Intranasal SARS-CoV-2 spike-based immunisation adjuvanted with polyethyleneimine elicits mucosal and systemic humoral responses in mice.

The SARS-CoV-2 pandemic continues despite the presence of effective vaccines, and novel vaccine approaches may help to reduce viral spread and associated COVID-19 disease. Current vaccine administration modalities are based on systemic needle-administered immunisation which may be suboptimal for mucosal pathogens. Here we demonstrate in a mouse model that small-volume intranasal administration of purified spike (S) protein in the adjuvant polyethylenemine (PEI) elicits robust antibody responses with modest systemic neutralisation activity. Further, we test a heterologous intranasal immunisation regimen, priming with S and boosting with RBD-Fc. Our data identify small volume PEI adjuvantation as a novel platform with potential for protective mucosal vaccine development.

Pathogen-sugar interactions revealed by universal saturation transfer analysis.

Many pathogens exploit host cell-surface glycans. However, precise analyses of glycan ligands binding with heavily modified pathogen proteins can be confounded by overlapping sugar signals and/or compounded with known experimental constraints. Universal saturation transfer analysis (uSTA) builds on existing nuclear magnetic resonance spectroscopy to provide an automated workflow for quantitating protein-ligand interactions. uSTA reveals that early-pandemic, B-origin-lineage severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike trimer binds sialoside sugars in an "end-on" manner. uSTA-guided modeling and a high-resolution cryo-electron microscopy structure implicate the spike N-terminal domain (NTD) and confirm end-on binding. This finding rationalizes the effect of NTD mutations that abolish sugar binding in SARS-CoV-2 variants of concern. Together with genetic variance analyses in early pandemic patient cohorts, this binding implicates a sialylated polylactosamine motif found on tetraantennary N-linked glycoproteins deep in the human lung as potentially relevant to virulence and/or zoonosis.

High thermostability improves neutralizing antibody responses induced by native-like HIV-1 envelope trimers.

Soluble HIV-1 envelope glycoprotein (Env) immunogens are a prime constituent of candidate vaccines designed to induce broadly neutralizing antibodies. Several lines of evidence suggest that enhancing Env immunogen thermostability can improve neutralizing antibody (NAb) responses. Here, we generated BG505 SOSIP.v9 trimers, which displayed virtually no reactivity with non-neutralizing antibodies and showed increased global and epitope thermostability, compared to previous BG505 SOSIP versions. Chemical crosslinking of BG505 SOSIP.v9 further increased the melting temperature to 91.3 °C, which is almost 25 °C higher than that of the prototype SOSIP.664 trimer. Next, we compared the immunogenicity of a palette of BG505-based SOSIP trimers with a gradient of thermostabilities in rabbits. We also included SOSIP.v9 proteins in which a strain-specific immunodominant epitope was masked by glycans to redirect the NAb response to other subdominant epitopes. We found that increased trimer thermostability correlated with increased potency and consistency of the autologous NAb response. Furthermore, glycan masking steered the NAb response to subdominant epitopes without decreasing the potency of the autologous NAb response. In summary, SOSIP.v9 trimers and their glycan masked versions represent an improved platform for HIV-1 Env based vaccination strategies.

Immunological and pathological outcomes of SARS-CoV-2 challenge following formalin-inactivated vaccine in ferrets and rhesus macaques.

There is an urgent requirement for safe and effective vaccines to prevent COVID-19. A concern for the development of new viral vaccines is the potential to induce vaccine-enhanced disease (VED). This was reported in several preclinical studies with both SARS-CoV-1 and MERS vaccines but has not been reported with SARS-CoV-2 vaccines. We have used ferrets and rhesus macaques challenged with SARS-CoV-2 to assess the potential for VED in animals vaccinated with formaldehyde-inactivated SARS-CoV-2 (FIV) formulated with Alhydrogel, compared to a negative control vaccine. We showed no evidence of enhanced disease in ferrets or rhesus macaques given FIV except for mild transient enhanced disease seen 7 days after infection in ferrets. This increased lung pathology was observed at day 7 but was resolved by day 15. We also demonstrate that formaldehyde treatment of SARS-CoV-2 reduces exposure of the spike receptor binding domain providing a mechanistic explanation for suboptimal immunity.

Disassembly of HIV envelope glycoprotein trimer immunogens is driven by antibodies elicited via immunization.

Rationally designed protein subunit vaccines are being developed for a variety of viruses including influenza, RSV, SARS-CoV-2, and HIV. These vaccines are based on stabilized versions of the primary targets of neutralizing antibodies on the viral surface, namely, viral fusion glycoproteins. While these immunogens display the epitopes of potent neutralizing antibodies, they also present epitopes recognized by non-neutralizing or weakly neutralizing ("off-target") antibodies. Using our recently developed electron microscopy polyclonal epitope mapping approach, we have uncovered a phenomenon wherein off-target antibodies elicited by HIV trimer subunit vaccines cause the otherwise highly stabilized trimeric proteins to degrade into cognate protomers. Further, we show that these protomers expose an expanded suite of off-target epitopes, normally occluded inside the prefusion conformation of trimer, that subsequently elicit further off-target antibody responses. Our study provides critical insights for further improvement of HIV subunit trimer vaccines for future rounds of the iterative vaccine design process.