Hematopoietic stem cell transplantation and cellular therapy in sickle cell disease: where are we now?

Sickle cell disease (SCD) is a common monogenic disorder that is characterized by an A to T substitution in the β-globin gene that leads to the production of hemoglobin S (HbS). Polymerization of HbS leads to significant morbidity including vaso-occlusion, pain, hemolytic anemia, and end organ damage. Allogeneic hematopoietic cell transplantation (allo-HCT) is the only curative treatment; however, suitable donors are not always readily available. This study reviews the current status of allo-HCT and autologous cellular therapies for SCD.

Alternative sources of allogeneic stem cells from unmatched donors such as cord blood and haploidentical donors are gaining traction. Early experience has shown that better conditioning regimens and graft-versus-host disease prophylaxis are needed before these donor sources can gain widespread use. Clinical trials are underway to determine the feasibility and efficacy of autologous transplantation with gene modified hematopoietic stem cells. Gene therapy strategies include HbS gene correction, gene addition, and hemoglobin F induction. Preliminary results are very encouraging.

Matched sibling allo-HCT for patients with SCD results in more than 90% overall survival and more than 80% event-free survival. Because only 25-30% of patients have a matched sibling donor, alternative donor options such as matched unrelated donors, related haploidentical donors and unrelated umbilical cord blood donors are being considered. Clinical trials investigating various strategies for gene therapy followed by autologous transplantation are underway. One major challenge is obtaining sufficient hematopoietic stem cells for gene therapy. Studies are being conducted on the optimal mobilization regimen and collection strategy.