As researchers reprogram a skin cell into an induced pluripotent stem cell (iPS cell), the cell goes through three stages. Stage 1 cells show the least progress in their reprogramming. Stage 2 cells are further along in theirreprogramming. Only Stage 3 cells are fully reprogrammed and able to turn into any kind of cell in the human body.

Spotlight

• When is an iPS cell really an iPS cell?

  The production of induced pluripotent stem cells is often imprecise, yielding many incompletely reprogrammed cells. Now, Thorsten Schlaeger, PhD, and George Daley, MD, PhD, of Children’s Stem Cell Program have developed a battery of tests to ensure that he has the real thing: pure pluripotent stem cells. The new work creates a standard of analysis in the field. Read more.