Native forms of therapeutic monoclonal antibodies (mAbs) coexist with various acidic and basic charge variants throughout process development and into drug product formulation. During downstream purification, a product's charge variant composition is controlled, as necessary, primarily through peak fractionation and pooling of elution fractions using cation-exchange chromatography (CEX). This can be a cumbersome process with poor resolution and it may result in a significant reduction in product yield. In the present work, separation and enrichment of the native form of a mAb and of basic and acidic variants is achieved using self-displacement chromatography in a multi-column continuous chromatography set-up. Basic mAb variants are more strongly retained in CEX owing to their higher charge, and can displace the native and the acidic variants. Similarly, the native variant can displace the acidic variants if the amount loaded exceeds the total resin capacity. To this end, we utilized a three-column continuous system to consecutively displace acidic, native and basic charge variants of a therapeutic mAb in the order of increasing binding strength during product loading. Using our optimized operating parameters, we were able to enrich the native variant from 65% to 90% while loading above the capacity of the column, with a process yield of above 90%. This method and approach will help to control and reduce in particular the charged variant heterogeneity, and, in general, aid in the separation of charged proteins at preparative scale.
Keywords: Continuous chromatography; Dual gradient; Ion-exchange chromatography; Multi-column chromatography; Recycling; Self-displacement chromatography.
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