ABSTRACT
Several effective SARS-CoV-2 vaccines are currently in use, but in the light of waning immunity and the emergence of novel variants, effective boost modalities are needed in order to maintain or even increase immunity. Here we report that intranasal vaccinations with adenovirus 5 and 19a vectored vaccines following a systemic DNA or mRNA priming result in strong systemic and mucosal immunity in mice. In contrast to two intramuscular injections with an mRNA vaccine, the mucosal boost with adenoviral vectors induced high levels of IgA and tissue-resident memory T cells in the respiratory tract. Mucosal neutralization of virus variants of concern was also enhanced by the intranasal boosts. Importantly, priming with mRNA provoked a more comprehensive T cell response consisting of circulating and tissue-resident memory T cells after the boost, while a DNA priming induced mostly mucosal T cells. Concomitantly, the intranasal boost strategies provided protection against symptomatic disease. Therefore, a mucosal booster immunization after mRNA priming is a promising approach to establish mucosal immunity in addition to systemic responses.
ABSTRACT
TRIANNI mice carry an entire set of human immunoglobulin V region gene segments and are a powerful tool to rapidly generate human monoclonal antibodies. After immunizing these mice against the spike protein of SARS-CoV-2, we identified 29 hybridoma antibodies that reacted with the SARS-CoV-2 spike protein. Nine antibodies neutralized SARS-CoV-2 infection at IC50 values in the subnanomolar range. ELISA-binding studies and DNA sequence analyses revealed one cluster of clonally related neutralizing antibodies that target the receptor-binding domain and compete with the cellular receptor hACE2. A second cluster of neutralizing antibodies binds to the N-terminal domain of the spike protein without competing with the binding of hACE2 or cluster 1 antibodies. SARS-CoV-2 mutants selected for resistance to an antibody from one cluster are still neutralized by an antibody from the other cluster. Antibodies from both clusters markedly reduced viral spread in mice transgenic for human ACE2 and protected the animals from SARS-CoV-2 induced weight loss. Thus, we report two clusters of potent non-competing SARS-CoV-2 neutralizing antibodies providing potential candidates for therapy and prophylaxis of COVID-19. The study further supports the use of transgenic animals with human immunoglobulin gene repertoires in pandemic preparedness initiatives.
ABSTRACT
Advantages of DNA vaccination against infectious diseases over more classical immunization methods include the possibilities for rapid manufacture, fast adaptation to newly emerging pathogens and high stability at ambient temperatures. In addition, upon DNA immunization the antigen is produced by the cells of the vaccinated individual, which leads to activation of both cellular and humoral immune responses due to antigen presentation via MHC I and MHC II molecules. However, so far DNA vaccines have shown most efficient immunogenicity mainly in small rodent models, whereas in larger animals including humans there is still the need to improve effectiveness. This is mostly due to inefficient delivery of the DNA plasmid into cells and nuclei. Here, we discuss technologies used to overcome this problem, including physical means such as in vivo electroporation and co-administration of adjuvants. Several of these methods have already entered clinical testing in humans.
