The isolation of super-sensitive anti-hapten antibodies from combinatorial antibody libraries derived from sheep

The complexity and expense of producing anti-hapten monoclonals via the traditional hybridoma route and the preferential selection of antibodies that recognise the conjugated form of the hapten, over antibodies that specifically recognise free hapten, are two of the more important problems that have limited the development and application of anti-hapten antibodies. The advent of phage display technology allows the rapid isolation of monoclonal antibody fragments from libraries of different antibodies (>10(8)) displayed on the surface of filamentous bacteriophages. Much of the power of this new approach lies in the flexibility with which these libraries can be screened for suitable binders. Using an optimised selection procedure, we have isolated from a sheep antibody phage display library, super-sensitive anti-hapten antibodies specific for the herbicide and environmental pollutant, atrazine. In particular, two phage clones have been isolated that can be expressed cheaply and in quantity in Escherichia coli, demonstrate excellent stability in nonphysiological conditions and are exciting prospects for immunoassay applications including ELISA, dip-stick formats, on-line monitoring and biosensor technologies. In ELISA formats they show low levels of cross reactivity with related molecules and a limit of detection of a 1-2 parts per trillion (p.p.t.), well within the 100 p.p.t. required by EC legislation.