776 A role for immune checkpoint blockade to enhance T cell-mediated responses in combination with chemotherapy in oesophageal adenocarcinoma

Background Combining immune checkpoint inhibitors (ICIs) with immunogenic chemotherapies is a promising approach in oesophageal adenocarcinoma (OAC) to convert ‘cold’ tumours to ‘hot’ tumours expanding the efficacy of ICIs to a greater spectrum of patients.1 However, there is a vast array of immune checkpoints (ICs) expressed by T cells and the effect of ICIs in combination with chemotherapy regimens is largely unknown.2 Methods The expression profile of a range of ICs on circulating and tumour-infiltrating T cells was assessed using flow cytometry prior to and post-neoadjuvant treatment and correlated with clinical parameters (n=20). PBMCs isolated from OAC blood were treated with single agent ICIs alone (single agent anti-PD-1, anti-PD-L1, anti-A2aR and anti-TIM-3 inhibition) and in combination with FLOT (5-Fluorouracil, oxaliplatin and docetaxel) and CROSS (carboplatin and paclitaxel) chemotherapy regimens. The production of anti-tumour cytokines by T cells was assessed in vitro by flow cytometry (n=6). Results In the treatment-naive and post-treatment setting, a range of ICs were expressed by circulating T cells and were significantly increased on tumour-infiltrating T cells, which included PD-L1, PD-L2, CD160, PD-1, CTLA-4, TIGIT, TIM-3, LAG-3, A2aR and ICOS (p Conclusions T cells expressing ICs in circulation and infiltrating OAC tissue were adverse prognostic markers in the pre-treatment setting, perhaps due to their role in enabling tumour immune evasion and subsequent tumour progression. In contrast, T cells expressing ICs post-chemotherapy treatment in peripheral circulation were favorable prognostic markers. ICs are typically expressed by ‘hot’ tumours2 therefore, the presence of ICs in the post-treatment setting may be as a result of an induced-anti-tumour immune response following immunogenic chemotherapy/chemoradiotherapy treatment and may be a useful strategy for stratifying patients into chemotherapy/chemoradiotherapy responders or non-responders. A therapeutic rationale is also highlighted for combining ICIs with chemotherapy regimens in OAC patients to enhance anti-tumour T cell-mediated responses and potentially boost response rates to chemotherapy treatment. Acknowledgements We would like to thank all the patients who kindly donated their samples to our research Ethics Approval The work was performed in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving human samples. Consent Patients provided informed consent for sample and data acquisition, and the study received full ethical approval from the St. James’s Hospital/AMNCH Ethical Review Board. References Davern M, Lysaght J. Cooperation between chemotherapy and immunotherapy in gastroesophageal cancers. Cancer Lett 2020. https://doi.org/10.1016/j.canlet.2020.09.014 Emens LA, Middleton G. The interplay of immunotherapy and chemotherapy: harnessing potential synergies. Cancer Immunol Res 2015;3:436–443.