Hematopoietic stem progenitor cells lacking HLA differ from those lacking GPI-anchored proteins in the hierarchical stage and sensitivity to immune attack in patients with acquired aplastic anemia

To characterize glycosylphosphatidylinositol-anchored protein-deficient (GPI[−]) and HLA-class I allele-lacking (HLA[−]) hematopoietic stem progenitor cells (HSPCs) in acquired aplastic anemia (AA), we studied the peripheral blood (PB) of 56 AA patients in remission who possessed both ( n = 13, Group A) or either GPI(−) ( n = 34, Group B) and HLA(−) ( n = 9, Group C) cell populations. Seventy-seven percent (10/13) of Group A had HLA(−) cells in all lineages of PB cells, including platelets, while only 23% (3/13) had GPI(−) cells in all lineages, and the median percentage of HLA(−) granulocytes in the total granulocytes (21.2%) was significantly higher than that of GPI(−) granulocytes (0.28%, P