DISCUSSION
Figure 6: Sartobind STIC was tested to replace two unit operations in Bay-A002 purification process. The step yield is 96%.
The host cell protein (HCP) in STIC FT is 0.1 µg/dose, a 6-fold reduction from STIC load and comparable to the HCP level in
current process. The DNA level in STIC FT is below the limit of detection.
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In this study, proof-of-concept for using Sartobind STIC as a platform-polishing unit operation was achieved. When operated
in flow-through mode, Sartobind STIC is capable of removing HCP and DNA from high-salt feed streams with good product recovery.
A new purification process incorporating Sartobind STIC has fewer unit operations than the current platform process, but produces
drug substance with similar yield and comparable quality attributes. Sartobind STIC allows a further streamlined, future manufacturing
platform for complex recombinant proteins. This new platform will have only three chromatography unit operations: a reusable
Q MA capturing step, an affinity column providing the majority of purification, and a single-use Sartobind STIC polishing
step. This one-column-two-MA platform process is well suited for purifying low titer, unstable, complex proteins, which are
an important part of Bayer's biologics pipeline. With fewer unit operations and a single-use polishing step, the new platform
process is expected to reduce process time, increase productivity, and reduce the cost of goods.
Q MA in flow-through mode also provides viral clearance in mAb processes (19). The conductivity for the process, however,
has to be low (3–4 mS/cm) to prevent viral particles from breaking through the membrane. Low conductivity is often feasible
with mAbs because many mAbs have high pI and will not bind to an anion-exchanger, even at low conductivity. XMuLV and PPV
clearance by Sartobind STIC was tested under the process conditions described in this paper. No significant clearance was
observed at 30–39 mS/cm at 5 °C. Because of the strong binding of the products to Sartobind STIC, the conductivity cannot
be lowered further to achieve viral clearance without severely affecting product yield. The lack of viral clearance, however,
does not disqualify Sartobind STIC as a platform polishing step. For example, no viral clearance claim was made on any of
the polishing steps in the Bay-A001 process; hence, replacing those polishing steps with Sartobind STIC as shown in Figure 1 has no effect on the viral clearance claims of the process. With proteins that bind less strongly to anion-exchangers, such
as mAbs, Sartobind STIC could provide significant viral clearance at conductivity settings higher than what would be required
for a Q MA step. This could be a significant advantage that may eliminate the need for a dilution step.
The authors will continue to evaluate Sartobind STIC for processing new protein therapeutics, including mAbs, in Bayer's pipeline
and will also seek opportunities to test the new platform process at the pilot scale to demonstrate its scalability. It could
also be beneficial to evaluate other salt tolerant anion exchange MAs, such as ChromaSorb from EMD Millipore, for the same
application. These new-generation membrane adsorbers show how new ligand chemistry and new matrix structure can lead to improved
separation performance, which is not achievable with older generation chromatography media. This type of technological innovation
allows continuous improvement of platform manufacturing processes, as demonstrated in this study.
ACKNOWLEDGEMENTS
The authors thank the Bayer Berkeley GBD Analytical Development group for performing all the assays.
Min Lin*, PhD, is a staff development scientist, Ashley Hesslein, PhD, is a senior staff development scientist, and Jens H. Vogel, PhD, is director of isolation and purification, all at Global Biological Development, Bayer HealthCare, Berkeley, CA; Nathalie Frau, PhD, is a senior scientist, R&D Process Technologies, at Sartorius Stedim North America, Bohemia, NY; and Rene Faber is vice-president, R&D Process Technologies, at Sartorius Stedim Biotech GmbH, Goettingen, Germany.
*To whom correspondence should be addressed, min.lin@bayer.com
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