Induction of systemic, mucosal and cellular immunity against SARS-CoV-2
in mice intratracheally vaccinated with a viral S1 protein combined with
a pulmonary surfactant-derived adjuvant SF-10
Abstract
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.