Synthetic bacterial analogs of mammalian oligomannose for eliciting neutralizing antibodies to the high-mannose patch on HIV env

PROJECT SUMMARY A number of Abs targeting oligomannose-type glycans on the HIV envelope spike (Env) have been described in recent years that exhibit broad neutralizing activity (bnAbs). However, eliciting such nAbs by immunization has not been very successful so far. A principal problem may be the host origin of the glycans, with immune tolerance mechanisms limiting the frequency or development of B cells capable of producing Abs with specificity for mammalian oligomannose. For example, Abs elicited by glycoconjugate immunogens presenting oligomannosides are generally unable to bind oligomannose on Env and even when Env-binding Abs have been obtained, such as with recombinant yeast, they appear to bind insufficiently avid to the virus and fail to exert meaningful neutralizing activity. Here, we propose to utilize bacterially derived oligosaccharide analogs of oligomannose to overcome these challenges. We focus in this application on a fairly conserved patch of high-mannose glycans at and surrounding Asn301 and Asn332 on HIV gp120. Prototypic for Abs targeting these oligomannose-type glycans is the PGT128 family of nAbs, which are potent and broadly active, suggesting that a vaccine component able to elicit similar nAbs could offer protection at even modest serum Ab concentrations. We not long ago discovered a bacterial oligosaccharide that closely resembles the D1 arm of mammalian oligomannose and subsequently made synthetic derivatives of it with a D3 arm-like extension. One of these derivatives, in the form of a neoglycoconjugate, is bound avidly by PGT128 family members and, notably, their predicted germline predecessor. More importantly, data from a pilot immunization with the lead conjugate in transgenic animals harboring an unarranged human Ab repertoire show elicitation of oligomannose-specific Abs with HIV cross-neutralizing activity. Here, we propose to expand on these encouraging preliminary studies. Specifically, we wish to elaborate on our conjugate design to heighten Ab responses and continue to utilize transgenic animals to identify an optimal adjuvant+conjugate combination. We also will dissect antibody responses at the serum and repertoire levels to determine similarities between the elicited responses and existing nAbs. Finally, we propose to test our strategy also in macaques to assess the extent to which it may work in outbred systems. In sum, this project will investigate whether glycan mimicry can serve to readily trigger the development of cross-reactive Abs to the highly vulnerable oligomannose patch on HIV Env. If so, this work could inform strategies for targeting other glyco-epitopes on HIV-1.