Metabolic regulation of T lymphocyte motility and migration

In order to fulfill their effector and patrolling functions, lymphocytes traffic through the body and need to adapt to different tissue microenvironments. First, mature lymphocytes egress the bone marrow and the thymus into the vascular system. Circulating lymphocytes can exit the vasculature and penetrate into the tissues, either for patrolling in search for pathogens or to eliminate infection and activate the adaptive immune response. The cytoskeletal reorganization necessary to sustain migration require high levels of energy thus presenting a substantial bioenergetic challenge to migrating cells. The metabolic regulation of lymphocyte motility and trafficking has only recently begun to be investigated. In this review we will summarize current knowledge of the crosstalk between cell metabolism and the cytoskeleton in T lymphocytes, and discuss the concept that lymphocyte metabolism may reprogram in response to migratory stimuli and adapt to the different environmental cues received during recirculation in tissues.

Oncolytic Adenovirus ORCA-010 Activates Proinflammatory Myeloid Cells and Facilitates T Cell Recruitment and Activation by PD-1 Blockade in Melanoma

Immune checkpoint inhibitors have advanced the treatment of melanoma. Nevertheless, a majority of patients are resistant, or develop resistance, to immune checkpoint blockade, which may be related to prevailing immune suppression by myeloid regulatory cells in the tumor microenvironment (TME). ORCA-010 is a novel oncolytic adenovirus that selectively replicates in, and lyses, cancer cells. We previously showed that ORCA-010 can activate melanoma-exposed conventional dendritic cells (cDCs). To study the effect of ORCA-010 on melanoma-conditioned macrophage development, we used an in vitro co-culture model of human monocytes with melanoma cell lines. We observed a selective survival and polarization of monocytes into M2-like macrophages (CD14⁺CD80^-CD163⁺) in co-cultures with cell lines that expressed macrophage colony-stimulating factor. Oncolysis of these melanoma cell lines, effected by ORCA-010, activated the resulting macrophages and converted them to a more proinflammatory state, evidenced by higher levels of PD-L1, CD80, and CD86 and an enhanced capacity to prime allogenic T cells and induce a type-1 T cell response. To assess the effect of ORCA-010 on myeloid subset distribution and activation in vivo, ORCA-010 was intratumorally injected and tested for T cell activation and recruitment in the human adenovirus nonpermissive B16-OVA mouse melanoma model. While systemic PD-1 blockade in this model in itself did not modulate myeloid or T cell subset distribution and activation, when it was preceded by i.t. injection of ORCA-010, this induced an increased rate and activation state of CD8α⁺ cDC1, both in the TME and in the spleen. Observed increased rates of activated CD8⁺ T cells, expressing CD69 and PD-1, were related to both increased CD8α⁺ cDC1 rates and M1/M2 shifts in tumor and spleen. In conclusion, the myeloid modulatory properties of ORCA-010 in melanoma, resulting in recruitment and activation of T cells, could enhance the antitumor efficacy of PD-1 blockade.

Influenza-Specific Lung-Resident Memory CD8+ T Cells

Despite the availability of seasonal vaccines, influenza A (IAV) prevails as a leading cause of respiratory infection worldwide. Current vaccination efforts aim at increasing protection against heterologous and potentially pandemic IAV strains. Lung-resident CD8⁺ T cells (Trm) generated upon IAV infection are vital for heterosubtypic immunity to IAV reexposure and provide quick and robust responses upon reactivation. Yet, protection wanes with time as lung Trm cell numbers decline, a contrasting feature with Trm cells at other mucosal sites such as the skin. In this review, we discuss current data on lung Trm compared to Trm cells in other tissues. Furthermore, major knowledge gaps in the generation and maintenance of IAV-specific lung Trm are addressed and mechanisms that may contribute to their decline are discussed. Further understanding in the mechanisms that govern effector function versus immunopathology is paramount for future IAV vaccine design in enhancing durability of lung Trm cells.

Differential Changes in Inflammatory Mononuclear Phagocyte and T-Cell Profiles within Psoriatic Skin during Treatment with Guselkumab vs. Secukinumab

Cellular sources of IL-23 and IL-17A driving skin inflammation in psoriasis remain unclear. Using high-dimensional unsupervised flow cytometry analysis, mononuclear phagocytes and T cells were examined in the same lesions of patients before and during guselkumab (IL-23p19 blocker) or secukinumab (IL-17A blocker) treatment. Among CD11c⁺HLA-DR⁺ mononuclear phagocytes, CD64^brightCD163^-CD14^brightCD1c^-CD1a^‒ inflammatory monocyte‒like cells were the predominant IL-23-producing cells and, together with CD64^-CD163^-CD14^-IL-23p19^-TNF-α⁺ inflammatory dendritic cell‒like cells, were increased in lesional compared with those in nonlesional skin taken from the same patient. Within T cells, CD8⁺CD49a⁺ and/or CD103⁺ tissue-resident memory T cells, CD4⁺CD25⁺FoxP3⁺ regulatory T cells, and CD4⁺CD49a^-CD103^- T cells were increased. Moreover, CD4⁺CD49a^-CD103^- T cells and the relatively rare CD8⁺ memory T cells equally contributed to IL-17A production. Both treatments decreased the frequencies of inflammatory monocyte‒like, inflammatory dendritic cell‒like, and CD4⁺CD49a^-CD103^- T cells. In contrast, guselkumab reduced memory T cells while maintaining regulatory T cells and vice versa for secukinumab. Neither drug modified the frequencies of IL-17A⁺IL^‒17F⁺/^- CD4⁺ or CD8⁺ T cells. This study reveals the identity of the major IL-23⁺ mononuclear phagocyte and IL-17⁺ T-cell subsets in psoriatic skin lesions and paves the way for a better understanding of the mode of action of drugs targeting the IL-23/IL-17A pathway in psoriasis.

CD8+ T Lymphocytes: Crucial Players in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease associated with damage to multiple organs and glands. The most common clinical manifestations are dry eyes, dry mouth, and enlarged salivary glands. Currently, CD4+ T lymphocytes are considered to be key factors in the immunopathogenesis of pSS, but various studies have shown that CD8+ T lymphocytes contribute to acinar injury in the exocrine glands. Therefore, in this review, we discussed the classification and features of CD8+ T lymphocytes, specifically describing the role of CD8+ T lymphocytes in disease pathophysiology. Furthermore, we presented treatment strategies targeting CD8+ T cells to capitalize on the pathogenic and regulatory potential of CD8+ T lymphocytes in SS to provide promising new strategies for this inflammatory disease.

T Cell Immunity against Influenza: The Long Way from Animal Models Towards a Real-Life Universal Flu Vaccine

Current flu vaccines rely on the induction of strain-specific neutralizing antibodies, which leaves the population vulnerable to drifted seasonal or newly emerged pandemic strains. Therefore, universal flu vaccine approaches that induce broad immunity against conserved parts of influenza have top priority in research. Cross-reactive T cell responses, especially tissue-resident memory T cells in the respiratory tract, provide efficient heterologous immunity, and must therefore be a key component of universal flu vaccines. Here, we review recent findings about T cell-based flu immunity, with an emphasis on tissue-resident memory T cells in the respiratory tract of humans and different animal models. Furthermore, we provide an update on preclinical and clinical studies evaluating T cell-evoking flu vaccines, and discuss the implementation of T cell immunity in real-life vaccine policies.

