Immune-induced cytopenia: bone marrow failure syndrome.

Myelodysplastic syndromes, a heterogeneous group of clonal stem cell disorders, are characterized by ineffective and dysplastic hematopoiesis and increased risk of leukemic transformation. The clonal disorder may result in cumulative cytogenetic abnormalities in a multistep process. Intrinsic and extrinsic factors contributing to ineffective hematopoiesis include genetic predisposition, environmental effects, and iatrogenic causes. The common and often overlapping features of myelodysplastic syndrome, aplastic anemia, T-cell large granular lymphocyte lymphoproliferative disorder, and paroxysmal nocturnal hemoglobinuria suggest a shared pathophysiologic mechanism of marrow failure. Recent studies suggest that dominant clonal T cells, which may be driven to expand by hematopoietic antigenic stimuli, result in the T-cell-mediated inhibition of hematopoietic progenitors, thus contributing to cytopenia.