PDCD1 and neoplasm: Of the two remaining PD1-resistant brain melanoma tumors, high CD45+ immune cell infiltration was associated with accumulation of immune-suppressive myeloid cells (SMU17-0263, Fig. 3A, Supplementary Fig. S7A) or elevated tumor PD-L1 expression and actively proliferating and immunosuppressive regulatory T cells, as indicated by high CTLA4, PD1, CD39, OX40, and ICOS expression37 (SMU15-0229; Supplementary Fig. S7B, Table 1).