Dr. Shinya Yamanaka and his team have done it again. This time they have produced induced pluripotent stem cells (iPS cells) without using viruses. Yamanaka was the first to show that stem cells equivalent to embryonic stem cells could be produced from normal cells such as skin, without ever using human embryos or human embryonic stem cells in his research. The process involved adding four genes to cells using retroviruses. The added genes "reprogram" the gene expression of the normal cells, making them behave like embryonic stem cells, but without the use of embryos, eggs, or cloning. However, there has been some concern that the retroviruses, which integrate into the cell's DNA, have the potential to induce cancer (beyond that usually seen with embryonic stem cells.) Yamanaka has now accomplished in mouse cells the reprogramming without the use of any virus, by using plasmids (circular pieces of DNA.) Using the same four genes, the cells were reprogrammed to iPS cells and behaved like embryonic stem cells, but without any of the added DNA integrating into the cell's DNA. Published online 9 October by Science, this advance continues the avalanche of results for iPS cells seen in just the last year, emphasizing the lack of results with embryonic stem cells as well as the growing movement away from the use of embryos and cloning.