The authors thank Dr. Michael N. Sack (National Heart, Lung, and Blood Institute) for support and discussion. This study was supported by the Intramural Research Programs of the National Institutes of Health, National Cancer Institute and National Heart, Lung, and Blood Institute.&#160;JT is supported by the Ramon y Cajal program (grant RYC2018-026050-I) of MICINN (Spain).

All the experiments were performed in accordance with the Declaration of Helsinki&#8217;s ethical principles of medical research. Peripheral blood samples from donors were obtained from the NIH Department of Transfusion Medicine under the 99-CC-0168 IRB approved protocol, with patient written informed consent.
1. Reagent preparation
<ol>
	<li>Reagents for the isolation of NK cells 
	NOTES: Prepare these reagents in a cell culture hood.
	<ol>
		<li>Prepare NK separation buffer: Supplement PBS (pH 7.4) with 1 mM EDTA and 2% Fetal Calf Serum (FCS) that has previously been heat-inactivated (at 56 &#176;C for 30 min).</li>
		<li>Prepare NK culture medium: Supplement Iscove&#39;s Modified Dulbecco&#39;s Media (IMDM) with 10% Human Serum (HS). Sterile filter and store at 2-8 &#176;C. Warm the medium to 37 &#176;C before adding to the cells.</li>
		<li>Resuspend Human IL-15 in PBS at 200 &#181;g/mL.</li>
	</ol>
	</li>
	<li>Reagents for extracellular flux assay
	<ol>
		<li>Prepare assay media: For mitochondrial stress test medium, add 1 mM sodium pyruvate, 2 mM L-glutamine and 10 mM glucose to the base medium; for glycolysis stress test medium, add 2 mM L-glutamine to the base medium. 
		NOTE: The concentrations of glucose, pyruvate and glutamine are provided as recommended by the extracellular flux analyzer manufacturer. However, media composition can be altered by researchers to perfectly match that of the culture medium, if desired.</li>
		<li>Adjust the pH of both media to 7.4 with 0.1 N NaOH using a benchtop pH meter, sterile filter through a 0.2 &#181;M pore size and store at 2-8 &#176;C. Warm media to 37 &#176;C, check pH and readjust to 7.4 before use if required. 
		NOTE: Only ambient CO2 is contained in the atmosphere of the extracellular flux analyzer, the use of media without bicarbonate is critical.</li>
		<li>Prepare stock solutions for reagents: Oligomycin (ATP synthase inhibitor), 10 mM stock solution in DMSO; 2,4-dinitrophenol (DNP, uncoupler), 1 M stock solution in DMSO; antimycin A (complex III inhibitor), 10 mM stock solution in DMSO; rotenone (complex I inhibitor), 10 mM stock solution in DMSO. Make 30 &#181;L aliquots of all reagents and store at -20 &#176;C. 
		NOTE: These guidelines are intended for reagents purchased individually and prepared by the researcher. If reagents are purchased from the analyzer manufacturer instead, follow their guidelines for reagent preparation.</li>
	</ol>
	</li>
</ol>
2. NK cells isolation from peripheral blood
<ol>
	<li>Peripheral blood mononuclear cells (PBMCs) preparation from human blood 
	NOTE: Perform these steps in a cell culture hood. Decontaminate all residues and material in contact with blood with bleach and discard them into the appropriate container to be incinerated.
	<ol>
		<li>Pipette 20 mL of Lymphocyte Separation Medium (LSM) into a 50 mL conical tube.</li>
		<li>Carefully, while keeping the tube at a 30&#730; angle, pipette 20 mL of blood over the LSM, very gently and touching the wall of the tube. Avoid the mixing of blood with the LSM and create a visible and well-defined interphase between the two fluids. 
		NOTE: Peripheral blood or enriched leukapheresis products can be used.</li>
		<li>Centrifuge the tubes for 25 min, 1000 x g at room temperature. Do not use brake, as it could make both phases in the tube (LSM and blood) mix.</li>
		<li>Carefully take out the tubes from the centrifuge and place them in a rack. Check for the presence of a conspicuous layer of cells (mononuclear cells) that will form at the interphase between LSM (clear) and plasma (yellow), while red blood cells pellet at the bottom of the tube.</li>
		<li>Gently aspirate the mononuclear cell layer with a 10 mL plastic pipette (around 5-8 mL) and place it in a new 50 mL conical tube. The lymphocyte interphase of up to 2 different tubes can be pooled together.</li>
		<li>Wash the mononuclear cells 2x by resuspending in 45 mL PBS and centrifuging at 800 x g for 5 min, at room temperature. 
		NOTE: After this step, a pellet of peripheral blood mononuclear cells (PBMCs) is obtained and the researcher can proceed to the NK isolation step.</li>
	</ol>
	</li>
	<li>NK isolation from PBMCs
	<ol>
		<li>Count the cells from 2.1.6 and resuspend them in NK Separation Buffer (1x 108 PBMCs/mL).</li>
		<li>Take 10 mL of the cell resuspension (109 PBMCs ) and place them into a 50 mL tube.</li>
		<li>Add 500 &#181;L (50 &#181;L/mL of buffer) of NK cell isolation antibody mix and 10 &#181;L (1 &#181;L/ mL of buffer) of anti-CD3 positive isolation antibody mix to the PBMCs and incubate at room temperature for 10 min.</li>
		<li>Vortex the magnetic beads and add 1 mL to the mix of PBMCs with antibodies (100 &#181;L beads/ml PBMCs). Incubate for 10 min at room temperature with occasionally stirring.</li>
		<li>Add 35 mL of NK isolation buffer (3.5 ml buffer/ml PBMCs), mix and place on the magnet for 15 min (2.2 x 107 PBMCs/mL). After that time, the beads and cells positively selected (all but NK cells) will have adhered to the walls of the tube.</li>
		<li>Carefully collect the supernatant (containing NK cells) with a 50 mL plastic pipette without touching the sides or the bottom of the tube.</li>
		<li>Count the cells using a cell counter and centrifuge at 800 x g for 5 min.</li>
		<li>Resuspend isolated NK cells at 5 x 106 cells/mL in IMDM containing 10% HS and place them in an incubator at 37 &#730;C with 5% CO2 until the experiment is performed. 
		NOTE: This NK isolation protocol states cell numbers and reagent volumes adapted for the use of a 50 mL tube and a big magnet. This protocol can be scaled up (in case more PBMCs are obtained) by repeating the isolation steps in different tubes or scaled down by reducing the volume in the tube. For final volumes of 14-45 mL a 50 mL polystyrene tube is used, for volumes 4-14, a 15 mL polystyrene tube is used and for volumes 1-4 mL, a 5 mL polystyrene tube is used. The magnet is different and fit the appropriate tube in each case. The amount of antibody mix and magnetics beads can also be scaled according to the number of cells and the final volume.</li>
	</ol>
	</li>
	<li>NK cell population staining for flow cytometry
	<ol>
		<li>Take 0.25 x 106 cells per sample from step 2.2.8, remove the medium by centrifuging at 800 x g for 5 min at room temperature and resuspend the cell pellet in 500 &#181;L of PBS.</li>
		<li>Add viability dye according to the manufacturer&#8217;s recommendation (1 &#181;L of DMSO-reconstituted dye to 1 mL of cell resuspension) and incubate at room temperature for 30 min.</li>
		<li>Wash 2x by resuspending in 5 mL PBS and centrifuging at 800 x g for 5 min, at room temperature.</li>
		<li>Stain with the corresponding anti-human antibodies in 100 &#181;L of IMDM containing 10% HS for 30 min on ice protected from light (see Table 1). All the antibodies can be combined and used in a single staining step.</li>
		<li>Analyze the samples by flow cytometry to evaluate the purity of the NK cell population obtained. Use the cell gating and analysis method that have been previously described18,19.</li>
	</ol>
	</li>
	<li>NK cells stimulation with soluble IL-15
	<ol>
		<li>Resuspend 0.75 x 106 cells from steps 2.2.8 or 2.4.3 in 100 &#181;L of IMDM containing 10% HS in a well of a 96 well-plate (round bottom).</li>
		<li>Dilute human IL-15 to 1 &#181;g/mL in IMDM containing 10% HS. Add 100 &#181;L of the diluted human IL-15 to the cells to reach a final concentration of 0.5 &#181;g/mL. 
		NOTE: 0.5 &#181;g/mL is a saturating concentration of IL-15. Lower concentrations of IL-15 or other cytokines such as IL-2, IL-12 or IL-18 may be tested by researchers if desired.</li>
		<li>Place the cells in the incubator at 37 &#176;C and stimulate for 48 h before performing the extracellular flux assay. Resuspend unstimulated (control) cells at the same concentration and volume in IMDM containing 10% HS without IL-15, and place them in the same incubator for 48 h.</li>
	</ol>
	</li>
</ol>
3. Hydration of sensor cartridge
NOTE: The 96 probe tips of the sensor cartridge contain individual solid-state fluorophores for O2 and H+ that need to be hydrated in order to detect O2 and pH changes.
<ol>
	<li>Turn on the analyzer and let it warm up to 37 &#176;C.</li>
	<li>Open the sensor cartridge package and separate the sensor cartridge from the utility plate. Add 200 &#181;L of the calibrant solution in each well of the utility plate and put back the sensor cartridge onto the plate, validating that the sensors are completely submerged in the solution. For optimum results incubate the cartridge overnight at 37 &#176;C in a CO2-free incubator that is properly humidified to prevent evaporation. Prevent bubble formation under the sensors during hydration. 
	NOTE: The minimum cartridge hydration time is 4 h at 37 &#176;C in a CO2-free incubator. Alternatively, overnight hydration of the sensor cartridge with 200 &#181;L of sterile water at 37 &#176;C in a CO2-free incubator, followed by an incubation of the sensor cartridge with 200 &#181;L of pre-warmed calibrant solution 45 &#8211; 60 min prior to the start of the run, can be used.</li>
