Stem cells could be turned into killing machines to fight brain cancer, scientists from Harvard Medical School have discovered.

In experiments on mice, the stem cells were genetically engineered to produce and secrete toxins which kill brain tumors, without killing normal cells or themselves.

Researchers said the next stage was to test the procedure in humans.

A stem cell expert said this was “the future” of cancer treatment.

The study, published in the journal Stem Cells, was the work of scientists from Massachusetts General Hospital and the Harvard Stem Cell Institute.

For many years, they had been researching a stem-cell-based therapy for cancer, which would kill only tumor cells and no others.

They used genetic engineering to make stem cells that spewed out cancer-killing toxins, but, crucially, were also able to resist the effects of the poison they were producing.

They also posed no risk to normal, healthy cells.

In animal tests, the stem cells were surrounded in gel and placed at the site of the brain tumor after it had been removed.

Their cancer cells then died as they had no defense against the toxins.

Stem cells could be turned into killing machines to fight brain cancer

Dr. Khalid Shah, lead author and director of the molecular neurotherapy and imaging lab at Massachusetts General Hospital and Harvard Medical School, said the results were very positive.

“After doing all of the molecular analysis and imaging to track the inhibition of protein synthesis within brain tumors, we do see the toxins kill the cancer cells.”

He added: “Cancer-killing toxins have been used with great success in a variety of blood cancers, but they don’t work as well in solid tumors because the cancers aren’t as accessible and the toxins have a short half-life.”

But genetically engineering stem cells has changed all that, he said.

“Now, we have toxin-resistant stem cells that can make and release cancer-killing drugs.”

Dr. Khalid Shah now plans to test the technique using a number of different therapies on mice with glioblastoma, the most common brain tumor in human adults. He hopes the therapies could be used in clinical trials within the next five years.