PDCD1 and cancer: Currently, there are four types of immune checkpoint inhibitors (ICIs) approved by FDA for cancer treatment: (1) anti-CTLA-4 therapies: ipilimumab and tremelimumab (238, 239), (2) anti-PD-1 therapies: cemiplimab, dostarlimab, nivolumab, pembrolizumab, retifanlimab-dlwr and tislelizumab (240–245), (3) anti-PD-L1 therapies: atezolizumab, avelumab and durvalumab (246, 247), (4) anti-LAG-3 therapy: relatlimab (248).