Abstract Immune Reconstitution and Clinical Outcome After Donor Lymphocyte Infusion for Relapsed Disease After Reduced-Intensity Allogeneic Hematopoietic Stem Cell Transplantation in Diseases Other Than Chronic Myelogenous Leukemia Daniela S. Krause, Julie Aldridge, Haesook T Kim, Sean McDonough, Laura Gatzos, Joseph H. Antin, Vincent T. Ho, Corey Cutler, Philippe Armand, John Koreth, Robert Soiffer, Jerome Ritz, Grace Kao Evidence suggests that immune responses after allogeneic hematopoietic stem cell transplantation (HSCT) play a major role in the prevention of disease relapse, called the graft-versus-tumor (GVT) effect. In patients relapsing after reduced-intensity conditioning (RIC) HSCT, donor lymphocyte infusion (DLI) may boost donor-T cell chimerism and induce a therapeutic GVT effect. Our intent was to study the effect of infused T cell subsets on immune reconstitution and clinical outcomes in patients with relapsed hema-tological malignancies who underwent RIC HSCT. The administered DLI products were analyzed for CD3+, CD4+, and CD8+ T cell subsets. Peripheral blood (PB) obtained before and after DLI was analyzed for CD3+ CD4+, CD8+, CD19+, CD20+, and CD14+ cells. The 2-year overall survival (OS) and progression-free-survival (PFS) after DLI were 41% and 22%, respectively. The 2-year-relapse rate was 77.8%, but treatment- related mortality (TRM) was 0%. A complete response was achieved in 18% of the patients. The cumulative incidences of grade II-IV acute graft-versus-host- disease (aGVHD) and chronic GvHD (cGvHD) were 9.1% at 200 days and 27.8% at 2 years after DLI, respectively. A significant decrease in CD4+ and a significant increase in PB CD8+ cell frequency were observed after DLI infusion. Infused total and lymphocyte subset cell dose had no effect on any of the clinical outcomes. Higher pre-infusion PB CD4+ and lower pre-infusion CD14+ cell frequencies in the recipient were associated with better OS. Lower pre-infusion CD14+ cell frequency was associated with better PFS. Clinical responses to DLI in patients with relapsed hematological malignancies other than chronic myelogenous leukemia remain unsatisfactory, although the associated risk of GVHD and TRM are low. The dose of CD3, CD4 and CD8 cells in the DLI product was not correlated with clinical outcome. However, pre-infusion immune status and demonstration of significant changes in immune reconstitution after DLI can affect clinical outcomes. Strategies to modulate pre- and post-immune status of the recipients warrant further investigation to improve the efficacy of DLI. To study the effect of infused T cell subsets on immune reconstitution and clinical outcomes such as aGvHD and cGvHD, OS and PFS in patients with relapsed hematological malignancies other than CML who underwent RIC HSCT. Objective Conclusions The infused total and lymphocyte subset cell dose had no effect on any of the clinical outcomes, but this may be due to the small number of patients studied.. None of the changes in immune parameters after DLI were associated with cGVHD. The degree of chimerism prior to DLI had no influence on immune reconstitution. The complete response rate was 18%. Clinical responses to DLI in patients with relapsed hematological malignancies other than CML remain unsatisfactory the associated risk of GVHD and TRM is low the dose of CD3, CD4 and CD8 cells in the DLI product was not correlated with clinical outcome pre-infusion immune status and demonstration of significant changes in immune reconstitution after DLI can affect clinical outcomes Strategies to modulate pre- and post-immune status of the recipients warrant further investigation to improve the efficacy of DLI Figure 2: The incidence of grade II-IV aGvHD is 9.1% at 200 days and the incidence of grade II-IV cGvHD is 27.8% Figure 3: Treatment-related mortality of DLI is 0%, but the 2-year-relapse rate is 77.8% Figure 4: 2-year-overall survival post DLI is 41% and 2-year progression-free survival is 22% Table 4: Immune reconstitution data and clinical outcomes There are no relevant conflicts of interest to disclose for all authors. Results Table 2: Infused DLI product data (in 10 6 cells per kg) Table 3: Peripheral blood immune reconstitution data pre and post DLI (p=percent, a=absolute numbers per  l ); times of testing as in figure 1 Low risk disease: acute leukemia in CR1 or refractory anemia (RA) or refractory anemia with ringed sideroblasts (RARS) RIC: fludarabine, intravenous busulfan GvHD prophylaxis (in 77.3%): tacrolimus, sirolimus, methotrexate Treatment period: (median follow-up:1.1 years) Donor (>80%) (Donor <20%) Days post DLI Figure 1: Percent peripheral blood CD4+ cells significantly decrease and CD8+ cells significantly increase after DLI (data collection range: 200 days before and 200 days after DLI) P=.01P=.04 Pre DLIPost DLIPre DLIPost DLI Table 1: Patient characteristics Patient Characteristics