Here, we present a protocol for an antibody-dependent, cell-mediated cytotoxicity (ADCC) assay using an ADCC bioassay kit. This method offers a valuable tool for elucidating the ADCC mechanism and evaluating the therapeutic potential of antibodies in cancer immunotherapy.
The method for antibody-dependent, cell-mediated cytotoxicity (ADCC) represents an important tool to assess the efficacy of therapeutic antibodies in cancer immunotherapy. Evaluating ADCC activity in cancer cells is essential for the development and optimization of antibody-based treatments. Here, we propose a methodological approach of utilizing an ADCC bioassay kit for quantitative assessment of ADCC reaction using thyroid cancer cells as effector cells. The protocol involves the co-culture of effector cells with target cancer cells in different ratios in the presence of a therapeutic antibody. The ADCC bioassay kit used in this experiment includes the genetically engineered effector cells expressing a luciferase reporter gene under the control of Nuclear Factor of Activated T-cell (NFAT) response elements. Upon the binding of the surface antigen on the target cells with the antibodies and effector cells, the effector cells release luciferase, enabling quantification of cytotoxicity through measurement of luminescence signal. In contrast to conventional ADCC assays, this method proved the binding of target antigen with antibodies and effector cells, which can produce reliable results in a short period.
Antibody-dependent, cell-mediated cytotoxicity (ADCC) is an important mechanism by which antibodies exert immune-mediated cell-killing effects1,2,3. The immune cells are activated by binding to the therapeutic antibody, which interacts with surface antigens of the target cells to release granzymes, perforin, leading to the target cell death. These immune cells include natural killer (NK) cells and neutrophils2,3,4,5,6,7. The ADCC assay has become an important tool to evaluate the efficacy of therapeutic antibody8,9.
In the conventional ADCC assay, peripheral blood mononuclear cells (PBMCs) or natural killer cells are used as effector cells to monitor the efficacy of a therapeutic antibody by quantitating the target's cell death rate. Our method uses an ADCC bioassay kit that includes genetically engineered effector cells expressing a luciferase reporter gene under the control of Nuclear Factor of Activated T-cell (NFAT) response elements. We then quantify the binding of the surface antigen on the target cells with the antibody and the effector cells. This method is based on the ADCC reaction occurring in a short period without requiring human PBMC cells. The experimental steps include the co-culture of effector cells with target cells in the presence of therapeutic antibodies.
During incubation, the therapeutic antibody binds to the target antigen on the surface of the target cells, which leads to the binding of the effector cells and the Fc fragment of an antibody. This activates the NFAT response element and releases luminescence signals for the quantitative assessment of the ADCC reaction.
Before performing the experiment, the expression of the target antigen in the target cells must be confirmed by either flow cytometry or western blotting. Target cells are cultured and passaged into 96-well plates for 24 h before the experiment. Different concentrations of a therapeutic antibody are added together with different cell counts of effector cells to achieve the calculated effector-to-target cell ratio.
Key steps in this method include (1) preparation of target cells and effector cells, (2) effector-to-target cell ratios, (3) Preparation of different concentrations of the antibody, and (4) varying duration of incubation. After the incubation, luminescence signals are measured using a luminometer, providing a quantitative readout of ADCC activity. Compared to other methods for measuring ADCC, this method is relatively simple to operate, and the results are accurate.
The ADCC reporter bioassay indicates the binding of the target antigen, therapeutic antibody, and immune cells in the ADCC pathway activation. This binding activates gene transcription through the NFAT pathway in the effector cells-engineered Jurkat cells with stably expressing FcγRIIIa receptor, the V158 (high-affinity) variant. The NFAT response element mediates the expression of luciferase in the effector cells10,11. The biological activity of the antibody in the Mechanism of action (MOA) of ADCC is quantified through the luciferase signal produced from the NFAT pathway. Luciferase signal in the effector cells-FcγRIIIa receptor-expressing Jurket cells-is quantified using a luminescence reader (Figure 1). The signal-to-noise ratio of the assay is high.
1. Detection of EGFR and VEGFR expression in target cells
NOTE: Use western blotting to detect the expression of the target antigen in the target cells.
