Integrated system for temperature-controlled fast protein liquid chromatography. III. Continuous downstream processing of monoclonal antibodies

Abstract

Three different applications of travelling heating zone reactor (THZR) chromatography for the downstream processing of monoclonal antibodies (mAbs) are described. mAb containing feedstocks were applied to a fixed bed of the thermoresponsive rProtein A matrix, Byzen Pro™, contained in a bespoke column (held at 15 °C) fitted with a travelling heating (42 °C) device encircling a narrow section of the column. For the demonstration of continuous concentration, uninterrupted loading of 1.0 g/L mAb in a pH 8 binding buffer was synchronized with 5 repeated movements of the heating zone along the column's full length at a velocity of 0.1 mm/s. Elution of mAbs was induced solely by the travelling heating zone's action, each full movement generating a sharp concentrated elution peak accompanied by a small transient mAb concentration-dependent dip in conductivity. Quasi-steady-state operation occurred from the third elution onwards, delivering a mean mAb concentration of 4.9 g/L and process yield >93%. Quasi-continuous separation of the target mAb (1.41 g/L) from bovine serum albumin, BSA (1.0 g/L), was achieved by cyclically alternating the feeding of the mAb + BSA feedstock, with that of the binding buffer alone; supply of the latter was timed to coincide with movement of the heating zone. Accurate coordination of the heating zone's travel and switching from feed to buffer permitted quasi-steady-state collection (elutions 3-6) of sharp peaks of mAb in high purity (98.7%) and yield (88.7%) in 4.5-fold concentrated form, with BSA exiting in the flow through fractions between successive mAb elution peaks. Fully automated THZR-mediated quasi-continuous buffer exchange of 1.34 g/L mAb from a phosphate buffer pH 8 into a HEPES buffer pH 8 of slightly lower conductivity was performed over a 19 h period by carefully timed switching from one feed solution to the other and back again, whilst synchronising movement of the heating zone with feeding of the exchange buffer. Quasi-steady-state operation (elutions 2-9) resulted in an average eluted mAb yield of 94.5% and concentration of 4.8 g/L. Triggering movement of the heating zone slightly ahead of the switch from mAb feed to exchange buffer permitted the positioning of mAb elution peaks in 9 mL volume segments with the lowest recorded conductivity. Measurements of buffer exchange performance conducted with two 'protein-free' systems demonstrated that compared to tangential flow filtration in diafiltration mode, which represents the 'state-of-the-art' technology for buffer exchange, the THZR chromatography based approach affords a >60% saving in minimum volume of exchange buffer required to remove 99.9% of the original buffer. Combined far and near UV circular dichroism, intrinsic fluorescence and thermal melting experiments showed that, unlike conventional Protein A/G affinity chromatography, the conditions for THZR Protein A chromatography respect maintenance of a favourable structural profile for mAbs.

Keywords: Bioseparation; Buffer exchange; Continuous chromatography; Immunoglobulins; Protein A/G affinity; Thermoresponsive ligands.