HLA-DRB5 and acquired polycythemia vera: Expression of human leukocyte antigen (HLA)-related genes, such as HLA-DRB5, HLA-DPA1, and HLA-DPB1, was significantly higher in peripheral blood monocytes of PV patients compared with HCs, suggesting increased antigen processing and presentation in the peripheral blood monocytes of PV patients (Supplementary Figure 5C, Supplementary Table 7).