This Phase 3 efficacy study will enroll 3,800 HIV-negative men and transgender people aged 18 to 60 years who have sex with men and/or transgender people. It is anticipated to open for enrollment at clinical research sites in the United States later this year. In addition, clinical research sites in Argentina, Brazil, Italy, Mexico, Peru, Poland, and Spain will participate in the study.
The Phase 3 Mosaico study and the complementary Phase 2b study, Imbokodo, are evaluating investigational vaccines based on “mosaic” immunogens—vaccine components comprising elements from multiple HIV subtypes—that aim to induce immune responses against the wide variety of global HIV strains. Different HIV subtypes, or clades, predominate in various geographic regions around the world. Clade C HIV is common in southern Africa, where Imbokodo is being conducted, while clade B is predominant in the regions of Europe and the Americas where Mosaico will enroll participants.
Mosaico will be the third HIV vaccine efficacy trial in progress worldwide. Imbokodo completed enrollment in May 2019 of 2,600 sexually active women aged between 18 and 35 years across Malawi, Mozambique, South Africa, Zambia, and Zimbabwe. Initial results from this Phase 2b trial are anticipated in 2021. The ongoing NIAID-sponsored Phase 2b/3 HVTN 702 study, which launched in late 2016, is evaluating a newer version of the vaccine regimen tested in the RV144 Thai trial—the only candidate HIV vaccine regimen to date shown to provide some modest protection against the virus. In June 2019, HVTN 702 completed enrollment of 5,400 sexually active men and women aged 18 to 35 years in South Africa.
All Mosaico participants will be offered a comprehensive HIV prevention package, including access to pre-exposure prophylaxis (PrEP), and will be randomly assigned to receive either the investigational vaccine regimen or a placebo. Vaccinations will be given at four time points over one year. The experimental regimen comprises four doses of Ad26.Mos4.HIV, a vaccine candidate that uses an engineered common-cold virus that does not cause illness (adenovirus serotype 26, or Ad26) to deliver four mosaic immunogens. The final two vaccinations will be given together with a bivalent (two-component) HIV envelope protein formulation, combining clade C gp140 and mosaic gp140 envelope proteins, adjuvanted by aluminum phosphate to boost immune responses. Imbokodo is evaluating essentially the same vaccine regimen, but the final two vaccinations in that study do not include mosaic gp140; they comprise Ad26.Mos4.HIV and clade C gp140.