Adenoviral-Based Vaccine Elicits Robust Systemic and Mucosal Cross-Reactive Responses in African Green Monkeys and Reduces Shedding after SARS-CoV-2 Challenge

As new SARS-CoV-2 variants continue to emerge and impact communities worldwide, efforts to develop next generation vaccines that enhance mucosal immunity would be beneficial for protecting individuals and reducing community transmission. We have developed a non-replicating recombinant adenovirus vector (rAd5) vaccine delivered by mucosal administration engineered to express both a protein antigen and a novel molecular adjuvant in the same cell. Here we describe the immunogenicity of three unique SARS-CoV-2 rAd5 vaccine preclinical candidates and their efficacy following viral challenge in African green monkeys. Animals were prime and boost immunized intranasally twenty-nine days apart with rAd5 vaccine candidates containing viral SARS-CoV-2 spike protein alone or in combination with viral nucleocapsid. Mucosal immunization elicited significant increases in antigen-specific serum antibody responses and functional neutralizing activity against multiple variants of concern. Robust antigen specific mucosal IgA responses were observed after a single administration of rAd5 and generated strong cross-reactive neutralizing antibodies against multiple variants including delta. Importantly, all vaccinated animals exhibited a significant reduction in viral loads and infectious particle shedding in both the nasal passages and lower airways compared to unvaccinated controls following challenge with SARS-CoV-2. These findings demonstrate that mucosal immunization using rAd5 is highly immunogenic, confers protective cross-reactive humoral responses in both the circulation and mucosa, and reduces viral loads and shedding upon challenge with multiple SARS-CoV-2 variants.

Mucosal Immunization of Cynomolgus Macaques with Adenoviral Vector Vaccine Elicits Neutralizing Nasal and Serum Antibody to Several SARS-CoV-2 Variants

The emergence of SARS-CoV-2 variants continues to be a major obstacle for controlling the global pandemic. Despite the currently authorized SARS-CoV-2 vaccines ability to reduce severe disease and hospitalization, new immunization strategies are needed that enhance mucosal immune responses, inhibit community transmission, and provide protection against emerging variants. We have developed a mucosally delivered, non-replicating recombinant adenovirus vector (rAd5) vaccine, that has proven efficacy in the clinic against other respiratory viruses [1]. Here we evaluated the immunogenicity of three candidate SARS-CoV-2 vaccines in cynomolgus macaques that contained spike (S) and/or nucleocapsid (N) from either the Wuhan or the beta variant to select a candidate for future clinical development. Mucosal immunization with the Wuhan specific S vaccine (ED90) induced significant cross-reactive serum IgG responses against to Wuhan, beta, gamma and delta lineages, and generated substantial serum neutralizing activity. In nasal samples, ED90 immunization induced 1000-fold increases in IgA to all variants of concern tested and had neutralizing activity against Wuhan and delta. While immunization with the beta specific vaccine (ED94) enhanced IgG and IgA responses to homologous beta variant S and RBD, this approach resulted in less cross-reactive responses to other variants in the serum and nasal passages compared to ED90. As ED90 immunization induced the most robust cross-reactive systemic and mucosal antibody responses, this candidate was chosen for future clinical development.