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HIV Vaccine Primer: Basic Science and Concepts

May 13, 2013

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Getting to zero new HIV infections is already possible with our current HIV prevention methods -- condom use, pre-exposure prophylaxis, education, testing and so forth. But the holy grail of getting to zero remains an HIV vaccine. With an effective vaccine, HIV could eventually be eradicated, as with smallpox.

Just to be clear: No HIV vaccine currently exists. But there are many ongoing efforts to develop one, and those efforts have been revived in recent years. Some experts say we are at least 10 years away from an HIV vaccine, while others say it may be much longer than that.

So why is it taking so long? What makes developing a vaccine for HIV so difficult? Some of the science behind HIV vaccines can be tricky, but here are the basics to help you better understand what goes on in the human body and how a successful vaccine may be developed.


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The Biggest Obstacle in Developing an HIV Vaccine

"The one biggest [obstacle] is HIV itself," as top researcher Nicole Frahm, Ph.D., puts it. "It's an extremely complicated bug because it basically infects the cells of the immune system that are supposed to help you prevent an infection in the first place. The fact that it infects CD4 cells makes it very hard to build a good immune response against it."

Not only does HIV infect and disable the very system that's supposed to fight against it, but by the time the immune system catches up and develops a response, HIV mutates. There are also different strains of the virus, each of which attacks the immune system slightly differently -- another reason why HIV is very good at evading our natural defenses.

Even when researchers create a potential vaccine that's ready for testing, the clinical trials required to test it take considerable time and aren't cheap, to say the least. There are three trial phases a vaccine candidate has to pass before it can be approved by an official authority, such as the U.S. Food and Drug Administration, for medical use in the general public. Each trial phase requires more time, money, vaccine product and study volunteers than the last.

This doesn't mean an HIV vaccine isn't possible. It will just take time and a considerable amount of investment.


What Is a Vaccine?

A preventive vaccine is a substance that, when introduced into the body, can protect a person against developing a particular infection or disease in the future. A vaccine prepares the body, particularly the immune system, to defend against a specific pathogen (a disease-causing microorganism, such as a virus, bacteria or parasite) by creating an immune response.

In general, vaccines are given to uninfected individuals who may be exposed to the pathogen in the future. "When HIV infects you, it's ahead of the game. It's got two weeks to a month while your immune system is gearing up and responding," explains Rick King, vice president of vaccine design at the International AIDS Vaccine Initiative (IAVI). "What we're trying to do is to get the immune system there in advance."

The vaccines that are currently available for other diseases save millions of lives every year. These include the polio, tetanus and measles vaccines. Like these vaccines, an HIV vaccine would prepare the body ahead of time, so that it's ready to fight HIV if exposed to it. An important thing to keep in mind: Vaccines don't have to be 100 percent effective to be approved, or to stop an outbreak in its tracks. Most licensed vaccines in the U.S. are 70 to 95 percent effective.

Vaccines can be given in many ways, including injections into the muscle, injections into or under the skin, as a patch applied onto the skin or inside the nose, or as a pill taken orally.

(In addition to preventive vaccines, there is some research going on to develop a therapeutic vaccine for people living with HIV. If effective, it would use the person's immune system to help control the HIV and delay disease progression. But we will focus on preventive vaccines in this article.)

For a more in-depth overview, watch "How an AIDS Vaccine Might Work" from IAVI:



Types of Vaccines

The most straightforward vaccine would be a live attenuated vaccine, which uses a weakened version of the pathogen. This is how the vaccines for measles and mumps work. However, live attenuated HIV is never used in HIV vaccine trials, in order to avoid any risk of HIV infection via the vaccine itself. Therefore, HIV vaccine trial participants are never actually exposed to HIV, and have no chance of becoming infected.

A whole-cell inactivated vaccine is made from whole viruses or bacteria whose ability to grow and reproduce has been eliminated. Currently, there is only one HIV vaccine trial testing an HIV vaccine candidate made from inactivated whole HIV that has been genetically modified. Phase 1 results demonstrated safety and tolerability, and the researchers are moving into phase 2.

A subunit vaccine uses purified pieces of the pathogen (known as antigens) to trigger a strong, protective immune response. This is how the vaccines for influenza and hepatitis B work. The first HIV vaccine candidate tested in humans (AIDSVAX) used this approach, but it failed to show protection. However, subunit vaccine approaches are still being researched.

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This article was provided by TheBody.com.
 
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More on Preventive HIV Vaccines

 

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