Tumor-infiltrating lymphocytes (TIL) are potent mediators of an antitumor response. However, their function is attenuated in solid tumors. CD8+ T-cell effector functions, such as cytokine and granzyme production, depend on cytoplasmic Ca2+, which is controlled by ion channels. In particular, Kv1.3 channels regulate the membrane potential and Ca2+ influx in human effector memory T (TEM) cells. In this study, we assessed the contribution of reduced Kv1.3 and Ca2+ flux on TIL effector function in head and neck cancer (HNC). We obtained tumor samples and matched peripheral blood from 14 patients with HNC. CD3+ TILs were composed of 57% CD4+ (82% TEM and 20% Tregs) and 36% CD8+ cells. Electrophysiology revealed a 70% reduction in functional Kv1.3 channels in TILs as compared with peripheral blood T cells from paired patients, which was accompanied by a decrease in Ca2+ influx. Immunofluorescence analysis showed that CD8+ TILs expressing high Kv1.3 preferentially localized in the stroma. Importantly, high expression of Kv1.3 correlated with high Ki-67 and granzyme B expression. Overall, these data indicate that defective Kv1.3 channels and Ca2+ fluxes in TILs may contribute to reduced immune surveillance in HNC. Cancer Res; 77(1); 53–61. ©2016 AACR.

Head and neck cancers (HNC) represent a heterogeneous group of malignant tumors that originate primarily in the nasopharynx, nasal cavity, paranasal sinuses, oral cavity, oropharynx, salivary glands, larynx, and hypopharynx and affect more than half a million individuals worldwide (1, 2). A majority of HNC cases present histologically as squamous cell carcinomas (SCC; ref. 2). Head and neck squamous cell carcinoma is the sixth most common type of cancer, with a 5-year survival of 50% (2–4). The heterogeneity of HNC tumors, the complex anatomy of the head and neck region, and the proximity of these tumors to several vital organs and structures present a challenge in conventional treatment modalities of these cancers (2). The immune system plays an important role in the pathogenesis of HNC, and immunotherapies aimed to boost the immune system are showing promising results in HNC patients (5, 6).

The response of the host immune system to the developing tumor is complex in nature and is poorly understood. Typically, tumors create a tumor microenvironment (TME), which enables them to survive and proliferate by evading recognition and initiation of an immune response from the host immune system (6, 7). The TME is infiltrated by a heterogeneous population of tumor-infiltrating lymphocytes (TIL; refs. 6–8). The extent of cytotoxic CD8+ (that are capable of killing the tumor cells) and CD4+ [helper T cells that facilitate the killing of tumor cells and/or regulatory T cells (Treg) that have an immunosuppressive effect on other T cells] T cells' infiltration into the HNC tumor mass has repercussions on disease prognosis and responsiveness to therapy (5, 8, 9). Furthermore, the functional status of CD8+ and Th1 CD4+ TILs determines their ability to eradicate cancer cells. In various solid tumors, including HNC, TILs exhibit multiple functional defects that include reduced locomotion, proliferation, cytotoxicity and cytokine production (IL2 and IFNγ), and increased cell death (3, 7, 10–15).

The function of T lymphocytes depends on Ca2+ signaling, which is controlled by multiple ion channels to regulate the Ca2+ influx into the T cell (16). Particularly, Kv1.3 channels regulate the membrane potential of human T lymphocytes and provide the electrochemical driving force for Ca2+ influx through Ca2+ release–activated Ca2+ channels (CRAC), which is necessary for downstream effector functions (16–19). Unequivocal evidence exists of the importance of Kv1.3 and CRAC channels in T-cell activation, as their blockade suppresses cytokine production and proliferation (16, 18, 20). Although these ion channels play an important role in T-cell function, their implications in cancer are poorly understood. Evidence for a role of ion channels in the failure of immune surveillance in cancer has been provided by conditional knockout mice lacking functional CRAC channels in T cells. These mice have increased susceptibility to tumor engraftment because their CD8+ cells are ineffective in killing tumor cells and producing IFNγ and TNFα (21). Currently, no information is available on either the ion channel expression or function in TILs in HNC. Understanding the ion channel dysregulation in TILs could be of value in developing new and effective cancer immunotherapies.

The current study was undertaken to unveil the Kv1.3 channel expression and function in TILs in HNC. Herein, we present evidence that Kv1.3 channels are downregulated in HNC TILs, and this deficiency is associated with loss of effector functions, such as decreased Ca2+ influx, cell proliferation, and granzyme B (GrB) production.

Human subjects

Peripheral blood and tumor samples from 14 HNC patients were obtained from the University of Cincinnati Cancer Institute's (UCCI; Cincinnati, OH) Tumor Bank. Eligibility criteria for patient inclusion were a diagnosis of SCC as confirmed by tissue biopsy and no preoperative administration of radiation or chemotherapy. Eligible patients underwent surgical removal of the solid tumors, and a piece of the surgically resected tumor (>0.1 g) was provided for TIL isolation. From the same patient, 2 mL of peripheral blood was obtained preoperatively. Blood samples were also drawn from 3 healthy volunteers (2 female, 1 male) between the ages of 35 and 67 and were used as healthy controls for electrophysiology and calcium measurement experiments. Informed written consent was obtained from all patients and healthy volunteers. The study and the informed consent forms were approved by the Institutional Review Board at the University of Cincinnati. Pathologic and clinical data on the enrolled patients were provided by the UCCI tumor bank and are presented in Tables 1 and 2, respectively. Time to median follow-up for the HNC patients was 16 months (range, 3–40 months).

