CD8 ⁺ T cell proximity analysis of the tumor microenvironment (TME) in patients with pancreatic ductal adenocarcinoma (PDAC) and associated clinical outcomes.

754 Background: Immunosuppressive cells (cancer-associated fibroblasts [CAFs], tumor associated neutrophils [TANs], M2/M1 macrophages) can influence CD8 + T cell infiltration in the PDAC TME. The spatial proximity of these cells to CD8 + T cells and association with clinical outcomes is not well known. We hypothesize the cell distances between CD8 + T cells and these phenotypes: CXC chemokine receptor 4 (CXCR4) + TANs, CAFs, focal adhesion kinase (FAK) + tumor cells, FAK + M2 and M1 macrophages will correlate with survival outcomes. Methods: Twenty-two stage I/II PDAC patients who consented for tissue collection were stratified into two groups: standard responders (n=11) with overall survival (OS) >2 years and poor responders (n=11) with OS ≤ 2 years. Multiplex IHC was performed on specimens using multiple biomarkers (CD8, CXCR4, CD66b, FAK, FAP, CD68, CSF1R, CD163, EPCAM) to identify cell phenotypes. Comprehensive spatial analysis with HALO software was used to measure mean cell distance between CD8 + T cells and other cells. The mean cell-to-cell distance among evaluable specimens was determined by phenotype. Patients were divided into two groups with average cell distance below or above the mean by phenotype. OS of each subgroup was compared using Kaplan-Meier method. Results: Median OS for standard and poor responders was 47.6 months vs 13.1 months (p<.0001), respectively. There was a higher % of CD8 + T cells closer (<50 µm) to CXCR4 + TANs in standard responders (56% vs 28%, p<.0001). There were no significant differences in CD8 + T cell distance to other phenotypes. Longer survival was seen with average cell distance below the mean when comparing CD8 + T cells to FAK + tumor cells (1274 d vs 742 d, p=.306), to CXCR4 + TANs (854 d vs 442 d, p=.947) and to FAP + FAK + CAFs (890.5 d vs 672 d, p=.662). In contrast, longer survival was seen with a distance above the mean comparing CD8 + T cells to M2 (622 d vs 1274 d, p=.732) and to M1 (613 d vs 1397 d, p=.517) macrophages. Conclusions: Our study shows clinical outcomes may be correlated with spatial distance among TME immune cells in PDAC. Longer survival was seen when CD8 + T cells were closer to FAK + tumor cells, CXCR4 + TANs, and CAFs and further away from M2 and M1 macrophages. Larger cohort analyses may better elucidate the prognostic and biological significance of cell distance among TME phenotypes, which may have potential implications for response to immunotherapy.