Advancing HIV Vaccine Development with a Lipid Nanodisc Platform - The envelope (Env) glycoprotein of HIV is the only viral protein on the surface of virions, making it the sole target of B cell-based HIV vaccines. While Env is natively a transmembrane protein, most vaccine development relies on soluble versions of the trimer. These versions lack the membrane-proximal external region (MPER) epitope, the native bilayer environment, and the transmembrane (TM) and C-terminal (CT) domains. Broadly neutralizing antibodies (bnAbs) targeting MPER have remarkable breadth, reaching near- complete coverage of all circulating HIV strains, thus making MPER an attractive target for vaccine development. Recent progress in MPER-targeted vaccine development has been notable on two fronts. First, in the HVTN133 clinical trial, MPER peptide presented in a liposome formulation induced a B cell lineage for bnAbs and their precursors and reached 15 % neutralization breadth of a global tier 2 panel. Second, two studies described the development of a germline targeting immunogen for 10E8-class MPER bnAb, and affinity maturation process of the primed antibodies in pre-clinical mouse models. While mRNA technology can now deliver membrane-bound Env immunogens with a complete MPER, circumventing the need to produce recombinant transmembrane Env, the characterization of new immunogen candidates and the MPER-targeting responses they elicit will still require biophysical and structural analysis. As a result, challenges in handling Env as a recombinant transmembrane protein persist. This project incorporates engineered transmembrane Env vaccine candidates into stable lipid nanodiscs using membrane scaffold proteins and a selection of lipid molecules. This solution enables scalable and reproducible in vitro characterization and optimization of engineered transmembrane Env-based immunogens and evaluation of in vivo responses from MPER-targeting immunizations. Env nanodiscs allow using transmembrane Envs under identical conditions that have been established for soluble Envs in commonly used iterative vaccine development methods. In the first specific aim of this proposal, Env nanodisc structures are solved in complex with MPER-targeting antibodies to give guideposts for vaccine development. In the second, nanodiscs are assembled with controlled lipid compositions to elucidate the contribution of the bilayer surface to MPER antibody binding. Lastly, the third specific aim establishes conditions for utilizing Env nanodiscs in electron microscopy-based polyclonal epitope mapping (EMPEM). All aims will collectively contribute to improved nanodisc assembly pipeline that can be scaled to serve multiple HIV MPER targeting vaccine development projects. This pipeline can also serve the development of any transmembrane Env immunogen that targets other epitopes, and which will be administered as mRNA- LNPs. Ultimately, the tools will be made available for other virus glycoprotein vaccine development projects beyond HIV.
