Viral gene therapy Computer artwork of a strand of DNA deoxyribonucleic acid red being carried by a virus blue illustrating the concept of gene therapy using viruses The two objects are drawn at different scales The geometric blue structure is the capsid protein shell of the virus The spiral strand is DNAs double helix molecular structure The first approved gene therapy took place in Since then a variety of methods and diseases have been investigated and several pioneering treatments attempted Viruses are the usual delivery method for gene therapy