Krummel et al reported CTLA‐4 is a restricting factor for T cells in 1995.80 CTLA‐4 antibody therapy was the first immunotherapy drug to significantly prolong overall survival in patients with metastatic melanoma.81 In recent years, a new immune checkpoint inhibitor therapy, targeting CTLA‐4 for pancreatic cancer, showed limited efficacy.21, 82, 83, 84 However, in a tumor microenvironment in which immune reaction has been stimulated, checkpoint inhibition may be more effective. Here, CTLA4 is linked to metastatic melanoma.