Co-Inhibition of the Immunoproteasome Subunits LMP2 and LMP7 Ameliorates Immune Thrombocytopenia

The immunoproteasome, a special isoform of the 20S proteasome, is expressed when the cells receive an inflammatory signal. Immunoproteasome inhibition proved efficacy in the treatment of autoimmune diseases. However, the role of the immunoproteasome in the pathogenesis of immune thrombocytopenia (ITP) remains unknown. We found that the expression of the immunoproteasome catalytic subunit, large multifunctional protease 2 (LMP2), was significantly upregulated in peripheral blood mononuclear cells of active ITP patients compared to those of healthy controls. No significant differences in LMP7 expression were observed between patients and controls. ML604440, an specific LMP2 inhibitor, had no significant impact on the platelet count of ITP mice, while ONX-0914 (an inhibitor of both LMP2 and LMP7) increased the number of platelets. In vitro assays revealed that ONX-0914 decreased the expression of FcγRI in ITP mice and decreased that of FcγRIII in ITP patients, inhibited the activation of CD4+ T cells, and affected the differentiation of Th1 cells in patients with ITP. These results suggest that the inhibition of immunoproteasome is a potential therapeutic approach for ITP patients.

Total Recall: Intestinal TRM Cells in Health and Disease

Tissue-resident memory T cells (TRM cells) have crucial functions in host defense in mucosal tissues. They provide local adaptive immune surveillance and allow the fast initiation of targeted adaptive immune responses in case of antigen re-exposure. Recently, an aberrant activation in the case of immunologically mediated diseases has been increasingly acknowledged. As the organ with the largest interface to the environment, the gastrointestinal tract faces billions of antigens every day. Tightly balanced processes are necessary to ensure tolerance towards non-hazardous antigens, but to set up a powerful immune response against potentially dangerous ones. In this complex nexus of immune cells and their mediators, TRM cells play a central role and have been shown to promote both physiological and pathological events. In this review, we will summarize the current knowledge on the homeostatic functions of TRM cells and delineate their implication in infection control in the gut. Moreover, we will outline their commitment in immune dysregulation in gastrointestinal chronic inflammatory conditions and shed light on TRM cells as current and potential future therapeutic targets.

Functional Heterogeneity and Therapeutic Targeting of Tissue-Resident Memory T Cells

Tissue-resident memory T (T_RM) cells mediate potent local innate and adaptive immune responses and provide long-lasting protective immunity. T_RM cells localize to many different tissues, including barrier tissues, and play a crucial role in protection against infectious and malignant disease. The formation and maintenance of T_RM cells are influenced by numerous factors, including inflammation, antigen triggering, and tissue-specific cues. Emerging evidence suggests that these signals also contribute to heterogeneity within the T_RM cell compartment. Here, we review the phenotypic and functional heterogeneity of CD8⁺ T_RM cells at different tissue sites and the molecular determinants defining CD8⁺ T_RM cell subsets. We further discuss the possibilities of targeting the unique cell surface molecules, cytokine and chemokine receptors, transcription factors, and metabolic features of T_RM cells for therapeutic purposes. Their crucial role in immune protection and their location at the frontlines of the immune defense make T_RM cells attractive therapeutic targets. A better understanding of the possibilities to selectively modulate T_RM cell populations may thus improve vaccination and immunotherapeutic strategies employing these potent immune cells.

Inhibitory signaling sustains a distinct early memory CD8+ T cell precursor that is resistant to DNA damage

The developmental origins of memory T cells remain incompletely understood. During the expansion phase of acute viral infection, we identified a distinct subset of virus-specific CD8⁺ T cells that possessed distinct characteristics including expression of CD62L, T cell factor 1 (TCF-1), and Eomesodermin; relative quiescence; expression of activation markers; and features of limited effector differentiation. These cells were a quantitatively minor subpopulation of the TCF-1⁺ pool and exhibited self-renewal, heightened DNA damage surveillance activity, and preferential long-term recall capacity. Despite features of memory and somewhat restrained proliferation during the expansion phase, this subset displayed evidence of stronger TCR signaling than other responding CD8⁺ T cells, coupled with elevated expression of multiple inhibitory receptors including programmed cell death 1 (PD-1), lymphocyte activating gene 3 (LAG-3), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), CD5, and CD160. Genetic ablation of PD-1 and LAG-3 compromised the formation of this CD62L^hi TCF-1⁺ subset and subsequent CD8⁺ T cell memory. Although central memory phenotype CD8⁺ T cells were formed in the absence of these cells, subsequent memory CD8⁺ T cell recall responses were compromised. Together, these results identify an important link between genome integrity maintenance and CD8⁺ T cell memory. Moreover, the data indicate a role for inhibitory receptors in preserving key memory CD8⁺ T cell precursors during initial activation and differentiation. Identification of this rare subpopulation within the memory CD8⁺ T cell precursor pool may help reconcile models of the developmental origin of long-term CD8⁺ T cell memory.

The downregulation of IL-18R defines bona fide kidney-resident CD8+ T cells

Stepwise induction of CD69 and CD103 marks distinct differentiation stages of mucosal Trms. But the majority of non-mucosal Trm lacks CD103 expression. The expression of CD69 alone cannot faithfully define Trm cells in heavily vascularized non-mucosal tissues, such as the kidney. Here, we found that a subset of kidney Trms downregulated IL-18 receptor during differentiation. Via global transcriptional analysis and parabiosis experiments, we have discovered that the downregulation of interleukin-18 receptor (IL-18R) is associated with the establishment of tissue residency. Together with the expression of CD69, IL-18R^lo exclusively identify tissue-resident cells whereas IL-18R^hi population contains both tissue-resident and migratory ones. Local cytokines including transforming growth factor β (TGF-β) and interferon α (IFN-α)/β as well as TGF-β-dependent suppression of transcription factor Tcf-1 are essential for IL-18R downregulation during kidney Trm differentiation. Together, we identified a convenient surface marker to distinguish bona fide kidney-resident CD8⁺ T cells as well as underlying molecular mechanisms controlling this differentiation process.

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CD8⁺ Trm cells downregulate IL-18 receptor during differentiation

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IL-18R^hi population is composed of both migratory and resident subsets

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IL-18R^lo population is exclusively tissue-resident

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TGF-β promotes, whereas IFN-α/β inhibits, IL-18R downregulation

Pharmacokinetics and Immunological Effects of Romidepsin in Rhesus Macaques

HIV/SIV persistence in latent reservoirs requires lifelong antiretroviral treatment and calls for effective cure strategies. Romidepsin (RMD), a histone deacetylase inhibitor, was reported to reactivate HIV/SIV from reservoirs in virus-suppressed individuals. We characterized in detail the pharmacokinetics and safety profile of RMD in three SIV-naïve rhesus macaques which received two rounds of treatment. In plasma, RMD mean terminal half-life was 15.3 h. In comparison, RMD mean terminal half-life was much longer in tissues: 110 h in the lymph nodes (LNs) and 28 h in gastrointestinal tract. RMD administration was accompanied by transient liver and systemic toxicity. Isoflurane anesthesia induced near-immediate transient lymphopenia, which was further exacerbated and extended with the extensive immune modifications by RMD. The effect of RMD on circulating immune cells was complex: (i) slight increase in lymphocyte death rates; (ii) transient, robust increase in neutrophils; (iii) massive downregulation of lymphocyte surface markers; (iv) important migration of CD3⁺ T cells to the gut and LNs; and (v) hindrance to CD8⁺ T cell functionality, yet without reaching significance. Our results show that, in contrast to transient plasma concentrations, RMD has a long-term presence in tissues, with multiple immunomodulatory effects and minimal to moderate kidney, liver, and lymphocyte toxicities. As such, we concluded that RMD can be used for “shock and kill” approaches, preferentially in combination with other latency reversal agents or cytotoxic T lymphocyte boosting strategies with consideration taken for adverse effects.

