Impact of infiltrating T cell subtypes on survival and response to FLOT chemotherapy in resectable oesophagogastric adenocarcinoma (OGA).

Abstract

443 Background: The prognostic and predictive relevance of tumour infiltrating T cell subtypes and of PD-L1 expression in localised OGA treated with FLOT chemotherapy (CTx) and surgery is poorly understood. Methods: Pre-CTx biopsy tissue was retrospectively collected from 46 patients (pts) with localised OGA who received perioperative FLOT and underwent surgery at a single institution. Opal Multicolour immunofluorescence was performed with primary antibodies against CD4, CD8, FOXP3, CD45RO, PD-1 and cytokeratin. Digital image analysis was performed using inForm and HALO softwares. PD-L1 CPS was determined using the E1L3N clone and the standard CPS assessment algorithm (CPS≥5 = high; CPS <5 = low). CTx responses were assessed according to Mandard Tumour Regression Grade (TRG). For each immune cell marker and T cell phenotype, high vs low groups were defined using median cell density (count/mm2) as the cut-off. Association of high vs low cell density with disease free survival (DFS) was assessed using the log-rank test and correlation with pathological response to CTx was assessed using the Chi-squared test. The paired Wilcoxon rank-sum test was used to compare differences in immune cell densities between paired pre-CTx biopsy and post-CTx resection samples in a subset of 35 pts. Results: Pts with a PD-1+ cell density above median in biopsy had significantly longer DFS compared to those with a density below median (median DFS not reached vs 1111 days; HR 0.3, 95% CI 0.1 – 0.8; p=0.028). A trend towards longer survival was also observed in the CD8+ high, FOXP3+ high, and activated CD8+ (CD8+ PD-1+) high groups. There was no association between PD-L1 CPS, CD4+, CD45RO+, memory CD8+ (CD8+ CD45RO+), regulatory CD4+ (CD4+ FOXP3+), memory CD4+ (CD4+ FOXP3- CD45RO+), and activated CD4+ (CD4+ FOXP3- PD-1+) cells and survival. Pts with higher density of PD-1+ cells achieved better responses than those with low PD-1+ cells (TRG1/2 48% vs 9%, p=0.017). Pts with PD-L1 CPS ≥10 in biopsy were numerically more likely to achieve better responses to FLOT (46% TRG1/2). PD1+ cell density decreased in resection specimens in good CTx responders but did not differ in non-responders. FOXP3+ cells significantly decreased whereas CD45RO+ cells and memory CD8+ cells significantly increased in non-responders only. Conclusions: These results indicate prognostic and predictive value of PD-1 expressing tumour infiltrating T cells in resectable OGA treated with perioperative FLOT CTx. CD8+, activated CD8+ and FOXP3+ cells were associated with a trend in longer survival. This analysis provides candidate biomarkers for further study in larger cohorts on the association between infiltrating immune cells and prognosis as well as response to standard cytotoxic CTx in Western patients.