Dendritic cell-induced memory T cell activation in nonlymphoid tissues

Dissecting the immune response of CD4+ T cells in Alzheimer's disease

The formation of amyloid-β (Aβ) plaques is a neuropathological hallmark of Alzheimer's disease (AD), however, these pathological aggregates can also be found in the brains of cognitively unimpaired elderly population. In that context, individual variations in the Aβ-specific immune response could be key factors that determine the level of Aβ-induced neuroinflammation and thus the propensity to develop AD. CD4+ T cells are the cornerstone of the immune response that coordinate the effector functions of both adaptive and innate immunity. However, despite intensive research efforts, the precise role of these cells during AD pathogenesis is still not fully elucidated. Both pathogenic and beneficial effects have been observed in various animal models of AD, as well as in humans with AD. Although this functional duality of CD4+ T cells in AD can be simply attributed to the vast phenotype heterogeneity of this cell lineage, disease stage-specific effect have also been proposed. Therefore, in this review, we summarized the current understanding of the role of CD4+ T cells in the pathophysiology of AD, from the aspect of their antigen specificity, activation, and phenotype characteristics. Such knowledge is of practical importance as it paves the way for immunomodulation as a therapeutic option for AD treatment, given that currently available therapies have not yielded satisfactory results.

Local Power: The Role of Tissue-Resident Immunity in Human Genital Herpes Simplex Virus Reactivation

From established latency, human herpes virus type 2 (HSV-2) frequently reactivates into the genital tract, resulting in symptomatic ulcers or subclinical shedding. Tissue-resident memory (TRM) CD8+ T cells that accumulate and persist in the genital skin at the local site of recrudescence are the "first responders" to viral reactivation, performing immunosurveillance and containment and aborting the ability of the virus to induce clinical lesions. This review describes the unique spatiotemporal characteristics, transcriptional signatures, and noncatalytic effector functions of TRM CD8+ T cells in the tissue context of human HSV-2 infection. We highlight recent insights into the intricate overlaps between intrinsic resistance, innate defense, and adaptive immunity in the tissue microenvironment and discuss how rapid virus-host dynamics at the skin and mucosal level influence clinical outcomes of genital herpes diseases.

Intestinal tissue-resident memory T cells maintain distinct identity from circulating memory T cells after in vitro restimulation

Resident memory T (TRM) cells have been recently established as an important subset of memory T cells that provide early and essential protection against reinfection in the absence of circulating memory T cells. Recent findings showing that TRM expand in vivo after repeated antigenic stimulation indicate that these memory T cells are not terminally differentiated. This suggests an opportunity for in vitro TRM expansion to apply in an immunotherapy setting. However, it has also been shown that TRM may not maintain their identity and form circulating memory T cells after in vivo restimulation. Therefore, we set out to determine how TRM respond to antigenic activation in culture. Using Listeria monocytogenes and LCMV infection models, we found that TRM from the intraepithelial compartment of the small intestine expand in vitro after antigenic stimulation and subsequent resting in homeostatic cytokines. A large fraction of the expanded TRM retained their phenotype, including the expression of key TRM markers CD69 and CD103 (ITGAE). The optimal culture of TRM required low O2 pressure to maintain the expression of these and other TRM-associated molecules. Expanded TRM retained their effector capacity to produce cytokines after restimulation, but did not acquire a highly glycolytic profile indicative of effector T cells. The proteomic analysis confirmed TRM profile retention, including expression of TRM-related transcription factors, tissue retention factors, adhesion molecules, and enzymes involved in fatty acid metabolism. Collectively, our data indicate that limiting oxygen conditions supports in vitro expansion of TRM cells that maintain their TRM phenotype, at least in part, suggesting an opportunity for therapeutic strategies that require in vitro expansion of TRM.

CD8+ Tissue-Resident Memory T Cells: Versatile Guardians of the Tissue

Tissue-resident memory T (Trm) cells are a subset of T cells maintained throughout life within nonlymphoid tissues without significant contribution from circulating memory T cells. CD8+ Trm cells contribute to both tissue surveillance and direct elimination of pathogens through a variety of mechanisms. Reactivation of these Trm cells during infection drives systematic changes within the tissue, including altering the state of the epithelium, activating local immune cells, and contributing to the permissiveness of the tissue for circulating immune cell entry. Trm cells can be further classified by their functional outputs, which can be either subset- or tissue-specific, and include proliferation, tissue egress, and modulation of tissue physiology. These functional outputs of Trm cells are linked to the heterogeneity and plasticity of this population, and uncovering the unique responses of different Trm cell subsets and their role in immunity will allow us to modulate Trm cell responses for optimal control of disease.

CD8+ Trms against malaria liver-stage: prospects and challenges

Attenuated sporozoites provide a valuable model for exploring protective immunity against the malarial liver stage, guiding the design of highly efficient vaccines to prevent malaria infection. Liver tissue-resident CD8+ T cells (CD8+ Trm cells) are considered the host front-line defense against malaria and are crucial to developing prime-trap/target strategies for pre-erythrocytic stage vaccine immunization. However, the spatiotemporal regulatory mechanism of the generation of liver CD8+ Trm cells and their responses to sporozoite challenge, as well as the protective antigens they recognize remain largely unknown. Here, we discuss the knowledge gap regarding liver CD8+ Trm cell formation and the potential strategies to identify predominant protective antigens expressed in the exoerythrocytic stage, which is essential for high-efficacy malaria subunit pre-erythrocytic vaccine designation.

"All for One and One for All": The Secreted Heat Shock Protein gp96-Ig Based Vaccines

It has been 50 years since Peter Charles Doherty and Rolf M Zinkernagel proposed the principle of "simultaneous dual recognition", according to which adaptive immune cells recognized "self" and "non-self" simultaneously to establish immunological efficacy. These two scientists shared the 1996 Nobel Prize in Physiology or Medicine for this discovery. Their basic immunological principle became the foundation for the development of numerous vaccine approaches against infectious diseases and tumors, including promising strategies grounded on the use of recombinant gp96-Ig developed by our lab over the last two decades. In this review, we will highlight three major principles of the gp96-Ig vaccine strategy: (1) presentation of pathogenic antigens to T cells (specificity); (2) activation of innate immune responses (adjuvanticity); (3) priming of T cells to home to the epithelial compartments (mucosal immunity). In summary, we provide a paradigm for a vaccine approach that can be rapidly engineered and customized for any future pathogens that require induction of effective tissue-resident memory responses in epithelial tissues.

Tissue-Resident Memory T Cell: Ontogenetic Cellular Mechanism and Clinical Translation

Mounting evidence has indicated the essential role of tissue-resident memory T (TRM) cells for frontline protection against viral infection and for cancer immune surveillance (Mueller SN, Mackay LK. Tissue-resident memory T cells: local specialists in immune defense. Nat Rev Immunol 2016, 16, 79-89. doi:10.1038/nri.2015.3.). TRM cells are transcriptionally, phenotypically, and functionally distinct from circulating memory T (Tcirm) cells. It is necessary to understand the unique ontogenetic mechanism, migratory regulation, and biological function of TRM cells. In this review, we discuss recent insights into cellular mechanisms and discrete responsiveness in different tissue microenvironments underlying TRM cell development. We also emphasize the translational potential of TRM cells by focusing on their establishment in association with improved protection in mucosal tissues against various types of diseases and effective strategies for eliciting TRM cells in both pre-clinical and clinical studies.

