In my last post (Might the sun be setting on process-scale chromatography for the purification of biopharmaceuticals?) I discussed how the trend of increasing bioreactor productivity at a near exponential rate has outstripped developments in packed-bed chromatography leading to bottlenecks in downstream processing.
Addressing the need for purification methods with higher throughputs will be the subject of presentations at the BioProcess International 2015 conference, however, seeking ways to eliminate chromatography steps is not necessarily the only solution to the problem of throughput-constraints in purification.
Flocculation and cell culture harvests
Ken Kang from Eli Lilly and Company is scheduled to present on “Monoclonal flocculation with smart polymers for efficient clarification of high titer cell cultures and improved removal of impurities”. In 2013, Kang and collaborators from both Eli Lilly and Company and EMD Millipore published an article in the journal ‘Biotechnology and Bioengineering, 2013;110:2928-2937’ describing an alternative harvest process for monoclonal antibodies (mAbs) using the stimulus responsive polymer, benzylated poly(allylamine) as a flocculent followed by depth filtration.
Highly productive bioreactor processes also typically generate both high cell densities and levels of impurities that put additional pressure on purification trains. Although a relatively low resolution purification technique, flocculation can be used to remove considerable amounts of cells, host cell proteins and DNA in a quickly and cheaply. This decreases the burden on chromatography columns allowing a reduction in the number of cycles that must be performed and increasing the usable lifetime of resins. An additional benefit is that flocculation process are relatively easy to fit into existing equipment configurations without having to perform a whole-scale redesign of manufacturing facilities.
Residual levels of impurities in Protein A chromatography eluates
The process described in the article was not only high yielding and improved the clearance of cell debris but also reduced aggregated product, HCP and Nucleic Acids. The burden on polishing chromatography steps was considerably reduced as the investigators were able to show that once the clarified cell culture filtrate was purified by Protein A chromatography the impurities in the eluate were so low they potentially met drug substance requirements. Crucially the team were able to demonstrate the clearance of residual polymer using fluorescence tagging.
Could flocculation improve your antibody harvest step?
The results from studies on flocculation such as this one seem both to present a path forward to reduce the impact of downstream bottlenecks while also being readily implementable. Flocculation processes seem relatively easy to develop, scale and operate without requiring sophisticated or expensive new equipment. What do you see as the benefits and challenges associated with this bioprocessing technique?
About the Author: Dr Nick Hutchinson has a Masters and Doctorate in Biochemical Engineering from University College London, UK where he focused on laboratory tools for rapid bioprocess development and characterization. He then worked at Lonza Biologics in an R&D function investigating novel methods for large-scale antibody purification before moving to an operational role scaling-up and transferring manufacturing processes between Lonza sites in the UK, Spain and USA. Nick now works in Market Development at Parker domnick hunter where his focus is in bringing Parker's strengths in Motion & Control to Bioprocessing. This will enable customers to improve the quality and deliverability of existing and future biopharmaceuticals.
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