Producers of consumer goods and food products often rely on platform processes. When suitable, platform bioprocesses make life easy for manufacturers of therapeutic proteins as well.
“Monoclonal antibodies are not difficult to adapt to platform processes,” says Andrew Bulpin, Ph.D., head of process solutions at MilliporeSigma. “IgG4 and IgG1 molecules conform nicely to platform systems. However cell culture media must be optimized for bispecifics, as well as other modified monoclonal antibody architecture as we tend to see more variation in performance in these molecules.”
Non-traditional recombinant proteins, however, are difficult to adapt to a platform process because results are inconsistent. For example, recombinant proteins targeting hemophilia, such as blood clotting Factor 8, do not work well in platform processes. “In those instances processes must be designed specifically to the clone and to the molecule,” Bulpin adds.
Space program
Early in 2017, contract manufacturing and development firm Fujifilm Diosynth Biotechnologies expanded its mAb-related services through the debut of its Saturn™ mAb Platform. Saturn is an offshoot of Fujifilm’s experience with its Apollo™ Mammalian Expression Platform, a robust manufacturing service providing high protein expression levels and manufacturability for a product’s entire lifecycle.
Saturn supports both late-stage manufacturing developed by customers, and early-stage cell-line discovery, and production work, for monoclonal antibodies. Although built around Fujifilm’s DG44 CHO cell line, the platform accommodates customers’ established cell lines as well.
Saturn’s development components include use of the ambr™ 250 bioreactor system, which enables rapid process development through design-of-experiment, and GE’s XDR bioreactors (10 L, 50 L, and 200 L), which are based on the same technology as the larger Xcellerex bioreactors, allowing smooth scale-up. The downstream platform incorporates GE’s ÄKTA Chromatography Systems using Unicorn 7 software and Pall TFF Systems with single-use flow paths among others.
Tying everything together are Saturn’s built-in analytics. Although fully compliant with the platform idea, the analytical method qualification is performed specifically for each molecule with a standardized approach using generic protocols and report templates.
“A good platform process is based on the application of process and analytical development experience,” says Greg Adams, senior director, global analytical strategy and development at Fujifilm Diosynth. “The end goal is a smooth GMP implementation. Another feature of a good platform is to have a simplified off-the-shelf supply chain and batch documentation. This not only reduces risks (material availability, etc.) but reduces initial investment as there is no need to purchase back-up materials. This also supports fast re-supply needs.”
Platform bioprocesses do not absolve developers of the obligation to match the production steps, operations, and equipment to the specific requirements of their molecule.
Platform bioprocesses do not absolve developers of the obligation to match the production steps, operations, and equipment to the specific requirements of their molecule. Typical tweaks will include depth filtration sizing, elution collection gating, binding capacity, load/elution optimization (pH/conductivity), and flux optimizations for ultrafiltration/diafiltration.
Difficult-to-express proteins aside, even monoclonal antibodies may present challenges. “Some mAbs have a propensity to self associate and can be difficult to platform,” says Adams. “Some mAbs bind to host cell proteins, some have clipping that occurs during cell culture expression, and galactosylated mAbs are also a challenge.”
Difficult proteins
As Bulpin notes, platform processes, both upstream and downstream, are best-suited to monoclonal antibodies. Biomanufacturers have the most experience with these molecules and their CHO expression systems.
By their very definition, difficult-to-express therapeutic proteins don’t lend themselves to traditional fed-batch processes and require case-by-case process development, says Emily Wozniak, Ph.D., marketing manager at Cell Culture Company (C3). “Difficult-to-express proteins are different. In our experience, perfusion bioreactors offer the closest you can get to a broadly applicable platform process for these diverse molecules, at least on the upstream side.”
A good platform process, Wozniak continues, should be broadly applicable to a category of products. “This becomes challenging with biologics, whose production entails a wide range of variability in design and other considerations that hamper the application of a standardized, broadly applicable process.”
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For example for high-expressing CHO cell lines churning out human IgGs at around three grams per liter one expects to run a fed-batch, stirred tank culture upstream, with protein A and additional chromatography and filtration steps for purification.
“The design of our perfusion bioreactor solves many of these challenges, and therefore can serve as a platform process for upstream production of challenging molecules or in challenging cell lines,” Wozniak says. “This carries the caveat that exists for the easily expressed proteins, namely that all bioprocesses are inherently unique and that every molecule will require process development.
Difficult-to-express proteins include non-antibody recombinant proteins, processes involving low-expression cell lines (typically less than 500 mg/L), proteins with properties (e.g. auto-inhibition), labile molecules, or proteins generated in sensitive cell lines.
The way to look at platform processes in biomanufacturing, Wozniak explains, is to consider the history of therapeutic biotech itself. Stirred tank reactors have been around forever, beginning with chemical synthesis and bacterial and then adapted to mammalian cell cultures. The manufacturing process for the first biologic, approved in the late 1980s, was in a stirred tank, which set a precedent of de-risking clinical manufacturing for other biologics.At the time protein analytics were rudimentary compared with today. To achieve consistency, manufacturers and regulators decided to adopt manufacturing practices that were as consistent as possible, even when process performance was sub-optimal.
Today protein analytics are such that demonstrating the identity and consistency of biologic drugs is relatively simple. “Add to that advances in built-in automation, in-line process monitoring, and process control and production quality is far easier to achieve,” Wozniak says. “Now the burden of proving product quality can be placed on the actual product itself, and there is less need for process sameness, or platforming. Bioprocessors now have the luxury to experiment with upstream production methods that might work better. This is good since even in the 1990s scientists knew that the traditional fed-batch processes in stirred tank bioreactors weren’t universally applicable. There are far better ways to manufacture proteins for certain cell lines.”
In other words, bioprocessors consider fed-batch/protein A, even for CHO expressing mAbs. That platform works very well for robust cell lines expressing high levels of naturally occurring proteins like human IgGs, which comprised all early biologics. Plus FDA is familiar with the platform, which is viewed as less risky. “But there's all the rest of the molecules that for one reason or another are a challenge to manufacturing in this platform process,” Wozniak says. C3 focuses on those molecules, for which it views its perfusion bioreactor as the closest platform for difficult-to-express proteins. “We've improved titers without compromising quality for low-expressing CHO lines—they’re not all producing at seven grams per liter—as well as sensitive proteins/cells, etc.”
Image: Even with platform processes sponsors must fine-tune process culture parameters. For this purpose, the ambr system from Sartorius has become the platform of choice. Image courtesy Fujifilm Diosynth.