Here, we present a protocol to perform the isolation and expansion of peripheral blood mononuclear cells-derived cytokine-induced CD3+CD56+ killer cells and illustrate their cytotoxicity effect against hematological and solid cancer cells by using an in vitro diagnosis flow cytometry system.
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Hsiao, C. H., Chiu, Y. H., Chiu, S. C., Cho, D. Y., Lee, L. M., Wen, Y. C., Li, J. J., Shih, P. H. Isolation and Expansion of Cytotoxic Cytokine-induced Killer T Cells for Cancer Treatment. J. Vis. Exp. (155), e60420, doi:10.3791/60420 (2020).
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Adoptive cellular immunotherapy focuses on restoring cancer recognition via the immune system and improves effective tumor cell killing. Cytokine-induced killer (CIK) T cell therapy has been reported to exert significant cytotoxic effects against cancer cells and to reduce the adverse effects of surgery, radiation, and chemotherapy in cancer treatments. CIK can be derived from peripheral blood mononuclear cells (PBMCs), bone marrow, and umbilical cord blood. CIK cells are a heterogeneous subpopulation of T cells with CD3+CD56+ and natural killer (NK) phenotypic characteristics that include major histocompatibility complex (MHC)-unrestricted antitumor activity. This study describes a qualified, clinically applicable, flow cytometry-based method for the quantification of the cytolytic capability of PBMC-derived CIK cells against hematological and solid cancer cells. In the cytolytic assay, CIK cells are co-incubated at different ratios with prestained target tumor cells. After the incubation period, the number of target cells are determined by a nucleic acid-binding stain to detect dead cells. This method is applicable to both research and diagnostic applications. CIK cells possess potent cytotoxicity that could be explored as an alternative strategy for cancer treatment upon its preclinical evaluation by a cytometer setup and tracking (CS & T)-based flow cytometry system.
Cytotoxic T lymphocytes are a specific immune effector cell population that mediates immune responses against cancer. Several effector cell populations including lymphokine-activated killer (LAK) cells, tumor-infiltrating lymphocytes (TILs), natural killer (NK) cells, γδ T cells, and cytokine-induced killer (CIK) cells have been developed for adoptive T cell therapy (ACT) purposes1. There is a growing interest in CIK cells, because they represent a mixture of cytokine-induced cytotoxic cell populations expanded from autologous peripheral blood mononuclear cells (PMBCs)2.
The uncontrolled growth of lymphoid progenitor cells, myeloblasts, and lymphoblasts leads to three main types of blood cancers (i.e., leukemia, lymphoma, and myeloma), solid tumors, including carcinomas (e.g., lung cancer, gastric cancer, cervical cancer), and sarcomas, among other cancers3. CIK cells are a mixture of cell populations that exhibit a wide range of major histocompatibility complex (MHC)-unrestricted antitumor activity and thus hold promise for the treatment of hematological and advanced tumors4,5,6,7. CIK cells comprise a combination of cells, including T cells (CD3+CD56−), NK-T cells (CD3+CD56+), and NK cells (CD3–CD56+). Optimization of the CIK induction protocol by use of a fixed schedule for the addition of IFN-γ, anti-CD3 antibody, and IL-2, results in the expansion of CIK cells8. The cytotoxic capability of CIK cells against cancer cells mainly depends on the engagement of NK group 2 member D (a member of the C-type lectin-like receptor family) NKG2D ligands on tumor cells, and on perforin-mediated pathways9. The results of a preclinical study revealed that IL-15-stimulated CIK cells induced potent cytotoxicity against primary and acute myeloid leukemia cell lines in vitro and exhibited a lower alloreactivity against normal PBMCs and fibroblasts9. Recently, the outcome of one-time healthy donor-derived CIK (1 x 108/kg CD3+ cells) infusion as consolidation following nonmyeloablative allogeneic transplantation for myeloid neoplasms treatment in a phase II clinical study was published10.
In the present study, we developed an optimized cell culture formula composed of IFN-γ, IL-1α, anti-CD3 antibody, and IL-2 added to the hematopoietic cell medium to increase CIK production, and investigated the cytotoxic effect of CIK cells against human chronic myeloid leukemia (K562) cells and ovarian cancer (OC-3) cells.
