Abstract
Background: Tumor immunity in the tumor microenvironment is activated in patients with feasible clinical responses to immune checkpoint inhibitors. The immunological profile of tumor-infiltrating lymphocytes (TILs) obtained from patients with oral squamous cell carcinoma (OSCC) was examined in relation to their prognosis. Materials and Methods: Surface antigens, including immune checkpoint molecules, on TILs from 31 patients with primary OSCC were analyzed by flow cytometry. The activation status of TILs was examined through a heatmap analysis and unsupervised clustering classified patients into groups with activated or inactivated TILs. A supervised machine-learning algorithm for single-cell analyses in relation to prognosis was run using the Cluster Identification, Characterization, and Regression (CITRUS) program. Results: None of surface antigens were related to prognosis. The CITRUS program revealed a relationship between CD45RA−CD4+ CD25high inducible T-cell co-stimulator (ICOS)+ TILs and recurrence, and also identified a similar fraction significantly specific to the group with activated TILs. The disease-free survival rate for patients with ≥95% ICOS+ TILs was significantly lower than that for those with <95% ICOS+ TILs. Furthermore, a review of clinicopathological factors related to prognosis identified the percentage of ICOS+ TILs to be an independent prognostic factor for patients with OSCC. Conclusion: CD25highICOS+ regulatory T-cells in TILs have potential as a biomarker for predicting recurrence after surgical treatment and clinical responses to immune checkpoint inhibitors in patients with OSCC.
- Oral squamous cell carcinoma
- immune checkpoint
- tumor-infiltrating lymphocytes
- flow cytometry
- regulatory T-lymphocytes
Among head and neck squamous cell carcinomas, oral squamous cell carcinoma (OSCC) is the most common malignant neoplasm originating in the oral cavity, with an estimated incidence of 6.3 and 3.2 per 100,000 males in Northern America and South-Eastern Asia, respectively, in 2018 (1-3). Surgical resection is the basic treatment for OSCC; however, decision-making regarding adjuvant therapy relies on risk factors identified in a pathological examination using resected specimens, e.g., the depth of invasion, extranodal extension, and pathological TNM staging (4-6). Recent advances in morphological analyses of the prognosis of patients has led to the identification of several factors, e.g., tumor budding, tumor-infiltrative growth pattern (INF), Y-K classification, and an immunohistochemical analysis of infiltrating immune-related cells (7-11).
Due to the success of immune checkpoint inhibitors (ICIs) in recent years, tumor-infiltrating immune-related cells have been attracting increasing interest. Greater CD3+ or CD8+ T-cell infiltration being associated with a better prognosis was proposed as an ‘immunoscore’ by Galon et al. using immuno-histochemistry (12), and subsequent studies pathologically detected different grades of immune activation in the tumor microenvironment (TME) in cases showing feasible clinical responses to ICIs (13-16). TME can be classified based on three characteristics, which are further subclassified into three categories: Components (prevalence of effectors/equilibrium/prevalence of suppressors), location (inflamed/excluded/‘desert’), and T-cell activation (activated effectors/equilibrium/exhausted effectors). Non-responders to ICIs often have TMEs with characteristics of prevalence of suppressors, immune desert, and exhausted effectors; tumors with these characteristics are considered ‘cold’, as opposed to ‘hot’ ones, with activated tumor immunity (16-22).
Comprehensive gene-based studies to identify predictors of outcomes to ICIs have also been performed using pretreatment tumor biopsies. Due to the difficulties associated with identifying a single factor, a profile analysis using multiple factors is often applied to biomarker research for ICI responders and some clusters, e.g., the regulation of mesenchymal transition, cell adhesion, and angiogenesis, have been identified (16, 17, 19). Immune-related signatures, particularly that associated with tumor-infiltrating lymphocytes (TILs), have been also targeted based on gene expression. Although there are few reports of TIL analysis by flow cytometry due to the difficulty of purifying TILs from small samples of fresh tumor tissue, Kumagai et al. reported that the expression of immune-related proteins was generally strongly positive in activated T-cell clusters, which appeared to be more remarkable in TILs from responders to ICIs (23). Such profile analysis of the expression signature of TILs has also been applied to the prediction of the general prognosis of patients with cancer, such as in the ‘immunoscore’ (12, 14, 21).
