Development of recombinant single-chain variable fragment against hepatitis A virus and its use in quantification of hepatitis A antigen

Phage display technology has been utilized for identification of specific binding molecules to an antigenic target thereby enabling the rapid generation and selection of high affinity, fully human antibodies directed towards disease target appropriate for antibody therapy. In the present study, single chain Fv antibody fragment (scFv) to hepatitis A virus (HAV) was selected from phage displayed antibody library constructed from peripheral blood lymphocytes (PBLs) of a vaccinated donor. The variable heavy (V(H)) and light chains (V(L)) were amplified using cDNA as template, assembled into scFv using splicing by overlap extension PCR (SOE PCR) and cloned into phagemid vector as a fusion for display of scFv on bacteriophage. The phage displaying antibody fragments were subjected to three rounds of panning with HAV antigen on solid phase. High affinity antibodies reactive to hepatitis A virus were identified by phage ELISA and cloned into a bacterial expression vector pET20b. The scFv was purified by immobilized metal affinity chromatography (IMAC) on a nickel-nitrilotriacetic acid (NTA) agarose column and characterized. The binding activity and specificity of the scFv was established by its non-reactivity towards other human viral antigens as determined by ELISA and immunoblot analysis. The scFv was further used in the development of an in-house IC-ELISA format in combination with a commercially available mouse monoclonal antibody for the quantification of hepatitis A virus antigen in human vaccine preparations. The adjusted r2 values obtained by subjecting the values obtained by quantification of the NIBSC standards using the commercial and the in-house ELISA kits by regression analysis were 0.99 and 0.95. 39 vaccine samples were subjected to quantification using both the kits. Regressional statistical analysis through the origin of the samples indicated International Unit (IU) values of 0.0416x and 0.0419x, respectively for the commercial and in-house kit respectively.