Abstract 2809: The induction of CD8+ T lymphocytes and PD-L1+ immune cells by neoadjuvant chemoradiotherapy for rectal cancer

Background; The relationship between tumor immunological microenvironment and irradiation has been studied so far. Based on these findings, we examined a tumor microenvironment of rectal cancer performed by neoadjuvant chemoradiotherapy (NACRT) with immunohistochemical analysis of surgical specimens. But, for introduction to clinical settings, the analysis is not yet sufficient. So, in more detail, we investigate tumor infiltrating CD8+ T cells by irradiation in mouse CT26 colon tumor model. Methods; Locally advanced rectal cancer were enrolled and 68 were eligible for this study. Immunohistochemical staining of programmed cell death- lignad1(PD-L1), CD8, and CD163 was performed on specimens of all cases. In a mouse model, CT26 tumor cells were inoculated in mouse, tumors are irradiated with a single dose of 10Gy after 14 days. We analyzed CD8+ T cells infiltration of both irradiated mouse and no treated mouse by flow cytometry. Results; There were 44 cases in which NACRT was performed (NA group) and 24 cases in which surgery alone was performed (SA group). In the SA group, there was no significant change in the infiltration of PD-L1+immune cells (PD-L1+IC) nor CD8 +cells before and after treatment, but in the NA group, the infiltrations of them were significantly increased. In multivariate analysis, low infiltration of CD8 +cells were identified as poor prognostic factors in disease-free survival. Moreover, in our mouse model, elevated numbers of tumor-infiltrating CD8+ T cells between day11 and day18 after irradiation were observed in tumors of irradiated mice compared to no treated mouse. We observed that among CD8+ T cells, cells that coexpress PD-1 and Tim-3 comprise the major population in irradiated mouse. PD-1+Tim-3+ CD8+ T cells produced more INF-γ compared to that by PD-1+Tim-3-CD8+ T cells and PD-1-Tim-3- CD8+ T cells in irradiated mouse and no treated mouse. Among the three populations PD-1+Tim-3+ population contained the largest fraction of central memory (CD44hiCD62Llow) cells, but the lowest fraction of central memory (CD44hiCD62Lhi) cells. Conclusion; The infiltration of PD-L1+IC and CD8 +cells was induced by NACRT. In the mouse model, we confirmed the kinetical and phenotypical changes of tumor-infiltrating CD8+ T cells. Citation Format: Eiji Fukuoka, Kimihiro Yamashita, Yutaka Sugita, Akira Arimoto, Tetsu Nakamura, Yoshihiro Kakeji. The induction of CD8+ T lymphocytes and PD-L1+ immune cells by neoadjuvant chemoradiotherapy for rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2809.