In vivo gene therapy is a process by which the genetic makeup of cells is altered to produce a therapeutic effect that prevents or treats diseases. Defective or missing hereditary material — DNA — in the nucleus of the patient’s cells is altered or replaced by healthy genes. Specially modified viruses act as the carriers of the new genetic material, delivering it to the patient’s targeted cells or tissues. The transfer of genetic material takes place within the patient’s body during this procedure.
The process of in vivo gene therapy is differentiated from ex vivo gene therapy in that the latter procedure takes cells from the patient’s body, inserting genes and culturing the cells in the laboratory rather than inside the patient’s body. The cells containing the new DNA are later reintroduced to the necessary tissues in the patient. The Latin term ex vivo means “out of the living,” and in vivo means “in the living.” This treatment generally requires extraction and replacement of the patient’s bone marrow in two separate surgeries.
The carriers or vectors delivering the therapeutic genetic material are retroviruses, adenoviruses, herpes viruses and other viruses. The viruses’ own genetic material is removed or inactivated, making them harmless and incapable of transmitting disease. The genetic material is then replaced by the therapeutic genes. Different viruses target different cells and tissues within the body. They deliver the new genetic material in a manner similar to the method used by disease-causing viruses when they inject genes into host cells while transmitting a disease.
Gene delivery is effective only if dividing cells are targeted. For the therapeutic genes delivered during in vivo gene therapy to be expressed in the tissue, they must be inserted into cells that are undergoing mitosis, the process of cell division. This allows the new DNA to spread through the patient’s tissues. After the virus delivers the new DNA, it dies or is attacked by the immune system.
Medical professionals are using gene therapy to treat various cancers, hereditary diseases caused by a genetic defect, human immunodeficiency virus (HIV) and other diseases. The technique works best with diseases that are caused by single defective genes. Many chronic diseases are caused by multiple gene disorders and present a greater challenge.
In vivo gene therapy research focuses on perfecting specific vectors for targeted cells and tissues, increasing the efficiency of gene transfer, increasing the consistency of gene delivery to an exact location in the patient’s DNA sequence and researching new disease-fighting applications for this technique. Research also has addressed the issues of rejection of the inserted therapeutic DNA and increasing the long-term effectiveness of gene transfer. Effective, noninvasive methods of detecting gene expression in the patient’s tissues and cells after in vivo gene therapy also have been researched.