Since it was first identified in 1983, HIV has infected more than 85 million people and caused some 40 million deaths worldwide.
While medication known as pre-exposure prophylaxis, or PrEP, can significantly reduce the risk of getting HIV, it has to be taken every day to be effective. A vaccine to provide lasting protection has eluded researchers for decades. Now, there may finally be a viable strategy for making 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 pivotal studies in the HIV vaccine field to date,” says Glenda Gray, an HIV expert and the 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 to stimulate the precursor cells needed to make these rare antibodies in people. The Duke study goes a step further to generate these antibodies, albeit at low levels.
“This is a scientific feat and gives the field great hope that one can construct an HIV vaccine regimen that directs the immune response along a path that is required 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 piece of it, for example, or a weakened version of it—and by doing so, spur the body’s B cells into producing protective antibodies against it. Those antibodies stick around so that when a person later encounters the real virus, the immune system remembers and is poised to attack.
While researchers were able to produce Covid-19 vaccines in a matter of months, creating a vaccine against HIV has proven much more challenging. The problem is the unique nature of the virus. HIV mutates rapidly, meaning it can quickly outmaneuver immune defenses. It also integrates into the human genome within a few days of exposure, hiding out from the immune system.
“Parts of the virus look like our own cells, and we don’t like to make antibodies against our own selves,” says Barton Haynes, director of the Duke Human Vaccine Institute and one of the authors on the paper.
The particular antibodies that researchers are interested in are known as broadly neutralizing antibodies, which can recognize and block different versions of the virus. Because of HIV’s shape-shifting nature, there are two main types of HIV and each has several strains. An effective vaccine will need to target many of them.
Some HIV-infected individuals generate broadly neutralizing antibodies, although it often takes years of living with HIV to do so, Haynes says. Even then, people don’t make enough of them to fight off the virus. These special antibodies are made by unusual B cells that are loaded with mutations they’ve acquired over time in reaction to the virus changing inside the body. “These are weird antibodies,” Haynes says. “The body doesn’t make them easily.”