The invention relates to the provision of antibody therapeutics and prophylactics that are tailored specifically for human use. The present invention provides libraries, vertebrates and cells, such as transgenic mice or rats or transgenic mouse or rat cells. Furthermore, the invention relates to methods of using the vertebrates to isolate antibodies or nucleotide sequences encoding antibodies. Antibodies, heavy chains, polypeptides, nucleotide sequences, pharmaceutical compositions and uses are also provided by the invention.