Development of replicative adenovirus vectored oral vaccines using Mouse Adenovirus type 1 as a model

This thesis focuses on investigating the potential of Mouse Adenovirus type 1 (MAV-1) as a model for developing oral replication-competent adenovirus-vectored vaccines. The ability of MAV-1 to induce subclinical infection when entering through the gastrointestinal route, while respiratory entry causes a severe respiratory disease (Goffin et al., 2019), is an interesting property that has been extensively used by oral vaccines for Human Adenovirus-4 (HAdV-4) and -7. Replication competent AdVs have emerged as attractive candidates for vaccine platforms, particularly for oral administration. However, the mechanisms underlying AdV oral immunizations are still poorly understood, and the potential of these viruses as oral vaccine vectors has been insufficiently investigated so far. One important reason for the lack of knowledge regarding replication-competent AdV vaccines is that human AdV do not replicate efficiently in laboratory animals. Our study uses MAV-1 in mice, its natural host, to develop a small animal model for oral replication-competent AdV-based vaccines under conditions that support fully replicative infection. MAV-1 interaction with mice serves as a natural virus-host model that facilitates the development of oral replication-competent vaccine vectors in a small animal model that can be easily used for various experiments. The first part involves the development of MAV-1 strains expressing different antigens of Canine Distemper Virus (CDV) and testing them as oral vaccines in mice. CDV is a fatal and highly contagious pathogen affecting multiple carnivores. While injectable vaccines are very effective in protecting domestic animals, their use in the wild is not feasible. Therefore, alternative vaccines are needed. Based on these observations, the use of oral administration of replication-competent AdV-vectored vaccines has emerged as a promising tool, especially for wildlife vaccination. First, different vaccine vectors expressing the entire or partial H or F proteins of CDV were constructed. These different strains were then used as oral vaccines in BALB/c mice, and the immune response to CDV was evaluated. Only the strain expressing the fulllength H protein of CDV generated a detectable and neutralizing immune response against CDV. Secondly, using this strain, we were able to demonstrate that although this type of vaccine is sensitive to pre-existing immunity to the vector, a second oral administration of the same vaccine is able to boost the immune response against CDV. Overall, this study demonstrates the feasibility of using replicating AdVs as oral vaccine vectors to immunize against CDV. The second part aims to address the development of effective and flexible vaccine platforms in the context of influenza vaccines that need to be updated every year. Here, we orally vaccinated mice with a MAV-1 vector expressing influenza hemagglutinin (HA) to assess the protection conferred against an intranasal challenge with influenza. We showed that a single oral immunization with this vaccine generates influenza-specific and neutralizing antibodies, and completely protects mice against clinical signs and viral replication, similar to traditional inactivated vaccines. Finally, the third part focussed on using luciferase (Luc)/green fluorescent protein (GFP)-expressing MAV-1 to study AdV infection and tropism in vivo, using different infection routes in mice. Different strains of mice were used as they exhibit varying susceptibility to MAV-1. In the end, our results allowed showing that brain infection is not dependent on monocyte infiltration but could involve brain pericytes and crossing the blood brain barrier via transcytosis. Altogether, this work allowed to better characterize the usage of replicationcompetent AdV oral vaccines in eliciting adaptive immunity against infectious diseases. This work could contribute to the development of effective vaccines to protect humans and animals from future epidemic.