Increased prevalence of tumor-infiltrating regulatory T cells is closely related to their lower sensitivity to H2O2-induced apoptosis in gastric and esophageal cancer.

PURPOSE AND EXPERIMENTAL DESIGN: Although an increase in regulatory T cells (Tregs) is observed in tumor microenvironments, the underlying mechanism is not fully clarified. Since it was suggested that Tregs showed a lower sensitivity toward oxidative stress in comparison with conventional T cells, in the present study, we investigated the H(2)O(2) production and apoptosis of Tregs in gastric and esophageal cancer tissues, employing flow cytometric analysis using fresh samples (n = 93) and immunohistochemical analysis (n = 203). RESULTS: The increased tumor-infiltrating Tregs coexisted with elevated H(2)O(2) production according to disease progression. The grade of apoptosis in Tregs was less pronounced than that in conventional T cells, and there was a positive correlation between H(2)O(2) production and the grade of apoptosis in conventional T cells, while there was no correlation between H(2)O(2) production and the grade of apoptosis in Tregs. Moreover, Tregs were less sensitive to H(2)O(2)-induced apoptosis compared with conventional T cells in vitro. CONCLUSIONS: We have demonstrated that the increased prevalence of tumor-infiltrating Tregs closely related to their lower sensitivity to H(2)O(2)-induced apoptosis.

Immunogenic tumor cell death induced by chemoradiotherapy in patients with esophageal squamous cell carcinoma.

Although it has been shown that chemoradiotherapy may induce immunogenic cell death, which could trigger T-cell immunity mediated by high-mobility group box 1 protein (HMGB1) and calreticulin, there is still limited information to support this theory directly in a clinical setting. In the present study, we evaluated antigen-specific T-cell responses against six cancer-testis antigens in peripheral blood lymphocytes from patients with esophageal squamous cell carcinoma (ESCC) receiving chemoradiation. Expression of HMGB1 and calreticulin within tumor microenvironment was also analyzed in resected samples with and without chemoradiotherapy in relation to patients survival. Tumor antigen-specific T-cell responses were confirmed in six (38%) of 16 patients with ESCC after chemoradiotherapy coexisting with elevated serum HMGB1. In addition, HMGB1 within tumor microenvironment was significantly upregulated in patients with ESCC with preoperative chemoradiotherapy, but not in those without chemoradiotherapy, and the degree of HMGB1 positively correlated with patient survival (n=88). Both irradiation and chemotherapeutic drugs induced upregulation of HMGB1 and calreticulin in nine ESCC cell lines. Furthermore, HMGB1 was able to induce maturation of dendritic cells. Together, our findings indicate that chemoradiation induces tumor antigen-specific T-cell responses, and HMGB1 production is related to clinical outcome after chemoradiation.

H2O2 production within tumor microenvironment inversely correlated with infiltration of CD56(dim) NK cells in gastric and esophageal cancer: possible mechanisms of NK cell dysfunction.

Human NK cells can be divided into two subsets, CD56(dim)CD16(+)NK and CD56(bright)CD16(-)NK cells, based on their expression of CD56 and CD16. In the present study, we analyzed the relationship between CD56(dim)/CD56(bright) NK cells and H2O2 in tumor-infiltrating NK cells in patients with gastric (n = 50) and esophageal (n = 35) cancer. The ratio of CD56(dim) NK cells infiltrating tumors gradually decreased according to disease progression. H2O2 was abundantly produced within tumor microenvironments, and there was an inverse correlation between CD56(dim) NK cell infiltration and H2O2 production. CD56(dim) NK cells are more sensitive to apoptosis induced by physiological levels of H2O2 than CD56(bright) NK cells. Furthermore, the exposure of NK cells to H2O2 resulted in the impairment of ADCC activity. In conclusion, H2O2 produced within tumor microenvironments inversely correlated with the infiltration of CD56(dim) NK cells, possibly due to their preferentially induced cell death. These observations may explain one of the mechanisms behind NK cell dysfunction frequently observed in tumor microenvironments.

Distribution of Th17 cells and FoxP3(+) regulatory T cells in tumor-infiltrating lymphocytes, tumor-draining lymph nodes and peripheral blood lymphocytes in patients with gastric cancer.

Although Th17 cells reportedly play critical roles in the development of autoimmunity and allergic reactions, information on Th17 cells in cancer-bearing hosts is still limited. In the present study, we investigated the distribution of Th17 cells in relation to regulatory T cells (Treg) in the tumor-infiltrating lymphocytes (TILs), regional lymph node lymphocytes, and peripheral blood lymphocytes of gastric cancer patients. Interleukin (IL)-17-producing CD4(+) cells as Th17 cells and CD4(+)CD25(+)FoxP3(+) cells as Treg were evaluated by flow cytometry and expressed as a percentage of the total CD4(+) cells, in addition to performing a Th1/Th2 balance assay. Moreover, immunohistochemical staining for IL-17 and FoxP3 were performed. In TILs from patients with early disease (n = 27), the frequency of Th17 cells was significantly higher than that in the normal gastric mucosa (23.7 ± 8.9 vs 4.5 ± 3.1%). In TILs from patients with advanced disease (n = 28), the frequency of Th17 cells was also significantly higher, but lower compared to early disease, than that in the normal gastric mucosa (15.1 ± 6.2 vs 4.0 ± 2.0%). This observation for Th17 cell-distribution was also confirmed by immunohistochemistry. When the ratio of Th17/Treg in TILs was evaluated in individual cases, it was more markedly increased in early than in advanced disease. In conclusion, the accumulation of Th17 cells as well as Treg in the tumor microenvironment of gastric cancer occurred in early disease and then the infiltration of Th17 cells gradually decreased according to the disease progression, in contrast to increased Treg.