Favorable outcome of non-myeloablative allogeneic transplantation in adult patients with severe sickle cell disease: A single center experience of 200 patients

Allogeneic hematopoietic stem cell transplant (HSCT) for adults with severe sickle cell disease (SCD) is potentially curative but not commonly utilized therapy due to complications such as graft failure (GF) and organ toxicity. Herein, we are reporting our long-term outcome data of non-myeloablative (NMA) HSCT in adults with severe SCD with emphasis on factors predicting event free survival (EFS). Adults with severe SCD undergoing NMA match-related donor allogeneic HSCT from 2015 to 2021 with at least 12 months of follow-up were included. A total of 200 patients were included with a median age of 26 years (14-43) and 56% were male. The median infused CD34 dose was 13.7 (5.07-25.8), respectively. Median absolute neutrophil count engraftment was 19 (13-39) days with 51% of patients receiving GCSF to expedite recovery. A total of 17 patients experienced GF; 3 as primary and 14 as secondary within a median time of 204 days (40-905). A 76% successfully discontinued sirolimus at the last follow-up. Median follow-up for the cohort is 29.2 (2.1-71.4) months. Estimated 3-year EFS and OS were 88.2% (81.9-92.5) and 94.6% (89.2-97.3). At multivariable analysis, minor ABC incompatibility hazard ratio (HR) 4 (1.3-12.1; 0.014) and allo-antibody against non-ABO donor antigens HR 4.3 (1.3-14.1; 0.016) were significant for EFS. No clonal evolution or myeloid malignancies were seen. This largest single-center report of NMA HSCT in adults with severe SCD further delineated its feasibility, potential toxicities, and fertility outcomes. GF remains a major impediment and appears dependent on ABO matching and non-ABO antibodies.