Allowing a type of stem cell to mature before transplanting it into monkeys seems to prevent the cells from forming tumours or triggering inflammation — two safety concerns that have plagued the field. Instead, the cells generated new tissue.

Induced pluripotent stem (iPS) cells can form a variety of tissues and can be made using a patient's own cells. Cynthia Dunbar at the National Institutes of Health in Bethesda, Maryland, and her team made iPS cells from the skin and bone marrow cells of two monkeys, and transplanted the cells back into the donor monkeys. These immature cells generated tumours and stimulated an inflammatory response. However, iPS cells that had developed into bone precursor cells before being transplanted did not cause tumours or inflammation during the nearly year-long study, and formed new bone.

The findings show the promise of iPS cells for repairing tissue in humans, the researchers say.

Cell Rep. http://doi.org/stw (2014)