Live Monkey AIDS Vaccine Safe After All?

A pilot study of a live vaccine against the monkey version of the AIDS virus may ease one fear about such vaccines: that they should never be used in newborns. The findings, in the January issue of Nature Medicine, have prompted some AIDS researchers to suggest that a live vaccine for humans--an idea shelved because of safety concerns--should get another look.

A team led by virologist Ronald Desrosiers of the New England Regional Primate Research Center injected 18 newborn macaque monkeys with a genetically weakened strain of simian immunodeficiency virus (SIV). Previous studies had found that massive doses of SIV vaccine protected adult monkeys but caused disease in newborns. The new study, which explored the effects of doses five to 300 times smaller, found that only those infants exposed to the largest dose of attenuated virus--283 nanograms--came down with the disease.

The results are perplexing, because the conventional wisdom has been that the progression from SIV infection to full-blown disease is unrelated to the initial viral dose. The New England group's experiment "may be taken as evidence for a dose effect, which is difficult to explain," says AIDS researcher David Montefiore of Duke University. But the findings suggest that SIV vaccine may be safe and effective in newborn and adult monkeys, says Desrosiers. "Yes, a high dose of the virus in an absolute newborn under extreme conditions can still result in disease," he says. "But we don't think that this is a natural scenario."

Proponents of live-attenuated HIV vaccines face an uphill battle in convincing their colleagues that the benefits of this approach outweigh potential risks, however. These vaccines, such as one for polio, carry a risk of causing the disease: Each year about 10 people contract polio from vaccine. Nonetheless, live-attenuated HIV vaccines "bear serious attention," says Michael Murphey-Corb of the Tulane Regional Primate Center in Los Angeles. "After all these years of hard effort," she says, "it's the only thing we've got going for us."