Since I was First identified in 1983, HIV has infected more than 85 million people and caused about 40 million deaths worldwide.
While medications known as pre-exposure prophylaxis, or PrEP, can significantly reduce the risk of contracting HIV, they must be taken every day to be effective. For decades, researchers have eluded finding a vaccine that provides lasting protection. Now, there may finally be a viable strategy for creating one.
An experimental vaccine developed at Duke University triggered an elusive type of broadly neutralizing antibody in a small group of people enrolled in a 2019 clinical trial. The findings were published today in the scientific journal Cell.
“This is one of the most fundamental studies in the HIV vaccine field to date,” says Glenda Gray, an HIV expert and president and CEO of the South African Medical Research Council, who was not involved in the study.
A few years ago, a team from Scripps Research and the International AIDS Vaccine Initiative (IAVI) showed that it was possible stimulate the necessary precursor cells to produce these rare antibodies in people. The Duke study goes a step further by generating these antibodies, albeit at low levels.
“This is a scientific feat and gives the field great hope that an HIV vaccine regimen can be constructed that directs the immune response down the path necessary for protection,” Gray says.
Vaccines work by training the immune system to recognize a virus or other pathogen. They introduce something that looks like the virus (a fragment, for example, or a weakened version of it) and, in doing so, stimulate the body’s B cells to produce protective antibodies against it. Those antibodies remain so that when a person later encounters the real virus, the immune system remembers it and is prepared to attack.
While researchers were able to produce Covid-19 vaccines in a matter of months, creating an HIV vaccine has proven much more challenging. The problem is the unique nature of the virus. HIV mutates rapidly, meaning it can quickly overcome immune defenses. It also integrates into the human genome within a few days of exposure, hiding from the immune system.
“Parts of the virus look like our own cells, and we don’t like to make antibodies against ourselves,” says Barton Haynes, director of the Duke Human Vaccine Institute and one of the paper’s authors.
The particular antibodies that researchers are interested in are known as broadly neutralizing antibodies, which can recognize and block different versions of the virus. Due to the changing nature of HIV, there are two main types of HIV and each has several strains. An effective vaccine will have to target many of them.
Some HIV-infected people generate broadly neutralizing antibodies, although it often takes years of living with HIV to achieve this, Haynes says. Even then, people are not producing enough quantities to combat the virus. These special antibodies are produced by unusual B cells that are loaded with mutations that they have acquired over time in reaction to the virus changing within the body. “These are foreign antibodies,” says Haynes. “The body doesn’t produce them easily.”