The occurrence of an immune response against therapeutic proteins poses a major risk for the development of biologics and for successful treatment of patients. Generation of anti-drug antibodies (ADAs) can lead to formation of immune complexes (ICs), consisting of drug and ADAs, with potential impact on safety, efficacy and exposure. Here, we focus on the effects of IC formation, i.e., specific IC sizes, ADA and drug properties, on drug pharmacokinetics. Pre-formed IC preparations of an IgG 1 drug (with wild type or with an ablated effector function at the Fc domain) and different ADA surrogates (directed against the complementarity-determining regions or Fc domain of the drug) were administered to rats and collected serum was analyzed to determine the total drug concentration. A combination of size-exclusion chromatography and ELISA enabled a size-specific evaluation of IC profiles in serum and their changes over time. Within five minutes, total drug concentration decreased by ~20–60% when the drug was complexed. Independent of the ADA surrogate and drug variant used, increasing IC size led to increased clearance. Comparing ICs formed with the same ADA surrogate but different IgG 1 variants, we observed that complexed drug with a wildtype Fc domain showed faster clearance compared to immune effector function modified drug. Data generated in this study indicated that clearance of drug due to ADA generation is driven by size and structure of the formed ICs, but also by the immune effector functions of the Fc domains of IgGs. Abbreviations Ab: antibody, ADA: anti-drug antibody, AUC: area under the curve, Bi: biotin, CDR: complementary-determining region, c max : maximal concentration, Dig: digoxigenin, ELISA: enzyme-linked immunosorbent assay, Fc: fragment crystallizable, FcRn: neonatal Fc receptor, HMW: high molecular weight, IC: immune complex, IC-QC: immune complex quality control, IgG: immunoglobulin G, mAb: monoclonal antibody, mADA: monoclonal ADA, pAb: polyclonal antibody, pADA: polyclonal ADA, PD: pharmacodynamics; PK: pharmacokinetic, QC: quality control, SEC: size-exclusion chromatography, WT: wildtype

Clinical anti-drug-antibody (ADA) responses represent a substantial obstacle to the development of efficacious therapeutic antibodies. The enhanced ADA production against the idiotype (Id) often displayed by cancer immunotherapy antibodies (CitAbs) can lead to exposure loss and subsequently affect anti-tumor efficacy and cause undesired effects on safety. Thus, ADA responses contribute to prolonged clinical development and high attrition rates. Most conventional therapeutic antibodies are now of human origin or humanized proteins, and are hence immunologically tolerized in most patients. In contrast, the contribution of additional factors, other than the protein sequence, to the higher rates of clinical ADA to certain CitAbs, remains poorly understood. Here, we used human immunoglobulin gamma 1 (IgG1) transgenic mice (named “hIgG1 transgenic mice” or “TG”), which are immunologically tolerant to human IgG1, to study the immunogenicity of 13 conventional antibodies and 2 CitAbs. We found that tolerance to non-germline encoded Ids is maintained in part by the function of neonatal Fc-receptor (FcRn). Additionally, the incorporation of T cell-engaging moieties like an interleukin 2 (IL-2)-based immunocytokine or a CD3ε-specific antigen-binding fragment (Fab) was sufficient to revert tolerance and trigger ADA production directed to the Id of these compounds. We postulate that T cell receptor or IL-2 receptor activation may result in activation of unresponsive T cells specific for the crystallizable fragment (Fc) that typically inactivate Id-specific B cells and mediate “linked-antigen tolerance”. Reversal of this unresponsiveness by the action of CitAbs on T cells may be the cause of undesired ADA responses. Abbreviations ADA Anti-Drug Antibodies; BCR B Cell Receptor; BId Idiotype-specific B Cell; BiTE Bispecific T cell Engager; BMC Bone Marrow Chimeric Mice; BSA Bovine Serum Albumin; CDR Complementary Determining Region; CEA Carcinoembryonic Antigen; CIT Cancer Immunotherapy; CitAbs Cancer Immunotherapy Antibodies; DC Dendritic Cell; ELISA Enzyme-Linked Immunosorbent Assay; FcRn Neonatal Fc Receptor; FcyR Fc gamma Receptor; GM-CSF Granulocyte-Macrophage Colony Stimulating Factor; gMFI Geometric Mean Fluorescence Intensity; H Heavy Chain; IC Immune Complex; Id Idiotype; IgA Immunoglobulin alpha; IgG1 Immunoglobulin gamma 1; IL-2 Interleukin 2; IL-2R Interleukin 2 Receptor; IL2v Interleukin 2 Variant; IVIG1 Intravenous Immunoglobulin 1; KLH Keyhole Limpet Hemocyanin; L Light Chain; MAPPs MHC-associated Peptide Proteomics; MHC Major Histocompatibility Complex; PBMC Peripheral Blood Mononuclear Cells; PBS Phosphate Buffered Saline; SHM Somatic Hypermutation; scFv Single-chain Variable Fragment; TCR T cell Receptor; TFc Fc-specific T cell; TId Id-specific T cell; UV Ultraviolet; V Variable.

Aim: The presence of di-/multimeric forms of soluble target in biological samples can interfere in anti-drug antibody (ADA) assays, leading to increased background values and potentially false positivity. The authors investigated the use of the high ionic strength dissociation assay (HISDA) to reduce target interference in two different ADA assays. Results: Interference caused by homodimeric FAP was successfully eliminated to enable cut point determination after applying HISDA. Biochemical experiments confirmed the dissociation of homodimeric FAP after treatment with high ionic strength conditions. Conclusion: HISDA is a promising approach to simultaneously achieve high drug tolerance and reduced interference by noncovalently bound dimeric target molecules in ADA assays without extensive optimization, which is particularly advantageous in routine use.