New cancer treatments use body's own immune system to kill melanoma tumours

Nov 13 2006

Scientists are claiming that the body's own immune system could be used to fight the most serious form of skin cancer, malignant melanoma.

Two teams of researchers in the U.S. have been able to manipulate immune cells to boost the attack on cancer cells and the treatment appears to stop skin cancer progressing.

Experts say the studies are "significant", but much more research is needed before the treatment could be offered to patients.

Advanced melanoma is a devastating disease for which there is no effective treatment and the average life expectancy after diagnosis of the most serious form of the disease, stage four, is around nine months.

Though surgery or high doses of chemotherapy drugs are used to treat the cancer, while they can reduce the size of tumours they cannot prevent the disease recurring.

The immune system that attacks cancer cells is a delicately balanced defence system; the number of T cells, which recognise and attack foreign bodies such as tumour cells, are controlled by a T cells called Tregs.

Tregs role is to act as a break stop to prevent the immune attack going into overdrive and turning on the body.

One study found it was possible to suppress Tregs by blocking the activity of a protein on the cells' surface which left other parts of the immune system free to attack.

Dr. Jeffrey Weber, a professor of medicine at the University of Southern California in Los Angeles, and colleagues treated 25 patients with injections of an antibody to block the protein; eighteen months later, 24 of the patients are still alive and three are free of cancer.

In the second study, Dr. Jason Chesney from the J.G. Brown Cancer Center in Louisville, Kentucky found that when patients with advanced melanoma were given a drug combination of the diphtheria toxin and interleukin 2 to knock out their T-regulatory cells, tumors shrank or remained stable in five of seven participants.

The five patients on the higher dose saw their tumours shrink or remained stable and all seven are still alive 12 months after the treatment was given.

Mice studies have already found that the combination led to another part of the immune system armoury called CD8+T lymphocytes being freed up to attack and kill melanoma cells.

Dr. Chesney says the results show that depleting Treg cells in patients with melanoma may allow the immune system to be activated successfully to kill cancer cells.

Chesney says the patients have survived longer than the median average life expectancy of a patient with stage four melanoma and he believes that, in the future, immunotherapies that depend on depleting Treg cells may prove to be useful in all types of cancer.

Experts in the field say the studies represent a fundamentally different approach to treating cancer but there are risks in tampering with the body's immune system's control mechanism.

There are concerns it could lead to autoimmune diseases such as hepatitis, colitis or dermatitis.

However most say those conditions are manageable, and are outweighed by the prospect of beating melanoma.

The preliminary research was presented to a European cancer research conference in Prague.