Characterizing Effector Function in Antibody Development, Part 2: Cytotoxicity Assays

In our last blog, we covered Fc gamma receptor (FcγR) binding and its role in antibody MoA, safety, and regulatory requirements. Functional cytotoxicity assays play an important complementary role to FcγR binding, providing confirmation of a therapeutic antibody’s intended MoA or safety liabilities using cell-based, instead of biochemical, methodology.

In oncology indications, immune-mediated tumor killing is often the objective of therapeutic strategies. Monoclonal antibodies (mAb) that target tumor antigens frequently rely on effector pathways such as antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and antibody-dependent cellular phagocytosis (ADCP) to eliminate tumor cells.

In these settings, measuring cytotoxicity provides direct evidence that a mAb or other antibody-based therapy not only binds its target, but also translates that binding into meaningful biological activity. Functional assays confirm that natural killer (NK) cells, complement proteins, or macrophages are properly engaged.

However, the therapeutic landscape of antibodies has expanded beyond oncology, into immunology and autoimmunity. In these indications, unintended cell killing can represent a major safety risk. Depleting the wrong immune cell population or triggering excessive immune activation may lead to infection, tissue damage, or loss of immune tolerance. In these contexts, ADCC, CDC, and ADCP are no longer linked to potential efficacy; they are liabilities.

In this blog, we discuss the challenges of functional cytotoxicity assays and explain how Eurofins Discovery can address comprehensive assessment of effector function for your therapeutic antibody candidates.

Navigating the Challenges of ADCC, CDC, and ADCP Assays

While cell-based cytotoxicity studies fill the gaps left by FcγR binding assays, functional cytotoxicity testing presents its own challenges. ADCC assays often rely on primary human peripheral blood mononuclear cells (PBMCs) or primary NK cells isolated from PBMCs, introducing donor-dependent variability that must be mitigated by using multiple donors. These assays are also highly sensitive to antibody glycosylation, particularly FcγRIIIa-mediated NK cell ADCC assays.

Complicating matters further, FcγR polymorphisms such as the V158 and F158 variants of FcγRIIIa or the H131 and R131 variants of FcγRIIa influence receptor affinity and patient response. Additionally, in vitro and cell-based systems struggle to model the high serum IgG concentrations present in vivo, where FcγR are largely preoccupied.

Because of this, cytotoxicity evaluation requires a multi-assay strategy, pairing precise FcγR binding measurements using SPR with carefully controlled functional assays to establish a complete biological profile.

Regulatory Expectations

Regulatory agencies, including the FDA and EMA, increasingly require functional potency assays that reflect in vivo biological activity. The FDA specifically emphasizes FcγRIIIa-mediated ADCC assays because of their sensitivity to glycosylation and manufacturing changes. Even for antibodies engineered to silence effector function, such as IgG1(null) or IgG4 backbones, regulators require empirical functional data.

How Eurofins Discovery Can Help

In therapeutic antibody development, cytotoxicity testing must be closely aligned to a molecule’s intended MoA, whether to confirm immune-mediated killing in oncology or to rule out safety concerns in autoimmune and inflammatory indications.

Eurofins Discovery has extensive expertise in selecting and developing the most appropriate cell-based assays for your target and therapeutic area, including custom ADCC assays beyond oncology. Multiple assay formats, including colorimetric, chemiluminescent, fluorescent, LDH release, or live/dead staining, allow flexibility in sensitivity and throughput to match your program’s needs.

To address biological variability, Eurofins recommends using at least three distinct PBMC donors, as we’ve demonstrated with trastuzumab, for ADCC assays and can document or source specific donor characteristics to strengthen reproducibility. Assays can be performed using primary cells, including your patient samples, or with engineered cell lines that feature controlled antigen expression levels to enable consistent functional screening. Together, this tailored approach ensures cytotoxicity data that clearly fulfill regulatory requirements and expectations.

Contact us to find out how our cytotoxicity assays, coupled with our FcγR binding assays, can accelerate your therapeutic antibody development.

Characterizing Effector Function in Antibody Development, Part 2: Cytotoxicity Assays

Navigating the Challenges of ADCC, CDC, and ADCP Assays

Regulatory Expectations

How Eurofins Discovery Can Help

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