Rapid Chimerization of Antibodies.

We previously developed the in vitro method to generate monoclonal antibodies (mAbs) from libraries constructed with chicken B-cell line DT40 (referred to as the "ADLib system"). As the wild-type DT40 cells express immunoglobulin M (IgM), the original ADLib system provides monoclonal antibodies in chicken IgM format. For the therapeutic, diagnostic, and research purposes, the Fc regions of IgMs should be exchanged to other classes and species, for example human or murine IgG. However, the Fc engineering by conventional bioengineering process is laborious and takes plenty of time. Here, we developed a method to enable the seamless replacement of the Fc regions of antibodies generated by the ADLib system, using recombination-mediated cassette exchange (RMCE). In this system, two Cre recombinase recognition sites were inserted into the IgM's Fc region of the DT40 genome, allowing the exchange of the Fc region to the sequences of interest by co-transfection of a donor sequence and a Cre recombinase expression vector. We describe the detailed protocol of the technology: how to construct the RMCE host strains, select mAbs by the ADLib system, and exchange their Fc regions to generate chimeric mAbs.