CREBBP and neoplasm: Lastly, CREBBP loss-of-function mutations (genocopied by TET2 loss-of-function mutation) contribute to immune evasion via a decrease of class II trans-activator (CIITA)-dependent MHC class II expression (of both transcript and protein), leading in the tumor bed to a decrease of infiltration of both CD4+ helper and CD8+ memory cytotoxic T cells (25).