Trivalent SARS-CoV-2 S1 Subunit Protein Vaccination Induces Broad Humoral Responses in BALB/c Mice

Abstract

This paper presents a novel approach for improving the efficacy of COVID-19 vaccines against emergent SARS-CoV-2 variants. We have evaluated the immunogenicity of unadjuvanted wild-type (WU S1-RS09cg) and variant-specific (Delta S1-RS09cg and OM S1-RS09cg) S1 subunit protein vaccines delivered either as a monovalent or a trivalent antigen in BALB/c mice. Our results show that a trivalent approach induced a broader humoral response with more coverage against antigenically distinct variants, especially when compared to monovalent Omicron-specific S1. This trivalent approach was also found to have increased or equivalent ACE2 binding inhibition, and increased S1 IgG endpoint titer at early timepoints, against SARS-CoV-2 spike variants when compared monovalent Wuhan, Delta, or Omicron S1. Our results demonstrate the utility of protein subunit vaccines against COVID-19 and provide insights into the impact of variant-specific COVID-19 vaccine approaches on the immune response in the current SARS-CoV-2 variant landscape. Particularly, our study provides insight into effects of further increasing valency of currently approved SARS-CoV-2 vaccines, a promising approach for improving protection to curtail emerging viral variants.

Second Boost of Omicron SARS-CoV-2 S1 Subunit Vaccine Induced Broad Humoral Immune Responses in Elderly Mice

“…Female BALB/c mice (n = 5 animals per group) primed with adenovirus-based COVID-19 vaccine (Ad5.S1) SC or IN at 8 weeks old (1) and boosted with 15 μg of rS1Beta (25) IM at week 52 post-priming (60 weeks old). Subsequently, these mice (n = 3 or 4 animals per group) received a secondary boost by IM with 15 μg of rS1RS09OM (49) at week 92 post-priming (100 weeks old) in the thigh or PBS was administered as a negative control. Blood samples were collected via the retro-orbital vein at weeks 0, 2, 4, and 6 after the secondary boost immunization.…”

“…The recombinant protein Omicron S1 with TLR4 agonist (RS09) was produced by transient expression in Expi293 cells, as previously reported (25,48,49). In brief, rS1RS09OM was produced by transient expression in Expi293 cells with pAd/S1RS09OM, using ExpiFectamie TM 293 Transfection Kit (ThermoFisher) as reported previously (25,48,49).…”

Fourth dose of Microneedle Array Patch of SARS-CoV-2 S1 Protein Subunit Vaccine Elicits Robust Long-lasting Humoral Responses in mice

“…Similarly, for codon-optimized Delta ( B.1.617.2) SARS-CoV-2-S1 glycoprotein, spanning amino acids 1 to 661 and equipped with the RS09 TLR4 agonist and C-tag, synthesis and cloning into pAdlox were performed using the same method. The production of rS1WU, rS1Beta, and rS1RS09Delta involved transient expression in Expi293 cells with pAd/S1WU, pAd/S1Beta, and pAd/S1RS09Delta, respectively, utilizing the ExpiFectamie TM 293 Transfection Kit (ThermoFisher) as previously reported (56, 57). Subsequently, the recombinant proteins were purified using a CaptureSelect TM C-tagXL Affinity Matrix prepacked column (ThermoFisher), followed the manufacturer’s guidelines as previously detailed (56, 57).…”

“…The production of rS1WU, rS1Beta, and rS1RS09Delta involved transient expression in Expi293 cells with pAd/S1WU, pAd/S1Beta, and pAd/S1RS09Delta, respectively, utilizing the ExpiFectamie TM 293 Transfection Kit (ThermoFisher) as previously reported (56, 57). Subsequently, the recombinant proteins were purified using a CaptureSelect TM C-tagXL Affinity Matrix prepacked column (ThermoFisher), followed the manufacturer’s guidelines as previously detailed (56, 57). In brief, the C-tagXL column underwent conditioning with 10 column volumes (CV) of equilibrate/wash buffer (20 mM Tris, pH 7.4) before sample application.…”

Tetravalent SARS-CoV-2 S1 Subunit Protein Vaccination Elicits Robust Humoral and Cellular Immune Responses in SIV-Infected Rhesus Macaque Controllers

“…We have previously demonstrated the immunogenicity of a trivalent protein subunit vaccine in BALB/c mice. 22 Here, we assessed our S1 protein subunit vaccine, at an increased valency to tetravalent, in an advanced animal model more closely related to humans. Nonhuman primates (NHPs) are commonly used as preclinical models to evaluate the safety and efficacy of vaccines and therapeutics for infectious diseases, including SARS-CoV-2.…”