Diagnosis of immune pathophysiology in patients with bone marrow failure.

Differential diagnosis of pancytopenia with bone marrow (BM) hypoplasia represented by aplastic anemia (AA) is often challenging for physicians, because no laboratory tests have been established, until recently, to distinguish immune-mediated BM failure, which includes acquired AA (aAA) and a subset of low-risk myelodysplastic syndrome (MDS), from non-immune BM failure, which is primarily caused by genetic abnormalities in hematopoietic stem cells (HSCs). HSCs of healthy individuals often undergo somatic mutations, and some acquire phenotypic changes that allow them to escape immune attack against themselves. Once an immune attack against HSCs occurs, HSCs that undergo somatic mutations survive the immune attack and continue to produce their progenies with the same genetic or phenotypic changes. The presence of mature blood cells derived from mutated HSCs in the peripheral blood serves as evidence of the immune-mediated destruction of HSCs. Glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) blood cells and HLA class I allele-lacking (HLA[-]) leukocytes are two major aberrant cell types that represent the immune mechanism underlying BM failure. This review focuses on the importance of identifying immune mechanisms using laboratory markers, including GPI(-) cells and HLA(-) leukocytes, in the management of BM failure.