Minimum Significant Ratio for Defining Treatment-Boosted ADA Responses Using Signal-to-Noise as an Alternative to Titer.

Abstract

Signal-to-noise ratio (S/N) has emerged as a practical alternative to endpoint titer for evaluating anti-drug antibody (ADA) response magnitude. When titration is not performed, a scientifically justified threshold is needed to interpret longitudinal increases in S/N, particularly for identifying treatment-boosted ADA responses in subjects with pre-existing ADA. In conventional titer-based assessments, treatment-boosted responses are typically defined by an increase of two dilution steps relative to the pre-dose titer. In the absence of titer testing, an alternative threshold is needed to determine whether a post-dose/pre-dose increase in S/N exceeds expected analytical variability. This study evaluated minimum significant ratio (MSR) as a project-specific, analytical variability-based threshold for treatment-boosted ADA response classification using S/N. Two MSR calculation approaches were assessed across 11 validated clinical ADA assays representing diverse assay formats, therapeutic modalities, and analytical platforms. MSR_POS was derived from inter-assay precision data using positive controls, whereas MSR_NEG was derived from ADA-negative individual samples and negative-control data generated during assay validation. Retrospective clinical ADA data from two projects were analyzed to compare longitudinal titer ratios with S/N ratios and evaluate treatment-boosted classifications using conventional titer-ratio and MSR-based S/N approaches. Longitudinal titer ratios and S/N ratios were strongly correlated, and MSR-based classifications were broadly consistent with conventional titer-ratio-based classifications. Compared with MSR_POS, MSR_NEG showed higher positive percent agreement while maintaining high negative and overall percent agreement. Overall, these findings support MSR as a practical, project-specific, and statistically justified analytical framework for applying S/N to longitudinal treatment-boosted ADA response characterization.