasury stock: 677,463 shares held at September 30, 2018 and December 31, 2017	(5,056)	(5,056)
Additional paid-in capital	490,436	411,922
Accumulated other comprehensive loss	(35)	(46)
Accumulated deficit	(393,328)	(322,512)
Total stockholders’ equity	92,457	84,648
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 143,972	$ 135,528

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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)	44,028,622	33,962,640
Common stock, outstanding (in shares)	43,351,159	33,285,177
Treasury stock, shares (in shares)	677,463	677,463

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
REVENUES
Revenues	$ 292	$ 126	$ 808	$ 254
OPERATING EXPENSES
Research and development	16,413	18,101	51,361	51,355
General and administrative	6,968	4,579	18,027	15,992
Total operating expenses	23,520	22,831	69,707	68,196
Loss from operations	(23,228)	(22,705)	(68,899)	(67,942)
OTHER INCOME (EXPENSE):
Interest income	492	284	1,196	788
Interest expense	(1,065)	(1,010)	(3,113)	(2,707)
Total other expense	(573)	(726)	(1,917)	(1,919)
NET LOSS	$ (23,801)	$ (23,431)	$ (70,816)	$ (69,861)
Net loss per common share attributable to common shareholders, basic and diluted (in dollars per share)	$ (0.55)	$ (0.71)	$ (1.81)	$ (2.24)
Weighted-average shares outstanding, basic and diluted (in shares)	43,334,727	33,178,611	39,168,559	31,204,521
Other comprehensive income (loss):
Unrealized gain (loss) on investment securities	$ 33	$ 22	$ 11	$ (1)
Comprehensive loss	(23,768)	(23,409)	(70,805)	(69,862)
Grants
REVENUES
Revenues	292	126	808	254
License fees
OPERATING EXPENSES
License fees	$ 139	$ 151	$ 319	$ 849

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (70,816)	$ (69,861)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	10,854	10,217
Depreciation expense	4,916	2,524
Amortization of premium on investment securities, net	118	214
Amortization of lease liability	(198)	(71)
Amortization of deferred financing costs	663	604
Changes in operating assets and liabilities:
Receivables	(218)	(134)
Prepaid expenses and other assets	162	(685)
Accounts payable	(1,444)	(923)
Accrued liabilities and other	2,390	(2,046)
Deferred revenue	(808)	0
NET CASH USED IN OPERATING ACTIVITIES	(54,381)	(60,161)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities	(50,641)	(36,283)
Proceeds from sale of investment securities	52,239	45,536
Purchases of property and equipment	(1,321)	(10,554)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	277	(1,301)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock offering, net of offering costs	64,665	64,568
Proceeds from exercise of stock options	2,996	1,453
Proceeds from issuance of common stock - ESPP	99	167
Proceeds from notes payable	0	10,000
Payment of debt issuance costs	0	(75)
Payment on capital lease obligations	(23)	(16)
NET CASH PROVIDED BY FINANCING ACTIVITIES	67,737	76,097
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	13,633	14,635
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT BEGINNING OF PERIOD	45,029	42,780
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD	58,662	57,415
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	2,451	2,014
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Purchases of property and equipment in accounts payables and accrued liabilities	55	1,695
Accrued debt issuance costs	0	695
Capital lease obligations incurred for equipment	$ 0	$ 23

ORGANIZATION AND BUSINESS DESCR

ORGANIZATION AND BUSINESS DESCRIPTION	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION AND BUSINESS DESCRIPTION	ORGANIZATION AND BUSINESS DESCRIPTION Bellicum Pharmaceuticals, Inc., (“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, TCR, 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, for the purpose of developing and commercializing product candidates in Europe. Bellicum, Bellicum Pharma Limited and Bellicum Europe GmbH are collectively referred to herein as the “Company”.