2. Preparation of target cells
3. Preparation of varying concentrations of the therapeutic antibody
4. Preparation of effector cells
5. Incubation of effector cells with antibody and target cells
6. Quantitative readout of ADCC activity
The expression of EGFR and VEGFR in the target BHT-101 and SW-1736 cells was detected using western blotting. EGFR expression was detected in both BHT-101 and SW-1736 cells but not VEGFR expression (Figure 3).
Using the ADCC bioassay kit, we detected the ADCC reaction of the anti-EGFR antibody, cetuximab, using EGFR-positive cell lines, BHT-101 and SW-1736, as target cells. Bevacizumab, a VEGF inactivator, was used as a negative control antibody. Different concentrations of antibodies and effector cells were incubated with the target cells. The luminescence signal was detected using a plate reader (Figure 2). A higher fold of ADCC activity induction was found in Cetuximab (anti-EGFR antibody) groups, but no ADCC activity was seen in Bevacizumab (VEGF antagonist) for both cell lines. This demonstrated the ADCC effect targeting EGFR extracellular membrane antigens for both cell lines. By using this method, the ADCC reaction was validated in the presence of Cetuximab in two anaplastic thyroid cancer cell lines (BHT101 and SW1736) (Figure 4).
Figure 1: A schematic diagram showing the ADCC reaction with the ADCC bioassay kit. Antigen-binding sites in the therapeutic antibody bind to surface antigens in target cells. This binding leads to the binding of the Fc portion of the antibody to the FcƳRIIIa receptors of effector cells, which have been genetically engineered with NFAT-RE luc, producing a luminescence signal in the effector cells. This figure was modified from the ADCC Reporter Bioassay Core kit manual with permission12. Abbreviations: ADCC = Antibody-dependent cell-mediated cytotoxicity; Fc = Fragment crystallizable region; NFAT = Nuclear Factor of Activated T-cell; RE = Response element; luc = Luciferase. Please click here to view a larger version of this figure.
Figure 2: Luminescence reading and experimental diagram of 96-well plate design of the ADCC co-culture system. Luminescence signals are read by a luminescence reader. Row A: 1st-9th wells contain ADCC Bioassay Buffer. Row B: 3rd-8th wells contain BHT101's ADCC reaction system (target cells+ antibody + effector cells). The 2nd well is without antibody. The 9th well contains just ADCC Bioassay buffer. Row C: 3rd-8th wells contain SW-1736's ADCC reaction system (target cell+ antibody + effector cells). The 2nd well is without antibody. The 9th well contains just ADCC Bioassay buffer. Row D: 1st-9th wells contain Assay Buffer. Abbreviations: ADCC = Antibody-dependent cell-mediated cytotoxicity; AB = ADCC Bioassay buffer; VEGFR = Vascular Epithelial Growth Factor Receptor; EGFR = Epidermal Growth Factor Receptor; mAb = monoclonal antibody. Please click here to view a larger version of this figure.
Figure 3: Detection of EGFR and VEGFR expression in BHT-101 and SW-1736 thyroid carcinoma using western blotting. Expression of EGFR, but not VEGFR, was detected in both cell lines. B-actin was used as the loading control. Abbreviations: EGFR = epidermal growth factor receptor; VEGFR = vascular epidermal growth factor. Please click here to view a larger version of this figure.
Figure 4: Fold induction of ADCC activity. (A) Thyroid cancer cell line BHT-101 exhibits an ADCC effect in the presence of the anti-EGFR antibody Cetuximab. (B) The thyroid cancer cell line SW-1736 exhibits an ADCC effect in the presence of the anti-EGFR antibody Cetuximab. Please click here to view a larger version of this figure.
Here, we have presented the ADCC Bioassay method for assessing the ADCC reaction of a therapeutic antibody. The method is straightforward and employs a simple “add-mix-read” format for measurement.
Before doing the experiment, the expression of the target antigen in the target cells must be confirmed by either flow cytometry or western blotting. Flow cytometry will be a better tool to detect the surface antigen. However, using flow cytometry can stress the cells, causing apoptosis and affecting the viability of the cell and, therefore, the overall analysis. In addition, it costs more than western blotting. In this experiment, we used western blotting as a faster and more cost-effective method because targeted antigens are known cell surface antigens.