Monocyte differentiation within tissues: a renewed outlook

When recruited to mammalian tissues, monocytes differentiate into macrophages or dendritic cells (DCs). In the past few years, the existence of monocyte-derived DCs (moDCs) was questioned by the discovery of new DC populations with overlapping phenotypes. Here, we critically review the evidence for monocyte differentiation into DCs in tissues and highlight their specific functions. Recent studies have shown that monocyte-derived macrophages (moMacs) with distinct life cycles coexist in tissues, both at steady state and upon inflammation. Integrating studies in mice and humans, we highlight specific features of moMacs during inflammation and tissue repair. We also discuss the notion of monocyte differentiation occurring via a binary fate decision. Deciphering monocyte-derived cell properties is essential for understanding their role in nonresolving inflammation and how they might be targeted for therapies.

Inflammation and viral infection as disease modifiers in schizophrenia

Numerous studies have now implicated a role for inflammation in schizophrenia. However, many aspects surrounding this aspect of the disease are still controversial. This controversy has been driven by conflicting evidence on the role of both pro-and anti-inflammatory factors and by often contentious findings concerning cytokine and immune cell profiles in the central nervous system and periphery. Current evidence supports the point that interleukin-6 is elevated in CSF, but does not support activation of microglia, resident macrophage-like cells in the brain. Furthermore, the mechanisms involving transit of the peripheral immune system factors across the blood brain barrier to central parenchyma have still not been completely elucidated. This process appears to involve perivascular macrophages and accompanying dendritic cells retained in the parenchyma by the chemokine and cytokine composition of the surrounding milieu. In addition, a number of studies have shown that this can be modulated by infection with viruses such as herpes simplex virus type I which may disrupt antigen presentation in the perivascular space, with long-lasting consequences. In this review article, we discuss the role of inflammation and viral infection as potential disease modifiers in schizophrenia. The primary viral hit may occur in the fetus in utero, transforming the immune response regulatory T-cells or the virus may secondarily remain latent in immune cells or neurons and modify further immune responses in the developing individual. It is hoped that unraveling this pathway further and solidifying our understanding of the pathophysiological mechanisms involved will pave the way for future studies aimed at identification and implementation of new biomarkers and drug targets. This may facilitate the development of more effective personalized therapies for individuals suffering with schizophrenia.

Gastrointestinal Delivery of an mRNA Vaccine Using Immunostimulatory Polymeric Nanoparticles

mRNA vaccines can be translated into protein antigens, in vivo, to effectively induce humoral and cellular immunity against these proteins. While current mRNA vaccines have generated potent immune responses, the need for ultracold storage conditions (- 80 °C) and healthcare professionals to administer the vaccine through the parenteral route has somewhat limited their distribution in rural areas and developing countries. Overcoming these challenges stands to transform future deployment of mRNA vaccines. In this study, we developed an mRNA vaccine that can trigger a systemic immune response through administration via the gastrointestinal (GI) tract and is stable at 4 °C. A library of cationic branched poly(β-amino ester) (PBAE) polymers was synthesized and characterized, from which a polymer with high intracellular mRNA delivery efficiency and immune stimulation capacity was down-selected. mRNA vaccines made with the lead polymer-elicited cellular and humoral immunity in mice. Furthermore, lyophilization conditions of the formulation were optimized to enable storage under refrigeration. Our results suggest that PBAE nanoparticles are potent mRNA delivery platforms that can elicit B cell and T cell activation, including antigen-specific cellular and humoral responses. This system can serve as an easily administrable, potent oral mRNA vaccine.

Tumor-resident memory T cells as a biomarker of the response to cancer immunotherapy

Tumor-infiltrating lymphocytes (TIL) often include a substantial subset of CD8+ tissue-resident memory T (TRM) cells enriched in tumor-specific T cells. These TRM cells play a major role in antitumor immune response. They are identified on the basis of their expression of the CD103 (αE(CD103)β7) and/or CD49a (α1(CD49a)β1) integrins, and the C-type lectin CD69, which are involved in tissue residency. TRM cells express several T-cell inhibitory receptors on their surface but they nevertheless react strongly to malignant cells, exerting a strong cytotoxic function, particularly in the context of blocking interactions of PD-1 with PD-L1 on target cells. These TRM cells form stable conjugates with autologous tumor cells and interact with dendritic cells and other T cells within the tumor microenvironment to orchestrate an optimal in situ T-cell response. There is growing evidence to indicate that TGF-β is essential for the formation and maintenance of TRM cells in the tumor, through the induction of CD103 expression on activated CD8+ T cells, and for the regulation of TRM effector functions through bidirectional integrin signaling. CD8+ TRM cells were initially described as a prognostic marker for survival in patients with various types of cancer, including ovarian, lung and breast cancers and melanoma. More recently, these tumor-resident CD8+ T cells have been shown to be a potent predictive biomarker of the response of cancer patients to immunotherapies, including therapeutic cancer vaccines and immune checkpoint blockade. In this review, we will highlight the major characteristics of tumor TRM cell populations and the possibilities for their exploitation in the design of more effective immunotherapy strategies for cancer.

Functional heterogeneity of human skin-resident memory T cells in health and disease

The human skin is populated by a diverse pool of memory T cells, which can act rapidly in response to pathogens and cancer antigens. Tissue-resident memory T cells (TRM ) have been implicated in range of allergic, autoimmune and inflammatory skin diseases. Clonal expansion of cells with TRM properties is also known to contribute to cutaneous T-cell lymphoma. Here, we review the heterogeneous phenotypes, transcriptional programs, and effector functions of skin TRM . We summarize recent studies on TRM formation, longevity, plasticity, and retrograde migration and contextualize the findings to skin TRM and their role in maintaining skin homeostasis and altered functions in skin disease.

Advances and challenges in studying the tissue-resident T cell compartment in the human female reproductive tract

Tissue-resident memory T cells (TRM ) are considered to be central to maintaining mucosal barrier immunity and tissue homeostasis. Most of this knowledge stems from murine studies, which provide access to all organs. These studies also allow for a thorough assessment of the TRM compartment for each tissue and across tissues with well-defined experimental and environmental variables. Assessing the functional characteristics of the human TRM compartment is substantially more difficult; thus, notably, there is a paucity of studies profiling the TRM compartment in the human female reproductive tract (FRT). The FRT is a mucosal barrier tissue that is naturally exposed to a wide range of commensal and pathogenic microbes, including several sexually transmitted infections of global health significance. We provide an overview of studies describing T cells within the lower FRT tissues and highlight the challenges of studying TRM cells in the FRT: different sampling methods of the FRT greatly affect immune cell recovery, especially of TRM cells. Furthermore, menstrual cycle, menopause, and pregnancy affect FRT immunity, but little is known about changes in the TRM compartment. Finally, we discuss the potential functional plasticity of the TRM compartment during inflammatory episodes in the human FRT to maintain protection and tissue homeostasis, which are required to ensure reproductive fitness.

Human circulating and tissue-resident memory CD8+ T cells

Our current knowledge of human memory CD8⁺ T cells is derived largely from studies of the intravascular space. However, emerging data are starting to challenge some of the dogmas based on this work, suggesting that a conceptual revision may be necessary. In this review, we provide a brief history of the field and summarize the biology of circulating and tissue-resident memory CD8⁺ T cells, which are ultimately responsible for effective immune surveillance. We also incorporate recent findings into a biologically integrated model of human memory CD8⁺ T cell differentiation. Finally, we address how future innovative human studies could improve our understanding of anatomically localized CD8⁺ T cells to inform the development of more effective immunotherapies and vaccines, the need for which has been emphasized by the global struggle to contain severe acute respiratory syndrome coronavirus 2.

NOD2 in monocytes negatively regulates macrophage development through TNFalpha

Objective

It is believed that intestinal recruitment of monocytes from Crohn's Disease (CD) patients who carry NOD2 risk alleles may repeatedly give rise to recruitment of pathogenic macrophages. We investigated an alternative possibility that NOD2 may rather inhibit their differentiation from intravasating monocytes.

