Home » Stem Cell Therapy » Heart disease and stem-cell treatments: caught in a clinical stampede

There are important lessons to be learnt from the rush to develop stem-cell treatments for heart disease, says Roger Highfield.

Stem-cell treatment for heart disease was leapt upon by clinicians – but the evidence for it is lacking Photo: AP

It can be a long way from the laboratory to the hospital. Elegant, targeted anti-cancer therapies took decades to emerge after President Nixon declared his “war on cancer” in 1971. Gene transplants are only now beginning to be successful, after the first trial in 1990. The human genome, unveiled in 2000, generated a deluge of data but has had little impact so far on medicine.

Now there’s another story that sheds some light on why treatments can lag years behind the hype. The story concerns stem cells, the “all-purpose”, undifferentiated cells that can be harvested (controversially) from embryos or (less controversially) from adults to be grown into replacement tissue.

The hope was that stem-cell therapy could be used to treat heart disease, which claimed the lives of 17 million people worldwide last year. Only there is a disturbing twist to the tale. Despite an investment of billions of pounds in research, it seems that these new treatments may rely as much on faith as science.

The details emerged at the recent opening of the £60 million Scottish Centre for Regenerative Medicine in Edinburgh (SCRM), chaired by Sir Ian Wilmut, whose cloning of Dolly the sheep provided one way to grow stem cells. In a talk at the opening ceremony, Christine Mummery of the Leiden University Medical Centre in the Netherlands described how there was a “rush to the clinic” when an American team claimed in 2001, on the basis of experiments in mice, that bone-marrow cells could mend a heart damaged by coronary disease.

Since the development of the heart transplant, cardiologists have garnered a reputation for being gung-ho. This was no different. Without anything in the way of systematic research in animals, the first patients were treated the next year. Scientists usually damn with faint praise – but in this case, Prof Mummery went so far as to say that the paper that launched the stampede was “completely wrong”, and was overturned in follow-up studies. Yet the 2001 paper has never been withdrawn.

A few years ago, concerns over these heart trials were voiced by a Norwegian professor, Harald Arnesen. He concluded in 2007 that they “are not convincing” and that one German team had achieved striking results only because the control group in its trial had done particularly badly. Prof Arnesen called for a moratorium on this kind of stem-cell therapy.

That still did not deter the clinicians. This January, another trial funded by the EU was announced – the largest of all, with 3,000 heart-attack patients recruited from across Europe.

The idea behind the trials is straightforward. During a heart attack, a clogged blood vessel starves heart muscle of oxygen. Up to a billion heart muscle cells, called cardiomyocytes, can be damaged, and the body responds by replacing them with relatively inflexible scar tissue, which can lead to fatal heart failure. So why not implant stem cells that can grow into cardiomyocytes?

Stem cells, of course, come in many kinds: the embryonic variety have the potential to turn into all 200 cell types in the body. Adult stem cells, harvested from the patient, have a more limited repertoire: bone marrow stem cells generate blood cells, for example. So to claim, as was done in 2001, these bone marrow stem cells could turn into heart muscle was both surprising and exciting.

Analysis shows that, at best, the amount of blood pumped during a contraction of one heart chamber rose by 5 per cent after treatment. In a patient where heart efficiency has fallen to 30 per cent of normal, that could be significant – but it is relatively meagre, none the less. And it turns out that this level of improvement results whatever the cells injected into the damaged muscle – even if they have no prospect of forming cardiomyoctes.

Even the believers in the technique now agree that implanted cells exert a “paracrine action”, triggering a helpful inflammatory response or secreting chemicals that boost blood vessel formation. But we’re still waiting for convincing evidence that a patient’s lost heart muscle cells can be replaced.

Embryonic stem cells offer one route to that goal, though it is difficult to turn them into the right cell type reliably, and there are other risks, such as uncontrolled growths. Another option has come from work by Prof Richard Lee at the Harvard Stem Cell Institute, who has found that some adult stem cells can recruit other stem cells already in the heart to become cardiomyocytes.

Meanwhile, other fields of medicine that have seen more systematic research on stem cells are making real progress in using them – for example, to treat Parkinson’s, diabetes and macular degeneration. The lesson here is that, ultimately, it takes careful experiments, not belief, to make that huge leap from the laboratory to the hospital.

Roger Highfield is director of external affairs at the Science Museum Group



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