Pure red cell aplasia (PRCA) results from the failure of erythrocyte differentiation and may respond to immunosuppressive therapies. We have treated 9 patients with PRCA refractory to steroids and/or cyclophosphamide with anti-thymocyte globulin (ATG). Six patients had normal numbers of erythroid bursts (from erythroid burst-forming units) or erythroid colonies (from erythroid colony-forming units) detectable in vitro, and all responded to therapy with ATG. In vitro studies suggested T-cell inhibition of erythropoiesis in 4 of these 6 patients and humorally mediated erythroid suppression in one. In 3 individuals, virtually no erythroid progenitors were detected in marrow culture. None of these patients responded to ATG. Myelofibrosis, 5q- chromosomal abnormality, or the subsequent development of thrombocytopenia in these individuals suggested that PRCA resulted from an intrinsic stem cell disorder. Our studies demonstrate that ATG is effective therapy for PRCA, and it may be especially useful in children or other patients in whom alkylating agents are not appropriate. We also confirm that erythroid growth in marrow culture predicts those patients who will respond to ATG or other immunosuppressive therapies.
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