London - Dr Jonathan Stoye, head of virology at the institute has revealed that his team has detected a human gene, which holds the key to prevent AIDS; only a single change is required.

They have found a great difference between the gene of a human and the gene of a rhesus monkey.  The gene of that monkey also thwarts the infection.

According to Jonathan, if the gene had been the same in the human being, scientists at the National Institute of Medical Research in London feel that there would not have been the AIDS epidemic that now affects 40 million people worldwide.

"If it had recognized HIV, we probably would never have had AIDS. I believe it is a key change," said Dr Jonathan Stoye.

Scientists have found a great difference between the human and monkey genes; however, they feel it is quite difficult to infect monkey cells with HIV than human cells in laboratory experiments. They believe further that there is something different in the animal cells that block the spreading.

The experts say that it is a gene called Trim 5 alpha later found to be the reason why in monkeys and not in humans, it stops the virus from replicating.

Stoye pointed out one precise change in a protein, which is important in blocking HIV. By substituting a human protein is a monkey-derived protein they found could make the human cells defiant to HIV.

"The discovery has significant implications for the development of effective gene therapy to combat AIDS," Stoye, who reported the findings in the journal Current Biology.  He is sure that by introducing the gene carrying that single change back into human cells would certainly make those cells resistant to HIV infection.

According to Reuters, Gene therapy is an experimental technique, which introduces genetic material into cells to fight disease. The technique has been used for Parkinson's disease and in trials for illnesses such as cystic fibrosis and cancer.

Two French boys with severe immune deficiency were cured with gene therapy but they later developed leukemia.