PDCD1 and cancer: Although these MAbs have been used individually in onco-immunotherapy, it is combinations of MAbs, which target different immune checkpoint inhibitors, particularly CTLA-4 and PD-1 using ipilimumab and nivolumab, respectively, which have been shown to be most effective in prolonging progression-free survival and overall response rates in patients with metastatic/unresectable melanoma and other types of cancer.