Engineered Jurkat cells, which stably expressed the FcγRIIIa receptor, the V158 (high affinity) variant, and an NFAT response element that drives the expression of firefly luciferase, were used as effector cells. Activation of the NFAT pathway results in the production of luciferase, and its activity is quantified in the form of luminescence readout. The signal also represents the activity of ADCC.
First, target cells (T) are incubated with effector cells (E) in the presence of varying amounts of antibody in 96-well plates for 6 h at 37 °C in a humidified CO2 incubator. The effector:target ratio of 5:1 is used to optimize the signal. For example, 75,000 effector cells were added to 15,000 target cells. At the end of incubation, Bio-Glo luciferase assay reagent is added to each well, incubated for 30 min, and the luminescence (RLU, relative luciferase units) is measured using a luminescence plate reader.
The key critical steps in this protocol are: (1) The handling of effector cells. The cell vial should not be inverted during the thawing process, rock gently, and must be used immediately after thawing to prevent unwanted cell death or affecting the performance of biological detection. (2). It is important to use white polystyrene 96-well microplates with clear, flat bottom for luminescence measurements because the luminescence is captured from the bottom of the reader.
In this study, we observed the stronger and weaker ADCC reactions of the anti-EGFR antibody, cetuximab, depending on the amount of target cells and antibody concentration. Some reasons for handling the calibration of weak ADCC reactions: (1) The readings of the ADCC reporter bioassay come from effector cells (E), with a constant number of 75,000 cells per well in the ADCC reaction system of this study. Therefore, optimizing the quality of target cells (T) is one aspect that can be improved. The E:T ratio in this study was 5:1, which could be adjusted up to 20:1. (2) Antibody concentration is also one of the important factors affecting ADCC reaction. Adjustments can be made through serial dilution of antibodies to explore the optimal concentration range, thus achieving maximum response in the ADCC report. (3) The incubation time of antibodies, target cells, and effector cells is also crucial for experimental results. In this study, we incubated for 6 h, which can be extended up to 24 h to achieve the optimal ADCC reaction. (4) Additionally, the concentration of the buffer solution (low IgG) for ADCC assay also needs to be explored. The optimal serum concentration for ADCC response can be achieved within the range of 1% to 10%.
This experimental method is rapid and straightforward, allowing completion within one day through a simple “add-mix-read” protocol. The results are stable and amenable to batch testing. However, this bioassay kit does not detect cell death like conventional ADCC methods that use PBMC or NK cells as effector cells12,13. Instead, it uses FcγRIIIa receptor expressed Jurkat cells as effector cells, which will cost more because the cells are genetically modified. In comparison to traditional ADCC experiments13,14, it eliminates the requirement of blood donations from healthy individuals and avoids the complex process of extracting immune cells, thus mitigating individual variations that could impact the results. The detected luminescence signals are from the binding of effector cells to target cells, not from the actual death of target cells. Therefore, there may be discrepancies compared to standard ADCC detection methods. Furthermore, cell dissociation buffer, which is more expensive than trypsin, is used to detach the adherent cells to maintain the membrane integrity.
ADCC reporter gene analysis demonstrates excellent accuracy and stability, serving as an efficacy analysis method for the mass detection of therapeutic antibody drugs. It can also function as a critical analysis method for the characterization of therapeutic molecules and process development15.
In summary, ADCC is an important immune mechanism, and the quantitative detection of ADCC holds great importance in the field of immunotherapy. This experimental method offers an effective means for the quantitative measurement of ADCC15.
The authors have nothing to disclose.
We are grateful to Prof. Zeng (IMCB, A*STAR) for supporting this work. This study was supported by the Youth Foundation of National Natural Science Foundation of China (NSFC) (82202231), and the Medical and Health Science and Technology Project of Zhejiang Province, China (2021KY110,2024KY824).
