The relevance of vaccine protection in rhesus monkeys to clinical efficacy in humans remains unclear.
Scientists have developed a new vaccine that can safely and effectively elicit immune response against a wide variety of HIV strains, an advance which may help prevent the deadly infection in the future.
Researchers, including those from Harvard Medical School in the US, found that the 'mosaic' vaccine, created by combining pieces of different HIV viruses, is well-tolerated and generated comparable and robust immune responses against HIV in healthy adults and rhesus monkeys.
"These results represent an important milestone," said Dan Barouch, the lead author of the study published in The Lancet journal.
"This study demonstrates that the mosaic Ad26 prime, Ad26 plus gp140 boost HIV vaccine candidate induced robust immune responses in humans and monkeys with comparable magnitude, kinetics, phenotype, and durability and also provided 67 per cent protection against viral challenge in monkeys," said Barouch.
Nearly 37 million people worldwide are living with HIV/AIDS, with an estimated 1.8 million new cases every year. A safe and effective preventative vaccine is urgently needed to curb the HIV pandemic, the researchers said.
A key hurdle to HIV vaccine development has been the lack of direct comparability between clinical trials and preclinical studies, the they said.
To address these methodological issues, the scientists evaluated the leading mosaic adenovirus serotype 26 (Ad26)-based HIV-1 vaccine candidates in parallel clinical and pre-clinical studies to identify the optimal HIV vaccine regimen to advance into clinical efficacy trials.
The trial recruited 393 healthy, HIV-uninfected adults (aged 18-50 years) from 12 clinics in east Africa, South Africa, Thailand, and the US.
Volunteers were randomly assigned to receive either one of seven vaccine combinations or a placebo, and were given four vaccinations over the course of 48 weeks.
To stimulate, or 'prime', an initial immune response, each volunteer received an intramuscular injection of Ad26.Mos.HIV at the start of the study and again 12 weeks later.
The vaccine containing 'mosaic' HIV Env/Gag/Pol antigens was created from many HIV strains, delivered using a non-replicating common-cold virus (Ad26).
Results showed that all vaccine regimens tested were capable of generating anti-HIV immune responses in healthy individuals and were well tolerated, with similar numbers of local and systemic reactions reported in all groups, most of which were mild-to-moderate in severity.
The researchers also noted several limitations, including the fact that that the relevance of vaccine protection in rhesus monkeys to clinical efficacy in humans remains unclear.
There is no definitive immunological measurement that is known to predict protection against HIV-1 in humans, they said.
"These results should be interpreted cautiously. The challenges in the development of an HIV vaccine are unprecedented, and the ability to induce HIV-specific immune responses does not necessarily indicate that a vaccine will protect humans from HIV infection, Barouch said.