Scientists could not explain how two infection-fighting proteins in humans affected the rate of HIV infection in participants of the vaccine trial in Thailand known as RV144 – until now.
The six-year clinical trial was the first to produce evidence of an HIV vaccine that had shown some protective effect against HIV infection. Volunteers who received a vaccine combination were 31 percent less likely to be infected than those who did not, according to findings reported in 2009.
Barton Haynes, from Duke University in the US, the coordinator of the follow-up study, said: “Without knowing what immune responses might be involved... we have uninformed clues. Now we have informed hypotheses, we have directions.”
Vaccine recipients with high levels of one type of antibody response had the lowest rate of HIV infection, and those with high levels of another type had the highest rate of infection.
Presenting the team’s findings to almost 800 researchers gathered at the ongoing 2011 AIDS Vaccine conference in Bangkok, Haynes said the findings were not in themselves a solution to finding a vaccine, but rather a “hypothesis generator”.
Jim Mullins from the University of Washington told IRIN/PlusNews the findings gave researchers something to test. “Up until this tour-de-force analysis, everything [all hypotheses] was negative.”
Haynes said analysis was ongoing as scientists combed data for more “clues” to see how they are related to immunity. “How can we anticipate what might help in another clinical trial?”
Some of the vaccinated volunteers from the RV144 study are soon to be given a booster vaccine to discover if this can extend and increase immunity to HIV, in a study known as RV305.
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Thai and US researchers are also designing a study, RV306, in Thailand with an estimated 300 participants, who will receive similar vaccinations as those in RV144, plus an additional booster at 12 months, said Punnee Pitisuttithum from Mahidol University in Thailand. The earliest the trial is expected to take place is 2012.
Also in the pipeline – the earliest would be 2014, according to the US Military HIV Research Program (MHRP) – are plans to test an HIV vaccine in Thailand with men who have sex with men (MSM).
Sanjay Gurunathan from Sanofi Pasteur, manufacturer of one of the vaccines used in RV144, said a new partnership of the US National Institute of Allergy and Infectious Diseases, The Bill & Melinda Gates Foundation, HIV Vaccine Trials Network, MHRP, and Sanofi Pasteur – known as the Pox Protein Public Private Partnership, or P5 – will aim to increase vaccine efficacy from the 31.2 percent of the RV144 trial to 50 percent.
In addition to the proposed study with MSM in Thailand, a similar one is planned in South Africa, said Gurunathan. The trial is expected to start in 2014, with about 8,000 participants, and the vaccine will have to be modified to contain the strain of HIV most common in South Africa.
There are 23 ongoing preventative HIV vaccine trials as of May 2011, according to the US-based NGO Global Advocacy for HIV Prevention.