The small population of PIG-A mutant cells in myelodysplastic syndromes do not arise from multipotent hematopoietic stem cells

Background Patients with paroxysmal nocturnal hemoglobinuria harbor clonal glycosylphosphatidylinositol-anchor deficient cells arising from a multipotent hematopoietic stem cell acquiring a PIG-A mutation. Many patients with aplastic anemia and myelodysplastic syndromes also harbor small populations of glycosylphosphatidylinositol-anchor deficient cells. Patients with aplastic anemia often evolve into paroxysmal nocturnal hemoglobinuria; however, myelodysplastic syndromes seldom evolve into paroxysmal nocturnal hemoglobinuria. Here, we investigate the origin and clonality of small glycosylphosphatidylinositol-anchor deficient cell populations in aplastic anemia and myelodysplastic syndromes. Design and Methods We used peripheral blood flow cytometry to identify glycosylphosphatidylinositol-anchor deficient blood cells, a proaerolysin-resistant colony forming cell assay to select glycosylphosphatidylinositol-anchor deficient progenitor cells, a novel T-lymphocyte enrichment culture assay with proaerolysin selection to expand glycosylphosphatidylinositol-anchor deficient T lymphocytes, and PIG-A gene sequencing assays to identify and analyze PIG-A mutations in patients with aplastic anemia and myelodysplastic syndromes. Results Twelve of 15 aplastic anemia patients were found to harbor a small population of glycosylphosphatidylinositol-anchor deficient granulocytes; 11 of them were found to harbor a small population of glycosylphosphatidylinositol-anchor deficient erythrocytes, 10 patients were detected to harbor glycosylphosphatidylinositol-anchor deficient T lymphocytes, and 3 of them were detected only after T-lymphocyte enrichment in proaerolysin selection. PIG-A mutation analyses on 3 patients showed that all of them harbored a matching PIG-A mutation between CFUGM and enriched T lymphocytes. Two of 26 myelodysplastic syndromes were found to harbor small populations of glycosylphosphatidylinositol-anchor deficient granulocytes and erythrocytes transiently. Bone marrow derived CD34⁺ cells from 4 patients grew proaerolysin-resistant colony forming cells bearing PIG-A mutations. No glycosylphosphatidylinositol-anchor deficient T lymphocytes were detected in myelodysplastic syndrome patients. Conclusions In contrast to aplastic anemia and paroxysmal nocturnal hemoglobinuria, where PIG-A mutations arise from multipotent hematopoietic stem cells, glycosylphosphatidylinositol-anchor deficient cells in myelodysplastic syndromes appear to arise from more committed progenitors.