LONDON - Scientists have developed a technique that uses a library of DNA taken from organs in which tumours can form and harnesses the body's immune response to create a vaccine designed to treat cancer.

In a study published in the journal Nature Medicine on Sunday, researchers from Britain and the United States said that in early tests in mice with prostate cancer, their experimental vaccine was able to shrink tumours, suggesting it could be developed in future into a treatment for cancer patients.

"Using the immune system to treat cancer is a very exciting area at the moment," Alan Melcher of Leeds University, who co-led the study, said in an interview. "What we've done is to develop a new approach which builds on a promising foundation."

He said the method could potentially be used against other forms of cancer such as skin or breast cancer, but added that the research was at an early stage and it would be several years before a vaccine could be developed for testing in humans.

Immunotherapy treatments - medicines that enlist the help of the body's immune system to fight disease - are a relatively new form of potential cancer treatment.

An immunotherapy drug called ipilimumab, or Yervoy, made by Bristol-Myers Squibb, was approved by the US Food and Drug Administration (FDA) in March as the first drug to help advanced melanoma patients live longer.

And last April, the FDA approved Dendreon Corp's Provenge, a therapeutic vaccine designed to stimulate the immune system to attack prostate cancer.

CELLS

Unlike traditional vaccines, therapeutic vaccines are not designed to prevent disease, but to treat it. They contain genes to stimulate the immune system to produce proteins called antigens, which activate the immune system to kill cancer cells.

Several drugmakers are trying to develop cancer vaccines but the work is proving difficult because each tumour has specific proteins and identifying the right antigens is tricky. There are also concerns that if more genes are used to increase the chances of producing successful antigens, this might trigger an immune response that is too strong for the body to handle.

Working with scientists from the Mayo Clinic in Rochester in the United States, Melcher's team made a vaccine made from a virus which they genetically engineered to contain a "library" of DNA including multiple fragments of genes - and therefore many possible antigens.

They found that this approach did not send the immune system into overdrive. Instead, the range of DNA meant the vaccine was able to target the tumour through many routes, they said.

Importantly, the DNA library was harvested from the same organ as the tumour, Melcher explained. This meant that the immune system "self-selected" the cancer antigens to respond to and did not react against other healthy parts of the body.

"The biggest challenge in immunology is developing antigens that can target the tumour without causing harm elsewhere," he said. "By using DNA from the same part of the body as the tumour ... we may be able to solve that problem."

Melcher said his team now planned to develop the technique further and have an experimental vaccine ready for testing in humans within a few years.