Animal studies have shown that broadly neutralizing HIV antibodies (bNAbs) can protect against infection, and are likely to be required for an effective HIV vaccine. However, despite over 20 years of research and many different immunogen designs, bNAbs have proven impossible to elicit. In contrast, many studies have confirmed that some HIV-infected individuals naturally develop bNAbs, though normally only after years of infection. Studying these natural examples of bNAbs may provide valuable insights for immunogen design. Most broadly neutralizing monoclonal antibodies (mAbs) isolated thus far have been obtained from cross- sectional screens of chronically infected individuals, which provides limited information on the ontogeny of these bNAbs. However, in the last year the developmental pathways for some bNAbs have been elucidated, by ourselves and others, in studies of longitudinal samples from infected subjects. We hypothesize that these kinds of studies are invaluable in providing an accurate roadmap from elicitation to maturation of bNAbs, with a focus on the very earliest events in their ontogeny. They enable the identification of the antibody precursors and of developmental intermediates, as well as of the viral envelope responsible for eliciting the bNAb lineage. Here, we will focus on bNAbs to the glycan-V2 and -V3 epitopes, which are the most common bNAb targets during the first years of infection. Here, we will use several parallel approaches and technologies to isolate glycan-directed bNAbs from the CAPRISA cohort of subtype C infected donors, and perform mapping and structural studies to define the antibody epitopes. As well as providing valuable tools for our proposed studies, these mAbs will help address the relative dearth of subtype C mAbs, a significant gap in the field as subtype C is the predominant global subtype. Making use of rare stored serial samples from acute infection through to the development of breadth, we will use next generation immunoglobulin gene sequencing to determine the timing of the development of antibody lineages, and to infer an unmutated common ancestor for each lineage. In parallel, viral envelope sequencing at key time points prior to and during the maturation of breadth will enable us to identify viruses that triggered these lineages, and later viral variants that shaped the maturation of breadth. Finally, we will use the knowledge gleaned regarding the ontogeny of bNAbs, to design and characterize novel structure-based immunogens based on envelopes selected specifically for their ability to bind bNAb unmutated common ancestors. In this way, we aim to harness lessons learned from infected people who naturally developed bNAbs, and apply these to the design of an HIV vaccine.
A protective HIV vaccine will likely need to elicit broadly neutralizing antibodies. These kinds of antibodies are occasionally made by infected people such as those we propose to study. Understanding how these antibodies develop will provide a roadmap from elicitation to maturation of these antibodies, which we will harness here to design new vaccine strategies.
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