Bone marrow failure syndromes (BFS) including aplastic anemia (AA), myelodysplastic syndromes (MDS), and paroxysmal nocturnal hemoglobinuria (PNH) are considered to harbor immune-mediated marrow injury. Indeed, immunosuppressive therapy (IST) with antithymocyte globulin and cyclosporine ameliorates the hematopoiesis in BFS patients, despite its limit: infrequent relapse of marrow failure after IST, resistance of some patients to IST, and untoward effects like infection. To overcome the difficulties, molecular targeted therapy is alternative. However, neither incitement of marrow injury nor target molecules on marrow cells recognized by cytotoxic lymphocytes has been identified. We have currently suggested that NKG2D ligands such as ULBP and MICA/B serve as triggers for immune-mediated marrow injury in PNH (
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