Gene Transfer for X-Linked Severe Combined Immunodeficiency in Newly Diagnosed Infants

Inclusion Criteria: \* Treatment Eligibility Criteria: * Age \<2 years at the time of enrollment. * No prior therapy with allogeneic stem cell transplantation. * A clinical diagnosis of SCID-X1 documented in the medical record. * A proven mutation in the common gamma chain gene as defined by direct sequencing of patient DNA. * Age \> 2 months to \< 1 year of age at the time of busulfan administration. * Less than 300 CD3+ T-cells by flow cytometry or higher if evidence of maternal engraftment as supported by peripheral blood FISH analysis for XY and XX. * Lymphocyte proliferation to phytohemagglutinin (PHA) \<10% of the lower limit of normal for the laboratory. Treatment Exclusion Criteria: * Availability of a HLA matched sibling for allogeneic transplantation * Prior therapy with allogeneic stem cell transplantation * Positive for HIV infection by genome PCR * Presence of a medical condition indicating that survival will be less than 16 weeks such as the requirement for mechanical ventilation, severe failure of a major organ system, or evidence of a serious, progressive infection that is refractory to medical therapy. * The presence of any medical contraindications to general anesthesia and bone marrow harvest by aspiration * A social situation indicating that the family may not be able to comply with protocol procedures and recommended medical care.