Targeting Skin-Resident Memory T Cells via Vaccination to Combat Staphylococcus aureus Infections

Tissue-resident memory T cells are important in adaptive immunity against many infections, rendering these cells attractive potential targets in vaccine development. Genetic and experimental evidence highlights the importance of cellular immunity in protection from Staphylococcus aureus skin infections, yet skin-resident memory T cells are, thus far, an untested component of immunity during such infections. Novel methods of generating and sampling vaccine-induced skin memory T cells are paralleled by discoveries of global, skin-wide immunosurveillance. We propose skin-resident memory CD4⁺ T cells as a potential missing link in the search for correlates of protection during S. aureus infections. A better appreciation of their phenotypes and functions could accelerate the development of preventive vaccines against this highly virulent and antibiotic-resistant pathogen.

T Cell Immunity and the Quest for Protective Vaccines against Staphylococcus aureus Infection

Staphylococcus aureus is a wide-spread human pathogen, and one of the top causative agents of nosocomial infections. The prevalence of antibiotic-resistant S. aureus strains, which are associated with higher mortality and morbidity rates than antibiotic-susceptible strains, is increasing around the world. Vaccination would be an effective preventive measure against S. aureus infection, but to date, every vaccine developed has failed in clinical trials, despite inducing robust antibody responses. These results suggest that induction of humoral immunity does not suffice to confer protection against the infection. Evidence from studies in murine models and in patients with immune defects support a role of T cell-mediated immunity in protective responses against S. aureus. Here, we review the current understanding of the mechanisms underlying adaptive immunity to S. aureus infections and discuss these findings in light of the recent S. aureus vaccine trial failures. We make the case for the need to develop anti-S. aureus vaccines that can specifically elicit robust and durable protective memory T cell subsets.

Long-term skin-resident memory T cells proliferate in situ and are involved in human graft-versus-host disease

The skin contains a population of tissue-resident memory T cells (Trm) that is thought to contribute to local tissue homeostasis and protection against environmental injuries. Although information about the regulation, survival program, and pathophysiological roles of Trm has been obtained from murine studies, little is known about the biology of human cutaneous Trm Here, we showed that host-derived CD69+ αβ memory T cell clones in the epidermis and dermis remain stable and functionally competent for at least 10 years in patients with allogeneic hematopoietic stem cell transplantation. Single-cell RNA sequencing revealed low expression of genes encoding tissue egress molecules by long-term persisting Trm in the skin, whereas tissue retention molecules and stem cell markers were displayed by Trm The transcription factor RUNX3 and the surface molecule galectin-3 were preferentially expressed by host T cells at the RNA and protein levels, suggesting two new markers for human skin Trm Furthermore, skin lesions from patients developing graft-versus-host disease (GVHD) showed a large number of cytokine-producing host-derived Trm, suggesting a contribution of these cells to the pathogenesis of GVHD. Together, our studies highlighted the relationship between the local human skin environment and long-term persisting Trm, which differs from murine skin. Our results also indicated that local tissue inflammation occurs through host-derived Trm after allogeneic hematopoietic stem cell transplantation.

Divergent Impact of Glucose Availability on Human Virus-Specific and Generically Activated CD8 T Cells

Upon activation T cells engage glucose metabolism to fuel the costly effector functions needed for a robust immune response. Consequently, the availability of glucose can impact on T cell function. The glucose concentrations used in conventional culture media and common metabolic assays are often artificially high, representing hyperglycaemic levels rarely present in vivo. We show here that reducing glucose concentration to physiological levels in culture differentially impacted on virus-specific compared to generically activated human CD8 T cell responses. In virus-specific T cells, limiting glucose availability significantly reduced the frequency of effector-cytokine producing T cells, but promoted the upregulation of CD69 and CD103 associated with an increased capacity for tissue retention. In contrast the functionality of generically activated T cells was largely unaffected and these showed reduced differentiation towards a residency phenotype. Furthermore, T cells being cultured at physiological glucose concentrations were more susceptible to viral infection. This setting resulted in significantly improved lentiviral transduction rates of primary cells. Our data suggest that CD8 T cells are exquisitely adapted to their niche and provide a reminder of the need to better mimic physiological conditions to study the complex nature of the human CD8 T cell immune response.

Tissue-Resident Memory T Cells in the Liver-Unique Characteristics of Local Specialists

T cells play an important role to build up an effective immune response and are essential in the eradication of pathogens. To establish a long-lasting protection even after a re-challenge with the same pathogen, some T cells differentiate into memory T cells. Recently, a certain subpopulation of memory T cells at different tissue-sites of infection was detected-tissue-resident memory T cells (T_RM cells). These cells can patrol in the tissue in order to encounter their cognate antigen to establish an effective protection against secondary infection. The liver as an immunogenic organ is exposed to a variety of pathogens entering the liver through the systemic blood circulation or via the portal vein from the gut. It could be shown that intrahepatic T_RM cells can reside within the liver tissue for several years. Interestingly, hepatic T_RM cell differentiation requires a distinct cytokine milieu. In addition, T_RM cells express specific surface markers and transcription factors, which allow their identification delimited from their circulating counterparts. It could be demonstrated that liver T_RM cells play a particular role in many liver diseases such as hepatitis B and C infection, non-alcoholic fatty liver disease and even play a role in the development of hepatocellular carcinoma and in building long-lasting immune responses after vaccination. A better understanding of intrahepatic T_RM cells is critical to understand the pathophysiology of many liver diseases and to identify new potential drug targets for the development of novel treatment strategies.

Area under Immunosurveillance: Dedicated Roles of Memory CD8 T-Cell Subsets

Immunological memory, defined as the ability to respond in an enhanced manner upon secondary encounter with the same pathogen, can provide substantial protection against infectious disease. The improved protection is mediated in part by different populations of memory CD8 T cells that are retained after primary infection. Memory cells persist in the absence of pathogen-derived antigens and enable secondary CD8 T-cell responses with accelerated kinetics and of larger magnitude after reencounter with the same pathogen. At least three subsets of memory T cells have been defined that are referred to as central memory CD8 T cells (Tcm), effector memory CD8 T cells (Tem), and tissue-resident memory CD8 T cells (Trm). Tcm and Tem are circulating memory T cells that mediate bodywide immune surveillance in search of invading pathogens. In contrast, Trm permanently reside in peripheral barrier tissues, where they form a stationary defensive line of sentinels that alert the immune system upon pathogen reencounter. The characterization of these different subsets has been instrumental in our understanding of the strategies that memory T cells employ to counter invading pathogens. It is clear that memory T cells not only have a numerical advantage over naive T cells resulting in improved protection in secondary responses, but also acquire distinct sets of competencies that assist in pathogen clearance. Nevertheless, inherent challenges are associated with the allocation of memory T cells to a limited number of subsets. The classification of memory T cells into Tcm, Tem, and Trm may not take into account the full extent of the heterogeneity that is observed in the memory population. Therefore, in this review, we will revisit the current classification of memory subsets, elaborate on functional and migratory properties attributed to Tcm, Tem, and Trm, and discuss how potential heterogeneity within these populations arises and persists.

