Development of a second generation monoclonal single chain variable fragment antibody against Venezuelan equine encephalitis virus: expression and functional analysis

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.

Functional enhancement of a partially active single-chain variable fragment antibody to Venezuelan equine encephalitis virus

Previously cloned recombinant A116 single chain fragment variable (scFv) antibody gene has been re-engineered for enhanced reactivity to Venezuelan equine encephalitis virus (VEE) successfully. A PCR-based site-directed mutagenesis approach was adopted to re-introduce the three single-base deletions in the 5' region of the V(L) gene of A116, corresponding to the framework-1 region. The mutagenized A116 was designated as MA116. The introduction of these three bases corrected a localized frame-shift to a consensus framework-1 amino acid sequence. Four MA116 clones (MA116-4, MA116-14, MA116-15, and MA116-16) have been analysed in detail for their reactivity to VEE antigen, and all showed varying degrees of reactivity to VEE antigen. ScFv antibody expressed by MA116-14, MA116-15, and MA116-16 clones showed three to five-fold enhanced enzyme-linked immunosorbant assay reactivity to VEE antigen over the parental A116 clone, while scFv antibody from MA116-4 was less reactive than A116 clone. MA116-15 purified scFv protein showed comparable reactivity to the parental 1A4A-1 monoclonal antibody in recognizing VEE antigen. Sequence analysis revealed that only MA116-15 had incorporated the three intended base insertions. The varying degrees of reactivity of MA116 clones are discussed in light of their molecular changes.

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

A recombinant gene encoding a single-chain variable fragment (scFv) antibody against Venezuelan equine encephalitis virus (VEE) was cloned into a prokaryotic T7 RNA polymerase-regulated expression vector. A streptavidin-binding peptide gene fused to a 6His tag was attached downstream to the scFv gene. The recombinant fusion protein was expressed in bacteria as inclusion bodies that were subsequently solubilized with 8 M urea and renatured by an arginine system. Purification of the fusion protein was achieved by immobilized metal affinity chromatography. Enzyme-linked immunosorbent assay (ELISA) and Western blotting results revealed that the fusion protein not only retained VEE antigen binding and specificity properties similar to those of its parent native monoclonal antibody (MAb), but also possessed streptavidin-binding activity. This experimental approach can eliminate the need for chemical biotinylation of antibodies and the risk associated of antibody denaturation and can provide a stable and reproducible reagent for rapid and efficient immunoassay of VEE when detected by horseradish peroxidase (HRP)-conjugated streptavidin.