Transforming HIV vaccine design with a hybrid technology that leverages features of mRNA and protein nanoparticle platforms - Proposal Summary/Abstract The HIV-1/AIDS epidemic continues to affect ~40 million people globally, yet there is still no effective vaccine largely due to HIV-1’s enormous genetic diversity. The primary goal for HIV-1 vaccine efforts is to elicit broadly neutralizing antibodies (bNAbs) that neutralize a wide range of HIV-1 strains by targeting conserved epitopes on the HIV-1 envelope (Env) surface protein. However, eliciting bNAbs through vaccination is challenging as inferred germline B cell receptor precursors of most bNAbs do not bind Env and are present at low frequencies. Moreover, bNAbs exhibit unusual features, including high levels of somatic hypermutation. Germline-targeting (GT) vaccination strategies aim to elicit bNAbs through sequential immunization. GT immunogens have been engineered to bind bNAb precursor B cells to initiate the response. Subsequent sequential boosting with increasingly native-like Env immunogens is intended to promote sustained affinity maturation and drive bNAb development. However, regular mRNA and protein nanoparticle (NP) approaches to deliver GT prime and boost immunogens have produced only weak heterologous NAb responses in animal models. Thus, innovative vaccine strategies that promote bNAb evolution are urgently needed. We recently developed a hybrid mRNA vaccine technology that leverages features of both mRNA and protein NP vaccines through genetic encoding of self- assembling enveloped virus-like particles (eVLPs). eVLP assembly is achieved by inserting an ESCRT-recruiting domain (ERD) into the cytoplasmic tail of viral surface proteins, which recruits proteins from the Endosomal Sorting Complex Required for Transport (ESCRT) pathway. SARS-CoV-2 immunizations in mice have shown that a 1st generation hybrid mRNA vaccine elicited superior NAb potency, breadth, and durability compared to regular mRNA and protein NP vaccines, in concert with potent T cell responses. To further increase the effectiveness of hybrid mRNA vaccines, we have designed optimized ERDs that substantially increase eVLP production compared to the 1st generation design. Building on the promise of this technology to elicit Ab responses with enhanced potency and breadth, we propose to evaluate hybrid mRNA vaccines as a platform for GT vaccination in preclinical models. Our proposed research seeks to accomplish the following goals: i) Using a model GT immunogen, design and evaluate optimized ERDs for enhanced immunogenicity in wild-type mice to downselect candidates for studies in humanized mice; ii) Evaluate the ability of optimized hybrid mRNA vaccines encoding GT prime and boost immunogens to activate and mature bNAb precursors in a stringent humanized mouse model with low bNAb precursor frequency; iii) Investigate if sequential hybrid mRNA immunizations delivering GT prime and boost immunogens elicit heterologous NAb and potent cellular responses in non-human primates and protect against viral challenges. We expect that hybrid mRNA vaccines will promote bNAb evolution and induce robust T cell responses more effectively than existing vaccine approaches in preclinical models. Thus, the hybrid mRNA vaccine platform could have a transformative impact on HIV-1 vaccine development.
