SARS-CoV-2 Spike(395-404) is identified as a murine CD8(+) T cell epitope in the receptor-binding domain of the SARS-CoV-2 spike protein

Abstract Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative pathogen of the COVID-19 pandemic. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is considered an important antigen of SARS-CoV-2 vaccines, while the cytotoxic T lymphocyte (CTL) activity is critical for evaluating cell-mediated immune response for vaccine efficacy. Human angiotensin-converting enzyme 2 (hACE2)-expressing transgenic mice with a C57BL/6 genetic background have widely used as an animal model of SARS-CoV-2 study. However, the CTL epitope of SARS-CoV-2 RBD has not yet been identified in C57BL/6 mice and quantifying the CTL activity has used RBD peptide pools with limitations such as expensive and time-consuming synthesis of peptides. In this study, we identified a murine CD8+ T cell epitope of the SARS-CoV-2 spike RBD using C57BL/6 wild-type and hACE2-expressing transgenic (K18-hACE2) mice. Mice were immunized with the adjuvanted SARS-CoV-2 RBD recombinant protein and then the CTL activities were evaluated by determining numbers of the IFN-γ-producing T cells in the splenocytes of the immunized mice upon exposure to overlapping peptide pools or individual peptides via an enzyme-linked immunospot assay and flow cytometry. We found SARS-CoV-2 S395–404 (VYADSFVIRG) as a major histocompatibility complex class I-restricted epitope for the RBD-specific CTL activity in C57BL/6 mice. Supported by a grant from Korea Research Institute of Bioscience and Biotechnology (KRIBB) Research Initiative Program (KGM9942112).