T cell memory. Skin-resident memory CD8⁺ T cells trigger a state of tissue-wide pathogen alert

Selective Janus kinase 1 inhibition resolves inflammation and restores hair growth offering a viable treatment option for alopecia areata

Background

Janus Kinase (JAK) inhibition has recently demonstrated therapeutic efficacy in both restoring hair growth and resolving inflammation in Alopecia Areata (AA). These effects are dose dependent and mainly efficacious at ranges close to a questionable risk profile.

Objectives

We explored the possibility to separate the beneficial and adverse effects of JAK inhibition by selectively inhibiting JAK1 and thereby avoiding side effects associated with JAK2 blockade.

Methods

The C3H/HeJ mouse model of AA was used to demonstrate therapeutic efficacy in vivo with different regimens of a selection of JAK inhibitors in regards to systemic versus local drug exposure. Human peripheral blood lymphocytes were stimulated in vitro to demonstrate translation to the human situation.

Results

We demonstrate that selective inhibition of JAK1 produces fast resolution of inflammation and complete restoration of hair growth in the C3H/HeJ mouse model of AA. Furthermore, we show that topical treatment does not restore hair growth and that treatment needs to be extended well beyond that of restored hair growth in order to reach treatment-free remission. For translatability to human disease, we show that cytokines involved in AA pathogenesis are similarly inhibited by selective JAK1 and pan-JAK inhibition in stimulated human peripheral lymphocytes and specifically in CD8+ T cells.

Conclusion

This study demonstrates that systemic exposure is required for efficacy in AA and we propose that a selective JAK1 inhibitor will offer a treatment option with a superior safety profile to pan-JAK inhibitors for these patients.

High Frequencies of Antiviral Effector Memory TEM Cells and Memory B Cells Mobilized into Herpes Infected Vaginal Mucosa Associated With Protection Against Genital Herpes

Vaginal mucosa-resident anti-viral effector memory B- and T cells appeared to play a crucial role in protection against genital herpes. However, how to mobilize such protective immune cells into the vaginal tissue close to infected epithelial cells remains to be determined. In the present study, we investigate whether and how, CCL28, a major mucosal-associated chemokine, mobilizes effector memory B- and T cells in leading to protecting mucosal surfaces from herpes infection and disease. The CCL28 is a chemoattractant for the CCR10 receptor-expressing immune cells and is produced homeostatically in the human vaginal mucosa (VM). We found the presence of significant frequencies of HSV-specific memory CCR10+CD44+CD8+ T cells, expressing high levels of CCR10 receptor, in herpes-infected asymptomatic (ASYMP) women compared to symptomatic (SYMP) women. A significant amount of the CCL28 chemokine (a ligand of CCR10), was detected in the VM of herpes-infected ASYMP B6 mice, associated with the mobilization of high frequencies of HSV-specific effector memory CCR10+CD44+ CD62L- CD8+ TEM cells and memory CCR10+B220+CD27+ B cells in the VM of HSV-infected asymptomatic mice. In contrast, compared to wild-type (WT) B6 mice, the CCL28 knockout (CCL28(-/-)) mice: (i) Appeared more susceptible to intravaginal infection and re-infection with HSV-2; (ii) Exhibited a significant decrease in the frequencies of HSV-specific effector memory CCR10+CD44+ CD62L- CD8+ TEM cells and of memory CD27+B220+ B cells in the infected VM. The results imply a critical role of the CCL28/CCR10 chemokine axis in the mobilization of anti-viral memory B and T cells within the VM to protect against genital herpes infection and disease.

Memory T cells possess an innate-like function in local protection from mucosal infection

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

Early immune pressure initiated by tissue-resident memory T cells sculpts tumor evolution in non-small cell lung cancer

Tissue-resident memory T (TRM) cells provide immune defense against local infection and can inhibit cancer progression. However, it is unclear to what extent chronic inflammation impacts TRM activation and whether TRM cells existing in tissues before tumor onset influence cancer evolution in humans. We performed deep profiling of healthy lungs and lung cancers in never-smokers (NSs) and ever-smokers (ESs), finding evidence of enhanced immunosurveillance by cells with a TRM-like phenotype in ES lungs. In preclinical models, tumor-specific or bystander TRM-like cells present prior to tumor onset boosted immune cell recruitment, causing tumor immune evasion through loss of MHC class I protein expression and resistance to immune checkpoint inhibitors. In humans, only tumors arising in ES patients underwent clonal immune evasion, unrelated to tobacco-associated mutagenic signatures or oncogenic drivers. These data demonstrate that enhanced TRM-like activity prior to tumor development shapes the evolution of tumor immunogenicity and can impact immunotherapy outcomes.

