Advances in gene therapy over the past 15 years are finally allowing investigators to safely treat a growing number of carefully selected patients with a broad range of defective or missing genes, as reported by Ricki Lewis in the March issue of Scientific American. One of the biggest obstacles researchers have learned to overcome is the immune system’s propensity to over-react when thousands of copies of the stripped-down viruses carrying normal genes are injected into the body, mistakenly treating them as foreign invaders.

Lewis describes the problem and various solutions that are being used in detail in her article. This animation, created by Cortical Studios and Cyberfish, demonstrates one technique that scientists now use to circumvent the immune system in the liver.