Patent ID: 7884054

Claim:
A method for enriching for variant antibodies that bind to a molecule with different affinity than does an original antibody that binds to the molecule comprising the steps of: (a) providing a library of nucleic acids that encodes about 100 or more different variant antibodies, each having a variant antibody amino acid sequence, wherein the variant antibody amino acid sequences are identical to an original antibody amino acid sequence, except that they differ from the original antibody amino acid sequence at one or more selected sites within one or more complementarity determining regions, wherein the variant antibody amino acid sequences comprise an amino-terminal signal sequence in their immature form, wherein the library encodes variant antibodies including a membrane association sequence downstream from the variant antibody amino acid sequence, and wherein the variant antibodies can be expressed from the library of nucleic acids as cell surface antibodies in mammalian cells; (b) transfecting the library of nucleic acids into mammalian cells, thereby enabling the mammalian cells to express the variant antibodies as cell surface proteins; and (c) isolating cells that express variant antibodies that bind to the molecule with different affinity than do cells expressing the original antibody, wherein most of the individual mammalian cells expressing the variant antibodies express only variant antibodies having a single sequence, and wherein the mammalian cells comprise a FLP recombination target (FRT) site and the library of nucleic acids comprises an FRT site.