CHO cells are the most popular and most successful host system for the production of high value proteins for therapeutic use since 30 years. However, the genomic and phenotypic diversity of CHO cells is poorly understood and vastly underestimated. Knowledge about many aspects of this diversity has been known for decades, but is buried now in part in pre-internet publications rarely read or not accessible. Recent information, both from genomic sequence analysis and from phenotypic observations of hundreds of clonally derived cell lines enforce the notion that CHO cells are in fact highly dynamic in terms of their genetics, and their phenotypes are rapidly modified in culture. Most interestingly, any CHO population will respond efficiently towards “survival” while further enhancing their genetic and phenotypic diversity, each clone with a different type of response. The resulting genetic modifications, occurring in millions of cells of clonally or non-clonally derived cell lines, can and will happen within the timeframes of the 100 or so population doublings that are typically necessary, starting from a Master Cell Bank, when used for the manufacture of a given protein product under cGMP.
The talk will try to summarize the unique and remarkable history of Chinese hamster ovary cells, in culture now for more than 50 years. While doing so, both the phenotypic and genotypic features of the many academically well-studied cell lines as well as their genomic structures as they were analysed in the 60s-80s will be presented. Very recent genomic DNA sequence analysis of a few “known” host cell lines will be added to this discussion. Based on this, a case will be made to apply to CHO cells (and any other immortalized cell line) the notion of belonging to a class of replication competent organisms, termed “quasi-species”. Population genetics theory and praxis predicts that such systems increase their genetic diversity when forced through narrow population bottlenecks – the cloning of cells being one of the most stringent of such bottlenecks. In conclusion, the talk will try to provide a better understanding of what CHO cells really are, how they evolve in the setting of product manufacture, and what one can do to enhance the robustness and quality of products derived from these remarkable cells.