Monkey Vaccine Hints at How to Stop HIV

A trial of an experimental vaccine in rhesus monkeys found it significantly reduced their risk of infection by simian immunodeficiency virus, which is related to HIV. Some of the immune responses for the SIV vaccine were the same observed in the only HIV vaccine trial in humans to have shown even partial protection against HIV infection.

Lead study author Dan Barouch, a virologist with Beth Israel Deaconess Medical Center in Boston, and colleagues treated groups of rhesus monkeys with several different two-stage vaccines: a prime vaccine composed of a virus genetically altered to contain SIV genes, followed half a year later with a booster made up of another virus expressing the same genes. Six months later, the team began exposing the monkeys to an SIV strain different from the vaccine strain, and against which monkeys have trouble mounting a strong immune response. The team continued exposing the animals at one-week intervals, and most vaccinated monkeys eventually contracted SIV.

The best at preventing infection was a vaccine consisting of a prime using modified adenovirus, and a booster using modified poxvirus. Three-quarters of non-vaccinated monkeys developed SIV infection after just one exposure, compared with 12 percent of those that received the best vaccine. The researchers calculated this vaccine reduced a monkey’s chance of contracting SIV after a single exposure by more than 80 percent.

Animals that produced high levels of antibodies that attach to the envelope protein that surrounds the virus were the most protected against SIV. Different immune responses against the envelope and the SIV protein called “Gag” were found in infected animals that kept viral levels low.

The study, “Vaccine Protection Against Acquisition of Neutralization-Resistant SIV Challenges in Rhesus Monkeys,” was published ahead of the print edition of Nature (2012;doi:10.1038/nature10766).

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