Design

The monocyte fate decision was examined by using germ-free mice, mixed bone marrow chimeras and a culture system yielding macrophages and monocyte-derived dendritic cells (mo-DCs).

Results

We observed a decrease in the frequency of mo-DCs in the colon of Nod2-deficient mice, despite a similar abundance of monocytes. This decrease was independent of the changes in the gut microbiota and dysbiosis caused by Nod2 deficiency. Similarly, the pool of mo-DCs was poorly reconstituted in a Nod2-deficient mixed bone marrow (BM) chimera. The use of pharmacological inhibitors revealed that activation of NOD2 during monocyte-derived cell development, dominantly inhibits mTOR-mediated macrophage differentiation in a TNFα-dependent manner. These observations were supported by the identification of a TNFα-dependent response to muramyl dipeptide (MDP) that is specifically lost when CD14-expressing blood cells bear a frameshift mutation in NOD2.

Conclusion

NOD2 negatively regulates a macrophage developmental program through a feed-forward loop that could be exploited for overcoming resistance to anti-TNF therapy in CD.

Tissue-resident memory CAR T cells with stem-like characteristics display enhanced efficacy against solid and liquid tumors

Chimeric antigen receptor (CAR) T cells demonstrate remarkable success in treating hematological malignancies, but their effectiveness in non-hematopoietic cancers remains limited. This study proposes enhancing CAR T cell function and localization in solid tumors by modifying the epigenome governing tissue-residency adaptation and early memory differentiation. We identify that a key factor in human tissue-resident memory CAR T cell (CAR-TRM) formation is activation in the presence of the pleotropic cytokine, transforming growth factor β (TGF-β), which enforces a core program of both "stemness" and sustained tissue residency by mediating chromatin remodeling and concurrent transcriptional changes. This approach leads to a practical and clinically actionable in vitro production method for engineering peripheral blood T cells into a large number of "stem-like" CAR-TRM cells resistant to tumor-associated dysfunction, possessing an enhanced ability to accumulate in situ and rapidly eliminate cancer cells for more effective immunotherapy.

Tumor eradication by hetIL-15 locoregional therapy correlates with an induced intratumoral CD103intCD11b+ dendritic cell population

Locoregional monotherapy with heterodimeric interleukin (IL)-15 (hetIL-15) in a triple-negative breast cancer (TNBC) orthotopic mouse model resulted in tumor eradication in 40% of treated mice, reduction of metastasis, and induction of immunological memory against breast cancer cells. hetIL-15 re-shaped the tumor microenvironment by promoting the intratumoral accumulation of cytotoxic lymphocytes, conventional type 1 dendritic cells (cDC1s), and a dendritic cell (DC) population expressing both CD103 and CD11b markers. These CD103intCD11b+DCs share phenotypic and gene expression characteristics with both cDC1s and cDC2s, have transcriptomic profiles more similar to monocyte-derived DCs (moDCs), and correlate with tumor regression. Therefore, hetIL-15, a cytokine directly affecting lymphocytes and inducing cytotoxic cells, also has an indirect rapid and significant effect on the recruitment of myeloid cells, initiating a cascade for tumor elimination through innate and adoptive immune mechanisms. The intratumoral CD103intCD11b+DC population induced by hetIL-15 may be targeted for the development of additional cancer immunotherapy approaches.

Photonic Hyperthermia Synergizes with Immune-Activators to Augment Tumor-Localized Immunotherapy

Photothermal immunotherapy, the combination of photothermal hyperthermia and immunotherapy, is a noninvasive and desirable therapeutic strategy to address the deficiency of traditional photothermal ablation for tumor treatment. However, insufficient T-cell activation following photothermal treatment is a bottleneck to achieve satisfactory therapeutic effectiveness. In this work, a multifunctional nanoplatform is rationally designed and engineered on the basis of polypyrrole-based magnetic nanomedicine modified by T-cell activators of anti-CD3 and anti-CD28 monoclonal antibodies, which have achieved robust near infrared laser-triggered photothermal ablation and long-lasting T-cell activation, realizing diagnostic imaging-guided immunosuppressive tumor microenvironment regulation following photothermal hyperthermia by reinvigorating tumor-infiltrating lymphocytes. By virtue of high-efficient immunogenic cell death and dendritic cell maturation combined with T-cell activation, this nanosystem markedly restrains primary and abscopal tumors as well as metastatic tumors with negligible side effects in vivo, exerting the specific function for suppressing tumor recurrence and metastasis by establishing a long-term memory immune response.

Hepatocyte growth factor-mediated apoptosis mechanisms of cytotoxic CD8+ T cells in normal and cirrhotic livers

Intrahepatic stem/progenitor cells and cytotoxic CD8⁺ T cells (CD8⁺ T cells) in the cirrhotic liver undergo apoptosis, which potentially facilitates progression to cancer. Here, we report that hepatocyte growth factor (HGF) signaling plays an important role in promoting normal and damaged liver CD8⁺ T cell Fas-mediated apoptosis through its only receptor, c-Met. In addition to binding with HGF, c-Met also binds to Fas to form a complex. Using a diethylnitrosamine (DEN)-induced liver fibrosis/cirrhosis mouse model, immunostaining, and terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining, we found that HGF secretion was significantly higher at 10 weeks post-DEN, the liver cirrhotic phase (LCP), than at 3 weeks post-DEN, the liver fibrotic phase (LFP). Correspondingly, differences in CD8⁺ T cell proliferation and apoptosis were noted between the two phases. Interestingly, staining and TUNEL assays revealed lower smooth muscle actin (α-SMA)⁺ cell apoptosis, a marker for hepatic stellate cells (HSCs), in the LFP group than in the LCP group, which suggested a beneficial correlation among HGF, CD8⁺ T cells and HSCs in improving the fibrotic load during damaged liver repair. In cultures, when met different concentrations of recombinant HGF (rHGF), phytohemagglutinin (PHA)-stimulated naive mouse splenic CD8⁺ T cells (pn-msCD8⁺ T cells) responded differently; as increases in rHGF increased were associated with decreases in the clonal numbers of pn-msCD8⁺ T cells, and when the rHGF dose was greater than 200 ng/mL, the clonal numbers significantly decreased. In the presence of 400 ng/mL rHGF, the death-inducing signaling complex (DISC) can be directly activated in both nsCD8⁺ T cells and healthy human peripheral blood CD8⁺ T cells (hp-CD8⁺ T cells), as indicated by recruitment of FADD and caspase-8 because DISC forms via the recruitment of FADD and caspase-8, among others. These findings suggest that Fas-mediated apoptosis, may also indicate a regulatory role of HGF signaling in hepatic homeostasis.

Exploring Mast Cell-CD8 T Cell Interactions in Inflammatory Skin Diseases

The skin is exposed to environmental challenges and contains skin-resident immune cells, including mast cells (MCs) and CD8 T cells that act as sentinels for pathogens and environmental antigens. Human skin MCs and their mediators participate in the maintenance of tissue homeostasis and regulate the recruitment and activity of immune cells involved in the pathogenesis of skin diseases. The cutaneous CD8 T cell compartment is comprised of long-persisting resident memory T cells (TRM) and migratory or recirculating cells; both populations provide durable site immune surveillance. Several lines of evidence indicate that MC-derived products, such as CCL5 and TNF-α, modulate the migration and function of CD8 T cells. Conversely, activated CD8 T cells induce the upregulation of MC costimulatory molecules. Moreover, the close apposition of MCs and CD8 T cells has been recently identified in the skin of several dermatoses, such as alopecia areata. This review outlines the current knowledge about bidirectional interactions between human MCs and CD8 T cells, analyses the alteration of their communication in the context of three common skin disorders in which these cells have been found altered in number or function-psoriasis, atopic dermatitis, and vitiligo-and discusses the current unanswered questions.