γδ T cell migration: Separating trafficking from surveillance behaviors at barrier surfaces

γδ T cells are found in highest numbers at barrier surfaces throughout the body, including the skin, intestine, lung, gingiva, and uterus. Under homeostatic conditions, γδ T cells provide immune surveillance of the epidermis, intestinal, and oral mucosa, whereas the presence of pathogenic microorganisms in the dermis or lungs elicits a robust γδ17 response to clear the infection. Although T cell migration is most frequently defined in the context of trafficking, analysis of specific migratory behaviors of lymphocytes within the tissue microenvironment can provide valuable insight into their function. Intravital imaging and computational analyses have been used to define "search" behavior associated with conventional αβ T cells; however, based on the known role of γδ T cells as immune sentinels at barrier surfaces and their TCR-independent functions, we put forth the need to classify distinct migratory patterns that reflect the surveillance capacity of these unconventional lymphocytes. This review will focus on how γδ T cells traffic to various barrier surfaces and how recent investigation into their migratory behavior has provided unique insight into the contribution of γδ T cells to barrier immunity.

T cell fate mapping and lineage tracing technologies probing clonal aspects underlying the generation of CD8 T cell subsets

T cells responding to acute infections generally provide two key functions to protect the host: (1) active contribution to pathogen elimination and (2) providing long‐lived cells that are poised to rapidly respond to renewed infection, thus ensuring long‐lasting protection against the particular pathogen. Extensive work has established an astonishing amount of additional diversity among T cells actively contributing to pathogen elimination, as well as among resting, long‐lived antigen‐experienced T cells. This led to the description of a variety of functionally distinct T cell ‘subsets’. Understanding how this heterogeneity develops among T cells responding to the same antigen is currently an active area of research, since knowledge of such mechanisms may have implications for the development of vaccines and immunotherapy. The number of naïve T cells specific to a given antigen span a great range. Considering this, one mechanistic angle focusses on how individual naïve T cells contribute to the development of the distinct T cell subsets. In this review, we highlight the current technologies that enable one to address the contributions of individual naïve T cells to different T cell subsets, with a focus on CD8 T cell subsets generated in the context of acute infections. Moreover, we discuss the requirements of new technologies to further our understanding of the mechanisms that help generate long‐lasting immunity.

Next-Generation Pertussis Vaccines Based on the Induction of Protective T Cells in the Respiratory Tract

Immunization with current acellular pertussis (aP) vaccines protects against severe pertussis, but immunity wanes rapidly after vaccination and these vaccines do not prevent nasal colonization with Bordetella pertussis. Studies in mouse and baboon models have demonstrated that Th1 and Th17 responses are integral to protective immunity induced by previous infection with B. pertussis and immunization with whole cell pertussis (wP) vaccines. Mucosal Th17 cells, IL-17 and secretory IgA (sIgA) are particularly important in generating sustained sterilizing immunity in the nasal cavity. Current aP vaccines induce potent IgG and Th2-skewed T cell responses but are less effective at generating Th1 and Th17 responses and fail to prime respiratory tissue-resident memory T (TRM) cells, that maintain long-term immunity at mucosal sites. In contrast, a live attenuated pertussis vaccine, pertussis outer membrane vesicle (OMV) vaccines or aP vaccines formulated with novel adjuvants do induce cellular immune responses in the respiratory tract, especially when delivered by the intranasal route. An increased understanding of the mechanisms of sustained protective immunity, especially the role of respiratory TRM cells, will facilitate the development of next generation pertussis vaccines that not only protect against pertussis disease, but prevent nasal colonization and transmission of B. pertussis.

CD103+CD8+ TRM Cells Accumulate in Tumors of Anti-PD-1-Responder Lung Cancer Patients and Are Tumor-Reactive Lymphocytes Enriched with Tc17

Accumulation of CD103⁺CD8⁺ resident memory T (T_RM) cells in human lung tumors has been associated with a favorable prognosis. However, the contribution of T_RM to anti-tumor immunity and to the response to immune checkpoint blockade has not been clearly established. Using quantitative multiplex immunofluorescence on cohorts of non-small cell lung cancer patients treated with anti-PD-(L)1, we show that an increased density of CD103⁺CD8⁺ lymphocytes in immunotherapy-naive tumors is associated with greatly improved outcomes. The density of CD103⁺CD8⁺ cells increases during immunotherapy in most responder, but not in non-responder, patients. CD103⁺CD8⁺ cells co-express CD49a and CD69 and display a molecular profile characterized by the expression of PD-1 and CD39. CD103⁺CD8⁺ tumor T_RM, but not CD103⁻CD8⁺ tumor-infiltrating counterparts, express Aiolos, phosphorylated STAT-3, and IL-17; demonstrate enhanced proliferation and cytotoxicity toward autologous cancer cells; and frequently display oligoclonal expansion of TCR-β clonotypes. These results explain why CD103⁺CD8⁺ T_RM are associated with better outcomes in anti-PD-(L)1-treated patients.

A high density of CD103⁺CD8⁺ cells in tumors correlates with response to anti-PD-(L)1

The density of CD103⁺CD8⁺ cells increases after anti-PD-1 in most responder patients

CD103⁺CD8⁺ T_RM cells are enriched with tumor-specific T cells

A subset of CD103⁺CD8⁺ T_RM cells display a Tc17 differentiation program

Resident Memory T Cells and Their Effect on Cancer

Resident memory T (T_RM) cells are a unique subset of CD8⁺ T cells that are present within certain tissues and do not recirculate through the blood. Long term memory establishment and maintenance are dependent on tissue population of memory T cells. They are characterized by dual CD69/CD103 positivity, and play a role in both response to viral infection and local cancer immunosurveillance. Human T_RM cells demonstrate the increased expression of adhesion molecules to facilitate tissue retention, have reduced proliferation and produce both regulatory and immune responsive cytokines. T_RM cell phenotype is often characterized by a distinct expression profile driven by Runx3, Blimp1, and Hobit transcription factors. The accumulation of T_RM cells in tumors is associated with increased survival and response to immunotherapies, including anti-PD-1 and anti-CTLA-4. In this review, we explore potential mechanisms of T_RM cell transformation and maintenance, as well as potential applications for the use of T_RM cells in both the development of supportive therapies and establishing more accurate prognoses.

