Intestinal CD8+ tissue-resident memory T cells: From generation to function

Tissue-resident memory T cells in immunotherapy and immune-related adverse events by immune checkpoint inhibitor

Tissue-resident memory T cells (TRM) are a specialized subset of T cells that reside in tissues and provide long-term protective immunity against pathogens that enter the body through that specific tissue. TRM cells have specific phenotype and reside preferentially in barrier tissues. Recent studies have revealed that TRM cells are the main target of immune checkpoint inhibitor immunotherapy since their role in cancer immunosurveillance. Furthermore, TRM cells also play a crucial part in pathogenesis of immune-related adverse events (irAEs). Here, we provide a concise review of biological characteristics of TRM cells, and the major advances and recent findings regarding their involvement in immune checkpoint inhibitor immunotherapy and the corresponding irAEs.

Tissue-Resident Memory T Cells in Gastrointestinal Cancers: Prognostic Significance and Therapeutic Implications

Gastrointestinal cancers, which include a variety of esophageal and colorectal malignancies, present a global health challenge and require effective treatment strategies. In the evolving field of cancer immunotherapy, tissue-resident memory T cells (Trm cells) have emerged as important players in the immune response within nonlymphoid tissues. In this review, we summarize the characteristics and functions of Trm cells and discuss their profound implications for patient outcomes in gastrointestinal cancers. Positioned strategically in peripheral tissues, Trm cells have functions beyond immune surveillance, affecting tumor progression, prognosis, and response to immunotherapy. Studies indicate that Trm cells are prognostic markers and correlate positively with enhanced survival. Their presence in the tumor microenvironment has sparked interest in their therapeutic potential, particularly with respect to immune checkpoint inhibitors, which may improve cancer treatment. Understanding how Trm cells work will not only help to prevent cancer spread through effective treatment but will also contribute to disease prevention at early stages as well as vaccine development. The role of Trm cells goes beyond just cancer, and they have potential applications in infectious and autoimmune diseases. This review provides a thorough analysis of Trm cells in gastrointestinal cancers, which may lead to personalized and effective cancer therapies.

Local antigen encounter promotes generation of tissue-resident memory T cells in the large intestine

Upon infection, CD8+ T cells that have been primed in the draining lymph nodes migrate to the invaded tissue, where they receive cues prompting their differentiation into tissue-resident memory cells (Trm), which display niche-specific transcriptional features. Despite the importance of these cells, our understanding of their molecular landscape and the signals that dictate their development remains limited, particularly in specific anatomical niches such as the large intestine (LI). Here, we report that LI Trm-generated following oral infection exhibits a distinct transcriptional profile compared to Trm in other tissues. Notably, we observe that local cues play a crucial role in the preferential establishment of LI Trm, favoring precursors that migrate to the tissue early during infection. Our investigations identify cognate antigen recognition as a major driver of Trm differentiation at this anatomical site. Local antigen presentation not only promotes the proliferation of effector cells and memory precursors but also facilitates the acquisition of transcriptional features characteristic of gut Trm. Thus, antigen recognition in the LI favors the establishment of Trm by impacting T cell expansion and gene expression.

Tissue-Resident Memory T Cells in Allergy

Tissue-resident memory T (TRM) cells constitute a distinct subset within the memory T cell population, serving as the vanguard against invading pathogens and antigens in peripheral non-lymphoid tissues, including the respiratory tract, intestines, and skin. Notably, TRM cells adapt to the specific microenvironment of each tissue, predominantly maintaining a sessile state with distinctive phenotypic and functional attributes. Their role is to ensure continuous immunological surveillance and protection. Recent findings have highlighted the pivotal contribution of TRM cells to the modulation of adaptive immune responses in allergic disorders such as allergic rhinitis, asthma, and dermatitis. A comprehensive understanding of the involvement of TRM cells in allergic diseases bears profound implications for allergy prevention and treatment. This review comprehensively explores the phenotypic characteristics, developmental mechanisms, and functional roles of TRM cells, focusing on their intricate relationship with allergic diseases.