Table 1.

Clinicopathologic features of individual HNC cases (N = 14)

#Case IDAgeGenderLocation of squamous cell carcinomaPathologic stagep16 statusCD3+ infiltration
HDN 684 60 Male Parotid pT3N2bMx N/A 
HDN 731 68 Male Oral cavity rpT4N2BMx N/A Poor 
HDN 733 65 Female Oral cavity pT3N0Mx N/A Good 
HDN 741 54 Male Larynx pT4aN2cMx N/A Good 
HDN 753 60 Male Sinonasal pT4bN2bMx Poor 
HDN 972 50 Male Oral Cavity pT4aN2bMx − Good 
HDN 974 58 Male Cutaneous pT3N0Mx N/A Good 
HDN 1036 77 Male Oral Cavity pT4aN0Mx N/A N/A 
HDN 1056 59 Male Larynx pT3N0Mx N/A Good 
10 HDN 1260 64 Male Oral Cavity pT4aN0Mx N/A Poor 
11 HDN 1331 74 Male Oral Cavity pT2N1Mx − Good 
12 HDN 1351 72 Male Parotid Not given N/A Good 
13 HDN 1358 49 Male Hypopharynx pT3N0Mx N/A Good 
14 HDN 1459 62 Male Oropharynx pT1N0Mx Good 
#Case IDAgeGenderLocation of squamous cell carcinomaPathologic stagep16 statusCD3+ infiltration
HDN 684 60 Male Parotid pT3N2bMx N/A 
HDN 731 68 Male Oral cavity rpT4N2BMx N/A Poor 
HDN 733 65 Female Oral cavity pT3N0Mx N/A Good 
HDN 741 54 Male Larynx pT4aN2cMx N/A Good 
HDN 753 60 Male Sinonasal pT4bN2bMx Poor 
HDN 972 50 Male Oral Cavity pT4aN2bMx − Good 
HDN 974 58 Male Cutaneous pT3N0Mx N/A Good 
HDN 1036 77 Male Oral Cavity pT4aN0Mx N/A N/A 
HDN 1056 59 Male Larynx pT3N0Mx N/A Good 
10 HDN 1260 64 Male Oral Cavity pT4aN0Mx N/A Poor 
11 HDN 1331 74 Male Oral Cavity pT2N1Mx − Good 
12 HDN 1351 72 Male Parotid Not given N/A Good 
13 HDN 1358 49 Male Hypopharynx pT3N0Mx N/A Good 
14 HDN 1459 62 Male Oropharynx pT1N0Mx Good 

Abbreviation: N/A, not available.

Table 2.

Clinical data of HNC patients (N = 14 cases)

From pathology report related to surgical resection
#Case IDSurvivalAdjuvant radiation (Y/N)Adjuvant chemo (Y/N)Extracapsular spread (Y/N)Positive surgical margins (Y/N)Perineural invasion (Y/N)Lymphovascularinvasion (Y/N)
HDN 684 Unknown Indeterminate 
HDN 731 Unknown 
HDN 733 Alive 
HDN 741 Unknown 
HDN 753 Deceased 
HDN 972 Alive Indeterminate 
HDN 974 Alive 
HDN 1036 Alive 
HDN 1056 Alive Indeterminate 
10 HDN 1260 Alive 
11 HDN 1331 Unknown 
12 HDN 1351 Alive 
13 HDN 1358 Alive 
14 HDN 1459 Alive 
From pathology report related to surgical resection
#Case IDSurvivalAdjuvant radiation (Y/N)Adjuvant chemo (Y/N)Extracapsular spread (Y/N)Positive surgical margins (Y/N)Perineural invasion (Y/N)Lymphovascularinvasion (Y/N)
HDN 684 Unknown Indeterminate 
HDN 731 Unknown 
HDN 733 Alive 
HDN 741 Unknown 
HDN 753 Deceased 
HDN 972 Alive Indeterminate 
HDN 974 Alive 
HDN 1036 Alive 
HDN 1056 Alive Indeterminate 
10 HDN 1260 Alive 
11 HDN 1331 Unknown 
12 HDN 1351 Alive 
13 HDN 1358 Alive 
14 HDN 1459 Alive 

NOTE: Unknown, lost to follow-up.

Abbreviations: N, no; Y, yes.

Cell isolation

Peripheral blood mononuclear cells (PBMC) and CD3+ T cells were isolated from whole blood as described previously (22). Briefly, PBMCs were isolated from centrifugation of whole blood using Ficoll–Paque (GE Healthcare Bio-Sciences) density gradient, and CD3+ cells were further isolated from the PBMCs by negative selection using EasySep Human T Cell Enrichment Kit (STEMCELL Technologies). T cells were maintained in RPMI1640 medium supplemented with 10% human serum, 200 U/mL penicillin, 200 mg/mL streptomycin, 1 mmol/L l-glutamine, and 25 mmol/L HEPES (Sigma-Aldrich), and cells were used immediately for calcium measurement and electrophysiology.

