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Will We Have A Single-Shot HIV Vaccine Soon?

SHOT IN THE DARK

Thirty-eight years ago, when the first cases of HIV started appearing in the United States, no one could have predicted the crisis that would ensue. Since the first wave of the epidemic hit in the 1980s and ‘90s, over 675,000 people have died of AIDS complications in the United States. Medical breakthroughs have given HIV-positive people a new lease on life and for many, suppressed viral loads to such low levels that it’s impossible for those people to transmit the virus. Even though those who are diagnosed now have nearly the same life expectancy as those without HIV, they currently must rely on daily medication taken for the rest of their lives.

Moreover, there are still Americans converting to HIV stage 3 (or AIDS). In 2014 alone, over 6,700 deaths were directly attributable to AIDS complications. In 2016, over 18,000 Americans saw their HIV progress to stage 3.

All of this had made the hope for an HIV vaccine tantalizing for both scientists and those at risk for HIV. For decades, it was thought an effective vaccine would be developed in just a year or two (reports claimed this as early as the 1980s). Instead, failures have pushed scientists to embrace multi-injection vaccines. Now, a new study has renewed researchers’ optimism about the potential for a single-shot vaccine.

Nearly all potential HIV vaccination strategies currently being studied involve a series of shots, required to slowly train the immune system to recognize and attack the virus. That’s been necessary to combat the way HIV hijacks our own T cells and uses them to replicate. The two most significant vaccine clinical trials ongoing in Africa (Imbokodo and Uhambo) employ four and five shots respectively over the course of a year.

But now, researchers from the Scripps Research Institute in La Jolla, Calif., have manufactured a single-shot HIV vaccine that could be a game changer.

According to findings published in the January issue of Immunity, other vaccines being studied produce normal anti-HIV antibodies that have significant effects on preventing HIV contraction. But what makes Scripps’s vaccine (called the SOSIP BG505 env trimer vaccine) unique is that it induces the body to make bNAbs, antibodies that are normally only seen in people who’ve lived with HIV for many years. This marks the first time scientists have ever induced a mammal other than cows to produce these rare and potent antibodies in response to a vaccine.

The researchers believe this effect means the vaccine will also make a strong and “complete response” to HIV more likely if exposure does occur. In essence, the vaccine would be “sterilizing immunity,” and would be able to not only repel the virus but also contain any infection that occurs, according to NAM’s AIDSmap.

The data is based on a proof of concept study vaccinating 78 monkeys and further comparing those with the six highest antibody responses to those with the six lowest responses. It also compared the two responses to those of six other monkeys that were not vaccinated.

The vaccine was somewhat effective in the low-response group. Two of the monkeys contracted HIV after a round of six weekly rectal exposures, and the other four after a second round. In contrast, only one of the high-response monkeys contracted HIV after the first round of exposures. One other monkey in that group developed a viral load between the two rounds of exposures, and two more contracted HIV in the second. Still, two monkeys (a third of the high-response group) remained HIV-negative throughout the duration of the study, leaving researchers immensely optimistic.

Again, this was just a proof of concept study; researchers will next look at the overall safety and efficacy of the vaccine compared to other options available. But the study is giving scientists confidence that similar vaccines designed to produce broadly neutralizing antibodies could be even more effective for longer periods of time. And it has revived the hope that a one-shot HIV vaccine could still be in the cards. 

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