Perfusion culture has been widely used in multiple clinical production projects due to its advantages of continuous addition of nutrients, timely removal of metabolic waste, and the ability to maintain high cell density and high cell viability over a long period of time, thereby achieving yield increasing effects. Cobetter's self-developed 0.2μm ATF hollow fiber product show excellent performance in N-1 perfusion culture, with CHO cell density reaching 60E6 cells/mL at D7 and maintaining high cell viability.

Enterprises hope to reduce costs and increase production capacity by applying new technologies without making significant changes to existing factory facilities. Perfusion cell culture utilizes cell retention devices and continuous medium exchange to achieve and maintain high cell density and activity over a longer period of time. The cell retention device retains cells in the bioreactor, while adding fresh culture medium and continuously removing target products, waste, and nutrient depleted culture medium, providing a strong culture environment for cell growth and metabolism. Due to its ability to quickly enhance upstream processes, N-1 perfusion technology is an efficient method for improving expression levels and shortening process time, and has been increasingly applied by biopharmaceutical companies.

This article will summarize the insights of N-1 perfusion based on existing application cases of N-1 perfusion technology, and introduce the product solutions that Cobetter can provide in perfusion cultivation process.

N-1 Perfusion and Advantages

In order to reduce the amplification of bioreactors, users usually use smaller bioreactors to prepare high-density seed train, which are directly inoculated into the last stage (i.e. N-stage) bioreactor for protein production or virus amplification. This method is called the high-density N-1 strategy.

N-1 perfusion is a form of seed train aimed at enhancing cell growth in the preceding step of the production bioreactor (N). This enhanced process can be achieved by connecting a cell retention device (such as an ATF device) to the N-1 bioreactor to obtain high cell density and activity, thereby seeding the production bioreactor with a higher initial cell density and shortening the operating time of the production bioreactor. This can significantly increase factory output without directly changing the core production process. Therefore, the N-1 strategy can achieve savings in seed cell culture time and cost, which is of great significance for the development of cell culture processes in biopharmaceutical companies.

Experimental Materials：

Hollow Fiber Filter (HFF): Cobetter 0.2μm
Bioreactor: WAVE 25 and self-produced 20L WAVE perfusion reaction bag
ATF2 perfusion component: C24 controller
Cell type: CHO cells
Perfusion system: Basal medium: dynamics Feed: feed C

Figure 1 Cell density in perfusion culture

Methods: CHO were seeded into the WAVE bioreactor at a density of 0.4E6 cells/mL. After the cell density reached 5E6 cells/mL, perfusion was initiated, and the perfusion ratio was adjusted according to cell growth for N-1 high-density seed train. On the 7th day of cultivation, the cell density reached 60E6 cells/mL, and the cell viability remained above 95% throughout the entire cultivation stage, indicating good cell growth status.

Figure 2 Cell viability in perfusion culture

Cobetter self-produced WAVE 25 perfusion reaction bag is equipped with dip tube and connected to ATF components. Feed/Basal medium is continuously pumped into a 10L culture system at a ratio of 5% to achieve high-density seed N-1 perfusion culture. During the logarithmic growth period, the seed density of this cultivation system can meet the production amplification of 1000L feed batch.

N-1 Perfusion Conclusion：

Compared with traditional feeding culture and N-1 seed enrichment, under the same culture medium and reactor optimization strategy, the increase in inoculation density in N-1 perfusion is the main factor for yield improvement, and the significant increase in expression level is mainly due to higher VCD and cell specific productivity. By perfusion culture, the growth period of cell index is prolonged, thereby achieving high-density cell culture. The high-density seeds cultivated by N-1 perfusion can be inoculated into the production bioreactor at a ratio of 1:100, greatly reducing the number of seed tanks, saving seed chain time, and ultimately achieving the goal of cost reduction.

Cobetter N-1 Perfusion Solutions

Hollow fiber filters, with their unique open flow path structure and low shear force, can better meet the concentration and filtration needs of shear sensitive biomolecules and complex biological samples at different scales. At present, it has been widely used in various fields such as antibodies, recombinant proteins, viral vaccines, nucleic acids, biochemical drugs, and dairy beverages.

Cobetter's self-developed hollow fiber modules are made by encapsulating hollow fibers in a polypropylene shell. The casing has end fittings, each of which includes two ports: an inlet feeding port, a reflux port, and two permeate ports. Ports can use different types and sizes of adapters and connectors. The length of the hollow fiber is consistent with the shell, flowing from the injection port to the reflux port. When in use, pump the liquid from the feeding port under the pressure. Most of the liquid flows through the hollow fibers and exits through the reflux port. Some of the liquid material passes through the hollow fiber wall, enters the shell, and then flows out from the permeate port.

Cobetter Hollow Fiber Modules Performance:

• Low bioburden, non-toxic to cell culture
• 100% integrity testing
• Meet flow path biocompatibility standards and has no animal derived characteristics
• Promote cell growth and increase cell density in perfusion mode