TIL isolation

TILs were isolated by mechanical dissociation of surgically resected tumors within 2 hours of their removal. Briefly, the tumors were rinsed with PBS, dissected into approximately 2-mm3 fragments, and transferred to a gentleMACS C-tube (Miltenyi Biotec) in sterile RPMI1640 medium. The tumor fragments were dissociated in the gentleMACS dissociator (Miltenyi Biotec) using the A01 program for 25 seconds. This dissociation was repeated three times, till a tumor cell suspension was obtained. This suspension was then filtered through a 100-μm sterile nylon mesh cell strainer, washed twice in PBS, resuspended in PBS + 2% FBS, layered over Ficoll–Paque density gradient, and the TIL fraction was recovered after centrifugation. CD3+ TILs were isolated by negative selection from this fraction as mentioned above. These cells were assessed for viability and purity and were used immediately for phenotyping, electrophysiology, and calcium measurements.

Cell surface antibody staining

Cell viability was assessed by live labeling 0.1 × 106 TILs with 7-AAD viability staining solution (BioLegend; ref. 22). For purity, cells were stained with FITC anti-CD3 and PerCP anti-CD19 antibodies. For phenotyping, approximately 0.5 × 106 TILs were stained for measuring the percentages of Treg and effector memory T (TEM) cells using standard flow cytometry staining protocols (22). Briefly, for Treg cells, TILs were labeled live with the following antibodies: FITC anti-CD3, PE anti-CD127, PerCP anti-CD8, APC anti- CD4, APC-Cy7 anti-CD25, and PB anti-CD45. For TEM cells, TILs were labeled live with the following antibodies: FITC anti-CD45, PE anti-CD4, PerCP anti-CD8, PE-Cy7 anti-CCR7, APC anti-CD45RO, APC-Cy7 anti-CD3, and PB anti-CD45RA (all flow cytometry antibodies from BD Biosciences). Samples were fixed in 1% paraformaldehyde solution, read on a BD FACSCanto flow cytometer (BD Biosciences), and analyzed by FCS Express Software (De Novo Software).

Calcium measurements

Ca2+ was measured using the Ca2+ add-back method (23). Briefly, 0.5–1 × 106 peripheral T cells and TILs were loaded with 1:1,000-fold of 2 mg/mL Indo-1-AM ratiometric dye and 0.015% Pluronic F-127 (Life Technologies) in Hank's balanced salt solution (HBSS) containing 1 mmol/L CaCl2, 1 mmol/L MgCl2, and 1% FCS for 30 minutes at 37°C, then washed three times in HBSS supplemented with 10 mmol/L HEPES (pH 7.0) and 1% FCS. Prior to measurements, cells were resuspended in a calcium-depleted solution prepared from the HBSS/HEPES solution mentioned above and supplemented with 0.5 mmol/L EGTA (pH 7.4). The Indo-1 fluorescence ratio (indicative of the [Ca2+]i) in T cells was measured by flow cytometry on a LSRII flow cytometer (BD Biosciences). The following protocol was implemented: cells were exposed to thapsigargin (TG, 1 μmol/L) in 0 mmol/L Ca2+ solution followed by 2 mmol/L Ca2+-containing solution (23). Analysis of the kinetics was performed using FlowJo software (FlowJo, LLC). Ca2+ fold change was measured as the ratio between the peak intensity ratio of Indo-1 upon addition of 2 mmol/L Ca2+ and the mean baseline Indo-1 ratio at 0 mmol/L Ca2+.

Electrophysiology

Kv1.3 currents were measured in whole-cell voltage-clamp configuration using Axopatch 200B amplifier (Molecular Devices). The external solution contained (in mmol/L) 145 NaCl, 5 KCl, 1 MgCl2, 2.5 CaCl2, 5.5 glucose, and 10 HEPES (pH 7.35). The pipette solution contained (in mmol/L) 140 KF, 11 K2EGTA, 1 CaCl2, 2 MgCl2, and 10 HEPES (pH 7.22; ref. 24). Kv1.3 currents were elicited by 2-second–long voltage-step pulses of +50 mV from a holding potential of −120 mV. The amplitude of the peak current was read at +50 mV, and the current density was defined as the ratio of the peak current at +50 mV and the whole-cell cell capacitance (which is a measurement of cell surface area). The current density is proportional to the number of Kv1.3 channels per unit area. The inactivation kinetics was described with the inactivation time constant (τi), which was determined upon fitting single-exponential function (I(t) = I0 × e−t/τi + C, where I0, current amplitude; C, steady-state current at the end of depolarization) to the decay part of the current trace.

Immunohistochemical and immunofluorescence analysis

Formalin-fixed paraffin-embedded (FFPE) and frozen blocks from tumor tissue resected from enrolled HNC patients (n = 14) and surrounding normal tissue (n = 9) were obtained from the UCCI tumor bank. Six 5-μm sections per case were provided for IHC studies. One slide per case prepared from the tumor and normal tissue FFPE blocks was stained with hematoxylin–eosin (H&E), reviewed for histopathology by a pathologist affiliated with the UCCI tumor bank, and the histopathology report is presented in Supplementary Table S1. IHC was performed on slides from FFPE tumor sections to assess for the presence of CD3+ cells in the tumor area, and the slides were classified as “well infiltrated” or “poorly infiltrated” for each case (see Supplementary Methods).