CD4+ regulatory T-cells (Tregs) expressing the critical transcriptional factor, forkhead box protein 3 (FOXP3) play an important role in maintaining immune homeostasis. In tumor immunity, the induction, proliferation, recognition, and responses of T-cells in a tumor-specific manner are suppressed through the consumption of interleukin-2 (IL2), binding of cytotoxic T-lymphocyte-associated protein 4, and combined immune-inhibitory functions with other molecules, e.g., transforming growth factor β, IL10, and T-cell immunoreceptor with Ig and ITIM domains, resulting in an environment that is suitable for the survival and proliferation of tumor cells (21, 24-28). Since effector Tregs (eTregs) with strong immunosuppressive functions express high levels of FOXP3 and CD25, previous studies examined markers specific to the FOXP3/CD25high eTreg fraction and successfully identified some, including inducible co-stimulatory receptor (ICOS), C-C chemokine receptor types 4 and 8 (29, 30).
In this study, to investigate the immunological profile of the TME in relation to patient prognosis, we investigated the immune-related molecules on TILs purified from fresh OSCC using multicolor flow cytometry.
Materials and Methods
Patients and tissue samples. Fresh tumor tissues were obtained from 31 treatment-naïve patients with OSCC at surgery as standard therapy between December 2018 and February 2021. Tissue-infiltrating T-cells were purified using a Tumor Dissociation Kit for humans (Miltenyi Biotec, Bergisch Gladbach, Germany) and gentleMACS Dissociator (Miltenyi Biotec) according to the manufacturer’s instructions. The present study was approved by the Osaka University Dental Hospital Ethics Committee (H30-E49-3, Osaka, Japan), and written informed consent was obtained from each patient according to the Declaration of Helsinki.
Antibodies. The following antibodies were purchased for flow cytometry analysis: CD45RA-fluorescein isothiocyanate (clone HI100), CD25-phycoerythrin (PE) (BC96), tumor necrosis factor (TNF) receptor superfamily member 9 (4-1BB/CD137)-BV421 (4B4-1), CD8-BV510 (RPA-T8), CD103-BV605 (Ber-ACT8), CD4-BV711 (OKT4), CD45-BV786 (HI30), T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3)-allophycocyanin, (F38-2E2), CD3-Alexa Fluor 700 (UCHT1), and IgG1 isotype control (MOPC-21) from BioLegend (San Diego, CA, USA), ICOS-peridinin-chlorophyll-protein eFluor 710 (ISA-3) and IgG1 isotype control (P3.6.2.8.1) from eBioscience (San Diego, CA, USA), and TNF receptor superfamily member 4 (OX40/CD134)-PE-CF594 (ACT35), programmed cell death 1 (PD1)-PE cyanine7 (EH12.1), and IgG1 isotype control (X40) from BD Bioscience (San Jose, CA, USA).
Flow cytometry. Cells were stained with fluorophore-conjugated antibodies after a Fc receptor block (Human TruStain FcX Fc Receptor-blocking solution; BioLegend) and incubated with the Live/Dead Fixable Yellow Dead Cell Stain Kit (Life Technologies, Carlsbad, CA, USA) at 4°C for 30 min. Stained cells were analyzed by LSR Fortessa (BD Biosciences), and the frequencies of cell populations were obtained and analyzed with DiVA software (BD Biosciences). To assess positive staining, an isotype control of the primary antibody conjugated with each fluorophore was used.
