The primary purpose of the Phase I portion of the study is to assess the therapeutic safety and preliminary efficacy of a hematopoietic cell-based gene therapy consisting of autologous CD34+ enriched cells transduced with the therapeutic lentiviral vector, Chim-CD18-WPRE, RP-L201. The primary objectives of the Phase II portion of the study are evaluation of survival, as determined by the proportion of subjects alive at age 2 (24 months) and at least 1-year post-infusion without allogeneic hematopoietic stem cell transplant (HSCT) and characterization of the safety and toxicity associated with the infusion.