Phage display technology is a very powerful tool widely used to select antibody fragments such as Fabs, scFvs and VHHs. The resulting phage display selected antibody fragments are then usually converted to immunoglobulins or to Fc fusion proteins and expressed in mammalian cells. The resulting final molecules are bivalent, possess Fc effector function and a half-life comparable to natural immunoglobulins. This conversion process is a bottleneck in antibody discovery, labour intensive and time-consuming. Moreover, for some antibody fragments the conversion to Fc fusion proteins result in loss of activity. To circumvent these drawbacks, we have generated a vector (“triple vector”) containing the elements necessary to produce VHH and scFv fragments fused to human Fc in bacteria, and production in mammalian cells.
Ultimately the selection of immunological effector function bearing bivalent molecules, bypassing the cloning into mammalian expression vectors, will accelerate the drug discovery process. The selection of anti-human CXCR4 VHH-human Fc molecules from naïve repertoires using the generated triple vector is shown as case study under the “Case Studies” section.