Cluster Identification, Characterization and Regression (CITRUS). CITRUS in the Cytobank program (Beckman Coulter, Brea, CA, USA) is a supervised machine-learning algorithm for single-cell analyses. The CITRUS algorithm clusters and identifies cell populations that are significantly different to distinguish outcome groups (31). The CITRUS algorithm was run using the raw data of 10 cell-surface markers (CD4, CD8, CD45RA, CD25, PD1, TIM3, CD103, ICOS, 4-1BB, and OX40) obtained from flow cytometric analyses of patients with >1,600 CD3+ cells.
Statistical analysis. The significance of differences in each experimental data set between two groups was assessed using the Kruskal–Wallis test, Fisher’s exact test, and Pearson’s chi-squared test. The disease-free survival (DFS) rate was analyzed by the Kaplan–Meier method and compared using the log-rank test. Survival time was calculated from the time of surgery until June 2021. Univariate and multivariate analyses were performed using Cox regression analysis. The expression profiles of T-cell surface markers were visualized by heat mapping after individual data were transformed to Z-scores for standardization, and a hierarchical clustering algorithm was performed using Ward’s method. All statistical analyses were performed using JMP Pro 15 (SAS Institute, Cary, NC, USA). To detect the optimal cut-off value, the area under the receiver operating characteristic (ROC) curve was calculated. A value of p<0.05 was considered to be significant.
Results
Clinicopathological factors in enrolled patients with OSCC. Thirty-one patients with OSCC were enrolled in the present study (Table I). Their median age at surgery was 72 years, and pathological stages were diagnosed as I/II in 15 patients and III/IV in 16 patients. After curative surgical treatment, six patients were diagnosed with recurrence during the observation period. When clinicopathological factors, including tumor stage, tumor grade, and INF, were compared between the six patients with and 25 without recurrence, no significant differences were observed.
Patient characteristics.
Analysis of the expression of surface molecules on TILs in relation to prognosis. The characteristics of CD4+ and CD8+ TILs purified from surgically resected specimens were evaluated by the expression of surface molecules representing activation (CD45RA and CD103), immune checkpoints (PD1, TIM3, ICOS, 4-1BB, and OX40), and eTregs (CD25). To investigate marker candidates that predict the prognosis of patients, the frequency of CD4+ and CD8+ in CD3+ cells; CD45RA+, PD-1+, TIM3+, ICOS+, 4-1BB+, OX40+, CD25+, and CD103+ cells in CD4+ or CD8+ cells; and CD45RA−CD25high cells in CD4+ cells among populations of live, singlet, CD45+, and CD3+ cells were compared between patients with and without recurrence. For each marker, patients with and without recurrence showed similar patterns of expression (Figure 1). A profiling analysis with the CITRUS algorithm using the raw data of all markers obtained from flow cytometric analyses was performed to identify specific populations to patients with recurrence. The CITRUS analysis identified cluster 40119 (Figure 2A and B), and T-cells in this population showed clear expression of CD4, strong expression of CD25 and ICOS, and relatively higher expression of OX40 and 4-1BB than all TILs as the control (Figure 2C and Supplementary Figure 1). A scatter plot of the flow cytometric analyses revealed that most of the CD4+ TILs expressing OX40 and 4-1BB were included in the CD4+ CD25high ICOS+ population in all patients (Figure 2D). When the percentage of ICOS+CD4+ CD25high cells analyzed by flow cytometry was compared between patients with and without recurrence, it was non-significantly higher in the former than in the latter (p=0.117, Figure 2E). Furthermore, when patients with OSCC were divided based on the median percentage of ICOS+ cells in CD4+CD25high cells (82.1%), five out of six patients with recurrence were classified into the group with a higher proportion of ICOS+ cells (compared with 11/25 patients without recurrence p=0.0834).
Relationship between recurrence and the expression of surface markers on tumor-infiltrating lymphocytes. The percentages of CD8+, CD4+, CD45RA+, programmed cell death 1 (PD1)+, T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3)+, inducible T-cell co-stimulator (ICOS)+, tumor necrosis factor receptor superfamily member 9 (4-1BB/CD137)+, TNF receptor superfamily member 4 (OX40/CD134)+, CD25+, CD103+, and CD45RA−CD25high cells in CD3+ (A), CD8+ (B), and CD4+ (C) T-cells were compared between patients with and without recurrence.