</ol>
4. Extracellular flux assay
<ol>
	<li>Preparation of adhesive-coated plates 
	NOTE: Since the measurement of metabolic parameters takes place in a microchamber formed at the bottom of the 96-well assay plate, suspension cells must first be adhered to the bottom of the well. A cell adhesive extracted from the mussel Mytilus edulis is employed. The manufacturer of the cell adhesive recommends a coating concentration of 1 to 5 &#181;g/cm2. The well of the analyzer cell culture microplate has a surface of approximately 0.110 cm2. Thus, for a 5 &#181;g/cm2 concentration, around 0.55 &#181;g of adhesive are required. As 25 &#181;L of the adhesive solution will be used to coat each well, the optimal adhesive solution concentration for the analyzer cell culture microplates is around 22.4 &#181;g/mL (22.4 &#181;g/mL x 0.025 mL = 0.56 &#181;g).
	<ol>
		<li>Prepare 2.5 mL of cell adhesive solution (22.4 &#181;g/mL) in 0.1 M sodium bicarbonate, pH 8.0. Bicarbonate provides the optimum pH for cell adherent performance which, according to the manufacturer, is between 6.5 and 8.0.</li>
		<li>Pipette 25 &#181;L of the cell adhesive solution to each well of the assay plate and incubate at room temperature for 20 min. After that, remove the solution and wash 2x with 200 &#181;L of sterile water/well. Let the wells dry by keeping the plate open for 15 minutes inside a cell culture hood. 
		NOTE: Coated plates may be stored for up to 1 week at 4 &#176;C.</li>
	</ol>
	</li>
	<li>Cell seeding in plates coated with adhesive
	<ol>
		<li>Centrifuge cells from step 2.4.3&#160;at 200 x g for 5 min at room temperature. Remove supernatants and wash cells in warmed mitochondrial stress test medium (if a mitochondrial stress test is being performed) or glycolysis stress test medium (if a glycolysis stress test is being performed). Pellet cells again and resuspend to the preferred cell concentration in the same medium (resuspension volume will depend on the cell concentration chosen; since each well will contain 180 &#181;L of the cell suspension, prepare 0.26 x 106, 0.52 x 106, 1.04 x 106, 2.08 x 106, 4.17 x 106 and 8.33 x 106 cells/mL cell suspensions for 0.047 x 106, 0.094 x 106, 0.187 x 106, 0.375 x 106, 0.75 x 106 and 1. 5 x 106 cells per well respectively).</li>
		<li>Plate 180 &#181;L of cell suspension per well along the side of each well. A multichannel pipette is recommended. Use wells A1, A12, H1, and H12 of the analyzer culture plate as control wells for background correction. Add 180 &#181;L of the assay medium in these wells (no cells). Additional control wells can be used if desired and if there is enough space in the plate. 
		NOTE: The presence of serum may cause poor cell attachment.</li>
		<li>Incubate the plate for 30 min at 37 &#176;C in a CO2-free incubator. Prepare 10x compounds in the meantime (see step 4.3 below).</li>
		<li>Change the centrifuge settings to zero braking. Centrifuge the plate at 200 x g for 5 min. Observe the cells under the microscope to check that they form a monolayer at the bottom of the well. Transfer the plates back to the CO2-free incubator for 25 min. For best results, total time after plating should be no greater than around 1 h.</li>
	</ol>
	</li>
	<li>Preparation of 10x working solutions to load into sensor cartridge 
	NOTE: Each of the 96 probe tips of the sensor cartridge harbors 4 ports (A, B, C and D) that can be used to inject compounds sequentially into individual wells.
	<ol>
		<li>To perform mitochondrial stress test, prepare 2.5 mL each of 10 &#181;M oligomycin, 1 mM DNP, and a mixture of 10 &#181;M rotenone and 10 &#181;M antimycin A, in mitochondrial stress assay medium (use the stock solutions from step 1.2.3). Final concentrations in the well after injection will be 1 &#181;M oligomycin, 0.1 mM DNP and 1 &#181;M antimycin A/rotenone.</li>
		<li>To perform glycolysis stress test, prepare 2.5 mL of a mixture of 10 &#181;M rotenone and 10 &#181;M antimycin A in glycolysis stress assay medium (use the stock solutions from step 1.2.3). Dissolve glucose in glycolysis stress test medium for a 100 mM solution and 2-deoxy-glucose (2-DG) in glycolysis stress test medium for a 500 mM solution. Final concentrations in the well after injection will be 10 mM glucose, 1 &#181;M antimycin A/rotenone and 50 mM 2-DG.</li>
		<li>Warm solutions to 37 &#176;C, check pH and readjust to 7.4 if required. Load compounds prepared in step 4.3.1. (for a mitochondrial stress test) or 4.3.2 (for a glycolysis stress test) into ports A, B and C of the hydrated sensor cartridge (from step 3.2) using a multichannel micropipettor and the port-loading guides provided with the cartridge, as shown in Table 2. 
		NOTE: To ensure proper injection in all wells during the assay, each series of ports that are used (e.g., all ports A) must contain the same injection volume across the entire sensor cartridge. This applies to background correction wells and even to those wells not used in the experiment.</li>
		<li>Incubate the loaded sensor cartridge at 37 &#176;C in a CO2-free incubator while setting up the program.</li>
	</ol>
	</li>
	<li>Setting up extracellular flux assay protocols
	<ol>
		<li>Open the extracellular flux analyzer software, and using the Group Definitions and Plate Map tabs indicate groups of wells that have similar conditions (e.g., wells with the same number of cells, or wells with either resting cells or IL-15-stimulated cells). Also, indicate background correction wells (by default A1, A12, H1, and H12 will be set, but additional wells can be used) and empty wells.</li>
		<li>Set up the program described in Table 3 in the software using the Protocol tab.</li>
		<li>Begin the program using the Run Assay tab. Place the sensor cartridge (hydrated and loaded with 10x compounds) and utility plate onto the tray. After the calibration step (15 &#8211; 20 min), when prompted, replace the calibrant plate for the assay plate (without lid) with attached cells. After this, the run is fully automated (the machine will perform all measurements and injections). 
		NOTE: It is possible to perform a mitochondrial stress test and a glycolytic stress test in the same plate, as long as the specific compounds are loaded into the proper ports (oligomycin, DNP and antimycin/rotenone in ports A, B and C respectively of the wells where a mitochondrial stress test is performed; glucose, antimycin/rotenone and 2-DG in ports A, B and C respectively of the wells where a glycolysis stress test is performed), the same volumes for injections are used in each series of ports and wells for each test are properly identified using the Group Definitions and Plate Map tabs of the software.</li>
		<li>After the completion of the run, retrieve the data and analyze them using the software.</li>
	</ol>
	</li>
</ol>
5. Cell number determination
NOTE: Results can be normalized to account for possible differences in cell number. Two major approaches described below can be used.
<ol>
	<li>DNA content determination
	<ol>
		<li>Remove the remaining assay medium with a pipette from each well. When aspirating medium, take care not to disturb the cells. The plate can be stored at -20 &#176;C until analysis. 
		NOTE: The freezing step is important for the efficient cell lysis and DNA content determination.</li>
		<li>Prepare a 1x solution of cell proliferation assay cell-lysis buffer (20x) in distilled water (200 &#181;L/well).</li>
		<li>Add the cell proliferation assay dye stock solution (400x) into the 1x cell-lysis buffer. For the detection of 50 to 50.000 cells per well, use 1x cell proliferation assay dye. For higher cell numbers, using the cell proliferation assay dye at a final concentration higher than 1x is recommended. In this case, use the cell proliferation assay dye at a 5x final concentration (dilute the cell proliferation assay stock solution 80-fold into 1x cell-lysis buffer).</li>
		<li>Add 200 &#181;L of the cell proliferation assay reagent to each well. Incubate the samples for 2&#8211;5 min at room temperature. Protect from light.</li>
		<li>Measure the fluorescence of the samples at excitation: 480 nm; emission: 520 nm using a fluorescence microplate reader according to manufacturer&#39;s recommendations.</li>
	</ol>
	</li>
	<li>Protein content determination
	<ol>
		<li>Carefully, aspirate completely the assay medium from each well without touching the cells and freeze the cells at -20 &#730;C for at least 1 h. Alternatively, the cells can be kept frozen for longer times (up to 1 week) until the analysis&#160;is performed.</li>
		<li>Add 50 &#181;L of radioimmunoprecipitation assay (RIPA) lysis medium supplemented with 1x protease inhibitors (from a 100x stock solution) to each well. Place the plate on a shaker for 5 min at room temperature, and then incubate the plate on ice for 30 min for a complete cell lysis.</li>
		<li>Centrifuge the plate for 5 min at 200 x g at room temperature. This step will pellet cellular debris to prevent interference with the protein measurement.</li>