The clinical protocol was performed and approved in accordance with the guidelines of the Institutional Review Board of the China Medical University and Hospital Research Ethics Committee. Peripheral blood specimens were harvested from healthy volunteers with their informed consent.
1. Preparation of materials
- Store reagents, antibodies, and chemicals as shown in the Material Safety Data Sheet (MSDS). Dissolve the drugs or cytokines in solvents as stock solutions and then aliquot for storage at -20 °C or -80 °C.
NOTE: Detailed information for material preparation is noted in the Table of Materials.
2. PBMC isolation
- Warm the density gradient solution (Table of Materials) to 18–20 °C before use. Invert the solution bottle several times to ensure thorough mixing.
- Collect 3−5 mL of human venous blood sample in a heparinized vial and mix well by gently inverting the tube several times.
- Prepare 4 mL of density gradient solution in a 15 mL sterile tube.
- Carefully layer 1 mL of the blood sample onto the density gradient solution.
- Centrifuge at 400 x g for 30 min at 18−20 °C (turn off the break).
- Carefully and immediately aspirate the buffy coat layer of mononuclear cells (about 1 mL) at once to avoid disturbing the layers to a sterile 15 mL tube using a 1 mL sterile pipette.
- Add at least 3 volumes (~3 mL) of phosphate-buffered saline (PBS) to the buffy coat in the centrifuge tube. Suspend the cells by gently pipetting them up and down at least 3x with a sterile pipette.
- Centrifuge at 400 x g for 10 min at 18−20 °C. Aspirate the supernatant.
- Suspend the cell pellet with 5 mL of basal medium (Table of Materials) and transfer into a flask. Culture the cells in a cell culture incubator at 37 °C and 5% CO2.
3. CIK induction and expansion
- On Day 0, culture the PBMCs (1 x 106) in fresh basal medium containing 1,000 IU/mL of IFN-γ for 24 h in a humidified cell culture incubator at 37 °C and 5% CO2.
- On Day 1, refresh the medium with fresh basal medium containing 50 ng/mL of anti-CD3 antibody, 1 ng/mL of rh IL-1α, and 1,000 U/mL of rh IL-2. Refresh the medium every 3 days.
- On Day 7, refresh the medium with fresh basal medium containing 1,000 U/mL of rh IL-2. Refresh the medium every 3 days until the end of cell expansion (Day 14).
4. Immunophenotyping for assessment of CIK cells
- Wash the CIK cells with 10 mL of sterile PBS. Centrifuge for 10 min at 300 x g and 18−20 °C, aspirate the supernatant, and resuspend the cells with 10 mL of PBS. Count the cell number and test cell viability using the trypan blue exclusion assay.
- Aliquot the CIK cells into six sterile 1.5 mL tubes at a density of ~5–10 x 105 cells/mL PBS. Label and treat as follows: Tube 1, Blank (no antibody); Tube 2, add 20 µL of isotype IgG1-FITC; Tube 3, add 20 µL of isotype IgG1-APC mAbs; Tube 4, add 20 µL of CD3-FITC; Tube 5, add 20 µL of CD56-APC mAbs; and Tube 6, add 20 µL of CD3-FITC and 20 µL of CD56-APC mAbs.
- Gently mix the CIK cells with the antibodies by gently pipetting them up and down at least 3x with a 1 mL sterile pipette, and then incubate for 30 min at room temperature in the dark.
- Centrifuge the tubes for 10 min at 300 x g and 18−20 °C. Aspirate the supernatant and suspend the cell pellet once with 1 mL of PBS. Gently pipet them up and down at least 3x with a 1 mL sterile pipette.
- Repeat step 4.4.
- Leave the tubes in the dark before flow cytometric analysis.
5. CD marker recognition
- Transfer the cell suspension to a sterile 5 mL polystyrene round bottom tube with a cell strainer cap (100 μm mesh) by gently pipetting through the cap. Put the tubes on the carousel in order.
