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Outline the treatment of SCID using viral vectors - Be specific and thorough.
Genetic screening shows SCID, stem cells taken from umbilical cord, allele coding for ADA inserted into retrovirus, retrovirus mixed w/ stem cells and insert the gene into the chromosomes, stem cells w/ functional ADA gene inserted into blood stream, these stem cells become T-cells that create the ADA enzyme. This treatment worked for 4 years before more gene therapy had to occur.