BASIS OF PRESENTATION

BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2018
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 (“GAAP”) and follow the requirements of the U.S. Securities and Exchange Commission (“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, 2017 (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 (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company has not generated any revenue from product sales to date and, if the Company does not successfully obtain regulatory approval and commercialize any of its product candidates, the Company will not be able to generate product revenue or achieve profitability. As of September 30, 2018, the Company had an accumulated deficit of $393.3 million . The Company is subject to risks common to companies in the biotechnology industry and the future success of the Company is dependent on its ability to successfully complete the development of, and obtain regulatory approval for, its product candidates, manage the growth of the organization, obtain additional financing necessary in order to develop, launch and commercialize its product candidates, and compete successfully with other companies in its industry.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Use of Estimates The preparation of the 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, neither of which have had any material activity to date. 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, 2018 and 2017 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. 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. Rent and Deferred Rent The Company recognizes rent expense for leases with increasing annual rents on a straight-line basis over the term of the lease. The amount of rent expense in excess of cash payments is classified as deferred rent. Any lease incentives received are deferred and amortized over the term of the lease. 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 (“FDIC”) and Security Investor Protection Corporation (“SIPC”). 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 September 30, 2018 and December 31, 2017, on the Company’s balance sheet was comprised of the net unrealized holding gains and losses on the Company’s investment securities. 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 September 30, 2018 2017 Common Stock Equivalents: Number of shares Options to purchase common stock 5,868,433 5,299,158 Unvested shares of restricted stock units 205,155 96,250 Unvested shares of restricted stock 14,707 44,119 Total common stock equivalents 6,088,295 5,439,527 New Accounting Requirements and Disclosures In February 2016, the FASB issued ASU 2016-02, “Leases” , which established new ASC Topic 842 (“ASC 842”), to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. Under the new guidance, a lessee will be required to recognize assets and liabilities for leases with lease terms of more than 12 months. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, unlike current GAAP which requires only capital leases to be recognized on the balance sheet, the new standard will require both types of leases to be recognized on the balance sheet. ASC 842 also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. ASC 842 was previously required to be adopted using the modified retrospective approach. However, in July 2018, the FASB issued ASU 2018-11, which allows for retrospective application with the recognition of a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Under this option, entities would not need to apply ASC 842 (along with its disclosure requirements) to the comparative prior periods presented. ASC 842 is effective for the Company in the first quarter of 2019 and management expects that most of its operating leases (primarily office space) will be recognized as operating lease liabilities and right of use assets on its balance sheet. Management is continuing to evaluate the impact that the adoption of this standard will have on the consolidated financial statements but currently believe it is likely that the Company will elect to adopt certain of the optional practical expedients, including the package of practical expedients, which, among other things, gives the option to not reassess: 1) whether expired or existing contracts are or contain leases; 2) the lease classification for expired or existing leases; and 3) initial direct costs for existing leases. In 2018, the FASB issued ASU No. 2018-07, “ Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting”, which changes the measurement date for share-based awards to the grant date, instead of the previous requirement to remeasure the awards through the performance completion date. ASU No. 2018-07 is effective for the Company for fiscal years beginning after December 31, 2018, including interim periods within that fiscal year. Early adoption is permitted. The Company does not believe adopting ASU No. 2018-07 will have a material impact on its consolidated financial statements. In 2018, the FASB issued ASU No. 2018-13, “ Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”, which modifies fair value disclosures and removes some disclosure requirements for both public and private companies. In addition, public companies are subject to some new disclosure requirements which requires to disclose the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU No. 2018-13 is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not believe adopting ASU No. 2018-13 will have a material impact on its consolidated financial statements.

CASH, CASH EQUIVALENTS AND REST

CASH, CASH EQUIVALENTS AND RESTRICTED CASH	9 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
CASH, CASH EQUIVALENTS AND RESTRICTED CASH	CASH, CASH EQUIVALENTS AND RESTRICTED CASH As of September 30, 2018, and December 31, 2017, respectively, the Company maintained $ 5.6 million and $ 6.2 million as restricted cash. During 2017, the Company received $4.2 million from the Cancer Prevention and Research Institute of Texas, or “CPRIT”, which 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. During the nine months ended September 30, 2018, CPRIT authorized the release of $88,000 of restricted funds from the CPRIT account, leaving a balance of $4.1 million at September 30, 2018. No funds were released during the three months ended September 30, 2018. For more information about the CPRIT grant, see Note 9. The remaining $ 1.5 million of restricted cash as of September 30, 2018 and the $2.0 million in 2017 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, 2018 December 31, 2017 (in thousands) Cash and cash equivalents (1) $ 53,027 $ 38,839 Restricted cash, noncurrent 5,635 6,190 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 58,662 $ 45,029 (1) As of September 30, 2018, and December 31, 2017, the Company invested approximately $37.1 million and $25.6 million , respectively, in cash equivalent instruments.

FAIR VALUE MEASUREMENTS AND INV

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 and December 31, 2017 : Fair Value Measurements at Reporting Date 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 $ 37,085 $ 37,085 $ — $ — Total Cash Equivalents $ 37,085 $ 37,085 $ — $ — Investment Securities: U.S. government agency-backed securities $ 15,930 $ — $ 15,930 $ — Corporate debt securities 43,790 — 43,790 — Total Investment Securities $ 59,720 $ — $ 59,720 $ — Fair Value Measurements at Reporting Date 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 $ 25,550 $ 25,550 $ — $ — Total Cash Equivalents $ 25,550 $ 25,550 $ — $ — Investment Securities: U.S. government agency-backed securities $ 22,604 $ — $ 22,604 $ — Corporate debt securities 38,821 — 38,821 — Total Investment Securities $ 61,425 $ — $ 61,425 $ — 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, 2018 and December 31, 2017: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value September 30, 2018 (in thousands) Investment Securities: U.S. government agency-backed securities $ 15,944 $ — $ (14 ) $ 15,930 Corporate debt securities 43,811 1 (22 ) 43,790 Total Investment Securities $ 59,755 $ 1 $ (36 ) $ 59,720 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value December 31, 2017 (in thousands) U.S. government agency-backed securities $ 22,632 $ — $ (28 ) $ 22,604 Corporate debt securities 38,839 13 (31 ) 38,821 Total $ 61,471 $ 13 $ (59 ) $ 61,425 The Company's investment securities as of September 30, 2018 , will reach maturity between October 2018 and September 2019 , with a weighted-average maturity date in February 2019.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERT Y AND EQUIPMENT Property and equipment consists of the following: September 30, 2018 December 31, 2017 Estimated Useful Lives (in thousands) Leasehold improvements 5 Years $ 21,633 $ 21,462 Lab equipment 5 Years 8,373 7,766 Office furniture 5 Years 1,702 1,701 Manufacturing equipment 5 Years 1,891 1,815 Computer and office equipment 3 to 5 Years 1,431 1,074 Equipment held under capital leases 5 Years 204 204 Software 3 Years 378 216 Total 35,612 34,238 Less: accumulated depreciation (13,210 ) (8,296 ) Property and equipment, net $ 22,402 $ 25,942 During the nine months ended September 30, 2018 and 2017, the Company recorded $4.9 million and $2.5 million of depreciation expense, respectively. Leasehold improvements as of September 30, 2018 and December 31, 2017 includes $2.5 million related to costs incurred by the landlord.

