Transgenic chicken that makes antibodies with long CDR-H3S stabilized by multiple disulfide bridges and diversified by gene conversion

A transgenic chicken whose genome comprises an endogenous immunoglobulin heavy chain locus comprising:

• (a) a functional immunoglobulin heavy chain gene comprising a nucleic acid encoding a heavy chain variable domain comprising a FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4 in which:
• i) the FR1, CDR1, FR2, CDR2, and FR3, collectively, are at least 90% identical to a VH domain encoded by a germline human VH segment, and
• ii) the CDR3 is in the range of 30-67 amino acids in length and comprises 4-10 cysteine residues;
• and
• (b) a plurality of pseudogenes that are operably linked to said functional immunoglobulin heavy chain gene, wherein each pseudogene comprises nucleic acid sequences that encode a FR1, CDR1, FR2, CDR2, FR3 and CDR3, wherein:
• i) the nucleic acid sequences encoding the FR1, FR2, and FR3 in each pseudogene are, collectively, at least 80% identical to the collective nucleic acid sequences that encode the corresponding FR1, FR2, and FR3 in the variable domain of (a), and
• ii) the CDR3 encoded by each pseudogene is in the range of 30-67 amino acids in length and comprises 4-10 cysteine residues,
• wherein the pseudogenes are upstream or downstream of the functional immunoglobulin heavy chain gene,
• wherein the pseudogenes of (b) donate nucleotide sequence to the nucleic acid encoding the heavy chain variable domain of (a) by gene conversion in B cells of the chicken, and
• wherein the transgenic chicken produces a population of antibodies that have a diversified CDR3 region in the range of 30-67 amino acids in length and comprising 4-10 cysteine residues.