- Open the flow cytometry analysis software and create an experimental folder. Click the New Specimen button to add a specimen and tube to the experiment and name the tubes as follows: Tube 1, Blank; Tube 2, Isotype IgG1-CD3; Tube 3, Isotype IgG1-CD56; Tube 4, CD3; Tube 5, CD56; Tube 6, CD3CD56.
- Create a scatter gating system for the CIK cell populations (Figure 2A).
- Select Tube 1 (Blank) and click on the Dot Plot button to create an FSC-A/SSC-A plot. Draw a rectangle gate over the entire cell population with an FSC-A threshold >5 x 104 to exclude cell debris.
- Select the SSC-A/SSC-H parameter for the new dot plot and draw a polygon gate around all single cells. Select the Count/FITC (CD3) and Count/APC (CD56) parameter for the new histogram plot, respectively. Select the FITC (CD3)/APC (CD56) parameter for the new dot plot and draw a four quadrant gate to define the four subpopulations.
- Record the data from 20,000 single cells in each specimen. Click the Load Sample button to analyze the Blank control sample first. Identify the whole CIK cell population by using the CD56 and CD3 channel parameters.
- Repeat step 5.3 for the investigation of all specimens.
- Open the files containing the statistical values of the individual specimen to analyze CIK cell populations and reprint them into analysis files.
6. Culturing and staining of human chronic myeloid leukemia K562 cells and ovarian cancer OC-3 cells
- K562 cells
- Culture K562 cells in complete media (RPMI basal medium containing 10% fetal bovine serum [FBS] and 50 U/mL antibiotics and adjust glucose to 4.5 g/L) at a density of 0.5−1 x 106 cells/mL in a cell culture flask and incubate in a humidified incubator at 37 °C and 5% CO2.
- Transfer the culture media containing the K562 cells into 50 mL sterile tubes and pellet the cells at 300 x g for 10 min at 18−20 °C on the day of the experiment.
- Aspirate the supernatant, resuspend the cells in 5 mL of sterile PBS, and mix well gently.
- Pellet the cells at 300 x g for 10 min. Aspirate the supernatant, resuspend the cells in PBS, and adjust the K562 cells to a concentration of 0.5-1 x 106 cells/mL.
- Add 0.5 µL of CFSE dye to the 1 mL of K562 cell suspension in a 15 mL sterile tube at a final concentration of 5 μM. Gently mix the suspension by pipetting up and down at least 3x.
- Leave the tube in a cell culture incubator at 37 °C and 5% CO2 for 10–15 min.
- Add 9 mL of PBS to the tube and pellet the cells at 300 x g for 10 min. Decant the supernatant and then suspend the cell pellet in 10 mL of complete media. Transfer the cell suspension to a cell culture flask and place in the incubator.
- OC-3 cells
- Culture OC-3 cells in complete media (DMEM/F12 medium containing 10% FBS and 50 U/mL antibiotics) at a density of 0.5–1 x 106 cells in a cell culture flask at 37 °C and 5% CO2.
- Aspirate the culture media and wash the cells with PBS 1 day before the experiment.
- Detach the cells by adding 1 mL of cell dissociation enzyme solution (Table of Materials) and incubate for 5 min at 37 °C.
- Suspend the cells by adding 5 mL of PBS and mix well gently. Pellet the cells at 300 x g for 10 min and aspirate the supernatant. Resuspend the cells in PBS and adjust the cells to a concentration of 0.5–1 x 106 cells/mL.
- Add 0.5 µL of CFSE dye to 1 mL of the OC-3 cell suspension in a 15 mL sterile tube at a final concentration of 5 μM. Gently mix the suspension by pipetting up and down at least 3x.
- Leave the tube in a cell culture incubator at 37 °C and 5% CO2 for 10–15 min.
- Add 9 mL of PBS to the tube and pellet the cells at 300 x g for 10 min. Decant the supernatant and then suspend the cell pellet with complete media. Seed 5 x 105 cells/well into a 6 well plate and incubate in a humidified incubator at 37 °C and 5% CO2 overnight.
7. Cytotoxic assay
- Coculture of CIK and K562 cells (CIK-K562)
- Count the K562 cells from step 6.1.7 and test the cell viability by trypan blue exclusion assay. Add 1 mL of K562 cells to each well in a 6 well plate at a density of 5 x 105/mL.
