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CROI 2015: Neutralizing Antibodies Provide Hope for an HIV Vaccine

, by Emily Newman

BETA is attending and reporting from the 2015 Conference on Retroviruses and Opportunistic Infections this week in Seattle from February 23 to 26—bringing you the latest news, updates, and research on HIV treatment and prevention.

“There’s one fact that everyone in this room—everyone at this conference—can agree on. And this is that the development and the discovery of a safe and effective HIV vaccine is the most effective path forward to ending this epidemic,” said Galit Alter, PhD, of the Ragon Institute of MGH, MIT, and Harvard during a motivating, rapid-fire talk about the search for an HIV vaccine on Monday.

The field hasn’t, in the last five years, shared much of the CROI limelight, says Alter. But still, “there’s been a lot of momentum in the HIV vaccine field.”

A big part of that momentum includes research on “broadly-neutralizing antibodies,”. These antibodies—produced by the immune system in response to HIV—actually block HIV infections.

“One of the most exciting phenomenon that has come up in research in the last few years is the understanding that the induction of neutralizing antibodies is not a rare event. About one in every three individuals who is infected will evolve antibodies that will target and neutralize many of the viruses from across the globe. They evolve B cell responses that—while they don’t neutralize their own virus—can neutralize many viruses,” explained Alter.

The challenge for researchers is to develop a vaccine that leads to the production of these neutralizing antibodies before the person is exposed to HIV, that can account for the enormous diversity of the strains of the virus that can develop and evolve after infection. An additional challenge is that—because HIV establishes a reservoir within days of infection—the vaccine must act quickly, “within the first two days,” according to Alter, to protect someone from infection.

An encouraging development she points to is the somewhat recent discovery that there are relatively few different types of sites on the outside HIV “envelope” that are targeted by neutralizing antibodies. This means that researchers have been able to create a “roadmap” of the conserved sites that are present on many different types of HIV—a discovery which could guide future research on a neutralizing antibody vaccine.

Even though we don’t yet have successful data from a human HIV vaccine study, Alter shared that researchers are making significant strides.

“Let me convince you of this: What we know is that if we take a neutralizing antibody and put it in a monkey, there’s no question we can block infection. We can block infection at really low doses of that antibody. We can learn from natural infection where these protective responses do evolve. They come up. People have them. If they never evolved, we’d have a real challenge. But they do exist. The question now is, how do we generate vaccines that will induce those? And do that in sufficiently abundant levels so that they can actually provide protection when somebody sees the virus?”

She began, and ended, her talk on a promising note, saying, “What I want to convince you of today is that the glass is not half empty. It is half full, and there is incredible discovery on the horizon.”

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