PDCD1LG2 and melanoma: In 2011, ipilimumab, a kind of anti-CTLA4 monoclonal antibody, was approved by the US Food and Drug Administration for the first-line clinical treatment of advanced melanoma.[22] PD-1, a T-lymphocyte surface receptor, suppresses cell immune response through interaction with ligands including PD-L1 and PD-L2.[21,23] PD-1 inhibitor (lambrolizumab and nivolumab) and PD-L1 inhibitor (MPDL3280A) enhance antitumor immunity through the blockade of PD-1 interaction with its ligands.[21,24] Since there were solely phase I/II clinical trials, their toxicity or resistance has not been clear and defined.