Following clone screening, the next key stage in the cell line development workflow is to identify clones with good growth characteristics coupled with a consistently high expression of the product of interest. High expression of a biotherapeutic product is particularly important in monoclonal antibody production, where large yields are necessary to fulfil requirements for long-term treatment. Correct assessment of clone quality at this stage therefore provides the foundation for a successful cell line and reduces the risk of costly failures later on.
Clones selected from screening are now assessed for growth rate, typically in 96- or 24-well microplates. Cell Metric CLD™ rapidly determines which clones have formed viable colonies without sample removal or disturbance. The Cell Metric CLD™ can automatically plot an unlimited number of data points for the growth curves and updates these curves every time a new reading is taken. The colony growth data can be used to identify just the clones that have formed colonies in 96-well plates, so that they can be consolidated into 24-well microplates. Excluding the non-viable clones saves on reagents, sample handling and downstream assay time.
The viable cell number, determined by Trypan Blue assay, is then correlated to a protein productivity assay such as an ELISA assay for protein amount and quality. Growth rates are plotted and protein productivity normalised to cell number to calculate specific protein productivity (Qp).
Where clones have previously been selected by a robotic clone picking approach, one potential problem is that the cells now need to adapt from semi-solid media back to liquid suspension culture. It has been observed that apparent ranking or productivity of clones at picking does not correlate well to their ranked performance and behaviour in liquid media.
Clone growth characteristics and protein productivity must be assessed not only during cell line development, but also repeatedly and periodically on banked master cell line clones because protein productivity declines as cells age.
The most promising clones (typically 12-24) are taken forward for process and media optimization while unsuitable clones are eliminated from further study.
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