Abstract B75: Immune cell infiltration as an indicator of the immune microenvironment of pancreatic cancer.
Authors: Hiraoka Nobuyoshi 
Published: August 2014

Purpose: The tumor microenvironment plays important roles in the biological behavior of cancer. The host immune reaction contributes to the characteristics of the tumor microenvironment, which is represented by tumor-infiltrating immune cells. In addition to the clinicopathological impact of individual infiltrating immune cell types, it is important to observe the interactions among them in order to understand the actual conditions within the microenvironment, as the effects of specific cell combinations may also be of clinicopathological significance. In this study, we systematically analyzed the tumor-infiltrating immune cells in pancreatic ductal carcinoma (PDC) and evaluated their clinicopathological impact.

Methods: 212 patients with PDC were examined, who underwent initial surgical resection at our center. We performed immunohistochemistry to examine tumor-infiltrating CD68+ pan-macrophages, HLA-DR+CD68+ M1 macrophages (M1), CD163+ or CD204+ M2 macrophages (M2), CD66b+ neutrophils (Neu), CD4+ T cells (CD4T), CD8+ T cells (CD8T), and FOXP3+CD4+ regulatory T cells (Treg). After immunohistochemistry three areas at low magnification were selected, where the immunolabeled cells had infiltrated into tumor most densely. The immunolabeled cells were counted and their average counts were used as the final count. Patients were divided into two groups by the median value for survival and correlation analyses. Kaplan-Meier analysis and Cox regression multivariate survival analysis were performed. We also examined various combinations of tumor-infiltrating immune cells and performed survival analysis. Patients were divided into four groups based on combinations of two groups of two factors (i.e., A(high)B(high), A(high)B(low), A(low)B(high), and A(low)B(low)).

Results: Tumor-infiltrating pan-macrophages, M2, and Neu had positive correlations with each other, and that all of them were negatively correlated with the ratio of tumor-infiltrating M1 to pan-macrophages (%M1). Tumor-infiltrating CD4T showed a positive correlation with tumor-infiltrating CD8T and a negative correlation with the ratio of tumor-infiltrating Treg to CD4T (%Treg). No significant correlation was found between tumor-infiltrating myeloid cells and T cells, except for the close correlation between myeloid cells and %Treg.

Univariate and multivariate survival analyses revealed that tumor-infiltrating CD4T, CD8T, and %M1 were independently prognostic of overall survival (OS) and disease-free survival (DFS) and that tumor-infiltrating pan-macrophages, M2, Neu, and %Treg were independent prognosticators of poor OS and DFS.

When pairs of the six variables were combined and subjected to survival analyses, the four combinations (CD4T and CD8T, CD4T and %Treg, CD8T and %Treg, and %M1 and M2) showed that only one specific patient group (CD4T(high)CD8T(high), CD4T(high)%Treg(low), CD8T(high)%Treg(low), and %M1(high)M2(low)) had longer survival whereas the other three groups had shorter survival with similar degrees. The factors involved in these combinations were then connected, and two new variables emerged: tumor-infiltrating CD4Thigh/CD8Thigh/%Treglow and %M1high/M2low. These corrected for the unbalanced patient distribution. Multivariate survival analysis revealed that these variables were significantly correlated with longer survival and had a higher hazard ratio.

Conclusions: It is suggested that systematic analysis of several tumor-infiltrating immune cells is important for providing the findings of effects of specific cell combination in immune-microenvironment more precisely, and that tumor-infiltrating CD4Thigh/CD8Thigh/%Treglow and tumor-infiltrating %M1high/M2low are suitable variables for evaluating the immune-microenvironment of PDC.

Citation Format: Nobuyoshi Hiraoka. Immune cell infiltration as an indicator of the immune microenvironment of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B75.