Abstract 3958: The importance of co-localized resting CD8+ T cells and proliferating tumor cells in gastric cancer
Authors: Yigitsoy Mehmet , Earle Sophie , Meier Armin , Harder Nathalie , Hale Matthew , Zuraw Aleksandra , Yoshikawa Takaki , Schmidt Günter , Huss Ralf , Grabsch Heike I. 
Published: July 2017

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide. With the advent of immunotherapies, there is a need to characterize the phenotype of tumor infiltrating immune cells and co-localized cancer cells. We have shown previously that high density of CD45R0+ T cells is related to better prognosis in Japanese GC. However, the variation of T-cell infiltration in GC is still not understood. We hypothesized that an increased CD8+ T-cell infiltration is related to T-cell activation (high T cell Ki67 proliferation index).

Purpose: To establish the frequency of co-occurrence of Ki67+ and CD8+ in T cells and their co-localization with tumor cells and evaluate the relationship with clinicopathological variables including survival.

Patients and Methods: Immunohistochemistry for T cells (CD8), proliferation (Ki67), and epithelial cells (CK) was performed on tissue microarrays (TMAs) from 213 GC from the Kanagawa Cancer Centre Hospital (Yokohama, Japan). Stained slides were scanned, quality controlled, and analyzed using Tissue Phenomics (Definiens, Munich, Germany) for cell/nuclei segmentation and automatic co-registration of consecutive sections. The TMA cores were subdivided into tiles of size 64 µm2 to count co-localized positive cells. Average ratio of CD8+ cells and Ki67+ cells per tile/patient was used for statistical analyses. The relationship with pT, pN and histological tumor type was assessed using the Kruskal-Wallis test. Prognostic features were determined by univariate stratification which optimizes Kaplan-Meier p-value using 50 independent pre-validations with 3 folds and ranked by the median pre-validation p-values. P-values &lt; 0.05 were considered significant.

Results: 60887 tiles were analyzed in total. Median (range) number of tiles analyzed per patient was 291 (81-345). Median (range) CD8+/Ki67+ ratio was 0.39 (0.01-0.92). Manual inspection of selected image tiles showed that CD8+ cells are rarely Ki67+. Median (range) % of tiles/patient where CD8+Ki67- cells co-localized with Ki67+ tumor cells was 17% (0%-93%). Significant difference of ratio was observed between histological subtypes (p=0.0096). There was no significant relationship between CD8+/Ki67+ and pT or pN. A high CD8+/Ki67+ ratio was related to better survival (p=0.012).

Conclusions: This is the first study to suggest that the majority of CD8+ T cells in GC appear to be resting (Ki67-) T cells rejecting our hypothesis that high numbers of intratumoral T cells are due to high intratumoral T cell proliferation. The co-localization of CD8+ T cells and Ki67+ tumor cells seems to be clinically relevant and characterize certain histological phenotypes in GC. However, the potential underlying biological mechanisms of interaction between T cells and tumor cells are currently unknown. Further studies are needed to validate our findings and characterize the interface between tumor and immune cells.

Citation Format: Mehmet Yigitsoy, Sophie Earle, Armin Meier, Nathalie Harder, Matthew Hale, Aleksandra Zuraw, Takaki Yoshikawa, Günter Schmidt, Ralf Huss, Heike I. Grabsch. The importance of co-localized resting CD8+ T cells and proliferating tumor cells in gastric cancer [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 3958. doi:10.1158/1538-7445.AM2017-3958