Identification of Patients Who May Benefit From Prophylactic Immunotherapy After Bone Marrow Transplantation for Acute Myeloid Leukemia on the Basis of Lymphocyte Recovery Early After Transplantation

Two hundred and one patients (median age, 29 years) with acute myeloid leukemia (AML) underwent bone marrow transplantation (BMT) from HLA-identical sibling donors after conditioning with melphalan-total-body irradiation (TBI) (57%), cyclophosphamide-TBI (35%), or chemotherapy alone (8%). Graft-versus-host disease (GVHD) prophylaxis included cyclosporine alone (68%), cyclosporine-methotrexate (26%), or T-cell depletion (6%). The probability of relapse was calculated as a function of the absolute lymphocyte count (109/L) on days 27 to 30 posttransplant (<0.1 v ≥0.1, <0.2 v ≥0.2, and <0.3 v≥0.3). In each of these 12 comparisons, the probability of relapse was higher for the group with the lower lymphocyte count. Because the difference was most significant (P = .004) for an absolute lymphocyte count of <0.2 on day 29 (3-year relapse probability, 42%) versus ≥ 0.2 (16%), this variable was included in a Cox model to determine factors independently affecting relapse. Multivariate analysis showed that conditioning regimens other than melphalan-TBI, a low lymphocyte count on day 29, French-American-British (FAB) subtypes M4-7, and a nucleated cell dose of > 2.42 × 108/kg was associated with a higher risk of relapse. We conclude that slow lymphocyte recovery after allogeneic BMT, to < 0.2 × 109/L 29 days in this analysis, appears to be associated with a higher risk of relapse in patients with AML. This group of patients may benefit from posttransplant immune manipulations such as abbreviated GVHD prophylaxis, or donor cell or cytokine administration to enhance graft-versus-leukemia reactions to reduce relapse.