Immunodominance of epitopes and protection efficacy of RBD antigen are differentially altered by different adjuvants and immune routes

Abstract Background Previous studies have revealed that the receptor-binding domain (RBD) of the spike protein is immunogenic in both mice and healthy volunteers, and the humoral immune response plays key roles in RBD-mediated protection. In this study, we evaluated the immunodominant humoral response of RBD with different adjuvants and different immune routes in inducing neutralizing antibodies and immunodominant epitopes in RBD. Methods In this study, we investigated the protective efficacy of immunization with RBD plus three different adjuvants (Al(OH)3, ASO3 or AddaVax) and two different routes (intramuscular immunity or intranasal immunity) in a mouse model. Results The results showed that RBD-mediated protection was altered in response to different adjuvants; even with the same adjuvant, RBD-mediated protection was altered in different immune routes. Using antisera from immunized mice, we identified six B-cell immunodominant epitopes in the RBD, including 2 novel epitopes (RBD1 − 18 and RBD49 − 66) in intramuscular immunity and 3 novel epitopes (RBD31 − 48, RBD61 − 78, RBD97 − 114) in intranasal immunity. The B-cell immunodominant epitopes identified from mice immunized with RBD plus different adjuvants were also different from each other, which may explain the differences in protective immunity observed in each immunized group. Conclusions This study indicate that adjuvants and immune routes largely affect the immunodominance of epitopes and the protective efficacy of RBD, which may guide further adjuvant screening for vaccine development and optimization.