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. A gene can be delivered to a cell using a carrier. The most common types of carriers used in gene therapy are altered safe viruses. The technology is still in its infancy, but it has been used with some success as outlined below (see also video 6).