CTLA4 and melanoma: Several mechanisms have been reported to suppress effector T-cell responses via co-inhibitory molecule interaction with melanoma cells, including PD-L1:PD-112, CTLA-4:B7-1/213, LSECtin:LAG-314, CD155:TIGIT15, etc. Using the YUMM3.3 (BRAFmut) melanoma model in C57BL/6 mice, we found that ~30% of CD45− cells, including melanoma cells, are PD-L1+, while ~80% of CD8+ T cells are PD-1+ in the tumor microenvironment (TME) (Supplementary Fig. 7a).