Gene Therapy

One of the most challenging problems in gene therapy is to achieve long-lasting expression of the therapeutic gene, also called the transgene. Often the virus used to deliver the transgene causes the patient's body to produce an immune response that destroys the very cells that have been treated. This is especially true when an adenovirus is used to deliver genes. The human body raises a potent immune response to prevent or limit infections by adenovirus, completely clearing it from the body within several weeks. This immune response is frequently directed at proteins made by the adenovirus itself.

To combat this problem, researchers have deleted more and more of the virus's own genetic material. These modifications make the viruses safer and less likely to raise an immune response, but also make them more and more difficult to grow in the quantities necessary for use in the clinic. Expression of therapeutic transgenes can also be lost when the regulatory sequences that control a gene and turn it on and off (called promoters and enhancers) are shut down. Although inflammation has been found to play a role in this process, it is not well understood, and much additional research remains to be done.