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	9 Months Ended
	Sep. 30, 2018
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: September 30, 2018 December 31, 2017 (in thousands) Accrued construction costs $ 457 $ 565 Accrued payroll 2,619 2,682 Accrued patient treatment costs 2,104 1,392 Accrued sponsored research 937 85 Accrued manufacturing costs 340 370 Accrued other 2,380 1,298 Total accrued expenses and other current liabilities $ 8,837 $ 6,392

DEBT

DEBT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Hercules Loan On March 10, 2016, the Company, entered into a Loan and Security Agreement with Hercules Capital, Inc. Hercules Technology II, L.P., and Hercules Technology III, L.P., or collectively, Hercules, as a lender, under which the Company borrowed $15.0 million . The Company borrowed an additional $5.0 million and $10.0 million on September 15, 2016 and March 8, 2017, respectively. The total debt was secured by a lien covering substantially all of the Company's assets, excluding intellectual property, but including proceeds from the sale, license, or disposition of intellectual property. The Company paid expenses related to the loan of $0.3 million which, along with a final facility charge of $2.1 million was recorded as deferred financing costs. Interest expense in the three and nine months ended September 30, 2017 included $0.2 million and $0.6 million , respectively, of amortized deferred financing costs. For additional information about the Hercules Loan Agreement, see Note 8 to the audited financial statements in the Annual Report. On December 21, 2017, the Company repaid the outstanding balance, accrued interest and final facility charges totaling $32.9 million , which included a prepayment charge of $0.6 million with proceeds from a new loan from Oxford Finance, LLC, discussed below. Oxford Loan On December 21, 2017 (the “Oxford Closing Date”), the Company entered into a loan and security agreement (the “Oxford Loan Agreement”) with Oxford Finance LLC, as the collateral agent and a lender, pursuant to which the Company borrowed $35.0 million in a single term loan (the “Oxford Loan”) on the Oxford Closing Date. As discussed above, on the Oxford Closing Date, the Company used approximately $32.9 million of the proceeds from the Oxford Loan to repay its indebtedness to Hercules. 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, which offset 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. During the three and nine-month periods ended September 30, 2018, interest expense included $0.3 million and $0.7 million , respectively, of amortized deferred financing costs. 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	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
GRANT REVENUE	GRANT REVENUE Cancer Research Grant Contract During 2017, the Company entered into a Cancer Research Grant Contract (the “Agreement”) with CPRIT, pursuant to which CPRIT awarded a grant (the “Award”) of approximately $16.9 million to the Company to fund development of rivo-cel for hematologic cancer. The Award is contingent upon funds being available during the term of the Agreement and subject to CPRIT’s ability to perform its obligations under the Agreement. For additional information about the Agreement, see Note 9 to the audited financial statements in the Annual Report. During 2017, the Company received $4.2 million in advance funding from CPRIT, which was recorded as deferred revenue. During the three and nine-month periods 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. NIH Grant During 2013, the Company entered into a grant agreement with the National Institute of Health, or NIH. The grant was a modular multi-year grant with funds being awarded each year based on the progress of the program being funded. The Company recorded grant revenue of $0.1 million in the nine months ended September 30, 2017. The grant expired on March 31, 2017.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY On March 29, 2017, the Company completed an underwritten public offering of 5,750,000 shares of its common stock at a price of $12.00 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 $64.6 million . These costs have been recorded as a reduction of the proceeds received from the offering. 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 . These costs have been recorded as a reduction of the proceeds received from the offering.

