CALR and myeloproliferative neoplasm: Finally, we found that both CD4+ and CD8+ T cells isolated from fresh BM samples of MPN patients (N = 16) express the PD‐L1 receptor PD‐1, and that this expression is not influenced by the presence of the MPN disease‐driving mutations JAK2, CALR, or MPL (Figures 3C and S8).