Divergence of Tissue-Memory T Cells: Distribution and Function-Based Classification

Tissue-resident memory T cells (Trm) comprise the majority of memory cells in nonlymphoid tissues and play a predominant role in immunity at barrier surfaces. A better understanding of Trm cell maintenance and function is essential for the development of vaccines that confer frontline protection. However, it is currently challenging to precisely distinguish Trm cells from other T cells, and this has led to confusion in the literature. Here we highlight gaps in our understanding of tissue memory and discuss recent advances in the classification of Trm cell subsets based on their distribution and functional characteristics.

Tissue-resident memory-like T cells in tumor immunity: Clinical implications

Tissue-resident memory (T_RM) T cells are distinct population of non-circulating lymphocytes that play an important role in mediating regional immunity. T_RM- like cells have now been identified as a component of tumor-infiltrating lymphocytes in several human tumors and correlate with outcome and response to immunotherapy. T_RM cells have also been shown to mediate anti-tumor immunity in murine models. Biology of T_RM cells has several implications for clinical cancer immunotherapy. Here we discuss newer insights into the biology of T_RM T cells and discuss their implications for understanding the heterogeneity of immune microenvironment in tumors as well as improving the efficacy of cancer vaccines, immune-checkpoint blockade and adoptive cellular therapies in the clinic.

Decreased Frequency of Intestinal CD39+ γδ+ T Cells With Tissue-Resident Memory Phenotype in Inflammatory Bowel Disease

The ectoenzymes CD39 and CD73 play a major role in controlling tissue inflammation by regulating the balance between adenosine triphosphate (ATP) and adenosine. Still, little is known about the role of these two enzymes and ATP and its metabolites in the pathophysiology of inflammatory bowel disease (IBD). We isolated mononuclear cells from peripheral blood and lamina propria of the large intestine of patients diagnosed with IBD and of healthy volunteers. We then comprehensively analyzed the CD39 and CD73 expression patterns together with markers of activation (HLA-DR, CD38), differentiation (CCR7, CD45RA) and tissue-residency (CD69, CD103, CD49a) on CD4⁺, CD8⁺, γδ⁺ T cells and mucosa-associated invariant T cells using flow cytometry. CD39 expression levels of γδ⁺ and CD8⁺ T cells in lamina propria lymphocytes (LPL) were much higher compared to peripheral blood mononuclear cells. Moreover, the frequency of CD39⁺ CD4⁺ and CD8⁺, but not γδ⁺ LPL positively correlated with T-cell activation. The frequency of CD39⁺ cells among tissue-resident memory LPL (Trm) was higher compared to non-Trm for all subsets, confirming that CD39 is a marker for the tissue-resident memory phenotype. γδ⁺ Trm also showed a distinct cytokine profile upon stimulation – the frequency of IFN-γ⁺ and IL-17A⁺ cells was significantly lower in γδ⁺ Trm compared to non-Trm. Interestingly, we observed a decreased frequency of CD39⁺ γδ⁺ T cells in IBD patients compared to healthy controls (p = 0.0049). Prospective studies need to elucidate the exact role of this novel CD39⁺ γδ⁺ T-cell population with tissue-resident memory phenotype and its possible contribution to the pathogenesis of IBD and other inflammatory disorders.

Tissue-Resident Memory T Cells Mediate Immune Homeostasis in the Human Pancreas through the PD-1/PD-L1 Pathway

Non-recirculating tissue-resident memory T cells (TRMs) are the predominant T cell subset in diverse tissue sites, where they mediate protective immune responses in situ. Here, we reveal a role for TRM in maintaining immune homeostasis in the human pancreas through interactions with resident macrophages and the PD-1/PD-L1 inhibitory pathway. Using tissues obtained from organ donors, we identify that pancreas T cells comprise CD8⁺PD-1^hi TRMs, which are phenotypically, functionally, and transcriptionally distinct compared to TRMs in neighboring jejunum and lymph node sites. Pancreas TRMs cluster with resident macrophages throughout the exocrine areas; TRM effector functions are enhanced by macrophage-derived co-stimulation and attenuated by the PD-1/PD-L1 pathways. Conversely, in samples from chronic pancreatitis, TRMs exhibit reduced PD-1 expression and reduced interactions with macrophages. These findings suggest important roles for PD-1 and TRM-macrophage interactions in controlling tissue homeostasis and immune dysfunctions underlying inflammatory disease, with important implications for PD-1-based immunotherapies.

The human tissue-resident CCR5+ T cell compartment maintains protective and functional properties during inflammation

CCR5 is thought to play a central role in orchestrating migration of cells in response to inflammation. CCR5 antagonists can reduce inflammatory disease processes, which has led to an increased interest in using CCR5 antagonists in a wide range of inflammation-driven diseases. Paradoxically, these antagonists appear to function without negatively affecting host immunity at barrier sites. We reasoned that the resolution to this paradox may lie in the CCR5⁺ T cell populations that permanently reside in tissues. We used a single-cell analysis approach to examine the human CCR5⁺ T cell compartment in the blood, healthy, and inflamed mucosal tissues to resolve these seemingly contradictory observations. We found that 65% of the CD4 tissue-resident memory T (TRM) cell compartment expressed CCR5. These CCR5⁺ T_RM cells were enriched in and near the epithelial layer and not only limited to T_H1-type cells but also contained a large T_H17-producing and a stable regulatory T cell population. The CCR5⁺ T_RM compartment was stably maintained even in inflamed tissues including the preservation of T_H17 and regulatory T cell populations. Further, using tissues from the CHARM-03 clinical trial, we found that CCR5⁺ T_RM are preserved in human mucosal tissue during treatment with the CCR5 antagonist Maraviroc. Our data suggest that the human CCR5⁺ T_RM compartment is functionally and spatially equipped to maintain barrier immunity even in the absence of CCR5-mediated, de novo T cell recruitment from the periphery.

Non-human Primate Determinants of Natural Killer Cells in Tissues at Steady-State and During Simian Immunodeficiency Virus Infection

Natural killer (NK) cells play essential roles in immunity to viruses and tumors. Their function is genetically determined but also modulated by environmental factors. The distribution and functional regulation of these cells vary depending on the tissue. NK cell behavior in lymphoid tissues is so far understudied. Non-human primate (NHP) models are essential for the development of therapies and vaccines against human diseases, and access to NHP tissues allows insights into spatial regulations of NK cells. Here, we investigated tissue-specific parameters of NK cells from NHP species, i.e., cynomolgus macaque (Macaca fascicularis), African green monkey (Chlorocebus sabaeus), rhesus macaque (Macaca mulatta), and baboon (Papio anubis). By comprehensive multi-dimensional analysis of NK cells from secondary lymphoid organs, intestinal mucosa, liver, and blood, we identified tissue- and species-specific patterns of NK cell frequencies, phenotypes, and potential activity. Also, we defined the tissue-specific characteristics of NK cells during infection by the simian immunodeficiency virus. Altogether, our results provide a comprehensive anatomic analysis of NK cells in different tissues of primates at steady-state and during a viral infection.

