Affimed uses Phage Display to screen its antibody libraries to select appropriate antibodies for a specific target. Phage Display is the process by which bacteria is infected with a harmless virus (or bacteriophage) that can only infect bacteria such as E. coli. Antibody genes from Affimed's libraries of antibodies are fused to the pIII gene coding for the minor coat protein of a filamentous bacteriophage in such a way that they form a phage-display library expressing the full breath of the Affimed libraries.
The fusion gene is inserted into a phagemid containing the packaging signal for the bacteriophage and transfected into E. coli for protein expression. The additional proteins required for packaging the phagemid into a phage particle are provided by infection with a wild type bacteriophage. Each phage particle therefore displays a specific antibody whose genetic information is packed in the same particle. This phage-display library is then added to a dish coated with the target protein. Only phage with antibodies that recognize the target molecule bind to the target, while the other phage are removed in a wash step.
DNA from the interacting phage contain the identifiable sequences of only interacting antibodies. After infection of E. coli with the interacting phage, antibody fragments with the selected specifications are produced based on the genetic information delivered to the bacteria. These antibody fragments can be repeatedly presented on the surface of the phage. After several screenings, only those antibodies that bind specifically to the designated target are isolated.
Phage display enables the screening of numerous potential antibody candidates and the isolation of binding antibodies with particular specifications. In contrast, antibodies generated by the traditional hybridoma technology after the immunization of mice are often specific for immune-dominant epitopes (the binding position of the antibodies on the target). It is also not possible to screen differentially using immunization for the isolation of antibodies against difficult target molecules, something that is entirely possible with the Affimed research engine.