Although fully human antibodies are ideal for therapeutic development, humanized antibodies currently dominate the therapeutic antibody market, since historically, many murine antibodies generated as research reagents were later shown to have properties of interest for therapeutic development. These antibodies were then humanized to minimize immunogenicity and to provide effector functions in humans. There are many approaches to humanize murine antibodies. The most common approach is to graft the 6 CDRs from a murine antibody onto a human antibody acceptor framework. However, such CDR grafting often results in partial or complete loss of affinity of the humanized antibody, and some residues from the murine framework sequences need to be retained to replace the human residues at the corresponding positions (back mutations) in order to restore some of the lost affinity, as illustrated in the following example.
Therefore, it is critically important to accurately pinpoint the key residues to be retained and to select a suitable human antibody germline acceptor that can support the structure of humanized antibodies with goodthermo-stability and solubility for downstream development. AvantGen has extensive antibody modeling and engineering expertise to successfully restore and, if necessary, improve on the binding affinity of the humanized antibody with superior developability.
In addition, AvantGen has also developed an improved antibody humanization technology using its advanced yeast display system. Using this technology, the CDR3-H region alone from an antibody to be humanized is grafted into the relevant VH antibody sublibrary in place of the existing human CDR3-H regions, which in turn is coupled with the relevant existing human VL library to generate a focused library of humanized antibodies. This library is then screened for higher affinity binders using a FACS epitope-guided approach. The resulting humanized antibodies will have fully human antibody sequences in the variable regions, except for CDR3-H which is from the original non-human monoclonal antibody; therefore, the humanized antibody greatly reduces potential immunogenicity, while maintaining or improving affinity of the original antibody.