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS	9 Months Ended
	Sep. 30, 2018
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. At September 30, 2018 , the Company had share-based awards outstanding under four share-based compensation plans, as follows: 2006 Stock Option Plan The 2006 Stock Option Plan (the “2006 Plan”) provided for the issuance of incentive and non-qualified stock options to employees, including officers, non-employee directors and consultants to the Company. As of September 30, 2018, there were 96,293 shares of common stock reserved for issuance pursuant to outstanding options granted under the 2006 Plan. The 2006 Plan was terminated by the Board in October 2014. 2011 Stock Option Plan The 2011 Stock Option Plan (the “2011 Plan”) provided for the issuance of incentive and non-qualified stock options to employees, including officers, non-employee directors and consultants to the Company. As of September 30, 2018, there were 825,828 shares of common stock reserved for issuance pursuant to outstanding options granted under the 2011 Plan. The 2011 Plan replaced the 2006 Plan. The 2011 Plan terminated upon the effectiveness of the 2014 Plan described below. 2014 Equity Incentive Plan The 2014 Equity Incentive Plan (the “2014 Plan”) became effective in December 2014 upon the closing of the IPO. The 2014 Plan provides for the issuance of equity awards, including incentive and non-qualified stock options and restricted stock awards to employees, including officers, non-employee directors and consultants to the Company or its affiliates. The 2014 Plan also provides for the grant of performance cash awards and performance-based stock awards. On June 14, 2017, the stockholders approved an amendment to the 2014 Plan to, among other things, increase the number of shares of common stock authorized for issuance under the 2014 Plan by 3,100,000 shares and eliminate the prior provision in the 2014 Plan that allowed the Company’s Board of Directors to reprice stock options without stockholder approval. The aggregate number of shares of common stock that are authorized for issuance under the 2014 Plan is 6,090,354 shares, plus any shares subject to outstanding options that were granted under the 2011 Plan or 2006 Plan that are forfeited, terminated, expired or are otherwise not issued. As of September 30, 2018, there were 5,166,174 outstanding awards, comprised of 4,021,312 options, 925,000 inducement option awards, 14,707 shares of restricted stock, 51,250 inducement restricted stock units and 153,905 restricted stock units outstanding. There were 1,900,685 shares available for issuance under the 2014 Plan at September 30, 2018. 2014 Employee Stock Purchase Plan The 2014 Employee Stock Purchase Plan (the “ESPP”) provides for eligible Company employees, as defined by the ESPP, to be given an opportunity to purchase the Company's common stock at a discount, through payroll deductions, with stock purchases being made upon defined purchase dates. The ESPP authorizes the issuance of up to 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 13,779 and 19,204 shares purchased by the ESPP in the nine-month periods ended September 30, 2018 and 2017, respectively. There were no ESPP purchases in the three-month periods ended September 30, 2018 and 2017. As of September 30, 2018, there were 446,248 shares available for issuance under the ESPP. A summary of activity within the ESPP follows: Nine months ended September 30, 2018 2017 (amounts in thousands) Deductions from employees $ 168 $ 226 Share-based compensation expense recognized $ 111 $ 183 Remaining share-based compensation expense $ 285 $ 311 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: Nine months ended September 30, 2018 2017 Risk-free interest rate 2.63 % 2.06 % Volatility 72.1 % 71.7 % Expected life (years) 6.08 6.08 Expected dividend yield — % — % Share-based compensation expense by classification for the nine months ended September 30, 2018 and 2017 are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 (in thousands) (in thousands) Research and development $ 1,606 $ 1,802 $ 4,898 $ 4,870 General and administrative 2,070 1,861 5,956 5,347 Total $ 3,676 $ 3,663 $ 10,854 $ 10,217 At September 30, 2018 , total compensation cost not yet recognized was $17.6 million and the weighted-average period over which this amount is expected to be recognized is 2.46 years. The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2018: Options and Inducement awards Weighted- (in years) Weighted- Aggregate Intrinsic Value (1) (in thousands) Outstanding at December 31, 2017 5,286,472 $ 12.35 7.35 $ 7,223 Granted (2) 1,965,191 $ 7.83 Exercised (837,392 ) $ 3.58 $ 4,225 Forfeited (545,838 ) $ 16.27 Outstanding at September 30, 2018 5,868,433 $ 11.72 7.80 $ 1,794 Exercisable at September 30, 2018 2,929,150 $ 13.62 6.55 $ 1,658 (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2017 and September 30, 2018. (2) Includes 295,000 of inducement option awards granted in 2018. The following table summarizes the stock award activity for all stock plans during the nine months ended September 30, 2018: Restricted Stock Awards and Units Aggregate Intrinsic Value (1) (in thousands) December 31, 2017 (2) 140,663 $ 1,183 Granted (3) 161,250 Vested (38,770 ) $ 342 Forfeited (43,281 ) Outstanding at September 30, 2018 219,862 $ 1,354 (1) The aggregate intrinsic value is calculated as the fair value of restricted stock and restricted stock units at December 31, 2017 and September 30, 2018. (2) At December 31, 2017, there were 29,413 shares of restricted common stock and 111,250 restricted stock units outstanding. (3) Includes 40,000 of inducement restricted stock units granted during 2018.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES 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 (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 and motions were filed by putative class members for appointment as lead plaintiff and approval of lead counsel. The District Court has yet to rule on the motions. 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.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On October 5, 2018, the Company entered into an Open Market Sale Agreement SM with Jefferies LLC, as sales agent, 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. The Company will pay Jefferies LLC a commission of up to 3.0% of the aggregate gross proceeds from each sale of shares, reimburse certain legal fees and disbursements and provide Jefferies LLC with customary indemnification and contribution rights. The Sales Agreement may be terminated by Jefferies LLC or the Company at any time upon notice to the other party.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2018
