Nonmyeloablative Conditioning for Mismatched Hematopoietic Stem Cell Transplantation for Severe Sickle Cell Disease

The aim of this study is to evaluate the overall safety and feasibility of using haploidentical or one antigen mismatch unrelated hematopoietic stem cell transplant (HSCT) for adult patients with severe sickle cell disease (SCD) who undergo a non-myeloablative preparative regimen consisting of total body irradiation (TBI), cyclophosphamide and alemtuzumab (and fludarabine for haplo-SCT only) and graft vs. host disease (GvHD) prophylaxis consisting of post-transplant cyclophosphamide (PT-Cy), mycophenolate mofetil (MMF), and sirolimus. The investigators anticipate that this approach will expand the donor pool and offer a safe and less toxic curative intervention.