A Self-Biomineralized Novel Adenovirus Vectored COVID-19 Vaccine for Boosting Immunization of Mice

SARS-CoV-2 has caused more than 3.8 million deaths worldwide, and several types of COVID-19 vaccines are urgently approved for use, including adenovirus vectored vaccines. However, the thermal instability and pre-existing immunity have limited its wide applications. To circumvent these obstacles, we constructed a self-biomineralized adenovirus vectored COVID-19 vaccine (Sad23L-nCoV-S-CaP) by generating a calcium phosphate mineral exterior (CaP) based on Sad23L vector carrying the full-length gene of SARS-CoV-2 spike protein (S) under physiological condition. This Sad23L-nCoV-S-CaP vaccine was examined for its characteristics of structure, thermostability, immunogenicity and avoiding the problem of preexisting immunity. In thermostability test, Sad23L-nCoV-S-CaP could be stored at 4 °C for over 45 days, 26 °C for more than 8 days and 37 °C for approximately 2 days. Furthermore, Sad23L-nCoV-S-CaP induced higher level of S-specific antibody and T cell responses, and was not affected by the pre-existing anti-Sad23L immunity, suggesting it could be used as boosting immunization on Sad23L-nCoV-S priming vaccination. The boosting with Sad23L-nCoV-S-CaP vaccine induced high titers of 105.01 anti-S1, 104.77 anti-S2 binding antibody, 103.04 pseudovirus neutralizing antibody (IC50), and robust T-cell response of IFN-γ (1466.16 SFCs/106 cells) to S peptides, respectively. In summary, the self-biomineralization of the COVID-19 vaccine Sad23L-nCoV-S-CaP improved vaccine efficacy, which could be used in prime-boost regimen for prevention of SARS-CoV-2 infection in humans.