An oral recombinant human type 5 adenovirus vector vaccine encoding the S protein of Type I feline coronavirus effectively protection against FCoV challenge in cats.

Feline coronavirus (FCoV) poses a significant threat to the lives of cats, and there is currently no commercial vaccines available. In the present study, a vaccine was developed using a human type 5 adenovirus vector to express the FCoV-I S protein (rAd5-FCoV-S) to induce the immunogenicity of rAd5-FCoV-S through oral and intramuscular immunization in mice and cats. Both vaccination methods stimulated a higher IgG antibody response. However, oral vaccination led to a significantly higher SIgA antibody level, which was 4.8 times and 2.4 times greater than that induced by intramuscular vaccination in mice and cats, respectively, with the highest level reaching 1:128. In addition, oral vaccination increased the count of IFN-γ-producing and IL-4-producing splenocytes in mice, effectively boosting cellular immune responses. Challenge protection experiments in cats showed that oral vaccination with rAd5-FCoV-S provided 100 % protection compared to a survival rate of only 33 % for unvaccinated cats. Compared to the PBS group, oral rAd5-FCoV-S administration substantially decreased the FCoV viral load within the feces, rectal tissues, and colon tissues of cats. Hematoxylin and eosin (HE) staining and immunohistochemical analysis of rectal and colonic tissues revealed that cats in the oral group exhibited minimal intestinal damage, whereas PBS cats presented significant inflammatory cell infiltration and shedding of intestinal epithelial cells. These findings demonstrate that oral administration of rAd5-FCoV-S induces a robust humoral immune response and a strong cell-mediated immune response in cats, thereby conferring immunity against FCoV infection.