For immunofluorescence experiments, 5-μm–thick sections prepared from frozen well-infiltrated tumor samples were fixed with precooled acetone and blocked with PBS + 10% FBS. To measure cell infiltration, slides were stained with following primary antibodies: mouse anti-human CD4 (R&D Systems) or mouse anti-human CD8 (R&D Systems) and guinea pig polyclonal anti-human Kv1.3 (Alomone Labs). The sections were washed and incubated with the following secondary antibodies: Alexa-647 anti-mouse and Alexa-555 anti-guinea pig (Thermo Fisher Scientific). Slides were then washed and directly labeled with Alexa-488 mouse anti-human pan-cytokeratin (PCK, eBioscience), whereas the nuclei were labeled with 4′,6-diamidino-2-phenylindole (DAPI, 1 μg/mL, Thermo Fisher Scientific). To measure proliferation and GrB production, frozen sections were fixed, blocked, and stained with the following primary antibodies: mouse anti-human CD8, guinea pig polyclonal anti-human Kv1.3, and rabbit monoclonal Ki-67 (Invitrogen). The sections were incubated with the following secondary antibodies: BV-480 anti-rabbit (BD Biosciences), Alexa-647 anti-mouse, and Alexa-555 anti-guinea pig. Slides were then washed and directly labeled with Alexa-488 mouse anti-human PCK and Alexa-405 mouse anti-human Granzyme B (Novus Biologicals). Confocal microscopy was performed on a Zeiss 710 laser scanning confocal microscope (Zeiss GmBH) using a 40× water immersion lens at room temperature; the pinhole was set at 1 airy unit. Data were obtained using the “Multi Track” option of the microscope to exclude the cross-talk between the channels, and images were acquired with the Zeiss Zen Image browser. The specificity of the polyclonal Kv1.3 antibody was determined by peptide adsorption studies (Supplementary Fig. S1). Staining was also performed with the addition of secondary antibodies only, and slides were imaged to assess the background fluorescence (Supplementary Figs. S2 and S3).

Image analysis

Images were analyzed using ImageJ software (NIH, Bethesda, MD). Briefly, in each field, a region of interest (ROI) was drawn around individual CD8+ or CD4+ cells. In the same ROI, the mean fluorescence intensities (MFI) were measured for Kv1.3 and either Ki-67 or GrB channels (at least 10 fields for each patient). For each individual, the Kv1.3 fluorescence intensities were sorted by values from low to high, and the median value was determined. Values above the median were considered as “Kv1.3high,” whereas those below the median were “Kv1.3low” (Supplementary Fig. S4). Thus, for each individual, we classified the CD8+ cells as being either Kv1.3high or Kv1.3low. Similarly, “high” or “low” MFI values were determined for Ki-67 and GrB. We then calculated the numbers of Ki-67high or GrBhigh cells within the Kv1.3high and Kv1.3low populations for every case. For measuring the infiltration, for each microscopic field, areas of tumor and stroma were defined on the basis of PCK fluorescence. CD8+ or CD4+ cells within the tumor and stroma were then manually counted for a minimum of 10 fields. The percentages of Kv1.3high cells were calculated within the tumor and stroma for each patient.

Statistical analysis

All data are presented as mean ± SEM, and the number of subjects or cells is indicated. Statistical analysis was performed using Student t test (paired or unpaired) with SigmaPlot (Systat Software, Inc); P value of less than or equal to 0.05 was considered as statistically significant.

Kv1.3 channels and Ca2+ fluxes are reduced in TILs of HNC patients

The TME in solid tumors is characterized by the infiltration of T lymphocytes, and the composition of this T-cell population along with its functional state can determine the outcome of the antitumor immune response of the individual (3, 8, 25). TILs isolated from HNC tumors were assessed for their phenotype, purity, and viability by flow cytometry. The TILs were 99% viable (Supplementary Fig. S5) and predominantly CD3+ (91 ± 2% n = 3). 56 ± 4% of the CD3+ TILs were CD4+, whereas 35 ± 3% cells were CD8+ (n = 3). The CD4+ TILs were 25 ± 4% CD4+CD25+CD127 Treg cells (n = 3), whereas 82 ± 6% of the CD4+ TILs were CD4+CD45RO+CCR7 TEM cells (n = 3; ref. 3). The functionality of T cells depends on the intracellular Ca2+ signaling that is regulated by the activity of Kv1.3 channels (26). So far, the functional status and expression of Kv1.3 channels in T cells within the tumor and in the peripheral blood of cancer patients are not fully understood. Hence, we measured activity of Kv1.3 channels in TILs by electrophysiology and compared it with that of peripheral blood T cells (PBT) from HNC patients (cPBT) and healthy donors (hPBT). We observed no differences in Kv1.3 activity in cPBTs and hPBTs, but the currents were highly suppressed in TILs as compared with those in cPBTs from the same individual (Fig. 1A). TILs also had a smaller capacitance than cPBTs (1.4 ± 0.2 pF, n = 18, in TILs vs. 1.8 ± 0.1 pF, n = 34, in cPBTs; P = 0.018), perhaps indicative of a reduced activation state (the cell capacitance is a measure of the cell size). There was no difference in cell capacitance between cPBTs and hPBTs (1.4 ± 0.1 pF, n = 11, in hPBTs, P = 0.24). The Kv1.3 currents in all cell types displayed C-type inactivation (characteristic of Kv1.3), and there were no differences in inactivation kinetics (463 ± 38 ms, n = 9, in TILs vs. 375 ± 18 ms, n = 27, in cPBTs and 392 ± 38 ms, n = 11, in hPBTs). On average, the Kv1.3 current density (number of channels/membrane unit surface) was the same in PBTs from healthy donors and patients, but TILs had a significantly lower number of channels (Fig. 1B). Moreover, several lymphocytes did not have detectable Kv1.3 currents (8.8% and 33.3% of cPBTs and TILs, respectively).

Figure 1.

