Our ADCC assays allow clients to evaluate and rank their mAb candidates ability to kill tumor/cancer cells through NK mediated cell lysis. An important mechanism utilized by the cell-mediated immune system to target and kill virus-infected or other diseased cells (e.g. cancer / tumor cells) is through antibody-dependent cell-mediated cytotoxicity (ADCC). This mechanism has been adopted to create in-vitro cell-killing assays to ascertain the efficacy of therapeutic monoclonal antibodies (mAb) to kill targeted tumor cells. This assay relies on a process (depicted below in graphic 1) using three key components; an effector cell that is typically an NK cell, mAb (IgG class) and tumor cell. ADCC is initiated when the bifunctional mAb (typically IgG1) links to the effector cell and tumor cell creating a ‘bridge’ that allows for cell killing. This process triggers release of lytic proteins (perforins and proteases) from the effector cell that enter the tumor cell and kills it through lytic mediated apoptosis.

Graphic 1 – ADCC process depicted utilizing natural killer (NK) cells from donors with Fc gamma IIIa receptor polymorphism V158+ that have been shown to bind more IgG1 therapeutic mAbs (compared to V158 negative donors) resulting in greater activity and killing in ADCC assay

Peripheral blood mononuclear cells (PBMCs) as well as isolated Natural Killer (NK) cells can be used in ADCC assays. However, within PBMCs, the NK cell is the mediator of the ADCC process as the principal effector cell. In drug development, the ability of NK cells to bind monoclonal antibodies to target tumor cell killing is considered to be important to the efficacy of the therapeutic monoclonal antibody screened in ADCC assays.

While the Fab fraction (mAb) binds to targeted cell-surface antigens (of tumor), the Fc component binds to NK cell CD16 Fc-gammaIIIa (FCGR3A) receptors. Various clinical oncology studies with therapeutic mAb’s (e.g. rituximab targeting CD20, trastuzumab targeting HER2 and cetuximab targeting EGFR) have revealed observations that indicate enhanced NK cell killing activity of tumor cells in certain types of patients. Supporting studies show that people with a specific polymorphism for FCGR3A (Homozygous for V158+ CD16), display enhanced NK cell activity vs. other genotypes.

We recognize the interest in utilizing pre-screened donor NK cells and incorporate them in our ADCC assays.