The only HIV vaccine trial to achieve moderate success took place four years ago, yet it continues to reveal new information about the virus and renew hopes for a future vaccine.
In 2009, researchers released the findings of a six-year HIV vaccine study carried out in Thailand known as RV144. Conducted among 16,000 HIV-negative men and women, the trial found that HIV infection rates were 31 percent lower among participants who received the vaccine than in those who had not.
It was an encouraging protection rate, but short of the minimum 50 percent prevention rate required to slow the epidemic, which afflicts an estimated 34 million people worldwide, according to researchers at Duke University in the US.
Now, researchers say they have a better understanding of why the vaccine might have worked - and possible new targets for future vaccines.
Released in a recent edition of the journal Immunity, the study found that the vaccine prompted an immune response from four different antibodies. Researchers from Duke University, the US Military HIV Research Programme and the Thailand Ministry of Public Health used data collected from three of the trial’s participants to determine that these antibodies worked on an important site on the surface of HIV-infected cells. These antibodies essentially marked infected cells for death by natural killer cells, part of the body’s immune response.
The research could change the way future HIV vaccines are designed.
According to study co-author and Duke Human Vaccine Institute director Barton Haynes, the findings show the importance of often ignored “variable” sites on the surface of infected cells for vaccine research. Traditionally, most researchers have shied away from pinning their hopes on such sites because they differ across strains of HIV, he told IRIN/PlusNews.
He cautions, however, that researchers cannot say for certain this kind of immune response was the reason behind the Thai trial’s limited success.
This study follows similar results from South African research that may have identified yet another novel vaccine target. The South African research looked at broadly neutralizing antibodies that target and bond with specific sugars, blocking the virus from infecting healthy cells. According to Haynes, an ideal HIV vaccine candidate would be able to induce both types of immune responses.