0.5% Trypsin-EDTA | Gibco | 15400-054 | Dilute 10x in PBS to make 0.05% Trypsin |
1x Tris Buffer Saline (TBS) | 1st BASE | BUF-3030-1X1L | For membrane washing in western blotting |
1.5 M Tris Buffer, pH 8.8 | 1st BASE | BUF-1419-1L-pH8.8 | For SDS gel preparation |
2-Mercaptoethanol | Sigma Aldrich | M7522-100ML | For sample preparation of western blotting |
30% Acrylamide/Bis solution | Bio-Rad | #1610158 | For SDS gel preparation |
4x Laemmli Buffer | Bio-Rad | #1610747 | For sample preparation of western blotting |
96-well white polystyrene microplate with clear flat bottom | Corning Incorporated | 3610 | For ADCC assay |
ADCC Bioassay Effector cells (0.65 mL) | Promega | G7011 | Includes in ADCC reporter bioassay core kit (Promega G7010), 1 x 1 vial |
ADCC reporter bioassay core kit | Promega | G7010 | Mentioned as ADCC bioassay kit for ADCC assay in this experiment |
Ammonium Persulfate | Sigma Aldrich | A3678-25G | For SDS gel preparation |
Bevacizumab (Humanized Anti VEGF-antibody) | MVASI | – | Use as negative control antibody in ADCC asssay |
BHT-101 | Leibniz Institute DSMZ | ACC279 | Human anaplastic papillary thyroid cancer cell line |
Bio-Glo Luciferase Assay Buffer | Promega | G7941 | Includes in ADCC reporter bioassay core kit (Promega G7010), 1 x 10 mL |
Bio-Glo Luciferase Assay Substrate (Lyophilized) | Promega | G7941 | Includes in ADCC reporter bioassay core kit (Promega G7010), 1 x 1 vial |
Cell scraper | GenFollower | GD00235 | To remove cell from culture flask |
Cetuximab (Chimeric anti-EGFR antibody) | ERBITUX | – | Use as therapeutic antibody in ADCC assay |
Chemiluminescent HRP substrate | Merck Millipore | WBKLS0500 | For protein detection in western blotting |
Distilled water | Gibco | 15230-162 | For SDS gel preparation |
Fetal Bovine Serum (FBS) | Gibco | 10270-106 | Culture media supplement |
iBright CL1500 imaging system | Thermo Scientific | 2462621100038 | For protein detection in western blotting |
L-glutamine, 200 mM | Gibco | 25030-081 | Culture media supplement |
Low IgG Serum | Promega | G7110 | Includes in ADCC reporter bioassay core kit (Promega G7010), 1 x 4 mL |
Megafuge 8R | Thermo Scientific | 42876589 | Centrifuge |
Mouse anti-EGFR monoclonal antibodies | BD Biosciences | 610016 | Primary antibody in western blotting |
Mouse anti-VEGFR monoclonal antibodies | BD Biosciences | 571194 | Primary antibody in western blotting |
non-enzymatic cell dissociation buffer | Sigma Aldrich | C5789-100ML | For cell harvesting from T75 flask |
Penicillin-Streptomycin | PAN Biotech | P06-07100 | Antibacterial for culture media |
Phosphate Buffered Saline (PBS), pH 7.2, Sterile filtered | 1st BASE | CUS-2048-1x1L | Use as washing solution for cells |
Pierce BCA assay kit | Thermo Scientific | 23225 | To measure protein concentration |
Protease and phosphatase inhibitor | Thermo Scientific | A32959 | For protein digestion in sample preparation for western blotting |
PVDF membrane (Immobilin-P) | Merck Millipore | IPVH00010 | For protein transfer in western blotting |
Rabbit anti-mouse IgG, Fcγ HRP-conjugated secondary antibody | Jackson ImmunoResearch | 315-035-046 | Secondary antibody in western blotting |
Roswell Park Memorial Institute (RPMI) medium | Capricorn Scientific | RPMI-XA | Cell culture media |
RPMI-1640 | Promega | G7080 | Includes in ADCC reporter bioassay core kit (Promega G7010), 1 x 36 mL |
Skim milk powder | Merck Millipore | 70166-500G | For membrane blocking in western blotting |
Sodium Dodecyl Sulfate | 1st BASE | BIO-2050-500g | For SDS gel preparation |
SW-1736 | Cytion | 300453 | Human thyroid squamous cell cancer cell line |
T75 culture flasks | SPL Lifesciences | 70075 | Cell culture flask |
Tecan Multimode Reader model Spark 10M | Tecan | 1607000294 | for luminicence quantification |
TEMED | Bio-Rad | #1610801 | For SDS gel preparation |
Tween-20 | Promega | H5151 | For membrane washing in western blotting |
Vi-cell XR cell viability analyzer | Beckman Coulter | AL15072 | Cell counter |
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