It’ll be awhile before scientists are able to use stem cells to grow entire organs within a laboratory, but it’s safe to say that every day the world inches a little closer to this dream. Now, in what is undoubtedly a major step forwards, a team of researchers has used skin-derived stem cells to revitalize the hearts of five living macaque monkeys.

Stem cells are able to turn into many different types of cell within the body. Unfortunately, the hearts of many animals have lost the ability to use stem cells to regenerate damaged or destroyed heart tissue. At best, only patchwork-like repairs can be made.

However, recent research has shown that specially engineering “progenitor” cells – those similar to stem cells but those already programmed to become a specific cell type – can be injected into the damaged hearts of mice, where they spontaneously make new vessels and tissue.

This new Nature study has revealed that a similar technique has worked successfully on monkeys.

Starting with skin cells from a single macaque, the team reverse engineered them back into neutral, juvenile cells known as pluripotent stem cells, those that have the capability of differentiating into any other type of cell. They were injected into the damaged hearts, and over the course of several weeks, they successfully integrated with the heart cells and began regenerating lost or damaged tissue.

Fairly rapidly, the ability of those hearts to contract improved, but the team did note that the macaques had some trouble with irregular heartbeats on occasion, a condition known as arrhythmia. “We still have some hurdles,” study co-author Yuji Shiba, a researcher at Shinshu University, told AFP.

Although the monkeys lived throughout the entire three-month-long study period, they were euthanized at the end of it – so the healing effect of these stem cells beyond this time isn’t yet clear.

^{Stem cell experimentation in action. It's a tricky process with many pitfalls. VILevi/Shutterstock}

Ideally, stem cells would be manufactured from the biological material of each individual monkey. That way, when they were implanted into each separate simian patient, their body would be far less likely to have a negative immune system reaction and reject the foreign genetic material.

However, the team thought that producing batches of individualized stem cells would be incredibly expensive and would take far too long. Instead, they made a batch from the skin of a single macaque, and made sure the extracted proteins most closely matched that of the types found in each of the recipient macaques.

They also gave the monkeys mild immunosuppressant drugs during the transplant. It worked – none of the monkeys’ immune systems rejected the transplanted cells.

These curious cells – technically known as induced pluripotent stem cells (iPSCs) – are seen by many as the path to a new age of medical prosperity. Although they are still poorly understood, small advances from time to time suggest that the future could feature revolutionary treatments that use our own cells to heal our hearts, cure blindness, and stop multiple sclerosis.

Remarkably, this is the first study to show that iPSCs can be used to fix – not merely patch up – heart damage. Around 610,000 people die from heart disease in the US alone every single year, so this research is a significant advance. After all, monkey hearts aren’t too dissimilar from our own.

However, the path is long and winding. There’s a long way to go before we can use easy-to-access stem cells to erase any damage anywhere in our body without any risky side effects.

^{The future of medical research? Stem cells in a cooled container. Elena Pavlovich/Shutterstock}