Somatic cell genome editing can happen outside the body (ex vivo) or inside the body (in vivo).
In ex vivo genome editing, the cells carrying the gene(s) causing a disease —for example, blood cells—are first removed from the patient, isolated and sustained in a laboratory before genome editing treatment is applied to correct the malfunctioning gene. Upon successful transformation, the corrected cells which were brought back to normal functioning are returned to the patient. Ex vivo editing can only be performed in cells that can be safely removed from the patient, kept alive in a laboratory, and then given back to the patient in exactly the right location in the body. This is why ex vivo genome editing has the potential to address mainly blood and immune disorders, both of which involve cells from the bloodstream or bone marrow that can be collected, grown, and corrected outside the body, and then returned to the patient. The return of healthy cells to the patient can be carried out by a procedure like intravenous infusion.
In vivo genome editing occurs inside a human body and can potentially address many more genetic diseases. The editing therapeutics are delivered directly to the target site of the malfunctioning gene which finds the target cells and transforms them with a curative effect. In some cases, genome editing can be used to create healthy cells containing corrected genes. In the ideal case, these cells will divide and reproduce inside the body until they crowd out and replace the unhealthy cells containing the malfunctioning gene, thus leading to a permanent benefit. An in vivo genome editing medicine may look like a direct injection or an inhalation.