Components of a HIV-1 vaccine mediate virus-like particle (VLP)-formation and display of envelope proteins exposing broadly neutralizing epitopes

The sequence diversity of HIV-1 is the biggest hurdle for the design of a prophylactic vaccine. Mosaic (Mos) antigens consisting of synthetically shuffled epitopes from various HIV-1 strains are currently tested in the clinical vaccine trial Mosaico (NCT03964415). Besides adenovirus vectors encoding variants of Mos.Gag-Pol and soluble Mos.Env proteins, the Mosaico vaccine entails vectors mediating gene transfer and expression of the membrane-anchored Env-variant Mos2S.Env. We thus examined whether the expression of mosaic Gag mediates the formation of virus-like particles (VLPs). Mos1.Gag- and Mos2.Gag-VLP-formation was readily detected using Western blot- and electron microscopic-analysis. Upon co-expression of both mosaic Gag variants with Mos2S.Env, incorporation of Env into Gag-formed VLPs was observed. The display of the respective neutralization-sensitive target epitopes on Mos2S.Env-decorated VLPs was demonstrated employing a panel of broadly neutralizing antibodies (bNAbs) in a VLP-capture assay. This opens new perspectives for future HIV vaccine designs.