A profiling analysis with the CITRUS algorithm identified a T-cell population specific to patients with recurrence. A: The CITRUS analysis identified cluster 40119. B: The frequency of T-cells in cluster 40119 was significantly higher in patients with than in those without recurrence. C: Expression patterns on T-cells in cluster 40119 in patients with recurrence relative to those in all tumor-infiltrating lymphocytes (TILs). D: Most of the CD4+ TILs expressing TNF receptor superfamily member 4 (OX40/CD134) and TNF receptor superfamily member 9 (4-1BB/CD137) were part of the population of CD4+ inducible T-cell co-stimulator (ICOS)+ CD25high TILs. A representative result is shown. E: The percentage of ICOS+ in CD4+CD25high TILs was compared between patients with (mean±standard deviation= 87.9±9.2%) and without (75.7±21.4%) recurrence (p=0.117). PD1: Programmed cell death 1; TIM3: T-cell immunoglobulin and mucin domain-containing protein 3.
Identification of ‘hot’ and ‘cold’ tumors using a heatmap analysis. The status of T-cells in tumor tissue was examined by a heatmap analysis using the frequencies of CD4+ and CD8+ in CD3+cells; CD45RA+, PD1+, TIM3+, ICOS+, 4-1BB+, OX40+, CD25+, and CD103+ cells in CD4+ and CD8+ cells, and CD45RA−CD25high in CD4+ cells. Unsupervised clustering classified 31 OSCC TILs into two clusters: Cluster A with immunologically inactivate TILs and cluster B with immunologically activated TILs (Figure 3). Twenty patients in cluster B with activated TIL profiles had a significantly higher maximum standardized uptake value (SUVmax) by 18F-fluoro-deoxyglucose positron-emission tomography imaging, a stronger INF, and shorter DFS than patients in cluster A (Table II).
Profiling and clustering analyses with a heatmap analysis. The activation status of tumor-infiltrating lymphocytes (TILs) was examined by a heatmap analysis using 31 sets (ORC No.) of TILs and the expression frequencies of 19 surface markers. A hierarchical clustering algorithm showed two clusters, A and B. Recurrence is shown under the heatmap. 4-1BB: Tumour necrosis factor receptor superfamily member 9 (CD137); ICOS: Inducible T-cell co-stimulator; N: no recurrence; OX40: TNF receptor superfamily member 4 (CD134); PD1: programmed cell death 1; R: recurrence; TIM3: T-cell immunoglobulin and mucin domain-containing protein 3.
Clinicopathological factors of patients with oral squamous cell carcinoma in clusters A and B defined by the heatmap analysis.
A profiling analysis with the CITRUS algorithm using the raw data of all markers was performed to examine specific populations of clusters. Two clusters abundant in cluster B, 40129 and 40140, and two clusters, abundant in cluster A, 40118 and 40144, were identified (Figure 4A-C and Supplementary Figure 2). T-Cells in cluster 40129 were CD4+, CD25+ and ICOS+, and had high expression of OX40 and 4-1BB, and this expression pattern was similar to that identified in the prognostic analysis. In the flow cytometric analysis, % ICOS+ in CD4+ CD25high was significantly higher in Cluster B than in Cluster A (p=0.03, Figure 4D). T-Cells in cluster 40140 had clear expression of CD4, intermediate expression of CD25 and ICOS, but did not express OX40 or 4-1BB (Figure 4C).
