Virus-like Particles Identify an HIV V1V2 Apex-Binding Neutralizing Antibody that Lacks a Protruding Loop

Cale EM, et al., 46(5):777-791.e10, Immunity, 2017

Neutralizing antibodies (NAbs) targeting V1V2 apex of the HIV-1 envelope (Env) trimer typically use long protruding loops to penetrate the glycan shield of HIV-1 and to contact underlying protein. Reported herein is the identification of an HIV V1V2 apex-directed NAb, N90-VRC38.01-11, by using virus-like particles and stabilized Env trimers. N90-VRC38 lineage targets the trimer apex without protruding binding loops. A crystal structure of N90-VRC38.01 with scaffolded V1V2-Env apex reveals a previously unknown binding mechanism involving side-chain-to-side-chain interactions. Binding stoichiometry of VRC38.01 to BG505 SOSIP trimers was investigated by using three techniques, including the Bio-Layer Interferometry (BLI). A Pall Foretbio Octet instrument equipped with HIS1K Biosensor probes was used to perform BLI assays. BG505.T332N.His8x SOSIP.664 was immobilized onto Biosensor probes. Biosensor tips were immersed in saturating concentrations of various mAbs (IgG or Fab fragments). Mean binding response were plotted against the known number of binding sites occupied by each mAb or mAb cocktail in order to develop a standard curve for trimer occupancy. By interpolation from a linear regression equation, it was determined that the two copies of VRC38.01 (Fab or IgG) occupy the trimer. Overall results of this study reveal a new immunological solution to target the HIV-1 V1V2 apex that may contribute significantly to the development of new vaccine strategies.

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