Consistently, a prior study demonstrated that CALR mutation-specific CD4+ and CD8+ T cells are in the peripheral blood of patients with CALR mutated MPN; however, their functional impairment may be due to the expression of exhaustion markers (programmed cell death receptor 1 (PD-1) or cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4)) [43]. Here, CTLA4 is linked to myeloproliferative neoplasm.