Cancer resistant mice

Mice that are resistant to cancer have been discovered by researchers in the US.

When white blood cells from the mice are injected into other mice, they eradicate advanced tumours and provide lifetime protection against the disease.

The findings could explain rare cases in which tumours in people spontaneously disappear.

Researchers led by Zheng Cui of Wake Forest University in Winston-Salem, North Carolina, said the natural cancer resistance appeared to be due to a genetic mutation that made white blood cells extremely good at finding and destroying cancer cells.

"Even highly aggressive forms of malignancy with very large tumours were eradicated," Dr Cui said. "The next step is to understand the exact way in which it works, and perhaps eventually design such a therapy for humans."

However, Dr Cui's team has been unable to identify the mutation, and other scientists have cautioned that such surprising findings need to be replicated in other laboratories.

The research, published in the Proceedings of the National Academy of Sciences yesterday, began with a stroke of luck in 1999.

A young researcher transplanting highly virulent cancer cells into mice noticed that one remarkable mouse did not develop cancer, no matter how many lethal doses it got.

The team bred the mouse, and found about half its offspring inherited this natural resistance to a range of cancers including leukemia, lung, liver and connective tissue tumours.

They discovered that injected cancer cells were killed within a day, after white blood cells clustered around them like a "rosette" and ruptured them.

The resistance to cancer was greatest when the mice were adolescent - about six weeks old. If cancer cells were injected at five months of age, the tumours grew like normal but suddenly shrank after a fortnight.

"In some cases this spontaneous regression of cancer was dramatic. A very large tumour mass disappeared overnight," Dr Cui said.

However, mice injected with cancer cells after one year - about half a lifetime - were no longer resistant.

If people had a similar cancer resistance gene, it might be possible to take white blood cells from a patient and introduce a mutated gene so their cells became more effective at fighting cancer, the researchers said.

Such an approach would be "complex and take many years to develop".