540. INFILTRATION OF RESECTED OESOPHAGEAL ADENOCARCINOMA WITH ANTIGEN-EXPERIENCED PD-1 AND CD39 POSITIVE CD8+ TISSUE RESIDENT MEMORY CELLS CORRELATE WITH IMPROVED SURVIVAL

Abstract Background The development of novel treatments for oesophageal adenocarcinoma (OAC) represents an area of significant unmet need. Despite the application of immune checkpoint blockade alongside chemotherapy as standard of care for some patients with metastatic OAC, responses to immunotherapies are modest and 5-year survival is 17%. The reasons for this remains unclear and while tumour infiltration with CD8+ T lymphocytes (TILs) at the time of resection is associated with improved outcomes, this heterogeneous population remains incompletely characterised in OAC. Tissue resident memory cells (TRM) are increasingly understood as key mediators of immunotherapy response but their role in OAC is poorly understood. Methods Tumour samples were accessed by punch biopsy from the central portion of cancers resected from 44 patients undergoing curative surgery for OAC. Samples were assessed by multi-parametric flow cytometry for the presence of antigen-experienced TILs and markers of activation and exhaustion. Populations of antigen-experienced PD-1 and CD39 positive CD8+ OAC TILs were sorted, and bulk RNA sequencing (RNAseq) undertaken using a modified SmartSeq2 protocol allowing differential gene expression analysis and gene set enrichment analysis. Flow cytometric assessment of functionality was completed. Results Resected OAC are often highly infiltrated with antigen experienced CD8+ TILs expressing high levels of PD-1 and CD39 and an abundance of this population correlates with improved survival (%PD-1/CD39+ >Median, OS HR 0.12). RNAseq of sorted TILs identified this PD-1+ and CD39+ lymphocyte population as enriched for precursor exhausted-like CD8+ TRM (NES 2.01 p=0.00). This is correlated by their CD103+ and TIM3- predominance on flow cytometry in keeping with TRMsassociated with immunotherapy response in other cancers. This population demonstrated a maintained proliferative potential, an ability to degranulate and produce the key effector molecules IFN-γ, TNF-α and Granzyme B. Conclusions An abundance of a PD-1 and CD39 positive CD8+ TIL population, consistent with a precursor exhausted-like TRM population with maintained proliferative and functional capacity, is observed to correlate with improved outcomes following curative surgery for OAC. This TRM population is consistent with analogous populations observed to be responsible for immunotherapy response in other cancers and their identification may predict benefit from such approaches in OAC and allow better patient selection for treatment with immune checkpoint inhibitors.