Target binding polypeptide

#This invention relates to the construction, application and production of novel polypeptides with enhanced or modified binding activity or specificity to haptens and antigens.

#The invention also relates to the construction, modification and selection of recombinant antibody-like molecules derived from expression of libraries of surface presenting antigen- or hapten-binding moieties, and to uses of these molecules.

#The polypeptides of the invention have utility in the diagnostic, therapeutic, predictive or preventative fields of the pharmaceutical and health care industries, as well as more general application in the detection and assay of chemical entities.

#Preferred embodiments of the invention include the following:

#1. The structure of the target binding polypeptides may be based on scFv molecules in which one TBR is formed by six surface polypeptide loops to provide contact region to antigen, and hence specificity. In a particularly preferred embodiment, the TBR may be formed by four CDR loops for contact with antigen to provide sufficient contact area and affinity (FIG. 14). Our results using NC10 indicate that it is feasible to randomly mutate these polypeptide sequences to modify target affinity.

#2. Bifunctional or polyfunctional reagents can be produced by covalent linkage of individual target binding polypeptides. The covalent linkage can be provided by polypeptide chains in the manner of single-chain Fv molecules. Specificities can be linked by joining together individual proteins, regions which have a propensity for dimerisation or aggregation. Thus it is not necessary for example to link two single-chain Fv fragments in their normal orientation by an additional polypeptide chain, but this can be achieved by linking Heavy and Light chains of differing specificity, or Heavy to Heavy chains, Light to Light chains which can then associate to form functional dimers or aggregates. Of course the method can also be used to join V domains with required specificity to other protein domains, including the Immmoglobulin-like domains derived from CD8, T-cell receptor fragments, or MHC fragments.