PDCD1 and melanoma: Immunologic therapy is the new frontier of anti-cancer treatment, and immune checkpoint inhibitors have rapidly enriched the therapeutic scenario of many cancers (melanoma, NSCLC, lymphomas, renal cancer, etc.)PD-1/PD-L1 and CTLA4/B7 axes are crucial under normal conditions to protect normal cells from T cells recognition (self-tolerance and exhaustion).