In the biopharmaceutical industry there is an ever-present drive to increase product yield and reduce cost. The industry is driven in this direction, not only by the drive to improve manufacturing techniques, but also by pressure from the government, physicians, and patients to reduce the overall cost of medications. However these cost savings must be achieved without compromising high safety standards.Since the inception of biopharmaceutical manufacturing in the 1980’s there have been continual improvements to the process. These improvements have culminated in the most common approach to biopharmaceutical manufacturing, fed batch suspension culture, most commonly expressed in CHO cells. While improvements have continued in areas including advancements in cloning, media formulation, removal of animal components, and downstream purification resins and columns, there has been little change to the actual fed batch paradigm. One technology that could perhaps make a big change in how biopharmaceuticals are manufactured is the use of perfusion bioreactors. Perfusion technology has improved extensively since its creation and its application to large-scale manufacturing and other applications in the production of biologics deserves a second, closer look.
How Perfusion Bioreactors Work
Traditional fed-batch bioreactor systems consist of tanks that are usually between 10,000-25,000 liters. Cells are cultured in batches that typically run between 7-21 days by which time media nutrients have been consumed and toxic waste has begun to accumulate. During the run, cells secrete the protein of interest into the media and at the end of the run the protein is separated from cell mass as a batch. Typical product yields are in the range of 1 to 4 grams per liter depending on the clone and antibody. While regular improvements have moved product yield from under 1 gram per liter to where they are now, it has not improved other issues in fed batch manufacturing including large manufacturing footprints and challenges with scalability.
In contrast, perfusion bioreactors culture cells over much longer periods, even months, by continuously feeding the cells with fresh media and removing spent media while keeping cells in culture. In perfusion there are different ways to keep the cells in culture while removing spent media. One way is to keep the cells in the bioreactor by using capillary fibers or membranes, which the cells bind to. Another does not bind the cells, but rather relies on filtration systems that keep the cells in the bioreactor while allowing the media to be removed. Another method is the use of a centrifuge to separate cells and return them to the bioreactor.
Examples of cell separation methods:
- GE Healthcare’s Hollow Fiber Microfiltration Cartridges – “In this system, the retentate consists of the cells, which flow past the membrane and are sent back to the bioreactor. The spent medium is the permeate that passes through the membrane.”
- ATMI’s iCELLis Single Use Fixed Bed – In this system, cells are bound to custom microcarriers, which allows cells to stay in place while media flows around them.
- Centrifuge method – In this system, a centrifuge is used to separate cells from culture media and then cells are returned to the bioreactor.
Advantages of Perfusion
Product Quality and Stability
By continuously removing spent media and replacing it with new media, nutrient levels are maintained for optimal growing conditions and cell waste product is removed to avoid toxicity. In addition, the product is regularly removed before being exposed to excessive waste that causes protein degradation. Product is also harvested and purified much more quickly, which is particularly helpful when producing a product that is unstable.
Scalability
With fed batch culture, demand quickly outpaces pilot scale facilities and more bioreactors need to be added to increase production. With the addition of additional bioreactors comes a decision, either to outsource to a contract manufacturer or build out a larger dedicated manufacturing space. Once the facility is built, scale flexibility is difficult. It takes money to operate the facility even if no drugs are being manufactured there. If for some reason demand goes down, companies can find themselves with a lot of costly extra capacity.
Perfusion bioreactors offer several advantages over traditional fed-batch bioreactors when addressing problems of scalability and increasing demand. Maybe the most critical advantage is that perfusion bioreactors are smaller in size and can produce the same product yield in less space. Typically perfusion bioreactors operate at 10-30x concentrations compared to fed-batch bioreactors. For example, it has been shown that a 50-liter perfusion bioreactor can produce the same yield as a 1,000-liter fed-batch bioreactor. Therefore, the use of perfusion should enable the replacement of typical 10,000 L bioreactors with 1,000L bioreactors without negatively impacting the yearly yield of manufactured product.
This size advantage is important because it means that facilities don’t need a significant increase in space to increase production. Similarly, perfusion bioreactors require less on utilities cost and they are less labor intensive to operate. Thus requiring significantly less capital investment on the front end and less on operating costs to manufacture the same yield as fed-batch bioreactors.
Cost Savings
Some proponents have argued that considerable cost savings is a further benefit of perfusion bioreactor manufacturing and this topic was covered in a Cell Culture Dish blog titled “Are Perfusion Cell Culture Systems the Future for Cell Culture Based Biomanufacturing.” The blog summarizes a talk given by John Bonham-Carter on the cost savings found in the use of Refine Technology’s ATF System.
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