A novel epitope-focused SHIV strain (SHIV.5MUT) rapidly and consistently induces potent V3-glycan broadly neutralizing antibodies in 64% of infected macaques through a two-step mechanism in which V1-directed antibodies select for viral variants with shortened, hypoglycosylated V1 loops that expose the underlying V3-glycan epitope to prime diverse bNAb precursors, which then mature to breadth through coevolution with viral quasispecies that sample key resistance mutations found in global HIV-1 strains, providing the first reproducible outbred animal model of bNAb induction and a molecular blueprint for sequential vaccine design.

A major obstacle confronting HIV-1 vaccine and cure research is the lack of an outbred animal model for rapid and consistent induction of broadly neutralizing antibodies (bNAbs). We designed an epitope-focused simian-human immunodeficiency virus (SHIV.5MUT) that elicited broad and potent V3-glycan-targeted antibodies within a year of infection in 14 of 22 macaques compared with 0 of 14 control animals. SHIV.5MUT elicited bNAbs by a novel two-step mechanism, inducing an initial wave of V1-directed antibodies that selected for Envs with shortened, hypoglycosylated V1 loops, which in turn primed V3-glycan bNAb precursors. Rhesus bNAbs were immunogenetically and structurally diverse, closely resembling human V3-glycan bNAbs. Env-bNAb coevolution revealed a diverse repertoire of bNAb precursors and the Env variants that matured them, yielding a molecular blueprint for vaccine design.