AIDS Virus Shows
Cunning Ability To Evolve


LONDON (Reuters) - The AIDS virus HIV demonstrated its resilience when a man whose immune system was controlling one strain of the deadly virus was infected with another, underscoring the enormous challenge facing vaccine developers.
The unidentified patient had received drug therapy after the initial infection, and his immune system had been boosted enough to allow him to interrupt treatment and still fight the virus.
But it wasn't strong enough to prevent infection with a second strain of HIV.
"We have always anticipated that the development of a vaccine is going to be difficult because there are so many closely related strains of virus out there," Bruce Walker, the director of the AIDS Division at Harvard Medical School in Massachusetts, said in an interview Wednesday.
"What we are seeing here is further evidence of just how difficult that may be," he added.
But the AIDS expert, who reported the case in the science journal Nature, said he is still optimistic about vaccine approaches against the virus.
"We are making progress, it's just that we are up against a tough foe," he explained.
An effective vaccine is seen as the best hope to end the AIDS epidemic that has infected 42 million people worldwide. Scientists are looking into several vaccine approaches including boosting an antibody response and mobilizing the so-called infantry of the immune system -- T killer cells -- to attack and destroy virus-infected cells.
The patient had been on supervised treatment interruption, in which patients take breaks from drugs that help the immune system launch a response to the virus in the same way scientists hope a vaccine will.
He was battling the virus on his own for several months when doctors noticed a rise in his viral level and a decline in his T cell response.
Walker and his team ran detailed tests, which picked up the second strain of the virus his immune system couldn't handle. The man admitted he had earlier had unprotected sex.
"Consenting partners who are both HIV infected should practice safe sex," said Walker.
"With the growing number of drug resistant viruses circulating in the population the last thing you would want to do is to be taking drugs or completely controlling your own virus and then be exposed to a virus that has already learned to escape from the effect of the drugs."
In a commentary on the research Andrew McMichael and Sarah Rowland-Jones of the John Radcliffe Hospital in Oxford, England, said the superinfection with a second viral strain raises questions about both supervised treatment interruption and vaccine development.
"Certainly, this single-patient analysis raises many questions, but whether the news is bad, neutral or even good remains to be seen."
But they added that nothing should slow or divert efforts to develop an HIV vaccine.
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