Artificial chromosome vectors and expression of complex proteins in transgenic animals

Artificial chromosome vectors are autonomous, replicating DNA sequences containing a centromere, two telomeres and origins of replication. Artificial chromosomes have been proposed as possible vectors for transferring very large sequences of DNA into animals. Our goal has been to insert the entire human heavy- and light-chain immunoglobulin loci into cattle as a step in developing a production system for large quantities of human therapeutic polyclonal antibodies. A mitotically stable fragment of chromosome 14, containing the human heavy-chain locus, was identified. A chromosome cloning system was used to transfer the human lambda locus from an unstable chromosome 22 fragment to the chromosome 14 fragment to create a human artificial chromosome (HAC) carrying both immunoglobulin loci. The HAC vector was introduced into bovine primary fibroblasts. Selected fibroblast clones were rejuvenated and expanded by producing cloned fetuses. Cloned fetal cells were selected and recloned to produce 21 healthy, transchromosomic (Tc) calves. Four were analyzed and shown to functionally rearrange both heavy- and light-chain human immunoglobulin loci and produce human polyclonal antibodies. These results demonstrate the feasibility of using HAC vectors for production of transgenic livestock. More importantly, Tc cattle containing human immunoglobulin genes may be used to produce novel human polyclonal therapeutics.