COLLABORATION AGREEMENTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 1,451	$ 828
Current portion of deferred revenue - related party	288		$ 301
Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	0	681
Zenas BioPharma
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Current portion of deferred revenue - related party	700		$ 800
Zenas BioPharma | Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 1,500
Servier | Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		$ 700