A profiling analysis with the CITRUS algorithm identified a population specific to cluster B. A: The CITRUS analysis identified clusters 40129, 40140, 40118, and 40144. B: The frequency of T-cells in clusters 40129 and 40140 was significantly higher in patients of cluster B than in patients of cluster A. Clusters 40118 and 40144 were abundant in cluster A. C: Expression patterns of clusters 40129, 40140, 40118 and 40144 in patients of cluster B relative to those in all patients. D: The percentage of inducible T-cell co-stimulator (ICOS)+ cells in CD4+ CD25high tumor-infiltrating lymphocytes were compared between patients of cluster A (mean±standard deviation=68.8±25.7) and cluster B (83.1±14.7) (p=0.03). 4-1BB: Tumour necrosis factor receptor superfamily member 9 (CD137); ICOS: Inducible T-cell co-stimulator; OX40: tumor necrosis factor receptor superfamily member 4 (CD134); PD1: programmed cell death 1; TIM3: T-cell immunoglobulin and mucin domain-containing protein 3.
ICOS expression in CD4+ CD25high T-cells and prognosis. Since the present results indicated that the percentage of ICOS+ cells in CD4+CD25high T-cells (mean±standard deviation=78.0±20.1%, median=82.1%) was closely associated with the activation of T-cells in the TME, we examined its relevance to the prognosis of these patients with OSCC. No significant difference was observed in DFS when analyzed by the log-rank test (p=0.095, Figure 5A) when the 31 patients were divided by the median percentage of ICOS+ cells of CD4+ CD25high cells. However, DFS was significantly shorter in patients with ≥95% ICOS+ in CD4+CD25high cells, the threshold selected by the ROC curve (Figure 5B and C) (p=0.0157). The percentages of different cell populations did not correlate with DFS even in re-evaluation using each respective ROC. We then reviewed clinicopathological factors in relation to prognosis, including the ICOS+ population. Even after the re-evaluation of age and SUVmax using ROC curves (data not shown), the percentage of ICOS+ cells in CD4+ CD25high TILs was identified as an independent prognostic factor for OSCC patients in univariate and multivariate analyses (Table III).
Disease-free survival curves for patients with oral squamous cell carcinoma according to the percentage of inducible T-cell co-stimulator (ICOS)+ cells in CD4+ CD25high tumor-infiltrating lymphocytes (TILs). A: Patients were divided into two groups based on the median percentage of ICOS+ cells (82%). Log-rank test showed disease-free survival was not significantly different between the two groups. B: A receiver operating characteristics analysis was performed to detect the optimal cut-off value for disease-free survival, which was found to be 95% ICOS+ cells in CD4+ CD25high TILs (area under the curve=0.713, sensitivity=50%, specificity=92%). C: Partitioning the patients by the value derived from the receiver operating characteristics analysis showed disease-free survival to be significantly better for those with <95% ICOS+CD4+CD25high TILs.
Univariate and multivariate analyses of prognostic factors for disease-free survival of patients with oral squamous cell carcinoma.
Discussion
CD25+CD4+ T-cells have been identified as Tregs. Miyara et al. detected eTregs with immunosuppressive functions in the CD25high fraction, while others reported the co-expression of ICOS and tumor necrosis factor receptor superfamily members, including OX40 and 4-1BB (29, 30). The fraction of cells with intermediate expression of CD25 has also been identified as non-Tregs, a heterogenous population with low or no immunosuppressive activity. The populations in cluster 40119 in Figure 2 and Cluster 40129 in Figure 4 may be regarded as eTregs because of the high expression of CD25, ICOS, OX40 and 4-1BB (32, 33). On the other hand, the population in cluster 40140 in Figure 4 may be non-Tregs with intermediate expression of CD25, low expression of ICOS, and no expression of OX40 or 4-1BB. Abundant expression of CD25, high affinity IL2 receptor, plays an important role in the immunosuppressive functions of eTregs because the consumption of IL2 by eTregs induces a deficiency in IL2 and affects T-cell antitumor activity around eTregs in the TME (24, 25).
