Development of an ELISA based bridging assay as a surrogate measure of ADCC

The Role of Fc Receptors on the Effectiveness of Therapeutic Monoclonal Antibodies

Since the approval of the first monoclonal antibody (mAb) in 1986, a huge effort has been made to guarantee safety and efficacy of therapeutic mAbs. As of July 2021, 118 mAbs are approved for the European market for a broad range of clinical indications. In order to ensure clinical efficacy and safety aspects, (pre-)clinical experimental approaches evaluate the respective modes of action (MoA). In addition to antigen-specificity including binding affinity and -avidity, MoA comprise Fc-mediated effector functions such as antibody dependent cellular cytotoxicity (ADCC) and the closely related antibody dependent cellular phagocytosis (ADCP). For this reason, a variety of cell-based assays have been established investigating effector functions of therapeutic mAbs with different effector/target-cell combinations and several readouts including Fcγ receptor (FcγR)-mediated lysis, fluorescence, or luminescence. Optimized FcγR-mediated effector functions regarding clinical safety and efficacy are addressed with modification strategies such as point mutations, altered glycosylation patterns, combination of different Fc subclasses (cross isotypes), and Fc-truncation of the mAb. These strategies opened the field for a next generation of therapeutic mAbs. In conclusion, it is of major importance to consider FcγR-mediated effector functions for the efficacy of therapeutic mAbs.

Dimeric Fcγ Receptor Enzyme-Linked Immunosorbent Assay To Study HIV-Specific Antibodies: A New Look into Breadth of Fcγ Receptor Antibodies Induced by the RV144 Vaccine Trial

Ab-dependent cellular cytotoxicity (ADCC) responses are of growing interest in the HIV vaccine field but current cell-based assays are usually difficult to reproduce across laboratories. We developed an ELISA and multiplex assay to model the cross-linking of Fcγ receptors (FcγR) by Abs, which is required to initiate an ADCC response. Our FcγR dimer ELISA readily detected Abs in samples from two separate cohorts of the partially efficacious Thai RV144 HIV vaccine efficacy trial. The FcγR dimer-binding Abs induced by the RV144 regimen correlated well with a functional measure of ADCC as well as IgG subclasses. The high-throughput multiplex assay allowed us to simultaneously measure FcγR dimer-binding Abs to 32 different HIV Ags, providing a measure of the breadth of FcγR-binding Abs induced by the RV144 trial. FcγR-binding Abs specific to V regions 1 and 2 were strongly associated with increased breadth of recognition of different Env proteins, suggesting anti-V regions 1 and 2 Abs may be a marker of ADCC breadth. This FcγR dimer provides an important tool for the further analysis and refinement of ADCC-inducing HIV and other antiviral vaccine regimens.

Methods for measuring antibody-dependent cell-mediated cytotoxicity in vitro

Antibody-dependent cell-mediated cytotoxicity (ADCC) is a relevant characteristic to measure for a number of therapeutic monoclonal antibodies (mAbs) under development. ADCC is a mechanism by which antibody-opsonized, infected, or cancerous cells are destroyed by FcγRIII (CD16)-expressing effector cells. Here we describe three methods that can be used to quantify the ADCC activity of mAbs by measuring distinct aspects of the ADCC mechanism.

Development of a cell-based assay measuring the activation of FcγRIIa for the characterization of therapeutic monoclonal antibodies

Antibody-dependent cellular cytotoxicity (ADCC) is one of the important mechanisms of action of the targeting of tumor cells by therapeutic monoclonal antibodies (mAbs). Among the human Fcγ receptors (FcγRs), FcγRIIIa is well known as the only receptor expressed in natural killer (NK) cells, and it plays a pivotal role in ADCC by IgG1-subclass mAbs. In addition, the contributions of FcγRIIa to mAb-mediated cytotoxicity have been reported. FcγRIIa is expressed in myeloid effector cells including neutrophils and macrophages, and it is involved in the activation of these effector cells. However, the measurement of the cytotoxicity via FcγRIIa-expressing effector cells is complicated and inconvenient for the characterization of therapeutic mAbs. Here we report the development of a cell-based assay using a human FcγRIIa-expressing reporter cell line. The FcγRIIa reporter cell assay was able to estimate the activation of FcγRIIa by antigen-bound mAbs by a very simple method in vitro. The usefulness of this assay for evaluating the activity of mAbs with different abilities to activate FcγRIIa was confirmed by the examples including the comparison of the activity of the anti-CD20 mAb rituximab and its Fc-engineered variants, and two anti-EGFR mAbs with different IgG subclasses, cetuximab (IgG1) and panitumumab (IgG2). We also applied this assay to the characterization of a force-oxidized mAb, and we observed that oxidation significantly decreased the FcγRIIa activation by EGFR-bound cetuximab. These results suggest that our FcγRIIa reporter assay is a promising tool for the characterization of therapeutic mAbs, including Fc-engineered mAbs, IgG2-subclass mAbs, and their product-related variants.