SARS-COV-2 RBD Oral Vaccine Boosted by Mucosal Immune Adjuvant LTB26 via DCs and B Cells Activation in Mice

Although several SARS-COV-2 vaccines have been approved, no one oral live vaccine is available. Here, an oral SARS-COV-2 RBD live vaccine containing LTB26 adjuvant has been developed. BALB/c mice are oral vaccinated with attenuated Salmonella typhimurium SL7207 containing pcDNA3.1-LTB26RBD or pcDNA3.1-RBD plasmids. The result shows that the high level of RBD specific antibody is produced in pcDNA3.1- LTB26RBD treatment. The mechanism indicates that LTB26 enhances RBD antibody production by significantly upregulating the activity of MHC II + DCs and CD19 + CD45 + B cells. LTB26 mutant is derived from heat-labile enterotoxin B subunit (LTB) wild type of Escherichia coli with enhanced immune adjuvanticity. Based on the pre-experiment result that SL7207 interferes the function of LTB26, the purified LTB26 was mixed with purified human rotavirus VP8 antigen to explore the mechanism of adjuvant. The results suggests that LTB26 enhances mucosal immune responses via increased of BCR and MHC II + expression. Furthermore, LTB26 promotes both Th1 and Th2 cell mediated immunity. Therefore, LTB26 maybe a potent adjuvant for mucosal vaccine development in view of the safety of LTB26 than LT toxin.