PDCD1 and melanoma: Interestingly, a few recent studies reveal that B cells are the strongest prognostic factor in patients with melanoma,67 68 sarcoma69 and renal cell carcinoma68 receiving PD-1 blockade therapy, even though the tumors have low level of CD8 T cell infiltration.69 Moreover, patients having tumors with high Treg infiltration should avoid anti-PD-1 antibody monotherapy, as it may lead to HPD due to increased expansion and immunosuppressive activity of Tregs.23 Further, the effect of PD-1 blockade therapy in such patients can be determined using patient derived xenograft models.