More than 35,000 people in the US die of liver disease each year. The new viral treatment targets liver fibrosis, the progressive scarring of the liver that leads to organ failure. Liver failure occurs when healthy cells called hepatocytes are damaged by alcohol and disease. The gaps left by these cells are filled with myofibroblasts, which generate scar tissue from collagen. Eventually the liver cannot generate new hepatocytes quickly enough to counteract the damage caused by the scar tissue and the organ fails. Gene cocktail Holger Willenbring of the University of California, San Francisco, and his colleagues worked out a way to transform myofibroblasts into healthy hepatocytes using a cocktail of liver gene switches called transcription factors. The problem was getting these transcription factors into a scarred liver. That?s where the virus comes in. They packed a cold-related virus called an adeno-associated virus, or AAV, with their transcription factors and used it to infect myofibroblasts in liver-damaged mice. Once inside the myofibroblasts, the virus downloads the transcription factors, which transform the cells into hepatocytes. The treatment increased the number of healthy liver cells in the mice, as well as reducing the collagen content of their livers by a third on average. ?We think the combination of making more hepatocytes and reducing collagen is the most promising approach to treating liver fibrosis,? says Willenbring. More treatments ahead This new piece of research has encouraging and exciting implications for the future, says Vanessa Hebditch, director of communications and policy at the British Liver Trust. ?The vector used in these studies is one that has already been used in the treatment of other human diseases so this is a promising approach.? ?These are remarkable data,? says Amit Nathwani at University College London, who is using AAVs in potential treatments for a blood disorder called haemophilia B. ?Liver fibrosis is a major clinical problem and if these data can be reproduced clinically, the National Health Service would save billions and patients would be given a new lease of life.? Willenbring says that more work is needed to optimise the liver treatment, so it may be five years before it can be tried out in people. Other treatments that regenerate livers are also in development, some rely on stem cells, others are aimed at building replacement organs from scratch. Journal reference: Cell Stem Cell, DOI: 10.1016/j.stem.2016.05.005