Germination-Arrest Spores as An Oral Delivery Vehicle of Grass Carp Reovirus (GCRV) Vp7 Antigen Augment Protective Immunity in Grass Carp ().

Oral vaccination is a practical method for the active immunization of farmed fish in the matter of animal welfare and handling costs. However, it always shows insufficient protective immunity, mainly due to antigen degradation in the gastrointestinal tract (GIT). spores have been shown to be able to protect surface-display heterologous antigens against degradation. Neverthless, the spores can germinate in GIT, which causes loss of the antigens with spore coat disassembly. Here, we developed a novel surface display system using the spore coat proteins CotB and CotC as anchors for the heterogenous antigen, and the germination-controlling genes and as the ectopic integration sites for the fusion genes. Using this display system, we engineered germination-arrest spores displaying the model antigen Vp7 of grass carp reovirus (GCRV) on their surface. Oral vaccination of the engineered spores could confer immune protection against GCRV in grass carp () via eliciting adaptive humoral and cellular immune responses. Most importantly, the germination-arrest spores were shown to significantly augment immunogenicity and protection above the engineered spores based on the existing surface display system. Therefore, the presently reported antigen expression strategy opens new and promising avenues for developing oral vaccines for the immunization of farmed fish species.