Automated Screening of High Producer HEK293F Clones and Analysis of Post-Translational Modifications of Secreted Proteins

Abstract

A novel, high throughput method to identify human cell clones secreting highest levels of a clotting factor with human-identical post-translational modifications (PTMs) was established. Automation of the selection process involves the ClonePix^FL technology not only for picking of clones, but also for visualization of secreted protein and characterization of PTMs prior to picking. In order to generate highly optimized therapeutics for haemophilia patients, a human cell line was selected as the host for production clones. This cell line is engineered to produce and secrete recombinant clotting factors in a completely serum- and protein-free process. In this new type of high throughput setting, single-cell clones are screened and secreted monomeric clotting factors are quantified in semi-solid medium. Automatically identified clones were shown to secrete significantly higher levels of recombinant protein than randomly picked clones. Calculation of productivity per cell was important to identify the very best producer clones. Detection of human-identical PTMs of the secreted proteins prior to picking and without the need to purify protein from the cell culture supernatant could be successfully shown in a proof-of-concept study. The automated selection process turned out to be highly efficient as it substantially reduces workload and screening time, while the throughput increases from only a few hundreds to many thousands of analyzed clones.