Bridge (HAHA) and binding inhibition assay (inhibition of hu14.18K322A detection) data are shown for three PATA+ patients and one PATA− patient (pretreatment and post-treatment) who developed an increase in bridging activity, as well as reactivity by serum from a healthy control donor and a pool of patients with previously demonstrated anti-idiotypic antibody induced by prior treatment with anti-GD2 mAbs (anti-ID serum pool). In the binding inhibition assay, the pretreatment (pre-tx) serum from the PATA− Pt #32, and the three PATA+ patients have similar “background” reactivity as the healthy donor serum. The post-treatment serum from Pt #32 and the anti-ID serum pool show strong binding inhibition, consistent with the presence of anti-idiotypic reactivity. In contrast, the pretreatment serum from Pt #32 is negative in the bridge assay, whereas the pretreatment sera from the three PATA+ patients are clearly positive (and stronger than the Pt #32 post-treatment serum) in this bridge assay.

HAHA, human antihuman antibody; mAbs, monoclonal antibodies; PATA, pre-existing antitherapeutic antibodies.