Mammalian cell line for protein production and library generation

A plurality of recombinant mammalian B cells comprising:

• (a) an inducible synthetic somatic hypermutation (iSSHM) system comprising an activation-induced cytidine deaminase (AID) driven by an inducible promoter;
• and
• (b) a transgenic genomic DNA sequence encoding a protein of interest that is not endogenous to a mammalian B cell,
• wherein each member of the plurality of recombinant mammalian B cells comprises a transgenic genomic DNA sequence encoding a variant of the protein of interest,
• wherein the transgenic genomic DNA sequence is inserted into an endogenous immunoglobulin locus comprised in the recombinant mammalian B cell, and the endogenous immunoglobulin locus is knocked out;
• and
• wherein each variant of the protein of interest expressed by a member of the plurality of recombinant mammalian B cells is different from any other variant of the protein of interest expressed by another member of the plurality of recombinant mammalian B cells.