Scale-Up of Twin-Column Periodic Counter-Current Chromatography for MAb Purification

Periodic countercurrent (PCC) processes increasingly are being evaluated as alternatives to single-column batch capture processes. Some of the advantages of PCC processes over single-column processes include shortening of processing time and/or reduction of required resin volume through increased productivity; reduction in resin costs through improved resin capacity use; and reduction in buffer consumption through increased column loading. Those advantages, however, come with increased equipment complexity and hardware costs. PCC processes and systems with two to up 16 columns of the same type have been proposed. As the number of columns increases, a process becomes more complex, potentially adding pumps, detectors, valves, and plumbing. The PCC process investigated in this study was a CaptureSMB process: a PCC process using two columns and modulated feed flow rates. All PCC processes are based on the concept of loading the first affinity column beyond its dynamic breakthrough capacity and capturing what breaks through in a second column of the same type. So the first column can be loaded to values of 50−80% breakthrough, whereas in batch chromatography, loading is typically performed to values below 1% breakthrough to prevent product loss (1). Based on the adsorption kinetics and mass-transfer properties of commercially available protein A resins, interconnecting more than two columns in the load zone provided little improvement in performance (2, 3). Baur et al. compared the performance of CaptureSMB, threeand four-column PCC processes based on numerical optimization (4). Results showed that a high capacity use (>95%) was achieved across all formats, which is expected because all formats adopt the above-mentioned loading of two columns in series. The authors showed that among the three formats tested, CaptureSMB offers productivity advantages, especially with low and high expression titers. That is because the interconnected loading phase of that process can be adjusted in duration independently of other process steps as titer increases or decreases. Figure 1 outlines the principle of the CaptureSMB process schematically based on one process cycle. In the first step, the two affinity columns are interconnected. The first column is loaded beyond its dynamic breakthrough capacity, followed by a buffer wash to transfer unbound product from the first column to the second column. Product Focus: Antibodies