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A method for simultaneous humanization and affinity maturation of monoclonal antibodies has been developed using heavy chain complementarity-determining region (CDR) 3 grafting combined with somatic hypermutation in vitro. To minimize the amount of murine antibody-derived antibody sequence used during humanization, only the CDR3 region from a murine antibody that recognizes the cytokine hβNGF was grafted into a nonhomologous human germ line V region. The resulting CDR3-grafted HC was paired with a CDR-grafted light chain, displayed on the surface of HEK293 cells, and matured using in vitro somatic hypermutation. A high affinity humanized antibody was derived that was considerably more potent than the parental antibody, possessed a low pm dissociation constant, and demonstrated potent inhibition of hβNGF activity in vitro. The resulting antibody contained half the heavy chain murine donor sequence compared with the same antibody humanized using traditional methods.

A novel approach has been developed for the isolation and maturation of human antibodies that replicates key features of the adaptive immune system by coupling in vitro somatic hypermutation (SHM) with mammalian cell display. SHM is dependent on the action of the B cell specific enzyme, activation-induced cytidine deaminase (AID), and can be replicated in non-B cells through expression of recombinant AID. A library of human antibodies, based on germline V-gene segments with recombined human regions was used to isolate low-affinity antibodies to human β nerve growth factor (hβNGF). These antibodies, initially naïve to SHM, were subjected to AID-directed SHM in vitro and selected using the same mammalian cell display system, as illustrated by the maturation of one of the antibodies to low pM K(D). This approach overcomes many of the previous limitations of mammalian cell display, enabling direct selection and maturation of antibodies as full-length, glycosylated IgGs.