Recombinant viruses expressing the foot-and-mouth disease virus capsid precursor polypeptide (P1) induce cellular but not humoral antiviral immunity and partial protection in pigs

The importance of the induction of virus neutralizing antibodies to provide protection against foot-and-mouth disease virus (FMDV) infection is well e stablished. However, recent studies with recombinant adenovirus expressing the precursor polypeptide of the viral capsid (P1) indicate that cattle ino culated with this recombinant vector developed partial protection against F MDV infection, in the absence of a delectable specific humoral response. Ot her viral vectors have been widely used to induce protective immunity again st many pathogens, and it has been reported that the use of different vecto rs for priming and boosting injections can provide a synergistic effect on this response. In this work, we determined the immunogenicity of two recomb inant viruses (adenovirus and vaccinia) expressing P1-FMDV, administered ei ther individually or sequentially, and the protection that they induced aga inst FMDV challenge in pigs. A double immunization with the adeno-P1 virus was the most effective strategy at inducing protective immunity. In contras t to previous reports, the use of two different vectors for priming and boo sting did not show a synergistic effect on the protection induced against F MD. Interestingly, immunized pigs developed FMDV-specific T cell responses but not detectable antibodies. Thus, the protection observed was likely to be mediated by a cellular immune response.