STD Awareness: Searching for an HIV Vaccine

Ever since the dawn of the AIDS era, researchers have worked nonstop to develop an HIV vaccine. In 1984, Margaret Heckler of the U.S. Department of Health and Human Services famously (over)promised that a vaccine would be ready for testing in two years. But it’s taken much, much longer. This Saturday, May 18, is HIV Vaccine Awareness Day, a celebration of the patients, community members, and scientists who are hard at work bringing this vaccine into existence.

Only one vaccine — still in the experimental stage — has shown any effectiveness against HIV.

Hiding from the Immune System

Vaccines are inspired by our own bodies’ ability to fight disease. Usually, when our immune system encounters a threat, it takes note of the viral “antigens,” which are like facial features — a button nose, say, or dramatically arched eyebrows — that make it instantly recognizable. It creates “antibodies,” weapons that can target those antigens like guided missiles. Often, the immune system can remember the distinguishing facial features so it’s ready to attack if the enemy ever returns — giving us immunity, possibly for life.

Vaccines take advantage of our natural ability to create these immune memories by exposing our immune systems to antigens without actually exposing us to infectious viruses. Think of it as a “wanted” poster that helps the immune system recognize “bad guys” before it actually sees them on the street, enabling it to attack and destroy them before they cause disease.

HIV particles (colored yellow) cluster around an immune cell.

Unfortunately, the immune system has lots of trouble recognizing HIV, and isn’t able to fight off infections. When HIV copies its genetic code, it’s sloppy and makes a lot of mistakes. You know how you need a different flu shot each year, because influenza viruses mutate so rapidly that we’re constantly encountering new strains? HIV is kind of like that, only worse. A vaccine that protects against one HIV strain won’t necessarily protect against the millions of other strains out there. As science writer Ed Yong says, “Creating an HIV vaccine is like trying to fire a gun at millions of shielded, moving targets. Oh, and they can eat your bullets.”

With the virus changing its face so often, the immune system can’t keep up. HIV can establish an infection before the immune system can react, and so far we’re not sure how to make a vaccine that will give the immune system a sufficient heads up.

A Hint from Nature

It turns out, though, that our bodies offer us clues for defeating HIV. Even though it mutates rapidly, there are some regions of the virus that seem to stay the same — probably because they are so essential to the virus’s function that they’re necessary for its survival. Unfortunately, these common regions are literally covered by a shield that hides it from the immune system.

About 10 to 50 percent of people with HIV produce “broadly neutralizing antibodies,” a fancy term for antibodies that can pierce this shield and target the common regions of a wide range of HIV strains. The immune system takes years to figure out how to manufacture these special antibodies, and by that time it’s too late for them to be of much help. But they’re a hint from nature as to what kind of an immune response a vaccine needs to set in motion. If a vaccine could trigger the immune system to manufacture broadly neutralizing antibodies, they could be ready to be deployed in case of an HIV invasion.

In spite of all the challenges presented by this complicated virus, many vaccine candidates have been developed, and six of them have been fully tested in humans. Only one, the RV144 vaccine, showed any kind of positive result, with an early “peak” in effectiveness followed by modest protection — 60.5 percent effectiveness the first year, which fell to 31.2 percent afterward. Not great, but a good start. While even a partially effective vaccine could be a boon, the dream is to create an HIV vaccine with nearly 100 percent effectiveness.

Still, RV144 was the first major victory after decades of HIV vaccine research, and showed that vaccinating against HIV, despite all of the difficulties our immune systems have in mounting a response to the virus, might actually be possible — in part by stimulating the production of broadly neutralizing antibodies capable of targeting “common” viral regions. RV144 also gave scientists reams of data to examine, which may provide more clues about how to improve the next vaccine. Many follow-up trials aim to tweak RV144 and improve on its modest success, so stay tuned for future headlines!

Probably the top two items on the AIDS-era wish list are a cure and a vaccine, but both have eluded researchers for decades. In the meantime, we’ve made enormous headway with many prevention strategies — safer sex, medications, circumcision, and clean needles. To eradicate the virus from the face of the earth, though, an effective and globally distributed vaccine might be necessary to drive the last nail in AIDS’ coffin.

Any Planned Parenthood health center can help you reduce risk of transmitting or acquiring HIV. We offer condoms, HIV screening, education, and preventive medication, and can connect you to treatment if you test positive for the virus.

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