Role of Perfusion in Continuous Biomanufacturing

Perfusion cell culture is a continuous process used in biopharmaceutical manufacturing. During perfusion processes, cells are retained in a bioreactor with a constant exchange of growth medium. This process removes cell waste and spent medium while replacing nutrients and carbon sources with fresh medium. Perfusion allows high cell densities and viabilities over extended periods of time. Leading biomanufacturers integrate perfusion upstream with connected downstream bioprocesses enabling the fully end-to-end continuous manufacture of biopharmaceuticals.

Perfusion cell culture is a continuous process used in biopharmaceutical manufacturing. During perfusion processes, cells are retained in a bioreactor with a constant exchange of growth medium. This process removes cell waste and spent medium while replacing nutrients and carbon sources with fresh medium. Perfusion allows high cell densities and viabilities over extended periods of time. Leading biomanufacturers integrate perfusion upstream with connected downstream bioprocesses enabling the fully end-to-end continuous manufacture of biopharmaceuticals.

During a traditional fed batch culture, mammalian cells are grown within the production bioreactor for approximately 14 days. Bioreactors are filled with cell culture media at the beginning of the culture, inoculated and feeds added during the process. However, the collection of the biopharmaceutical product only occurs at the conclusion of the run.

Throughout the fed batch process, cell growth continues until it reaches a peak viability point, after which viability declines due to nutrient depletion and the accumulation of waste by-products. The dynamic conditions within a fed batch bioreactor can lead to fluctuations in the quality attributes of the product. Production engineers typically harvest the contents of the bioreactor at the end of the run using filters or a combination of centrifugation and filtration steps.

Biomanufacturers have the capability to maintain cell growth in perfusion processes for extended durations, ranging from weeks to months. Just - Evotec Biologics, for instance, typically operates perfusion bioreactors for approximately 15 to 25 days. The environment within the bioreactor remains notably stable over time due to the continuous addition of new media and replacement of spent media. This results in cells sustaining high density and viability for prolonged periods, leading to enhanced volumetric productivity. 

During a perfusion run, the biopharmaceutical product is continuously collected, allowing for seamless progression into downstream processing. Compared to fed batch operations, the product spends less time in the bioreactor during perfusion runs, reducing the risk of degradation. Particularly for labile products, the quality is often superior when produced via perfusion as they undergo minimal degradation within the bioreactor environment.

Perfusion technology is utilized in the production of diverse biological treatments like hormones, cytokines, and recombinant proteins. It is particularly beneficial for generating monoclonal antibodies (mAbs) in a continuous biomanufacturing setup. mAbs play a crucial role in treating conditions like cancer and autoimmune disorders. Just – Evotec Biologics also leverages perfusion cell culture techniques to manufacture bispecific antibodies and Fc-fusion proteins.

A perfusion process requires a high expressing cell line that have been proven to grow to high cell density and viability in perfusion culture. Cell lines used in perfusion must stably express biopharmaceutical product with the required quality attributes for the duration of the culture.

Perfusion cell cultures are fed with fresh media throughout their duration. The media is added at a pre-determined perfusion rate during production. Perfusion media are designed to promote cell growth and the right product quality while being fine-tuned for low cost biomanufacturing.

Biomanufacturers can use single-use or stainless-steel bioreactors for running perfusion processes. Perfusion bioreactors are often much smaller than fed batch bioreactors because of their high productivity. This makes perfusion steps very amenable to being run in single use bioreactors. The infrastructure needed to operate a single use bioreactor is not as extensive or capital intensive as that required for their stainless-steel equivalent. This allows facilities operating perfusion processes to have smaller footprints than those design for fed batch production. Just – Evotec Biologics uses single use bioreactors at the 500 L and 1000 L scales for manufacturing.

A critical part of a perfusion system for cells grown in suspension culture is a suitable cell retention device. Bioprocess engineers typically specify centrifuges, alternating tangential flow filtration devices or tangential flow filtration systems to retain cells within the bioreactor. These unit operations allow product to be harvested continuously and fed into downstream processing operations. Just – Evotec Biologics uses tangential flow filtration cell retention devices.

Automation is needed to control a perfusion system. Pumps are likely needed for feeding the perfusion bioreactor with media, allowing the operation of cell retention systems and for performing cell bleeds. Automation controls the flow through these pumps to maintain the bioreactor volume and deliver the correct perfusion rate. Just – Evotec Biologics uses deep industry experience in automation to control its perfusion bioreactors.

Perfusion offers a range of benefits compared to fed batch production for the biomanufacturing of biopharmaceuticals. These are:

1. Higher cell densities: Perfusion allows for continuous cell growth, leading to higher cell densities compared to batch or fed-batch processes. This results in increased productivity.
2. Stable product quality: The consistent environment in perfusion culture helps support consistent product quality over extended periods. This is crucial for biopharmaceuticals like monoclonal antibodies.
3. Reduced footprint: Perfusion systems can achieve the same production yield with smaller bioreactors, allowing patient demand to be met in smaller manufacturing facilities.
4. Longer production runs: Perfusion enables continuous operation, reducing downtime and improving overall facility throughput.
5. Flexibility: Output from perfusion processes can be ramped up without significant changes of scale, making them suitable for production from early clinical supply through to commercial manufacturing.
6. Improved process economics: Perfusion upstream processes reduce the manufacturing costs of biopharmaceuticals when integrated with a connected continuous downstream process.

Just – Evotec Biologics is expanding access to biotherapeutics with its continuous manufacturing platform that incorporates perfusion bioreactors.