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 (“GAAP”) and follow the requirements of the U.S. Securities and Exchange Commission (“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, 2017 (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 (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company has not generated any revenue from product sales to date and, if the Company does not successfully obtain regulatory approval and commercialize any of its product candidates, the Company will not be able to generate product revenue or achieve profitability. As of September 30, 2018, the Company had an accumulated deficit of $393.3 million . The Company is subject to risks common to companies in the biotechnology industry and the future success of the Company is dependent on its ability to successfully complete the development of, and obtain regulatory approval for, its product candidates, manage the growth of the organization, obtain additional financing necessary in order to develop, launch and commercialize its product candidates, and compete successfully with other companies in its industry.
Use of Estimates	Use of Estimates The preparation of the 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, neither of which have had any material activity to date. 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, 2018 and 2017 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.
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.
Rent and Deferred Rent	Rent and Deferred Rent The Company recognizes rent expense for leases with increasing annual rents on a straight-line basis over the term of the lease. The amount of rent expense in excess of cash payments is classified as deferred rent. Any lease incentives received are deferred and amortized over the term of the lease.
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 (“FDIC”) and Security Investor Protection Corporation (“SIPC”). 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 September 30, 2018 and December 31, 2017, on the Company’s balance sheet was comprised of the net unrealized holding gains and losses on the Company’s investment securities. 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	New Accounting Requirements and Disclosures In February 2016, the FASB issued ASU 2016-02, “Leases” , which established new ASC Topic 842 (“ASC 842”), to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. Under the new guidance, a lessee will be required to recognize assets and liabilities for leases with lease terms of more than 12 months. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a finance or operating lease. However, unlike current GAAP which requires only capital leases to be recognized on the balance sheet, the new standard will require both types of leases to be recognized on the balance sheet. ASC 842 also will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. ASC 842 was previously required to be adopted using the modified retrospective approach. However, in July 2018, the FASB issued ASU 2018-11, which allows for retrospective application with the recognition of a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Under this option, entities would not need to apply ASC 842 (along with its disclosure requirements) to the comparative prior periods presented. ASC 842 is effective for the Company in the first quarter of 2019 and management expects that most of its operating leases (primarily office space) will be recognized as operating lease liabilities and right of use assets on its balance sheet. Management is continuing to evaluate the impact that the adoption of this standard will have on the consolidated financial statements but currently believe it is likely that the Company will elect to adopt certain of the optional practical expedients, including the package of practical expedients, which, among other things, gives the option to not reassess: 1) whether expired or existing contracts are or contain leases; 2) the lease classification for expired or existing leases; and 3) initial direct costs for existing leases. In 2018, the FASB issued ASU No. 2018-07, “ Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting”, which changes the measurement date for share-based awards to the grant date, instead of the previous requirement to remeasure the awards through the performance completion date. ASU No. 2018-07 is effective for the Company for fiscal years beginning after December 31, 2018, including interim periods within that fiscal year. Early adoption is permitted. The Company does not believe adopting ASU No. 2018-07 will have a material impact on its consolidated financial statements. In 2018, the FASB issued ASU No. 2018-13, “ Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”, which modifies fair value disclosures and removes some disclosure requirements for both public and private companies. In addition, public companies are subject to some new disclosure requirements which requires to disclose the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU No. 2018-13 is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not believe adopting ASU No. 2018-13 will have a material impact on its consolidated financial statements.

