Quantification of the Impact of the HIV-1-Glycan Shield on Antibody Elicitation

Abstract

While the HIV-1-glycan shield is known to shelter Env from the humoral immune response, its quantitative impact on antibody elicitation has been unclear. Here we use targeted deglycosylation to measure the impact of the glycan shield on elicitation of antibodies against the CD4 supersite. We engineered diverse Env trimers with select glycans removed proximal to the CD4 supersite, characterized their structures and glycosylation, and immunized guinea pigs and rhesus macaques. Immunizations yielded little neutralization against wild-type viruses, but potent CD4-supersite neutralization (titers 1:>1,000,000 against 4-glycan-deleted autologous viruses with over 90% breadth against 4-glycan-deleted heterologous strains exhibiting tier-2 neutralization character). To a first approximation, the immunogenicity of the glycan-shielded protein surface was negligible, with Env-elicited neutralization (ID50) proportional to the exponential of the protein-surface area accessible to antibody. Based on these high titers and exponential relationship, we propose site-selective deglycosylated trimers as priming immunogens to increase the frequency of site-targeting antibodies.

Vaccine Induction of Heterologous Tier 2 HIV-1 Neutralizing Antibodies in Animal Models

“…To induce tier 2 nAbs in rabbits, we designed a CH505 TF chimeric (ch) SOSIP with the BG505 gp41, since this design increased trimeric Env formation (Figure S1; Zhou et al, 2017). We immunized rabbits with the CH505 TF ch.SOSIP and compared immunogenicity to BG505 6R.SOSIP.664 (Sanders et al, 2013).…”

“…However, autologous tier 2 (difficult-to-neutralize) CH505 TF neutralization was only elicited in rabbits that received the stabilized CH505 TF ch.SOSIP (6 of 8 rabbits) (Mann-Whitney test comparing stabilized versus unstabilized groups P <0.05; Figures 1C and 1D). Deletion of CD4bs shielding glycans (CH505 TF.gly4; Zhou et al, 2017) demonstrated that immunization with the stabilized trimer induced CD4bs antibodies more frequently and to a higher magnitude than unstabilized trimers (Figure 1C). …”

“…CH505 SOSIPs were designed as chimeras and stabilized with I203C and A433C (Zhou et al, 2017) or E64K and A316W mutations (de Taeye et al, 2015). See also Supplemental experimental procedures and Figure S1 for further details.…”

Effects of partially dismantling the CD4 binding site glycan fence of HIV-1 Envelope glycoprotein trimers on neutralizing antibody induction

“…Indeed, one or more fence glycans may be missing in some strains (as for the N197 glycan of the JR-FL strain). In this case, partial masking of underlying protein may still be achieved by rearrangement of the interlocking network of remaining glycans to partially fill the vacated space (Gristick et al, 2016; Stewart-Jones et al, 2016; Zhou et al, 2016). The remaining glycans may also undergo more complex differentiation, adding mass to partially fill glycan holes (Behrens et al, 2016).…”

Strategies for a multi-stage neutralizing antibody-based HIV vaccine

“…The use of naturally existing or artificially created glycan holes on Env trimer immunogens to increase accessibility of immunoquiescent epitopes or to improve germline Ab binding has also been extended to the CD4bs bnAb epitope [35,40,41]. However, the glycan shield protects the underlying protein from immune recognition, therefore these immunogens may also increase accessibility of immunodominant, non-bnAb epitopes.…”