Kv1.3 expression and Ca2+ signaling are impaired in TILs. A, Representative Kv1.3 currents recorded in whole-cell voltage-clamp configuration upon a 50 mV depolarization step in a cPBT and a TIL isolated from the same patient. B, Individual (empty circle) and average (triangle) Kv1.3 current density in hPBTs, (n = 11 cells, 2 cases), cPBTs (n = 34, 6 cases), and TILs (n = 18, 4 cases) isolated from the same donor. Error bar, SEM. C, Typical Ca2+ response (shown as a ratio of Indo-1 fluorescence at 400 and 480 nm) recorded in cPBTs and TILs isolated from the same HNC patient. Cells were loaded with Indo-1 ratiometric dye, and the fluorescence was recorded by flow cytometry (see Materials and Methods). D, The average change of the peak Ca2+ level as expressed with the Ca2+ fold change (n = 4 cases). Error bars, SEM.

Figure 1.

Kv1.3 expression and Ca2+ signaling are impaired in TILs. A, Representative Kv1.3 currents recorded in whole-cell voltage-clamp configuration upon a 50 mV depolarization step in a cPBT and a TIL isolated from the same patient. B, Individual (empty circle) and average (triangle) Kv1.3 current density in hPBTs, (n = 11 cells, 2 cases), cPBTs (n = 34, 6 cases), and TILs (n = 18, 4 cases) isolated from the same donor. Error bar, SEM. C, Typical Ca2+ response (shown as a ratio of Indo-1 fluorescence at 400 and 480 nm) recorded in cPBTs and TILs isolated from the same HNC patient. Cells were loaded with Indo-1 ratiometric dye, and the fluorescence was recorded by flow cytometry (see Materials and Methods). D, The average change of the peak Ca2+ level as expressed with the Ca2+ fold change (n = 4 cases). Error bars, SEM.

Close modal

The decrease in Kv1.3 activity leads to a reduction in the Ca2+ influx in T cells (16, 18, 23, 26). Thus, we measured the store-operated Ca2+ response of hPBTs and cPBTs and TILs. Representative recordings of intracellular Ca2+ levels in cPBTs and TILs from the same individual are shown in Fig. 1C: Using the Ca2+ add-back method, the endoplasmic reticulum (ER) Ca2+ stores are emptied with TG (a SERCA pump inhibitor) in Ca2+-free medium (23, 27), which leads to the opening of the CRAC channels and influx of Ca2+ upon readdition of extracellular Ca2+ (Fig. 1C). Changes in intracellular Ca2+ concentration upon reintroduction of extracellular Ca2+ are T-cell receptor (TCR) independent. These recordings show that there was no change in the amount and kinetics of the Ca2+ release from the ER in cPBTs and TILs, but the influx of Ca2+ is reduced. The peak Ca2+ levels achieved during Ca2+ influx were significantly reduced by 32%, from 4.3 ± 0.5 fold changes in intracellular Ca2+ concentration from the baseline value in cPBTs to 2.9 ± 0.2 in TILs (n = 4, P = 0.04; Fig. 1D). We also measured Ca2+ fluxes in hPBTs from three age-matched healthy donors and obtained a Ca2+ fold change of 4.9 ± 1.1, which was the same as for cPBTs (P = 0.64, Fig. 1D). There was no change in the kinetics of peak Ca2+ decay, indicating that there are no differences in Ca2+ reuptake into the stores or efflux through the plasma membrane Ca2+ ATPase (data not shown).

These data show that the Kv1.3 channel expression and function is significantly attenuated in HNC TILs, which contribute to the suppression of Ca2+ signaling. Still, there is a variability of expression of Kv1.3 in TILs that warranted their further investigation (Fig. 1B). We thus determined the spatial distribution of TILs with variable Kv1.3 expression levels (and thus different Ca2+ handling capabilities) in relation to their proximity to cancer cells, as this would define, for CD8+ T cells, the efficacy of the antitumor immune response.

CD4+ and CD8+ TILs preferentially localize in the tumor stroma

Histopathologic analysis of the H&E-stained tumor sections of 14 HNC patients revealed the presence of SCC tumor cells in 13 of 14 sections (HDN 1036 sections had 0% tumor cells, Supplementary Table S1). One case (HDN 684) was excluded from subsequent analysis as the histopathology diagnosis of “squamous cell carcinoma with sarcomatoid features” (Supplementary Table S1) did not fit our inclusion criteria. Immunohistochemical staining with anti-CD3 antibody was performed on the remaining 12 cases to determine TIL infiltration. FFPE sections from normal tissue resected adjacent to the tumor were stained as negative controls (n = 9 cases), whereas sections from tonsil were stained as positive control (Supplementary Fig. S6). We observed that 9 of the total 12 cases had “well-infiltrated” tumors, which were further used for immunofluorescence studies, whereas 3 cases were “poorly infiltrated” (Supplementary Fig. S6) and therefore excluded from further experiments (Table 1).

To determine the tumor infiltration by CD4+ and CD8+ TILs, slides from well-infiltrated HNC cases were stained with anti-PCK (tumor cell marker), anti-Kv1.3, and either anti-CD8 (Fig. 2A) or anti-CD4 antibodies (Fig. 2B). Intratumoral and stromal areas were defined on the basis of PCK staining. CD4+ or CD8+ TILs that were present in the tissue areas showing PCK staining were regarded as “intratumoral lymphocytes” (iTIL), whereas the rest of CD4+ or CD8+ TILs were defined as “stroma-infiltrating lymphocytes” (sTIL). As shown in Fig. 2C and D, a higher number of CD8+ TILs (P = 0.05, n = 9 cases, Fig. 2C) and CD4+ TILs (P < 0.001, n = 8 cases Fig. 2D) are present in the tumor stroma compared with the tumor epithelium. Still, the functional status of TILs in the two compartments is not known.

