SCID Bu/Flu/ATG Study With T Cell Depletion

The study is being conducted to assess the following: * overall survival * event-free survival (events are defined as: death,non-engraftment/2nd transplant, immune reconstitution failure) * acute toxicity of the conditioning regimen * engraftment frequency immune reconstitution frequency and tempo acute and chronic graft-versus-host disease (GVHD), frequency and severity. The outcome from this protocol will be compared to the retrospective cohort consisting of all patients who have undergone haplo-identical HSCT for SCID at CHLA from 1984-2006 based on the assessment of the above-listed endpoints. The CliniMACS device will be used for CD34+ selection in place of the Isolex 300i. The CliniMACS CD34 Reagent System is an investigational medical device that has not yet been approved by the FDA. This device is used in vitro to select and enrich specific cell populations. When using the CliniMACS CD34 Reagent, the system selects CD34+ cells from heterogenous hematological cell populations for transplantation in cases where this is clinically indicated.