US virologists have developed a HIV vaccine using a weakened rabies virus to carry a piece of the HIV virus safely into the cells of laboratory mice.

The cells responded by creating immune system antibodies to attack the fragment, thus increasing their long-term capacity to fight off the HIV virus.

Scientists from Thomas Jefferson University in Philadelphia hope their work will lead to a human version of the vaccine. It would not prevent infection by HIV, but would enable the body to fight the virus successfully.

If this works then it would mean that all somebody who had been infected with the HIV virus would have to do would be to have an infrequent injection

Dr Jeffrey Williams Terrence Higgins Trust

Professor Roger Pomerantz, director of the Center for Human Virology at the university, said: "It's not only the first use of a rabies virus for an HIV vaccine, it's the first use of a whole group of viral vectors - non-segmented negative-stranded RNA viruses - for HIV vaccines."

Once the artificially created virus was inserted into the mice cells it began to manufacture a protein found in the outer coating of the HIV virus.

The scientists found that the mouse immune system was able to recognise this protein and began to develop antibodies against HIV, as well as releasing white blood cells called cytotoxic lymphocytes, which kill virus-infected cells.

However, the scientists had to give the mice a booster jab of a different HIV protein to kick-start the immune system to release anti-HIV antibodies.

Live virus

If the researchers work can be translated into humans, it could prove to be a significant breakthrough because it would allow a vaccine to be developed from a live virus.

Previous attempts at developing a vaccine have used viruses that have been killed, but researchers have found that dead material does not provoke a sufficiently robust response from the immune system.

Using a live virus would enable HIV protein to be created on an on-going basis. Theoretically, this would mean that the immune system was continually primed for action.

Dr Jeffrey Williams, health promotion officer for the Aids charity The Terrence Higgins Trust, said similar work was being done using a smallpox virus, while another study was testing the impact of directly injecting part of the HIV coat into cells.

He said: "If this works then it would mean that all somebody who had been infected with the HIV virus would have to do would be to have an infrequent injection, and that would boost their immune system, rather than having to take up to 15 pills day."

Dr Williams said current HIV drugs had side effects such as nausea. Also, they had to be taken every day to ensure the HIV virus does not have a chance to mutate and render them ineffective.

The researchers are now also working on using the same approach against other viruses such as hepatitis C.