Professional technology integration to support the entire R&D process

Immuno-oncology (I-O) assay validation is a formal process of demonstrating that a cell co-culture-based functional assay (such as immune cell activation and tumor cell killing assays) is reliable, specific, accurate, and robust within its intended use. Because I-O assays typically involve the dynamic interaction between primary immune cells and tumor cells, their validation is more challenging than that of simple biochemical assays. This document strictly adheres to the framework of the Pharmacopoeia of the People's Republic of China (ChP), particularly the scientific principles of General Chapter 9401 "Guiding Principles for Validation of In Vitro Bioactivity/Potency Assays for Biological Products" and <9101> "Guiding Principles for Validation of Analytical Methods," providing a systematic strategy and practical approach for the validation of I-O functional assays (such as antibody-dependent cell-mediated cytotoxicity (ADCC), T cell activation/reactivation, and immune checkpoint blockade assays).

The core of I-O assay validation lies in demonstrating that the method accurately and consistently reflects the biological activity of drugs (such as monoclonal antibodies, bispecific antibodies, and fusion proteins) in the target immunological function. Validation should be based on a pre-approved validation protocol and focused on the overall analytical objectives. Key strategies include:

1."Relative Potency" Assay Principle: Most I-O assays do not determine absolute content but rather the relative potency or relative activity of the test sample by comparison with a collaboratively calibrated reference standard. The reference standard should be stable and have well-defined activity.

2."System Suitability" Prerequisite: Each experiment must undergo a system suitability test including both a reference standard and a control to confirm that the system is under control for the data to be acceptable.

3.Key Validation Indicators: Depending on the assay objective, system validation is typically required for specificity, precision, accuracy, linearity and range, and robustness.

1. Specificity 

Pharmacopoeia Requirements: Demonstrate that variations in assay results originate from the specific biological activity of the test sample, rather than non-specific interference. 

I-O Validation Practices: 

Target Specificity Validation:

Perform parallel experiments using target cells or effector cells with target gene knockout (KO). In cases where the target site is absent, the activity of the test sample should be significantly reduced or absent (e.g., using PD-L1 KO tumor cells to verify the activity of anti-PD-1 antibodies).

Using an excess of soluble target protein (such as recombinant PD-L1 Fc fusion protein) to compete with the antibody drug should dose-dependently neutralize its activity.

Functional specificity validation: Demonstrating that the measured functional readings are biologically significant. For example, in ADCC assays, the addition of an Fc receptor blocker should inhibit the cytotoxic activity of the antibody; in T-cell activation assays, the addition of a calcineurin inhibitor (such as cyclosporine A) should inhibit the activation signal.

2. Precision

Pharmacopoeia requirements: Including repeatability, intermediate precision, and reproducibility.

I-O validation practices:

Reproducibility: At least six independent assays should be performed on the same plate by the same operator using the same reagents on the same sample (usually a sample with a titer of 80%-120% of the labeled amount) and reference sample. Calculate the geometrical coefficient of variation (GCV) of the potency estimate, typically requiring a GCV ≤ 20-25%.

Intermediate precision: Experiments are conducted on different dates, by different operators, and possibly using different batches of primary immune cells (e.g., PBMCs from different donors). Assess the variability of potency assay results under different conditions. This step is crucial because donor variability is an inherent property of I-O assays. Acceptable criteria should be pre-defined based on historical data or assay requirements.

3. Relative accuracy

Pharmacopoeia requirement: The degree of agreement between the assay result and the reference value. For bioassays, this is often determined through collaborative calibration or comparison with recognized references.

I-O validation practice:

Use collaboratively calibrated national or international references, or internally established, stable working references.

In validation experiments, the reference is measured at at least three independent potency levels (e.g., 50%, 100%, 150%). Calculate the ratio of the geometric mean of the potency measured at each level to the labeled potency (i.e., relative potency). Calculate the geometric mean of the relative potency at each level and its 90% or 95% confidence interval, which should fall within a pre-defined acceptable range (e.g., 80%–125%).

4. Linearity and Range 

Pharmacopoeia requirement: The ability of the assay results to be proportional to the concentration (or dilution) of the test sample within a given range.

I-O Validation Practice:

Perform serial dilutions of the reference sample covering its expected effective dose range (typically EC₂₀ to EC₈₀).

Plot the logarithmic concentration on the X-axis and the reaction values ​​(e.g., specific cleavage rate, fluorescence intensity) on the Y-axis. The data should fit well with a four-parameter logistic equation. The linear range is typically defined as R² > 0.95 or an acceptable range for the sum of squared residuals of the curve fit. This range should be sufficient to cover the expected potency of the test sample.

5. Robustness

Pharmacopoeia requirement: The ability of the assay results to remain unaffected by small, deliberate changes in assay conditions.

I-O Validation Practice:

Consciously modify key operational parameters that may affect the results, such as:

Effective cell to target cell ratio (E:T ratio) within the optimal range (e.g., ±20%).

Co-culture time within the optimal range (e.g., ±1-2 hours).

Post-resuscitation resting time of primary cells (e.g., PBMCs).

Incubation time of the assay reagent.

Assess the impact of these subtle changes on the final titer assay results (e.g., EC₅₀ or relative titer). Changes should not cause results to exceed pre-defined acceptable standards.

Validation must begin with a detailed validation protocol that clearly defines:

1.Assay summary and ATP. 

2.Samples and references.

3.Specific experimental design and acceptance criteria for each validation step.

4.Statistical analysis methods. 

Upon completion of validation, a validation report should be issued, including:

1.All raw data.

2.Calculations performed according to the protocol, statistical analysis results, and graphs.

3.Comparison with acceptance criteria.

4.Conclusion: Clearly state whether the method has passed validation, and clearly define its applicability, limitations, and revalidation conditions (e.g., revalidation or partial validation is required if the main reagent or cell source changes).

Immuno-oncology assay validation is a rigorous evidence-generating process, its complexity stemming from the variability of biological systems. Following the guidelines of the Chinese Pharmacopoeia, a carefully designed validation strategy can effectively quantify and control this variability, thereby demonstrating the reliability and robustness of the method for its intended use. A successfully validated I-O assay is not only crucial for supporting non-clinical studies and clinical trial applications, but also serves as the scientific basis for quality control and batch release throughout the product lifecycle. All validation activities should be faithfully documented to ensure traceability and reliability.