PDCD1 and viral encephalitis: ICI–induced inflammation in the central nervous system (CNS irAE), causing encephalitis or aseptic meningitis, is a rare but serious irAE.7, 8, 9, 10, 11 The risk of CNS irAE is higher with ipi + nivo (simultaneous blockade of CTLA-4 and PD-1) than with single nivo (PD-1 inhibition).12