Oral pretreatment with β-lactoglobulin derived peptide and CpG co-encapsulated in PLGA nanoparticles prior to sensitizations attenuates cow's milk allergy development in mice

Cow's milk allergy is a common food allergy among infants. Improved hygiene conditions and loss of microbial diversity are associated with increased risk of allergy development. The intestinal immune system is essential for oral tolerance induction. In this respect, bacterial CpG DNA is known to drive Th1 and regulatory T-cell (Treg) development via Toll-Like-Receptor 9 (TLR-9) signaling, skewing away from the allergic Th2 phenotype. We aimed to induce allergen specific tolerance via oral delivery of poly (lactic-co-glycolic acid) nanoparticles (NP) co-encapsulated with a selected β-lactoglobulin derived peptide (BLG-Pep) and TLR-9 ligand CpG oligodeoxynucleotide (CpG). In vivo, 3-4-week-old female C3H/HeOuJ mice housed in individually ventilated cages received 6-consecutive-daily gavages of either PBS, whey, BLG-Pep/NP, CpG/NP, a mixture of BLG-Pep/NP plus CpG/NP or co-encapsulated BLG-Pep+CpG/NP, before 5-weekly oral sensitizations with whey plus cholera toxin (CT) or only CT (sham) and were challenged with whey 5 days after the last sensitization. The co-encapsulated BLG-Pep+CpG/NP pretreatment, but not BLG-Pep/NP, CpG/NP or the mixture of BLG-Pep/NP plus CpG/NP, prevented the whey-induced allergic skin reactivity and prevented rise in serum BLG-specific IgE compared to whey-sensitized mice. Importantly, co-encapsulated BLG-Pep+CpG/NP pretreatment reduced dendritic cell (DC) activation and lowered the frequencies of PD-L1+ DC in the mesenteric lymph nodes compared to whey-sensitized mice. By contrast, co-encapsulated BLG-Pep+CpG/NP pretreatment increased the frequency of splenic PD-L1+ DC compared to the BLG-Pep/NP plus CpG/NP recipients, in association with lower Th2 development and increased Treg/Th2 and Th1/Th2 ratios in the spleen. Oral administration of PLGA NP co-encapsulated with BLG-Pep and CpG prevented rise in serum BLG-specific IgE and symptom development while lowering splenic Th2 cell frequency in these mice which were kept under strict hygienic conditions.

Unique properties of tissue-resident memory T cells in the lungs: implications for COVID-19 and other respiratory diseases

Tissue-resident memory T (T_RM) cells were originally identified as a tissue-sequestered population of memory T cells that show lifelong persistence in non-lymphoid organs. That definition has slowly evolved with the documentation of T_RM cells having variable terms of tissue residency combined with a capacity to return to the wider circulation. Nonetheless, reductionist experiments have identified an archetypical population of T_RM cells showing intrinsic permanent residency in a wide range of non-lymphoid organs, with one notable exception: the lungs. Despite the fact that memory T cells generated during a respiratory infection are maintained in the circulation, local T_RM cell numbers in the lung decline concomitantly with a decay in T cell-mediated protection. This Perspective describes the mechanisms that underpin long-term T cell lodgement in non-lymphoid tissues and explains why residency is transient for select T_RM cell subsets. In doing so, it highlights the unusual nature of memory T cell egress from the lungs and speculates on the broader disease implications of this process, especially during infection with SARS-CoV-2.

Cell atlas of the immune microenvironment in gastrointestinal cancers: Dendritic cells and beyond

Gastrointestinal (GI) cancers occur in the alimentary tract and accessory organs. They exert a global burden with high morbidity and mortality. Inside the tumor microenvironment, dendritic cells (DCs) are the most efficient antigen-presenting cells and are necessary for adaptive immune responses such as T and B-cell maturation. However, the subsets of DCs revealed before were mostly based on flow cytometry and bulk sequencing. With the development of single-cell RNA sequencing (scRNA-seq), the tumor and microenvironment heterogeneity of GI cancer has been illustrated. In this review, we summarize the classification and development trajectory of dendritic cells at the single-cell level in GI cancer. Additionally, we focused on the interaction of DCs with T cells and their effect on the response to immunotherapy. Specifically, we focused on the newly identified tumor-infiltrating dendritic cells and discuss their potential function in antitumor immunity.

CD103 fate mapping reveals that intestinal CD103- tissue-resident memory T cells are the primary responders to secondary infection

Tissue-resident memory T (T_RM) cells remain poised in the tissue and mediate robust protection from secondary infection. T_RM cells within the intestine and other tissues are heterogeneous in their phenotype and function; however, the contributions of these T_RM subsets to secondary infection remain poorly defined. To address the plasticity of intestinal T_RM subsets and their role in local and systemic immunity, we generated mice to fate map intestinal CD103⁺ T_RM cells and track their location and function during secondary infection with Yersinia pseudotuberculosis. We found that CD103⁺ T_RM cells remained lodged in the tissue and were poorly reactivated during secondary challenge. CD103^- T_RM cells were the primary responders to secondary infection and expanded within the tissue, with limited contribution from circulating memory T cells. The transcriptional profile of CD103^- T_RM cells demonstrated maintenance of a gene signature similar to circulating T cells along with increased cytokine production and migratory potential. CD103^- T_RM cells also expressed genes associated with T cell receptor (TCR) activation and displayed enhanced TCR-mediated reactivation both in vitro and in vivo compared with their CD103⁺ counterparts. These studies reveal the limited recall potential of CD103⁺ T_RM subsets and the role of CD103^- T_RM cells as central memory-like T cells within peripheral tissues.

Does Aging Activate T-cells to Reduce Bone Mass and Quality?

PURPOSE OF REVIEW

Aging leads to decline in bone mass and quality starting at age 30 in humans. All mammals undergo a basal age-dependent decline in bone mass. Osteoporosis is characterized by low bone mass and changes in bone microarchitecture that increases the risk of fracture. About a third of men over the age of 50 years are osteoporotic because they have higher than basal bone loss. In women, there is an additional acute decrement in bone mass, atop the basal rate, associated with loss of ovarian function (menopause) causing osteoporosis in about half of the women. Both genetics and environmental factors such as smoking, chronic infections, diet, microbiome, and metabolic disease can modulate basal age-dependent bone loss and eventual osteoporosis. Here, we review recent studies on the etiology of age-dependent decline in bone mass and propose a mechanism that integrates both genetic and environmental factors.

RECENT FINDINGS

Recent findings support that aging and menopause dysregulate the immune system leading to sterile low-grade inflammation. Both animal models and human studies demonstrate that certain kinds of inflammation, in both men and women, mediate bone loss. Senolytics, meant to block a wide array of age-induced effects by preventing cellular senescence, have been shown to improve bone mass in aged mice. Based on a synthesis of the recent data, we propose that aging activates long-lived tissue resident memory T-cells to become senescent and proinflammatory, leading to bone loss. Targeting this population may represent a promising osteoporosis therapy. Emerging data indicates that there are several mechanisms that lead to sterile low-grade chronic inflammation, inflammaging, that cause age- and estrogen-loss dependent osteoporosis in men and women.