		<li>Measure protein concentration by bicinchoninic acid (BCA) assay according to manufacturer&#39;s recommendations.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Long, E. O., Kim, H. S., Liu, D., Peterson, M. E., Rajagopalan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+natural+killer+cell+responses:+integration+of+signals+for+activation+and+inhibition.">Controlling natural killer cell responses: integration of signals for activation and inhibition.</a> Annual Review of Immunology. 31, 227-258 (2013).</li><li>Caligiuri, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+natural+killer+cells.">Human natural killer cells.</a> Blood. 112 (3), 461-469 (2008).</li><li>Anton, O. M., Vielkind, S., Peterson, M. E., Tagaya, Y., Long, E. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NK+Cell+Proliferation+Induced+by+IL-15+Transpresentation+Is+Negatively+Regulated+by+Inhibitory+Receptors.">NK Cell Proliferation Induced by IL-15 Transpresentation Is Negatively Regulated by Inhibitory Receptors.</a> Journal of Immunology. 195 (10), 4810-4821 (2015).</li><li>Henney, C. S., Kuribayashi, K., Kern, D. E., Gillis, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interleukin-2+augments+natural+killer+cell+activity.">Interleukin-2 augments natural killer cell activity.</a> Nature. 291 (5813), 335-338 (1981).</li><li>Anton, O. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trans-endocytosis+of+intact+IL-15Ralpha-IL-15+complex+from+presenting+cells+into+NK+cells+favors+signaling+for+proliferation.">Trans-endocytosis of intact IL-15Ralpha-IL-15 complex from presenting cells into NK cells favors signaling for proliferation.</a> Proceedings of the National Academy of Sciences of the United States of America. 117 (1), 522-531 (2020).</li><li>Marcais, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+metabolic+checkpoint+kinase+mTOR+is+essential+for+IL-15+signaling+during+the+development+and+activation+of+NK+cells.">The metabolic checkpoint kinase mTOR is essential for IL-15 signaling during the development and activation of NK cells.</a> Nature Immunology. 15 (8), 749-757 (2014).</li><li>Mookerjee, S. A., Nicholls, D. G., Brand, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+Maximum+Glycolytic+Capacity+Using+Extracellular+Flux+Measurements.">Determining Maximum Glycolytic Capacity Using Extracellular Flux Measurements.</a> PloS One. 11 (3), 0152016 (2016).</li><li>Brand, M. D., Nicholls, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessing+mitochondrial+dysfunction+in+cells.">Assessing mitochondrial dysfunction in cells.</a> Biochemical Journal. 435 (2), 297-312 (2011).</li><li>Cheng, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+Proton+Leak+Plays+a+Critical+Role+in+Pathogenesis+of+Cardiovascular+Diseases.">Mitochondrial Proton Leak Plays a Critical Role in Pathogenesis of Cardiovascular Diseases.</a> Advances in Experimental Medicine and Biology. 982, 359-370 (2017).</li><li>Terren, I., Orrantia, A., Vitalle, J., Zenarruzabeitia, O., Borrego, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NK+Cell+Metabolism+and+Tumor+Microenvironment.">NK Cell Metabolism and Tumor Microenvironment.</a> Frontiers in Immunology. 10, 2278 (2019).</li><li>Felices, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+treatment+with+IL-15+exhausts+human+NK+cells+via+a+metabolic+defect.">Continuous treatment with IL-15 exhausts human NK cells via a metabolic defect.</a> Journal of Clinical Investigation Insight. 3 (3), 96219 (2018).</li><li>Miller, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+First-in-Human+Phase+I+Study+of+Subcutaneous+Outpatient+Recombinant+Human+IL15+(rhIL15)+in+Adults+with+Advanced+Solid+Tumors.">A First-in-Human Phase I Study of Subcutaneous Outpatient Recombinant Human IL15 (rhIL15) in Adults with Advanced Solid Tumors.</a> Clinical Cancer Research. 24 (7), 1525-1535 (2018).</li><li>Conlon, K. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IL15+by+Continuous+Intravenous+Infusion+to+Adult+Patients+with+Solid+Tumors+in+a+Phase+I+Trial+Induced+Dramatic+NK-Cell+Subset+Expansion.">IL15 by Continuous Intravenous Infusion to Adult Patients with Solid Tumors in a Phase I Trial Induced Dramatic NK-Cell Subset Expansion.</a> Clinical Cancer Research. 25 (16), 4945-4954 (2019).</li><li>Dubois, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IL15+Infusion+of+Cancer+Patients+Expands+the+Subpopulation+of+Cytotoxic+CD56(bright)+NK+Cells+and+Increases+NK-Cell+Cytokine+Release+Capabilities.">IL15 Infusion of Cancer Patients Expands the Subpopulation of Cytotoxic CD56(bright) NK Cells and Increases NK-Cell Cytokine Release Capabilities.</a> Cancer Immunology Research. 5 (10), 929-938 (2017).</li><li>Traba, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fasting+and+refeeding+differentially+regulate+NLRP3+inflammasome+activation+in+human+subjects.">Fasting and refeeding differentially regulate NLRP3 inflammasome activation in human subjects.</a> Journal of Clinical Investigation. 125 (12), 4592-4600 (2015).</li><li>Traba, J., Miozzo, P., Akkaya, B., Pierce, S. K., Akkaya, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Optimized+Protocol+to+Analyze+Glycolysis+and+Mitochondrial+Respiration+in+Lymphocytes.">An Optimized Protocol to Analyze Glycolysis and Mitochondrial Respiration in Lymphocytes.</a> Journal of Visualized Experiments. (117), e54918 (2016).</li><li>Horan, M. P., Pichaud, N., Ballard, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review:+quantifying+mitochondrial+dysfunction+in+complex+diseases+of+aging.">Review: quantifying mitochondrial dysfunction in complex diseases of aging.</a> Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. 67 (10), 1022-1035 (2012).</li><li>Tognarelli, S., Jacobs, B., Staiger, N., Ullrich, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+Cytometry-based+Assay+for+the+Monitoring+of+NK+Cell+Functions.">Flow Cytometry-based Assay for the Monitoring of NK Cell Functions.</a> Journal of Visualized Experiments. (116), e54615 (2016).</li><li>Theorell, J., Bryceson, Y. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+Intracellular+Ca(2+)+Mobilization+in+Human+NK+Cell+Subsets+by+Flow+Cytometry.">Analysis of Intracellular Ca(2+) Mobilization in Human NK Cell Subsets by Flow Cytometry.</a> Methods in Molecular Biology. 1441, 117-130 (2016).</li><li>Mookerjee, S. A., Gerencser, A. A., Nicholls, D. G., Brand, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+intracellular+rates+of+glycolytic+and+oxidative+ATP+production+and+consumption+using+extracellular+flux+measurements.">Quantifying intracellular rates of glycolytic and oxidative ATP production and consumption using extracellular flux measurements.</a> Journal of Biological Chemistry. 292 (17), 7189-7207 (2017).</li><li>O'Brien, K. L., Finlay, D. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunometabolism+and+natural+killer+cell+responses.">Immunometabolism and natural killer cell responses.</a> Nature Reviews: Immunology. 19 (5), 282-290 (2019).</li><li>Ahn, B. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+role+for+the+mitochondrial+deacetylase+Sirt3+in+regulating+energy+homeostasis.">A role for the mitochondrial deacetylase Sirt3 in regulating energy homeostasis.</a> Proceedings of the National Academy of Sciences of the United States of America. 105 (38), 14447-14452 (2008).</li><li>Stram, A. R., Payne, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Post-translational+modifications+in+mitochondria:+protein+signaling+in+the+powerhouse.">Post-translational modifications in mitochondria: protein signaling in the powerhouse.</a> Cellular and Molecular Life Sciences. 73 (21), 4063-4073 (2016).</li><li>Armstrong, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxidative+stress+alters+mitochondrial+bioenergetics+and+modifies+pancreatic+cell+death+independently+of+cyclophilin+D,+resulting+in+an+apoptosis-to-necrosis+shift.">Oxidative stress alters mitochondrial bioenergetics and modifies pancreatic cell death independently of cyclophilin D, resulting in an apoptosis-to-necrosis shift.</a> Journal of Biological Chemistry. 293 (21), 8032-8047 (2018).</li><li>Mookerjee, S. A., Goncalves, R. L. S., Gerencser, A. A., Nicholls, D. G., Brand, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+contributions+of+respiration+and+glycolysis+to+extracellular+acid+production.">The contributions of respiration and glycolysis to extracellular acid production.</a> Biochimica et Biophysica Acta. 1847 (2), 171-181 (2015).</li><li>Mookerjee, S. A., Brand, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+and+Analysis+of+Extracellular+Acid+Production+to+Determine+Glycolytic+Rate.">Measurement and Analysis of Extracellular Acid Production to Determine Glycolytic Rate.</a> Journal of Visualized Experiments. (106), e53464 (2015).</li><li>Lichtshtein, D., Kaback, H. R., Blume, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+a+lipophilic+cation+for+determination+of+membrane+potential+in+neuroblastoma-glioma+hybrid+cell+suspensions.">Use of a lipophilic cation for determination of membrane potential in neuroblastoma-glioma hybrid cell suspensions.</a> Proceedings of the National Academy of Sciences of the United States of America. 76 (2), 650-654 (1979).</li><li>Michelet, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+reprogramming+of+natural+killer+cells+in+obesity+limits+antitumor+responses.">Metabolic reprogramming of natural killer cells in obesity limits antitumor responses.</a> Nature Immunology. 19 (12), 1330-1340 (2018).</li></ol>

