Scientists Successfully Test Stem Cell Therapy in Monkeys; Generate New Bone

Last week, researchers came that much closer to one day regrowing human bone lost to disease or injury.

In the latest issue of the journal Cell Reports, scientists from the National Institutes of Health announced that they have transformed skin cells from rhesus macaque monkeys into new bone—marking the first time such a procedure has been done in a primate. These findings are an important step towards regenerating bone in humans.

The research team, led by the National Heart, Lung and Blood Institute’s Dr. Cynthia Dunbar, used induced pluripotent stem cell (iPS cell) technology to transform the extracted cells from skin into bone. One of the main concerns of iPS cell technology, which transforms adult skin cells into embryonic-like stem cells, is the risk that those stem cells will spur tumor growth. But unlike studies in other animal models, such as mice, the team did not observe any tumor growth in the monkeys.

In this study, the research team first used standard iPS cell technology to transform adult rhesus macaque skin cells into iPS cells, which closely resembled embryonic stem cells. They then coaxed these cells into becoming early-stage bone cells, called ‘bone progenitor cells.’

At this point, the team engrafted these progenitor cells onto a type of implanted ceramic scaffold normally used by reconstructive surgeons. After a short period of time, the team noticed new bone growth.

But what was even more interesting was what they didn’t see growing on the scaffold: tumors. In fact, the only time they did observe tumor growth was in a separate set of experiments involving incredibly high doses of iPS cells. As Dunbar elaborated in last week’s news release:

“We have
used this model to demonstrate that tumor formation of a type called a ‘teratoma’ from…iPSCs does occur; however, tumor formation is very slow and requires large numbers of iPSCs given under very hospitable conditions. We have also shown that new bone can be produced from… iPSCs, as a model for their possible clinical application.”

And even though some tumor growth occurred, stem cells such as these iPS cells would never be directly injected into humans – they would always be matured into a specific cell type first like the main set of bone progenitor cell experiments in this study.

The results presented in this study present the strong possibility that therapies based on this approach—engrafting these iPS cell-derived bone progenitor cells—could offer a solution to patients suffering from congenital bone defects or even traumatic injuries resulting in significant bone loss. While there are many potential hurdles to overcome before testing this approach in humans, the results from this primate model are far superior to similar experiments in a dish, or even in other models, such as mice. As Dunbar explained, this so-called large animal preclinical model is essential to move potential treatments from the lab bench into the clinic:

“The testing of human-derived cells in vitro or in profoundly immunodeficient mice simply cannot model these crucial preclinical safety and efficiency issues.”

Want to learn more about how stem cells can be used to rebuild bone? Check out CIRM’s recent video series: Spotlight on Bone Repair.

Anne Holden