Hematopoietic Stem Cell Transplantation from HLA Identical Sibling Forsickle Cell Disease an International Survey on Behalf of Eurocord-Monacord, EBMT Paediatric Disease Working Party and CIBMTR

Introduction:

Hematopoietic stem cell transplantation (HSCT) is, to date, the only curative therapy for sickle cell disease (SCD).  However, HSCT is offered to relatively few patients with SCD for a number of reasons including lack of a suitable HLA-matched donor, lack of consensus on indications for HSCT, the potential for trading one chronic condition (i.e., SCD) for another, such as chronic graft-versus-host disease (GVHD), and the mortality associated with the procedure.  To-date, most HSCTs for SCD have utilized matched siblings as donors and are performed in children and adolescents.  We report outcomes after HLA-matched sibling HSCT of patients reported to the Eurocord-Monacord/European Group for Blood and Marrow Transplantation (EBMT) and Center for International Blood and Marrow Transplant Research (CIBMTR).

Material and methods:

One thousand patients with SCD received HLA identical sibling HSCT between 1991 and 2013; n=439 from CIBMTR and n=561 from EBMT centers. HSCTs were performed in 90 centers in 23 countries.

Results:

Median age at HSCT was 9 years (range 1-54y); 85% of patients were aged <16 years.  Approximately half of patients were female and 53% of HSCTs were performed after 2007.  Most patients (94%) were homozygotes for hemoglobin S (HBS).   The most common indication for HSCT was stroke.  Other indications included: central nervous system event lasting longer than 24 hours, elevated cerebral arterial velocity, acute chest syndrome or vaso-occlusive crisis requiring hospitalization. Red blood cell transfusions were given before HSCT to 93% and hydroxyurea to 56% of the evaluable patients (N=510).  Most HSCTs (n=872; 87%) used myeloablative-conditioning regimens, mainly based on the combination of busulfan with cyclophosphamide (n=719; 82%) or fludarabine (n=82; 9%).  One hundred and twenty six patients (13%) received reduced intensity conditioning regimens; fludarabine with cyclophosphamide was the predominant regimen (n=48; 38%). Most regimens included in vivo T-cell depletion (71%) with anti-thymocyte globulin (n=630) or alemtuzumab (n=76). The predominant GVHD prophylaxis regimens were cyclosporine alone (19%), or combined with methotrexate (56%).  The predominant stem cell source was bone marrow (84%); peripheral blood and cord blood were employed in 7% and 9% of patients, respectively. The median follow-up was 45 (1.1-324.6) months.

The cumulative incidence (CI) of neutrophil engraftment at day+60 was 98% (96.6% for CB, 98.3% for BM and 95.2% for PB) with a median time to recovery of 19 days, while that for platelet engraftment was 98 % (96±2% for CB, 99±1% for BM and 98±9% for PBSC) with a median time to recovery of 25 days.  Twenty-six patients experienced primary and 47 patients secondary graft failure; 67 patients died mainly due to GVH or infection. The 3-year probabilities of overall (OS) and event-free survival (EFS, alive with engraftment) were 94% (95% CI 92-95) and 90% (95% CI 68-82), respectively. According to stem cell source, 3-year OS was 99% after CB, 94% after BM and 80% after PBS (p<0.0001). In multivariate analysis, every year in age increment (HR 1.1, 95% CI 1.07-1.14, p<0.001) and use of peripheral blood (HR 3.43, 95% CI 1.49-7.88, p=0.004) were associated with higher mortality. In univariate analysis, EFS was better in patients receiving myeloablative compared to reduced intensity conditioning (91±1% vs 82 ±1%, respectively; p<0.001). In multivariate analysis, EFS was lower with every year in age increment (HR 1.05, 95% CI 1.02-1.07, p<0.001), peripheral blood grafts (HR 1.83, 95% CI 1.07-3.15, p=0.03) and HSCTs prior to 2000 (HR 0.77, 95% CI 0.64-0.92, p=0.005). CI of acute GVHD grade 2-4 was 14.4% (12.2-16.7) of chronic GVH 13.3 (11-15.8). Risks of acute GVHD were higher with increasing age (HR1.04 95% CI 1.01-1.07, p=0.008). None of the variables tested were associated with chronic GVHD. 

Conclusion:

This large registry based international study shows that HLA identical sibling transplant is successful more than 90% of the patients with severe SCD with limited transplant related complications (rejection, GVHD). Strategies aimed at lowering graft failure and GVHD are desirable to further optimize the observed 3-year event-free survival. Importantly, these data should increase awareness to early referral to HSCT of patients with severe SCD.