The authors declare that they have no competing financial interests.

In this paper, we have established a protocol for efficiently isolating and culturing pure and viable primary human NK cells from peripheral blood. We have also optimized the conditions for the measurement of the metabolic activity of these NK cells assessed by oxygen consumption rate and extracellular acidification rate by using an extracellular flux analyzer. Compared to other respirometric methods, the extracellular flux analyzer is fast, requires small numbers of cells, and allows high throughput screenings. However, its reagents are expensive, and injections of compounds are limited to just four. Metabolic remodeling and activation of glycolysis and oxidative phosphorylation by cytokines in NK cell is essential for robust NK cell responses21, and the techniques described here allow the study of the metabolic profile of NK cells in real time. This protocol could be extended to cells activated by other cytokines, such as IL-2, IL-12 and IL-18, or antibodies that bind to activating receptors. We have addressed several key steps that are often overlooked, such as plating the cells at the optimal confluence or using the optimal concentration of uncoupler to stimulate maximal oxygen consumption. Nevertheless, we recommend checking the actual O2 level curves (Figure 3C), if other stimuli different to IL-15 are given to the cells, to make sure that O2 is not being depleted in the wells. If that was the case, the cell number should be decreased until a linear O2 consumption is observed to prevent an underestimation of the real OCR.
Basal respiration reflects the basal metabolic state of the cell, which is largely controlled by the activity of the mitochondrial ATP synthase8, and is an indication of the basal ATP demand (for protein synthesis, cytoskeleton dynamics, ATPases such as the Na+/K+-ATPase, etc). Typically, in the presence of sufficient substrates this parameter increases in metabolically active or stressed cells. Addition of oligomycin, which blocks the ATP synthase, reveals ATP-linked respiration and the proton leak, which can happen across the lipid bilayer or proteins of the inner mitochondrial membrane, but can also be inducible through proteins such as the Uncoupling Proteins (UCPs)9, implicated in the regulation of adaptive thermogenesis and thus converting mitochondrial energy potential to heat in brown adipocytes. Maximal respiration is determined by factors including the availability of substrates for the mitochondrial respiratory chain and the amount and activity of respiratory complexes. Mitochondrial respiratory complexes and their activity can also be modified by posttranslational modifications such as acetylation or phosphorylation22,23. This parameter can also indicate the health of the cells and their capacity for responding to acute insults. Under situations of mitochondrial dysfunction, maximal respiration decreases, and this limits the capacity of the cell to respond to changes in ATP demand and leads to cell death24.
It is very important to remark that, for every time point of the mitochondrial and glycolysis stress tests, ECAR is the sum of glycolysis-derived acidification (via generation of lactate + H+) and respiratory-derived acidification (via generation of CO2, which dissolves in H2O to generate HCO3- and H+), and importantly, respiratory-derived acidification may account for a substantial proportion of the total ECAR in some cell types25. For interested researchers, there are published protocols to calculate actual glycolytic rates. To that end, oxygen consumption rates during the glycolytic stress test (Figure 4G) can be used to calculate the proton production rate by respiration at each time point, and that value can be subtracted from the total proton production rate, which is obtained using ECAR values and the buffering power of the medium7,25,26.
An important modification of this protocol compared to the manufacturer&#8217;s recommendation is the second injection of the glycolysis stress test. Antimycin A and rotenone are preferred to oligomycin, for several reasons that have already been described7: 1) some cells display a high glycolytic capacity that may fully meet the basal ATP demand of the cell, even in the absence of oxidative phosphorylation; 2) blocking the ETC with antimycin A and rotenone artificially increases the ATP demand of the cell, as it causes ATP hydrolysis by the ATP synthase (the mitochondria become an ATP sink), which reverses to pump protons in an attempt to recover the mitochondrial membrane potential that collapses after respiratory inhibition; 3) blocking the ETC prevents respiratory acidification of the medium (respiratory CO2 generated in the TCA cycle that is converted to HCO3- and H+) which can confound the ECAR results. Thus, observed maximal ECAR with antimycin A and rotenone is only attributable to glycolysis. Interestingly, it has been reported that the ECAR observed with respiratory inhibitors alone may still be submaximal7, and an additional mechanism to increase cellular ATP demand (and therefore maximal ECAR) has been described: the addition of the ionophore monensin, which increases the import of Na+ into the cell27 and stimulates the rate of ATP hydrolysis by the plasma membrane Na+/K+-ATPase, to the mixture of antimycin A and rotenone7.
A second important concept is that we do not recommend the subtraction of the non-glycolytic acidification, which probably corresponds to respiratory CO2 that is converted to HCO3- and H+, from the entire trace to calculate glycolytic parameters as recommended by the manufacturer, as this amount changes considerably during each stage of the Glycolysis Stress Test (it is highest in the basal state, decreases after addition of glucose due to the Crabtree effect20, and is virtually abolished with antimycin A and rotenone) (Figure 5).
To summarize, this protocol shows a simple and efficient tool to test the metabolic activity of human natural killer cells with an extracellular flux analyzer. This method can be used to interrogate the metabolic state in these cells, which is known to change with cell activation by cytokine stimulation or under certain pathological conditions, including obesity, cancer or viral infections28.

Natural Killer (NK) cells are innate lymphocytes that mediate anti-tumor and anti-viral responses. NK cells comprise 5-15% of all lymphocytes in human peripheral blood, and can be also found in spleen, liver, bone marrow and lymph nodes. NK cells do not express polymorphic clonotypic receptors, such as T-cell receptors (TCR) or B-cell receptors (BCR). In contrast, the activation of their cytolytic functions is prompted by the engagement of receptors that recognize invariable ligands on the surface of a target cell1,2.
Resting human NK cells isolated from peripheral blood can survive for several days in culture medium supplemented with human serum. Activation of NK cells by cytokines such as IL-15 or IL-2 drives the cells to proliferation and to an increase of their killing ability, amongst other effects3,4,5. Several studies have shown a direct correlation between NK cell activation and changes in their metabolic activity6. These metabolic changes are destined to meet the particular requirements of the cells in terms of energy and biosynthesis.
Aerobic cells and organisms obtain energy through a series of chemical reactions that involve the catabolism and oxidation of carbohydrates, fat and proteins. Through a combination of glycolysis, the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, eukaryotic cells meet the majority of their ATP demand and obtain intermediates required as building blocks for macromolecules essential for cell growth and proliferation. The process of glycolysis (Figure 1A) starts with the entry of glucose in the cell. In the cytosol, glucose is phosphorylated and transformed into pyruvate (with a net production of 2 molecules of ATP per glucose molecule), which can be reduced to lactate or transported into the mitochondria to be transformed into Acetyl-CoA and enter the TCA cycle. The TCA cycle continues cycling fueled with more molecules of Acetyl-CoA and produces CO2 (that eventually will diffuse outside the cell and, by reacting with H2O in the medium, will generate carbonic acid that will lead to the acidification of the medium) and NADH, the molecule in charge of donating electrons to the electron transport chain (ETC). The electrons travel through different protein complexes and are finally accepted by oxygen. These complexes (I, III and IV) also pump H+ from the mitochondrial matrix into the intermembrane space. As a consequence of the electrochemical gradient generated, the H+ will enter again to the matrix through the complex V (ATP-synthase), investing the potential energy accumulated into the generation of ATP.
Both glycolysis and mitochondrial respiration can be blocked at different points by using inhibitors. The knowledge and usage of these inhibitors was the basis for the development of the extracellular flux assay. By measuring two simple parameters in real time such as pH and oxygen, the extracellular flux analyzer infers the rate of glycolysis and mitochondrial respiration in a 96-well plate. The glycolysis stress test is performed in a basal medium without glucose (Figure 1B)7. The first measurements of the extracellular acidification rate (ECAR) are indicative of glycolysis-independent acidification. It is referred to as non-glycolytic acidification and correlates with CO2 produced by the TCA that, as explained before, combines with H2O in the medium to generate H+ (TCA-linked ECAR). The first injection is glucose to induce glucose utilization and boost glycolysis. The second injection combines both rotenone, a Complex I inhibitor, and antimycin A, a Complex III inhibitor together, to block the ETC. Cells respond to this dramatic decrease in mitochondrial ATP production by activating glycolysis to maintain cellular ATP levels, and this represents the amount of glycolysis that is not used by the cell in the basal state but could be potentially recruited in response to increases in ATP demand (compensatory glycolysis). The third injection is the glucose analog 2-Deoxyglucose (DG), which competes with glucose as a substrate for the enzyme hexokinase. The product of this phosphorylation, 2-deoxyglucose-6-phosphate cannot be transformed into pyruvate, and therefore glycolysis is blocked, which lowers the ECAR to its minimum. The ECAR measured at this point includes other sources of extracellular acidification that are not attributed to glycolysis or respiratory activity as well as any residual glycolysis not fully inhibited by 2-DG (post 2-DG-acidification).
The mitochondrial stress test is performed in a medium with glucose (Figure 1C)8. The first measurements of the oxygen consumption rate (OCR) correspond to the base line of mitochondrial respiration (basal respiration). The first injection is oligomycin, which inhibits the return of protons through the ATP synthase (complex V), blocking ATP synthesis and thus rapidly hyperpolarize the mitochondrial membrane, which prevents further proton pumping through respiratory complexes, and leads to a decrease in OCR. The comparison between the baseline respiration and the value given by addition of oligomycin represents the ATP-linked respiration. The remaining oligomycin-insensitive rate of oxygen consumption is called proton leak, which represents the flow of protons through the lipid bilayer or proteins in the inner mitochondrial membrane such as the adenine nucleotide translocase9. The second injection is the uncoupler 2,4-dinitrophenol (DNP), an ionophore that induces a massive entry of H+ into the mitochondrial matrix, which leads to depolarization of the mitochondrial membrane and disruption of mitochondrial ATP synthesis. Cells respond to the dissipation of the proton-motive force by increasing the rate of electron transport and oxygen consumption to maximum levels in a futile attempt to recover membrane potential (maximal respiratory capacity). The difference between the maximal respiratory capacity and the basal respiration is the spare respiratory capacity of the cell, which represents the amount of respiration that is not used by the cell to generate ATP in the basal state but could be potentially recruited in response to increases in ATP demand or under conditions of stress8. The third injection is a combination of rotenone and antimycin A. This injection completely stops the ETC and OCR decreases to its lowest level, with the remaining oxygen consumption being non-mitochondrial (caused by NADPH-oxidases, etc.).
Changes in metabolic pathways could somehow predict the functioning of NK cells, as it has been suggested that continuous activation of NK cells with cytokines in vitro could lead to NK cell exhaustion by the study of different metabolic pathways10,11. The correlation between NK cell metabolic status and function is very important from the point of view of cancer immunotherapy. In this field, activation of NK cells with infusion of IL-15, alone or in combination with monoclonal therapeutic antibodies have been tested in order to improve tumor cell killing12,13,14. The knowledge of the metabolic status of the NK cells in response to these treatment strategies would provide a valuable predictor of NK cell activation status and killing function.
The study of metabolic pathways in other myeloid and lymphoid cells such as monocytes, T and B cells has been described15 and optimized methods have been published16. In this protocol we provide a method that combines both an NK isolation protocol that yields high numbers of pure and viable NK cells and an optimized protocol to measure metabolic activity using an extracellular flux analyzer. Here we show that this is a valid method for the study of metabolic changes in resting and IL-15 activated human NK cells. For the extracellular flux assay, parameters such as cell number and drug concentrations have been tested and optimized. Compared with other respirometric methods, the extracellular flux analyzer is fully automated and able to test in real time, with very low quantities of cells, up to 92 samples simultaneously, and thus allows high throughput screenings (with multiple samples and replicates) in a relatively quick manner17.
This method can be used by researchers interested in assessing NK cell function by studying NK cell metabolism. It could be applied as well to cells activated by other cytokines, antibodies or soluble stimuli.

