Human gene therapy involves the insertion of DNA (or RNA) into somatic cells to produce a therapeutic effect. Gene therapy was first envisaged as an approach to treating genetic disorders. In this scenario, missing or mutant genes could be replaced or repaired. Today, gene therapy has broader applications, with trials covering many clinical problems including genetic diseases, cancer, infections such as HIV, and degenerative diseases.

The transfer of genetic material into cells can be undertaken in many ways, most commonly using a viral vector. For this, viruses are genetically engineered to remove infectious potential while retaining the capacity to carry a therapeutic gene(s) into selected target cells. The inserted sequences can encode a missing or mutant product as might occur in the case of cancer, or alternatively could be used to inhibit a foreign protein as would be found in HIV infection. Viral vectors have been derived from a number of different viruses. Some, …