How to improve the viability of your cell product

When we first developed the anti-viral T-cells product using the old method, the process to generate these cells took 8-12 weeks of cell culture to complete. I remember rare occasions when the viability of the final product did not meet the acceptance criteria, and we had to reject the product and start over.

Safe, pure, and viable are the 3 required criteria of cell & gene therapy products to be approved for clinical use. I’ll focus in this post on the viability, and on the practices that improve it, or at least reduce the negative impact on viability.

Viability read out is an indication of the health of the cell and gene therapy product; the percentage of the healthy cells in the product. There are several ways to measure the viability where the definition of “viable” varies from one method to the other. Each cell processing facility should define both the method they use to measure the viability, and define the acceptance criteria of viability for each product type they process.

It is critical to measure the initial product viability at the beginning of processing to set a baseline. However, improving or even maintaining a good viability throughout the processing is a challenge.

Once the cells leave the human body and enter the collection bag, cells face a new environment with drastic change in physiological conditions. This change of environment stresses the cells, if not alleviated can lead to cells apoptosis. To minimize this impact, we need to pay attention to several aspects. I will list the common ones and briefly discuss each of them.

• Age: The product age is the time (usually in hours) the cells spent since being collected. Generally, freshly collected products demonstrate better yield and viability compared to old products. Besides, fresh an old varies based on the product type. For instance, compared to apheresis collection, bone marrow collection contains high amount of plasma which acts as nutrient to the cells and prolong their freshness and their life span exvivo. Regardless, try to process your products as soon as possible to maintain the highest viability.
• Storage: Occasionally, product processing is delayed. For example, if the product was received after hours, or if the facility was at maximum processing capacity. Is such a case, the product is stored until processing is initiated. While controlled room temperature is suitable for short term storage of some products, overnight storage should be done in a controlled refrigerator.

• Concentration: The cell concentration in bone marrow collection is usually in the average range and is suitable for processing or storage. However, apheresis collections are almost always of high cell concentration. Each cell processing facility should have a procedure that defines the suitable cell concentration range for both processing and storage. The same procedure would also define how to adjust the cell concentration. For example, autologous plasma (if available) should be used to dilute the product, if not, an approved nutrient solution is used.
• Parameters: There are indicators that cellular characteristics (phenotype or density) of collected products can change over time. Therefore, processing that relies on such characteristics should account for this potential change. Ideally, processing of an old product should utilize a separate set of optimized processing parameters for the best outcomes.
• Physiology: For processing that involve cell culture, it is critical to reduce the time the cells are outside the incubator. Studies indicate better outcomes with products that were kept in the incubator conditions during processing and analysis. While most processing facilities are not equipped to do this, they still can reduce the time of processing and analysis as much as possible. A general way to do this is to do a good preparation and be ready for processing or analysis before taking the product out of the incubator.

Although cellular products vary biologically, they still have common basic requirements that when addressed can improve the overall yield. Product viability is the outcome of the listed factors, when you employ these and other factors you improve the chances of meeting the viability acceptance criteria.

Let us know if we missed anything, or if you would like a specific subject to be discussed, write to us. 

About the author

Naseem Almezel, earned his MSc degree in Cellular Therapies in 2010, since then his career focus is to support Bone Marrow Transplant and Oncology programs. Naseem likes to work in the lab doing translational research, or in the cleanroom doing GMP production. When he is not working, Naseem likes to read and to spend time outdoors. Find more about Naseem here