An investigational HIV vaccine regimen was capable of generating immune responses against HIV and was well-tolerated among healthy adults, according to findings from the APPROACH trial presented at the IAS 2017 Conference on HIV Science in Paris, France.

The early-stage clinical trial studied “mosaic” vaccines created to induce immune responses against various HIV subtypes responsible for infections across the world. Four hundred volunteers were randomized to receive one of seven experimental vaccine regimens or a placebo. Over 48 weeks, participants received two doses of an initial (prime) vaccine followed by two doses of a booster vaccine.

The prime vaccination contained Ad26.Mos.HIV while the booster contained combinations of the Ad26.Mos.HIV components or a different component called MVA-Mosaic, and/or two different doses of clade C HIV gp140 envelope protein containing an aluminum adjuvant to help enhance immune responses. The vaccine uses a strain of common-cold virus (designed so that it does not cause illness) as a vector to deliver three mosaic antigens created from genes from many HIV variants.

The data showed different mosaic vaccine regimens were well-tolerated and were able to induce anti-HIV immune responses in healthy, HIV-negative adults. Regimens using these mosaic vaccines had previously protected monkeys against an HIV-like viral infection called simian HIV (SHIV). In the animal studies, the most effective regimen lowered the risk of infection per exposure to SHIV by 94%. Moreover, there was 66% complete protection seen after six exposures.

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After identifying the immune responses associated with this protection, the authors reported that the regimen that conferred the most protection in these preclinical animal studies also generated the greatest immune responses among study participants. After the third vaccination, most study participants developed antibody and cellular immune responses against HIV; the level of immune responses rose after the fourth vaccination.

Future studies would focus on a regimen containing two Ad26 mosaic primes and two prime boosts with Ad26 mosaic and clade C gp140. TRAVERSE, another early-stage clinical trial, is currently comparing Ad26-based trivalent regimens vs. tetravalent regimens; results are expected in late 2017.

“The promising, early-stage results from the APPROACH study support further evaluation of these candidate vaccines to assess their ability to protect those at risk of acquiring HIV,” said Dr. Dan H. Barouch, a principal investigator for APPROACH.

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