PDCD1 and neoplasm: Accordingly, the immune checkpoint inhibitors targeted at PD-1 (nivolumab and pembrolizumab), PD-L1 (atezolizumab, avelumab and durvalumab) and CTLA-4 (ipilimumab and tremelimumab) are capable of blocking these essential routes and thereby tightening up the immune surveillance over tumor cells.