The role of antiviral CD8+ T cells in cognitive impairment

The impact of the immune system on the etiopathogenesis of neurodegenerative diseases, including Alzheimer's disease, is a rapidly growing area of investigation. Evidence from human patients and animal models implicates neurotropic viral infections, and specifically the antiviral immune response of brain-infiltrating CD8⁺ T cells, as potential drivers of disease pathology. While infiltration and retention of CD8⁺ T cells within the brain following viral infection is associated with improved survival, CD8⁺ T cells also contribute to neuronal death and gliosis which underlie cognitive impairment in several disease models. Here we review the role of antiviral CD8⁺ T cells as potential mediators of cognitive impairment and highlight the mechanisms by which brain-resident CD8⁺ T cells may contribute to neurodegenerative disease pathology.

Tissue-resident memory T cells in the urogenital tract

Our understanding of T cell memory responses changed drastically with the discovery that specialized T cell memory populations reside within peripheral tissues at key pathogen entry sites. These tissue-resident memory T (T_RM) cells can respond promptly to an infection without the need for migration, proliferation or differentiation. This rapid and local deployment of effector functions maximizes the ability of T_RM cells to eliminate pathogens. T_RM cells do not circulate through peripheral tissues but instead form isolated populations in the skin, gut, liver, kidneys, the reproductive tract and other organs. This long-term retention in the periphery might allow T_RM cells to fully adapt to the local conditions of their environment and mount customized responses to counter infection and tumour growth in a tissue-specific manner. In the urogenital tract, T_RM cells must adapt to a unique microenvironment to confer protection against potential threats, including cancer and infection, while preventing the onset of auto-inflammatory disease. In this Review, we discuss insights into the diversification of T_RM cells from other memory T cell lineages, the adaptations of T_RM cells to their local environment, and their enhanced capacity to counter infection and tumour growth compared with other memory T cell populations, especially in the urogenital tract.

Presence of Skin Tissue-Resident Memory T Cells in Human Nonmalignant and Premalignant Melanocytic Skin Lesions and in Melanoma

ABSTRACT

The infiltration of tissue-resident memory (TRM) cells in melanoma correlates with improved survival, suggesting an important role for TRM cells in immunity against melanoma. However, little is known about the presence of TRM cells in nonmalignant and premalignant melanocytic lesions. This study aimed to evaluate the presence of TRM cells in human skin melanocytic lesions, representing the spectrum from healthy skin to metastatic melanoma. FFPE sections from healthy skin, sun-exposed skin, benign nevi, lentigo maligna (LM), primary LM melanoma, and primary cutaneous and metastatic melanoma were analyzed by immunohistochemistry. The number of infiltrating cells expressing TRM-associated markers, CD3, CD4, CD8, CD69, CD103, and CD49a, was quantified by digital analyses. Multiplex immunofluorescence was performed to analyze coexpression of TRM cell markers. More T cells and CD69+ cells were found in melanoma lesions, as compared with healthy skin and nevi. CD103+ and CD49a+ cell numbers did not significantly differ. More importantly, no differences were seen in expression of all markers between healthy skin and benign nevi. Similar results, except for CD69, were observed in LM melanoma, as compared with LM and sun-exposed skin. Interestingly, multiplex immunofluorescence showed that nevi tissues have comparable CD103+ T cell numbers with healthy skin but comprise more CD103+ CD8+ cells. Expression of TRM cell markers is significantly increased in melanoma, as compared with nonmalignant skin. Our data also show that TRM cells are not abundantly present already in premalignant tissues. Further studies on the specificity of TRM cells for melanocyte/melanoma antigens may reveal their significance in cancer immunosurveillance.

Epigenetics of Dendritic Cells in Tumor Immunology

Dendritic cells (DCs) are professional antigen-presenting cells with the distinctive property of inducing the priming and differentiation of naïve CD4+ and CD8+ T cells into helper and cytotoxic effector T cells to develop efficient tumor-immune responses. DCs display pathogenic and tumorigenic antigens on their surface through major histocompatibility complexes to directly influence the differentiation of T cells. Cells in the tumor microenvironment (TME), including cancer cells and other immune-infiltrated cells, can lead DCs to acquire an immune-tolerogenic phenotype that facilitates tumor progression. Epigenetic alterations contribute to cancer development, not only by directly affecting cancer cells, but also by their fundamental role in the differentiation of DCs that acquire a tolerogenic phenotype that, in turn, suppresses T cell-mediated responses. In this review, we focus on the epigenetic regulation of DCs that have infiltrated the TME and discuss how knowledge of the epigenetic control of DCs can be used to improve DC-based vaccines for cancer immunotherapy.

Trained immunity in type 2 immune responses

Immunological memory of innate immune cells, also termed "trained immunity", allows for cross-protection against distinct pathogens, but may also drive chronic inflammation. Recent studies have shown that memory responses associated with type 2 immunity do not solely rely on adaptive immune cells, such as T- and B cells, but also involve the innate immune system and epithelial cells. Memory responses have been described for monocytes, macrophages and airway epithelial cells of asthmatic patients as well as for macrophages and group 2 innate lymphoid cells (ILC2) from allergen-sensitized or helminth-infected mice. The metabolic and epigenetic mechanisms that mediate allergen- or helminth-induced reprogramming of innate immune cells are only beginning to be uncovered. Trained immunity has been implicated in helminth-driven immune regulation and allergen-specific immunotherapy, suggesting its exploitation in future therapies. Here, we discuss recent advances and key remaining questions regarding the mechanisms and functions of trained type 2 immunity in infection and inflammation.

Tissue resident memory T cells in the respiratory tract

Owing to their capacity to rapidly spread across the population, airborne pathogens represent a significant risk to global health. Indeed, several of the past major global pandemics have been instigated by respiratory pathogens. A greater understanding of the immune cells tasked with protecting the airways from infection will allow for the development of strategies that curb the spread and impact of these airborne diseases. A specific subset of memory T-cell resident in both the upper and lower respiratory tract, termed tissue-resident memory (Trm), have been shown to play an instrumental role in local immune responses against a wide breadth of both viral and bacterial infections. In this review, we discuss factors that influence respiratory tract Trm development, longevity, and immune surveillance and explore vaccination regimes that harness these cells, such approaches represent exciting new strategies that may be utilized to tackle the next global pandemic.

Tissue-resident immunity in the female and male reproductive tract

The conception of how the immune system is organized has been significantly challenged over the last years. It became evident that not all lymphocytes are mobile and recirculate through secondary lymphoid organs. Instead, subsets of immune cells continuously reside in tissues until being reactivated, e.g., by a recurring pathogen or other stimuli. Consequently, the concept of tissue-resident immunity has emerged, and substantial evidence is now available to support its pivotal function in maintaining tissue homeostasis, sensing challenges and providing antimicrobial protection. Surprisingly, insights on tissue-resident immunity in the barrier tissues of the female reproductive tract are sparse and only slowly emerging. The need for protection from vaginal and amniotic infections, the uniqueness of periodic tissue shedding and renewal of the endometrial barrier tissue, and the demand for a tailored decidual immune adaptation during pregnancy highlight that tissue-resident immunity may play a crucial role in distinct compartments of the female reproductive tract. This review accentuates the characteristics of tissue-resident immune cells in the vagina, endometrium, and the decidua during pregnancy and discusses their functional role in modulating the risk for infertility, pregnancy complications, infections, or cancer. We here also review data published to date on tissue-resident immunity in the male reproductive organs, which is still a largely uncharted territory.

