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.