CD4 and myeloproliferative disorder: Specifically, spontaneous CALR mutant-specific CD4+ T lymphocytes are in the peripheral blood of many MPN patients, and ex vivo co-cultures of T cells specific to CALR mutations, as well as JAK2V617F-specific CD8+ T cells, with CALR or JAK2 mutated cells induces recognition and elimination of the mutated cells [40,41,42].