Figure 2.

Decreased Kv1.3 expression in intratumoral CD8+ but not CD4+ TILs. Representative confocal images of frozen HNC tumor sections stained for PCK (tumor cell marker, yellow), nuclei (DAPI, blue), Kv1.3 channels (red), and CD8 (green, A) or CD4 (green, B). C and D, Percentage of iTILs and sTILs for HNC tumor sections stained for CD8+ TILs (C; n = 9 cases, ≥10 fields/case) and CD4+ TILs (D; n = 8 cases, ≥10 fields/case). Black full triangles, mean; error bars, SEM for each group. E and F, Percentage of CD8+ (E; n = 9 cases, ≥10 fields/case) and CD4+ (F; n = 8 cases, ≥10 fields/case) iTILs and sTILs with high (Kv1.3high) and low (Kv1.3low) Kv1.3 expression. For definition of “Kv1.3high” cell, see Materials and Methods and Supplementary Fig. S4. Solid black triangles, mean for each population; error bars, SEM.

Figure 2.

Decreased Kv1.3 expression in intratumoral CD8+ but not CD4+ TILs. Representative confocal images of frozen HNC tumor sections stained for PCK (tumor cell marker, yellow), nuclei (DAPI, blue), Kv1.3 channels (red), and CD8 (green, A) or CD4 (green, B). C and D, Percentage of iTILs and sTILs for HNC tumor sections stained for CD8+ TILs (C; n = 9 cases, ≥10 fields/case) and CD4+ TILs (D; n = 8 cases, ≥10 fields/case). Black full triangles, mean; error bars, SEM for each group. E and F, Percentage of CD8+ (E; n = 9 cases, ≥10 fields/case) and CD4+ (F; n = 8 cases, ≥10 fields/case) iTILs and sTILs with high (Kv1.3high) and low (Kv1.3low) Kv1.3 expression. For definition of “Kv1.3high” cell, see Materials and Methods and Supplementary Fig. S4. Solid black triangles, mean for each population; error bars, SEM.

Close modal

Kv1.3 expression is lower in the intratumoral CD8+ but not in CD4+ TILs

As described above, electrophysiological experiments showed decreased Kv1.3 channel activity in TILs compared with cPBTs. These data revealed a widespread distribution in channel density among the TIL population (Fig. 1B). Immunofluorescence was performed to determine whether sTILs and iTILs have different Kv1.3 expressions. We quantitated the Kv1.3 fluorescence intensity in the iTILs and sTILs and determined the percentage of Kv1.3high CD4+ and CD8+ iTILs and sTILs (for definition of Kv1.3high or Kv1.3low TILs, see Materials and Methods and Supplementary Fig. S4). We found that CD8+ iTILs have lower Kv1.3 expression than sTILs (P = 0.02, n = 9 cases, Fig. 2E), whereas we did not observe any difference in Kv1.3 levels between the iTILs and sTILs in the CD4+ population (P = 0.080, n = 8 cases, Fig. 2F). These data indicate that CD8+ TILs not only fail to enter the tumor but also have reduced Kv1.3 expression. As Kv1.3 channels control effector functions, such as cytokine and GrB production, we determined whether the downregulation of Kv1.3 expression in CD8+ iTILs was associated with decreased effector functions.

Low Kv1.3 expression in CD8+ TILs is associated with low levels of Ki-67 and GrB

Tumor cells can be eliminated via secretion of GrB by cytotoxic CD8+ lymphocytes, which induces apoptosis in tumor cells (28). The GrB production and secretion depends on the Ca2+ signaling, which is regulated by Kv1.3 channels (19). Furthermore, Kv1.3 channels are responsible for the activation and proliferation of T cells (16, 20). To establish whether the decreased Kv1.3 expression in CD8+ TILs results in a suppression of activation and GrB production, we stained tissue sections from the 9 well-infiltrated HNC cases with DAPI and anti-PCK, anti-CD8, anti-Kv1.3, anti-GrB, and anti-Ki-67 (proliferation marker) antibodies (Fig. 3). CD8+ TILs were classified as either Kv1.3high or Kv1.3low based on the median Kv1.3 fluorescence. In these populations, the percentage of Ki-67high and GrBhigh cells (defined by the median Ki-67 and GrB fluorescence) were also calculated. We observed in all of the 9 patients that the percentage of proliferating (Ki-67high) cells is higher in Kv1.3high as compared with Kv1.3low CD8+ TILs (P < 0.0.001, n = 9 donors, Fig. 3B), whereas in 8 of 9 cases, we observed that GrB level was lower in Kv1.3low CD8+ TILs as compared with Kv1.3high CD8+ TILs (Fig. 3C, P = 0.0505 n = 9; P = 0.00221, n = 8 without the “outlier” HDN 1358). Overall, these data indicate that the Kv1.3 expression in CD8+ cells is associated with a more active state, but unfortunately, these more active CD8+ cells preferentially localize in the stroma.

Figure 3.