Immunological Regulation of Gut-Tropic Immune Cells by Extracellular Vesicles

The remarkable diversity of lymphocytes, essential components of the immune system, serves as an ingenious mechanism for maximizing the efficient utilization of limited host defense resources. While cell adhesion molecules, notably in gut-tropic T cells, play a central role in this mechanism, the counterbalancing molecular details have remained elusive. Conversely, we've uncovered the molecular pathways enabling extracellular vesicles secreted by lymphocytes to reach the gut's mucosal tissues, facilitating immunological regulation. This discovery sheds light on immune fine-tuning, offering insights into immune regulation mechanisms.

T Cell Repertoire Homogeneity and Blood-Gut Overlap in Patients With Inflammatory Bowel Disease

BACKGROUND & AIMS

Inflammatory bowel disease (IBD) causes a marked increase in the number of T cells in the intestinal mucosa. Debate exists about whether these excess cells arise from local clonal proliferation or recruitment from the periphery.

METHODS

CD8+ T cells were sorted from colon biopsy specimens and blood for T-cell receptor (TCR) β-chain sequencing. Biopsy specimens from inflamed or uninflamed colon from ulcerative colitis or Crohn's disease cohorts were compared with colon biopsy specimens from people without IBD, as well as with autologous blood α4β7+, α4β7- effector/memory, terminal effector/memory CD45RA+ T cell, and mucosal-associated invariant T-cell CD8 subpopulations.

RESULTS

CD8 TCR diversity in mucosa and blood did not correlate with inflammation. Repertoire overlap between any 2 distinct locations of a given person's colon was consistently high, although often lower between inflamed and uninflamed sites. CD8 TCR repertoires overlapped between the colon and each peripheral blood subpopulation studied, with the highest overlap seen for integrin α4β7+ T cells. Inflamed tissue consistently overlapped more than uninflamed tissue with each blood subpopulation.

CONCLUSIONS

CD8 T-cell clones are spread homogenously throughout the length of the colon. Although TCR repertoire overlap is greater within than between inflamed and uninflamed colon segments, a similar TCR diversity in both argues against local clonal expansion being the main source of excess cytotoxic T cells in inflamed mucosa. Rather, the increased TCR overlap observed between blood and inflamed mucosa supports the significance of T-cell trafficking in IBD pathogenesis, particularly concerning α4β7+ T-cell populations.

Novel T cell/organoid culture system allows ex vivo modeling of intestinal graft-versus-host disease

Acute graft-versus-host disease (GvHD) remains the biggest clinical challenge and prognosis-determining complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Donor T cells are acceptedly key mediators of alloreactivity against host tissues and here especially the gut. In support of previous studies, we found that the intestinal intra-epithelial lymphocyte (IEL) compartment was dynamically regulated in the course of MHC class I full mismatch allo-HSCT. However, while intestinal epithelial cell (IEC) damage endangers the integrity of the intestinal barrier and is a core signature of intestinal GvHD, the question whether and to what degree IELs are contributing to IEC dysregulation is poorly understood. To study lymphoepithelial interaction, we employed a novel ex vivo T cell/organoid co-culture model system. Here, allogeneic intra-epithelial T cells were superior in inducing IEC death compared to syngeneic IEL and allogeneic non-IEL T cells. The ability to induce IEC death was predominately confined to TCRβ+ T cells and was executed in a largely IFNγ-dependent manner. Alloreactivity required a diverse T cell receptor (TCR) repertoire since IELs genetically modified to express a TCR restricted to a single, non-endogenous antigen failed to mediate IEC pathology. Interestingly, minor histocompatibility antigen (miHA) mismatch was sufficient to elicit IEL-driven IEC damage. Finally, advanced live cell imaging analyses uncovered that alloreactive IELs patrolled smaller areas within intestinal organoids compared to syngeneic controls, indicating their unique migratory properties within allogeneic IECs. Together, we provide here experimental evidence for the utility of a co-culture system to model the cellular and molecular characteristics of the crosstalk between IELs and IEC in an allogeneic setting ex vivo. In the light of the emerging concept of dysregulated immune-epithelial homeostasis as a core aspect of intestinal GvHD, this approach represents a novel experimental system to e.g. screen therapeutic strategies for their potential to normalize T cell/IEC- interaction. Hence, analyses in pre-clinical in vivo allo-HSCT model systems may be restricted to hereby positively selected, promising approaches.