In 2006, Shinya Yamanaka and his colleagues at Kyoto University, in Japan, reported that they could reprogram mouse skin cells to an embryonic-like state by adding four genes, since dubbed the Yamanaka factors. These cells, called induced pluripotent cells, can be transformed into different types of cells and tissues, and hold promise for studying disease and developing cell replacement therapies. However, scientists inserted the genes using viruses, making the cells unsuitable for human use. Now, for the first time, British and Canadian scientists have developed a way to reprogram stem cells without viruses.

According to an article on NatureNews,

Stem-cell researchers led by Andreas Nagy, of the Samuel Lunenfeld Research Institute at Mount Sinai Hospital in Toronto, Canada, and Keisuke Kaji, of the University of Edinburgh, UK, inserted genes encoding Yamanaka's factors into a piece of DNA, or cassette, that also contained a jumping gene known as piggyBAC. The teams showed that this cassette could be inserted into the DNA of mouse and human skin cells and could reprogram them back to an embryonic-like state (K. Kaji et al. Nature doi:10.1038/nature07864; 2009, K. Woltjen et al. Nature doi:10.1038/nature07863; 2009).

The teams then used an enzyme called transposase to remove the cassette from the mouse cells. But some scientists say that until the cassette is removed from human cells, the technique is not a major advance over viral methods.

Nagy, however, is confident that he will be able to use transposase to remove the cassette from human cells. He is currently trying to use his method to reprogram cat and dog cells.