<table><tbody><tr><td>2-Deoxy-D-glucose (2-DG)</td><td>MilliporeSigma</td><td>D8375-5G</td><td>Glycolyisis stress test injector compound</td></tr><tr><td>2,4-Dinotrophenol (2,4-DNP)</td><td>MilliporeSigma</td><td>D198501</td><td>ETC uncoupler / mitochondrial stress test injector compound</td></tr><tr><td>96 Well Cell Culture Plate/ Round bottom with Lid</td><td>Costar</td><td>3799</td><td>NK cell culture</td></tr><tr><td>Antimycin A</td><td>MilliporeSigma</td><td>A8674</td><td>Complex III inhibitor / glycolysis and mitochondrial stress test injector compound</td></tr><tr><td>BD FACSDIVA Software</td><td>BD Biosciences</td><td></td><td>Flow data acquisition</td></tr><tr><td>BD LSR Fortessa</td><td>BD Biosciences</td><td></td><td>Flow data acquisition</td></tr><tr><td>Cell-Tak</td><td>Corning</td><td>354240</td><td>Cell adhesive</td></tr><tr><td>CyQUANT cell proliferation assay</td><td>ThermoFisher Scientific</td><td>C7026</td><td>Cell proliferation Assay for DNA quantification. Contains cell-lysis buffer and CyQUANT GR dye</td></tr><tr><td>EasySep Human CD3 Positive Selection Kit II</td><td>Stemcell technologies</td><td>17851</td><td>NK cell isolation from PBMCs</td></tr><tr><td>EasySep Human NK cell Enrichment Kit</td><td>Stemcell technologies</td><td>19055</td><td>NK cell isolation from PBMCs</td></tr><tr><td>EasySep Magnet</td><td>Stemcell technologies</td><td>18001</td><td>NK cell isolation from PBMCs</td></tr><tr><td>EDTA 0.5 M, pH 8</td><td>Quality Biological</td><td>10128-446</td><td>NK sell separation buffer</td></tr><tr><td>FACS tubes</td><td>Falcon-Fisher Scientific</td><td>352235</td><td>Flow cytometry experiment</td></tr><tr><td>Falcon 50 ml Conical tubes</td><td>Falcon-Fisher Scientific</td><td>14-432-22</td><td>NK cell separation</td></tr><tr><td>Fetal Calf Serum (FCS)</td><td>Gibco</td><td>10437-028</td><td>NK cell separation buffer</td></tr><tr><td>FlowJo Software</td><td>BD Biosciences</td><td></td><td>Flow data analysis</td></tr><tr><td>Glucose</td><td>MilliporeSigma</td><td>G8270</td><td>Component of mitochondrial stress test medium. Glycolysis stress test injector compound</td></tr><tr><td>Halt Protease Inhibitor Cocktail</td><td>ThermoFisher Scientific</td><td>78429</td><td>Protease inhibitor 100X. Use in RIPA lysis buffer</td></tr><tr><td>Human IL-15</td><td>Peprotech</td><td>200-15-50ug</td><td>NK cell stimulation</td></tr><tr><td>Human serum (HS)</td><td>Valley Biomedical</td><td>9C0539</td><td>NK cell culture medium supplement</td></tr><tr><td>IMDM</td><td>Gibco</td><td>12440053</td><td>NK cell culture medium</td></tr><tr><td>L-Glutamine (200 mM)</td><td>ThermoFisher Scientific</td><td>25030-081</td><td>Component of stress test media</td></tr><tr><td>LIVE/DEAD Fixable Aqua Dead Cell Stain Kit</td><td>ThermoFisher Scientific</td><td>L34965</td><td>Viability dye for flow cytometry staining</td></tr><tr><td>LSM</td><td>mpbio</td><td>50494X</td><td>PBMCs separation from human blood</td></tr><tr><td>Mouse anti-human CD3 BV711</td><td>BD Biosciences</td><td>563725</td><td>T cell flow cytometry staining</td></tr><tr><td>Mouse anti-human CD56 PE</td><td>BD Pharmingen</td><td>555516</td><td>NK flow cytometry staining</td></tr><tr><td>Mouse anti-human NKp46 PE</td><td>BD Pharmingen</td><td>557991</td><td>NK flow cytometry staining</td></tr><tr><td>Oligomycin</td><td>MilliporeSigma</td><td>75351</td><td>Complex V inhibitor / mitochondrial stress test injector compound</td></tr><tr><td>PBS pH 7.4</td><td>Gibco</td><td>10010-023</td><td>NK cell separation buffer</td></tr><tr><td>Pierce BCA Protein Assay Kit</td><td>ThermoFisher Scientific</td><td>23225</td><td>For determination of protein concentration</td></tr><tr><td>RIPA Buffer</td><td>Boston BioProducts</td><td>BP-115</td><td>Cell lysis</td></tr><tr><td>Rotenone</td><td>MilliporeSigma</td><td>R8875</td><td>Complex II inhibitor / glycolysis and mitochondrial stress test injector compound</td></tr><tr><td>Seahorse Wave Controller Software</td><td>Agilent</td><td></td><td>Controller for the Seahorse XFe96 Analyzer</td></tr><tr><td>Seahorse Wave Desktop Software</td><td>Agilent</td><td></td><td>For data analysis</td></tr><tr><td>Seahorse XF Base Medium</td><td>Agilent</td><td>102353-100</td><td>Extracellular Flux assay base medium</td></tr><tr><td>Seahorse XFe96 Analyzer</td><td>Agilent</td><td></td><td>Extracellular Flux Analyzer</td></tr><tr><td>Seahorse XFe96 FluxPak</td><td>Agilent</td><td>102416-100</td><td>Includes 20 XF96 cell culture plates, 18 XFe96 sensor cartridges, loading guides for transferring compounds to the assay cartridge, and 1 bottle of calibrant solution (500 ml).</td></tr><tr><td>Sodium bicarbonate</td><td>MilliporeSigma</td><td>S5761</td><td>To prepare the Cell-Tak solution</td></tr><tr><td>Sodium pyruvate (100 mM)</td><td>ThermoFisher Scientific</td><td>11360-070</td><td>Component of mitochondrial stress test medium</td></tr></tbody></table>

analysis of human natural killer cell metabolism

Natural Killer (NK) cells mediate mainly innate anti-tumor and anti-viral immune responses and respond to a variety of cytokines and other stimuli to promote survival, cellular proliferation, production of cytokines such as interferon gamma (IFN&#947;) and/or cytotoxicity programs. NK cell activation by cytokine stimulation requires a substantial remodeling of metabolic pathways to support their bioenergetic and biosynthetic requirements. There is a large body of evidence that suggests that impaired NK cell metabolism is associated with a number of chronic diseases including obesity and cancer, which highlights the clinical importance of the availability of a method to determine NK cell metabolism. Here we describe the use of an extracellular flux analyzer, a platform that allows real-time measurements of glycolysis and mitochondrial oxygen consumption, as a tool to monitor changes in the energy metabolism of human NK cells. The method described here also allows for the monitoring of metabolic changes after stimulation of NK cells with cytokines such as IL-15, a system that is currently being investigated in a wide range of clinical trials.

