Optimizing Immunogenicity and Product Presentation of a SARS-CoV-2 Subunit Vaccine Composition: Effects of Delivery Route, Heterologous Regimens With Self-Amplifying RNA Vaccines, and Lyophilization

Authors

William R Lykins
Jeroen Pollet
Jessica A White
Brian Keegan
Leroy Versteeg
Ulrich Strych
Wen-Hsiang Chen
Raodoh Mohamath
Gabi Ramer-Denisoff
Sierra Reed
Christina Renshaw
Samuel Beaver
Alana Gerhardt
Emily A Voigt
Mark A Tomai
Robert Sitrin
Robert K M Choy
Frederick J Cassels
Peter J Hotez
Maria Elena Bottazzi
Christopher B Fox

Publication Date

1-1-2024

Journal

Frontiers in Immunology

DOI

10.3389/fimmu.2024.1480976

PMID

39737197

PMCID

PMC11683073

PubMedCentral® Posted Date

12-16-2024

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Animals, COVID-19 Vaccines, SARS-CoV-2, COVID-19, Mice, Vaccines, Subunit, Antibodies, Viral, Female, Immunogenicity, Vaccine, Administration, Intranasal, Freeze Drying, Antibodies, Neutralizing, Adjuvants, Vaccine, mRNA Vaccines, Mice, Inbred BALB C, Adjuvants, Immunologic, Spike Glycoprotein, Coronavirus, Injections, Intramuscular, Humans, RNA vaccine, heterologous vaccine, intranasal vaccine, receptor binding domain, adjuvant formulation, vaccine development, lyophilized vaccine

Abstract

INTRODUCTION: Dozens of vaccines have been approved or authorized internationally in response to the ongoing SARS-CoV-2 pandemic, covering a range of modalities and routes of delivery. For example, mucosal delivery of vaccines via the intranasal (i.n.) route has been shown to improve protective mucosal responses in comparison to intramuscular (i.m.) delivery. As we gain knowledge of the limitations of existing vaccines, it is of interest to understand if changes in product presentation or combinations of multiple vaccine modalities can further improve immunological outcomes.

METHODS: We investigated a commercial-stage SARS-CoV-2 receptor binding domain (RBD) antigen adjuvanted with a clinical-stage TLR-7/8 agonist (3M-052) formulated on aluminum oxyhydroxide (Alum). In a murine immunogenicity model, we compared i.n. and i.m. dosing of the RBD-3M-052-Alum vaccine. We measured the magnitude of antibody responses in serum and lungs, the antibody-secreting cell populations in bone marrow, and antigen-specific cytokine-secreting splenocyte populations. Similarly, we compared different heterologous and homologous prime-boost regimens using the RBD-3M-052-Alum vaccine and a clinical-stage self-amplifying RNA (saRNA) vaccine formulated on a nanostructured lipid carrier (NLC) using the i.m. route alone. Finally, we developed a lyophilized presentation of the RBD-3M-052-Alum vaccine and compared it to the liquid presentation and a heterologous regimen including a previously characterized lyophilized form of the saRNA-NLC vaccine.

RESULTS AND DISCUSSION: We demonstrate that i.n. dosing of the RBD-3M-052-Alum vaccine increased IgA titers in the lung by more than 1.5 logs, but induced serum IgG titers 0.8 logs lower, in comparison to i.m. dosing of the same vaccine. We also show that the homologous prime-boost RBD-3M-052-Alum regimen led to the highest serum IgG and bronchial IgA titers, whereas the homologous saRNA-NLC regimen led to the highest splenocyte interferon-γ response. We found that priming with the saRNA-NLC vaccine and boosting with the RBD-3M-052-Alum vaccine led to the most desirable immune outcome of all regimens tested. Finally, we show that the lyophilized RBD-3M-052-Alum vaccine retained its immunological characteristics. Our results demonstrate that the route of delivery and the use of heterologous regimens each separately impacts the resulting immune profile, and confirm that multi-product vaccine regimens can be developed with stabilized presentations in mind.