( C) Densitometry and statistical analysis of Western blots. ( B) Western blot of exosome protein SARS-CoV-2 spike protein S2 at day 0, day 7, and day 14-1, day 14-2, and 4 mo after second dose of vaccine. ( A) Levels of SARS-CoV-2 spike Ab in vaccinated healthy individuals at day 0, day 7, and day 14 after first dose of vaccine (14-1), day 14 after second dose of vaccine (14-2), and 4 mo after second dose of vaccine. This is further supported by our finding that immunization of mice with exosomes from the vaccinated individual with the SARS-CoV-2 spike protein resulted in the development of Abs specific to SARS-CoV-2 spike protein. These results strongly support an important role for exosome induction conferring immune responses following immunization. Circulating Abs were detectable only after the second booster dose of vaccine (days 14), and the amount of exosomes containing spike protein was increased up to ∼12-fold maximum. Our results demonstrated the induction of circulating exosomes carrying the SARS-CoV-2 spike protein by day 14, when Abs to the spike protein were not detectable in the sera using an ELISA method developed in our laboratory. In the current study, we analyzed eight healthy adults who received both doses of the SARS-CoV-2 vaccine (Pfizer–BioNTech). The beneficial effect of vaccination is often determined by measuring Ab responses to the spike protein ( 6). These vaccines protect recipients from a SARS-CoV-2 infection by developing humoral and cellular immune responses. MRNA-based vaccines against the SARS-CoV-2 virus infection developed by Pfizer–BioNTech and Moderna were granted emergency use authorization by the U.S. This is further documented by induction of humoral and cellular immune responses in mice immunized with exosomes carrying spike protein. These results demonstrate an important role of circulating exosomes with spike protein for effective immunization following mRNA-based vaccination. Exosomes with spike protein and Abs decreased in parallel after four months. Transmission electron microscopy of exosomes also demonstrated spike protein Ags on their surface. Exosomes with spike protein, Abs to SARS-CoV-2 spike, and T cells secreting IFN-γ and TNF-α increased following the booster dose. Results demonstrated induction of circulating exosomes expressing spike protein on day 14 after vaccination followed by Abs 14 d after the second dose.
To determine the mechanism, we analyzed the kinetics of induction of circulating exosomes with SARS-CoV-2 spike protein and Ab following vaccination of healthy individuals. mRNA vaccines directed at the SARS-CoV-2 spike protein resulted in development of Abs and protective immunity.
Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) causes severe acute respiratory syndrome.
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