Antibodies have become the foundation of the new field of protein therapeutics. They are used to treat immune related diseases and proliferative disorders such as cancer. Six different human antibody therapeutics have already been approved by the FDA for treatment of cancer, autoimmune diseases and to prevent transplant rejection and many more of these protein therapeutics are in clinical development. ? The generation of completely human antibodies in animals provides for the development of molecules that will avoid the problems of rejection and immunogenicity .inherent in the development of """"""""humanized"""""""" or """"""""chimeric"""""""" animal antibodies. However, the generation and development of human antibodies in animals is has been challenging The process involves insertion of near-mega base length human sequences encoding portions of one or more immunoglobulin (Ig) loci into embryonic stem (ES) cells and then transfer to animals whose host immune system have been knocked out. Transgenic animals are then challenged with antigen to produce human antibodies and B-cells isolated to manufacture the desired monoclonal antibody via hybridoma technology. While many methods have been used to generate animals that express various human proteins, most approaches are not capable of reliable and accurately transferring the large amounts of genetic material needed for antibody production. In additional, the initial approaches used to transfer the human Ig loci into immune deficient mice, YAC and transchromosomal technology, have a number of significant drawbacks. ? Aliva is a new start-up biotechnology company that has developed a technology that can provide important advantages over present approaches to generating human antibodies in animals. Aliva is focused on developing bacterial artificial chromosome (BAG) technology, first invented by Aliva's founder and Chief Scientific Officer, Dr.Hiroaki Shizuya, as a new generation system that will for the first time allow both targeted and sequential transfer of large stretches of genetic material to a host animal to produce a diverse repertoire of fully human therapeutic antibodies. We propose in this phase I SBIR grant, proof of principle studies .to demonstrate the sequential and targeting capabilities of the Aliva BAG technology, and to begin to generate a mouse that will produce true human antibodies. For this, we will create and use BAG to replace a major portion of the mouse heavy chain constant region with a 600-700Kb region of the human heavy chain in an ES cell line. This will provide the foundation for future phase II SBIR studies to generate Fl mice from the ES cells and replace the remaining heavy and light chain regions to generate mice capable of produce a full repertoire of human antibodies ? ?