Outcomes of matched sibling donor hematopoietic stem cell transplantation for severe sickle cell disease with myeloablative conditioning and intermediate-dose of rabbit anti-thymocyte globulin.

BACKGROUND: Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapy for sickle cell disease (SCD) in children. Despite excellent outcomes of matched sibling donor (MSD) HSCT, there is still 5-10% chance of rejection and transplant related mortality (TRM) with 12-23% incidence of graft versus host disease (GVHD). We postulated that an intermediate dose of rabbit anti-thymocyte globulin (r-ATG, 10 mg/kg cumulative) would be effective in preventing both rejection and GVHD.

PATIENTS AND METHODS: Fifteen patients, median age 5 (range 1.5-18) years, underwent MSD HSCT using busulfan (≥ 12.8 mg/kg with first dose pharmacokinetics), cyclophosphamide (total 200 mg/kg) and r-ATG. Bone marrow was the stem cell source; tacrolimus and methotrexate were given for GVHD prophylaxis.

RESULTS: All patients achieved donor engraftment and there was no TRM. One patient rejected donor cells at 2 months post-transplant. Majority of the patients had high and sustained level of donor chimerism. None of the patients developed ≥ Grade II GVHD. Incidence of CMV (10%) and EBV (9%) reactivations was low with rapid immune-reconstitution. Overall survival was 100% with event free survival of 93%.

CONCLUSIONS: Eliminating the risks of TRM and GVHD by optimizing the regimen may lead to further acceptance of HSCT for SCD.