Discloses a rodent that has undergone immunoglobulin gene sequence rearrangement so that it comprises a B cell that includes in its genome: (i) a rearranged human heavy chain variable region sequence operably linked to a rodent heavy chain constant region sequence, wherein the rearranged human heavy chain variable region sequence comprises a human VH gene segment, a human DH gene segment, and/or a human JH gene segment； and (ii) an inserted nucleic acid sequence encoding an ADAM6 protein on the same chromosome as the rearranged immunoglobulin sequence, wherein the ADAM6 protein is expressed from the nucleic acid sequence. Further discloses methods of generating antibodies using cells of said CDJ recombinant ADAM6 rodent.
