Amber suppression coupled with inducible surface display identifies cells with high recombinant protein productivity

Cell line development (CLD) for biotherapeutics is a time- and resource-intensive process requiring the isolation and screening of large numbers of clones to identify high producers. Novel methods aimed at enhancing cell line screening efficiency using markers predictive of productivity early in the CLD process are needed to reliably generate high-yielding cell lines. To enable efficient and selective isolation of antibody expressing Chinese hamster ovary cells by fluorescence-activated cell sorting, we developed a strategy for the expression of antibodies containing a switchable membrane-associated domain to anchor an antibody to the membrane of the expressing cell. The switchable nature of the membrane domain is governed by the function of an orthogonal aminoacyl transfer RNA synthetase/tRNApyl pair, which directs a nonnatural amino acid (nnAA) to an amber codon encoded between the antibody and the membrane anchor. The process is "switchable" in response to nnAA in the medium, enabling a rapid transition between the surface display and secretion. We demonstrate that the level of cell surface display correlates with productivity and provides a method for enriching phenotypically stable high-producer cells. The strategy provides a means for selecting high-producing cells with potential applications to multiple biotherapeutic protein formats.