Genes can be delivered into a group of cells in a patient's body in two ways. The first, calledin vivo (in VEE-voh), is to inject the vector directly into the patient, aiming to target the affected cells.
The second, calledex vivo (ex VEE-voh), is to deliver the gene to cells that have been removed from the body and are growing in culture. After the gene is delivered, integration and activation are confirmed, and the cells are put back into the patient.
Ex vivo approaches are less likely to trigger an immune response, because no viruses are put into patients. They also allow researchers to make sure the cells are functioning properly before they're put in the patient. Several gene therapy successes useex vivo gene delivery as an alternative to bone marrow transplants.
Bone marrow contains stem cells that give rise to many types of blood cells. Bone marrow transplants are used to treat many genetic disorders, especially those that involve malfunctioning blood cells. Ideally, a "matched" donor, often a relative, donates bone marrow to the patient. The match decreases the chances that the patient's immune system will reject the donor cells. However, it's not always possible to find a match. In these cases, the patient's own bone marrow cells can be removed and the faulty gene corrected with gene therapy. The corrected cells can then be returned to the patient.
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