Takashi Kimoto

and 6 more

Background There is a need for vaccines that can induce effective systemic, respiratory mucosal and cellular immunity to control the COVID-19 pandemic. We reported previously that a synthetic mucosal adjuvant SF-10 derived from human pulmonary surfactant works as an efficient antigen delivery vehicle to antigen presenting cells in the respiratory and gastrointestinal tracts and promotes induction of influenza virus antigen-specific serum IgG, mucosal IgA and cellular immunity. Methods The aim of the present study was to determine the effectiveness of a new administration method of intratracheal (IT) vaccine comprising recombinant SARS-CoV-2 spike protein 1 (S1) combined with SF-10 (S1-SF-10 vaccine) on systemic, local and cellular immunity in mice, compared with intramuscular injection (IM) of S1 with a potent adjuvant AS03 (S1-AS03 vaccine). Results S1-SF-10-IT vaccine induced S1-specific IgG and IgA in serum and lung mucosae. These IgG and IgA induced by S1-SF-10-IT showed significant protective immunity in a receptor binding inhibition test of S1 and angiotensin converting enzyme 2, a receptor of SARS-CoV-2, which were more potent and faster achievement than S1-AS03-IM. Enzyme-linked immunospot assay showed high numbers of S1-specific IgA and IgG secreting cells (ASCs) and S1-responsive IFN-γ, IL-4, IL-17A cytokine secreting cells (CSCs) in the spleen and lungs. S1-AS03-IM induced IgG ASCs and IL-4 CSCs in spleen higher than S1-SF10-IT, but the numbers of ASCs and CSCs in lungs were low and hardly detected. Conclusion Based on the need for effective systemic, respiratory and cellular immunity, the S1-SF-10-IT vaccine seems promising mucosal vaccine against respiratory infection of SARS-CoV-2.