Current Perspectives on the Immunosuppressive Niche and Role of Fibrosis in Hepatocellular Carcinoma and the Development of Antitumor Immunity

Immune checkpoint inhibitors have become the mainstay of treatment for hepatocellular carcinoma (HCC). However, they are ineffective in some cases. Previous studies have reported that genetic alterations in oncogenic pathways such as Wnt/β-catenin are the important triggers in HCC for primary refractoriness. T-cell exhaustion has been reported in various tumors and is likely to play a prominent role in the emergence of HCC due to chronic inflammation and cirrhosis-associated immune dysfunction. Immunosuppressive cells including regulatory T-cells and tumor-associated macrophages infiltrating the tumor are associated with hyperprogressive disease in the early stages of immune checkpoint inhibitor treatment. In addition, stellate cells and tumor-associated fibroblasts create an abundant desmoplastic environment by producing extracellular matrix. This strongly contributes to epithelial to mesenchymal transition via signaling activities including transforming growth factor beta, Wnt/β-catenin, and Hippo pathway. The abundant desmoplastic environment has been demonstrated in pancreatic ductal adenocarcinoma and cholangiocarcinoma to suppress cytotoxic T-cell infiltration, PD-L1 expression, and neoantigen expression, resulting in a highly immunosuppressive niche. It is possible that a similar immunosuppressive environment is created in HCC with advanced fibrosis in the background liver. Although sufficient understanding is required for the establishment of immune therapies of HCC, further investigations are still required in this field.

Human mucosal tissue-resident memory T cells in health and disease

Memory T cells are fundamental to maintain immune surveillance of the human body. During the past decade, it has become apparent that non-recirculating resident memory T cells (TRMs) form a first line memory response in tissues to tackle re-infections. The fact that TRMs are essential for local immunity highlights the therapeutic potential of targeting this population against tumors and infections. However, similar to other immune subsets, TRMs are heterogenous and may form distinct effector populations with unique functions at diverse tissue sites. Further insight into the mechanisms of how TRM function and respond to pathogens and malignancies at different mucosal sites will help to shape future vaccine and immunotherapeutic approaches. Here, we review the current understanding of TRM function and biology at four major mucosal sites: gastrointestinal tract, lung, head and neck, as well as female reproductive tract. We also summarize our current knowledge of how TRM targets invading pathogens and developing tumor cells at these mucosal sites and contemplate how TRMs may be exploited to protect from infections and cancer.

Staphylococcus aureus specific lung resident memory CD4+ Th1 cells attenuate the severity of influenza virus induced secondary bacterial pneumonia

Staphylococcus aureus is a major cause of severe pulmonary infections. The evolution of multi-drug resistant strains limits antibiotic treatment options. To date, all candidate vaccines tested have failed, highlighting the need for an increased understanding of the immunological requirements for effective S. aureus immunity. Using an S. aureus strain engineered to express a trackable CD4⁺ T cell epitope and a murine model of S. aureus pneumonia, we show strategies that lodge Th1 polarised bacterium specific CD4⁺ tissue resident memory T cells (Trm) in the lung can significantly attenuate the severity of S. aureus pneumonia. This contrasts natural infection of mice that fails to lodge CD4⁺ Trm cells along the respiratory tract or provide protection against re-infection, despite initially generating Th17 bacterium specific CD4⁺ T cell responses. Interestingly, lack of CD4⁺ Trm formation after natural infection in mice appears to be reflected in humans, where the frequency of S. aureus reactive CD4⁺ Trm cells in lung tissue is also low. Our findings reveal the protective capacity of S. aureus specific respiratory tract CD4⁺ Th1 polarised Trm cells and highlight the potential for targeting these cells in vaccines that aim to prevent the development of S. aureus pneumonia.

Transition of lymphocyte subsets in peritoneal dialysis effluent and its relationship to peritoneal damage

Objective: Peritoneal function during peritoneal dialysis (PD) declines over time due to peritoneal inflammation; however, the immunological mechanism has not been fully clarified. Here, we examined changes in each cellular fraction in the peritoneal dialysis effluent by flow cytometry and their relationship to peritoneal damage.

Patients and Methods: We enrolled 23 patients who began PD between 2006 and 2017 and had available datasets of the peritoneal equilibration test and flow cytometric analysis for at least three consecutive visits, with an interval of six months from six months after introducing PD. The levels and changes in each cellular fraction, dialysate/plasma (D/P) creatinine ratio, and the forward scatter (FSC) ratio of mesothelial cells to lymphocytes were compared using a simple linear regression analysis.

Results: Among the examined variables, only the fraction of CD8⁺ T_CM cells during the first observation was significantly correlated with the change rate in the D/P creatinine ratio (β=1.47, P=0.001, adjusted R²=0.379). The CD8⁺ naïve T and CD8⁺ T_CM cell fractions were negatively correlated with the change rate of the D/P creatinine ratio (naïve T cells: β=−0.058, P=0.022, adjusted R²=0.188; T_CM cells: β=−0.096, P=0.046, adjusted R²=0.137). In addition, the change rates of the D/P creatinine ratio tended to be higher, though not significantly (one way ANOVA; P=0.080), in accordance with the increase in the change rate of the CD8⁺ effector memory T cells (T_EM).

Conclusion: The CD8⁺ naïve T and T_CM cells may transition into T_EM cells by repeated exposure to the dialysate over time. The T_EM cells residing in the peritoneum may play a significant role in the progression of peritoneal damage.

TLR or NOD receptor signaling skews monocyte fate decision via distinct mechanisms driven by mTOR and miR-155

Monocytes are rapidly recruited to inflamed tissues where they differentiate into monocyte-derived macrophages (mo-mac) or dendritic cells (mo-DC). At infection sites, monocytes encounter a broad range of microbial motifs. How pathogen recognition impacts monocyte fate decision is unclear. Here, we show, using an in vitro model allowing the simultaneous differentiation of human mo-mac and mo-DC, that viruses promote mo-mac while Mycobacteria favor mo-DC differentiation. Mechanistically, we found that pathogen sensing through toll-like receptor (TLR) ligands increases mo-mac differentiation via mTORC1. By contrast, nucleotide-binding oligomerization domain (NOD) ligands favor mo-DC through the induction of TNF-α secretion and miR-155 expression. We confirmed these results in vivo, in mouse skin and by analyzing transcriptomic data from human individuals. Overall, our findings allow a better understanding of the molecular control of monocyte differentiation and of monocyte plasticity upon pathogen sensing.

Pathogenesis and virulence of herpes simplex virus

Two of the most prevalent human viruses worldwide, herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2, respectively), cause a variety of diseases, including cold sores, genital herpes, herpes stromal keratitis, meningitis and encephalitis. The intrinsic, innate and adaptive immune responses are key to control HSV, and the virus has developed mechanisms to evade them. The immune response can also contribute to pathogenesis, as observed in stromal keratitis and encephalitis. The fact that certain individuals are more prone than others to suffer severe disease upon HSV infection can be partially explained by the existence of genetic polymorphisms in humans. Like all herpesviruses, HSV has two replication cycles: lytic and latent. During lytic replication HSV produces infectious viral particles to infect other cells and organisms, while during latency there is limited gene expression and lack of infectious virus particles. HSV establishes latency in neurons and can cause disease both during primary infection and upon reactivation. The mechanisms leading to latency and reactivation and which are the viral and host factors controlling these processes are not completely understood. Here we review the HSV life cycle, the interaction of HSV with the immune system and three of the best-studied pathologies: Herpes stromal keratitis, herpes simplex encephalitis and genital herpes. We also discuss the potential association between HSV-1 infection and Alzheimer's disease.