Low Kv1.3 expression in CD8+ TILs is associated with low levels of Ki-67 and GrB. A, Representative confocal images of frozen HNC tumor sections from a single patient stained for cytokeratin (tumor cell marker, PCK, yellow), CD8 (green), GrB (blue), Ki-67 (cell proliferation marker, magenta), and Kv1.3 (red). B, Percentage of Ki-67high cells (proliferating cells) in CD8+ TILs with low and high Kv1.3 expression. C, Percentage of high GrB-expressing cells in Kv1.3high and Kv1.3low CD8+ TILs. B and C, Solid black triangles, mean; error bars, SEM. Sections from 9 HNC patients were stained for Ki-67 and GrB, ≥10 fields were analyzed/case.

Figure 3.

Low Kv1.3 expression in CD8+ TILs is associated with low levels of Ki-67 and GrB. A, Representative confocal images of frozen HNC tumor sections from a single patient stained for cytokeratin (tumor cell marker, PCK, yellow), CD8 (green), GrB (blue), Ki-67 (cell proliferation marker, magenta), and Kv1.3 (red). B, Percentage of Ki-67high cells (proliferating cells) in CD8+ TILs with low and high Kv1.3 expression. C, Percentage of high GrB-expressing cells in Kv1.3high and Kv1.3low CD8+ TILs. B and C, Solid black triangles, mean; error bars, SEM. Sections from 9 HNC patients were stained for Ki-67 and GrB, ≥10 fields were analyzed/case.

Close modal

Although controversy still exists as to the role that T-cell infiltrates play in cancer, it is generally accepted that a high number of cytotoxic and helper Th1 T cells in the tumors is of good prognostic value (8, 9, 29, 30). Yet, other features, such as the location of TILs within the tumor and their functional state, are crucial for TIL effectiveness in attacking and destroying cancer cells (8, 31, 32). Herein, we have presented evidence that HNC TILs have decreased Kv1.3 function and reduced Ca2+ signaling compared with circulating T cells. Furthermore, CD8+ and CD4+ TILs preferentially localize in the tumor stroma as opposed to the tumor epithelium, and intratumoral CD8+ TILs have lower Kv1.3 expression, which is indicative of reduced proliferative and cytotoxic abilities. Overall, the data we have presented point to Kv1.3 channels in T lymphocytes as possible markers of the functionality of cytotoxic TILs in HNC.

The importance of Kv1.3 channels in T-cell function is well established. Kv1.3 channels set the membrane potential and control the influx of Ca2+ through store-operated CRAC channels (16–18). In the current study, we show that Kv1.3 channels are suppressed in TILs of HNC patients, and this defect contributes to their functional incompetence. The reduced ability of TILs to secrete cytokines and kill cancer cells is well documented, and here, we have provided a possible mechanism contributing to these deficiencies (3, 7). Although TILs have reduced Kv1.3 currents compared with cPBTs, we observed that Kv1.3 currents in cPBTs are comparable with those recorded in age-matched hPBTs. This indicates no intrinsic defects of Kv1.3 in circulating T cells of HNC cancer patients, although it has been reported that some of the defects of TILs, like increased apoptosis and reduced proliferation in response to anti-CD3 antibody, are also present in cPBTs (3). Although there are no defects in Kv1.3 channels in resting/quiescent cPBT cells, we cannot exclude the possibility that cPBTs may fail to upregulate Kv1.3 upon activation or that signaling pathways that control Kv1.3 function upon activation may be altered in these cells (33). We observed not only a lower Kv1.3 channel density but also a significant fraction of TILs have no detectable Kv1.3 currents as compared with cPBTs. As there are no changes in current kinetics, it appears that there is a decrease in the number of functional Kv1.3 channels. The reduction of Kv1.3 channels exclusively in TILs points to the TME as the culprit. Diminished viability due to the isolation process cannot be claimed responsible, as the flow cytometry data indicated that TILs were 99% viable. Indeed, there are immunosuppressive features of the TME that can influence the activity and expression of Kv1.3. Hypoxia reduced the activity and expression of Kv1.3 (20, 34). Other factors, such as low pH, in the TME may have the ability to inhibit Kv1.3 (35). Nevertheless, our data clearly indicate a reduction in Kv1.3 in TILs, which has repercussions on Ca2+ signaling. Furthermore, Kv1.3 downregulation could have an effect on the accumulation of intracellular K+ that has been recently associated to the suppressed function of TILs in necrotic areas of the tumor (36). Interestingly, this study also reported that overexpressing Kv1.3 channels reduced tumor burden and improved survival of tumor-bearing mice, thus underscoring the importance of these channels in tumor clearance and their therapeutic potentials (36).

TILs have reduced Ca2+ fluxes compared with cPBTs (which have Ca2+ fluxes similar to hPBTs). Although we observed no differences in intracellular Ca2+ stores, the Ca2+ influx through the CRAC channels was decreased in TILs. The decreased intracellular Ca2+ levels of TILs observed is in agreement with what has been reported previously both in mice and humans: TILs have lower Ca2+ influx and consequently a remarkable decrease in IFNγ production upon antigen stimulation (11, 37–39). In parallel with these findings, our data indicate that the defective Ca2+ influx in TILs can be attributed to the suppression of Kv1.3 channels. In contrast to what others have previously reported, we have conducted experiments using an experimental protocol that allows bypassing the TCR and measuring only the component of Ca2+ influx that depends on ion channels, transporters, and pumps, thus providing the mechanistic evidence that the decrease in Ca2+ in TILs, at least in part, is due to reduced Kv1.3 channel expression (22, 27). We cannot exclude the possibility that changes in other ionic pathways may contribute to the reduction in Ca2+ influx in TILs, but a previous study from our laboratory showed that a 70% reduction in Kv1.3 activity results in a 40% reduction in Ca2+ influx in PBTs, which coincides with our outcomes in TILs (23). To further support our conclusion, it has been reported that TILs produce significantly higher IFNγ level when an increase in Ca2+ influx was induced by activating them with PMA and ionomycin, that is, the restoration of an appropriate Ca2+ response corrected the functional defects of TILs (11). Furthermore, TILs were able to recover a Ca2+ response to TCR stimulation with time in culture, indicating that disruption of the TME is sufficient to restore the functionality of TILs (37).

