In the first study of its kind looking at the safety of stem cells in animals closely related to humans, scientists worked on rhesus macaques. Previous studies have focused on mice, and one of the main problems is that when stem cells are implanted, tumours are very likely to form. Reassuringly, this does not seem to be the case in monkeys.
In the study, published in Cell Reports, the researchers took cells from a monkey's skin and reprogrammed them into a stem-cell-like state, making induced pluripotent stem cells, or iPSCs. They then coaxed these iPSCs into becoming bone-forming cells, before implanting them into the same animal the cells were taken from.
It took 20 times as many cells to form tumours in the monkeys compared to what was previously seen in mice. Lead researcher Dr Cynthia Dunbar, of the National Heart, Lung, and Blood Institute in the USA said 'tumour formation is very slow and requires large numbers of iPSCs', a result that bodes well for the therapeutic use of stem cells in humans.
iPSCs, which are made from a patient's own cells, can theoretically be transformed into any other kind of cell. As such, developing their use in the clinic could lead to a range of treatments, for instance for conditions such as heart disease, diabetes or Parkinson's disease.
Martin Pera, professor of stem cell sciences at the University of Melbourne, told Discovery News that this work is 'another step towards the development of safe stem cell therapies for human disease'.
Speaking to Nature News, Dr Ashleigh Boyd, a stem cell researcher at University College London who was not involved in the work, said: 'It's important because the field is very controversial right now'. Because of the contentious nature and high clinical potential of the research, more work needs to be done to validate the results. Indeed, Professor Pera told Discovery News that 'the study is small, it relates to the safety of only one type of specialised cell, and does not show directly that the bone grafts would heal or repair fractures'.
Dr Dunbar now hopes to repeat the work using heart, liver and white blood cells. She said: 'We hope the robust model established in this paper can be used to improve the chance that first-in-human iPSC-derived therapies will be safe and effective'.