ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			1 Months Ended		3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 15, 2021 USD ($)	Feb. 26, 2021 USD ($)	Jun. 30, 2021 USD ($)	Apr. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) segment nominatedProgram subsidiary	Dec. 31, 2021 USD ($)	Mar. 26, 2021 USD ($)
Class of Stock [Line Items]
Number of wholly-owned subsidiaries formed | subsidiary								2
Number of reportable segments | segment								1
Number of operating segments | segment								1
Accumulated deficit								$ (575,425,000)	$ (550,452,000)
Operating lease, liability								0
Depreciation expense								$ 10,000.00	$ 110,000
Takeda
Class of Stock [Line Items]
Revenue recognized					$ 700,000
Minimum
Class of Stock [Line Items]
Estimated useful lives								3 years
Maximum
Class of Stock [Line Items]
Estimated useful lives								5 years
Lab equipment
Class of Stock [Line Items]
Estimated useful lives								5 years
San Francisco Office Space
Class of Stock [Line Items]
Lease termination fee	$ 900,000
Security deposits refund			$ 200,000
Operating lease, right-of-use asset										$ 600,000
Operating lease, liability										1,000,000
Loss on termination of lease						$ 500,000
San Francisco Office Space | Lab equipment
Class of Stock [Line Items]
Operating lease, right-of-use asset										$ 100,000
U.S. Manufacturing Facility
Class of Stock [Line Items]
Cash proceeds subject to escrow provisions				$ 1,500,000
Houston Office | Discontinued Operations, Disposed of by Sale
Class of Stock [Line Items]
Amount paid upon closing of asset sale		$ 1,100,000
Lease exit agreement, cash receivable		900,000
Lease exit agreement, note receivable		$ 200,000					$ 200,000
Simple interest		4.00%					4.00%
MD Anderson | Licensing Agreements
Class of Stock [Line Items]
Number of nominated programs, license maintenance fee earned | nominatedProgram								2
MD Anderson | Licensing Agreements | 2019 M.D. Anderson License Agreement
Class of Stock [Line Items]
License maintenance fee earned during period								$ 500,000
MD Anderson | Licensing Agreements | 2021 M.D. Anderson Option and License Agreement
Class of Stock [Line Items]
License maintenance fee earned during period								$ 1,000,000