Isolation of NK cells from peripheral blood provides a pure and viable population
The extracellular flux assay is based on the measurement of H+ and O2 concentration in the well and will not distinguish among different populations of cells or their viability. For this reason, obtaining a highly pure and viable population of the cell of interest was the key step to succeed in these experiments.
The isolation of NK cells from peripheral blood was performed as stated in section 2. In order to assess the purity and viability of the NK cells obtained, small aliquots from PMBCs and the isolated NK cell population were stained and analyzed by flow cytometry (Figure 2A). Mononuclear cells were gated in the plot showing forward (FSC-A) versus side scatter area (SSC-A). Within this population, single cells were gated along the diagonal in the plot showing FSC-A versus forward scatter height (FSC-H). Within the singlet populations, viability was assessed, and found to be higher than 98% in both, PMBCs and NK cell populations. The purity of the NK cell population isolated was established by double staining against CD3 (present in T cells, the dominant population among PBMCS) and CD56 or NKp46 (Figure 2B). NK cells are defined as the population negative for CD3 and positive for CD56 or NKp46. According to these criteria, the purity of the NK cells was around 88%, which represents an 18-fold enrichment on NK cells compared to those present in the PBMCs population.
OCR and ECAR values are dependent on cell number
For the mitochondrial stress test, cells were metabolically perturbed by the addition of three different compounds: oligomycin, DNP and antimycin A + rotenone. For every cell type, the number of cells per well were carefully optimized for an extracellular flux assay experiment. Figure 3A shows representative plots of mitochondrial oxygen consumption rate (OCR) using several human NK cell numbers (0.75 x 106, 0.375 x 106, 0.187 x 106, 0.094 x 106 and 0.047 x 106). All measurements were done in triplicate. Cell numbers correlate linearly with the amount of DNA or protein in the well (Figure 3B). As expected, high cell numbers displayed higher OCR values, whereas fewer than 0.187 x 106 cells per well did not provide robust results. On the other hand, higher cell numbers (1.5 x 106) were not optimal, as upon addition of DNP, the oxygen concentration in the well was totally depleted in each cycle (Figure 3C), which precludes the accurate calculation of the OCR. The concentration of uncoupler must be titrated carefully for each cell type, as not adding sufficient DNP results in submaximal OCR, whereas adding too much may inhibit maximal OCR as well. In human NK cells, 100 &#181;M DNP was found to be the optimal dose (Figure 3D). Other uncouplers such as carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP) or carbonyl cyanide m-chlorophenyl hydrazine (CCCP) may be used instead of DNP but would need to be titrated for each cell type as well.
For the glycolysis stress test, after a baseline measurement of the ECAR, glucose-starved cells were perturbed by the following compounds: glucose, antimycin A + rotenone and 2-DG. Figure 3E shows representative plots of ECAR using several NK cells numbers (0.75 x 106, 0.375 x 106, 0.187 x 106, 0.094 x 106 and 0.047 x 106). All measurements were done in triplicate. The glycolysis stress assay was most successful at the highest plating density, whereas fewer than 0.187 x 106 cells per well did not provide robust results.
IL-15 treatment increases OCR and ECAR basal and maximal values
The optimal seeding density of 0.75 x 106 cells per well was used for subsequent experiments. NK cells were cultured in the presence or absence of saturating concentrations of the cytokine IL-15 for 48 h, after which time their viability was found to be 93.7 &#177; 4.8% and 85.7 &#177; 12.0%, respectively. Figure 4A,B shows a typical mitochondrial stress test experiment with 0.75 x 106 NK cells per well. In this test, oligomycin leads to a dramatic decrease in oxygen consumption (Figure 4A) and to an increase in ECAR that represents a switch to glycolysis to try to maintain cellular ATP levels (Figure 4B). Activation of the NK cell by IL-15 caused an increase in both mitochondrial oxygen consumption and extracellular acidification. This result was consistent when several human subjects were compared (Figure 4C). Basal, maximal and ATP-linked respiration, but not proton leak or non-mitochondrial respiration, increased with IL-15 (Figure 4C,D). Also, the OCR/ECAR rate decreased, indicating a trend to shift to a glycolytic metabolism after IL-15 stimulation (Figure 4E).
Figure 4F,G shows a typical glycolysis stress test experiment with 0.75 x 106 NK cells per well. Addition of glucose triggerred a huge increase in ECAR due to glycolysis activation, while subsequent addition of antimycin A and rotenone drove compensatory glycolysis, and 2-DG caused an inhibition of the pathway and a decrease of ECAR to the minimum (Figure 4F). In parallel, glucose consistently caused a slight decrease in oxygen consumption, possibly by the Crabtree effect20, while antimycin A and rotenone fully blocked the respiration and 2-DG does not provide any further effects (Figure 4G). Activation of both extracellular acidification and mitochondrial oxygen consumption with IL-15 could be observed as well in this test, and again this is consistent when using cells from several donors (Figure 4H).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61466/61466fig1v5.jpg" /> 
Figure 1: Schematic of Extracellular flux assays. 
(A) Schematic of glycolysis, the tricarboxylic acid cycle (TCA) and the electron transport chain (ETC). Inhibitors of different steps are written in red. The electron flux in the ETC is represented in green with the NADH as donor and the O2 as final acceptor. (B) Glycolysis stress test schematic profile representing the extracellular acidification rate (ECAR) versus time. (C) Mitochondrial stress test schematic profile representing the oxygen consumption rate (OCR) versus time. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61466/61466fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/61466/61466fig2v3.jpg" /> 
Figure 2: Natural Killer (NK) cells purified from peripheral mononuclear cells (PBMCs). 
(A) Gating strategy followed to assess purity and viability of NK cells (right column) versus the total of PBMCs (left column). From the gate of mononuclear cells (top panels), single cells were selected (middle panels) and viability was measured (bottom panels). (B) Live cells were stained for CD3 and CD56 or NKp46. The numbers in the panels indicate the percentage of cells in the selected regions. The results are representative of three independent experiments. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61466/61466fig2v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/61466/61466fig3v2.jpg" /> 
Figure 3: Optimization of the mitochondrial and glucose stress tests in activated human NK cells. 
(A) Mitochondrial Stress test: OCR for each plating density (0.75 x 106, 0.375 x 106, 0.187 x 106, 0.094 x 106 and 0.047 x 106) is shown. Each data point represents the mean of 3 wells with standard deviation. Results are representative of 3 independent experiments. (B) DNA (upper panel) and protein (lower panel) levels in the well at different plating densities. Results are representative of at least three independent experiments. Each data point represents the mean of 3 wells with standard deviation. Results are representative of 3 independent experiments. (C) Raw oxygen level traces in wells containing no cells (black trace), 0.75 x 106 cells (blue trace) or 1.5 x 106 cells (green trace). In the green trace after addition of DNP, oxygen is completely depleted in every cycle. (D) The spare respiratory capacity of 0.75 x 106 cells was tested in the presence of several DNP concentration. (E) Glycolysis Stress Test: ECAR for each plating density (0.75 x 106, 0.375 x 106, 0.187 x 106, 0.094 x 106 and 0.047 x 106) is shown. Each data point represents the mean of 3 wells with standard deviation. Results are representative of 3 independent experiments. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61466/61466fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61466/61466fig4v2.jpg" /> 
Figure 4: Detection of metabolic changes after NK cell activation by IL-15. 
Mitochondrial Stress test: OCR (A) and ECAR (B) plots are shown for 0.75 x 106 resting or IL-15 activated cells. Each data point represents the mean of 3 wells with standard deviation. Results are representative of 5 independent experiments. Basal and Maximal Respiration changes for individual human donor are shown in (C), while ATP-linked respiration, proton leak, non-mitochondrial respiration (NMR) are shown in (D) and the OCR/ECAR ratio is shown in (E). Glycolysis Stress test: ECAR (F) and OCR (G) plots are shown for 0.75 x 106 resting or IL-15 activated cells. Each data point represents the mean of 3 wells with standard deviation. Results are representative of 5 independent experiments. Basal and Maximal extracellular acidification changes for individual human donor are shown in (H). ns: not significant; * p &#706; 0.05; ** p &#706; 0.01; *** p &#706; 0.001. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61466/61466fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61466/61466fig5v2.jpg" /> 
Figure 5: Contribution of the TCA and glycolysis on ECAR. 
The first measurements of ECAR correspond largely to acidification due to the CO2 produced in the TCA cycle. After addition of glucose to fuel glycolysis the contribution of TCA-derived acidification to ECAR decreases. Injection of Antimycin A and Rotenone blocks the TCA, and glycolysis compensates the increase in ATP demand by increasing to its maximal level (compensatory glycolysis). Blockade of glycolysis by 2-DG diminishes ECAR to minimal levels, corresponding to acidification that is not attributed to glycolysis or respiratory activity as well as any residual glycolysis not fully inhibited by 2-DG (post 2-DG-acidification). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61466/61466fig5v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Reagent</td>
			<td>Working Concentration</td>
			<td>Clone (for antibodies)</td>
			<td>Final staining volume</td>
		</tr>
		<tr>
			<td>Mouse anti-human CD3 BV711</td>
			<td>50 ng/ml</td>
			<td>UCHT1</td>
			<td>100 &#956;l</td>
		</tr>
		<tr>
			<td>Mouse anti-human CD56 PE</td>
			<td>1/50 dilution</td>
			<td>B159</td>
			<td>100 &#956;l</td>
		</tr>
		<tr>
			<td>Mouse anti-human NkP46 PE</td>
			<td>1/50 dilution</td>
			<td>9/E2</td>
			<td>100 &#956;l</td>
		</tr>
		<tr>
			<td>Viability Dye</td>
			<td>1/1000 dilution</td>
			<td></td>
			<td>500 &#956;l</td>
		</tr>
	</tbody>
</table>
Table 1: Reagents and antibodies used for flow cytometry.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td colspan="5">Mitochondrial Stress Test</td>
		</tr>
		<tr>
			<td>Port</td>
			<td>Volume</td>
			<td>Compound</td>
			<td>10x Stock</td>
			<td>Final Concentration in the assay</td>
		</tr>
		<tr>
			<td>A</td>
			<td>20 &#956;l</td>
			<td>oligomycin</td>
			<td>10 &#956;M</td>
			<td>1 &#956;M</td>
		</tr>
		<tr>
			<td>B</td>
			<td>22 &#956;l</td>
			<td>DNP</td>
			<td>1 mM</td>
			<td>0.1 mM</td>
		</tr>
		<tr>
			<td>C</td>
			<td>25 &#956;l</td>
			<td>antimycin A + rotenone</td>
			<td>10 &#956;M each</td>
			<td>1 &#956;M each</td>
		</tr>
		<tr>
			<td colspan="5">Glycolysis Stress Test</td>
		</tr>
		<tr>
			<td>Port</td>
			<td>Volume</td>
			<td>Compound</td>
			<td>10x Stock</td>
			<td>Final Concentration in the assay</td>
		</tr>
		<tr>
			<td>A</td>
			<td>20 &#956;l</td>
			<td>glucose</td>
			<td>100 mM</td>
			<td>10 mM</td>
		</tr>
		<tr>
			<td>B</td>
			<td>22 &#956;l</td>
			<td>antimycin A + rotenone</td>
			<td>10 &#956;M each</td>
			<td>1 &#956;M each</td>
		</tr>
		<tr>
			<td>C</td>
			<td>25 &#956;l</td>
			<td>2-DG</td>
			<td>500 mM</td>
			<td>50 mM</td>
		</tr>
	</tbody>
</table>
Table 2: Compound loading.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Step</td>
			<td colspan="3">Loop</td>
			<td>Repeat (times)</td>
		</tr>
		<tr>
			<td></td>
			<td>Mix</td>
			<td>Wait</td>
			<td>Measure</td>
			<td></td>
		</tr>
		<tr>
			<td>Calibration</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Equilibration</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Baseline readings</td>
			<td>3 minutes</td>
			<td>0 minutes</td>
			<td>3 minutes</td>
			<td>3</td>
		</tr>
		<tr>
			<td>End loop</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Inject Port A</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Measurements</td>
			<td>3 minutes</td>
			<td>0 minutes</td>
			<td>3 minutes</td>
			<td>3</td>
		</tr>
		<tr>
			<td>End loop</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Inject Port B</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Measurements</td>
			<td>3 minutes</td>
			<td>0 minutes</td>
			<td>3 minutes</td>
			<td>3</td>
		</tr>
		<tr>
			<td>End loop</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Inject Port C</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>Measurements</td>
			<td>3 minutes</td>
			<td>0 minutes</td>
			<td>3 minutes</td>
			<td>3</td>
		</tr>
		<tr>
			<td>End loop</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
		<tr>
			<td>End Program</td>
			<td colspan="3">&#8211;&#8211;</td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 3: Program layout.

