Pathogenesis of myelodysplastic syndromes II: The role of the immune system

Haema 2011; 2(2): 162-168

Michael Voulgarelis, Ioanna Vlahadami, Katerina Benekou

Department of Pathophysiology, University of Athens Medical School

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Myelodysplastic syndromes (MDS), first clearly defined as an entity, have long been perceived as pre-leukemic hematopoietic stem cell disorders, which cause bone marrow failure, and ultimately may transform to acute leukemia. Bone marrow failure, resulting in transfusion dependence and neutropenic infections, that characterize the disease, was assumed to be an intrinsic stem cell defect causing defective maturation. However, accumulating evidence has shown that marrow failure in some MDS is associated with autoimmunity, T-cell mediated myelosuppression and cytokine-induced cytopenias. MDS is sometimes seen in association with Raynaud’s syndrome, rheumatoid arthritis and polymyalgia rheumatica. Study of the autoimmune component in MDS pathophysiology has led to the development of immunosuppressive treatments. According to the working hypothesis regarding the relationship between the immune system and cytopenias in MDS, the MDS clones express a neoantigen or overexpress an autoantigen that triggers expansion of T-cell clones, cytotoxic for the MDS cell. These autoreactive T-cells secrete cytokines, TNF-α and IFN-γ, which promote apoptosis of the normal non-clonal progenitor cells, suppressing hematopoiesis. These observations raise many questions concerning the mechanism underlying the immune dysfunction of MDS. Much insight into these questions has been provided by studies of the cytopenia, associated with trisomy 8 MDS. FISH techniques showed that cytotoxic T-cells specifically targeted trisomy 8 bearing cells. Because the Wilm’s tumor antigen (WT1) is overexpressed on CD34+ cells in many patients with MDS, it is an obvious candidate antigen for an MDS specific T-cell response. This review illustrates the immune mechanisms in the pathophysiology of cytopenia in myelodysplastic syndromes and the response to immunosuppression.