Diversifying T-cell responses: safeguarding against pandemic influenza with mosaic nucleoprotein.

Pre-existing T-cell responses have been linked to reduced disease severity and better clinical outcomes during the 2009 influenza pandemic and the recent COVID-19 pandemic. We hypothesized that diversifying T-cell responses, particularly targeting conserved viral proteins such as the influenza A virus (IAV) nucleoprotein (NP), could protect against both epidemic and pandemic IAV strains. To test this, we created a mosaic nucleoprotein (MNP) by synthesizing a sequence that maximized the representation of 9-mer epitopes from 7422 NP sequences across human, swine, and avian IAVs. Notably, the MNP sequence showed high homology with the NP of the H5N1 strain affecting dairy cows in the ongoing outbreak. Mucosal immunization with the adjuvanted MNP vaccine induced robust CD8 and CD4 T-cell responses against both known immunodominant and IMPORTANCE: The World Health Organization (WHO) estimates that seasonal influenza causes 3-5 million cases of severe illness annually. The influenza virus frequently undergoes genetic changes through antigenic drift and antigenic shift, resulting in annual epidemics and occasional pandemics. Consequently, a major public health objective is to develop a universal influenza vaccine that offers broad protection against both current and pandemic influenza A strains. In this study, we designed a nucleoprotein (NP) antigen (termed mosaic NP) comprising antigenic regions found in thousands of influenza viruses, aiming to use it as a vaccine to induce broad anti-influenza T-cell responses. Our findings indicate that the mosaic NP vaccine provided significant protection against seasonal H1N1 and H3N2, as well as the pandemic H1N1 strain, demonstrating its effectiveness across various influenza subtypes. These findings suggest that the mosaic NP is a potential universal influenza vaccine antigen, capable of protecting against diverse strains of influenza viruses.