AIDS vaccine prompts powerful defense against virus, study shows


Friday, October 20th 2000, 12:00 am
By: News On 6



WASHINGTON (AP) _ An AIDS vaccine tested in monkeys fails to keep the animals from becoming infected but prompts their bodies to mount a powerful defense that keeps the disease in check, researchers report.

In a study appearing Friday in the journal Science, researchers report that rhesus monkeys inoculated with the vaccine, then injected with AIDS virus, developed a strong army of immune system cells that attacked and controlled the infection. The animals, in effect, did not become ill.

The results suggest, but do not prove, that a similar vaccine developed for humans and now in the early stages of testing might be effective in controlling HIV, said Dr. Norman Letvin, a Harvard Medical School professor and senior author of the study. The effectiveness in humans, however, may take years to determine, he said.

``The vaccine did not block infection, but it provides substantial containment of viral replication (spread),'' said Letvin, a researcher on the staff of Beth Israel Deaconess Medical Center in Boston.

Letvin said the vaccine works by invigorating CD8 lymphocytes in the immune system. It is the job of CD8 cells, also called killer lymphocytes, to seek out and destroy cells in the body that have been infected with virus. The CD8 attack controls the population of virus, but does not eradicate it.

Researchers have long thought that to successfully combat the AIDS virus, the body would have to make a large number of CD8 cells that are primed to target the virus.

The tested vaccine caused a rapid rise in the number of CD8 cells and enabled the immune system to keep the AIDS virus from causing serious illness in 12 inoculated monkeys, said Letvin.

In the seven of the eight control monkeys that received placebo injections and were then injected with the virus, symptoms of illness quickly developed. Half the control monkeys were dead within 140 days.

The special vaccine was made with a combination of DNA taken from HIV, which infects humans, and SIV, an AIDS virus that infects only monkeys. The virus used to test the vaccine was also a laboratory-made combination of the two viruses.

Letvin said this combination was used to get results quickly. If natural viruses were used, he said, ``the disease course would be so slow that it would be many years'' before there were results.

A DNA vaccine made for humans, he said, would use only the DNA from HIV.

The researcher emphasized that although the monkey study is encouraging, it does not prove that a DNA-based AIDS vaccine will cause such a strong reaction in humans.

``Using DNA vaccines is a very good way to induce CD8 lymphocyte response in monkeys,'' said Letvin, ``but it is may be a bad way to induce such a response in humans. We simply don't know yet. That remains to be determined.''

Dr. Tony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the study was ``an important proof of concept'' because it demonstrated that it is possible for a vaccine to prompt a powerful CD8 lymphocyte attack against the AIDS virus.

A vigorous CD8 defense, he said, is thought to be essential in controlling the AIDS virus in humans.