High Throughput Screening of Antibody Secretion in CHO Cells Using Split-GFP and Droplet Microfluidics

The commercial and clinical success of antibodies, both as tools in research and diagnostic and as therapeutics, has convincingly been shown in recent years.

Production of monoclonal antibodies is predominantly done by overexpression of antibody genes in Chinese hamster ovary (CHO) cells for their ability to generate correctly folded and glycosylated proteins a large scale. To meet the growing demands of high-yielding and cost-effective production strains numerous rational, undirected or combinatorial approaches have been employed to enhance level of antibody secretion. Access to scalable and fast ways of monitoring product secretion is however limiting the ability for a complete and efficient screening of such libraries of strains.

Here we describe a novel high throughput screening system allowing for single cell characterization and sorting of antibody secreting CHO cells using droplet microfluidics and split-GFP complementation. A short tag, comprising the 11-strand of GFP, was genetically fused to the monoclonal antibody Herceptin and expressed in CHO as fusion proteins. We demonstrate the ability to encapsulate and cultivate such single CHO cells in mono-disperse droplets in a microfluidic device. By adding GFP 1-10 complement to the droplets we further show the ability to monitor secretion of tagged antibody by detection of GFP fluorescence upon complementation. We also show the ability to enrich for CHO secreting tagged highly fluorescent antibodies in a library with a background of wild type Herceptin secreting cells.

Using this generic technology we anticipate a better ability to perform fluorescent screenings of libraries for the identification of CHO strains with improved antibody secretion.