Evaluation of a Live-Attenuated Foot-and-Mouth Disease Virus as a Vaccine Candidate

AbstractA variant of foot-and-mouth disease virus (FMDV) lacking the leader (L) coding region (A12-LLV2) was previously constructed and shown to be less virulent in cattle than its wild-type parent (A12-IC). In this study, cattle were tested for their clinical and immunological responses to subcutaneous inoculation with A12-LLV2 or A12-IC or to intramuscular vaccination with chemically inactivated A12-IC. Five weeks postinoculation animals were challenged by intradermal inoculation in the tongue with a virulent cattle-passaged virus. A12-LLV2-inoculated animals showed no clinical signs of disease and developed a neutralizing antibody response by 4 days postinoculation, whereas a companion control bovine did not seroconvert. After challenge, two of three inoculated animals did not develop lesions, but showed mild signs of infection. The third inoculated animal developed some lesions, but these were less severe than in the uninoculated control animal, which showed classical FMD. All animals inoculated with A12-IC developed a fever, two showed typical FMD lesions, and the companion control seroconverted, indicating that it had acquired infection by contact. The A12-IC-inoculated animals and the control were protected from challenge. Animals vaccinated with inactivated virus showed no clinical signs of disease and developed a neutralizing antibody response, and the control did not seroconvert. Upon challenge none of the vaccinated animals developed lesions, one developed a fever, and the control developed FMD. These experiments demonstrate the potential of a rationally designed live-attenuated FMDV vaccine

Construction of a Chimeric Theiler's Murine Encephalomyelitis Virus Containing the Leader Gene of Foot-and-Mouth Disease Virus

AbstractThe foot-and-mouth disease virus (FMDV) leader coding region (Lb) was cloned into a full-length cDNA of the DA strain of Theiler's murine encephalomyelitis virus (TMEV) replacing the complete L coding region of TMEV. This construct, pDAFSSC1-Lb, was engineered to contain cleavage sites, at the 3′ end of the Lb coding region, for both the FMDV Lb and the TMEV 3C proteases. Transcripts derived from this construct were translated in a cell-free system. Analysis of the translation products showed efficient synthesis and processing of TMEV structural and nonstructural proteins as well as a major band that comigrated with FMDV Lb and was reactive with Lb antiserum. A small plaque virus was recovered from BHK-21 cells transfected with RNA derived from pDAFSSC1-Lb. RT-PCR of RNA isolated from DAFSSC1-Lb virus demonstrated a product corresponding in size and sequence to FMDV Lb. DAFSSC1-Lb virus grew slower than parental virus, DAFSSC1, and to a lower titer. The pattern of viral proteins synthesized in DAFSSC1-Lb virus-infected cells was very similar to the pattern in DAFSSC1 virus-infected cells except that significant amounts of FMDV Lb were produced. In addition, extracts from DAFSSC1-Lb-virus-infected cells cleaved an exogenous source of the translation initiation factor, p220, while DAFSSC1-virus-infected extracts did not. Chimeric viruses that contain coding regions from different picornaviral genera may be valuable tools in investigating the function of particular viral proteins and in studying disease pathogenesis