Methods for MSC Concentration and Buffer Exchange

In the biomanufacturing of mesenchymal stem/stromal cells (MSCs), specific processes such as cell concentration and buffer exchange are critical. Read on to learn more.

Several stages of the MSC biomanufacturing process use cell concentration and buffer exchange techniques. These stages include the initial thawing of cells, during passages, following final harvest, and prior to the final therapeutic formulation. Such procedures ensure the removal of undesired components, such as dimethyl sulfoxide (DMSO), and the replacement of growth media with biologically inert buffers. All of which are crucial for the safety and efficacy of the final therapeutic products.

The two techniques play different roles. Researchers usually perform them sequentially, starting with concentration and followed by resuspension in a new buffer if required.

• Cell concentration reduces the volume of cell suspension without altering the liquid's composition.
• Buffer exchange replaces the liquid with a fresh liquid matrix, which may have the same or a different composition.

When choosing a method for these processes, consider factors such as volume ranges, cell viability, processing times, and whether the system remains closed during processing. This ensures the maintenance of a high number of viable and functionally active cells, which is paramount for successful clinical outcomes. Here are three methods to consider:

Centrifugation: Traditional Yet Limited

Centrifugation is a well-established method used in the concentration and buffer exchange of MSCs. Typically, this involves using conical tubes in a centrifuge to separate cells based on density differences from the liquid matrix. Researchers often use products like Falcon^® conical centrifuge tubes for these procedures.

Despite its simplicity and effectiveness, centrifugation has its drawbacks. It is generally limited to smaller volumes (from 15 mL to 500 mL), involves open system processing, and is highly reliant on the operator's skill, which can lead to variability between runs. Developers have created automated centrifugation technologies to address some of these limitations, offering more standardized procedures and enabling closed system processing.

Filtration-Based Methods: Advancing Beyond Centrifugation

Filtration methods, such as tangential flow filtration (TFF) and alternating tangential flow (ATF) represent advancements over traditional centrifugation. These methods use mechanical barriers (filters) to separate cells, which are larger than the filter pores, from the smaller components of the liquid matrix.

While these methods enhance process automation and can handle larger batch sizes in a closed system, they are not without their challenges. Filter fouling and limited options for pore size selection can restrict the efficiency of these methods, making them less suitable in scenarios where optimal cell size selection is crucial.

Elutriation-Based Methods: Precision in Cell Selection

Elutriation techniques blend centrifugation with directed fluid flow within a conical centrifugation cup, enabling fine-tuned cell selection.

Although these methods automate processing and support closed systems, the size of the centrifugation cup inherently limits their throughput. Additionally, retaining cells in the packed bed for extended periods makes it more challenging to maintain a single-cell suspension suitable for downstream applications.

The decision on which method to use for MSC concentration and buffer exchange should be informed by a balance of performance and cost considerations. Factors like cell recovery, processing time, and labor requirements play significant roles. Moreover, the system's ability to handle variations in cell size and adhesiveness—factors that can vary widely depending on the tissue source, donor, and cell batch—should also be considered.

For instance, while automation in filtration and elutriation methods offers significant advantages in terms of labor and reproducibility, the physical limitations of these technologies, such as filter fouling and throughput capacity, must be evaluated against the specific requirements of the MSC processing task at hand.

Effective MSC concentration and buffer exchange are crucial for the production of safe and effective cell therapies. Researchers should choose their method based on a thorough understanding of the processing requirements and the specific characteristics of the MSCs being handled. By carefully selecting the appropriate technology and considering all related factors, researchers can significantly impact the success of MSC-based therapies.