Impact of multiple hits with cognate antigen on memory CD8+ T-cell fate

Antigen-driven activation of CD8+ T cells results in the development of a robust anti-pathogen response and ultimately leads to the establishment of long-lived memory T cells. During the primary response, CD8+ T cells interact multiple times with cognate antigen on distinct types of antigen-presenting cells. The timing, location and context of these antigen encounters significantly impact the differentiation programs initiated in the cells. Moderate re-activation in the periphery promotes the establishment of the tissue-resident memory T cells that serve as sentinels at the portal of pathogen entry. Under some circumstances, moderate re-activation of T cells in the periphery can result in the excessive expansion and accumulation of circulatory memory T cells, a process called memory inflation. In contrast, excessive re-activation stimuli generally impede conventional T-cell differentiation programs and can result in T-cell exhaustion. However, these conditions can also elicit a small population of exhausted T cells with a memory-like signature and self-renewal capability that are capable of responding to immunotherapy, and restoration of functional activity. Although it is clear that antigen re-encounter during the primary immune response has a significant impact on memory T-cell development, we still do not understand the molecular details that drive these fate decisions. Here, we review our understanding of how antigen encounters and re-activation events impact the array of memory CD8+ T-cell subsets subsequently generated. Identification of the molecular programs that drive memory T-cell generation will advance the development of new vaccine strategies that elicit high-quality CD8+ T-cell memory.

CX3CL1 and IL-15 Promote CD8 T cell chemoattraction in HIV and in atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) remains an important cause of morbidity in the general population and risk for ASCVD is increased approximately 2-fold in persons living with HIV infection (PLWH). This risk is linked to elevated CD8 T cell counts that are abundant in atherosclerotic plaques and have been implicated in disease pathogenesis yet the mechanisms driving T cell recruitment to and activation within plaques are poorly defined. Here we investigated the role of CD8 T cells in atherosclerosis in a non-human primate model of HIV infection and in the HIV-uninfected elderly; we sought to identify factors that promote the activation, function, and recruitment to endothelium of CX3CR1+ CD8 T cells. We measured elevated expression of CX3CL1 and IL-15, and increased CD8 T cell numbers in the aortas of rhesus macaques infected with SIV or SHIV, and demonstrated similar findings in atherosclerotic vessels of HIV-uninfected humans. We found that recombinant TNF enhanced the production and release of CX3CL1 and bioactive IL-15 from aortic endothelial cells, but not from aortic smooth muscle cells. IL-15 in turn promoted CX3CR1 surface expression on and TNF synthesis by CD8 T cells, and IL-15-treated CD8 T cells exhibited enhanced CX3CL1-dependent chemoattraction toward endothelial cells in vitro. Finally, we show that CD8 T cells in human atherosclerotic plaques have an activated, resident phenotype consistent with in vivo IL-15 and CX3CL1 exposure. In this report, we define a novel model of CD8 T cell involvement in atherosclerosis whereby CX3CL1 and IL-15 operate in tandem within the vascular endothelium to promote infiltration by activated CX3CR1+ memory CD8 T cells that drive further endothelial activation via TNF. We propose that these interactions are prevalent in aging and in PLWH, populations where circulating activated CX3CR1+ CD8 T cell numbers are often expanded.

Development of an Immune-Related Risk Signature for Predicting Prognosis in Lung Squamous Cell Carcinoma

Lung squamous cell carcinoma (LSCC) is the most common subtype of non-small cell lung cancer. Immunotherapy has become an effective treatment in recent years, while patients showed different responses to the current treatment. It is vital to identify the potential immunogenomic signatures to predict patient' prognosis. The expression profiles of LSCC patients with the clinical information were downloaded from TCGA database. Differentially expressed immune-related genes (IRGs) were extracted using edgeR algorithm, and functional enrichment analysis showed that these IRGs were primarily enriched in inflammatory- and immune-related processes. "Cytokine-cytokine receptor interaction" and "PI3K-AKT signaling pathway" were the most enriched KEGG pathways. 27 differentially expressed IRGs were significantly correlated with the overall survival (OS) of patients using univariate Cox regression analysis. A prognostic risk signature that comprises seven IRGs (GCCR, FGF8, CLEC4M, PTH, SLC10A2, NPPC, and FGF4) was developed with effective predictive performance by multivariable Cox stepwise regression analysis. Most importantly, the signature could be an independent prognostic predictor after adjusting for clinicopathological parameters, and also validated in two independent LSCC cohorts (GSE4573 and GSE17710). Potential molecular mechanisms and tumor immune landscape of these IRGs were investigated through computational biology. Analysis of tumor infiltrating lymphocytes and immune checkpoint molecules revealed distinct immune landscape in high- and low-risk group. The study was the first time to construct IRG-based immune signature in the recognition of disease progression and prognosis of LSCC patients.

T Cell Immunity to Bacterial Pathogens: Mechanisms of Immune Control and Bacterial Evasion

The human body frequently encounters harmful bacterial pathogens and employs immune defense mechanisms designed to counteract such pathogenic assault. In the adaptive immune system, major histocompatibility complex (MHC)-restricted αβ T cells, along with unconventional αβ or γδ T cells, respond to bacterial antigens to orchestrate persisting protective immune responses and generate immunological memory. Research in the past ten years accelerated our knowledge of how T cells recognize bacterial antigens and how many bacterial species have evolved mechanisms to evade host antimicrobial immune responses. Such escape mechanisms act to corrupt the crosstalk between innate and adaptive immunity, potentially tipping the balance of host immune responses toward pathological rather than protective. This review examines the latest developments in our knowledge of how T cell immunity responds to bacterial pathogens and evaluates some of the mechanisms that pathogenic bacteria use to evade such T cell immunosurveillance, to promote virulence and survival in the host.

New Insights into the Role of Sphingolipid Metabolism in Melanoma

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Monocyte-Derived Cells in Tissue-Resident Memory T Cell Formation

There is currently much interest in how different dendritic cell and macrophage populations contribute to T cell-mediated immunity. Although conventional dendritic cell subsets have received much attention for their role in T cell priming, there is emerging evidence for a role for monocyte-derived APC (MoAPC) in tissue-resident memory T cell (Trm) formation. Cells of the monocyte/macrophage lineage play a key role in providing chemokines and cytokines for the localization, differentiation, and survival of Trm and Trm precursors. In addition, inflammatory MoAPC are the key providers of TNF superfamily costimulatory signals, a signal we refer to as signal 4 for T cell activation. Recent evidence suggests that signal 4 from MoAPC occurs postpriming and substantially increases Trm formation. Key questions remain, such as the Ag dependence of signal 4 and the specific mechanisms by which MoAPC-Trm interactions affect the long-term maintenance of Trm.

The relationship between CD4+ follicular helper T cells and CD8+ resident memory T cells: sisters or distant cousins?

Independent studies over the last decade have characterized the properties of non-circulating CD8+ 'resident' memory T cells (TRM), which offer barrier protective immunity in non-lymphoid tissues and CD4+ follicular helper T cells (TFH), which mediate B-cell help in lymphoid sites. Despite their very different biological roles in the immune system, intriguing parallels have been noted between the trafficking properties and differentiation cues of these populations, parallels which have only sharpened with recent findings. In this review, we explore the features that underlie these similarities and discuss whether these indicate meaningful homologies in the development of CD8+ TRM and CD4+ TFH or reflect resemblances which are only 'skin-deep'.

