The numerous discoveries of potent broadly neutralizing antibodies against HIV that have occurred in the last two years suggest that the human immune system is capable of making such antibodies against the virus more routinely than originally thought. This has made researchers more optimistic about the possibility of inducing antibodies that are capable of neutralizing a wide array of HIV strains at low concentrations. However, whether or not these antibodies, if induced by a vaccine, will actually protect humans against HIV infection is still an open question. And because there are no vaccine candidates yet that can induce these broadly neutralizing antibodies, researchers are instead planning to evaluate the protective efficacy of these antibodies in passive immunization studies.
All of the recently identified broadly neutralizing antibodies against HIV have been isolated from chronically HIV-infected volunteers. In a presentation at AIDS Vaccine 2011, Penny Moore of the National Institute of Communicable Diseases in Johannesburg, South Africa, addressed the question of whether the epitopes that are the targets of these broadly neutralizing antibodies that develop later in the course of infection are present in the transmitted founder virus that establishes infection.
What started as a trickle of new antibodies has become a steady downpour. In recent years, researchers have succeeded in isolating large numbers of broadly neutralizing antibodies from chronically HIV-infected individuals. Yesterday, on the opening day of the AIDS Vaccine 2011 conference in Bangkok, Thailand, Ian Wilson of IAVI’s Neutralizing Antibody Center at The Scripps Research Institute presented recently published data on a collection of 17 broadly neutralizing antibodies that he reported are "extremely potent." The collection of new antibodies are 10 times more potent than the recently isolated antibodies and 100 times more potent than the original handful of neutralizing antibodies, including b12, 2G12, and 4E10.
At the first plenary session of AIDS Vaccine 2011, which opened this morning in Bangkok, Thailand, researchers presented the results of a two-year-long effort to try to identify an immunological explanation for the modest 31% efficacy afforded by the prime-boost vaccine regimen tested in the RV144 trial, the first to show any efficacy in protecting against HIV infection. Barton Haynes, who led the scientific steering committee that oversaw the correlates search, reported that two immune responses were found to be significantly correlated with the HIV infection rate in RV144 vaccine recipients, a finding that generated several hypotheses about protective immune responses following vaccination and helped dispel doubts about whether the modest efficacy seen in the trial was real. "The findings lend credence to the vaccine efficacy seen in the RV144 trial," said Haynes, calling the results "intriguing clues on how the RV144 vaccine regimen may have protected."