The first trial came in 1990 on a four-year-old girl with a genetic mutation that crippled her immune system and left her at risk for infection. Doctors found a way to get functioning copies of the missing gene into the T cells of her blood system. The T cells were removed from her body, given the missing gene, and then reintroduced into her body. This led to a dramatic improvement of her immune system and allowed her to live a healthy life.
