PDCD1 and neoplasm: CTLA-4 inhibition with ipilimumab is thought to block the initial steps of T-cell activation and proliferation within lymph nodes, whereas PD-1/PD-L1 inhibitors (nivolumab, pembrolizumab, atezolizumab, avelumab, and durvalumab) target T cells at a later stage of the immune response within the tumor and peripheral tissues4.