Retinoic acid signaling during priming licenses intestinal CD103+ CD8 TRM cell differentiation

CD8 tissue-resident memory T (TRM) cells provide frontline protection at barrier tissues; however, mechanisms regulating TRM cell development are not completely understood. Priming dictates the migration of effector T cells to the tissue, while factors in the tissue induce in situ TRM cell differentiation. Whether priming also regulates in situ TRM cell differentiation uncoupled from migration is unclear. Here, we demonstrate that T cell priming in the mesenteric lymph nodes (MLN) regulates CD103+ TRM cell differentiation in the intestine. In contrast, T cells primed in the spleen were impaired in the ability to differentiate into CD103+ TRM cells after entry into the intestine. MLN priming initiated a CD103+ TRM cell gene signature and licensed rapid CD103+ TRM cell differentiation in response to factors in the intestine. Licensing was regulated by retinoic acid signaling and primarily driven by factors other than CCR9 expression and CCR9-mediated gut homing. Thus, the MLN is specialized to promote intestinal CD103+ CD8 TRM cell development by licensing in situ differentiation.

Bcl11b sustains multipotency and restricts effector programs of intestinal-resident memory CD8+ T cells

The networks of transcription factors (TFs) that control intestinal-resident memory CD8⁺ T (T_RM) cells, including multipotency and effector programs, are poorly understood. In this work, we investigated the role of the TF Bcl11b in T_RM cells during infection with Listeria monocytogenes using mice with post-activation, conditional deletion of Bcl11b in CD8⁺ T cells. Conditional deletion of Bcl11b resulted in increased numbers of intestinal T_RM cells and their precursors as well as decreased splenic effector and circulating memory cells and precursors. Loss of circulating memory cells was in part due to increased intestinal homing of Bcl11b^-/- circulating precursors, with no major alterations in their programs. Bcl11b^-/- T_RM cells had altered transcriptional programs, with diminished expression of multipotent/multifunctional (MP/MF) program genes, including Tcf7, and up-regulation of the effector program genes, including Prdm1. Bcl11b also limits the expression of Ahr, another TF with a role in intestinal CD8⁺ T_RM cell differentiation. Deregulation of T_RM programs translated into a poor recall response despite T_RM cell accumulation in the intestine. Reduced expression of MP/MF program genes in Bcl11b^-/- T_RM cells was linked to decreased chromatin accessibility and a reduction in activating histone marks at these loci. In contrast, the effector program genes displayed increased activating epigenetic status. These findings demonstrate that Bcl11b is a frontrunner in the tissue residency program of intestinal memory cells upstream of Tcf1 and Blimp1, promoting multipotency and restricting the effector program.

Tissue-resident memory T cell maintenance during antigen persistence requires both cognate antigen and interleukin-15

Our understanding of tissue-resident memory T (TRM) cell biology has been largely developed from acute infection models in which antigen is cleared and sterilizing immunity is achieved. Less is known about TRM cells in the context of chronic antigen persistence and inflammation. We investigated factors that underlie TRM maintenance in a kidney transplantation model in which TRM cells drive rejection. In contrast to acute infection, we found that TRM cells declined markedly in the absence of cognate antigen, antigen presentation, or antigen sensing by the T cells. Depletion of graft-infiltrating dendritic cells or interruption of antigen presentation after TRM cells were established was sufficient to disrupt TRM maintenance and reduce allograft pathology. Likewise, removal of IL-15 transpresentation or of the IL-15 receptor on T cells during TRM maintenance led to a decline in TRM cells, and IL-15 receptor blockade prevented chronic rejection. Therefore, antigen and IL-15 presented by dendritic cells play nonredundant key roles in CD8 TRM cell maintenance in settings of antigen persistence and inflammation. These findings provide insights that could lead to improved treatment of chronic transplant rejection and autoimmunity.

Cutting Edge: Influenza-Induced CD11alo Airway CD103+ Tissue Resident Memory T Cells Exhibit Compromised IFN-γ Production after In Vivo TCR Stimulation

Although tissue resident memory T cells (TRM) in the lung confer robust protection against secondary influenza infection, their in vivo production of IFN-γ is unknown. In this study, using a mouse model, we evaluated production of IFN-γ by influenza-induced TRM (defined as CD103+) that localize to the airways or lung parenchyma. Airway TRM consist of both CD11ahi and CD11alo populations, with low CD11a expression signifying prolonged airway residence. In vitro, high-dose peptide stimulation evoked IFN-γ from most CD11ahi airway and parenchymal TRM, whereas most CD11alo airway TRM did not produce IFN-γ. In vivo production of IFN-γ was clearly detectable in CD11ahi airway and parenchymal TRM but essentially absent in CD11alo airway TRM, irrespective of airway-instilled peptide concentration or influenza reinfection. The majority of IFN-γ-producing airway TRM in vivo were CD11ahi, suggesting recent airway entry. These results question the contribution of long-term CD11alo airway TRM to influenza immunity and reinforce the importance of defining TRM tissue compartment-specific contributions to protective immunity.

