In the first blog in our stem cell series, “New Strategies Key to the Clinical Manufacturing of Stem Cells for Therapeutic Use” three strategies were identified to improve clinical stem cell manufacturing. In part one of the series titled “Optimizing Media for Clinical Manufacturing of Stem Cells for Therapeutic Use,” we examined ways to optimize stem cell culture media for clinical manufacturing including strategies for removing animal-derived ingredients. In Part II of the stem cell series “Employing Innovative Platforms for Large Scale Stem Cell Culture,” we looked at ways to scale-up manufacturing of stem cells including innovative platforms that enable culture of large numbers of stem cells per batch. In Part III, we will explore downstream processing challenges and possible solutions.
In our previous blog we discussed ways to culture larger numbers of stem cells per batch. With successful increases in lot sizes, downstream processing then becomes the bottleneck. Optimization of this portion of the product manufacturing cycle is necessary as several of these potential therapeutic applications will require billions to trillions of stem cells per lot. To address these needs technologies are being adapted and developed to handle larger lot sizes downstream.
Downstream processing techniques are optimized and well defined for traditional biopharmaceutical manufacturing where the final product is secreted antibody or recombinant protein. Cell Therapy applications are much more challenging, as the final product is the cell itself. This means that extra care must be taken in all steps to ensure cell viability is maintained.
First, concentrating and washing of cells needs to be optimized. Traditionally cell concentration during cell harvesting has been performed using centrifugation tubes. However, existing technologies need to be adapted or new ones developed to meet the demands for large-scale manufacturing. One adaptation has been the use of tangential flow filtration systems to concentrate cells. Frequently used to concentrate proteins, tangential flow filtration relies on product being fed tangentially across the surface of a membrane; cells are captured while the solution is passed back to the tank. Some companies that manufacture these systems for Cell Therapy applications include Pall, Millipore and Spectrum Labs. Continuous centrifugation is another method for concentrating cells in Cell Therapy applications. It utilizes traditional centrifuge technology, but allows for much larger scale up. Some companies that manufacture continuous centrifuge systems for Cell Therapy are KBI Biopharma and New Brunswick. Most of these systems allow for cell washing and concentration in one machine and are scalable from tens of liters to one thousand liters. Another innovative product is the Ensura-Sep cell washing system, which permits increased flexibility by providing cell washing and concentration at point of care.
After cell concentration the final product needs to be packaged and stored for future therapeutic use. Many current Cell Therapy applications, including cord blood, are packaged and stored in bags. As volume increases in therapeutic applications, increased automation of this process will be necessary including taking advantage of existing finish/fill systems used in biopharmaceutical manufacturing. With adaptation cells could be stored in pharmaceutical grade vials and finish/fill systems could be adapted to process large volumes of cells.
Another challenge for Cell Therapy is large-scale cryopreservation and the maintenance of optimal storage conditions. Cryopreservation will need to be performed quickly and the rate of freezing will need to be carefully controlled across a large lot of product to ensure successful cryopreservation. Another topic that has been debated is whether DMSO, frequently used in stem cell freezing media to prevent cell death, is safe for use in cell therapies. The debate is centered on the issue that not all DMSO is removed from the cells and some ultimately ends up in the final product. The question is whether DMSO in the final product is safe and at what level. Please see our blog “DMSO Cryopreservation Comes With a Cost,” for more information.
Lastly, disposable options and automation can do a great deal to increase efficiency and consistency in this area. In particular, cells can vary greatly and conditions at all stages of the process need to be as consistent as possible. Disposable or single use components provide the attractive option of faster processing time between lots because there is much less cleaning and validation necessary. To the extent that downstream processing can be automated, would also be beneficial. Automation can aid in maintaining consistency, providing a closed system, reducing human error components, and streamlining the overall process.
These are just a few ideas of ways to improve downstream processing.