- Add 1 mL of basal medium with or without CIK cells from step 3.4 to the 6 well plate from step 7.1.1 as follows: Well 1 = Blank, K562 cells alone (5 x 105); Well 2 = CFSE-stained K562 cells alone (5 x 105); Well 3 = CIK cells (E [effector], 25 x 105) + CFSE-stained K562 cells (T [target], 5 x 105); Well 4 = CIK cells (E, 50 x 105) + CFSE-stained K562 cells (T, 5 x 105).
- Mix the cell suspensions by gently pipetting them up and down at least 3x. Place the plate in the incubator for 24 h.
- Coculture of CIK and OC-3 cells (CIK-OC-3)
- Add 1 mL of basal medium with or without CIK cells from step 3.4 to the 6 well plate from step 6.2.7 as follows: Well 1 = Blank, OC-3 cells alone (5 x 105); Well 2 = CFSE-stained OC-3 cells alone (5 x 105); Well 3 = CIK cells (E, 25 x 105) + CFSE-stained OC-3 cells (T, 5 x 105); Well 4 = CIK cells (E, 50 x 105) + CFSE-stained OC-3 cells (T, 5 x 105).
- Mix the cell suspensions by gently pipetting them up and down at least 3x. Put the plate in the incubator for 24 h.
- 7-Aminoactinomycin D (7-AAD) dye staining
- Harvest the CIK-K562 cell suspension from step 7.1.3 directly into a 15 mL sterile tube.
- Harvest both the suspension and adherent cells from the CIK-OC-3 groups from step 7.2.2.
- Transfer the cell suspension to a 15 mL sterile tube. Wash the well with 1 mL of sterile PBS, collect the PBS, and add to the tube. Add 0.5 mL of cell dissociation enzyme solution, and incubate for 5 min at 37 °C.
- Add 1 mL of the solution from the same tube to the corresponding well and gently mix the cells by pipetting them up and down at least 3x with a 1 mL sterile pipette. Collect all the cells in the same tube.
- Centrifuge at 300 x g for 10 min, aspirate the supernatant, and resuspend the cells in 1 mL of sterile PBS. Pellet the cells at 300 x g for 10 min, aspirate the supernatant, and resuspend cells in 100 µL of sterile PBS.
- Add 5 µL of 7-AAD dye (50 ng/µL stock) to the cell suspension. Gently mix the cells by pipetting them up and down at least 3x with a 1 mL sterile pipette. Incubate for 10 min and leave in the dark before analysis.
- Cytolytic capability assay
- Mix the cell suspension from step 7.3.4 and repeat steps 5.1 and 5.2 once.
- Click the New Specimen button to add a specimen and tube to the experiment and name the tubes as follows: Tube 1, K562 (or OC-3) cells only; Tube 2, CFSE-stained K562 (or OC-3) cells only; Tube 3, E:T = 5:1; Tube 4, E:T = 10:1.
- Create a Scatter Gating System for the cytolytic assay (Figure 3A).
- Select Tube 1 and click on the Dot Plot button to create an FSC-A/SSC-A plot. Draw a rectangle gate over all events with an FSC-A threshold >5 x 104 to exclude cell debris.
- Select the SSC-A/CFSE parameter for the new dot plot. Select the 7-AAD/CFSE parameter for the new dot plot and draw a four-quadrant gate to define the four subpopulations.
- Click the Load Sample button to analyze the blank control sample first.
- Adjust the voltage of SSC-A and FSC-A. Identify the dead cell population by using the CFSE and 7-AAD channel parameters. Record the data from >20,000 CFSE+ cells in each specimen.
- Repeat section 7.4.6 for the investigation of all specimens.
- Open the files containing the statistical values of each individual specimen to analyze the non-viable cell populations and export the data into analysis files.
The purpose of the present protocol is to isolate and expand cytokine-induced killer (CIK) T cells from peripheral blood monocytes and evaluate the cytotoxic effect of CIK against hematological malignancy and solid cancer cells, respectively. The induction of CIK was identified by the CD3/CD56 recognition. Figure 1A shows the protocol for CIK induction and expansion. The representative results of the gating strategy for analyzing the subpopulation of CD3+CD56+ T cells from healthy donors is illustrated in Figure 1B. Figure 1C shows the statistical analysis of the CIK proportion from three individuals.
