by In a groundbreaking study published in Science Immunology, researchers have delved into the gene expression profiles of different populations of intraepithelial lymphocytes (IELs) in various regions of the gastrointestinal (GI) tract. The study focused specifically on T-cell IELs (T-IELs) and their role in guarding against colon cancer.
To gain insights into the immune functions of distinct IEL populations in the GI tract, the researchers conducted single-cell ribonucleic acid sequencing (scRNA-seq) of more than 13,400 IELs isolated from the stomach, small intestine, cecum, and colon of naive C57BL/6 mice.
The researchers used unsupervised clustering to analyze the diversity of IELs in the GI tract, with a special emphasis on T-cell clusters one, two, four, five, eight, and 10. They also compared the gene expression profiles of 200 upregulated and downregulated genes in the colon and small intestine.
Flow cytometry (FC) was employed to measure IELs and the factors they expressed to regulate T-cell differentiation in the small and large intestines. This investigation revealed the crucial role of IELs in defending against colon cancer.
The small intestine serves as the primary site for nutrient absorption, consequently encountering a wide range of dietary antigens. In contrast, the colon absorbs fluids and harbors a higher microbial load and a more diverse microbial population.
Drawing upon the hypothesis that microbiota residing in the colon might drive the expression of T-cell factor-1 (TCF-1), the researchers examined TCF-1 expression in colon T-IELs of germ-free (GF) and specific pathogen-free (SPF) mice.
To study the role of the TCF7 gene and the antitumor properties of γδ T-IELs, the researchers utilized the Tcf7fl/flCD8αcre mouse model. In this model, the TCF-1 encoding TCF7 gene is knocked out from mature T-cells expressing Cd8α. Fluorescence-activated cell sorting (FACS) facilitated the exploration of the gene’s influence on colon T-IEL differentiation and function.
Furthermore, the researchers employed the MC-38 orthotopic murine model, which involves implanting MC-38 cells in the distal colon through colonoscopy, to investigate the effects of the TCF7 gene and the antitumor properties of γδ T-ΙΕLs. Previous studies have revealed the abundance of Vγ7 and Vγ1 (γδ T-IEL subsets) in the mouse colon, and their role in restricting tumor growth.
To contextualize these findings, the researchers examined the expression of IEL effector molecules in tissue samples from human patients with stage III colorectal cancer. The tissue microarray methodology was employed to assess the relative abundance of γδ T-cells in these samples.
The study revealed that stomach and small intestine IELs formed distinct clusters, while colon and cecal IELs mostly formed a single cluster. CD3 Epsilon Subunit Of T-Cell Receptor Complex (CD3e) expression indicated that the majority of IELs originating from the small intestine, cecum, and colon were T-cells, whereas only a smaller fraction of stomach-derived IELs were T-cells.
The major T-IEL subsets in the colon and small intestine were αβ and γδ T-IELs. γδ T-IELs displayed a significant increase in their cytotoxic phenotype compared to αβ T-IELs. Further analysis revealed a high concentration of mast cells among stomach IELs.
Previous research has demonstrated that heightened T-IEL defenses in the draining lymph nodes of the small intestine compensate for deficiencies in adaptive T-cell responses, preventing infection and cancer, and providing protection against dietary antigens. These findings underscore the distinct developmental requirements and functions of T-IELs across different compartments of the GI tract.
Although similar IEL subsets were found in both the small and large intestines, each region had its own unique molecular profile. Colon T-IELs exhibited higher expression of TCF-1 but lower expression of effector and cytotoxic molecules.
All T-IEL subsets in the small and large intestines, particularly in the colon, demonstrated elevated expression of nuclear receptor 77 (Nur77), a gene induced in T-cells upon TCR stimulation. Another distinguishing feature of colon T-IELs was their enhanced TCF-1 expression, suggesting the regulation of TCF-1 expression in T-IELs by several factors.
TCF-1 proved essential in maintaining the population of colon T-IELs over time, promoting self-renewal and the lifespan of conventional CD4+/CD8+ T-cell subsets. Moreover, TCF-1 directly regulated the expression of genes in αβ and γδ T-IELs, binding to the promoter regions of granzyme B (Gzmb), chemokine (C motif) ligand (XCL1), and tumor necrosis factor receptor superfamily (TNFRSF).
Studies have shown that the intrinsic histone deacetylase (HDAC) activity of TCF-1 plays a critical role in regulating the fate of T-IELs. However, further research is needed to confirm these reports.
The absence of TCF-1 expression in human γδ T-IELs was associated with the expression of XCL1 and granzyme B. Since TCF-1 suppresses the antitumor properties of γδ T-IELs in humans, γδ T-IELs with enhanced antitumor properties could be utilized in the development of immunotherapies using anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to treat colorectal cancer, particularly in its earlier stages.
Given the intricate mechanisms of γδ T-IEL activation, additional studies are necessary to elucidate how γδ T cells can drive an immunotherapy response in colorectal tumors lacking β2 microglobulin.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
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