LONDON (Reuters) — British researchers said they might have found a way to engineer a common cold virus to fight cancer while avoiding the danger of damaging the liver.

Using mice with cancer, the scientists modified a harmless virus called an adenovirus to keep its natural ability to infect cells while making it vulnerable to molecules in the liver that can destroy it.

Mice given the virus lived twice as long as untreated mice, and 20 percent were cured, Ryan Cawood of Oxford University, who worked on the study, said in a telephone interview.

"The beauty of what we do with viruses is they replicate where you want them to replicate," he said. "We have harnessed that ability in the tumour and prevented its ability to replicate in the liver where it can do damage."

Researchers believe viruses, which are highly effective at killing cells, could one day become a valuable addition to the medical armoury against cancer.

Adenoviruses had been used against cancer in clinical trials in Britain but had not yet been licensed for widespread use in the country, the researchers said.

A limitation with many of the viruses used to fight cancer cells was that they were modified into a weaker form to protect other parts of the body, a hurdle the Oxford team overcame by making the virus susceptible to molecules only found in the liver, Cawood said.

In most research, the virus was stopped from working and turned back on in a cancer cell, he said, adding: "We just turned it off in the liver and left it on to kill the cancer cells."

The researchers said it would be at least two years before they could begin testing their new method on humans because they needed to explore safety and other issues further.

The findings, published in the Public Library of Science journal PLoS Pathogens, shed light on better using viruses to fight cancer, said Leonard Seymour of the University of Oxford and a Cancer UK researcher, who led the study.

"The approach we developed is easy to use and flexible," he said in a statement. "It may help in the development of future therapeutic viruses that are specific to certain disease sites."