Hematopoietic Stem Cell Transplantation in Nigerian Children with Sickle Cell Anemia

Introduction: Sickle cell anemia (SCA) remains associated with high risks of morbidity and early death. Children with SCA are at high risk for ischemic stroke and transient ischemic attacks, secondary to intracranial arteriopathy involving carotid and cerebral arteries. Children with Black African variant SCA are prone to invasive infections caused by S. pneumonia, H. influenzae and Plasmodium falciparum (in malarias areas). In Africa, malaria contributes substantially to the early mortality of patients with SCA. Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment for SCA. We report our experience with transplantation in a group of Nigerian children affected by SCA.

Patients and Methods: This study included 36 consecutive SCA patients who underwent bone marrow transplantation from human leukocyte antigen (HLA)-identical sibling donors between 2010 and 2015 following a myeloablative-conditioning regimen. Patients received fludarabine (30 mg/m²/day) for 5 days and a conditioning regimen including targeted intravenous busulfan (14 mg/kg total dose) and cyclophosphamide (200 mg/kg total dose).

Blood samples were collected in different Nigerian Hospitals and shipped to the Laboratory of the IME Foundation in Italy where were processed for DNA preparation on a fully automated system (Maxwell, Promega, Madison, WI). Low resolution HLA-A, -B, -C, -DRB1 and -DQB1 typing was performed using the polymerase chain reaction-sequence specific oligonucleotide (PCR-SSO) technique (LABType - One Lambda, Canoga Park, CA).

Results: The median patient age was 10 years (range 2-17 years). Before transplantation, seventeen patients had recurrent, painful, vaso-occlusive crisis; twelve patients had recurrent painful crisis in association with acute chest syndrome; three patients experienced ischemic stroke and recurrent vaso-occlusive crisis; two patients experienced ischemic stroke; one patient exhibited leucocytosis; and one patient exhibited priapism. Of the 36 patients, 33 survived without sickle cell disease, with Lansky/Karnofsky scores of 100, following a myeloablative-conditioning regimen.

The probabilities of survival, SCA-free survival, and transplant-related mortality after transplant were 92%, 92%, and 8%, respectively. All surviving patients remained free of any SCA-related events after transplantation.

Within the frame of the HSCT program for the treatment of SCA, a total of 124 Nigerian families with 2 to 11 children (average 2.5) were typed for five HLA loci (A, B, C, DRB1 and DQB1) and the phased genotypes were unambiguously determined. Thirty-six percent of the patients had at his disposal within the family a HLA compatible sibling.

Conclusion: The protocols used for the preparation to the transplant in thalassemia are very effective also in the other severe hemoglobinopathy as in the sickle cell anemia with more than 90% disease free survival. If a SCA patient has a HLA identical family member, the allogeneic cellular gene therapy through the transplantation of the hematopoietic stem cells should be performed as soon as possible, before the disease progresses through a treatment-related irreversible organ damage.