Tissue-Resident NK Cells: Development, Maturation, and Clinical Relevance

Natural killer (NK) cells belong to type 1 innate lymphoid cells (ILC1) and are essential in killing infected or transformed cells. NK cells mediate their effector functions using non-clonotypic germ-line-encoded activation receptors. The utilization of non-polymorphic and conserved activating receptors promoted the conceptual dogma that NK cells are homogeneous with limited but focused immune functions. However, emerging studies reveal that NK cells are highly heterogeneous with divergent immune functions. A distinct combination of several activation and inhibitory receptors form a diverse array of NK cell subsets in both humans and mice. Importantly, one of the central factors that determine NK cell heterogeneity and their divergent functions is their tissue residency. Decades of studies provided strong support that NK cells develop in the bone marrow. However, evolving evidence supports the notion that NK cells also develop and differentiate in tissues. Here, we summarize the molecular basis, phenotypic signatures, and functions of tissue-resident NK cells and compare them with conventional NK cells.

Human T cells interacting with HNSCC-derived mesenchymal stromal cells acquire tissue-resident memory like properties

Tissue-resident memory (Trm) cells are specialized components of both CD4+ and CD8+ T cell subsets that persist in peripheral nonlymphoid tissues following infections and provide fast response in case of a secondary invasion by the same pathogen. Trm cells express the surface markers CD69, CD103, and the immune checkpoint molecule PD-1. Trm cells develop not only in the context of infections but also in tumors, where they can provide a line of defense as suggested by the positive correlation between the frequency of tumor-infiltrating Trm cells and patients' survival. Trm cells persistence in peripheral tissues depends on their adaptation to the local microenvironment and the presence of survival factors, mainly IL-7, IL-15, and Notch ligands. However, the cell sources of these factors are largely unknown, especially in the context of tumors. Here, we show that head-neck squamous cell carcinoma (HNSCC) is enriched in CD4+ and CD8+ T cells with a Trm phenotype. Moreover, we show that mesenchymal stromal cells that accumulate in HNSCC are a source of survival factors and allow proper expression of Trm-typical markers in a VCAM1-dependent manner.

Decidual CD8+T cells exhibit both residency and tolerance signatures modulated by decidual stromal cells

BACKGROUND

During early pregnancy, tolerance of the semi-allogeneic fetus necessitates comprehensive modifications of the maternal immune system. How decidual CD8+T (CD8+dT) cells balance maternal tolerance of the fetus with defense from invading pathogens remains undefined.

METHODS

We investigated the distribution patterns of CD8+T cells and their heterogeneity in paired peripheral blood and decidual tissue in the first trimester of pregnancy using flow cytometry and mRNA-Seq. Gene Set Enrichment Analysis was utilized to determine the transcriptional features of CD8+dT cells. Moreover, we examined activation of T cells when they were cocultured with trophoblasts, in addition to the effect of the fetal-maternal environment on peripheral CD8+T (CD8+pT) cells.

RESULTS

We found that, compared with CD8+pT cells, CD8+dT cells consisted mainly of effector memory cells (TEM) and terminally differentiated effector memory cells (TEMRA). Both TEM and TEMRA subsets contained increased numbers of CD27+CD28- cells, which have been shown to possess only partial effector functions. In-depth analysis of the gene-expression profiles of CD8+dT cells revealed significant enrichment in T cell exhaustion-related genes and core tissue residency signature genes that have been found recently to be shared by tissue resident memory cells and tumor-infiltrating lymphocytes (TILs). In accordance with gene expression, protein levels of the exhaustion-related molecules PD-1 and CD39 and the tissue resident molecules CD103 and CXCR3 were increased significantly with almost no perforin secretion in CD8+dT cells compared with CD8+pT cells. However, the levels of granzyme B, IFN-γ, and IL-4 in CD8+dT cells were increased significantly compared with those in CD8+pT cells. Both CD8+dT and CD8+pT cells were not activated after being cocultured with autologous trophoblast cells. Moreover, the production of granzyme B in CD103+CD8+dT cells decreased significantly compared with that in their CD103- counterparts. Coculture with decidual stromal cells and trophoblasts upregulated CD103 expression significantly in CD8+pT cells.

CONCLUSIONS

Our findings indicate that the selective silencing of effector functions of resident CD8+dT cells may favor maternal-fetal tolerance and that the decidual microenvironment plays an important role in promoting the residency of CD8+T cells and their tolerance-defense balance.

Tissue-Resident Memory T Cells in Mice and Humans: Towards a Quantitative Ecology

In recent years, tissue-resident memory T cells (T_RM) have emerged as essential components of immunological memory. Following antigenic challenge, T_RM remain in nonlymphoid tissues and defend against re-exposure. Although accumulating evidence suggests important roles for T_RM in mediating protective immunity, fundamental aspects of the population biology of T_RM remain poorly understood. In this article, we discuss how results from different systems shed light on the ecological dynamics of T_RM in mice and humans. We highlight the importance of dissecting processes contributing to T_RM maintenance, and how these might vary across phenotypically and spatially heterogeneous subsets. We also discuss how the diversity of T_RM communities within specific tissues may evolve under competition and in response to antigenic perturbation. Throughout, we illustrate how mathematical models can clarify inferences obtained from experimental data and help elucidate the homeostatic mechanisms underpinning the ecology of T_RM populations.

Memory CD8+ T cell responses to cancer

Long-lived memory CD8+ T cells play important roles in tumor immunity. Studies over the past two decades have identified four subsets of memory CD8+ T cells - central, effector, stem-like, and tissue resident memory - that either circulate through blood, lymphoid and peripheral organs, or reside in tissues where cancers develop. In this article, we will review studies from both pre-clinical mouse models and human patients to summarize the phenotype, distribution and unique features of each memory subset, and highlight specific roles of each subset in anti-tumor immunity. Moreover, we will discuss how stem-cell like and resident memory CD8+ T cell subsets relate to exhausted tumor-infiltrating lymphocytes (TIL) populations. These studies reveal how memory CD8+ T cell subsets together orchestrate durable immunity to cancer.

Tissue-resident CD8+ T memory cells with unique properties are present in human decidua during early pregnancy

PROBLEM

Resident memory T (T_RM ) cells reside in the uterus during pregnancy may play an important role in balancing maternal-fetal tolerance with anti-infectious immunity. Although CD8⁺ T_RM and decidual CD8⁺ T cells have been extensively characterized, the properties of decidual CD8⁺ T_RM (dT_RM ) cells remain poorly defined.

METHOD OF STUDY

We investigated the heterogeneity, phenotypes, and functions of dT_RM cells, and compared the proportion of dT_RM cells between normal pregnancy and recurrent spontaneous abortion (RSA) using flow cytometry. Moreover, we cocultured peripheral CD8⁺ T (CD8⁺ pT) cells with trophoblast, or decidual stomal cells (DSCs) in the presence or absence of anti-TGF-β antibody or TGF-β type I receptor inhibitor to explore the effects of maternal-fetal environment on decidual CD8⁺ T_RM cell formation.

RESULTS

We found that CD69⁺ CD103⁺ T_RM cells were abundant in CD8⁺ dT cells but not in CD4⁺ dT cells with effector-memory (EM, CD45RA^- CCR7^- ) phenotypes. The percentage of dT_RM cells from RSA patients was significantly higher than that from normal pregnancy. Furthermore, dT_RM  cells showed increased expressions of chemokine receptors, T-cell exhaustion-related molecules, and produced more anti-inflammatory cytokines and effector cytokines upon stimulation. Moreover, DSCs produced a considerable level of TGF-β and upregulated CD103 expression on CD69⁺ CD8⁺ pT cells, which can be significantly reversed by blocking TGF-β receptor.

