Abstract 5934: Cancer-associated fibroblasts contribute to tumor immunosuppression by regulating tumor-infiltrating lymphocytes
Authors: Kato Takuya , Noma Kazuhiro , Kashima Hajime , Katsura Yuki , Sato Hiroaki , Ninomiya Takayuki , Ohara Toshiaki , Shirakawa Yasuhiro , Fujiwara Toshiyoshi 
Published: July 2017

Background: As like rising of PD-1 antibody, targeting therapy to tumor immunosuppression have been shown dramatic cure responses in melanoma and other malignancies. However there are still problems that the responders of those checkpoint inhibitors are limited. Recently, it is considered that tumor immunosuppression may be caused by not only cancer cells but also tumor microenvironments (TME). Cancer-associated fibroblasts (CAFs) are one of the major components and have a central role for tumor progression in TME. It has been hypothesized that they can also play an essential role in tumor immunosuppression. In this study, we evaluated the correlation between CAFs and tumor immunity system, especially tumor-infiltrating lymphocytes (TILs) in clinical samples and further in vivo study.

Materials and methods: Total 140 cases of esophageal cancer were evaluated for the presence of CAFs and TILs by immunohistochemistry (IHC). CAFs were defined as fibroblasts expressing alpha smooth muscle actin. CD8+ cytotoxic T lymphocytes and FoxP3+ regulatory T cells were investigated as TILs in each specimen’s intratumoral and peritumoral tissues. The outcome was set as the correlation between CAFs and TILs, and Overall survival. In vivo experiments, we used a mouse-derived cancer cell (colon26-Luc) and mouse embryonic fibroblasts (NIH/3T3). BALB/c or BALB/c-nu/nu mice were inoculated with only cancer cells (control) or cancer cells with CAFs (co-CAFs) into right flank to examine the immunosuppression affected by CAFs. The proliferation was examined by in vivo imaging system.

Result: In clinical analysis, CD8+ TILs and CAFs demonstrated strong relations, which were significantly “negative” correlation and showed moderate correlation coefficient in intratumoral tissues (P&lt;0.001, r=-0.416). In FoxP3+ TILs, “positive” correlation was detected significantly (P&lt;0.001, r=0.484). In terms of prognosis, high group of CD8+ TILs had a good prognosis significantly (P&lt;0.001), whereas high group of FoxP3+ TILs had a poor prognosis significantly (P&lt;0.001) in intratumoral tissues. However, there was no difference of the correlation and the prognosis in peritumoral tissues. In vivo experiments demonstrated that promoted ratio of tumor progression by co-CAFs was more strongly demonstrated in BALB/c mice rather than BALB/c-nu/nu mice, suggesting that the group co-CAFs showed inducing immunosuppression in TME. IHC analysis of those tumors showed that accumulation of CD8+ TILs was decreased in tumors of co-CAFs as compared with tumors of control. On the other hand, accumulation of FoxP3+ TIL was increased, showing the same trends as clinical analysis.

Conclusion: Our results suggest that Both CD8+ and FoxP3+ TILs in intratumoral tissues are independent prognostic factors, and CAFs have a significant correlation to those TILs. We consider that CAFs may affect tumor immunosuppression by regulating the migration of TILs.

Citation Format: Takuya Kato, Kazuhiro Noma, Hajime Kashima, Yuki Katsura, Hiroaki Sato, Takayuki Ninomiya, Toshiaki Ohara, Yasuhiro Shirakawa, Toshiyoshi Fujiwara. Cancer-associated fibroblasts contribute to tumor immunosuppression by regulating tumor-infiltrating lymphocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5934. doi:10.1158/1538-7445.AM2017-5934