During monoclonal antibody (mAb) production, variability during cell culturing can compromise bioseparation efficiency and, therefore, therapeutic efficacy.

In a recent paper, Scottish researchers evaluated 44 polishing chromatography elution strategies in terms of yield and titer to reduce variability and maximize recovery yield and mAb titers. This appears to be one of only a few studies investigating the combination of mechanistic and hybrid models for integrated, downstream purification.

For this evaluation, Wil Jones, PhD candidate, and Dimitrios I. Gerogiorgis, PhD, deputy head, Research Institute for Materials and Processes, University of Edinburgh, combined a pH-dependent steric mass action model for polishing chromatography with a semi-empirical model. The goal was to achieve a 90% or greater target yield and a 100 g/L titer to enable industrial-scale formulations, while minimizing salt consumption and pressure drop.

Only nine of the 44 strategies achieved the target yield and titer, and only four achieved a targeted pH between 5.5 and 6.1. In these evaluations, the seven-stage ultrafiltration systems noticeably outperformed three-stage configurations.

Of the remaining 40 elutions, 19 achieve a minimum recovery yield of 90%. The purest elutions occurred at pH 6.1, because, as Jones and Gerogiorgis explain, “relative protein resin affinities change as pH increases.”

 When integrating the polishing chromatography columns to the ultrafilters, the scientists set the final concentration at 100 g/L. Nine of the 40 flowsheets achieved that target. (Of those, two used a step eluation and seven used a gradient elution.)

Production benefit  

For manufacturers, there is a distinct benefit to integrating ultrafilters with polishing chromatography columns that produce high concentration yields, they note.

Achieving high concentration yields is directly related to pressure drop in the ultrafilter systems. “Larger initial concentration allows…pressure drop to be increased without leading to system failure,” Jones and Gerogiorgis note. Basically, shorter polishing times prevent diluting the mAb in the columns and the ultrafilters.

They also found that step elutions use less salt than gradient elutions, “which could lead to significant savings,” they point out.

Whether biomanufacturers choose step or gradient elutions, “The key…is to ensure they produce a sharp peak and (that) the unit operates long enough to ensure the yield target is reached,” Jones and Gerogiorgis indicate.

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