Development of single-chain variable fragment (scFv) antibodies against hapten benzo[a]pyrene: a binding study

Due to its highly carcinogenic and mutagenic effect on humans, a maximum tolerable limit of 10 ng/L of benzo[a]pyrene (B[a]P) in drinking water was set by the European Commission (Council Directive 98/83/EC). Although several polyclonal and monoclonal antibodies (mAb) for the detection of B[a]P and other polycyclic aromatic hydrocarbons (PAH) have been developed by others, a traditional enzyme-linked immunosorbent assay (ELISA) with a limit of quantification of 10 ng/L for monitoring B[a]P has not been developed. With this in mind, several single-chain variable fragment (scFv) antibodies were created using existing mAbs against the extremely hydrophobic hapten B[a]P, and their heavy and light chains recombined to make unique variable light (V_L) and heavy (V_H) chain combinations. Their binding behaviour was investigated using microtiter plate ELISA and surface plasmon resonance techniques. Specifically, the coding sequences for V_L and V_H chains of 10 murine anti-B[a]P antibody producing hybridoma cell lines were isolated by degenerate oligonucleotide primer sets, cloned in phagemid pIT2 and transferred into Escherichia coli HB2151. To systematically investigate the interaction of the V_L and V_H domains, three high-affinity B[a]P-specific and one nonspecific clone were selected and recombined to build a set of 16 different V_L and V_H combinations. On the basis of our data, it was shown that the V_H plays the major role for specific binding of B[a]P, whilst the V_L can, in some cases, increase the final sensitivity of the assay by one order of magnitude. Furthermore, the sequence analysis of scFvs indicates that the complementarity determining region H3 plays a major role in affinity, whilst cross-reactivity to seven other PAHs demonstrates the importance of the V_L in providing cross-reactivity.