New Vaccines May Keep HIV in Check

Several experimental vaccines that do not prevent infection with HIV but do apparently allow laboratory animals to live more or less healthy lives with HIV were described Thursday in presentations at the AIDS Vaccine 2001 meeting in Philadelphia.

The vaccines, delivered by injection, or in one case, by nasal spray, work by stimulating the immune system to keep AIDS in check. The effect has worked for more than a year and a half, but it is not known whether it will continue to work or whether it will work in people.

"If we had a vaccine that did nothing else but contain infection, could it have an important effect on the epidemic?" asked Gary J. Nabel, head of the AIDS vaccine research center at the National Institutes of Health. "The answer is yes." Such a vaccine would preserve the health of newly infected people, which would lower the amount of virus in the bloodstream and make a person less likely to transmit the infection to others.

In one study, scientists from several institutions used as a vaccine a weakened form of the vesicular stomatitis virus (VSV) into which pieces of AIDS virus had been inserted. VSV causes a nonfatal infection in livestock and occasionally infects humans, causing flu-like symptoms. Vaccinated and control groups of rhesus monkeys were all given the AIDS virus. All became infected, and seven of the eight controls developed AIDS. The vaccinated monkeys all showed a drop in CD4 cells, but the decline was much less than that seen in other animals. The concentration of HIV virus in the vaccinated animals' blood was also less. Most important, the animals have remained healthy for as long as 11 months, so far.

Two other vaccines were also reported. One used a piece of DNA that encodes two genes from the AIDS virus and an injection with a gene for interleukin-2, a hormone-like substance that boosts immunity. The other used a virus called vaccinia into which HIV genes had been placed. Both methods proved effective in keeping HIV-infected animals healthy. In the latter study, 19 of 20 rhesus monkeys that got a high dose of vaccine were able to suppress the AIDS virus to below detectable levels.

All of the vaccines work by stimulating cell-mediated immunity, which is one of the two main arms of the immune system. The other is immunity arising from the action of antibodies. HIV surface molecules don't stimulate antibody production very well and the molecules are constantly changing. It is unlikely, but not impossible, that a preventive AIDS vaccine that doesn't force the body to make anti-HIV antibodies can be developed. Biotechnology firms are working on a strategy to trigger such responses to HIV.

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