We have presented evidence that TILs are functionally impaired because of a defect in Kv1.3 channels. Yet, there is variability in Kv1.3 channel expression in TILs (in Fig. 1B, it can be noted that one of the TILs has conserved the Kv1.3 current density of PBTs) that suggests a certain degree of functional variability. The antitumor importance of TILs depends on the number of T cells that infiltrate the tumor, their phenotype, where they localize within the tumor, and whether they maintain a certain degree of functionality (measured by Kv1.3 expression). High levels of CD3+ T-cell infiltration have been associated with positive prognostic outcomes in patients with HNC and many other solid malignancies (29, 30). Furthermore, the location within the tumor appears to be important in the resolution of the disease (40). HNC patients with high levels of CD3+ T lymphocytes in the proximity of malignant cells had an improved disease outcome, whereas robust CD3+ T-cell infiltration of the tumor stroma or periphery failed to have a prognostic value (40). We observed that both CD4+ and CD8+ TILs localize more in the stroma than in the tumor epithelia. This suggests that “forces” are in place to “trap” T cells in the stroma or “repel” T cells from the tumor epithelia. We also showed that the CD8+ TILs that enter the tumor mass have lower Kv1.3 expression than those that stay in the stroma. This suggests that not only fewer cytotoxic cells come in contact with tumor cells, but also that they are functionally more incompetent than those located in the stroma. This is not true for CD4+ TILs, whose Kv1.3 expression is not different regardless of their location within the tumor. The Kv1.3 expression in CD4+ iTILs is very variable, which might reflect the heterogeneity of this cell population. Our findings show that 25% of the CD4+ TILs are Tregs. This high percentage of Tregs is in agreement with the percentage reported before in HNC (3, 41).

Ki-67 and GrB are markers of CD8+ cell functionality, which are under the control of Kv1.3-regulated Ca2+ signaling and NFAT activity (19, 22, 23, 26). In cohorts of renal cell carcinoma, increased amounts of Ki-67 are associated with improved patient outcomes (29). One study in HNC patients reported an increased infiltration of CD8+GrB+ cells in the tumors, but the infiltration had a limited effect on the patient outcomes (42). In patients with colorectal and ovarian carcinomas, the presence of increased number of CD8+GrB+ cells is associated with better survival rates (5, 29). Here, we described that CD8+ TILs with higher Kv1.3 expression have higher GrB and proliferative capacities. Unfortunately, Kv1.3high CD8+ TILs localize in the stroma more than in the tumor, which may be predictive for the recovery from HNC. Further testing of a large cohort of patients is necessary to assess any prognostic clinical value to these findings.

Overall, our data showed that the suppression of Kv1.3 channels in TILs contributes to reduction in Ca2+ signaling and decreased effector function of CD8+ cells, thus raising the possibility that this channel may be used as a potential marker of functionally competent TILs in cancer.

No potential conflicts of interest were disclosed.

Conception and design: A.A. Chimote, L. Conforti

Development of methodology: A.A. Chimote, L. Conforti

Acquisition of data (provided animals, acquired and managed patients, provided facilities, etc.): A.A. Chimote, P. Hajdu, A.M. Sfyris, B.N. Gleich, K.A. Casper

Analysis and interpretation of data (e.g., statistical analysis, biostatistics, computational analysis): A.A. Chimote, P. Hajdu, A.M. Sfyris, T. Wise-Draper, L. Conforti

Writing, review, and/or revision of the manuscript: A.A. Chimote, P. Hajdu, T. Wise-Draper, K.A. Casper, L. Conforti

Study supervision: L. Conforti

The authors thank Dr. Alexandra H. Filipovich (Cancer and Blood Diseases Institute, Cincinnati Children's Hospital) for her help with TIL phenotyping experiments. The authors would also like to thank Drs. Julianne Qualtieri and Nives Zimmermann (Department of Pathology and Laboratory Medicine, University of Cincinnati) for their help with IHC experiments. All flow cytometry experiments were performed at the Research Flow Cytometry Core in the Division of Rheumatology at Cincinnati Children's Hospital Medical Center and Shriner's Hospital for Children Flow Cytometry Core, Cincinnati OH. Confocal microscopy images were acquired at the Live Microscopy Core, Department of Molecular and Cellular Physiology, University of Cincinnati. The authors thank Dr. Alex B. Lentsch (Department of Surgery, University of Cincinnati) for making the Zeiss AxioImager light microscope available to us.

This work was funded by grant support from the NIH (grant R01CA95286) and a Pilot grant from the University of Cincinnati Cancer Institute (L. Conforti). T. Wise-Draper was supported by a CTSA awarded KL2 Mentored grant and a HOTSA/HOPGA pilot grant from the Division of Hematology/Oncology at the University of Cincinnati.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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