CONCLUSION

Our findings demonstrate that T_RM cells with unique properties are present in the decidua during human early pregnancy. They possess an enhanced capacity to produce effector cytokines and regulatory molecules, which might be important in the balance between maternal-fetal immune tolerance and the capacity to aggressively respond to infections.

Characterization of tumour-infiltrating lymphocytes in a tumour rejection cynomolgus macaque model

Immunotherapy has emerged as a promising and effective treatment for cancer, yet the clinical benefit is still variable, in part due to insufficient accumulation of immune effector cells in the tumour microenvironment. Better understanding of tumour-infiltrating lymphocytes (TILs) from nonhuman primate tumours could provide insights into improving effector cell accumulation in tumour tissues during immunotherapy. Here, we characterize TILs in a cynomolgus macaque tumour model in which the tumours were infiltrated with CD4⁺ and CD8⁺ T cells and were eventually rejected. The majority of CD4⁺ and CD8⁺ TILs exhibited a CD45RA⁻CCR7⁻ effector memory phenotype, but unlike circulating T cells, they expressed CD69, a marker for tissue-resident memory T (T_RM) cells. CD69-expressing CD8⁺ TILs expressed high levels of the cytotoxic molecule granzyme B and the co-inhibitory receptor PD-1. Consistent with the T_RM cell phenotype, CD8⁺ TILs minimally expressed CX3CR1 but expressed CXCR3 at higher levels than circulating CD8⁺ T cells. Meanwhile, CXCL9, CXCL10 and CXCL11, chemokine ligands for CXCR3, were expressed at high levels in the tumours, thus attracting CXCR3⁺CD8⁺ T cells. These results indicate that tumour-transplanted macaques can be a useful preclinical model for studying and optimizing T cell accumulation in tumours for the development of new immunotherapies.

TRM integrins CD103 and CD49a differentially support adherence and motility after resolution of influenza virus infection

Current influenza vaccination strategies require annual immunizations, with fairly low efficacy rates. One technique to improve protection against a greater breadth of influenza viruses is to elicit broadly cross-reactive cell-mediated immunity and generate a local population of cytotoxic T cells to respond to conserved regions of circulating viruses. However, this approach requires improved understanding of how these cells migrate within and attach to the tissue in order to persist and offer long-term immunity. This study investigates how receptors on the T cell surface impact the cell’s ability to interact with the tissue and provide evidence of which of these receptors are essential for protection. Furthermore, these studies reveal functional in vivo mechanisms of cellular markers used to characterize T_RM.

Tissue-resident memory CD8 T (T_RM) cells are a unique immune memory subset that develops and remains in peripheral tissues at the site of infection, providing future host resistance upon reexposure to that pathogen. In the pulmonary system, T_RM are identified through S1P antagonist CD69 and expression of integrins CD103/β7 and CD49a/CD29(β1). Contrary to the established role of CD69 on CD8 T cells, the functions of CD103 and CD49a on this population are not well defined. This study examines the expression patterns and functions of CD103 and CD49a with a specific focus on their impact on T cell motility during influenza virus infection. We show that the T_RM cell surface phenotype develops by 2 wk postinfection, with the majority of the population expressing CD49a and a subset that is also positive for CD103. Despite a previously established role in retaining T_RM in peripheral tissues, CD49a facilitates locomotion of virus-specific CD8 T cells, both in vitro and in vivo. These results demonstrate that CD49a may contribute to local surveillance mechanisms of the T_RM population.

The Role of TRM Cells in the Pathogenesis of Vitiligo-A Review of the Current State-Of-The-Art

Vitiligo is the most common hypopigmentation disease affecting both the skin and mucous membranes. The pathogenesis of this disorder is complex and involves the influence of genetic and environmental factors, oxidative stress, and autoimmune responses. Recent studies have indicated that skin lesions observed in vitiligo tend to recur in the same places where they were found before treatment. This phenomenon is explained by the presence of recently discovered tissue-resident memory T cells (T_RM), whose primary function is to provide antiviral and antibacterial protection in non-lymphoid tissues. T_RM cells show the presence of CD49a, CD69, and CD103 markers on their surface, although not all of them express these particles. Due to their ability to produce and secrete perforin, IFN-γ, and granzyme B, T_RM cells demonstrate a cytotoxic effect on melanocytes, thus inducing depigmented lesions in the course of the vitiligo. It has been proved that the occurrence of T_RM cells largely depends on IL-15, which promotes the T_RM function ex vivo. The findings above, as well as their reference to the pathogenesis of autoimmune skin diseases will have a considerable influence on the development of new therapeutic strategies in the near future. This article presents an up-to-date review of information regarding the role of T_RM cells in the development and progression of vitiligo.

KLRG1 and CD103 Expressions Define Distinct Intestinal Tissue-Resident Memory CD8 T Cell Subsets Modulated in Crohn's Disease

Intestinal tissue-resident memory CD8 T cells (Trm) are non-recirculating effector cells ideally positioned to detect and react to microbial infections in the gut mucosa. There is an emerging understanding of Trm cell differentiation and functions, but their implication in inflammatory bowel diseases, such as Crohn's disease (CD), is still unknown. Here, we describe CD8 cells in the human intestine expressing KLRG1 or CD103, two receptors of E-cadherin. While CD103 CD8 T cells are present in high numbers in the mucosa of CD patients and controls, KLRG1 CD8 T cells are increased in inflammatory conditions. Mucosal CD103 CD8 T cells are more responsive to TCR restimulation, but KLRG1 CD8 T cells show increased cytotoxic and proliferative potential. CD103 CD8 T cells originate mostly from KLRG1 negative cells after TCR triggering and TGFβ stimulation. Interestingly, mucosal CD103 CD8 T cells from CD patients display major changes in their transcriptomic landscape compared to controls. They express Th17 related genes including CCL20, IL22, and IL26, which could contribute to the pathogenesis of CD. Overall, these findings suggest that CD103 CD8 T cells in CD induce a tissue-wide alert increasing innate immune responses and recruitment of effector cells such as KLRG1 CD8 T cells.

Finding a Way Out: S1P Signaling and Immune Cell Migration

The signaling lipid sphingosine 1-phosphate (S1P) plays critical roles in an immune response. Drugs targeting S1P signaling have been remarkably successful in treatment of multiple sclerosis, and they have shown promise in clinical trials for colitis and psoriasis. One mechanism of these drugs is to block lymphocyte exit from lymph nodes, where lymphocytes are initially activated, into circulation, from which lymphocytes can reach sites of inflammation. Indeed, S1P can be considered a circulation marker, signaling to immune cells to help them find blood and lymphatic vessels, and to endothelial cells to stabilize the vasculature. That said, S1P plays pleiotropic roles in the immune response, and it will be important to build an integrated view of how S1P shapes inflammation. S1P can function so effectively because its distribution is exquisitely tightly controlled. Here we review how S1P gradients regulate immune cell exit from tissues, with particular attention to key outstanding questions in the field.