The damaged hearts of laboratory monkeys have been repaired successfully for the first time with human stem cells, in a study that could lead to the first clinical trials on patients with heart disease within the next four years, scientists have announced.

The study demonstrates that human stem cells can be grown in sufficiently large quantities to form beating cardiac muscle tissue which can be stored in frozen form until needed for a transplant operation, the researchers said.

Experiments involving the injection of human stem cells into the damaged hearts of mice, rats and guinea pigs have already shown the potential for treating heart disease. But the latest study, published in the journal Nature, is the first to prove its potential in a non-human primate species, the pintail macaque monkey.

"The main significance of this study is that it shows for the first time that we can do heart regeneration at a scale that the world has never seen before," said Charles Murry, professor of pathology and bioengineering at the University of Washington, in Seattle.

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"Were able to grow large amounts of human heart-muscle cells in a dish. We can grow them in the billions, we can freeze them and keep them in cold storage until we can use them and then we can transplant them into the heart of a large animal that really mimics the human condition well," Professor Murry said.

Stem cells, sometimes known as the master cells of the body, are seen as offering new kinds of treatments for incurable or progressive illnesses, from heart disease to Parkinsons, but there are still immense practical and safety issues before they can be widely introduced.

"For treating human heart disease, for instance, it will be necessary to grow billions of cardiac-muscle cells in the laboratory from stem cells and to freeze them without impairing their ability to regenerate damaged cardiac muscle once they have been implanted into a patient," Professor Murry said.

"The principal focus is to understand stem cells to the point where we can grow large amounts of human heart muscle in a dish, to learn the science of how they differentiate and then to harness them in such a way that we can cure human heart disease," he said.

"Before this study, it was not known if it is possible to produce sufficient numbers of these cells and successfully use them to re-muscularise damaged hearts in a large animal whose physiology is similar to that of the human heart," he explained.

- The Independent