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Bone grown from monkey skin cells

Stem cell step Researchers have been able to grow new bone using a monkey's own skin cells.

The US study is the first time such a development has been shown in an animal that is similar to humans.

Professor Martin Pera, program leader of the ARC Stem Cells Australia, says the work, published today in Cell Reports, is "another step towards the development of safe stem cell therapies for human disease".

The study uses induced pluripotent stem cells (iPSC), which are derived from adult skin cells and can be reprogrammed to work as other cells.

Pera says pluripotent stem cells can be used to make any type of healthy human tissue and therefore have great potential for treatment of disease.

However, he adds, knowledge of whether stem cell therapies will be safe and effective in a clinical setting is limited.

Senior author of the new study, Dr Cynthia Dunbar, at the National Heart, Lung, and Blood Institute in the US, says their findings go some way in addressing these concerns and sidesteps ethical issues surrounding the use of embryonic stem cells.

Monkey advantage

Previous work in this field has relied on scientists giving human iPSC products to immunodeficient mice, she says.

"But because of the species differences, the cells do not behave normally in mice, and the lack of the immune system means that issues of immune rejection or inflammation cannot be studied," says Dunbar.

Because monkeys are the closest model species to humans, with similar organ and tissue structure and immunity, testing monkey iPSCs in monkeys should be indicative of the safety and efficacy of the process in humans, Dunbar says.

For the study, skin cells were taken from rhesus macaques to form stem cells (iPSCs), which were then turned into bone-forming cells.

Dunbar says those "bone" cells were then implanted into the monkeys on ceramic particles that were already in use by reconstructive surgeons attempting to fill in or rebuild bone.

The implants were retrieved at eight, 12 and 16 weeks with bone shown to be forming as early as eight weeks, the authors report.

Dunbar says unlike in studies involving mice injected with iPSCs the risk of tumours developing in the rhesus monkeys appeared to be low.

"The teratomas (tumours) only formed following injection of very high doses of undifferentiated iPSCs into animals, and even then the teratomas grew very slowly," she says.

Step for safety

Pera says because the approach uses a technique to produce stem cells that can be customised to individual patients, it avoids the potential for immune rejection of the graft.

He describes the results from the US study as "encouraging in terms of the safety of pluripotent stem cell therapy".

"However, 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," he adds.

"Nevertheless the work is another step towards the development of safe stem cell therapies for human disease."

Dunbar says the team is now working on creating iPSC models for treatment of liver, heart, and bone marrow disorders.

"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."