Gene Therapy is the introduction of genetic material into a host cell to treat or prevent a disease. It uses sections of DNA(usually genes) to replace the mutated gene and change the expression of protein(s) critical to the development and progress of the disease.

Several approaches to gene therapy:

• Replacing a mutated gene that causes diesease with a healthy copy of the gene.
• Inactivating, or "knocking out," a mutated gene that is not funcitoning properly.
• Introducing a new gene into the body to help fight a disease.

The genetic material can be delivered direclty as DNA or DNA complexes (non-viral methods) or packaged within a viral vector (recombinant virus) to efficiently taken up by appropriate cells. There are different viruses that can be used for human gene therapy as viral vectors, including retrovirus, adenovirus, lentivirus, herpes simplex, vaccinia and adeno-associated virus.