Summary:Allogeneic BMT is potentially curative for patients with acute myelogenous leukemia (AML) in first remission. However, many patients relapse after transplantation. Various immunotherapeutic options have been attempted with variable success in preventing relapse. Early identification of patients at high risk for relapse could allow prompt intervention. We examined the effect of slow lymphocyte recovery after siblingmatched allogeneic BMT on the risk of relapse in patients with AML. We also examined the effect of prednisone-containing GVHD prophylaxis on the rate of lymphocyte recovery. Patients with absolute lymphocyte count (ALC) Ͻ150 × 10 6 /l by day +30 had a 3.5-fold higher risk of relapse (P = 0.0088) and a lower overall survival (P = 0.0079) than patients with a higher ALC. We did not find correlation between lymphocyte count determined earlier in the post-transplantation course (day +21) and the risk of relapse. Patients receiving prednisone had a significantly lower ALC at day +30 than those who did not receive prednisone (289 vs 549 × 10 6 /l, P = 0.002). We conclude that a slow lymphocyte recovery after allogeneic BMT for AML is strongly predictive of subsequent relapse and that the type of GVHD prophylaxis should be considered when analyzing lymphocyte recovery. Bone Marrow Transplantation (2001) 28, 951-956. Keywords: allogeneic; bone marrow transplantation; cyclosporine; lymphocyte recovery; prophylaxis; relapse Allogeneic BMT offers the potential for cure in patients with acute myelogenous leukemia (AML). Several studies of allogeneic BMT have shown a benefit for patients in first remission with high-risk AML. [1][2][3][4][5] However, 10% to 40% of patients who have complete remission after allogeneic BMT for AML eventually relapse. Several factors, includ- ing FAB type, 6 associated karyotypic abnormalities, 7 stage of the disease, conditioning regimen used, 3,5 GVHD prophylaxis, 6 and development of acute and chronic GVHD, have been shown to influence the incidence of relapse after allogeneic BMT for AML. Therapeutic options are limited for those who relapse, as they tolerate further chemotherapy poorly, and repeat transplants have limited efficacy. 8,9 Immunotherapy offers a new approach to patients who relapse after allogeneic BMT. This has mostly been in the form of donor lymphocyte infusions (DLI), and several reports have demonstrated long-term survival with this approach. [10][11][12][13] These results have led to evaluation of its role in preventing relapse; however, DLI is also associated with a risk of severe GVHD. Other approaches for prevention of relapse have included the use of cytokines like interferon-alpha (IFN-␣) and interleukin-2 (IL-2) or rapid withdrawal of immunosuppression. Since only a quarter to a third of patients relapse after allogeneic BMT, a need exists for prognostic variables that can prospectively identify patients at risk for relapse and thereby help select appropriate patients for prophylactic immunotherapy.Slow recovery of the lymphocyte count after allog...