Abstract
SummaryThe elicitation of broadly neutralizing antibodies (bNAbs) against the HIV-1 envelope glycoprotein (Env) trimer remains a major vaccine challenge. Most cross-conserved protein determinants are occluded by self-N-glycan shielding, limiting B cell recognition of the underlying polypeptide surface. The exceptions to the contiguous glycan shield include the conserved receptor CD4 binding site (CD4bs) and glycoprotein (gp)41 elements proximal to the furin cleavage site. Accordingly, we performed heterologous trimer-liposome prime:boosting in rabbits to drive B cells specific for cross-conserved sites. To preferentially expose the CD4bs to B cells, we eliminated proximal N-glycans while maintaining the native-like state of the cleavage-independent NFL trimers, followed by gradual N-glycan restoration coupled with heterologous boosting. This approach successfully elicited CD4bs-directed, cross-neutralizing Abs, including one targeting a unique glycan-protein epitope and a bNAb (87% breadth) directed to the gp120:gp41 interface, both resolved by high-resolution cryoelectron microscopy. This study provides proof-of-principle immunogenicity toward eliciting bNAbs by vaccination.
Highlights
The HIV-1 surface-exposed functional envelope glycoprotein (Env) spike is the sole virally encoded target for broadly neutralizing antibodies.Remarkably, such bNAbs can neutralize diverse clinical strains but arise sporadically during the course of natural infection and usually after 2 or more years (McCoy and Burton, 2017)
Glycan Modification of Heterologous native flexibly linked (NFL) Trimers Preferentially Exposes the CD4 binding site (CD4bs) while Maintaining Trimer Integrity In selecting potential cross-conserved targets, we focused on the major protein surface required for viral entry and replication: the partially exposed CD4bs (Figure 1A, left)
A potential N-linked glycosylation site (PNGS) at position 332 was introduced in Envs naturally lacking N332 to maintain cross-conservation at the ‘‘N332 glycan supersite,’’ as needed (Dubrovskaya et al, 2017; Guenaga et al, 2017)
Summary
The HIV-1 surface-exposed functional Env spike is the sole virally encoded target for broadly neutralizing antibodies (bNAbs).Remarkably, such bNAbs can neutralize diverse clinical strains but arise sporadically during the course of natural infection and usually after 2 or more years (McCoy and Burton, 2017). The well-ordered SOSIP trimer adopts a near-native conformation, as confirmed by high-resolution structural analysis (Julien et al, 2013; Lyumkis et al, 2013; Pancera et al, 2014) Since this initial discovery, multiple efforts to produce more stable or homogeneous, soluble Env mimetics derived from various HIV-1 strains have been pursued. Multiple efforts to produce more stable or homogeneous, soluble Env mimetics derived from various HIV-1 strains have been pursued These include the cleavage-independent, native flexibly linked (NFL) trimers that we developed (Guenaga et al, 2015a, 2017; Karlsson Hedestam et al, 2017; Sharma et al, 2015), uncleaved prefusion-optimized trimers (Kong et al, 2016), and modified SOSIPs (Sanders and Moore, 2017). While these well-ordered trimers are efficiently recognized by HIV-directed bNAbs, their use in prime:boost strategies in animal models mostly elicit autologous NAbs to strain-restricted epitopes and not to cross-conserved elements needed for a broadly effective vaccine (Feng et al, 2016; Klasse et al, 2018; Martinez-Murillo et al, 2017; Pauthner et al, 2017; Sanders and Moore, 2017; Sanders et al, 2015; Torrents de la Pena et al, 2017; Torrents de la Pena and Sanders, 2018)
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