PR1 is a human leukocyte antigen (HLA)-A2 restricted nonapeptide (VLQELNVTV), which is derived from the serine proteases proteinase-3 (P3) and neutrophil elastase (NE), two myeloid azurophil granule proteases that are highly expressed in myeloid leukemia blasts (13). The gene discussed is TMEM37; the disease is myeloid leukemia.