Optimizing a linear 'Doggybone' DNA vaccine for influenza virus through the incorporation of DNA targeting sequences and neuraminidase antigen.

Influenza virus represents a challenge for traditional vaccine approaches due to its seasonal changes and potential for zoonotic transmission. Nucleic acid vaccines can overcome some of these challenges, especially through the inclusion of multiple antigens to increase the breadth of response. RNA vaccines were an important part of the response to the COVID-19 pandemic, but for future outbreaks DNA vaccines may have some advantages in terms of stability and manufacturing cost that warrant continuing investigation to fully realize their potential. Here, we investigate influenza virus vaccines made using a closed linear DNA platform, Doggybone™ DNA (dbDNA), produced by a rapid and scalable cell-free method. Influenza vaccines have mostly focussed on Haemagglutinin (HA), but the inclusion of Neuraminidase (NA) may provide additional protection. Here, we explored the potential of including NA in a dbDNA vaccine, looking at DNA optimization, mechanism and breadth of protection. We showed that DNA targeting sequences (DTS) improved immune responses against HA but not NA. We explored whether NA vaccine-induced protection against influenza virus infection was cell-mediated, but depletion of CD8 and NK cells made no impact, suggesting it was antibody-mediated. This is reflected in the restriction of protection to homologous strains of influenza virus. Importantly, we saw that including both HA and NA in a single combined vaccine did not dampen the immune response to either one. Overall, we show that linear dbDNA can induce an immune response against NA, which may offer increased protection in instances of HA mismatch where NA remains more conserved.

Reducing cell intrinsic immunity to mRNA vaccine alters adaptive immune responses in mice.

The response to mRNA vaccines needs to be sufficient for immune cell activation and recruitment, but moderate enough to ensure efficacious antigen expression. The choice of the cap structure and use of N1-methylpseudouridine (m1Ψ) instead of uridine, which have been shown to reduce RNA sensing by the cellular innate immune system, has led to improved efficacy of mRNA vaccine platforms. Understanding how RNA modifications influence the cell intrinsic immune response may help in the development of more effective mRNA vaccines. In the current study, we compared mRNA vaccines in mice against influenza virus using three different mRNA formats: uridine-containing mRNA (D1-uRNA), m1Ψ-modified mRNA (D1-modRNA), and D1-modRNA with a cap1 structure (cC1-modRNA). D1-uRNA vaccine induced a significantly different gene expression profile to the modified mRNA vaccines, with an up-regulation of Stat1 and RnaseL, and increased systemic inflammation. This result correlated with significantly reduced antigen-specific antibody responses and reduced protection against influenza virus infection compared with D1-modRNA and cC1-modRNA. Incorporation of m1Ψ alone without cap1 improved antibodies, but both modifications were required for the optimum response. Therefore, the incorporation of m1Ψ and cap1 alters protective immunity from mRNA vaccines by altering the innate immune response to the vaccine material.

Formulation, inflammation, and RNA sensing impact the immunogenicity of self-amplifying RNA vaccines.

To be effective, RNA vaccines require both in situ translation and the induction of an immune response to recruit cells to the site of immunization. These factors can pull in opposite directions with the inflammation reducing expression of the vaccine antigen. We investigated how formulation affects the acute systemic cytokine response to a self-amplifying RNA (saRNA) vaccine. We compared a cationic polymer (pABOL), a lipid emulsion (nanostructured lipid carrier, NLC), and three lipid nanoparticles (LNP). After immunization, we measured serum cytokines and compared the response to induced antibodies against influenza virus. Formulations that induced a greater cytokine response induced a greater antibody response, with a significant correlation between IP-10, MCP-1, KC, and antigen-specific antibody titers. We then investigated how innate immune sensing and signaling impacted the adaptive immune response to vaccination with LNP-formulated saRNA. Mice that lacked MAVS and are unable to signal through RIG-I-like receptors had an altered cytokine response to saRNA vaccination and had significantly greater antibody responses than wild-type mice. This indicates that the inflammation induced by formulated saRNA vaccines is not solely deleterious in the induction of antibody responses and that targeting specific aspects of RNA vaccine sensing might improve the quality of the response.