Mosaic HIV vaccine affords partial protection in monkeys

US researchers said Thursday that an experimental global vaccine may afford "partial protection " in monkeys against challenges with an especially deadly form of the AIDS virus, raising new hope for an effective vaccine in people. The so-called "mosaic vaccine" reduced the risk of infection by nearly 90 percent among monkeys exposed to a stringent simian- human immunodeficiency virus, which mixes HIV and the simian version of the virus, the team led by U.S. Beth Israel Deaconess Medical Center (BIDMC) reported in the journal Cell. "A global HIV vaccine would offer major biomedical and practical advantages over most other HIV vaccine candidates, which are limited to certain regions of the world," said lead author Dan Barouch, director of the Center for Virology and Vaccine Research at BIDMC. "To our knowledge, this study represents the first evaluation of the protective efficacy of a candidate global HIV antigen strategy in nonhuman primates." In their study, the researchers studied the immunogenicity of the "mosaic vaccine," a blend of three major HIV proteins, including Env, Gag and Pol, when it was administered to rhesus monkeys. After immunization, the monkeys were repetitively exposed to multiple to simian-human immunodeficiency virus challenges. "Although most vaccinated animals became infected by the end of the challenge series, we observed 87 percent to 90 percent reduction in the per-exposure probability of infection," the researchers wrote in their paper. In contrast, monkeys that received sham vaccines became infected more quickly, they said. The researchers said that most previous HIV vaccine candidates have typically only been tested in monkeys for protection against easy-to-neutralize viruses rather than against a difficult-to- neutralize virus like the one used in this study. Also, each viral challenge in the study was approximately 100- fold more infectious than typical sexual HIV exposures in humans, they noted. "These data suggest a path forward for the development of a global HIV vaccine and give us hope that such a vaccine might indeed be possible," Barouch said. "We are planning to advance this HIV vaccine candidate into clinical trials next year."