Watch this Scientific Journal Video about Analysis of Human Natural Killer Cell Metabolism at JoVE.com

Analysis of Human Natural Killer Cell Metabolism

In this paper, we describe a method to measure glycolysis and mitochondrial respiration in primary human Natural Killer (NK) cells isolated from peripheral blood, at rest or following IL15-induced activation. The protocol described could be easily extended to primary human NK cells activated by other cytokines or soluble stimuli.

Natural Killer (NK) cells mediate mainly innate anti-tumor and anti-viral immune responses and respond to a variety of cytokines and other stimuli to ...

analysis-of-human-natural-killer-cell-metabolism

Nanyang Technological University

Research

JoVE Journal

Immunology and Infection

6.8K Views.  National Institutes of Health. Deze methode zorgt voor de bepaling van natuurlijke killer cel metabolisme. Een belangrijke parameter in de activering door het meten van zuurstofverbruik en pH-veranderingen in het extracellulaire medium. Het voordeel van de extracellulaire flux analyzer is dat het volledig geautomatiseerd is en in staat is om tot 92 monsters in real time te testen met lage hoeveelheden cellen.Dus waardoor hoge doorvoerschermen. Een geldige methode om glycolyse en ademhaling in inktcellen te bepalen i...

Video: Analysis of Human Natural Killer Cell Metabolism

Natural Killer (NK) and CAR-NK Cell Expansion Method using Membrane Bound-IL-21-Modified B Cell Line

Chimeric antigen receptor (CAR)-modified immune cell therapy has become an emerging treatment for cancers and infectious diseases. NK-based immunotherapy, particularly CAR-NK cell, is one of the most promising 'off-the-shelf' development without severe life-threatening toxicity. However, the bottleneck for developing a successful CAR-NK therapy is achieving sufficient numbers of non-exhaustive, long-lived, 'off-the-shelf' CAR-NK cells from a third party. Here, we developed a new CAR-NK expansion method using an Epstein-Barr virus- (EBV) transformed B cell line expressing a genetically modified membrane form of interleukin-21 (IL-21). In this protocol, step-by-step procedures are provided to expand NK and CAR-NK cells from cord blood and peripheral blood, as well as solid organ tissues. This work will significantly enhance the clinical development of CAR-NK immunotherapy.

Natural Killer NK and CAR-NK Cell Expansion Method using Membrane Bound-IL-21-Modified B Cell Line

Here, we present a method to expand peripheral blood natural killer (PBNK), NK cells from liver tissues, and chimeric antigen receptor (CAR)-NK cells derived from peripheral blood mononuclear cells (PBMCs) or cord blood (CB). This protocol demonstrates the expansion of NK and CAR-NK cells using 221-mIL-21 feeder cells in addition to the optimized purity of expanded NK cells.

Chimeric antigen receptor (CAR)-modified immune cell therapy has become an emerging treatment for cancers and infectious diseases. NK-based immunotherapy, ...

Cancer Research

Flow Cytometry-based Assay for the Monitoring of NK Cell Functions

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and virus-infected or malignantly transformed cells due to a set of germline encoded inhibitory and activating receptors. Upon virus or tumor cell recognition a variety of different NK cell functions are initiated including cytotoxicity against the target cell as well as cytokine and chemokine production leading to the activation of other immune cells. It has been demonstrated that accurate NK cell functions are crucial for the treatment outcome of different virus infections and malignant diseases. Here a simple and reliable method is described to analyze different NK cell functions using a flow cytometry-based assay. NK cell functions can be evaluated not only for the whole NK cell population, but also for different NK cell subsets. This technique enables scientists to easily study NK cell functions in healthy donors or patients in order to reveal their impact on different malignancies and to further discover new therapeutic strategies.

A simple and reliable method is described here to analyze a set of NK cell functions such as degranulation, cytokine and chemokine production within different NK cell subsets.

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and ...

Flow Cytometric Analysis of Natural Killer Cell Lytic Activity in Human Whole Blood

NK cell cytotoxicity is a widely used measure to determine the effect of outside intervention on NK cell function. However, the accuracy and reproducibility of this assay can be considered unstable, either because of user&#39;s errors or because of the sensitivity of NK cells to experimental manipulation. To eliminate these issues, a workflow that reduces them to a minimum was established and is presented here. To illustrate, we obtained blood samples, at various time points, from runners (n = 4) that were submitted to an intense bout of exercise. First, NK cells are simultaneously identified and isolated through CD56 tagging and magnetic-based sorting, directly from whole blood and from as little as one milliliter. The sorted NK cells are removed of any reagent or capping antibodies. They can be counted in order to establish an accurate NK cell count per milliliter of blood. Secondly, the sorted NK cells (effectors cells or E) can be mixed with 3,3&#39;-Diotadecyloxacarbocyanine Perchlorate (DiO) tagged K562 cells (target cells or T) at an assay-optimal 1:5 T:E ratio, and analyzed using an imaging flow-cytometer that allows for the visualization of each event and the elimination of any false positive or false negatives (such as doublets or effector cells). This workflow can be completed in about 4 h, and allows for very stable results even when working with human samples. When available, research teams can test several experimental interventions in human subjects, and compare measurements across several time points without compromising the data&#39;s integrity.

This work describes an advanced workflow for the accurate and fast determination of NK (Natural Killer) cell count and NK cell cytotoxicity in human blood samples.

NK cell cytotoxicity is a widely used measure to determine the effect of outside intervention on NK cell function. However, the accuracy and ...

