A new virus-based vaccine may help cure a range of cancers that have already progressed into advanced stages, says a study.

The experimental vaccine, when tested in a small group of patients, provoked the required tumor-fighting immune response.

Researchers at Duke University Medical Center have genetically tweaked a virus to make this therapeutic vaccine. This virus, which causes the Venezuelan equine encephalitis virus, is an alphavirus that affects the nervous systems of horses and donkeys.

Because of its specificity to dentritic cells which stimulate the body's immune system, alphaviruses provide an attractive vector for vaccines.

The investigators removed the genetic material of the Venezuelan equine encephalitis virus and placed a gene for the carcinoembryonic antigen (CEA) for their study. CEA is an immune system biomarker which is overproduced in many different types of cancer.

They administered the experimental virus vaccine containing CEA in 28 patients diagnosed with advanced, recurrent forms of lung, colon, breast, appendix or pancreatic cancer and those who ahd failed to respond standard chemo drugs multiple times over a three-month period.

The researchers analyzed the data and found that five patients responded positively to the therapy while two patients, who had already been in remission, stayed in remission while two others got their cancers stabilized. In another person diagnosed with pancreatic cancer, a liver lesion disappeared after the treatment, the study says.

The responses tended to occur in patients with smaller tumors and in those receiving higher doses of the vaccine, which also managed to evade the immune system's regulatory T cells, which could have shut down the body's immune response. The vaccine was able to get around them, although T cell levels were elevated in some patients, the researchers said.

Study lead author Dr. Michael Morse, associate professor of medicine at Duke University Medical Center, says the theory behind therapeutic cancer vaccines is that people with cancer tend to have defects in their immune system that compromise their ability to respond to malignancy.

"A vaccine has to work by activating immune cells that are capable of killing tumours and those immune cells have to survive long enough [to] get to the tumour and destroy it," he says.

The study, co-authored by employees from drug maker Alphavax which develops new vaccine technology, was partially supported by the United States National Cancer Institute.