Challenging the Standard Immunogenicity Assessment Approach: 1-Tiered ADA Testing Strategy in Clinical Trials

The ADA testing strategy for protein therapeutics was established almost two decades ago when assay methodologies were rudimentary, and serious immunogenicity-related safety issues had recently been observed with some biotherapeutics. The current testing paradigm employs multiple tiers and stringent cut points to minimize false negatives, reflecting a conservative stance towards ADA analysis. The development of highly sensitive ADA assay platforms and technologies such as humanized or fully human monoclonal antibody (mAb) drugs has put the traditional, resource-intensive 3-tiered testing approach under scrutiny. ADA data from clinical studies for three different mAb programs were re-assessed to explore the feasibility of a simplified 1-tiered ADA testing strategy with a 1% false positive cut point versus the traditional 3-tiered approach. The analysis demonstrated moderate to strong correlations between screening results (signal-to-noise, S/N) and those of confirmation and titer results, with the vast majority of samples (~ 97%) across all studies having the same ADA positive/negative classification with either testing approach. Furthermore, at the subject level, over 92% had the same ADA category (pre-existing, treatment-emergent, treatment-boosted) under both testing approaches. The re-categorized subjects had low titer ADA responses with no observed clinical implications on pharmacokinetics, efficacy, or safety. Finally, the treatment-emergent ADA incidences were comparable between the 1-tiered and 3-tiered approaches. The results demonstrate that the 1-tiered testing strategy is suitable for ADA assessment in these programs and is likely more widely applicable. Additionally, the 1-tiered approach could expedite data delivery and reduce resource needs in clinical development without compromising data quality or clinical interpretation.