Anti-human T Lymphocyte Rabbit Immunoglobulin

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative therapy in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Most of the patients requiring an allo-HSCT are above 50 years of age and are transplanted with a reduced intensity conditioning (RIC) regimen. The optimal RIC and Graft Versus Host Disease (GVHD) prophylaxis regimen allowing a good control of the disease while preventing GVHD remains to be determined for elderly patients. A phase III trial comparing the conventional RIC fludarabine-busulfan 2 days to fludarabine-treosulfan demonstrated an advantage for the flu-treosulfan arm in terms of event free survival (EFS), that should therefore be considered as the new standard of RIC regimen for AML and MDS. GVHD prevention has a crucial role in post-transplant outcomes by potentially interfering with the graft-versus-leukemia (GVL) effect and immune reconstitution. Anti-thymocyte globulins (ATG) are recommended to reduce the risk of acute and chronic GVHD in transplants performed with matched unrelated donors. However, the optimal type of ATG between the 2 approved brands (ATG-thymoglobulin and ATLG-grafalon) displaying distinct characteristics and the optimal dose of ATG are still unknown. In a retrospective study of patients transplanted mainly with RIC with matched related and unrelated donors for haematological malignancies, we observed that Anti-T lymphocyte globulin (ATLG) was associated with a reduction of grade II-IV acute GVHD in comparison to ATG without increasing the incidence of relapse.
In this phase III randomised study, we propose to compare GVHD prevention with ATG versus ATLG in AML and MDS patients above 50 years of age transplanted with a matched unrelated donor following a fludarabine-treosulfan RIC, with the hypothesis that ATLG would better control GVHD in this population of patients thus limiting the risk of morbidity and mortality of the procedure.