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.

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