Induced Pluripotent Stem Cells are usually engineered with genes to become embryonic stem cells. However, some enterprising people have taken the proteins encoded by the four genes (c-Myc, Klf4, Oct4 and Sox2) that are typically used to reprogram cells. They placed a eleven-amino acid tag on the front of the protein that helped them pass through the cell membrane. Then they soaked mouse fibroblast cells in a solution that contained these proteins plus a chemical called valproic acid. This reprogrammed the cells so that they were “morphologically indistinguishable” from embryonic stem cells and expressed similar markers.
Thus they were able to make protein-induced pluripotent stem cells (piPSCs) with no genetic engineering. No embryos were killed in this process.