Example of ex vivo gene therapy This procedure has been used to treat severe combined immunodeficiency syndrome (SCID). People with this disease are susceptible to infections because their white blood cells do not produce an enzyme needed by their immune systems. This disease has been treated in two different ways. In a short-term solution, the white blood cells were removed and infected with a retrovirus that carried the needed gene. After the cells were replaced, many of the cells contained the gene. White blood cells, however, are short-lived and a long-term solution is to apply this technique to the cells that produce the white blood cells (called stem cells). In vivo In vivo gene therapy treats cells in the individual without removing them. Retroviruses can be used to introduce genes directly into the body. Synthetic carriers like liposomes can also be used to carry genes. Liposomes are microscopic lipid vesicles that are readily taken up by cells. If they are coated with DNA, the DNA is also
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