Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 27, 1999
Publication Date: N/A
Interpretive Summary: Protection against foot-and-mouth disease (FMD) correlates with the development of neutralizing antibodies against the foot-and-mouth disease virus (FMDV) in the vaccinated animals. During FMDV infection,the single large polyprotein made by the virus is cut into smaller functional pieces, including the proteins which make up the virus capsid particle, by a virus enzyme known as 3C. Portions of the FMD genome responsible for the capsid polyprotein (P12X) and the 3C enzyme were placed in an adenovirus-5 (Ad5) vector. This Ad5 vector cannot reproduce outside of special laboratory cell culture. Two different adenovirus constructs were made. Both contained the capsid polyprotein (P12X) coding portion of the FMDV genome. One construct contained the gene for a functional 3C enzyme (3CWT) which could cut the capsid polyprotein into individual capsid proteins, the other a mutated 3C gene, which produced an enzyme (3CMUT) which could not. Only in cells infected with the 3CWT virus could the polyprotein be cut into smaller proteins which could then make a foot-and-mouth virus-like particle. Precipitation with monoclonal antibodies against FMDV particles showed that the 3CWT infected cells made a structure similar to empty FMDV virus particles. Mice were vaccinated twice with the Ad5-P12X- 3CWT or 3CMUT viruses. Only mice given the Ad5-P12X3CWT developed a strong immune response capable of neutralizing FMD virus. The Ad5-P12X3CWT construct was used to vaccinate swine twice. Use of Ad5-P12X3CWT in swine showed that this construct could generate neutralizing antibodies against FMDV resulting in significant protection from challenge infection with FMDV.
Technical Abstract: A recombinant replication-defective human adenovirus serotype 5 vector containing FMDV capsid, P1-2A, and viral 3C protease coding regions was constructed. Two viral clones were isolated, Ad5 P12X3CWT, containing the wild type (WT) 3C protease that processes capsid polyprotein precursor into mature capsid proteins and, Ad5 P12X3CMUT, containing a point mutation in the protease coding region that inhibits processing. In 293 cells infected with either virus, synthesis of the FMDV capsid polyprotein precursor occurred, but processing of the polyprotein into structural proteins VP0, VP3, and VP1 occurred only in 3CWT virus infected cells. Immunoprecipitation with monospecific and monoclonal antibodies indicates possible higher order structure formation in Ad5 P12X3CWT virus infected cells. The viruses were used to elicit immune responses in mice inoculated intramuscularly (IM). Only virus containing the 3CWT elicited a neutralizing antibody response. After boosting, this neutralizing antibody response increased. Swine inoculated IM with Ad5 P12X3CWT virus developed a neutralizing antibody response and were either completely or partially protected from contact challenge with an animal directly inoculated with virulent FMDV. This adenovirus vector may be an efficient system for the delivery of FMDV cDNA into animals, leading to a high level of neutralizing antibody production and protection from FMDV challenge.