The first gene therapy approaches in X-CGD have shown that effective gene therapy requires bone-marrow (BM) conditioning with chemotherapy to make space for the gene-modified cells to engraft. These studies demonstrated that transplantation of gene modified stem cells led to production of white blood cells that could clear existing infections. However, some trials using mouse-derived retroviral vectors were complicated by the development of myelodysplasia and leukemia-like growth of blood cells. This trial will evaluate a new lentiviral vector that may be able to correct the defect, but have much lower risk for the complication.