Sickle Cell Anemia and HSCT: Relation Between ATG, Chimerism, Gvhd and Outcome In Myeloablative Genoidentical Transplants For The SFGM-TC

Background Sickle Cell Anemia (SCA) remains a disease with high risk of morbidity and early death. HSCT is currently the only curative treatment for SCA, but its use has been limited by the risks of transplant-related mortality (TRM) and GVHD. We have previously demonstrated that antithymocyte globulin (ATG) efficiently decreases the rejection rate in HSCT for SCA; however, its optimal dose has not been defined, prompting us to retrospectively analyse outcomes in patients from the SFGM-TC cohort receiving different ATG doses. Patients and Methods The cohort includes 236 SCA-patients (109F, 127M), (229 SS, 5 Sb0, 2 SDPunjab) transplanted in France (1988-2012) with geno-identical donors after homogeneous myeloablative conditioning regimen (CR; BU-CY), and rabbit ATG (n=215) at 5-15 mg/kg (n=35), 20 mg/kg (n=160) or no ATG (n=20). Cell sources were bone marrow (BM, n=197), cord blood (CB, n=30), CB+BM (n=8), and peripheral blood cells (PBC, n=1). Chimerism was assessed by quantitative real-time PCR from PBC at Day-30, 60, 90, Month-6, 12 and every year post-transplant, and defined as total donor chimerism (TDC): >95% donor (D); low (5-50%D) or high (50-95%D) mixed chimerism (MC),; or rejection (< 5%D). Disease-free survival (DFS) was defined as the absence of HSCT-related death and rejection. GVHD prophylaxis consisted of CSA-short MTX for BMT and CSA alone for CBT. Results Mean age at transplant was 9.7yr (range: 2.2-28.9), with 33 patients older than 15. With a mean follow-up of 5.6yr (range 0.5-22.5), TRM was not different with or without ATG (3.4%; 0.8-6%) whereas DFS was higher (p=0.004) with ATG (95.4%; 92-4-98.4) than without (72.7%; 51.7-93.7), due to differences in rejection rates (p15 (OR=7.9, 95%CI: 2.5-25.6,p Conclusion This study confirms that myeloablative CR with ATG offers 95% DFS to SCA-patients and that stable MC in absence of SCA-symptoms does not require intervention such as DLI. It reports for the first time in HSCT for SCA that donor’s age significantly increases GVHD risk, suggesting to choose the youngest sibling when possible, and that high ATG dose (20 mg/kg), which significantly reduces cGVHD risk without enhancing viral risk, should be recommended. Disclosures: Bernaudin: Novartis: Research Funding. Bertrand:ERYTECH Pharma: Principal Investigator Other. Gluckman:Cord use: Honoraria; gamida: Honoraria.