HIV vaccines fast-tracked

Researchers believe they've found a quick, accurate way to gauge the effectiveness of Aids vaccines about to be tested on several continents.

These vaccines are intended not to prevent infection with HIV, something most experts believe is beyond the reach of today's biomedical science. Instead, scientists hope immunisation will slow progression of the disease.

Now, a study using monkeys given a vaccine against SIV - the primate version of HIV - has shown that the response of a specific group of immune system cells predicts the shot's effectiveness.

Reporting in the June 9 issue of Science, the research team hopes the same will hold true for HIV vaccines.

"First, the magnitude of the response predicts how long the animal will survive after infection," said study author Dr Norman L. Letvin, a professor of medicine at Harvard Medical School and director of the division of viral pathogenesis at Beth Israel Deaconess Medical Centre, in Boston.

"Second, what we show in this manuscript is that a subset population of (immune) T-cells predicts survival," Letvin said.

T-cells are produced by the immune system in response to an infection. The T-cells whose response was critical in the vaccine's effectiveness were "central memory" T-cells, which have already been exposed to invading bacteria or viruses, the study showed.

"There are vaccines of this type in a more advanced clinical phase in humans," Letvin said. Trials of those vaccines are getting underway in the Caribbean and Africa, as well as the Americas, he said.

"How do we monitor these vaccines?" Letvin asked. "Do we have to wait 100, 200, 300 days after someone is infected to see how well they will do?"

The new study suggests that's not the case. The monkey findings show the response of these specific T-cells to infection gives an early indication of a vaccine's power to slow the progression of Aids.

"This can prove to be important in monitoring the human trials that are being originated," explained Letvin, who is also director of the Non-Human Primate Research Program at the Vaccine Research Centre, part of the US National Institutes of Health.

One trial, involving a vaccine developed by the US National Institute of Allergy and Infectious Diseases, is currently enrolling 480 HIV-free individuals in Africa, the Americas and Jamaica. The vaccine contains synthetically modified molecules found in HIV viruses that collectively account for 85 percent of HIV infections worldwide.

Two other trials of the vaccine are being planned for four African nations -Rwanda, Kenya, Uganda and Tanzania.

"If the data are reproduced, this is a really interesting observation," said Wayne C. Koff, senior vice president of vaccine research at the International Aids Vaccine Initiative, in New York City.

The current markers used to determine the effectiveness of HIV vaccines must be measured for years, Koff said. The new markers would enable "shorter and more intensive studies," he noted.

"This is preliminary data in a small number of animals," Koff cautioned. "But this is a very important observation if this is real." – (HealthDayNews)

June 2006