The investigational component of this study is the combination of the Alemtuzumab (immunotherapy) and Total Body Irradiation conditioning regimen and the HLA Haploidentical Transplant with post-transplant Cyclophosphamide. Investigators plan to study the engraftment rates (transplant success rates) at Day 60 in sickle cell patients undergoing an HLA haploidentical stem cell transplant with post transplant high dose cyclophosphamide.