Antithymocyte Globulin Treatment in Patients with Aplastic Anemia: A Prospective Randomized Trial

We evaluated the efficacy of antithymocyte globulin for the treatment of moderate to severe aplastic anemia in a randomized controlled study. Eleven of 21 patients initially randomized to receive antithymocyte globulin (given intravenously on eight consecutive days) had sustained improvement in hematopoiesis within three months of treatment; none of 21 control patients who received supportive care alone improved (P = 0.0005). Six of 12 control patients who subsequently received antithymocyte globulin improved. Responded had gradual improvement in hematopoiesis, but none recovered completely normal peripheral-blood counts. The severity of bone-marrow failure, age, cause of aplastic anemia, and transfusion history had no apparent bearing on treatment outcome. The interval from diagnosis to antithymocyte globulin treatment correlated inversely with the chance of a treatment response, although this correlation was not statistically significant. These data indicate that antithymocyte globulin is effective in improving hematopoiesis in some patients with aplastic anemia. (N Engl J Med. 1983; 308:113–8.) APLASTIC anemia is a life-threatening hematologic disorder characterized by pancytopenia and bone-marrow failure. In most cases the cause is uncertain, and several potential pathogenetic mechanisms have been implicated. Most data suggest that aplastic anemia usually results from the absence or defects of hematopoietic stem cells. Less common causes include defects in the bone-marrow microenvironment or abnormalities of hematopoietic regulatory cells or factors.^1,2 There has been considerable recent interest in the participation of the immune system in the regulation of normal hematopoicsis and the potential role of immune suppression of hematopoiesis in the pathogenesis of aplastic anemia.^3,4 Several studies have presented.