Adjuvant, mimicry and booster requirements for shepherding the development of neutralizing antibodies to the high-mannose patch on HIV-1

Simon Fraser University, Burnaby BC

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Abstract

PROJECT SUMMARY The HIV-1 envelope spike (Env) bears a cluster of oligomannose-type glycans that is a target for broadly neutralizing antibodies (bnAbs). However, while nAbs to this cluster, dubbed the high-mannose patch (HMP), are known to develop in at least some HIV-infected individuals, past attempts to elicit similar antibodies by immunization have been largely unsuccessful. Most previous approaches have involved presenting clusters of natural or synthetic high-mannose glycans on the surface of carrier proteins. The difficulty in eliciting high-mannose-targeting nAbs by immunization is believed to relate, at least in part, to the ‘self’ nature of the targeted glycans; naïve B cells bearing Ig receptors of the desired fine specificity or affinity might be anergic or at relatively low frequency due to tolerance mechanisms. The approach that we are pursuing is based on the scientific premise that antigenic mimicry of mammalian host structures can stimulate cross-reactive antibodies if such mimics are presented in the proper ‘foreign’ milieu. Our overarching hypothesis is that, upon immunization, an antigenic mimic of mammalian oligomannose will more readily elicit antibodies that bind the HMP than native or synthetic oligomannose. In our progress report, we show that a CRM197-conjugate of our lead oligomannose mimetic, the design of which is inspired by a bacterial polysaccharide with resemblance to mammalian oligomannose, is bound with high avidity by various HMP-specific bnAbs as well as their germline precursors. Furthermore, human antibody transgenic mice immunized with this neoglycoconjugate yield antibodies that bind recombinant HIV-1 SOSIP trimers, albeit only when the conjugate is formulated in the TLR4-stimulating Th1-adjuvant GLA-SE; not when formulated in Th2- or mixed Th1/2-adjuvants. Based on our findings so far, we propose in this renewal application to extend our investigations. A first step (Aim 1) will be to probe the relevance of Th1 stimulation further, by assessing immunogenicity of our lead glycoconjugate when formulated with other Th1-directing adjuvants. These additional adjuvants will not be agonistic for TLR4, thus helping to reveal whether stimulating TLR4 is relevant. We will assess also (Aim 2) the significance of antigenic mimicry for triggering high mannose-specific antibodies, by comparing the immunogenicity of our lead mimetic to synthetic oligomannose. We will evaluate also whether incorporating an archetypical component of gram-negative bacterial LPS –Kdo and lipid A—into our lead glycoside is immunologically beneficial. Our third step (Aim 3) will be to investigate whether injecting glycoconjugate-primed transgenic mice at specific time points with select SOSIP trimers boosts nAb titers. We expect our findings to help sharpen our strategy and critically inform the pursuit of future preclinical studies. Results from this research could inform other HIV vaccine design strategies also.