Gene therapy is an experimental treatment that involves introducing genetic material into a person’s cells to fight or prevent disease. Researchers are studying gene therapy for a number of diseases, such as severe combined immuno-deficiencies, hemophilia, Parkinson's disease, cancer and even HIV, through a number of different approaches (see video: 'Gene Therapy a new tool to cure human diseases'). A gene can be delivered to a cell using a carrier known as a “vector.” The most common types of vectors used in gene therapy are viruses. The viruses used in gene therapy are altered to make them safe, although some risks still exist with gene therapy. The technology is still in its infancy, but it has been used with some success.