An intranasal nucleocapsid-based vaccine offers broad-spectrum protection against SARS-CoV-2 variants in preclinical models

Abstract

<p><strong>Introduction</strong><strong>:</strong> Current spike-based COVID vaccines induce neutralizing antibodies to reduce severe diseases and deaths, but their efficacy decreases against emerging variants of SARS-CoV-2. The nucleoprotein is more conserved cross different SARS-CoV-2 variants. The mucosal SARS-CoV-2 vaccine to enhance the ability to block infection and confer broad-spectrum protection against evolving variants are pressing needed.</p><p><strong>Methods: </strong>This study reported an intranasal influenza virus-vectored SARS-CoV-2 vaccine candidate based on a live attenuated influenza virus with deleted NS1 gene and expressing the nucleoprotein (N) of the SARS-CoV-2, known as DelNS1- N. We evaluated immune response and the efficacy of protection against intranasal administration of DelNS1-N in mouse and hamster models.</p><p><strong>Results: </strong>DelNS1- N elicited high levels of IgG in serum and IgA in bronchoalveolar lavage specific to SARS-CoV-2 nucleoprotein. Moreover, it stimulated tissue-resident CD4+ T cell responses in mice following intranasal boosting. Single cell transcriptome profiling showed that both DelNS1- N and DelNS1 vector recruit T cells in the lung, particularly memory CD8⁺ T cells exhibiting cytotoxic and tissue-resident properties. Intranasal DelNS1-N vaccination demonstrated effective cross-protection against infection of SARS-CoV-2 variants in lower respiratory tracts of hamsters, including Delta, BQ1.1, XBB1.5 variants. We found that the protective efficacy of DelNS1-N waned after T cell depletion during virus challenge in a mouse model, supporting DelNS1-N has unique ability in induce T cell immunity against SARS-CoV-2 infection.</p><p><strong>Conclusion: </strong>Intranasal immunization with the DelNS1-N vaccine induced a robust immune response with cross-protection against SARS-CoV-2 variants. Importantly, T cell responses played a significant role in the efficacy of the DelNS1-N vaccine, providing protection against variants even in the absence of neutralizing antibodies. The DelNS1live attenuate viral vaccine system presents a promising vaccination strategy for making T cell vaccines against respiratory viruses.</p>