Transgenic non-human animals capable of producing heterologous antibodies of various isotypes

A method for obtaining secondary repertoire, somatically mutated human immunoglobulin V gene segments encoding immunoglobin V regions reactive with a pre-selected antigen the method comprising:

• antigenically stimulating a transgenic mouse with said pre-selected antigen said transgenic mouse having one or more transgenes containing DNA segments from unrearranged human immunoglobulin heavy and kappa light chain gene loci incorporated its germline DNA, said transgene or transgenes comprising a plurality of human V kappa gene segments, a plurality of human J kappa gene segments, a human kappa constant region gene segment, a plurality of human VH gene segments, a plurality of human DH gene segments, a plurality of human JH gene segments, a human mu switch segment, and a human mu constant region gene segment,
• wherein a first subset of B lymphocytes of said transgenic mouse produce IgM immunoglobulin molecules encoded by functional rearrangement of said immunoglobulin heavy and kappa light chain gene loci, said functionally rearranged immunoglobulin genes having variable region sequences including FR1, CDR1, FR2, CDR2, and FR3 portions from said human V kappa or VH gene segments of said unrearranged gene loci,
• and wherein a second subset of B lymphocytcs of said transgenic mouse produce non-IgM immunoglobulin molecules encoded by somatically mutated immunoglobulin heavy and kappa light chain gene loci, said somatically mutated immunoglobulin heavy and kappa light chin gene loci having variable region sequences including FR1, CDR1, FR2, CDR2, and FR3 portions of somatically mutated DNA sequences from said human V kappa or VH gene segments of said first subset;
• and
• obtaining said somatically mutated human immunoglobulin V gene segments by (1) collecting somatically mutated V gene segments from said second subset of B lymphocytes or (2) immortalizing said second subset of B lymphocytes and then collecting somatically mutated V gene segments from said lymphocytes, wherein one or more of the somatically mutated V gene segments encode immunoglobulin V regions reactive with the preselected antigen.