The Envelope (Env) trimer mediates fusion of the HIV-1 viral membrane with that of the target cell. As such, it is the sole target for neutralizing antibodies against the virus. Broadly neutralizing antibodies (bnAbs) that are capable of blocking entry of diverse viral strains hold therapeutic potential for people living with HIV-1 and may be utilized for prophylaxis, either through passive immunization or as templates for immunogen design. Chapter 1 of this thesis introduces relevant background to the HIV-1 virus, the Env trimer, antibodies, and antibody-antigen interactions, with an emphasis on bivalent antibody binding to enveloped viruses. Chapter 2 then describes the results of a preclinical sequential immunization study aimed at eliciting, and subsequently boosting, antibodies directed to the V3 glycan patch on Env. Electron microscopy-based polyclonal epitope mapping demonstrated initial V3-targeting, followed by an increase in off-target responses with boosting that was associated with the disassociation of trimeric Env immunogens. Nonetheless, monoclonal antibodies that competed with the V3-targeting bnAb 10-1074 and exhibited weak, heterologous neutralizing activity were isolated after the third boost. Cryo-electron microscopy structures of two of these monoclonal antibodies, reported in Chapter 3, revealed targeting of altered Env conformations. The results presented in Chapters 2 and 3 provide insight into Env structural dynamics and inform strategies for improved immunogen design. Chapters 4 and 5 of this thesis present new best-in-class human bnAbs targeting the CD4-binding site and V3 glycan patch on Env, respectively. These antibodies were identified from top elite neutralizers out of an international cohort of over 2, 300 people living with HIV-1. Multiple, distinct VRC01-class, CD4-binding site bnAbs were identified from one of these individuals. These bnAbs differed in the presence and length of framework region insertions and CDRH3 lengths. One bnAb, 04A06, exhibited an 11-amino acid long insertion, and structural analyses demonstrated this resulted in a protruding CDRH1 loop that recognized highly conserved residues on the adjacent gp120, contributing to the near pan-neutralizing breadth and resilience to escape mutations by 04A06. Chapter 5 then presents 007, a highly broad and potent V3 bnAb that binds Env independently of the gp120 N332 glycan. 007 exhibited weak monovalent binding affinity, and pseudovirus neutralization assays demonstrated antibody bivalency contributes to potency. Structures of 007 IgG in complex with engineered, soluble Env ectodomains revealed a dimer of Env trimers, crosslinked by three IgG molecules. The results presented in Chapters 4 and 5 advance our mechanistic understanding of Env recognition and neutralization by bnAbs and inform the development of antibody therapy and vaccines for HIV-1.
Andrew T. DeLaitsch (Wed,) studied this question.