Antibiotic-mediated gut dysbiosis alters innate-like T cell frequency and phenotype in tumor-bearing mice

Abstract

Abstract Innate-like T cells bind to non-peptide antigens in a TCR-dependent manner and are not MHC-restricted. This subpopulation of T cells consists of mucosal associated invariant T cells (MAIT), natural killer T cells (NKT), and gamma delta (γδ) T cells. Innate-like T cells can recognize microbially-derived antigens and interact with gut commensals to help maintain intestinal homeostasis. Additionally, they are implicated in tumour immunity as producers of cytokines and cytotoxic molecules. Thus, innate-like T cells may serve as an intermediary between the gut microbiota and tumor development. Using syngeneic mouse tumour models and flow cytometric analysis, we aim to evaluate the relationships between gut microbiota modulation, tumour growth, checkpoint inhibitor response, and innate-like T cell phenotype. Gut dysbiosis was induced using broad spectrum oral antibiotics two weeks prior to subcutaneous injection of MC38 colon adenocarcinoma cells. Mice with palpable tumours were treated twice with anti-PD-L1 during the experiment. Compared to vehicle control, tumor size reduction in response to anti-PD-L1 was not significantly altered with antibiotic treatment. The following observations were noted in antibiotic-treated mice. The frequency of γδ T cells was decreased in the tumour, blood, and spleen. MAIT, NKT, and γδ T cells in the spleen had lower expression of tissue localization-associated markers, CD103 and CXCR6. MAIT cell activation state, characterized by CD25 and CD69 expression, was also elevated in the spleen. These findings suggest that changes to the immune landscape of tumor-bearing mice due to antibiotic-driven dysbiosis is characterized by alterations in innate-like T cell abundance and phenotype.