Intranasal SARS-CoV-2 RBD decorated nanoparticle vaccine enhances viral clearance in the Syrian hamster model.

Multiple vaccines have been developed and licensed for SARS-CoV-2. While these vaccines reduce disease severity, they do not prevent infection, and SARS-CoV-2 continues to spread and evolve. To prevent infection and limit transmission, vaccines must be developed that induce immunity in the respiratory tract. Therefore, we performed proof-of-principle vaccination studies with an intranasal nanoparticle vaccine against SARS-CoV-2. The vaccine candidate consisted of the self-assembling 60-subunit I3-01 protein scaffold covalently decorated with the SARS-CoV-2 receptor binding domain (RBD) using the SpyCatcher-SpyTag system. We verified the intended antigen display features by reconstructing the I3-01 scaffold to 3.4A using cryo-EM, and then demonstrated that the scaffold was highly saturated when grafted with RBD. Using this RBD-grafted SpyCage scaffold (RBD+SpyCage), we performed two unadjuvanted intranasal vaccination studies in the "gold-standard" preclinical Syrian hamster model. Hamsters received two vaccinations 28 days apart, and were then challenged 28 days post-boost with SARS-CoV-2. The initial study focused on assessing the immunogenicity of RBD+SpyCage, which indicated that vaccination of hamsters induced a non-neutralizing antibody response that enhanced viral clearance but did not prevent infection. In an expanded study, we demonstrated that covalent bonding of RBD to the scaffold was required to induce an antibody response. Consistent with the initial study, animals vaccinated with RBD+SpyCage more rapidly cleared SARS-CoV-2 from both the upper and lower respiratory tract. These findings demonstrate the intranasal SpyCage vaccine platform can induce protection against SARS-CoV-2 and, with additional modifications to improve immunogenicity, is a versatile platform for the development of intranasal vaccines targeting respiratory pathogens.

Immune durability and protection against SARS-CoV-2 re-infection in Syrian hamsters.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a pandemic. As immunity to endemic human coronaviruses (i.e. NL63 or OC43) wanes leading to re-infection, it was unknown if SARS-CoV-2 immunity would also decline permitting repeat infections. Recent case reports confirm previously infected individuals can become re-infected; however, re-infection may be due to heterogeneity in the initial infection or the host immune response, or may be the result of infection with a variant strain that escapes pre-existing immunity. To control these variables, we utilized the Syrian hamster model to evaluate the duration of immunity and susceptibility to re-infection with SARS-CoV-2. Hamsters were given a primary mock or SARS-CoV-2 infection (culture media or 105 TCID50 USA/WA1/2020 isolate, respectively). Mock and SARS-CoV-2 infected hamsters were then given a secondary SARS-CoV-2 infection at 1, 2, 4, or 6 months post-primary infection (n = 14/time point/group). After the primary SARS-CoV-2 infection, hamsters developed anti-spike protein IgG, IgA, and neutralizing antibodies, and these antibodies were maintained for at least 6 months. Upon secondary SARS-CoV-2 challenge, previously SARS-CoV-2 infected animals were protected from weight loss, while all previously mock-infected animals became infected and lost weight. Importantly, despite having high titres of antibodies, one SARS-CoV-2 infected animal re-challenged at 4 months had a breakthrough infection with replicating virus in the upper and lower respiratory tract. These studies demonstrate immunity to SARS-CoV-2 is maintained for 6 months; however, protection may be incomplete and, even in the presence of high antibody titres, previously infected hosts may become re-infected.

CpG-oligodeoxynucleotides inhibit RSV-enhanced allergic sensitisation in guinea pigs.

Experimental respiratory syncytial virus (RSV) infection of guinea pigs is associated with enhanced allergic sensitisation to inhaled ovalbumin (OA) and low-level viral persistence in the lungs. Based on the T-helper (Th)1/Th2 paradigm, in which a Th2 shift is characteristic of an allergic response and less effective anti-viral immunity, the effects of immunotherapy with synthetic cytosine phosphate-guanine-oligodeoxynucleotides (CpG-ODN), which are potent Th1 stimuli, on OA sensitisation with and without RSV infection were evaluated. Measurements included quantitative histology for airway inflammation by T-cells and eosinophils, semiquantitative RT-PCR for lung Th1/Th2 balance (interferon (IFN)-gamma/interleukin (IL)-5 mRNA ratios), and serology for circulating titres of OA-specific immunoglobulin (Ig)G1 antibodies. RSV antigens were identified in lung tissue sections by immunohistochemistry. CpG-ODN immunotherapy did not prevent OA sensitisation of guinea pigs; however, in RSV-infected, OA-sensitised animals, CpG-ODN administration was associated with significant reductions of airway T-cells and eosinophils, increased lung IFN-gamma/IL-5 ratios, and decreased OA-specific IgG1 antibody titres to levels observed in uninfected, OA-sensitised animals. Viral antigens were identified in a similar proportion of the lungs of RSV-infected animals, irrespective of CpG-ODN immunisation status. In conclusion, cytosine phosphate-guanine-oligodeoxynucleotides immunotherapy protects guinea pigs against respiratory syncytial virus-enhanced ovalbumin sensitisation and might be a relevant intervention in the context of post-bronchiolitis allergic sensitisation in children.