Bypassing Immunization using Phage Display

In many instances, it is not feasible or ethical to immunize humans with antigens to which one desires to produce human antibodies. In addition, many antigens are evolutionarily conserved and not immunogenic.
Fortunately, phage display technology offers a route to produce human antibodies directly without immunization. Very large and diverse scFv or Fab phage antibody libraries are constructed from which it is theoretically possible to generate panels of antigens to virtually any antigen. In the first example, a human scFv gene repertoire was cloned into the phagemid pHEN-1 to create a non-immune phage antibody library of 3.0*10⁷ members. From this single non-immune library, scFvs were isolated against more than  different antigens, including a hapten, three different polysaccharides and  different proteins. The scFvs were highly specific for the antigen used for selection and had affinities typical of the primary immune response with dissociation equilibrium constants ranging from 1 mM to 15 nM. Larger or more diverse phage antibody libraries theoretically provide higher affinity antibodies against a greater number of epitopes on all antigens used for selection. At least five published examples of such very large libraries exist, with sizes ranging between 10⁹ and 10¹¹. For example, we have constructed a 6.7*10⁹ member scFv phage antibody library from the V genes of healthy humans. An average of nine scFvs with Kd as high as 3.7*10^-10 M were isolated to 10 different protein antigens. Antibodies from nonimmune libraries have been used for Western blotting, epitope mapping, cell agglutination assays, cell staining and FACS. A number have also entered human clinical trials for the treatment of a range of different diseases. The non-immune libraries described above represent the current state of the art in antibody engineering; the ability to generate highaffinity human monoclonal scFv or Fab antibody fragments to any antigen within weeks and without immunization.