Correction of X-linked Severe Combined Immunodeficiency (SCID-X1) by Gene Editing. The illustration of the stem/progenitor cell on the far left depicts the location of the gene mutation that causes the disorder. The affected cells are incubated in a cytokine cocktail that induces cell cycling without differentiation. Next, the targeted zinc finger nuclease (ZFN) is introduced into the cell by electroporation, followed by transduction with integrase deficient lentiviral vector (IDLV). The IDLV contains the cDNA for IL2RG exons 5-8 and green fluorescent protein (GFP) driven by the phosphoglycerate kinase (PGK) promoter. GFP functions as an easily identifiable marker expressed in parallel with IL2RG. This process results in high-fidelity homology directed repair (HDR), and thereby, corrects the gene mutation that caused SCID-X1. The corrected stem cells can be used therapeutically as, following transplant, their hematopoietic progeny, including T cells and NK cells, will expand in vivo and thereby restore normal immune function (far right).