BioEd Online

Embryonic stem cells, the controversial and versatile cells that seem able to do just about anything, have now expanded their repertoire into cancer prevention. A vaccine made from these cells shields mice against developing lung cancer under conditions thought to mimic the effects of smoking.

Safety concerns about injecting stem cells into humans mean that regulatory agencies are unlikely to approve human tests of the vaccine, says lead researcher John Eaton at the University of Louisville in Kentucky.

Nevertheless, he thinks the vaccine is worth testing in people at high risk of developing cancer, such as heavy smokers or people with certain genetic mutations.

Other researchers are more cautious. Cancer vaccines, particularly vaccines made from cells, are notoriously more effective in mice than people, says Jeffrey Weber, an immunotherapist at the University of Southern California in Los Angeles. "The idea is interesting, but the execution may be impossible," he says.

But both Weber and Eaton agree that the finding could lead to new ways to prevent or treat cancer.

A lot in common

Eaton's approach was inspired by the similarities between embryos, embryonic stem cells and tumours. "Embryos and tumours both grow as balls, they derive nutrients from the host, and they both express peculiar proteins - some of them in common," he says.

These shared proteins made Eaton think that a vaccine prompting an immune response to embryonic stem cells would also trigger an attack against tumours.

He and his colleagues injected mice with stem cells and gave the mice a booster shot ten days later. The researchers then transplanted lung cancer cells under the animals' skin a standard animal model for the disease.

The stem-cell injection protected 20 out of 25 mice from developing tumours, whereas tumours grew in all unvaccinated mice.

"We were absolutely shocked," Eaton says.

Even more effective was a mixture of stem cells and cells engineered to make a molecule that stimulates the immune system. None of the mice given this vaccine developed tumours when implanted with cancer cells.

Eight of nine animals given this treatment were also protected from lung cancer induced by chemicals thought to mimic the effects of cigarette smoke.

Eaton is now testing his approach against other types of cancer. The findings were reported on 8 November at a meeting in Prague on 'Molecular targets and cancer therapeutics', sponsored by a consortium of cancer-research organizations from Europe and the United States.

Weird protein

Although the mice seemed to suffer no ill effects from the vaccine, Eaton admits that injecting live stem cells into people raises safety issues such as whether the vaccine would make the body attack its own stem cells.

Eaton's team is now looking for the molecules on the embryonic stem cells that give the vaccine its tumour-killing power. That could potentially lead to more effective cancer vaccines with specific components.

The researchers have already discovered one such protein found mainly in embryos, placentas and tumours. As yet, Eaton is unwilling to say much about it, except: "It's weird."

Looking for such molecules holds more promise than injecting stem cells themselves, says Weber.

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