ORGANIZATION, BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)		1 Months Ended	3 Months Ended			9 Months Ended
	Mar. 15, 2021 USD ($)	Apr. 30, 2020 USD ($)	Sep. 30, 2022 USD ($) nominatedProgram	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2022 USD ($) subsidiary	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)	Mar. 26, 2021 USD ($)	Feb. 26, 2021 USD ($)
Class of Stock [Line Items]
Number of wholly-owned subsidiaries formed | subsidiary						2
Accumulated deficit			$ (569,228,000)			$ (569,228,000)		$ (550,452,000)
Cash and cash equivalents			28,756,000			28,756,000		$ 46,156,000
Operating lease liability			0			0
Loss on dispositions, net			0	$ 14,000		$ 0	$ 478,000
Licensing Agreements | MD Anderson
Class of Stock [Line Items]
License maintenance fee earned during period			$ 1,000,000
Number of nominated programs, license maintenance fee earned | nominatedProgram			2
U.S. Manufacturing Facility
Class of Stock [Line Items]
Cash proceeds subject to escrow provisions		$ 1,500,000
Leased R&D Facility In Houston, Texas
Class of Stock [Line Items]
Amount paid upon closing of asset sale										$ 1,100,000
Lease exit agreement, cash receivable										900,000
Lease exist agreement, note receivable										$ 200,000
San Francisco Office Space
Class of Stock [Line Items]
Lease termination fee	$ 900,000
Security deposit	$ 200,000
Operating lease, right-of-use asset									$ 600,000
Operating lease liability									1,000,000
Loss on dispositions, net					$ 500,000
San Francisco Office Space | Equipment
Class of Stock [Line Items]
Operating lease, right-of-use asset									$ 100,000