Potency Assay Development Challenges in Cell and Gene Therapy

Demonstrating the biological activity of a cell or gene therapy is one of the most complex analytical challenges facing therapy developers. Unlike conventional drugs, these products often have complex mechanisms of action involving multiple biological pathways. This makes potency assay development essential for demonstrating product quality, consistency, and functional activity throughout clinical and commercial manufacturing.

A robust potency strategy also needs to work alongside broader analytical controls and manufacturing processes. For many developers, working with an experienced cell and gene therapy CDMO can provide access to specialized analytical capabilities, while endotoxin testing services and other quality tests support a comprehensive product release strategy.

What Is Potency Assay Development?

Potency assay development involves creating an analytical method that measures the biological activity of a therapeutic product.

For cell therapies, this may involve evaluating:

• Cytotoxic activity
• Cytokine secretion
• Cell proliferation
• Immunomodulatory activity
• Target-cell killing
• Differentiation
• Receptor activation
• Other product-specific biological functions

The selected assay should have a clear scientific relationship with the therapy's mechanism of action (MoA).

Why Potency Assays Are Challenging for Cell Therapies

Complex Mechanisms of Action

Many cell therapies do not rely on a single biological function. For example, therapeutic activity may involve cell activation, target recognition, cytokine signaling, and subsequent immune responses.

A single analytical endpoint may therefore not fully represent product potency.

Biological Variability

Living cells naturally vary between donors, manufacturing batches, passages, and processing conditions. This variability can make it difficult to establish a consistent potency measurement.

Developers must distinguish genuine changes in product activity from normal biological variation.

Assay Reproducibility

A potency assay needs to generate consistent results across different analysts, instruments, laboratories, and manufacturing campaigns.

Poor reproducibility can create uncertainty during batch release and complicate regulatory review.

Reference Standards

Establishing appropriate reference materials can be particularly challenging for cell therapies because biological products may not have a stable, universally applicable standard.

Reference standards should be appropriately characterized and monitored throughout the product lifecycle.

Choosing the Right Potency Assay

The first step is to identify the biological activity that most closely reflects the product's intended therapeutic function.

Potential approaches include:

The most appropriate method depends on the product's mechanism of action, manufacturing process, and intended clinical application.

Potency Assay Development and Analytical Testing

Potency should not be considered independently from the broader analytical control strategy.

Comprehensive cell and gene therapy CDMO support may include:

• Potency assay development
• Identity testing
• Purity testing
• Viability assessment
• Sterility testing
• Mycoplasma testing
• Endotoxin testing
• Stability testing

Integrating these activities helps developers build a more complete understanding of product quality.

The Role of Endotoxin Testing Services

Potency testing evaluates biological activity, while endotoxin testing services address a separate but important product safety requirement.

Endotoxin contamination can create significant patient safety concerns and may affect manufacturing and release decisions. Including endotoxin testing within the overall analytical strategy helps ensure that potency results are considered alongside critical microbiological quality attributes.

A comprehensive quality program may therefore connect:

Process control → Potency testing → Endotoxin testing → Other analytical tests → Final release

Validation Challenges

Once a potency assay has been developed, it must demonstrate that it is suitable for its intended purpose.

Important performance characteristics may include:

• Accuracy
• Precision
• Specificity
• Linearity
• Range
• Robustness
• Repeatability
• Intermediate precision

The validation strategy should be appropriate for the assay's intended use and stage of product development.

Technology Transfer Challenges

An assay that performs well in one laboratory may behave differently after transfer to another facility.

Common technology transfer challenges include:

• Different equipment
• Reagent variability
• Analyst-to-analyst differences
• Reference standard availability
• Differences in cell handling
• Data analysis methods

Early standardization and transfer planning can reduce delays when manufacturing is moved from development laboratories to a cell and gene therapy CDMO.

Best Practices for Reliable Potency Assays

Developers can strengthen their potency strategies by:

1. Defining the mechanism of action early.
2. Selecting biologically relevant endpoints.
3. Using qualified reference materials.
4. Controlling critical assay variables.
5. Assessing assay variability during development.
6. Planning validation requirements early.
7. Considering technology transfer during assay development.
8. Integrating potency with the broader analytical control strategy.

Early planning can prevent significant analytical challenges later in clinical development and commercialization.

Commercialization Considerations

Potency assays must remain practical as manufacturing volumes increase. An assay that is suitable for early research may not be appropriate for routine commercial batch release.

Commercial-stage developers should consider:

• Testing turnaround time
• Laboratory capacity
• Reagent availability
• Automation potential
• Method robustness
• Cost per test
• Transferability
• Regulatory expectations

These factors should be evaluated before finalizing the commercial analytical strategy.

Conclusion

Potency assay development remains a major challenge in cell and gene therapy because biological activity can be complex, variable, and difficult to measure with a single analytical endpoint. Developers need assays that are scientifically relevant, reproducible, appropriately validated, and practical for long-term manufacturing.

Working with an experienced cell and gene therapy CDMO can provide access to integrated manufacturing and analytical capabilities, while endotoxin testing services and other quality control activities help create a comprehensive product testing strategy.

For developers moving toward clinical and commercial manufacturing, Xellera Therapeutics supports integrated cell and gene therapy manufacturing, bioanalytical testing, quality control, and analytical development to help build reliable quality strategies throughout the product lifecycle.