CALR and myeloproliferative disorder: PD‐L1 upregulation on progenitor cells and stem cells of CALR positive MPN patients is in line with the findings of Bozkus et al. who demonstrated that these patients develop T cells specific for the mutant CALR and that targeting the PD‐L1/PD‐1 interaction can lead to restoration of this T‐cell response against mutant CALR in MPN patients.51