450. TISSUE RESIDENT MEMORY CELLS: CORRELATING THE PHENOTYPIC AND FUNCTIONAL CAPABILITIES OF A POTENTIAL TUMOUR REACTIVE CELL POPULATION IN OESOPHAGEAL ADENOCARCINOMA

Abstract Background Oesophageal adenocarcinoma (OAC) is a disease with a high mortality and morbidity rate. Immunotherapy has recently demonstrated progress in the treatment of OAC but its impact on long term survival is currently uncertain. Tissue resident memory (TRM) T cells are a subset of lymphocytes within the tumour/tissue infiltrating lymphocyte (TIL) milieu that has attracted considerable interest within cancer immunology. Although TRM cells have been associated with better outcomes in multiple cancer types there is a lack of knowledge of their role in OAC. This study aims to critically correlate the phenotype of TRM with their functional capacity in this disease. Methods 33 patients undergoing surgical resection for OAC were recruited and consented for collection of fresh tumour (T), adjacent normal tissue (AN), and peripheral blood. Peripheral blood mononuclear cell (PBMC) from blood and infiltrating lymphocytes from T and AN were isolated using standard density gradient and enzymatic digestion protocols. Multiparametric flow cytometry was performed on 12 patients using matched PBMC, T and AN infiltrating lymphocytes for phenotypic analysis and 21 patients for functional analysis following cell stimulation assay. BD FACSymphony was used for data acquisition and data analysed on FlowJo version 10.10. Statistical analysis was carried out using GraphPad Prism. Results TRM (CD103+CD69+) dominated the CD8+ T cell population of T and AN TIL. Expression of checkpoint proteins PD1+ and CD39+, a marker of tumour reactivity, was identified on CD8+ TRM and CD8+ non TRM in TIL. The differentiation status of TRM within memory lineages demonstrated that TRM express a higher proportion of effector memory cells (CCR7-CD45RA) compared to those in blood. TRM cells also showed lower expression of the transcription factors EOMES, TBET and TCF compared to CD8+ cells within PBMC. Moreover, tumour CD8+ TRM populations had reduced ability to produce IL-2 following stimulation compared to adjacent normal TRM populations. Conclusion TRM make up a large proportion of CD8+ T cell within the tumour microenvironment (TME) of OAC. TRM generation is associated with the downregulation of T-Box transcription factors EOMES and TBET and expression of an effector memory phenotype with reduction of the stem-like transcription factor, TCF. High levels of CD39+ indicate a strong level of activation but the increased PD1 expression and reduced capability to produce IL2 indicate functional impairment suppressed within the TME. An opportunity may exist to reverse this with novel immunotherapeutic agents.