Diagnostic and prophylactic potential of a stabilized foot-and-mouth disease serotype Asia1 virus like particles designed through a structure guided approach.

Intact capsids of foot-and-mouth disease virus (FMDV) play a vital role in eliciting a protective immune response. Any change in the physico-chemical environment of the capsids results in dissociation and poor immunogenicity. Structural bioinfomatics studies have been carried out to predict the amino acids at the interpentameric region that resulted in the identification of mutant virus-like particles(VLPs) of FMDV serotype Asia1/IND/63/1972. The insect cell expressed VLPs were evaluated for their stability by sandwich ELISA. Among 10 mutants, S93H showed maximum retention of antigenicity at different temperatures, indicating its higher thermal stability as revealed by the in-silico analysis and retained the antigenic sites of the virus demonstrated by Sandwich ELISA. The concordant results of the liquid phase blocking ELISA for estimation of antibody titre of known sera with stable mutant VLP as antigen in place of virus antigen demonstrate its diagnostic potential. The stable mutant VLP elicited a robust immune response with 85.6 % protection in guinea pigs against virus challenge. The stabilized VLP based antigen requires minimum biosafety and cold storage for production and transit besides, complying with differentiation of infected from vaccinated animals. It can effectively replace the conventional virus handling during antigen production for prophylactic and diagnostic use.

Comparison of chemical extraction methods for determination of 146S content in foot-and-mouth disease oil-adjuvanted vaccine.

AIMS: To compare antigen extraction efficiency of chemical methods such as benzyl alcohol, chloroform, sodium citrate, extraction buffer with Tween-20 (EBT) and isopropyl myristate for determination of 146S content in the fresh and stored FMD oil-adjuvanted vaccines. METHODS AND RESULTS: Standard vaccine with antigen payload of 10, 5 and 5 µg per cattle dose (2 ml) for serotypes O, A and Asia1, respectively, was used to compare the antigen extraction efficiency of five chemical methods: benzyl alcohol, chloroform, sodium citrate, EBT buffer and isopropyl myristate. The purity of the extracted 146S antigen was quantified by caesium chloride (CsCl) ultracentrifugation. Serotype-specific sandwich ELISA (sELISA) was developed to identify the serotype and to compare the 146S in aqueous phase and ultrafractions. The antigen recovery was also tested in stored trivalent vaccine. Coefficient of regression was calculated to assess the predictive power of the benzyl alcohol extraction method. Of the five methods, benzyl alcohol showed consistent antigen recovery of >90% in monovalent as well as trivalent vaccines. Ultrafraction showed a 1·4 ratio at A259/239 nm in UV spectrophotometry indicating the presence of 146S. sELISA revealed that the antigen recovery was significantly less in ultrafractions than that of aqueous phase. Further, there was no significant difference in antigen recovery from stored trivalent vaccine for 12 months, indicating the usefulness of the benzyl alcohol method. Linear regression model revealed R2  = 0·99 with a narrow band of predictive interval. CONCLUSIONS: The benzyl alcohol method was efficient in extracting 146S from the monovalent and trivalent fresh and stored FMD vaccines. CsCl density gradient precisely quantified the 146S, while sELISA identified the serotype of the vaccine. SIGNIFICANCE AND IMPACT OF THE STUDY: When the benzyl alcohol method is coupled with CsCl density gradient and sELISA, it has the potential to determine the 146S content of FMD vaccine.

Generation of acid resistant virus like particles of vaccine strains of foot-and-mouth disease virus (FMDV).