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 2017 Common Stock Equivalents: Number of shares Options to purchase common stock 5,868,433 5,299,158 Unvested shares of restricted stock units 205,155 96,250 Unvested shares of restricted stock 14,707 44,119 Total common stock equivalents 6,088,295 5,439,527

CASH, CASH EQUIVALENTS AND RE_2

CASH, CASH EQUIVALENTS AND RESTRICTED CASH (Tables)	9 Months Ended
	Sep. 30, 2018
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. September 30, 2018 December 31, 2017 (in thousands) Cash and cash equivalents (1) $ 53,027 $ 38,839 Restricted cash, noncurrent 5,635 6,190 Total cash, cash equivalents and restricted cash shown in the statements of cash flows $ 58,662 $ 45,029 (1) As of September 30, 2018, and December 31, 2017, the Company invested approximately $37.1 million and $25.6 million , respectively, in cash equivalent instruments.

FAIR VALUE MEASUREMENTS AND I_2

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES (Tables)	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 and December 31, 2017 : Fair Value Measurements at Reporting Date 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 $ 37,085 $ 37,085 $ — $ — Total Cash Equivalents $ 37,085 $ 37,085 $ — $ — Investment Securities: U.S. government agency-backed securities $ 15,930 $ — $ 15,930 $ — Corporate debt securities 43,790 — 43,790 — Total Investment Securities $ 59,720 $ — $ 59,720 $ — Fair Value Measurements at Reporting Date 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 $ 25,550 $ 25,550 $ — $ — Total Cash Equivalents $ 25,550 $ 25,550 $ — $ — Investment Securities: U.S. government agency-backed securities $ 22,604 $ — $ 22,604 $ — Corporate debt securities 38,821 — 38,821 — Total Investment Securities $ 61,425 $ — $ 61,425 $ —
Available-For-Sale Securities	Investment securities, all classified as available-for-sale, consisted of the following as of September 30, 2018 and December 31, 2017: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value September 30, 2018 (in thousands) Investment Securities: U.S. government agency-backed securities $ 15,944 $ — $ (14 ) $ 15,930 Corporate debt securities 43,811 1 (22 ) 43,790 Total Investment Securities $ 59,755 $ 1 $ (36 ) $ 59,720 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Aggregate Estimated Fair Value December 31, 2017 (in thousands) U.S. government agency-backed securities $ 22,632 $ — $ (28 ) $ 22,604 Corporate debt securities 38,839 13 (31 ) 38,821 Total $ 61,471 $ 13 $ (59 ) $ 61,425

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and equipment consists of the following: September 30, 2018 December 31, 2017 Estimated Useful Lives (in thousands) Leasehold improvements 5 Years $ 21,633 $ 21,462 Lab equipment 5 Years 8,373 7,766 Office furniture 5 Years 1,702 1,701 Manufacturing equipment 5 Years 1,891 1,815 Computer and office equipment 3 to 5 Years 1,431 1,074 Equipment held under capital leases 5 Years 204 204 Software 3 Years 378 216 Total 35,612 34,238 Less: accumulated depreciation (13,210 ) (8,296 ) Property and equipment, net $ 22,402 $ 25,942

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2018
Payables and Accruals [Abstract]
Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consist of the following: September 30, 2018 December 31, 2017 (in thousands) Accrued construction costs $ 457 $ 565 Accrued payroll 2,619 2,682 Accrued patient treatment costs 2,104 1,392 Accrued sponsored research 937 85 Accrued manufacturing costs 340 370 Accrued other 2,380 1,298 Total accrued expenses and other current liabilities $ 8,837 $ 6,392

SHARE-BASED COMPENSATION PLANS

SHARE-BASED COMPENSATION PLANS (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
ESPP Activity	A summary of activity within the ESPP follows: Nine months ended September 30, 2018 2017 (amounts in thousands) Deductions from employees $ 168 $ 226 Share-based compensation expense recognized $ 111 $ 183 Remaining share-based compensation expense $ 285 $ 311
Valuation Assumptions	The fair value of the option grants has been estimated, with the following weighted-average assumptions: Nine months ended September 30, 2018 2017 Risk-free interest rate 2.63 % 2.06 % Volatility 72.1 % 71.7 % Expected life (years) 6.08 6.08 Expected dividend yield — % — %
Share-Based Compensation Expense by Classification	Share-based compensation expense by classification for the nine months ended September 30, 2018 and 2017 are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 (in thousands) (in thousands) Research and development $ 1,606 $ 1,802 $ 4,898 $ 4,870 General and administrative 2,070 1,861 5,956 5,347 Total $ 3,676 $ 3,663 $ 10,854 $ 10,217
Stock Option Activity	The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2018: Options and Inducement awards Weighted- (in years) Weighted- Aggregate Intrinsic Value (1) (in thousands) Outstanding at December 31, 2017 5,286,472 $ 12.35 7.35 $ 7,223 Granted (2) 1,965,191 $ 7.83 Exercised (837,392 ) $ 3.58 $ 4,225 Forfeited (545,838 ) $ 16.27 Outstanding at September 30, 2018 5,868,433 $ 11.72 7.80 $ 1,794 Exercisable at September 30, 2018 2,929,150 $ 13.62 6.55 $ 1,658 (1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2017 and September 30, 2018. (2) Includes 295,000 of inducement option awards granted in 2018.
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, 2018: Restricted Stock Awards and Units Aggregate Intrinsic Value (1) (in thousands) December 31, 2017 (2) 140,663 $ 1,183 Granted (3) 161,250 Vested (38,770 ) $ 342 Forfeited (43,281 ) Outstanding at September 30, 2018 219,862 $ 1,354 (1) The aggregate intrinsic value is calculated as the fair value of restricted stock and restricted stock units at December 31, 2017 and September 30, 2018. (2) At December 31, 2017, there were 29,413 shares of restricted common stock and 111,250 restricted stock units outstanding. (3) Includes 40,000 of inducement restricted stock units granted during 2018.

