ADCC Assays

Antibody-mediated cytotoxicity assay (ADCC) is a prominent mechanism in the host immune defense. The antigen-binding fragment (Fab) region of an antibody binds to a specific antigen on a target cell (Figure 1.), commonly an infected cell, or pathogen. The fragment crystallizable (Fc) region of the same antibody then binds to a FcγRIII or CD16 receptor on an effector cell, commonly a natural killer (NK) cell. The bound NK cell then secretes apoptosis-inducing agents, thus destroying the target cell.

adcc

Figure 1. ADCC assay mechanism.

The current gold standard target labeling species for ADCC is the stable isotope Chromium-5 (51Cr). The isotope is pre-loaded into the target cells prior to performing the assay. When lysed, the 51Cr loaded target cells release 51Cr into the supernatant; the measured radioactivity in the supernatant indicates the extent of cell lysis. Radioactive assays such as these pose obvious safety threats and waste disposal concerns. The labeling procedure can also be arduous and time consuming. Also, artifacts from the labeling process and chromate ion toxicity are possible.

Recently developed cell-based methods bypass the need for radioisotope-labeled cells. These methods rely on measurement of molecules released by lysed target cells, or measurement of binding of antibodies to target or FcγRIII receptors. The assays in the following list have their own strengths and are chosen depending on the lab’s needs and drug development research stage. When automated for medium- and high-throughput methods, these new assays create simple and robust processes. These assays require less active labor and increased consistency over time and with multiple users.

 

Application Notes

 

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