Gene therapy is a 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 growing fast and the first gene therapy products are available on the market.