Immunogenicity ADA Testing: Importance, Methods, and Interpretation
Therapeutic proteins can potentially induce immunogenicity. Immunogenicity is immune responses against a therapeutic protein that can influence drug pharmacokinetics, pharmacodynamics, efficacy, and safety. Hence, antibody immunogenicity assays are crucial in understanding these unwanted immune responses. Detection and analysis of antidrug antibody (ADA) formation is employed to study immunogenicity. Immunogenicity testing in clinical trials, particularly ADA induction or ADA influence on drug properties, is crucial for all biotherapeutic development programs.
Immunogenicity data, if applicable, should be present as a subsection entitled immunogenicity in the prescription information. Considering these critical requirements, immunogenicity testing services and immunogenicity bioanalytical services are focused increasingly on developing selective, specific, and sensitive immunoassays to measure antidrug antibody responses against biotherapeutic proteins. The current article discusses different elements of immunogenicity ADA testing and PK ADA assessment. However, robust biological assay validation remains crucial for generating reliable, reproducible, and accurate immunogenicity data.
Importance of immunogenicity ADA testing
The clinical implications of immunogenicity range from no direct evidence on clinical impact to life-threatening and severe responses. Studies have reported antidrug antibodies’ involvement in anaphylaxis and infusion reactions, along with diseases mediated through immune complexes. Antidrug antibodies have also resulted in secondary treatment failures and rare scenarios, serious events such as deficiency syndromes. Hence, antidrug antibodies are a significant concern for drug safety and efficacy, and it becomes essential to assess ADA development in subjects during immunogenicity testing in clinical trials.
Methods for immunogenicity ADA testing
The US FDA recommends a multi-tiered approach for ADA testing. This method begins with the primary screening assay to evaluate clinical samples. These screening assays should be sensitive enough to detect low levels of high and low-affinity antidrug antibodies for gaining deeper insights into the ADA response. Once samples are tested positive, they are subjected to demonstrate ADA specificity through a confirmatory assay. Finally, positively identified samples in confirmatory assays are further subjected to characterization via neutralization and titration assays.
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In some scenarios, researchers may use assays to identify cross-reactivity with other components, such as endogenous proteins. For example, cross-reactivity assessments may be required for therapeutic protein products with high homology to other proteins. Additionally, confirmed positive samples can be assessed further to identify antibody isotypes or evaluate the specificity of their epitopes.
Interpreting immunogenicity data
Researchers can use multiple approaches to report and interpret positive antibody responses. The most common method is qualitative testing, where study subjects report positive or negative responses.
Once subjects are confirmed as ADA positive, determining antibody levels is informative as it allows ADA assessment and their impact on efficacy and safety. Researchers can evaluate positive antibody levels using a titer. This approach is appropriate and usually considered in the medical community. The most frequent titer is identified using the reciprocal of the highest dilution with a value similar to or just above the cut point. Alternatively, researchers can determine the titer by extracting the assay cut point dilution through the linear section of the dose-response curve.
In Conclusion
Immunogenicity ADA testing is critical for determining the impact of antidrug antibodies on the safety and efficacy profile of a biopharmaceutical product.