PDCD1 and neoplasm: The differences in the frequency of irAEs could be explained by the different mechanisms of action between the blockers; while CTLA-4 blockade leads to nonspecific expansion of existing T cell clones and suppression of regulatory T cells (35), PD-1 signaling inhibition stimulates clonal expansion of T cell clones present in the tumor site (36), which intuitively could mean that there’s less chance of having auto-reactive activated T cells.