Impact of ATG Dose on the Outcome of Patients Undergoing Reduced Intensity Conditioning Followed by Allogeneic Hematopoietic Stem Cell Transplantation for Hematological Malignancies.

Reduced intensity conditioning for allogeneic hematopoietic stem cell transplantation (allo-HSCT) is often proposed for patients with comorbidities. To enhance engraftment and limit graft-versus-host disease (GVHD), antithymoglobulin (ATG) is usually used. However, the dose needed remains unclear unlike myeloablative conditioning. In order to clarify this point, we conducted a retrospective study on patients who received a reduced intensity conditioning allo-HSCT based on a 2-day fludarabine and busulfan treatment with either 1 or 2 days of ATG treatment. One hundred and eight patients received 2.5 mg/kg (ATG2.5) and another 60 patients 5 mg/kg (ATG5). The median follow-up was 36 months. The median overall survival was 39 months and the median disease-free survival 45 months. In multivariate analysis, overall nonrelapse mortality (NRM) was independently influenced by the acute GVHD grade III-IV (p < 0.001) and ATG dose (30 vs. 21% for ATG5; p = 0.008). Despite heterogeneity of populations, using proportional-hazard assumptions, we have been able to observe in multivariate analysis a lower NRM in the ATG5 group. This leads to a statistically higher overall survival for the ATG5 group. In conclusion, 2 days of ATG decrease NRM independently without increasing the risk of relapse or infectious disease.