ICOS has been identified as a surface molecule that is induced and activated by T-cell receptors, and is highly expressed by TILs, particularly eTregs in the TME (26, 34). Interactions with its counterpart ICOS-ligand mediate the induction, proliferation, and immunosuppressive functions of ICOS+ eTregs. In our previous studies on gastric cancer and colorectal cancer, we demonstrated that ICOS+ Tregs were unique to tumor tissues, were induced by ICOS-ligand+ plasmacytoid dendritic cells following stimulation with Helicobacter pylori through toll-like receptor 7 in the gastric mucosa, produced the highly immunosuppressive cytokine IL10 and were identified as a biomarker for a poor prognosis, while a very small population of effector T-cells expressed ICOS (27, 35, 36). ICOS+ Tregs have also been detected in tumor tissue from many cancer types, including melanoma, head and neck cancer, and breast cancer (26). Several clinical trials using anti-ICOS to target eTregs in TME as cancer immunotherapy are now being actively conducted (NCT02520791, NCT03829501, and NCT02723955). An antibody developed for clinical use achieved depletion of ICOShigh eTregs by antibody-dependent cellular cytotoxicity and, simultaneously, activated effector T-cells with low expression of ICOS (34).
Our CITRUS analysis revealed that abundant ICOS+ eTregs reflected the phenomenon of ‘hot’ OSCC tumors, which has been reported as a feasible immune status for ICI therapy. A biomarker other than the expression of PD-L1 that has already been established and is clinically applied is microsatellite instability (MSI)-high. Frequent mutations in tumor cells induce the MSI-high status and produce immunogenic proteins, so-called neoantigens, that elicit strong antitumor immune responses (14, 37-39). However, the sustained presence of tumors in patients indicates that the tumor immunity elicited does not function, due to several mechanisms including immunosuppressive pathways, such as PD1/PD-L1, and immunosuppressive cells such as Tregs. This is why we anticipate the effectiveness of combination therapy of ICOS antibodies and ICIs, such as through PD1/PD-L1 pathway blockade.
The results showing that CD8+ and CD4+ T-cells in CD3+ cell populations were not associated with prognosis, and that CD8+ T cells in CD3+ cells were not clearly distinguishable between the ‘hot’ and ‘cold’ tumors in the heatmap analysis were of interest (Figure 3). The activated state of T-cells identified by multivariate analysis, such as heatmapping, may be independent of the frequency of CD8+ cells, and this hypothesis is supported by recent studies by Galon et al. that added CD45RO as an activation marker for immunoscore analysis (12, 14). To overcome the limitations in the present study of the frequency, but not numbers, of T-cells and prognosis of DFS, but not overall survival, we intend to conduct an immunohistochemical analysis of archived OSCC specimens. We will also accumulate a larger number of cases including ICI-treated patients to confirm the present results.
In conclusion, we identified ICOS+ eTregs as a potential biomarker for the prediction of recurrence after surgery and activation status of TILs in patients with OSCC. A clinical study of ICOS antagonist in combination with the blockade of the PD1/PD-L1 pathway for patients with head and neck cancer is currently being carried out (NCT02723955), therefore, we are paying close attention to the results for patients with OSCC and hope that assay of ICOS may become a companion diagnostic method.
Acknowledgements
This study was supported by Grants-in-Aid for Scientific Research (B) grant no. 19H03729 from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The Authors thank all the patients who participated. We thank Junko Higuchi for her excellent assistance.
Footnotes
Authors’ Contributions
HK, NU, and HW designed the study; HK, Mhi, Mha, and AU performed the assays; AK and KI performed the statistical analysis; HK, KH, KM, ST, and NU collected samples and obtained clinical data; HK, NU, and HW analyzed the data; HK and HW wrote the article; HK, NU, and HW participated in article editing and discussions.
Supplementary Material
Supplementary Figure 1 is available at: https://doi.org/10.6084/m9.figshare.19388423.v1
Supplementary Figure 2 is available at: https://doi.org/10.6084/m9.figshare.19391159
Conflicts of Interest
The Department of Clinical Research in Tumor Immunology is a collaborating laboratory of Osaka University and Shionogi Co., Ltd. The Authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.
- Received March 1, 2022.
- Revision received March 22, 2022.
- Accepted March 24, 2022.
- Copyright © 2022 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.