CD274 and myeloproliferative disorder: To assess the effect of the 9p UPD on PD‐L1 expression in MPN cells, we compared the PD‐L1 mRNA expression between JAK2‐V617F‐positive patients with and without 9p UPD, and observed a significantly higher expression of PD‐L1 in MPN cells in patients with 9p UPD (p < .0001; Figure 1D).