Figure 2A shows that the CD3+CD56+ cell proportion (0.65% for the original PBMC, left lower panel and 27.4% for the CIK cells harvested on Day 14th, right lower panel) significantly increased after 14 days of expansion. In our culture system, the CIK cells yielded about half a hundred-fold changes compared to the original number of PBMCs (Figure 2B).
Figure 3 shows the cytotoxic effect of CIK against human chronic myeloid leukemia K562 cells and human ovarian cancer OC-3 cells. K562 or OC-3 cells (target, T) were stained with a non-fluorescent dye (CFSE), which was cleaved by intracellular esterases within viable cells and then became a highly fluorescent dye. In the cytotoxic coculture study, CFSE-stained K562 or OC-3 cells were cotreated with CIK cells for 24 h. At the end of incubation, the total cells were harvested and stained with 7-AAD dye, which is a nucleic acid-binding dye that is used as a viability probe for dead cell exclusion. The size and granularity of the CIK and CFSE+ cells are illustrated in Figure 3A. The CFSE-stained K562 cells (target cells, T) were co-treated with CIK cells (effector cells, E) at a ratio of E/T = 0:1, 5:1, and 10:1, respectively. The 7-AAD+ cells of CFSE+ K562 cells were all evaluated. The statistical results were from three independent experiments. Basal lysis means the percentage of cell death in the absence of effector cells (E:T = 0:1). Figure 3B shows the obvious cytotoxicity of CIK against OC-3 cells (E:T = 10:1) following 24 h of incubation.
Figure 1: Flow chart of cytokine-induced killer cells induction and expansion. (A) PBMCs from consented healthy donors were initially exposed to rhIFN-γ (Day 0), followed by rhIL-2, rhIL-1α, and anti-CD3 mAb (Day 1) every 3 days (Day 4). Subsequently, the medium was refreshed with rhIL-2-containing medium every 3 days and the cells were harvested on Day 14. (B) Morphology of CIK cells during 7 days of induction. The activation and expansion of CIK cells were conducted as described in the protocol. Cells were observed under a light microscope on Days 1, 5, and 7, respectively (magnification = 40x, scale bar = 200 μm). (C) Cell counts were performed weekly. Please click here to view a larger version of this figure.
Figure 2: The proportion of CD3+CD56+ T cells from a representative PBMC sample. (A) Lymphocytes were recognized by specific size and granularity. Selected single cell population for analysis by flow cytometry. (B) Statistical analysis of CIK expansion efficacy from three healthy donors was conducted using a t-test (*, p < 0.01). Please click here to view a larger version of this figure.
Figure 3: Cytotoxic effects of CIK cells against human chronic myeloid leukemia K562 and human ovarian cancer OC-3 cells. (A) Following coculture with the CIK cells for 24 h, K562 target cells were recognized and gated based on the staining of CFSE dye. Quadrant illustration of the total cell population under the selected 7-AAD/CFSE parameter and the cumulative cytotoxicity of CIK cells at the indicated E:T ratio. (B) The cytotoxic effect of CIK cells against OC-3 cells at a E:T = 10:1 ratio. Please click here to view a larger version of this figure.
The described method is a fast, convenient, and reliable protocol for the isolation and expansion of cytotoxic cytokine-induced killer (CIK) T cells from whole blood samples of healthy donors. It also shows the cytotoxic effect of CIK against leukemia (K562) and ovarian cancer cells (OC-3) using a flow cytometry setup and tracking (CS & T) system. CIK cells can be induced and expanded in good manufactory practices (GMP) conditions by using GMP-grade cytokines and serum-free medium for further clinical infusion11. However, the efficacy of CIK induction and expansion exhibits individual differences12,13,14. Moreover, safety is the advantage of the infusion of patient-derived CIK cells for cancer cell therapy. It has been reported that CIK cells exert cytolytic effects on epithelial solid cancer cells mostly in a NKG2D-dependent manner. In hematological cancer cells, blocking NKG2D with a specific antibody significantly inhibits CIK-induced cytotoxicity against NKG2D-low K562 cells; however, this treatment does not have any effect on HL-60 cells lacking NKG2D15. Furthermore, CIK cells exhibit less cell-killing activity against K562 cells as compared to CD8+ CIK cells16. In this study, we found that CIK exhibited a greater cytotoxic potential against ovarian cancer OC-3 cells compared to leukemia K562 cells. These data suggest that the exact molecular mechanisms through which CIK effectors kill tumor cells are not yet clear.
