Background Immunotherapy has changed the standard of care for multiple cancers; however, its efficacy is limited. Chemotherapy and radiation had little effect in pancreatic ductal adenocarcinoma (PDAC) outcome 1 in patients with metastatic disease, hence the urgency for new effective courses of treatment. Increasing evidence suggests mucosal-associated invariant T-cells (MAIT) play a role in anti-cancer T-cell responses, by recognizing transformed cells or bacterial products. MAIT respond towards microbial antigens and vitamin derivatives, produce pro-inflammatory cytokines 2 3 and have been found present in primary and metastatic cancer lesions. 3 4 Long-term survival PDAC patients present a unique microbiome pattern. In contrast, some microbial species may promote oncogenesis. 5 6 The focus of this project is the characterization of MAIT as immune effector cells in PDAC specimens. Methods We performed a retrospective analysis of long-term survivors (LTS) and short-term survivors (STS) patients with pancreatic cancer associating clinical endpoints with the presence of MAIT infiltration in the tumor tissue using immunofluorescence staining for MR1 (MHC class I-related gene, a MAIT ligand receptor), CD3 and TCR Vα7.2 (frequently reported chain in MAIT). Tumor infiltrating lymphocytes (TILs) were expanded and tested for recognition of microbial products presented to TILs or to PBMCs defined by cytokine production (ELISA), cytotoxicity (CD107a induction assay), CD69 or 4-1BB upregulation (flow cytometry). Reactive MAIT will be molecularly defined by deep TCR (T-cell receptor) sequencing which allows to ‘back-trace’ MR1 reactive TIL in the tumor specimen. The complex interaction of microbial antigen presentation from freshly harvested tumor specimens to TILs is being optimized for Nanolive technology that allows to follow live cell interactions for several days. Results TIL reactivity directed against microbial products from different bacterial species was detected by IFN-γ production and CD69 upregulation in responder TILs. A broader panel of TILs is currently being tested against bacterial species. TCRs will undergo laser microdissection for subsequent TCR repertoire sequencing. A more pronounced MAIT infiltration in close vicinity to tumor cells in LTS compared to STS is being studied, further supporting the anti-tumor role of MAIT. Conclusions MAIT cells may exhibit anti-tumor properties, based on cytokine production and cellular marker activation. TCRs directed against cancer cells can serve as viable blueprints to engage with MR1 on PDAC recognizing tumor-associated targets or microbial products that elicit IFN-γ production. This allows to explore MAIT TCRs for adoptive therapies or distinct microbial species that drive clinically relevant responses. Acknowledgements The authors would like to thank to Champalimaud Foundation Biobank and Vivarium Facility at Champalimaud Foundation. Ethics Approval This study was approved by the Champalimaud Foundation Ethics Committee and by Ethics Research Committee of NOVA Medical School of NOVA University of Lisbon. Consent For each patient, written informed consent and approval by the Ethical Committee of the Champalimaud Foundation will be obtained. The study will be in compliance with the Declaration of Helsinki.
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