A multinational team of researchers has shown that acute liver failure in a rat model can be prevented using a reversibly immortalized line of human hepatocytes. Though transplantation of primary hepatocytes has been suggested as a treatment for liver failure, the new work (Science 287, 1258–1262, 2000) is the first to demonstrate that liver cells can be reversibly immortalized for growth in culture, potentially overcoming the shortage of transplantable liver cells that limits this type of treatment. The team immortalized a differentiated hepatocyte line by inserting the SV40 T antigen gene flanked by LoxP recombination target sites. Once the cell population had expanded in culture, the SV40 gene was removed by expressing Cre recombinase, an enzyme that excises LoxP-flanked sequences, in the cells. Removing the SV40 gene aimed to lower the possibility of the cells causing tumors after transplantation. Transplanting the hepatocytes rescued rats that had undergone removal of 90% of the liver, a normally fatal operation that simulates acute liver failure. Philippe Leboulch, a senior author on the paper, says that the approach might eventually be used as “short-term therapy to bridge patients who have an acute liver failure…while they're waiting for a liver transplant.”