Critical reagent characterization and re-evaluation to ensure long-term stability: two case studies.

Characterization of critical reagents can mitigate adverse impact to ligand-binding assay performance. We investigated the conjugation conditions of a bispecific protein to SULFO-TAG NHS-Ester™ ruthenium to resolve a steady increase in ligand-binding assay background signal. Functional and biophysical attributes in stability samples revealed low pH (4.0) conjugation and formulation buffers were key to decrease aggregate formation. We also identified pH-specific (3.0) purification conditions to reduce aggregate levels from 37% to <5% of a mouse IgG3 reagent antibody. These case studies support the utility of biophysical and functional characterization of critical reagents as a proactive approach to maintain long-term stability and provide the basis for our recommendations a risk-based approach to establish re-evaluation intervals for traditional and novel reagents.