Generation of Natural Killer Cells from Human Expanded Potential Stem Cells

The differentiation of natural killer (NK) cells from human pluripotent stem cells allows for research on and the manufacture of clinical-grade cellular products for immunotherapy. Described here is a two-phase protocol that uses a serum-free commercial medium and a cocktail of cytokines (interleukin [IL]-3, IL-7, IL-15, stem cell factor [SCF], and FMS-like tyrosine kinase 3 ligand [Ftl3L]) to differentiate human expanded potential stem cells (hEPSCs) into cells that possess NK cell properties in vitro with both 3-dimensional (3D) and 2-dimensional (2D) culture technology. Following this protocol, CD3&#8722;CD56+ or CD45+CD56+ NK cells are consistently generated. When cocultured with tumor targets for 3 h, the differentiated products display mild cytotoxicity as compared to an IL-2-independent permanent cell line, NK92mi cells. The protocol preserves the complexity of the differentiation microenvironment by the generation of 3D structures, thus facilitating the study of the spatial relationships between immune cells and their niches. Meanwhile, the 2D culture system enables the routine phenotypical validation of cell differentiation without harming the delicate differentiation niche.

The present protocol shows how to differentiate CD3&#8722;/CD45+CD56+ cells with mild cytotoxicity from human expanded potential stem cells (hEPSCs) under both 3D and 2D culture conditions. This allows for routine phenotypical validation without the destruction of the complex microenvironment.

The differentiation of natural killer (NK) cells from human pluripotent stem cells allows for research on and the manufacture of clinical-grade cellular ...

Developmental Biology

A Flow Cytometry-Based Cytotoxicity Assay for the Assessment of Human NK Cell Activity

Within the innate immune system, effector lymphocytes known as natural killer (NK) cells play an essential role in host defense against aberrant cells, specifically eliminating tumoral and virally infected cells. Approximately 30 known monogenic defects, together with a host of other pathological conditions, cause either functional or classic NK cell deficiency, manifesting in reduced or absent cytotoxic activity. Historically, cytotoxicity has been investigated with radioactive methods, which are cumbersome, expensive and potentially hazardous. This article describes a streamlined, clinically applicable flow cytometry-based method to quantify NK cell cytotoxic activity. In this assay, peripheral blood mononuclear cells (PBMCs) or purified NK cell preparations are co-incubated at different ratios with a target tumor cell line known to be sensitive to NK cell-mediated cytotoxicity (NKCC). The target cells are pre-labeled with a fluorescent dye to allow their discrimination from the effector cells (NK cells). After the incubation period, killed target cells are identified by a nucleic acid stain, which specifically permeates dead cells. This method is amenable to both diagnostic and research applications and, thanks to the multi-parameter capabilities of flow cytometry, has the added advantage of potentially enabling a deeper analysis of NK cell phenotype and function.

A flow cytometry-based method to quantitatively determine the cytotoxic activity of human natural killer cells is shown here.

Within the innate immune system, effector lymphocytes known as natural killer (NK) cells play an essential role in host defense against aberrant cells, ...

Assessment of Human Natural Killer Cell Events Driven by Fc&#947;RIIIa Engagement in the Presence of Therapeutic Antibodies

One mechanism of action for clinical efficacy by therapeutic antibodies is the promotion of immune-related functions, such as cytokine secretion and cytotoxicity, driven by Fc&#947;RIIIa (CD16) expressed on natural killer (NK) cells. These observations have led to research focusing on methods to increase Fc receptor-mediated events, which include removal of a fucose moiety found on the Fc portion of the antibody. Further studies have elucidated the mechanistic changes in signaling, cellular processes, and cytotoxic characteristics that increase ADCC activity with afucosylated antibodies. Additionally, other studies have shown the potential benefits of these antibodies in combination with small molecule inhibitors. These experiments demonstrated the molecular and cellular mechanisms underlying the benefits of using afucosylated antibodies in combination settings. Many of these observations were based on an artificial in vitro activation assay in which the Fc&#947;RIIIa on human NK cells was activated by therapeutic antibodies. This assay provided the flexibility to study downstream effector NK cell functions, such as cytokine production and degranulation. In addition, this assay has been used to interrogate signaling pathways and identify molecules that can be modulated or used as biomarkers. Finally, other therapeutic molecules (i.e., small molecule inhibitors) have been added to the system to provide insights into the combination of these therapeutics with therapeutic antibodies, which is essential in the current clinical space. This manuscript aims to provide a technical foundation for performing this artificial human NK cell activation assay. The protocol demonstrates key steps for cell activation as well as potential downstream applications that range from functional readouts to more mechanistic observations.

A protocol for studying Fc&#947;RIIIa-driven events by therapeutic antibodies in human natural killer cells is described here. This artificial stimulation platform permits the interrogation of downstream effector functions such as degranulation, chemokine/cytokine production, and signaling pathways mediated by the Fc&#947;RIIIa and Fc portions of antibodies involved in binding.

One mechanism of action for clinical efficacy by therapeutic antibodies is the promotion of immune-related functions, such as cytokine secretion and ...

Profiling of the Human Natural Killer Cell Receptor-Ligand Repertoire

Natural killer (NK) cells are among the first responders to viral infections. The ability of NK cells to rapidly recognize and kill virally infected cells is regulated by their expression of germline-encoded inhibitory and activating receptors. The engagement of these receptors by their cognate ligands on target cells determines whether the intercellular interaction will result in NK cell killing. This protocol details the design and optimization of two complementary mass cytometry (CyTOF) panels. One panel was designed to phenotype NK cells based on receptor expression. The other panel was designed to interrogate expression of known ligands for NK cell receptors on several immune cell subsets. Together, these two panels allow for the profiling of the human NK cell receptor-ligand repertoire. Furthermore, this protocol also details the process by which we stain samples for CyTOF. This process has been optimized for improved reproducibility and standardization. An advantage of CyTOF is its ability to measure over 40 markers in each panel, with minimal signal overlap, allowing researchers to capture the breadth of the NK cell receptor-ligand repertoire. Palladium barcoding also reduces inter-sample variation, as well as consumption of reagents, making it easier to stain samples with each panel in parallel. Limitations of this protocol include the relatively low throughput of CyTOF and the inability to recover cells after analysis. These panels were designed for the analysis of clinical samples from patients suffering from acute and chronic viral infections, including dengue virus, human immunodeficiency virus (HIV), and influenza. However, they can be utilized in any setting to investigate the human NK cell receptor-ligand repertoire. Importantly, these methods can be applied broadly to the design and execution of future CyTOF panels.

Here we design two complementary mass cytometry (CyTOF) panels and optimize a CyTOF staining protocol with the aim of profiling the natural killer cell receptor and ligand repertoire in the setting of viral infections.

Natural killer (NK) cells are among the first responders to viral infections. The ability of NK cells to rapidly recognize and kill virally infected cells ...

Measurement of Natural Killer Cell-Mediated Cytotoxicity and Migration in the Context of Hepatic Tumor Cells

Natural killer (NK) cells are a subset of the cytotoxic lymphocyte population of the innate immune system and participate as a first line of defense by clearing pathogen-infected, malignant, and stressed cells. The ability of NK cells to eradicate cancer cells makes them an important tool in the fight against cancer. Several new immune-based therapies are under investigation for cancer treatment which rely either on enhancing NK cell activity or increasing the sensitivity of cancer cells to NK cell-mediated eradication. However, to effectively develop these therapeutic approaches, cost-effective in vitro assays to monitor NK cell-mediated cytotoxicity and migration are also needed. Here, we present two in vitro protocols that can reliably and reproducibly monitor the effect of NK-cell cytotoxicity on cancer cells (or other target cells). These protocols are non-radioactivity-based, simple to set up, and can be scaled up for high-throughput screening. We also present a flow cytometry-based protocol to quantitatively monitor NK cell migration, which can also be scaled up for high-throughput screening. Collectively, these three protocols can be used to monitor key aspects of NK cell activity that are necessary for the cells&#39; ability to eradicate dysfunctional target cells.

Evasion of natural killer (NK) cell-mediated eradication by cancer cells is important for cancer initiation and progression. Here, we present two non-radioactivity-based protocols to evaluate NK cell-mediated cytotoxicity toward hepatic tumor cells. Additionally, a third protocol is presented to analyze NK cell migration.

Natural killer (NK) cells are a subset of the cytotoxic lymphocyte population of the innate immune system and participate as a first line of defense by ...

Medicine

Real-Time Monitoring of Energy Metabolism in Human NK Cells Using an Extracellular Flux Analyzer

Source: Traba, J. et al., <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/61466">Analysis of Human Natural Killer Cell Metabolism.</a>&#160;J. Vis. Exp. (2020)
This video demonstrates the method to analyze energy metabolism in activated human NK cells using an extracellular flux analyzer. Different inhibitors of the electron transport chain complexes impact ATP synthesis, which is measured through the oxygen consumption rate or OCR, providing insights into cellular metabolism and bioenergetics.

All procedures involving sample collection have been performed in accordance with the institute&#39;s IRB guidelines.
1. Reagent preparation

	Reagents ...

JoVE Encyclopedia of Experiments

Immunology

Immunodiagnostics

Cellular Immunodiagnostics

Natural Killer Cell-Mediated Cytotoxicity Assay Sample Preparation for Flow Cytometric Analysis

Source: McBride, J. E., et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/54779">Flow Cytometric Analysis of Natural Killer Cell Lytic Activity in Human Whole Blood.</a> J. Vis. Exp. (2017).
This video demonstrates the lytic activity of natural killer cells against fluorescently-stained target cells. The method enables NK cell-induced cytotoxicity measurement by staining dead cells and using a flow cytometer to quantify live and dead target cells.

Analysis of Human Natural Killer Cell Metabolism

Samenvatting

Meer video's verkennen

Hoofdstukken in deze video