HCP Antigens and Antibodies from Different CHO Cell Lines

level: AdvAnced C ell lines derived from Chinese hamster ovary (CHO) cells are widely used in therapeutic protein production because they can perform human-compatible posttranslational modifications, they are easy to use for manufacturing, and they do not propagate most human pathogenic viruses (1, 2). Expressed therapeutic proteins are secreted into CHO culture supernatant along with impurities originating from the host cells themselves. Such host cell proteins (HCPs) are important contaminants for monitoring because they directly affect drug quality, safety, and efficacy. HCPs are complex mixtures with diverse physicochemical and immunological properties (3). The genome sequence of the ancestral CHO K1 cell line suggests that the CHO genome has more than 24,000 genes and 29,000 transcripts (2). The first proteomic study of CHO-K1 identified about 6,000 proteins (4). Considerable genomic heterogeneity has been revealed among different CHO cell lines (1). Recently, full-genome sequence analysis of seven CHO cell lines derived from the three CHO lineages used most frequently in therapeutic protein production (CHO K1, DG44, and CHO-S) demonstrated that each line harbors its own set of unique mutations (5). Those mutations can accumulate rapidly during cell line development (5). Because of instability and diversity in the CHO genome, HCP profiles can vary not only from cell line to cell line, but also within the same cell line used for expressing different proteins (unpublished data). During downstream purification, HCPs should be reduced to the lowest achievable levels. Multiple analytical techniques such as immunoassays, gel electrophoresis, high-performance liquid chromatography (HPLC), and mass spectrometry (MS) have been used for HCP quantitation, detection, and identification (3, 6–12). Each technique presents its own advantages and disadvantages. Changes in the abundance of HCP species during process development have created additional challenges for accurately monitoring HCPs during purification as well as in final drug substances. A preferred means for HCP detection is the multianalyte enzymelinked immunosorbent assay (ELISA) used with anti-HCP polyclonal