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Mucosal infections pose a significant global health burden. Antigen-specific tissue-resident T cells are critical to maintaining barrier immunity. Previous studies in the context of systemic infection suggest that memory [CD8.sup.+] T cells may also provide innate-like protection against antigenically unrelated pathogens independent of T cell receptor engagement. Whether bystander T cell activation is also an important defense mechanism in the mucosa is poorly understood. Here, we investigated whether innate-like memory [CD8.sup.+] T cells could protect against a model mucosal virus infection, herpes simplex virus 2 (HSV-2). We found that immunization with an irrelevant antigen delayed disease progression from lethal HSV-2 challenge, suggesting that memory [CD8.sup.+] T cells may mediate protection despite the lack of antigen specificity. Upon HSV-2 infection, we observed an early infiltration, rather than substantial local proliferation, of antigen- nonspecific [CD8.sup.+] T cells, which became bystander-activated only within the infected mucosal tissue. Critically, we show that Bystander-activated [CD8.sup.+] T cells are sufficient to reduce early viral burden after HSV-2 infection. Finally, local cytokine cues within the tissue microenvironment after infection were sufficient for bystander activation of mucosal tissue memory [CD8.sup.+] T cells from mice and humans. Altogether, our findings suggest that local bystander activation of [CD8.sup.+] memory T cells contributes a fast and effective innate-like response to infection in mucosal tissue., Introduction Maintaining a balance of protection from pathogens while minimizing pathology is a perpetual process in mucosal barrier tissues, and tissue-resident memory [CD8.sup.+] T cells ([CD8.sup.+] TRMs) have been shown [...]

We report the development of an optimized 50‐color spectral flow cytometry panel designed for the in‐depth analysis of the immune system in human blood and tissues, with the goal of maximizing the amount of information that can be collected using currently available flow cytometry platforms. We established and tested this panel using peripheral blood mononuclear cells (PBMCs), but included CD45 to enable its future use for the analysis of human tissue samples. The panel contains lineage markers for all major immune cell subsets, and an extensive set of phenotyping markers focused on the activation and differentiation status of the T cell and dendritic cell (DC) compartment. We outline the biological insight that can be gained from the simultaneous measurement of such a large number of proteins and propose that this approach provides a unique opportunity for the comprehensive exploration of the immune status in human samples with a limited number of cells. Of note, we tested the panel to be compatible with cell sorting for further downstream applications. Furthermore, to facilitate the wide‐spread implementation of such a panel across different cohorts and samples, we established a trimmed‐down 45‐color version which can be used with different spectral cytometry platforms. Finally, to generate this panel, we utilized not only existing panel design guidelines, but also developed new metrics to systematically identify the optimal combination of 50 fluorochromes and evaluate fluorochrome‐specific resolution in the context of a 50‐color unmixing matrix. [ABSTRACT FROM AUTHOR]

Summary: Mucosal‐associated invariant T (MAIT) cells have a semi‐invariant T‐cell receptor that allows recognition of antigen in the context of the MHC class I‐related (MR1) protein. Metabolic intermediates of the riboflavin synthesis pathway have been identified as MR1‐restricted antigens with agonist properties. As riboflavin synthesis occurs in many bacterial species, but not human cells, it has been proposed that the main purpose of MAIT cells is antibacterial surveillance and protection. The majority of human MAIT cells secrete interferon‐gamma (IFNg) upon activation, while some MAIT cells in tissues can also express IL‐17. Given that MAIT cells are present in human barrier tissues colonized by a microbiome, MAIT cells must somehow be able to distinguish colonization from infection to ensure effector functions are only elicited when necessary. Importantly, MAIT cells have additional functional properties, including the potential to contribute to restoring tissue homeostasis by expression of CTLA‐4 and secretion of the cytokine IL‐22. A recent study provided compelling data indicating that the range of human MAIT cell functional properties is explained by plasticity rather than distinct lineages. This further underscores the necessity to better understand how different signals regulate MAIT cell function. In this review, we highlight what is known in regards to activating and inhibitory signals for MAIT cells with a specific focus on signals relevant to healthy and inflamed tissues. We consider the quantity, quality, and the temporal order of these signals on MAIT cell function and discuss the current limitations of computational tools to extrapolate which signals are received by MAIT cells in human tissues. Using lessons learned from conventional CD8 T cells, we also discuss how TCR signals may integrate with cytokine signals in MAIT cells to elicit distinct functional states. [ABSTRACT FROM AUTHOR]

The mechanisms underlying rapid elimination of herpes simplex virus-2 (HSV-2) in the human genital tract despite low [CD8.sup.+] and [CD4.sup.+] tissue-resident T cell (Trm cell) density are unknown. We analyzed shedding episodes during chronic HSV-2 infection; viral clearance always predominated within 24 hours of detection even when viral load exceeded 1 x 107 HSV DNA copies, and surges in granzyme B and IFN-[gamma] occurred within the early hours after reactivation and correlated with local viral load. We next developed an agent-based mathematical model of an HSV-2 genital ulcer to integrate mechanistic observations of Trm cells in in situ proliferation, trafficking, cytolytic effects, and cytokine alarm signaling from murine studies with viral kinetics, histopathology, and lesion size data from humans. A sufficiently high density of HSV-2-specific Trm cells predicted rapid elimination of infected cells, but our data suggest that such Trm cell densities are relatively uncommon in infected tissues. At lower, more commonly observed Trm cell densities, Trm cells must initiate a rapidly diffusing, polyfunctional cytokine response with activation of bystander T cells in order to eliminate a majority of infected cells and eradicate briskly spreading HSV-2 infection., Introduction [CD8.sup.+] and [CD4.sup.+] tissue-resident T cells (Trm cells) rapidly identify and control recurrent human viral infections within peripheral sites (1-11). Trm cells lodge preferentially at prior sites of pathogen [...]

When used as therapy for hematopoietic malignancies, allogeneic BM transplantation (BMT) relies on the graft-versus-leukemia (GVL) effect to eradicate residual tumor cells through immunologic mechanisms. However, graft-versus-host disease (GVHD), which is initiated by alloreactive donor T cells that recognize mismatched major and/or minor histocompatibility antigens and cause severe damage to hematopoietic and epithelial tissues, is a potentially lethal complication of allogeneic BMT. To enhance the therapeutic potential of BMT, we sought to find therapeutic targets that could inhibit GVHD while preserving GVL and immune responses to infectious agents. We show here that T cell responses triggered in mice by either Listeria monocytogenes or administration of antigen and adjuvant were relatively well preserved in the absence of PKC isoform [theta] (PKC[theta]), a key regulator of TCR signaling. In contrast, PKC[theta] was required for alloreactivity and GVHD induction. Furthermore, absence of PKC[theta] raised the threshold for T cell activation, which selectively affected allo-responses. Most importantly, PKC[theta]-deficient T cells retained the ability to respond to virus infection and to induce GVL effect after BMT. These findings suggest PKC[theta] is a potentially unique therapeutic target required for GVHD induction but not for GVL or protective responses to infectious agents., Introduction The primary signal for T cell activation is delivered by engagement of the TCR with MHC/peptide complexes on APCs. In addition, a second signal is provided by costimulatory molecules [...]