Phenotypic, transcriptional and immunometabolic characterization of infiltrating MAIT cells in resectable non-small cell lung cancer

Introduction. Circulating mucosal-associated invariant T (MAIT) cells are innate-like effector memory T cells with pro-inflammatory and cytotoxic properties, accounting for up to 10% of circulating CD8+ T cells. Their contribution to tumor immunity remains controversial. MAIT cells are detectable within non-small cell lung cancer (NSCLC) lesions, but limited data are available on their position within the tumor microenvironment (TME), their interactions and their functional state. Objectives. To characterize MAIT cells in NSCLC at the phenotypic, functional, transcriptional and metabolic level, and to define their localization and cell-to-cell interactions within the TME. Methods. Patients undergoing surgical resection for NSCLC (stage I, II, IIIA, TNM 8th ed) were enrolled for this study. Spatial transcriptomic profiling (CosMx® Human 6K Discovery Panel) was performed on 5 patients to localize MAIT cells and to infer ligand-receptor communication using CellChat. Tumor-infiltrating (tMAIT) and circulating (bMAIT) MAIT cells, together with circulating conventional CD8+ T cells, were single-cell sorted and profiled by VASA-seq. A 17-color spectral flow cytometry panel was used to compare the phenotype and the functional profile of paired bMAIT and tMAIT from the same patients. Results. MAIT cells represented 1.39% of all segmented cells and were preferentially localized within tertiary lymphoid structures, close to CD4+ T cells and CLEC10A+ macrophages; predicted communication with this myeloid subset was mediated by COL1A1-CD44/SDC4 interactions. Transcriptionally, tMAIT cells were markedly different from their circulating counterpart, showing a higher exhaustion score, a program centered on memory and tissue residency, and a reduced predicted metabolic activity; two of the tumor-derived clusters were characterized by a Th1-Th17 signature. By flow cytometry, MAIT cells were more abundant in blood than within tumor tissue. tMAIT cells showed reduced expression of cytotoxic mediators and increased production of type 1 cytokines compared with blood, indicating a functional reorientation. Conclusion. Although less abundant within the TME than in circulation, MAIT cells occupy a defined position within the organized immune compartment of NSCLC lesions and undergo substantial transcriptional and functional reprogramming, accompanied by a reduced predicted metabolic activity, shifting from a cytotoxic profile in blood towards a predominantly type 1 profile within the tumor. These findings provide new insight into the functional landscape of MAIT cells in resectable NSCLC and underscore their potential significance in tumor immunity.