CTLA4 and metastatic melanoma: Although phase III clinical studies have demonstrated that anti-PD-1 agents such as nivolumab and pembrolizumab have superior efficacy over ipilimumab in metastatic melanoma [16], individual case reports suggest that anti-CTLA-4 agents may be preferred for use in SOTRs due to the non-peripheral tissue-specific mechanism of the CTLA-4 receptor compared to PD-1, which would be less likely to be associated with acute rejection of the allograft.