Location: Foreign Animal Disease Research2013 Annual Report
1a. Objectives (from AD-416):
The objective of this project is to improve recently developed novel strategies to control Foot-and-Mouth Disease (FMD). By mutating the leader protein (Lpro) coding region of the FMD virus, we were able to grow viruses which are less virulent than wild type viruses. This project will explore the incorporation of additional mutants in the Lpro region to decrease the probability of reversion to virulence and induce protective immune responses.
1b. Approach (from AD-416):
1. Test the virulence in swine of FHA mutant FMDV. In vivo studies will be conducted in swine to test the virulence of an available mutant FMDV strain containing mutations in a conserved domain (FHA) of the virus leader coding region. 2. Construction and in vitro characterization of FMDV strains with mutations in the CTE domain and/or the SAP and/or FHA domains. Several mutant FMDV strains will be constructed by using the infectious clone and targeting conserved residues contained in the CTE region of the leader coding region with the goal of obtaining new stable attenuated phenotypes that have a low probability of reversion to virulent wild type phenotype. 3. Test the virulence in swine of FMDV strains containing multiple mutations in the leader coding region (SAP and/or FHA and/or CTE mutations). In vivo studies will be conducted in swine with newly constructed FMDV containing multiple attenuating mutations in the leader coding region. 4. Test the efficacy of vaccination with attenuated FMDV SAP mutant of serotype A against infection with wild type FMDV of different subtypes and serotypes. Heterologus subypes/serotype specific cross-protection will be assayed by vaccination of swine with FMDV SAP mutant of serotype A followed by challenging with wild type FMDV of serotype A24 or O and/or Asia. The role of induction of protective innate immunity such as the interferon response will be evaluated.
3. Progress Report:
ARS, PIADC previously demonstrated that the Foot-and-Mouth Disease Virus (FMDV) leader proteinase, Lpro, is a virulence factor. Viruses with deletions of Lpro coding region, called “leaderless”, are viable and display an attenuated phenotype in vivo in swine and cattle. Attempts to use the leaderless virus as a vaccine have shown promising results but with limitations. In some instances the virus was virulent and in others adaptive immunity fell short of inducing protection against challenge. Recently, we have found that viruses with mutations in Lpro, specifically the SAP mutant, are viable and can mount a strong adaptive immunity in swine. Remarkably, SAP mutant virus inoculated animals developed a strong neutralizing antibody response and were completely protected against challenge with WT FMDV as early as 2 and for at least 21 days post inoculation. However, in rare occasions, SAP mutant virus reverted to virulence. Evaluated the possibility of adding other mutations in the Lpro coding region to increase stability and safety. We observed that some mutations, specifically H* mutants, were tolerated standing alone but not in combination with SAP however other mutants such as CTE, were viable and stable rendering viable viruses. FMDV with leader H* mutations have been characterized in vitro and in vivo displaying an attenuated phenotype although to a lesser extent than the SAP mutant. No technologies were transferred or publications produced in FY 2013.