[Clinical significance of detecting human leukocyte antigen class I allele-lacking leukocytes in aplastic anemia]

Human leukocyte antigen (HLA) class I allele-lacking [HLA (-)] leukocytes provide compelling evidence that cytotoxic T-lymphocytes are involved in the development of aplastic anemia (AA). However, the clinical significance and precise mechanisms underlying clonal hematopoiesis by HLA (-) hematopoietic stem progenitor cells remain unknown. In HLA (-) cells from patients with AA, we discovered a common nonsense mutation at codon19 (c.19C>T, p.R7X) in exon1 (Exon1^mut) of different HLA-A and HLA-B alleles. Exon1 mutation detection using droplet digital polymerase chain reaction (ddPCR) is a powerful tool for diagnosing immune pathophysiology in patients with bone marrow failure. We also looked at the prognosis of 633 patients with AA, including 127 with HLA (-) leukocytes who had been followed up for a long time. In Japanese patients with AA, HLA (-) leukocytes and concomitant aberrant clones were not associated with clonal evolution to MDS/AML. In patients with AA and both marker (-) leukocytes, HLA (-) leukocytes may indicate a lower risk of developing secondary paroxysmal nocturnal hemoglobinuria (PNH). Detecting HLA (-) leukocytes is critical for managing patients with AA and assisting physicians in selecting appropriate therapy.