"People argue that the current template [for this stage] is not broken, so why fix it?" asks Fred Mann, program manager for
Downstream Process Solutions at Millipore. "But you can refine it, improve productivity, and make the process more robust,"
he says. As a result, Millipore has restructured its depth filters to incorporate a medium specifically designed for high-titer
feedstock filtration, which, he says, will allow customers to run more liters of feedstock through the filters. In addition,
the filters are self-contained and installed into hardware with no product contact rather than in stainless-steel housings
that require hoists and cranes for assembly. The filtration system, which Millipore markets under the name MilliStak? Pod,
reduces the need for cleaning and cleaning validation of the filtration assembly between runs, is safer for operators, and
reduces labor costs, says Mann.
Other polishing steps include rounds—typically two—of ion-exchange chromatography. The material is put through a cation exchange
column to remove positively-charged host cell proteins and high-molecular-weight impurities such as protein aggregates. Following
that is an anion-exchange step, where negatively charged contaminants, including retroviruses, parvoviruses, host-cell protein,
and residual DNA, are removed. In the final steps, the product is run through filters and irradiation to remove any remaining
virus particles. After that, the now-pure mAb product is put into the formulation buffer.
Gottschalk is convinced that the ion-exchange steps present the greatest opportunity for improving the downstream paradigm.
He notes that when run in "flow-through," it becomes possible to replace a 100-L column with a (disposable) 1-L anion-exchange
membrane, thus reducing the requirement for space, among other things. As for cost? "In the worst case, the costs are equivalent
for membranes. Since so much cost is in fixed assets, virtually all processes benefit significantly from disposable strategies
in polishing," he says.
Overall, Gottschalk predicts that cost and efficiency considerations will force a whole new process to emerge for mAb purification.
"The paradigm will shift," he says. "And whatever it will be, I predict we'll see it within the next 5 to 10 years."
1. F. Detmers, P. Hermans, and M. Ten Hafft, "Affinity Chromatography Based upon Unique Single Chain Antibodies," LCGC The Peak, Sept. 2007.
2. G. Jagschies, "Where Is Biopharmaceutical Manufacturing Heading?," BioPharm Inter., 21 (10), 72–88 (2008).
3. L. Giovannoni, M. Ventani, and U. Gottschalk, "Antibody Purification Using Membrane Adsorbers," BioPharm Inter., 21 (12), 48–52 (2008).
4. U. Gottschalk, Ed., Process Scale Purification of Antibodies (John Wiley & Sons, 2009).
5. U. Gottschalk, "Downstream Processing of Monoclonal Antibodies: From High Dilution to High Purity," BioPharm Inter., 19 (6), (2005).
6. M. Rios, "Eluting Possibilities with Mixed-Mode Chromatography," Pharm. Technol.
31 (5) 40–48 (2007).