Guiding the humoral response against HIV-1 toward a MPER proximal region by immunization with a VLP-formulated antibody-selected envelope variant

Preventive HIV-1 vaccine strategies rely on the elicitation of broadly neutralizingantibody (bNAb) responses, but their induction in vivo by vaccination remainschallenging. Considering that the ability of an epitope to elicit effective humoralimmunity depends on its exposure on the virion, we have used a reverse geneticsapproach to select variants from an HIV-1 AC10_29 randomly mutated envelope librarythat showed increased affinity for a selected bNAb (4E10 bNAb targeting the HIV-1MPER region). Isolated envelope sequences were analyzed by deep-sequencingshowing a small number of dominant changes, including the loss of four potential Nlinkedglycosylation sites and disruption of the V1/V2 loop. Accordingly, the dominantvariant (LR1-C1), showed not only increased affinity for MPER bNAbs 4E10 and 2F5,but also higher affinity for an additional antibody targeting the V3 loop (447-52D) thatcould be a consequence of an open conformation tier 1-like. Furthermore, the aminoacids specific for the selected variant are associated with an increased sensitivity for4E10 and 2F5 antibodies. In vivo studies showed that sera from mice immunized withLR1-C1 viruses possessed an improved neutralizing activity compared to the wild-typeAC10_29 env. While Virus Like Particles (VLPs) carrying this envelope were unable toinduce detectable neutralizing activity in immunized rabbits, one animal showedantibody response to the 4E10-proximal region. Our data establish a novel approachthat has the potential to yield HIV envelope immunogen sequences that direct antibodyresponses to specific envelope regions.