CRISPR activation screening identifies VGLL3 and GATA2 as transcriptional regulators of PD-L1

The PD-L1/2 - PD-1 immune checkpoint is essential for the proper induction of peripheral tolerance and limits autoimmunity, whereas tumor cells exploit their expression to promote immune evasion. Many different cell types express PD-L1/2, either constitutively or upon stimulation, but the factors driving this expression are often not defined. Here, using genome-wide CRISPR-activation screening, we identified three factors that upregulate PD-L1 expression; GATA2, MBD6, and VGLL3. GATA2 and VGLL3 act as transcriptional regulators and their expression induced PD-L1 in many different cell types. Conversely, loss of VGLL3 impaired IFN{gamma}-induced PD-L1/2 expression in keratinocytes. Mechanistically, by performing a second screen to identify proteins acting together with VGLL3, we found that VGLL3 forms a complex with TEAD1 and RUNX1/3 to drive expression of PD-L1/2. Collectively, our work identified a new transcriptional network controlling PD-L1/2 expression and suggests that VGLL3, in addition to its known role in the expression of pro-inflammatory genes, can balance inflammation by upregulating the anti-inflammatory factors PD-L1 and PD-L2.