Phage Display Technology in Antibody Engineering: Design of Phagemid Vectors and in vitro Maturation Systems

The utilization of specific, high-affinity hutnan monoclonal antibodies in therapy of neoplasms, viral and bacterial infections and autoimmune disease has been a desire of clinicians since the introduction of monoclonal antibodies. The human hybridoma technology has, however, always been hampered by the fact that immunological specificity could in most cases, due to ethical reasons, not be generated by immunizing human individuals. Several in vitro immunization approaches have been developed that circumvent the ethical problems (Borrebaeck 1988, Ohlin & Borrebaeck 1992), although immunization of naive human B cells in vitro has only generated primary immune responses. Thus, human monoclonal antibodies generated by this approach are nonnally low-intermediate affmity IgM antibodies (Ohlin et al. 1989) and not directly applicable in a clinical situation. Recently, the advent of cloning antibody genes and displaying the antibody fragments on the surface ofa bacteriophage (McCafferty et al. 1990, Kang et al. 1991) has given us a unique tool to screen for immunological specificities. However, we still need to generate specific human B cells from which we can isolate the genes coding for the antibody variable domains, since the phage display technology does not per se generate any immunological specificities. The future will reveal if a combination of phage display technology with, e.g., in vitro immunization or primary/secondary immunization of Scid mice, transplanted with a human immune system (Carlsson et al. 1992), will provide the desired antibody specificities, or if so-called "naive libraries" in combination with in vitro afiinity maturation (see below) will offer the possibility to generate therapeutically useful human antibodies.