Human therapeutic antibody discovery has utilized a variety of systems, from in vivo immunization of human
immunoglobulin-expressing mice, to in vitro display of antibody libraries. Of the in vitro antibody display technologies,
mammalian cell display provides a number of advantages with the ability to co-select immunoglobulin molecules for high
expression level in mammalian cells, native folding, and biophysical properties appropriate for drug development. Mammalian
cell display has been achieved using either transient or stable expression systems, using a number of alternate
transmembrane domains to present antibody on the cell surface. The unique capability of mammalian cells to present IgG
in its fully post-translationally modified format also allows selection of antibodies for functional properties. One limitation
of mammalian cell based systems, however, has been the smaller library size that can be presented compared to phage
display approaches. Until recently, this has necessitated the use of libraries biased toward a particular antigen, such as libraries
derived from immunized donors, to achieve success. An alternative approach has now been developed which recapitulates
key aspects of the in vivo immune system through reproducing somatic hypermutation (SHM) in vitro. Libraries
representing a naïve human B lymphocyte antibody repertoire are created by PCR amplification of the rearranged (D)J
segments of heavy and light chain variable regions from human donors and incorporating the resulting sequence diversity
into panels of human germline VH and VL genes. The resulting antibodies are presented as full length IgG on the surface
of HEK293 cells. After isolation of antibodies binding to individual target antigens, subsequent affinity maturation using
in vitro SHM is induced by expression of activation-induced cytidine deaminase (AID). Selection of antibodies from naïve
fully human libraries using mammalian cell display coupled with in vitro SHM is an efficient methodology for the
generation of high affinity human antibodies with excellent properties for drug development.
Affinity maturation, AID, antibody libraries, cell display, SHM.
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