Intranasal VLP-RBD vaccine adjuvanted with BECC470 confers immunity against Delta SARS-CoV-2 challenge in K18-hACE2-mice (preprint)

As the COVID-19 pandemic transitions to endemic, seasonal boosters are a plausible reality across the globe. We hypothesize that intranasal vaccines can provide better protection against asymptomatic infections and more transmissible variants of SARS-CoV-2. To formulate a protective intranasal vaccine, we utilized a VLP-based platform. Hepatitis B surface antigen-based virus like particles (VLP) linked with receptor binding domain (RBD) antigen were paired with the TLR4-based agonist adjuvant, BECC 470. K18-hACE2 mice were primed and boosted at four-week intervals with either VLP-RBD-BECC or mRNA-1273. Both VLP-RBD-BECC and mRNA-1273 vaccination resulted in production of RBD-specific IgA antibodies in serum. RBD-specific IgA was also detected in the nasal wash and lung supernatants and were highest in VLP-RBD-BECC vaccinated mice. Interestingly, VLP-RBD-BECC vaccinated mice showed slightly lower levels of pre-challenge IgG responses, decreased RBD-ACE2 binding inhibition, and lower neutralizing activity in vitro than mRNA-1273 vaccinated mice. Both VLP-RBD-BECC and mRNA-1273 vaccinated mice were protected against challenge with a lethal dose of Delta variant SARS-CoV-2. Both vaccines limited viral replication and viral RNA burden in the lungs of mice. CXCL10 is a biomarker of severe SARS-CoV-2 infection and we observed both vaccines limited expression of serum and lung CXCL10. Strikingly, VLP-RBD-BECC when administered intranasally, limited lung inflammation at early timepoints that mRNA-1273 vaccination did not. VLP-RBD-BECC immunization elicited antibodies that do recognize SARS-CoV-2 Omicron variant. However, VLP-RBD-BECC immunized mice were protected from Omicron challenge with low viral burden. Conversely, mRNA-1273 immunized mice had low to no detectable virus in the lungs at day 2. Together, these data suggest that VLP-based vaccines paired with BECC adjuvant can be used to induce protective mucosal and systemic responses against SARS-CoV-2.

Reduced SARS-CoV-2 mRNA vaccine immunogenicity and protection in mice with diet-induced obesity and insulin resistance. (preprint)

Obesity and Type 2 Diabetes Mellitus (T2DM) are associated with an increased risk of severe outcomes from infectious diseases, including COVID-19. These conditions are also associated with distinct responses to immunization, including an impaired response to widely used SARS-CoV-2 mRNA vaccines. Establishing a connection between reduced immunization efficacy via modeling the effects of metabolic diseases on vaccine immunogenicity is essential for the development of more effective vaccines for this distinct vulnerable population. Here, we utilized a murine model of diet-induced obesity and insulin resistance to model the effects of comorbid T2DM and obesity on vaccine immunogenicity and protection. Mice fed a high-fat diet (HFD) developed obesity, hyperinsulinemia, and glucose intolerance. Relative to mice fed a normal diet (ND), HFD mice vaccinated with a SARS-CoV-2 mRNA vaccine exhibited significantly lower anti-spike IgG titers, predominantly in the IgG2c subclass, associated with a lower type 1 response, along with a 3.83-fold decrease in neutralizing titers. Furthermore, enhanced vaccine-induced spike-specific CD8+ T cell activation and protection from lung infection against SARS-CoV-2 challenge were seen only in ND mice but not in HFD mice. Overall, we demonstrate impaired immunity following SARS-CoV-2 mRNA immunization in a murine model of comorbid T2DM and obesity, supporting the need for further research into the basis for impaired anti-SARS-CoV-2 immunity in T2DM and investigation of novel approaches to enhance vaccine immunogenicity among those with metabolic diseases.

An adjuvanted SARS-CoV-2 RBD nanoparticle elicits neutralizing antibodies and fully protective immunity in aged mice (preprint)

Development of affordable and effective vaccines that can also protect vulnerable populations such as the elderly from COVID-19-related morbidity and mortality is a public health priority. Here we took a systematic and iterative approach by testing several SARS-CoV-2 protein antigens and adjuvants to identify a combination that elicits neutralizing antibodies and protection in young and aged mice. In particular, SARS-CoV-2 receptorbinding domain (RBD) displayed as a protein nanoparticle (RBD-NP) was a highly effective antigen, and when formulated with an oil-in-water emulsion containing Carbohydrate fatty acid MonoSulphate derivative (CMS) induced the highest levels of cross-neutralizing antibodies compared to other oil-in-water emulsions or AS01B. Mechanistically, CMS induced antigen retention in the draining lymph node (dLN) and expression of cytokines, chemokines and type I interferon-stimulated genes at both injection site and dLN. Overall, CMS:RBD-NP is effective across multiple age groups and is an exemplar of a SARS-CoV-2 subunit vaccine tailored to the elderly.

Alum:CpG adjuvant enables SARS-CoV-2 RBD-induced protection in aged mice and synergistic activation of human elder type 1 immunity (preprint)

Global deployment of vaccines that can provide protection across several age groups is still urgently needed to end the COVID-19 pandemic especially for low- and middle-income countries. While vaccines against SARS-CoV-2 based on mRNA and adenoviral-vector technologies have been rapidly developed, additional practical and scalable SARS-CoV-2 vaccines are needed to meet global demand. In this context, protein subunit vaccines formulated with appropriate adjuvants represent a promising approach to address this urgent need. Receptor-binding domain (RBD) is a key target of neutralizing antibodies (Abs) but is poorly immunogenic. We therefore compared pattern recognition receptor (PRR) agonists, including those activating STING, TLR3, TLR4 and TLR9, alone or formulated with aluminum hydroxide (AH), and benchmarked them to AS01B and AS03-like emulsion-based adjuvants for their potential to enhance RBD immunogenicity in young and aged mice. We found that the AH and CpG adjuvant formulation (AH:CpG) demonstrated the highest enhancement of anti-RBD neutralizing Ab titers in both age groups (~80-fold over AH), and protected aged mice from the SARS-CoV-2 challenge. Notably, AH:CpG-adjuvanted RBD vaccine elicited neutralizing Abs against both wild-type SARS-CoV-2 and B.1.351 variant at serum concentrations comparable to those induced by the authorized mRNA BNT162b2 vaccine. AH:CpG induced similar cytokine and chemokine gene enrichment patterns in the draining lymph nodes of both young adult and aged mice and synergistically enhanced cytokine and chemokine production in human young adult and elderly mononuclear cells. These data support further development of AH:CpG-adjuvanted RBD as an affordable vaccine that may be effective across multiple age groups.