The Science Behind AMP: It’s Not Like a Vaccine Study.
The AMP Study (also known as HVTN 704/HPTN 085) tests an experimental antibody against HIV. AMP stands for Antibody Mediated Prevention. This is the idea of giving people antibodies that fight HIV to see if they will protect people from becoming infected with HIV.
How do Antibodies Work?
Antibodies are one of the natural ways that our bodies fight infection. They are proteins that can be created by our own immune system or in a laboratory. Antibodies work by identifying and attaching to infectious agents that can make us sick, like HIV and other viruses. Giving people antibodies to prevent an infection is an accepted medical practice that is more than 100 years old. For example, doctors give people antibodies to prevent infections like hepatitis A and B as well as chicken pox.
Antibodies are specific, just like puzzle pieces: to attach to HIV, the antibody has to be the right fit for the HIV. When an antibody is able to attach to HIV, it “neutralizes” HIV, which means HIV cannot infect other cells. The challenge is that antibodies against HIV can only attach to specific parts of HIV—but there are many variations around these attachment sites that can vary from one viral particle to the next. For this reason, most antibodies against HIV can only attach to, or neutralize, a limited number of HIV particles, and therefore may not provide substantial protection. The antibody used in the AMP study is special because it’s a broadly neutralizing antibody, or “bnAb.” A bnAb can attach to a part of HIV that can’t vary from particle to particle. That means a bnAb has the power to neutralize a broad range of HIV, and therefore may provide protection against infection.
AMP vs. Vaccines: There is a Difference
The AMP study tests an antibody called VRC01, a manufactured antibody against HIV. This is a new idea for HIV prevention that is related to what has been done in HIV vaccine research, but slightly different. In traditional HIV vaccine studies, people get a vaccine and researchers wait to see if their bodies will make antibodies against HIV in response to the vaccine. In this study, we will skip that step, and give people the antibodies directly.
More About VRC01
The VRC01 antibody was originally discovered in the blood of a person who had been infected with HIV for many years, and whose body was able to control the infection without medicine (known as a “long term non-progressor” or “elite controller”).
The VRC01 antibody we are testing in the study is not made from the blood of people living with HIV. In fact, the VRC01 antibody just mimics the antibody found in the aformentioned person who was able to control their infection. VRCO1 is not made from any whole, live, killed, or weakened HIV, or HIV–infected human cells or blood. It cannot cause HIV infection or AIDS. The antibody is made in a laboratory, using the same kinds of processes used to make other medicines.
Is VRC01 Safe & Does it Work to Prevent HIV?
Laboratory tests have shown that the VRC01 antibody can prevent many different variations of HIV from around the world from infecting cells. VRC01 also prevented animals from getting infected. Over one hundred people have received VRC01 in previous studies, and these studies showed the antibody looked safe to give to people. The AMP study will help us learn if the VRC01 antibody will prevent HIV infection in people.
Unlike in HIV vaccine studies, people who get VRC01 in the AMP study are not expected to have positive results on common HIV tests. Samples of human blood with VRC01 have been tested using several common HIV test kits to see if getting VRC01 can cause a positive HIV test result. In these laboratory experiments, this did not happen. More experiments are being done to confirm this result.
It’s not yet known whether VRC01 can protect participants from getting infected with HIV. This study is the first one designed to find out if the VRC01 antibody prevents HIV infection. Participants should not expect to be protected from HIV by participating in the AMP study. In fact, one third of participants will get a placebo. All participants in this study will be counseled about ways to reduce their risk for HIV infection.