Local Immune Control of Latent Herpes Simplex Virus Type 1 in Ganglia of Mice and Man

Herpes simplex virus type 1 (HSV-1) is a prevalent human pathogen. HSV-1 genomes persist in trigeminal ganglia neuronal nuclei as chromatinized episomes, while epithelial cells are typically killed by lytic infection. Fluctuations in anti-viral responses, broadly defined, may underlay periodic reactivations. The ganglionic immune response to HSV-1 infection includes cell-intrinsic responses in neurons, innate sensing by several cell types, and the infiltration and persistence of antigen-specific T-cells. The mechanisms specifying the contrasting fates of HSV-1 in neurons and epithelial cells may include differential genome silencing and chromatinization, dictated by variation in access of immune modulating viral tegument proteins to the cell body, and protection of neurons by autophagy. Innate responses have the capacity of recruiting additional immune cells and paracrine activity on parenchymal cells, for example via chemokines and type I interferons. In both mice and humans, HSV-1-specific CD8 and CD4 T-cells are recruited to ganglia, with mechanistic studies suggesting active roles in immune surveillance and control of reactivation. In this review we focus mainly on HSV-1 and the TG, comparing and contrasting where possible observational, interventional, and in vitro studies between humans and animal hosts.

Memory CD8+ T cells mediate early pathogen-specific protection via localized delivery of chemokines and IFNγ to clusters of monocytes

While cognate antigen drives clonal expansion of memory CD8+ T (CD8+ TM) cells to achieve sterilizing immunity in immunized hosts, not much is known on how cognate antigen contributes to early protection before clonal expansion occurs. Here, using distinct models of immunization, we establish that cognate antigen recognition by CD8+ TM cells on dendritic cells initiates their rapid and coordinated production of a burst of CCL3, CCL4, and XCL1 chemokines under the transcriptional control of interferon (IFN) regulatory factor 4. Using intravital microscopy imaging, we reveal that CD8+ TM cells undergo antigen-dependent arrest in splenic red pulp clusters of CCR2+Ly6C+ monocytes to which they deliver IFNγ and chemokines. IFNγ enables chemokine-induced microbicidal activities in monocytes for protection. Thus, rapid and effective CD8+ TM cell responses require spatially and temporally coordinated events that quickly restrict microbial pathogen growth through the local delivery of activating chemokines to CCR2+Ly6C+ monocytes.

Age-related effects on thymic output and homeostatic T cell expansion following depletional induction in renal transplant recipients

Thymic output and homeostatic mature cell proliferation both influence T cell repopulation following depletional induction, though the relative contribution of each and their association with recipient age have not been well studied. We investigated the repopulating T cell kinetics in kidney transplant recipients who underwent alemtuzumab induction followed by belatacept/rapamycin-based immunosuppression over 36-month posttransplantation. We focused specifically on the correlation between repopulating T cell subsets and the age of patients. Substantial homeostatic Ki67-expressing T cell proliferation was seen posttransplantation. A repertoire enriched for naïve T (T_Naïve ) cells emerged posttransplantation. Analysis by generalized estimating equation linear models revealed a strong negative linear association between reconstituting T_Naïve cells and advancing age. A relationship between age and persistence of effector memory cells was shown. We assessed thymic output and found an increase in the frequency of recent thymic emigrants (RTEs, CD4⁺ CD31⁺ ) at 12-month posttransplantation. Patients under 30 years of age showed significantly higher levels of CD4⁺ CD31⁺ cells than patients over 55 years of age pre- and posttransplantation. IL-7 and autologous mature dendritic cells (mDCs) induced CD57^- cell proliferation. In contrast, mDCs, but not IL-7, induced CD57⁺ cell proliferation. This study establishes the relationship between age and thymic output during T cell homeostatic repopulation after alemtuzumab induction. Trial Registration: ClinicalTrials.gov - NCT00565773.

The Potential of Tissue-Resident Memory T Cells for Adoptive Immunotherapy against Cancer

Tissue-resident memory T cells (T_RM) comprise an important memory T cell subset that mediates local protection upon pathogen re-encounter. T_RM populations preferentially localize at entry sites of pathogens, including epithelia of the skin, lungs and intestine, but have also been observed in secondary lymphoid tissue, brain, liver and kidney. More recently, memory T cells characterized as T_RM have also been identified in tumors, including but not limited to melanoma, lung carcinoma, cervical carcinoma, gastric carcinoma and ovarian carcinoma. The presence of these memory T cells has been strongly associated with favorable clinical outcomes, which has generated an interest in targeting T_RM cells to improve immunotherapy of cancer patients. Nevertheless, intratumoral T_RM have also been found to express checkpoint inhibitory receptors, such as PD-1 and LAG-3. Triggering of such inhibitory receptors could induce dysfunction, often referred to as exhaustion, which may limit the effectiveness of T_RM in countering tumor growth. A better understanding of the differentiation and function of T_RM in tumor settings is crucial to deploy these memory T cells in future treatment options of cancer patients. The purpose of this review is to provide the current status of an important cancer immunotherapy known as TIL therapy, insight into the role of T_RM in the context of antitumor immunity, and the challenges and opportunities to exploit these cells for TIL therapy to ultimately improve cancer treatment.

Time-Dependent Serial Changes of Antigen-Presenting Cell Subsets in the Ocular Surface Are Distinct between Corneal Sterile Inflammation and Allosensitization in a Murine Model

The kinetics of antigen-presenting cells (APCs) vary depending on their resident tissues and the manner of immunization. We investigated the long-term changes in mature APC and T-cell subsets over 4 weeks in the ocular surface in murine models of corneal quiescent or potent sterile inflammation, and allosensitization using partial (PT), syngeneic (Syn), and allogeneic (Allo) corneal transplantation. In PT, CD11b^intCD11c^hiMHCII^hiCD86^hi cells increased until 4 weeks with an increase in IFNγ^hi T cells. In Syn, both CD11b^intCD11c^hiMHCII^hiCD86^hi and CD11b^hiCD11c^hiMHCII^hiCD86^hi APC subsets increased until 4 weeks with a brief increase in CD69^hi T cells at 2 weeks. In Allo, CD11b^intCD11c^hiMHCII^hiCD86^hi and CD11b^hiCD11c^hiMHCII^hiCD86^hi APC subsets increased until 4 weeks, and an early increase in CD69^hi T cells was observed at 2 weeks followed by a late increase in IFNγ^hi T cells at 4 weeks. The frequency of the IFNγ^hi T cell subset was positively correlated with the frequency of the CD11b^intCD11c^hiMHCII^hiCD86^hi subset, indicating the existence of APC–T cell interaction in the ocular surface. Together, the results indicate that allosensitization in mature APCs leads to T-cell activation in the ocular surface, whereas sterile inflammation merely induces a brief and non-specific T-cell activation in the ocular surface.

Skin-Resident Memory T Cells: Pathogenesis and Implication for the Treatment of Psoriasis

Tissue-resident memory T cells (T_RM) stay in the peripheral tissues for long periods of time, do not recirculate, and provide the first line of adaptive immune response in the residing tissues. Although T_RM originate from circulating T cells, T_RM are physiologically distinct from circulating T cells with the expression of tissue-residency markers, such as CD69 and CD103, and the characteristic profile of transcription factors. Besides defense against pathogens, the functional skew of skin T_RM is indicated in chronic skin inflammatory diseases. In psoriasis, IL-17A-producing CD8⁺ T_RM are regarded as one of the pathogenic populations in skin. Although no licensed drugs that directly and specifically inhibit the activity of skin T_RM are available to date, psoriatic skin T_RM are affected in the current treatments of psoriasis. Targeting skin T_RM or using T_RM as a potential index for disease severity can be an attractive strategy in psoriasis.

