Predictive factors for response to anti-thymocyte globulin in acquired aplastic anemia.

Lymphocyte phenotype, bone marrow cellularity, in vitro marrow growth potential, and treatment responses were examined in 22 patients with acquired aplastic anemia who were given anti-thymocyte globulin. Eleven of 22 patients (50 percent) had a significant hematologic response within three months of therapy, confirming the effectiveness of this therapy. Pretreatment fetal hemoglobin concentration, age, sex, severity of pancytopenia, degree of maximal lymphopenia, and total hemolytic complement consumption did not affect response. Patients with severe disease who were treated within 16 weeks after diagnosis had a higher response rate (55 percent) than those treated after 16 weeks (20 percent). In patients with severe disease, a higher pretherapy bone marrow cellularity (p less than 0.001) and presence of granulocyte-macrophage colony growth correlated with response. The actuarial survival of patients with response in the group with severe disease was 100 percent at 12 months as compared with 33 percent in patients without response. Following anti-thymocyte globulin therapy, a reduced number of blood lymphocyte T subpopulations was seen in all patients. At three months after therapy, the patients with response who had severe disease had increased T8-positive cells (+56 percent versus -4 percent for patients without response) and la-positive cells (+32 percent versus -62 percent).