The breakthrough could help develop vaccines against the most aggressive form of skin cancer, malignant melanoma, and eventually help boost the immune system to fight against other cancers.

A group of scientists at Oxford's John Radcliffe Hospital and Swiss scientists at the Ludwig Institute for Cancer Research have developed a new technique which creates fake targets for cells which attack cancer.

The technique is based on earlier research into cells which attack HIV.

The targets, known as tetrameters, mimic the cancer cells and contain three parts of the surface of a malignant melanoma cell.

They also contain a fluorescent dye so that the cancer-attacking cells show up under a microscope when they lock onto the tetrameters.

Resistance

The scientists have worked on skin cancer because many patients who suffer from it are known to go into regression spontaneously, suggesting that their immune system may develop a resistance to the cancer.

There has also been a lot of research on melanomas in the last five years, with scientists being able to identify fragments on the surface of the cancer cells.

Dr Vincenzo Cerundolo, who led the Oxford team, says this is partly because it is relatively easy to take a melanoma tumour and grow it in a test tube.

Work on vaccines for skin cancer is relatively advanced with some trials currently underway in Europe and US.

Dr Cerundolo said they were far from making the tumour go into regression, but they were well on the way to creating vaccines which could boost the immune system.

"With this new technique, they will be able to monitor very quickly whether the vaccines are boosting the immune system," he said.

More research needed

However, he said more research was needed to show whether the cancer-attacking cells could win the battle against the tumour if their numbers were increased.

His team's experiments had shown that the cancer-attacking cells could kill cancer in test tubes, but the presence of the cells did not appear to make a difference to real-life people.

"It may be a numbers game. The tumour cells may outnumber the attackers or it may be that the tumour is suppressing the immune response," he said.

He hopes eventually to expand the research to cover other types of cancer.

The results of the research so far are published in this week's Journal of Experimental Medicine.

Invaluable research

Professor Gordon McVie: "This research will be invaluable"

Professor Gordon McVie, Director General of the Cancer Research Campaign, which has backed the research, said: "Immunotherapy - the idea of using the body's own defence to recognise and fight cancer - is a very exciting area of cancer research.

"But up to this point there has been no accurate way of knowing what kind of response, if any, the body was making to cancer.

"Now Dr Cerundolo and his colleagues in Oxford and Switzerland have very skillfully and successfully used a recently discovered technique to show us the killer cells are there and already in the fray.