Patent ID: 7196187

Claim:
A synthetic or semi-synthetic expression library comprising a repertoire of nucleic acid sequences derived from a naïve library repertoire and not cloned from a source immunized with a target antigen, wherein the naïve library repertoire comprising nucleic acid sequences encoding various fragments of a variable domain of a heavy chain of an immunoglobulin; each nucleic acid sequence of the expression library encoding a fragment of a variable domain of a heavy chain of an immunoglobulin devoid of light chains, wherein said heavy chain of the immunoglobulin in the expression library forms a complete antigen binding site (VHH), said fragment comprising at least the three complementarity determining regions (CDRs) and the parts of the framework that link the CDRs, wherein said expression library is produced by a method comprising the step of introducing one or more mutations in more than one of the CDRs or by shuffling nucleic acid sequences encoding CDRs and framework regions of the variable domain of the immunoglobulin heavy chain in the naïve library repertoire to generate new combinations of CDR and framework regions, the framework-CDR-encoding nucleic acid sequences in the naïve library repertoire being modified by random or partially random mutation of more than one of the CDR sequences.