Anti-idiotypic antibodies were generated using the Fab fragment of a proprietary therapeutic antibody. Ten mice from 2 different strains were immunized 3 times and serum was collected. The antibody titer for each mouse was determined using an ELISA assay with the therapeutic Fab region used as the capture and a goat anti-mouse IgG-HRP was used for detection. Two mice with the highest titers were euthanized for generation of hybridomas with their lymphocytes from spleens and the myeloma fusion partner. This resulted in 18 clones with specific binding to the mAb from the primary screening of the anti-ID antibodies (Table ). This panel of anti-IDs were high affinity antibodies with most KD values less than 100 nM (Table ). The epitope binning data indicated that the 18 anti-IDs all bind to closely related epitopes and are in the same epitope bin with the response percentages <10% (Table ). The resultant 18 clones were chosen for further screening to determine the optimal anti-IDs to bind to the mAb in the presence of soluble antigen.