CD8+ tissue-resident memory T cells promote liver fibrosis resolution by inducing apoptosis of hepatic stellate cells

Non-alcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease that can progress to liver fibrosis. Recent clinical advance suggests a reversibility of liver fibrosis, but the cellular and molecular mechanisms underlying NASH resolution remain unclarified. Here, using a murine diet-induced NASH and the subsequent resolution model, we demonstrate direct roles of CD8⁺ tissue-resident memory CD8⁺ T (CD8⁺ Trm) cells in resolving liver fibrosis. Single-cell transcriptome analysis and FACS analysis revealed CD69⁺CD103⁻CD8⁺ Trm cell enrichment in NASH resolution livers. The reduction of liver CD8⁺ Trm cells, maintained by tissue IL-15, significantly delayed fibrosis resolution, while adoptive transfer of these cells protected mice from fibrosis progression. During resolution, CD8⁺ Trm cells attracted hepatic stellate cells (HSCs) in a CCR5-dependent manner, and predisposed activated HSCs to FasL-Fas-mediated apoptosis. Histological assessment of patients with NASH revealed CD69⁺CD8⁺ Trm abundance in fibrotic areas, further supporting their roles in humans. These results highlight the undefined role of liver CD8⁺ Trm in fibrosis resolution.

The cellular and molecular mechanisms underlying the resolution of non-alcoholic steatohepatitis remain incompletely understood. Here the authors report a single cell-based analysis that identified CD8 + tissue-resident memory T cells, which contribute to resolution of liver fibrosis potentially via elimination of hepatic stellate cells through Fas-mediated cytotoxicity.

CCR2 Regulates Vaccine-Induced Mucosal T-Cell Memory to Influenza A Virus

Elicitation of lung tissue-resident memory CD8 T cells (T_RMs) is a goal of T cell-based vaccines against respiratory viral pathogens, such as influenza A virus (IAV). C-C chemokine receptor type 2 (CCR2)-dependent monocyte trafficking plays an essential role in the establishment of CD8 T_RMs in lungs of IAV-infected mice. Here, we used a combination adjuvant-based subunit vaccine strategy that evokes multifaceted (T_C1/T_C17/T_H1/T_H17) IAV nucleoprotein-specific lung T_RMs to determine whether CCR2 and monocyte infiltration are essential for vaccine-induced T_RM development and protective immunity to IAV in lungs. Following intranasal vaccination, neutrophils, monocytes, conventional dendritic cells (DCs), and monocyte-derived dendritic cells internalized and processed vaccine antigen in lungs. We found that basic leucine zipper ATF-like transcription factor 3 (BATF3)-dependent DCs were essential for eliciting T cell responses, but CCR2 deficiency enhanced the differentiation of CD127^hi, KLRG-1^lo, OX40^+ve CD62L^+ve, and mucosally imprinted CD69^+ve CD103^+ve effector and memory CD8 T cells in lungs and airways of vaccinated mice. Mechanistically, increased development of lung T_RMs induced by CCR2 deficiency was linked to dampened expression of T-bet but not altered TCF-1 levels or T cell receptor signaling in CD8 T cells. T1/T17 functional programming, parenchymal localization of CD8/CD4 effector and memory T cells, recall T cell responses, and protective immunity to a lethal IAV infection were unaffected in CCR2-deficient mice. Taken together, we identified a negative regulatory role for CCR2 and monocyte trafficking in mucosal imprinting and differentiation of vaccine-induced T_RMs. Mechanistic insights from this study may aid the development of T-cell-based vaccines against respiratory viral pathogens, including IAV and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). IMPORTANCE While antibody-based immunity to influenza A virus (IAV) is type and subtype specific, lung- and airway-resident memory T cells that recognize conserved epitopes in the internal viral proteins are known to provide heterosubtypic immunity. Hence, broadly protective IAV vaccines need to elicit robust T cell memory in the respiratory tract. We have developed a combination adjuvant-based IAV nucleoprotein vaccine that elicits strong CD4 and CD8 T cell memory in lungs and protects against H1N1 and H5N1 strains of IAV. In this study, we examined the mechanisms that control vaccine-induced protective memory T cells in the respiratory tract. We found that trafficking of monocytes into lungs might limit the development of antiviral lung-resident memory T cells following intranasal vaccination. These findings suggest that strategies that limit monocyte infiltration can potentiate vaccine-induced frontline T-cell immunity to respiratory viruses, such as IAV and SARS-CoV-2.

The human memory T cell compartment changes across tissues of the female reproductive tract

Memory CD4 T cells in tissues fulfill numerous functions that are critical for local immune homeostasis and protection against pathogens. Previous studies have highlighted the phenotypic and functional heterogeneity of circulating and tissue-resident memory CD4 T cells across different human tissues such as skin, lung, liver, and colon. Comparatively little is known in regard to memory CD4 T cells across tissues of the female reproductive tract (FRT). We examined CD4 T cells in donor-matched vaginal, ecto- and endocervical tissues, which differ in mucosal structure and exposure to external environmental stimuli. We hypothesized that this could be reflected by tissue-specific differences in the memory CD4 T cell compartment. We found differences in CD4 subset distribution across these tissues. Specifically, CD69⁺CD103⁺ CD4 T cells were significantly more abundant in vaginal than cervical tissues. In contrast, the transcriptional profiles of CD4 subsets were fairly conserved across FRT tissues. CD69⁺CD103⁺ CD4 T cells showed a T_H17 bias independent of tissue niche. Our data suggest that FRT tissues affect T cell subset distribution but have limited effects on the transcriptome of each subset. We discuss the implications for barrier immunity in the FRT.

Local memory CD4 T cell niches in respiratory viral infection

Respiratory viral infections present a major threat to global health and prosperity. Over the past century, several have developed into crippling pandemics, including the SARS-CoV-2 virus. Although the generation of neutralizing serum antibodies in response to natural immunity and vaccination are considered to be hallmarks of viral immune protection, antibodies from long-lived plasma cells are subject to immune escape from heterologous clades of zoonotic, recombined, or mutated viruses. Local immunity in the lung can be generated through resident memory immune subsets that rapidly respond to secondary infection and protect from heterologous infection. Although many immune cells are required to achieve the phenomenon of resident memory, herein we highlight the pleiotropic functions of CD4 tissue resident memory T cells in the lung and discuss the implications of resident memory for vaccine design.

The Crosstalk Between Dendritic Cells, Cytokine-Induced Killer Cells And Cancer Cells From The Perspective Of Combination Therapy

Dendritic cells (DCs) are considered the most potent professional antigen-presenting cells (APCs) that elicit adaptive antitumour immunity. DCs integrate multiple environmental signals by efficiently processing tumour-associated antigens (TAAs) and migrating to draining lymph nodes (dLNs), where they present foreign antigens to T cells for priming. DCs thus serve as a major link between innate and adaptive immunity. Although DCs (mostly monocyte-derived DCs [mo-DCs]) have already been used in cancer therapies, such approaches have shown limited efficacy. Mo-DCs have the unique ability to present antigens to T cells in peripheral tissues. CD3+CD56+ cytokine-induced killer (CIK) cells are characterized by both MHC-restricted and MHC-unrestricted antitumour cytotoxicity against a broad range of cancer cells. This review presents an overview of the mechanisms by which mo-DCs and CIK cells’ interact with each other and with tumours. The maturation of DCs was identified as a crucial step in the development of effective DC-based vaccines against cancer. A further improved adoptive immunotherapy strategy involves a combination of mature mo-DCs and CIK cells. Combination therapy presents many opportunities for cancer treatment, as reported by a number of clinical trials. However, there is a lack of fundamental studies on the interaction of in vitro-generated mo-DCs with CIK cells. We discuss several methods of boosting DC-based vaccines and review the current knowledge of contact-dependent and cytokine-induced interactions of mo-DCs with CIK cells. We highlight that the combination of mo-DCs with CIK cells activates MHC-restricted and MHC-unrestricted immune responses.