Researchers have developed a vaccine that prevents the development of AIDS in monkeys infected with an HIV-like virus, according to a report published today in the journal Science. This relatively simple vaccine apparently offers the strongest protection of any AIDS vaccine yet developed, making it one of the most promising candidates for human clinical trials.

Harriet L. Robinson of Emory University and her colleagues administered the three-part regimenwhich consisted of two DNA-based priming vaccines, followed by a modified poxvirus boosterto 24 monkeys. Seven months later, these vaccinated monkeys and a control group were exposed to a highly virulent hybrid of simian and human immunodeficiency viruses (SHIV). All the animals became infected with SHIV. Two weeks later, however, the control monkeys had 10 times more virus in their blood than the vaccinated monkeys. At 28 weeks, the control animals had developed opportunistic infections associated with AIDS and were euthanized. The vaccinated monkeys, in contrast, kept the virus in check and continue to remain healthy.

Even monkeys that received a low-dose vaccine succeeded in controlling the virus, Robinson notes. She attributes the vaccine's success to its ability to turn on the expression of the three major HIV proteins. All three of these proteins, in turn, induce specific immune responses, thus better preparing the body to recognize and attack the virus. Whether the vaccine will be effective in humans remains to be seen. Human clinical trials are scheduled to take place next year.