Successful treatment of chronic refractory pure red cell aplasia with antithymocyte globulin: correlation with in vitro erythroid culture studies.

Two contrasting cases of chronic refractory pure red cell aplasia (PRCA) responsive to a commercial preparation of horse antihuman thymocyte globulin (ATG) are reported. Both cases were refractory to trials of cyclophosphamide, corticosteroids, and plasmapheresis. One patient developed a reticulocytosis after a single intravenous infusion of ATG; the other patient responded after administration of 14.7 g of ATG over a 28-day course. At presentation, erythroid progenitors (CFU-E and BFU-E) in one patient were normal; in the second patient, the number of erythroid progenitors was severely reduced. Neither patient had a serum IgG inhibitor to progenitor cells as judged by in vitro erythroid colony studies. Both patients had increased numbers of marrow T-cells and co-culture studies in one case were consistent with T-cell-mediated suppression of erythropoiesis. These studies confirm that ATG is a useful agent in the treatment of refractory PRCA. However, ATG may not act by removal of T suppressor cells in all cases.