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	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 393,328	$ 322,512

SIGNIFICANT ACCOUNTING POLICI_4

SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	9 Months Ended
	Sep. 30, 2018
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

SIGNIFICANT ACCOUNTING POLICI_5

SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share, Potentially Dilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	6,088,295	5,439,527
Options to purchase common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	5,868,433	5,299,158
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)	205,155	96,250
Unvested shares of restricted stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total common stock equivalents (in shares)	14,707	44,119

CASH, CASH EQUIVALENTS AND RE_3

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 5,635	$ 5,635		$ 6,190
Grant from CPRIT
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash			$ 4,100	4,200
Release of restricted cash	0	88
Held in escrow
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 1,500	$ 1,500		$ 2,000

CASH, CASH EQUIVALENTS AND RE_4

CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Cash, Cash Equivalents and Restricted Cash, Reconciliation (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 53,027	$ 38,839
Restricted cash, noncurrent	5,635	6,190
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	58,662	45,029	$ 57,415	$ 42,780
Cash equivalent instruments	$ 37,100	$ 25,600

FAIR VALUE MEASUREMENTS AND I_3

FAIR VALUE MEASUREMENTS AND INVESTMENT SECURITIES - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	$ 59,720	$ 61,425
U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	15,930	22,604
Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	43,790	38,821
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	37,085	25,550
Total Investment Securities	59,720	61,425
Fair Value, Measurements, Recurring | U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	15,930	22,604
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	43,790	38,821
Fair Value, Measurements, Recurring | Money market funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	37,085	25,550
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	37,085	25,550
Total Investment Securities	0	0
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | 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
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (Level 1) | Money market funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	37,085	25,550
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Total Investment Securities	59,720	61,425
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	15,930	22,604
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	43,790	38,821
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2) | Money market funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Cash Equivalents	0	0
Total Investment Securities	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | U.S. government agency-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3) | Corporate debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total Investment Securities	0	0
Fair Value, Measurements, Recurring | 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	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 59,755	$ 61,471
Gross Unrealized Gains	1	13
Gross Unrealized Losses	(36)	(59)
Aggregate Estimated Fair Value	59,720	61,425
U.S. government agency-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,944	22,632
Gross Unrealized Gains		0
Gross Unrealized Losses	(14)	(28)
Aggregate Estimated Fair Value	15,930	22,604
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	43,811	38,839
Gross Unrealized Gains	1	13
Gross Unrealized Losses	(22)	(31)
Aggregate Estimated Fair Value	$ 43,790	$ 38,821

PROPERTY AND EQUIPMENT (Details

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 35,612		$ 34,238
Less: accumulated depreciation	(13,210)		(8,296)
Property and equipment, net	22,402		25,942
Depreciation and amortization expense	4,916	$ 2,524
Leasehold improvements	2,500		2,500
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total	$ 21,633		21,462
Estimated Useful Lives	5 years
Lab equipment
Property, Plant and Equipment [Line Items]
Total	$ 8,373		7,766
Estimated Useful Lives	5 years
Office furniture
Property, Plant and Equipment [Line Items]
Total	$ 1,702		1,701
Estimated Useful Lives	5 years
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,891		1,815
Estimated Useful Lives	5 years
Computer and office equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,431		1,074
Equipment held under capital leases
Property, Plant and Equipment [Line Items]
Total	$ 204		204
Estimated Useful Lives	5 years
Software
Property, Plant and Equipment [Line Items]
Total	$ 378		$ 216
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

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued construction costs	$ 457	$ 565
Accrued payroll	2,619	2,682
Accrued patient treatment costs	2,104	1,392
Accrued sponsored research	937	85
Accrued manufacturing costs	340	370
Accrued other	2,380	1,298
Total accrued expenses and other current liabilities	$ 8,837	$ 6,392

DEBT (Details)

DEBT (Details) - USD ($)	Dec. 21, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 08, 2017	Sep. 15, 2016	Mar. 10, 2016
Line of Credit Facility [Line Items]
Expenses related to the loan				$ 0	$ 75,000
Amortized deferred financing costs				663,000	604,000
Hercules Loan
Line of Credit Facility [Line Items]
Borrowings								$ 15,000,000
Additional borrowings, second draw							$ 5,000,000
Additional borrowings, third draw						$ 10,000,000
Expenses related to the loan						300,000
Final facility charge						$ 2,100,000
Amortized deferred financing costs			$ 200,000		$ 600,000
Outstanding balance repaid	$ 32,900,000
Prepayment charge	600,000
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		$ 300,000		$ 700,000

GRANT REVENUE (Details)

GRANT REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 292	$ 126	$ 808	$ 254
Deferred revenue			(808)	0
Grants
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	292	$ 126	808	254
Grants | CPRIT
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues	$ 300		$ 800		$ 16,900
Deferred revenue					$ 4,200
Grants | NIH
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenues				$ 100

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - Underwritten public offering - USD ($) $ / shares in Units, $ in Millions	Apr. 20, 2018	Mar. 29, 2017
Subsidiary, Sale of Stock [Line Items]
Number of shares of common stock sold in offering (in shares)	9,200,000	5,750,000
Price per share (in dollars per share)	$ 7.50	$ 12
Aggregate offering size	$ 69	$ 69
Net proceeds from offering	$ 64.7	$ 64.6