Tracking target cell viability and evaluating the cytotoxic potential of effector cells using flow cytometry has become a standard and conventional method for clinical examination17. It is has been suggested that a negative effect is observed on the cell viability and the expression of activation markers, such as the CD3+ population in CFSE-stained lymphocytes with flow cytometry18,19. Thus, staining the target cancer cells is a more effective strategy for evaluating the cytotoxic effects of primary CIK cells. IFN-γ, OKT3, and IL-2 are major cytokines or stimulators for CIK differentiation and proliferation. Furthermore, other factors such as thymoglobulin, IL-1α, IL-10, IL-15, are also stimulators. Currently, human serum, human platelet-rich plasma, and even fetal bovine serum are used as medium supplements that can enhance the proliferation of CIK cells. Although serum or plasma are enriched with nutrients and growth factors, the addition of allogeneic animal products presents source, batch, and lot variations that result in experimental variability, and inevitably disconcert studies with therapeutic outcomes for cultured cells. In this study, we used a commercially available serum-free, albumin-free, and xeno-free GMP-grade media supplemented with clinical-grade cytokines to successfully culture the CIK cells. The disadvantage of using xeno-free or allogeneic-free supplements is that they reduce the efficacy of cell proliferation.
The two-color cell tracking methods provided in the protocols independently calculated viable or dead effector target cells in a direct cytotoxicity assay. In our gating strategies, CFSE+ target cells can be obviously distinguished from CIK effector cells (Figure 3). Most importantly, the process of CIK induction and expansion must be qualified and show high viability. For further multiple-dosage infusions, the condition of cryopreservation, and the viability and the cytotoxicity after thawing, are other critical challenges. The actual ratio of specific lysis equals the proportion of 100 x (%Sample lysis - %Basal lysis)/(100 - %Basal lysis). In contrast to other studies18,20, it is recommended that all target cells be investigated to reveal the exact and actual cytotoxicity of CIK cells.
In conclusion, the protocol described in this study is designed to increase the number of PBMC-derived CIK cells from healthy donors and to evaluate their cytotoxic functions against cancer cells with two-color photoactivatable probes for selective tracking of target cells by a flow cytometry with an in vitro diagnostic (IVD) system.
The authors declare no competing conflicts of financial interest.
This study was supported by China Medical University Hospital (DMR-Cell-1809).
|7-Amino Actinomycin D||BD||559925|
|APC Mouse Anti-Human CD56 antibody||BD||555518||B159|
|APC Mouse IgG1, κ Isotype Control||BD||555751||MOPC-21|
|BD FACSCanto II Flow Cytometer||BD||338962|
|Carboxyfluorescein diacetate succinimidyl ester (CFSE)||BD||565082|
|Dulbecco's Modified Eagle Medium/F12||HyClone||SH30023.02|
|Fetal bovine serum||HyClone||SH30084.03|
|Ficoll-Paque Plus||GE Healthcare Life Sciences||71101700-EK|
|FITC Mouse Anti-Human CD3 antibody||BD||555332||UCHT1|
|FITC Mouse IgG1, κ Isotype Control||BD||555748||MOPC-21|
|Human anti-CD3 mAb||TaKaRa||T210||OKT3|
|Recombinant Human Interferon-gamma||CellGenix||1425-050|
|Recombinant Human Interleukin-1 alpha||PEPROTECH||200-01A|
|Sigma 3-18K Centrifuge||Sigma||10295|
|TrypLE Express Enzyme||Gibco||12605028|
|X-VIVO 15 medium||Lonza||04-418Q|
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