The HIV vaccine regimen tested among MSM and transgender men was safe but did not provide protection against HIV acquisition, as determined by an independent Data and Safety Monitoring Committee (DSMB). The HPX3002/HVTN 706, or “Mosaico,” Phase 3 clinical trial began in 2019 and involved 3,900 volunteers between the ages of 18 and 60 in Europe, North America, and South America. On the recommendation of the DSMB, the study will be discontinued. Participants are notified of the results, and further analyzes of the study data are scheduled.
Janssen Vaccines & Prevention BV, part of the Janssen Pharmaceutical Companies of Johnson & Johnson, sponsored the Mosaico study with financial support from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. The trial was conducted by the NIAID-funded HIV Vaccine Clinical Trials Network, based at the Fred Hutchinson Cancer Research Center in Seattle. The US Army Medical Research and Development Command provided additional support for the study.
The experimental vaccine system was developed by Janssen. It was based on “mosaic” immunogens – vaccine components featuring elements from multiple HIV subtypes – with the goal of inducing immune responses against a wide range of global HIV strains. The investigational vaccine regimen consists of four injections over a year period of 26 Ad.Mos4. This vaccine candidate uses a common cold virus (adenovirus serotype 26, or Ad26) to deliver mosaic immunity. The last two vaccinations were combined with a bivalent (two-component) HIV envelope protein formulation, combining Clade C gp140 and Mosaic gp140 envelope proteins, fortified with aluminum phosphate to enhance immune responses. All study vaccines were completed in October 2022.
In a review of the tabulated data, the DSMB determined that there were no safety issues with the experimental vaccine regimen. However, the number of HIV infections was equivalent between the vaccine and placebo arm of the study. During the clinical trial, all participants were provided with comprehensive HIV prevention tools, including pre-exposure prophylaxis, or PrEP. Study staff made sure that participants who contracted HIV during the trial were immediately referred for medical care and treatment.
Mosaico’s results follow developments in the Phase 2b clinical trial “Imbokodo” (HPX2008/HVTN 705), which was testing a similar regimen of HIV vaccine in young women in sub-Saharan Africa. The DSMB determined in 2021 that the experimental vaccine regimen in that study was also safe but not effective in protecting against HIV acquisition.