Sartobind STIC (salt-tolerant interaction chromatography, Sartorius Stedim Biotech, Goettingen, Germany), a salt-tolerant
anion-exchange membrane adsorber, has demonstrated proof-of-concept in removing residual host-cell impurities from high-salt,
packed-bed affinity chromatography eluate. Although the new platform process using Sartobind STIC has fewer unit operations,
it produces drug substance with comparable quality attributes to current processes, thus significantly improving productivity
and reducing cost of goods. The study presented herein focuses on implementing a novel membrane adsorber for optimized polishing.
Packed-bed chromatography is the main workhorse for the downstream processing of therapeutic proteins and monoclonal antibodies
(mAbs). Packed-bed columns provide good binding capacity and scalability, combined with excellent resolution. The mass transfer
process in packed-bed chromatography comprises several steps, including convection, pore diffusion, and film diffusion. The
rate-limiting step of this process is pore diffusion (i.e., the slow diffusion of solutes into the dead-ended pores inside
the chromatography media where the majority of the binding sites are located). As a result, residence time is an important
parameter for column chromatography and often becomes the limiting factor of how fast the process can be run. High back pressure
is another concern when operating packed-bed columns at a high flow rate. Membrane-adsorber (MA) chromatography technology
was developed to overcome this mass transfer limitation (1). By coupling functional groups onto a filter-like porous matrix,
diffusion-based mass transfer is eliminated because the filter pores are flow-through pores and allow solutes to be transported
to the binding sites via convection. With MA chromatography, only film diffusion may limit mass transfer rate and the binding
capacity is generally independent of the load flow rate over a wide range (2,3). Importantly, MAs can be manufactured with
extremely shallow matrix beds (e.g., bed-heights in the mm range) that have very large cross-sectional area-to-volume ratio.
Thus, MAs can be operated at much shorter residence time compared with packed-bed columns (e.g., seconds vs. minutes), thereby
reducing the process time and increasing throughput at a large scale (4).