PROS1 and viral infectious disease: To study SARS-CoV-2-specific T cell response, we selected S protein for being a key protein for viral entry affecting viral infections and being a target for vaccines (Anderson et al., 2020; Polack et al., 2020; Wrapp et al., 2020; Voysey et al., 2021; Weinreich et al., 2021; Xia et al., 2021).