A protein produced by the body in the lymph glands can kill lung cancer cells, researchers have found.

They hope that a refined version may help to treat the disease - the most deadly form of cancer in the UK - by giving a helping hand to the human immune system.

When injected into laboratory mice, the protein, called SLC, destroyed lung cancer in 40% of the animals and dramatically slowed tumour growth in the rest.

The research team, lead by Dr Steven Dubinett, of the University of California Los Angeles, now hope to test the effect of the protein on human tumours.

Dr Dubinett said: "We're very encouraged by our results, and they have led us to the early stages of developing a genetic immunotherapy to maximise the cancer-fighting abilities of patients' immune systems."

SLC, or secondary lymphoid tissue chemokine, is a chemical which helps to send messages around the body's immune system and enables it to fight off disease.

It is one of many proteins found in recent years that slows or stops the growth of tumours by cutting off their blood supply.

Injected into tumours

Writing in the Journal of Immunology, Dr Dubinett said that when injected into tumours, SLC attracted immune cells known as lymphocytes and dendritic cells to the tumour.

These cells destroy invaders like bacteria but are also thought to kill off cells that develop faults, such as cancer cells.

Usually, dendritic cells do poorly against cancer cells.

Scientists think the cancer cells somehow disguise themselves.

However, SLC appeared to change the chemical balance when injected into the tumours, so that the cancer was less able to inhibit the action of the immune system.

Dr Dubinett said: "This shows that SLC can help prevent important immune cells from being tricked into ignoring invading cancer cells."

A spokesman for the Cancer Research Campaign said that the work using this chemical was "interesting", but stressed that it was a long way from treating tumours in mice to treating them in humans.

Lung cancer is the most common form of cancer in the world and is extremely deadly.

In the UK, only about 5% of people survive with the disease for more than five years.

Nine out of 10 cases are caused by smoking.