Enhancement of SARS-CoV-2 N Antigen-Specific T Cell Functionality by Modulating the Autophagy-Mediated Signal Pathway in Mice

The frequent SARS-CoV-2 variants have caused a continual challenge, weakening the effectiveness of current vaccines, and thus it is of great importance to induce robust and conserved T cellular immunity for developing the next-generation vaccine against SARS-CoV-2 variants. In this study, we proposed a conception of enhancing the SARS-CoV-2 specific T cell functionality by fusing autophagosome-associated LC3b protein to the nucleocapsid (N) (N-LC3b). When compared to N protein alone, the N-LC3b protein was more effectively targeted to the autophagosome/lysosome/MHC II compartment signal pathway and thus elicited stronger CD4(+) and CD8(+) T cell immune responses in mice. Importantly, the frequency of N-specific polyfunctional CD4(+) and CD8(+) T cells, which can simultaneously secrete multiple cytokines (IFN-γ(+)/IL-2(+)/TNF-α(+)), in the N-LC3b group was significantly higher than that in the N alone group. Moreover, there was a significantly improved T cell proliferation, especially for CD8(+) T cells in the N-LC3b group. In addition, the N-LC3b also induced a robust humoral immune response, characterized by the Th1-biased IgG2a subclass antibodies against the SARS-CoV-2 N protein. Overall, these findings demonstrated that our strategy could effectively induce a potential SARS-CoV-2 specific T cellular immunity with enhanced magnitude, polyfunctionality, and proliferation, and thus provided insights to develop a promising strategy for the design of a novel universal vaccine against SARS-CoV-2 variants and other emerging infectious diseases.