SHARE-BASED COMPENSATION PLAN_2

SHARE-BASED COMPENSATION PLANS - Narrative (Details) $ in Millions	Jun. 14, 2017shares	Sep. 30, 2018USD ($)planshares	Sep. 30, 2017shares	Dec. 31, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans | plan		4
Compensation cost not yet recognized | $		$ 17.6
Period for recognition		2 years 5 months 16 days
2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capital shares reserved for future issuance (in shares)		1,900,685
Increase to number of shares authorized (in shares)	3,100,000
Number of shares authorized (in shares)		6,090,354
Number of outstanding awards (in shares)		5,166,174
Shares outstanding (in shares)		4,021,312
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capital shares reserved for future issuance (in shares)		446,248
Number of shares authorized (in shares)		550,000
Discount rate from grant date fair market value		15.00%
Shares purchased by ESPP (in shares)		13,779	19,204
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Expiration period		10 years
Options | 2006 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capital shares reserved for future issuance (in shares)		96,293
Options | 2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capital shares reserved for future issuance (in shares)		825,828
Inducement option awards | 2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)		925,000
Restricted stock | 2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, nonvested (in shares)		14,707
Inducement restricted stock units | 2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding for non-option equity instruments (in shares)		51,250
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding for non-option equity instruments (in shares)				111,250
Restricted stock units | 2014 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, nonvested (in shares)		153,905
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding for non-option equity instruments (in shares)				29,413

SHARE-BASED COMPENSATION PLAN_3

SHARE-BASED COMPENSATION PLANS - ESPP Activity (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining share-based compensation expense	$ 10,854	$ 10,217
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deductions from employees	168	226
Share-based compensation expense recognized	111	183
Remaining share-based compensation expense	$ 285	$ 311

SHARE-BASED COMPENSATION PLAN_4

SHARE-BASED COMPENSATION PLANS - Valuation Assumptions (Details)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.63%	2.06%
Volatility	72.10%	71.70%
Expected life (years)	6 years 29 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

SHARE-BASED COMPENSATION PLAN_5

SHARE-BASED COMPENSATION PLANS - Share-Based Compensation Expense by Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 3,676	$ 3,663	$ 10,854	$ 10,217
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	1,606	1,802	4,898	4,870
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 2,070	$ 1,861	$ 5,956	$ 5,347

SHARE-BASED COMPENSATION PLAN_6

SHARE-BASED COMPENSATION PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Additional Disclosures
Weighted-average contractual life, Outstanding	7 years 9 months 18 days	7 years 4 months 6 days
Weighted-average contractual life, Exercisable	6 years 6 months 18 days
Options and Inducement awards
Options and Inducement awards
Outstanding at beginning of period (in shares)	5,286,472
Granted (in shares)	1,965,191
Exercised (in shares)	(837,392)
Forfeited (in shares)	(545,838)
Outstanding at end of period (in shares)	5,868,433	5,286,472
Exercisable (in shares)	2,929,150
Weighted- Average Exercise Price Per Share
Outstanding at beginning of period (in dollars per share)	$ 12.35
Granted (in dollars per share)	7.83
Exercised (in dollars per share)	3.58
Forfeited (in dollars per share)	16.27
Outstanding at end of period (in dollars per share)	11.72	$ 12.35
Exercisable (in dollars per share)	$ 13.62
Additional Disclosures
Aggregate intrinsic value, Outstanding at beginning of period	$ 7,223
Aggregate intrinsic value, Exercised	4,225
Aggregate intrinsic value, Outstanding at end of period	1,794	$ 7,223
Aggregate intrinsic value, Exercisable	$ 1,658
Inducement option awards
Options and Inducement awards
Granted (in shares)	295,000

SHARE-BASED COMPENSATION PLAN_7

SHARE-BASED COMPENSATION PLANS - Stock Award Activity For All Stock Plans (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)shares
Restricted Stock Awards and Units
Restricted Stock Awards and Units
Beginning balance (in shares)	140,663
Granted (in shares)	161,250
Vested (in shares)	(38,770)
Forfeited (in shares)	(43,281)
Ending balance (in shares)	219,862
Aggregate Intrinsic Value
Beginning balance | $	$ 1,183
Vested | $	342
Ending balance | $	$ 1,354
Restricted stock units
Restricted Stock Awards and Units
Beginning balance (in shares)	111,250
Inducement restricted stock units
Restricted Stock Awards and Units
Granted (in shares)	40,000
Unvested shares of restricted stock
Restricted Stock Awards and Units
Beginning balance (in shares)	29,413

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details)	Apr. 09, 2018lawsuit
Nipun Kakkar Action [Member]
Loss Contingencies [Line Items]
Lawsuits	2

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Subsequent Event $ in Millions	Oct. 05, 2018USD ($)
Subsequent Event [Line Items]
Aggregate offering size	$ 60
Commission percent of aggregate gross proceeds	3.00%