Foot-and-mouth disease (FMD) is a contagious viral disease affecting cloven hoofed livestock. Insect cell expressed virus like particles (VLPs) are potential alternative to overcome the limitations of inactivated vaccine. However, at pH < 6.5, virus particles disassociate into pentameric structure resulting in loss of antigenicity. Accordingly, we generated seven mutant VLPs containing mutations in the structural genes of FMDV vaccine strains (N17D and/or H145Y for serotypes O/IND/R2/75 and Asia1/IND/63/72; and H142D for serotype A/IND/40/00) by PCR based site directed mutagenesis. Acid resistant VLPs produced by baculovirus expression system were tested for acid stability at pH 7.5, 6.5, 6.0 and 5.5 followed by reactivity in sandwich-ELISA (s-ELISA), which revealed mutant-1 (N17D) of serotype O and Asia1 retained the antigenicity in s-ELISA even at pH 5.5 as compared to other VLPs and wild-types. Further, the 75S empty capsids obtained in sucrose density gradient, when tested in liquid phase blocking ELISA (LPBE) in comparison to cell culture antigen indicated that the VLPs were stable at acidic pH. Transmission electron microscopy of OM-1 confirmed the intact morphology of the empty VLPs. It is concluded that acid resistant VLPs could be useful for developing new generation vaccine or diagnostic for FMDV.

Construction and characterization of recombinant human adenovirus type 5 expressing foot-and-mouth disease virus capsid proteins of Indian vaccine strain, O/IND/R2/75.

AIM: Generation of recombinant human adenovirus type 5 expressing foot-and-mouth disease virus (FMDV) capsid protein genes along with full-length 2B, 3B and 3C(pro) and its characterization. MATERIALS AND METHODS: FMD viral RNA isolation, cDNA synthesis, and polymerase chain reaction were performed to synthesize expression cassettes (P1-2AB3BC(wt) and P1-2AB3BC(m)) followed by cloning in pShuttle-CMV vector. Chemically competent BJ5183-AD-1 cells were transformed with the recombinant pShuttle-CMV to produce recombinant adenoviral plasmids. HEK-293 cells were transfected with the recombinant adenoviral plasmids to generate recombinant adenoviruses (hAd5/P1-2AB3BC(wt) and hAd5/P1-2AB3BC(m)). Expression of the target proteins was analyzed by sandwich ELISA and indirect immunofluorescence assay. The recombinant adenoviruses were purified and concentrated by CsCl density gradient ultracentrifugation. Growth kinetics and thermostability of the recombinant adenoviruses were compared with that of non-recombinant replication-defective adenovirus (dAd5). RESULTS: The recombinant adenoviruses containing capsid protein genes of the FMDV O/IND/R2/75 were generated and amplified in HEK-293 cells. The titer of the recombinant adenoviruses was approximately 10(8), 10(9.5) and 10(11) TCID50/ml in supernatant media, cell lysate and CsCl purified preparation, respectively. Expression of the FMDV capsid protein was detectable in sandwich ELISA and confirmed by immunofluorescence assay. Growth kinetics of the recombinant adenoviruses did not reveal a significant difference when compared with that of dAd5. A decrement of up to 10-fold at 4°C and 21-fold at 37°C was recorded in the virus titers during 60 h incubation period and found to be statistically significant (p<0.01). CONCLUSION: Recombinant adenoviruses expressing capsid proteins of the FMDV O/IND/R2/75 were constructed and produced in high titers. In vitro expression of the target proteins in the adenovirus vector system was detected by sandwich ELISA and immunofluorescence assay.

Novel immunogenic baculovirus expressed virus-like particles of foot-and-mouth disease (FMD) virus protect guinea pigs against challenge.

Vaccination is a well accepted strategy for control of foot-and-mouth disease (FMD) in endemic countries. Currently, chemically inactivated virus antigens are used for preparation of FMD vaccine. To develop a non-infectious and safe recombinant vaccine, we expressed structural polypeptide of FMDV (O/IND/R2/75) using baculovirus expression system. We show that inclusion of mutated viral 3C protease in frame with the polypeptide (P1-2A), enhanced the yield of structural proteins. The structural proteins retained antigenicity and assembled into empty virus-like particles (VLPs). Immunization of guinea pigs with purified fractions of the VLPs resulted in humoral and cell mediated immune response by 4 weeks. The VLPs elicited comparable humoral immune response and relatively higher cell mediated immune response, when compared to conventional vaccine in guinea pigs. Further, up to 70% of the VLP immunized guinea pigs were protected against challenge with homologous guinea pig adapted virus. Our results highlight the application of recombinant FMDV VLPs in FMD vaccination.