MilliporeSigma - Viral Safety - 14

Viral Safety

Viral Safety in Monoclonal Antibody Manufacturing
Compressing processes by connecting unit operations,
the second level, presents modest challenges regarding
viral safety. However, such strategies, he notes, "need
not be serious, provided one remains vigilant that virus
removal is not compromised."
The third level of process intensification-continuous
processing-is where issues raised by connecting unit
operations appear "in spades," according to Dr. Phillips.
"Continuous processing is a huge change, a revolutionary
development with profound implications for viral safety."
As with some revolutions, however, this one will be
slow in coming. Although many companies and suppliers are evaluating continuous processing, Dr. Phillips
cautions not to expect the coup to occur overnight.
"There are regulatory concerns and technical gaps in
the ability to implement continuous processing in the
near future," he explains. For example, current-generation
sensors to ensure reliable operation of continuous
processes are lacking, as are control strategies. Dr.
Phillips believes that as the technology improves and
regulations coalesce around continuous processing,
viral safety within that environment will catch up.
"But don't expect it for at least five to ten years."
A more modest implementation of continuous
processing exists within the confines of individual
unit operations. Perfusion cell culture and variants of
simulated moving bed chromatography are two examples. Another is inline low pH virus inactivation. The
discovery that low-pH incubation could be significantly
shorter than the usual one-hour hold, coupled with the
inconvenience of standard two-tank virus inactivation,
led Dr. Phillips' group to investigate continuous low-pH
treatment of process fluid as it emerged from a protein
A chromatography capture column, obviating the need
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| October 1, 2017

for an intermediate incubation/hold step.
When viewed against the backdrop of an entire process,
these individual steps less represent continuous
processing than optimized or streamlined batch
operations in which feedstock enters, is processed,
and then awaits the next step. Under ideal continuous
operation, process fluids feed directly and continuously
into and through operations, and purified product continuously flows out. Continuous or "next-generation"
bioprocessing promises huge advances in productivity,
but process developers must be aware of how those
advances could affect viral safety. The improvements
as one progresses along various levels of process
intensification also bear a potential cost.
Herb Lutz, global principal consultant at MilliporeSigma, described recent results where a tangential
flow filtration-based protein concentration step was
performed before flow-through anion-exchange chromatography polishing. "We reduced the volume of the
protein solution by a factor of four to make the chromatography column more efficient, but we were obliged
to test how this might affect viral clearance," said Lutz.
Using this highly concentrated feed, they demonstrated
consistent 5 logs clearance of MVM and XMuLV at high
product loadings, confirming that viral clearance was
maintained in the smaller footprint process.

the concentration of virus before and after the operation
are measured and results are reported as a log reduction. Lutz, however, does not believe this accurately
represents conditions of continuous processing:
"Standard virus-spiking strategies are inadequate when the
feed solution changes because a protein peak is coming
through or some other event is occurring," he maintains.
To better assess such operations, Lutz developed a
technique termed inline spiking, which enables monitoring of viral clearance under more representative
conditions, when the process feed changes due to
fluctuating concentrations of proteins and salts.
It turns out that in most cases (e.g., during cationexchange chromatography), virus retention is fairly
constant over a wide range of protein concentrations.
Nevertheless, the value of inline spiking is that for a
minor investment in time it provides a clear answer.
"Regulators like that," Lutz adds. n

Inline Spiking

"We're running processes in new ways," he says. "The data
doesn't yet exist to guide processors on the implications
of all aspects of how process changes impact viral clearance.
Conventional viral-clearance testing assumes that
purification steps behave uniformly throughout their
operation. Aliquots of feed are spiked with model virus,
subjected to normal filtration or chromatography, and

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Herb Lutz
Global Principal
Consultant,
MilliporeSigma

http://www.GENengnews.com

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