Protection of swine by live and inactivated vaccines prepared from a leader proteinase-deficient serotype A12 foot-and-mouth disease virus.

Previously, we demonstrated that a genetically engineered variant of foot-and-mouth disease virus (FMDV) serotype A12 lacking the leader proteinase-coding region (A12-LLV2) was attenuated and induced an immune response that partially protected cattle from FMD. In this study, A12-LLV2 was tested in swine as a live or chemically inactivated vaccine. Animals vaccinated with chemically inactivated A12-LLV2 or wild-type (WT) virus in oil adjuvant developed high levels of neutralizing antibodies and were protected from FMD upon challenge. Animals vaccinated with live A12-LLV2 did not exhibit signs of FMD, did not spread virus to other animals, developed a neutralizing antibody response and antibodies to nonstructural protein 3D, and were partially protected from FMD. Animals given a similar dose of chemically inactivated A12-LLV2 in the absence of adjuvant developed a poor immune response and were not protected from FMD, indicating that limited replication was responsible for the improved immune response found in animals vaccinated with live A12-LLV2. The results demonstrate the potential of A12-LLV2 as a live-attenuated vaccine as well as a safe source of antigen for chemically inactivated vaccines.