Abstract 1741: Cancer-associated fibroblasts regulate intratumoral CD8+/FoxP3+ T cells via interleukin 6 in the tumor immune microenvironment
Authors: Kato Takuya , Noma Kazuhiro , Katsura Yuki , Sato Hiroaki , Kohmoto Satoshi , Ohara Toshiaki , Tazawa Hiroshi , Shirakawa Yasuhiro , Inagaki Masaru , Fujiwara Toshiyoshi 
Published: August 2018

Cancer-associated fibroblasts (CAFs) in the tumor microenvironment (TME) are the most abundant cell population and play a central role in tumor progression. It is currently considered that the TME may strongly affect tumor immunosuppression. We investigated whether CAFs can regulate tumor-infiltrating lymphocytes (TILs) and their role in tumor immunosuppression. 140 cases of esophageal cancer were analyzed for CAFs, and CD8+ or forkhead box protein 3 (FoxP3)+ TILs by immunohistochemistry (IHC). We performed cytokine assays in a co-culture model using murine or human fibroblasts and cancer cells. Murine-derived fibroblasts and cancer cells were also inoculated into BALB/c or BALB/c-nu/nu mice, and the tumors treated with recombinant interleukin 6 (IL-6) or anti-IL-6 antibody. In clinical samples, patients with high CD8+ TIL numbers in intra-tumoral sites had significantly longer OS than those with low numbers (HR = 0.42, 95% CI = 0.25-0.70; P = 0.001). On the other hand, the high FoxP3+ TIL group for intra-tumoral tissues had significantly a shorter OS (HR = 2.82, 95% CI = 1.66-4.78; P &lt; 0.001). However, in peri-tumoral tissues, no significant correlations between CD8+ or FoxP3+ TIL numbers and prognosis were identified. Furthermore, CD8+ TILs and CAFs were negatively correlated in intra-tumoral tissues (P &lt; 0.001), while FoxP3+ TILs and CAFs, were positively correlated (P &lt; 0.001). In vivo, Co-cultured Colon26 cancer cells and NIH/3T3 fibroblasts resulted in subcutaneous tumors with accelerated growth in BALB/c mice, along with decreased CD8+ and increased FoxP3+ TILs, compared with cancer cells alone. Furthermore, the tumor progression ratio of co-cultured group to cancer cells alone group was demonstrated more strongly in BALB/c rather than BALB/c-nu/nu mice, which are immunodeficient mice. In vitro, IL-6 was secreted at high levels in both murine and human cancer cell/fibroblast co-cultures rather than cancer cell/fibroblast alone. Treatment with IL-6 significantly increased growth of Colon26 subcutaneous tumors in immune-competent BALB/c mice (P &lt; 0.001), whereas no difference was observed in BALB/c-nu/nu mice. IHC demonstrated fewer CD8+ TILs in Colon26+IL-6 subcutaneous tumors than in untreated tumors (P &lt; 0.001). In contrast, FoxP3+ TILs increased in IL-6-treated tumors (P &lt; 0.001). IL-6 antibody blockade of tumors co-cultured with fibroblasts resulted not only in regression of tumor growth but also in the accumulation of CD8+ TILs in intra-tumoral tissues. In conclusion, CAFs regulate immunosuppressive TIL populations in the TME via IL-6. IL-6 blockade, or targeting CAFs, may improve pre-existing tumor immunity and enhance the efficacy of conventional immunotherapies.

Citation Format: Takuya Kato, Kazuhiro Noma, Yuki Katsura, Hiroaki Sato, Satoshi Kohmoto, Toshiaki Ohara, Hiroshi Tazawa, Yasuhiro Shirakawa, Masaru Inagaki, Toshiyoshi Fujiwara. Cancer-associated fibroblasts regulate intratumoral CD8+/FoxP3+ T cells via interleukin 6 in the tumor immune microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1741.