They then differentiated the stem cells (directed them “back down” the normal developmental path) to become adult retinal cells. Before the transplantation for the second patient, we checked the genome sequence of the patient’s iPS cells and we identified a mutation in the cells. We are developing allogenic stem cell lines — stem cells from donors. We are performing rigorous quality tests, including sequencing the stem cells’ genomes to be sure the cells are free from cancer-causing mutations. That’s very different from the way stem cell treatments were originally described to the public.

Source: New York Times January 16, 2017 18:10 UTC