Credit: Bob London

It was in Toronto, in the summer of 2006, that stem-cell research was turned upside down. I remember it clearly, but I didn't feel the earthquake at the time: a youngish, earnest Japanese researcher named Shinya Yamanaka gave a talk at the annual meeting of the International Society for Stem Cell Research, reporting that he could make mouse skin cells look and act like embryonic stem cells just by adding a few genes. The following year, both Yamanaka and Rudolf Jaenisch, a well-respected stem-cell researcher from MIT, reported that these induced pluripotent stem cells (known as iPS cells) passed the litmus test for pluripotency, or the ability to differentiate into all types of cells: when mouse iPS cells were injected into mouse embryos, the cells were incorporated into the developing mice.

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