Genetic engineering of streptavidin-binding peptide tagged single-chain variable fragment antibody to Venezuelan equine encephalitis virus

Isolation and characterisation of a human-like antibody fragment (scFv) that inactivates VEEV in vitro and in vivo

Venezuelan equine encephalitis virus (VEEV) belongs to the Alphavirus genus and several species of this family are pathogenic to humans. The viruses are classified as potential agents of biological warfare and terrorism and sensitive detection as well as effective prophylaxis and antiviral therapies are required.In this work, we describe the isolation of the anti-VEEV single chain Fragment variable (scFv), ToR67-3B4, from a non-human primate (NHP) antibody gene library. We report its recloning into the bivalent scFv-Fc format and further immunological and biochemical characterisation.The scFv-Fc ToR67-3B4 recognised viable as well as formalin and ß-propionolactone (ß-Pl) inactivated virus particles and could be applied for immunoblot analysis of VEEV proteins and immuno-histochemistry of VEEV infected cells. It detected specifically the viral E1 envelope protein of VEEV but did not react with reduced viral glycoprotein preparations suggesting that recognition depends upon conformational epitopes. The recombinant antibody was able to detect multiple VEEV subtypes and displayed only marginal cross-reactivity to other Alphavirus species except for EEEV. In addition, the scFv-Fc fusion described here might be of therapeutic use since it successfully inactivated VEEV in a murine disease model. When the recombinant antibody was administered 6 hours post challenge, 80% to 100% of mice survived lethal VEEV IA/B or IE infection. Forty to sixty percent of mice survived when scFv-Fc ToR67-3B4 was applied 6 hours post challenge with VEEV subtypes II and former IIIA. In combination with E2-neutralising antibodies the NHP antibody isolated here could significantly improve passive protection as well as generic therapy of VEE.

Microbead electrochemiluminescence immunoassay for detection and identification of Venezuelan equine encephalitis virus

An electrochemiluminescence (ECL) immunoassay, incorporating chemically biotinylated and ruthenylated antibodies down-selected from a panel of monoclonal and polyclonal reagents, was developed to detect and identify Venezuelan equine encephalitis virus (VEEV). The limit of detection (LOD) of the optimized ECL assay was 10(3)pfu/ml VEEV TC-83 virus and 1 ng/ml recombinant (r) VEEV E2 protein. The LOD of the ECL assay was approximately one log unit lower than that of a sandwich enzyme-linked immunosorbent assay (ELISA) incorporating the same immunoreagents. Repetition of ECL assays over time and by different operators demonstrated that the assay was reproducible (coefficient of variation 4.7-18.5% month-to-month; 3.3-8.8% person-to-person). The VEEV ECL assay exhibited no cross-reactivity with two closely related alphaviruses or with 21 heterologous biological agents. A genetically biotinylated recombinant VEEV antibody, MA116SBP, was evaluated for utility for detection of rE2; although functional in the ECL assay, the LOD was two log units higher (100 ng/ml vs 1 ng/ml) using MA116SBP than when chemically biotinylated antibody was used. The ECL assay detected VEEV at the lowest LOD (highest sensitivity) hitherto reported in the published literature and ECL assay results were generated in ∼60 min compared to a 6-8h period required for ELISA. Results have demonstrated a sensitive, rapid, and fully automated ECL immunoassay for detection and identification of VEEV.

Humanization and mammalian expression of a murine monoclonal antibody against Venezuelan equine encephalitis virus

The murine monoclonal antibody 1A4A1 can strongly neutralize Venezuelan equine encephalitis virus and is a good candidate for development of humanized antibody. Humanization of 1A4A1 variable domains was achieved by grafting 1A4A1 complementarity-determining regions (CDRs) onto the frameworks of human immunoglobulin germline variable and joining gene segments, whose CDRs have the highest similarities to 1A4A1 ones. The humanized 1A4A1 variable domains were further grafted onto human heavy and light chain constant domains to assemble the whole antibody gene, which was then synthesized and cloned to an adenoviral vector. After expression in HEK 293 cells and purification by protein L column, the humanized antibody was demonstrated to retain antigen-binding specificity and neutralizing activity.

Development of immunofiltration assay by light addressable potentiometric sensor with genetically biotinylated recombinant antibody for rapid identification of Venezuelan equine encephalitis virus

A genetically biotinylated single chain fragment variable antibody (scFv) against Venezuelan equine encephalitis virus (VEE) was applied in a system consisting of an immunofiltration enzyme assay (IFA) with a light addressable potentiometric sensor (LAPS) for the rapid identification of VEE. The IFA involved formation of an immunocomplex sandwich consisting of VEE, biotinylated antibody, fluoresceinated antibody and streptavidin, capture of the sandwich by filtration on biotinylated membrane, and labeling of the sandwich by anti-fluorescein urease conjugate. The concentration ratio of biotinylated to fluoresceinated antibodies was investigated and optimized. By the IFA/LAPS assay, the limit of detection (LOD) of VEE was approximately 30 ng/ml, similar to that achieved when chemically biotinylated monoclonal antibody (mAb) was applied. Total assay variance of the IFA/LAPS assay for both intra- and inter-assay precision was less than 20%. Assay accuracy was measured by comparing VEE concentrations estimated by IFA/LAPS standard curve to those obtained by conventional protein assay. VEE concentrations were found to differ by no more than 10%. The IFA/LAPS assay sensitivity was approximately equal to that of a conventional enzyme-linked immunosorbent assay (ELISA) utilizing polystyrene plates and a chromogenic substrate; however, less time and effort were required for performance of the IFA/LAPS assay. More importantly, use of genetically biotinylated scFv in the IFA/LAPS assay obviates the need for chemical biotinylation of antibody with resultant possible impairment of the antigen-binding site. Furthermore, the potential for batch-to-batch variability resulting from inequality in the number of biotin molecules labeled per antibody molecule is eliminated.