CTLA4 and myeloproliferative neoplasm: Increased expression of the immune checkpoint receptors PD‐1 and cytotoxic T‐lymphocyte protein 4 (CTLA‐4) on CD4+ and CD8+ T cells in MPN has been shown,88 and blockade of PD‐1 and CTLA‐4 can recover T‐cell reactivity against mutCALR ex vivo, and result in the production of IFNγ and TNFα.87