Non-human animals expressing pH-sensitive immunoglobulin sequences

A method of obtaining a lymphocyte that expresses an antigen-specific immunoglobulin variable domain with histidines encoded by germline histidine codons, comprising

• harvesting the lymphocyte from a non-human animal,
• wherein the non-human animal comprises in its germline genome either or both
• (i) at an endogenous immunoglobulin heavy chain locus, an unrearranged immunoglobulin heavy chain variable region gene sequence comprising an unrearranged human VH gene segment, an unrearranged DH gene segment, and an unrearranged human JH gene segment operably linked to an immunoglobulin heavy chain constant region gene sequence, wherein one or more of the unrearranged human VH, unrearranged DH, and unrearranged human JH gene segments comprise, in a complementarity determining region 3 (CDR3) encoding sequence, a substitution of at least one non-histidine codon with a histidine codon or an insertion of at least one histidine codon and
• (ii) at an endogenous immunoglobulin light chain locus, an unrearranged human immunoglobulin light chain variable region gene sequence comprising unrearranged human VL and unrearranged human JL gene segments operably linked to an endogenous immunoglobulin light chain constant region gene sequence, wherein one or more of the unrearranged human VL and JL gene segments comprise, in a CDR3 encoding sequence, a substitution of at least one non-histidine codon with a histidine codon or an insertion of at least one histidine codon;
• wherein the non-human animal further comprises in vivo a diverse repertoire of antibodies that bind an antigen of interest, wherein each of the diverse repertoire of antibodies comprises
• (a) an immunoglobulin heavy chain variable domain that retains, in a CDR3, at least one histidine amino acid encoded by the substituted or inserted histidine codon in the germline genome and/or
• (b) an immunoglobulin light chain variable domain that retains, in a CDR3, at least one histidine amino acid encoded by the substituted or inserted histidine codon in the germline genome;
• and
• wherein the lymphocyte expresses one of the diverse repertoire of antibodies.