Isolation of human anti-idiotypic antibodies by phage display for clinical immune response assays.

The clinical development of therapeutic proteins requires assays that measure the pharmacokinetic (PK) profile of, and the potential immune response (IR) to, the protein agent. Each assay requires reagents that are highly specific for the therapeutic protein. For therapeutic monoclonal antibodies, anti-CDR-specific, or anti-idiotypic (anti-id), antibodies are an ideal class of reagents suitable for these assays because of their high specificity and affinity to the drug antibody. We generated anti-ids to two human antibodies by antibody phage display using the MorphoSys HuCAL GOLD Fab library. To selectively target the CDR regions, serum and a framework-matched mAb were included as competitors during the phage selection process. Panels of CDR-specific Fabs, with low to sub-nM affinities, were isolated against both targets. The CDR specificity of these Fabs was shown by their lack of binding to a framework-matched control mAb and by competition of this binding with the soluble antigens of the respective therapeutic mAb targets. The candidate anti-id Fabs were able to detect both immobilized and soluble target Ab without being affected by serum, a requirement for both PK assay and the IR bridging assay format. Combinations of the Fabs for PK detection assays were identified by pairwise binding studies, although the pair for one target mAb lacks the desired sensitivity for PK assays. To evaluate their potential as anti-drug antibodies (ADAs), the best Fabs for one of the targets were converted and produced as the required bivalent human mAbs. In comparison to rodent mAbs and primate polyclonal serum, the phage display derived human mAbs were equally effective as reference standards. Our results demonstrate that competition-based phage selection can be an effective method for the isolation of anti-idiotypic antibodies for PK and IR assay development, and in this latter case, overcome limitations of current methods using rodent derived anti-ids.