As a global epidemic, the human immunodeficiency virus (HIV) is not a singular force, but a fractured, multifaceted challenge that scientists must fight with strategic approaches and large-scale solutions. Researchers from the Beth Israel Deaconess Medical Center (BIDMC) claim they may be of some help, as their latest tests of a global HIV vaccine have shown promise among nonhuman primates.
"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," lead author Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at BIDMC, said in a statement. "To our knowledge, this study represents the first evaluation of the protective efficacy of a candidate global HIV antigen strategy in nonhuman primates."
Published in the journal Cell, the study sought to better understand how a blend of three major HIV proteins — Env, Gag, and Pol — combated the virus among rhesus monkeys. These blends are called “mosaics,” and they offer scientists the chance to develop strains of HIV vaccines that retain their efficacy in the presence of diverse strains of the virus.
After immunization, the monkeys were repeatedly exposed to strains of the simian-human immunodeficiency virus (SHIV), which mixes HIV and the simian version of the virus. Scientists often use the hybrid as a way to parse out the differences between SIV and HIV. Although most animals that were exposed to the virus eventually became infected, the researchers found the probability of infection decreased 87 to 90 percent each time the monkeys were exposed to the virus.
Monkeys that received bunk vaccines became infected more quickly, ruling out any placebo effect.
"These findings indicate that these optimized vaccine antigens can afford partial protection in a stringent animal model," Barouch said.
He and his team found that the immune systems in vaccinated monkeys launched a robust antibody response, which attacked the virus through various defense channels. This suggested to researchers that multiple, coordinated responses may be necessary in order to combat thornier strains of the virus that are harder to neutralize. The monkeys also mounted cellular immune responses to multiple regions of the virus.
Perhaps the most heartening finding of the study was the researchers’ goal in tackling the most virulent strains of HIV, ones that were up to 100 times more potent in the lab than what a human would reasonably contract through sexual contact. The team argued their research was the first to critically test these harder-to-neutralize versions, as previous work has tended to focus on less complex strains.
By the World Health Organization’s current measure, 35.3 million people are living with HIV around the world. Fortunately, progress is being made. Between 2001 and 2012, new HIV infection rates dropped 33 percent.
"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," said Barouch. "We are planning to advance this HIV vaccine candidate into clinical trials next year.”