Ten Years of Downstream Processing

About halfway through our first decade in publication, we became well acquainted with a new buzzword phrase in the biopharmaceutical industry: downstream bottleneck (1). This followed on the heels of a manufacturing capacity crunch that had been forecast shortly before BPI made its debut. Thanks to herculean efforts by upstream process and cell line engineers, that crunch didn’t pan out. In its place, however, high-titer production moved the pressure downstream. Now separation and purification engineers were tasked with handling concentrated feed streams, hard-to-purify proteins, and new contaminant profiles as culture media transitioned from serum-based to chemically defined ingredients.

Meanwhile, a few high-profile incidents of adverse events in patients were focusing regulatory, public, and industry attention on the subject of viral safety. BPI acknowledged its importance in a dedicated supplement late in 2005. Editorial advisor Hazel Aranha urged a risk-based approach (2), following an FDA quality systems initiative that has gained momentum throughout the decade.

That regulatory perspective also affects how recovery and purification unit operations are designed and conducted. Process modeling software is becoming increasingly sophisticated, so engineers can play in a virtual space before working with real (often expensive) chromatography skids and other hardware. Using new and improved analytical methods and scalable equipment, a downstream group can establish a “design space” for a given process. Automation is beginning to make inroads. And process analytical technology (PAT) is enabling companies to better monitor and control what’s going on.

Anything But Chromatography? In September 2008, Uwe Gottschalk of Sartorius Stedim Biotech described the capture step (column chromatography, in most cases) as “the most serious bottleneck” in downstream processing (3). Vendors of resins and columns are pressed for higher capacities and throughput without sacrificing selectivity. David Kahn of Human Genome Sciences wrote for us in 2006, “This challenge also provides additional impetus for process scientists to further consider new and alternative technologies that can be adapted from related processing industries” (4). Thus arose the “anything but chromatography” (ABC) idea (1).

For antibodies, notoriously expensive protein A affinity media traditionally perform the capturefunction. By 2008, people were beginning to wonder whether it might be possible to find a less expensive alternative. But Judy Glynn of Pfizer reined us in on that question (3): “I believe we need to be creative in our use of protein A resin. Because of its fantastic selectivity, it is not on the way out, but we need to increase its capacity and lifetime and thus decrease our cost of goods. In true platform processes, it is almost unbeatable for quickly getting products through proof of concept.”

Even so, ABC was gaining steam — especially among academics who are under less regulatory scrutiny than the industry is. They continue to push the envelope, as we count on them to do, in protein separations. The best technologies will utimately get picked up by vendors and implemented by biopharmaceutical companies. Currently the most promise seems to be in certain types of precipitation (particularly involving polyethylene glycol, PEG), crystallization, and ever-improving filtration methods. Centrifugation may be one technology that’s on the way out — at least for harvest, clarification, and volume reduction — due to cost and scalability issues, as well as a lack of disposability. But the story is far from over.

Disposables: If you’re working downstream these days, you need all the help you can get. And vendors have recognized and responded to that need over the past 10 years. Bioprocessors first became familiar with single-use technology (SUT) in the form of disposable filter cartridges well before the turn of the century. Since then, SUT has expanded in the downstream area to include all kinds of filter membranes, fluid management, and even chromatography in the form of monoliths (5, 6).

In Februry 2007, we asked John Liddell of Avecia whether disposables would revolutionize the industry. “To an extent,” he told us, “that revolution is already here…At Avecia, we make extensive use of disposables (e.g., buffer bags and filters) across all scales of operation” (7). Indeed, about a year later, Joe Zhou at Amgen asserted, “One solution to overcoming the bottleneck of downstream process for future 10-g/L cell culture titers is to make full use of disposable systems” (3). Certainly SUT has helped to lower costs, as predicted by David Kahn in October 2006 (4) long before the current economic hardships made that a real imperative.

Platforms and Purifiability: We hear a lot lately about “integrating upstream and downstream” and “optimizing products for purifiability” (8) — that is, including downstream considerations when we make upstream choices. This kind of talk may give the false impression that the lines are blurring between upstream and downstream processing. But what it really points to is the complete disintegration of that old “silo mentality,” wherein a production group would do its thing and then throw the results “over the wall” to the recovery and purification folks.

It’s true that you’re all talking to one another more now than ever before — and that companies are beginning to see the benefits, as always, of more communication. However, the work you do is still fundamentally different, evidenced most clearly in manufacturing plant design: Upstream and downstream will always be separate physical areas with their own concerns and environmental controls. One group molds and nurtures biological entities to coax them into producing harvestable material — the ultimate science-fiction extension of farming. The other group takes that material and cleans it up, refining it into a high-quality, safe, and efficacious product. Upstream’s output is downstream’s raw material — but like a good vendor, the production group can do its best to make sure that raw material starts out in as “user-friendly” a form as possible.

Over the past decade, antibody manufacturers have come to rely on platform purification — a “boilerplate” downstream process beginning with protein A and usually involving some other chromatography as well as filtration unit operations in predictable sequence. Later this year, I’ll be exploring the idea of platforms for other proteins. Is it possible? And if so, how? What will such processes look like?

In 2008 (3), Tim Hermman of Bayer HealthCare opened the door: “An ideal purification platform should be robust in terms of its applicabiltiy to the whole pipeline of upcoming drug candidates. Without requiring more resources than about one full-time employee and a timeline of several days to a few weeks, it should be possible to adjust the platform to the current drug candidate while delivering acceptable to good yields with no cutbacks in purity and quality of the product. For different types of proteins, a purification platform would be a predefined ‘catalog’ of process development steps on the experimental side as well as on the data analysis and prediction/simulation side.”

I look forward to hearing your thoughts this summer when I delve into the subject in more detail — and I hope you enjoy the results in my special report this fall.

About the Author

Author Details
Cheryl Scott is cofounder and has been senior technical editor of BioProcess International since the first issue.

REFERENCES

1.) Rosin, L. 2008. Anything But Chromatography?. BioProcess Int. 6:74.

2.) Aranha, H. 2005. Virological Safety of Biopharmaceuticals: A Risk-Based Approach. BioProcess Int. 3:S17-S20.

3.) BPI Staff, 2008. Recovery and Purification. BioProcess Int. 6:S36-S43.

4.) Kahn, D. 2006. Overcoming the Downstream Bottleneck: Sharing Experience. BioProcess Int. 4:S34.

5.) Gagnon, P. 2008. The Emerging Generation of Chromatography Tools for Virus Purification. BioProcess Int. 6:S24-S30.

6.) Gagnon, P. 2010. Monoliths Open the Door to Key Growth Sectors. BioProcess Int. 8:20-23.

7.) Scott, C. 2007. Recovery and Purification. BioProcess Int. 5:S24-S29.

8.) Chapman, P, and M. Krishnan. 2011. Shifting the Bioprocess Paradigm. BioProcess Int. 9:10-13.