Intratumor childhood vaccine-specific CD4+ T-cell recall coordinates antitumor CD8+ T cells and eosinophils

BACKGROUND

Antitumor mechanisms of CD4⁺ T cells remain crudely defined, and means to effectively harness CD4⁺ T-cell help for cancer immunotherapy are lacking. Pre-existing memory CD4⁺ T cells hold potential to be leveraged for this purpose. Moreover, the role of pre-existing immunity in virotherapy, particularly recombinant poliovirus immunotherapy where childhood polio vaccine specific immunity is ubiquitous, remains unclear. Here we tested the hypothesis that childhood vaccine-specific memory T cells mediate antitumor immunotherapy and contribute to the antitumor efficacy of polio virotherapy.

METHODS

The impact of polio immunization on polio virotherapy, and the antitumor effects of polio and tetanus recall were tested in syngeneic murine melanoma and breast cancer models. CD8⁺ T-cell and B-cell knockout, CD4⁺ T-cell depletion, CD4⁺ T-cell adoptive transfer, CD40L blockade, assessments of antitumor T-cell immunity, and eosinophil depletion defined antitumor mechanisms of recall antigens. Pan-cancer transcriptome data sets and polio virotherapy clinical trial correlates were used to assess the relevance of these findings in humans.

RESULTS

Prior vaccination against poliovirus substantially bolstered the antitumor efficacy of polio virotherapy in mice, and intratumor recall of poliovirus or tetanus immunity delayed tumor growth. Intratumor recall antigens augmented antitumor T-cell function, caused marked tumor infiltration of type 2 innate lymphoid cells and eosinophils, and decreased proportions of regulatory T cells (Tregs). Antitumor effects of recall antigens were mediated by CD4⁺ T cells, limited by B cells, independent of CD40L, and dependent on eosinophils and CD8⁺ T cells. An inverse relationship between eosinophil and Treg signatures was observed across The Cancer Genome Atlas (TCGA) cancer types, and eosinophil depletion prevented Treg reductions after polio recall. Pretreatment polio neutralizing antibody titers were higher in patients living longer, and eosinophil levels increased in the majority of patients, after polio virotherapy.

CONCLUSION

Pre-existing anti-polio immunity contributes to the antitumor efficacy of polio virotherapy. This work defines cancer immunotherapy potential of childhood vaccines, reveals their utility to engage CD4⁺ T-cell help for antitumor CD8⁺ T cells, and implicates eosinophils as antitumor effectors of CD4⁺ T cells.

Mycobacterium bovis BCG Given at Birth Followed by Inactivated Respiratory Syncytial Virus Vaccine Prevents Vaccine-Enhanced Disease by Promoting Trained Macrophages and Resident Memory T Cells

Respiratory syncytial virus (RSV) infects more than 60% of infants in their first year of life. Since an experimental formalin-inactivated (FI) RSV vaccine tested in the 1960s caused enhanced respiratory disease (ERD), few attempts have been made to vaccinate infants. ERD is characterized by Th2-biased responses, lung inflammation, and poor protective immune memory. Innate immune memory displays an increased nonspecific effector function upon restimulation, a process called trained immunity, or a repressed effector function upon restimulation, a process called tolerance, which participates in host defense and inflammatory disease. Mycobacterium bovis bacillus Calmette-Guérin (BCG) given at birth can induce trained immunity as well as heterologous Th1 responses. We speculate that BCG given at birth followed by FI-RSV may alleviate ERD and enhance protection through promoting trained immunity and balanced Th immune memory. Neonatal mice were given BCG at birth and then vaccinated with FI-RSV+Al(OH)3. BCG/FI-RSV+Al(OH)3 induced trained macrophages, tissue-resident memory T cells (TRM), and specific cytotoxic T lymphocytes (CTL) in lungs and inhibited Th2 and Th17 cell immune memory, all of which contributed to inhibition of ERD and increased protection. Notably, FI-RSV+Al(OH)3 induced tolerant macrophages, while BCG/FI-RSV+Al(OH)3 prevented the innate tolerance through promoting trained macrophages. Moreover, inhibition of ERD was attributed to trained macrophages or TRM in lungs but not memory T cells in spleens. Therefore, BCG given at birth to regulate trained immunity and TRM may be a new strategy for developing safe and effective RSV killed vaccines for young infants. IMPORTANCE RSV is the leading cause of severe lower respiratory tract infection of infants. ERD, characterized by Th2-biased responses, inflammation, and poor immune memory, has been an obstacle to the development of safe and effective killed RSV vaccines. Innate immune memory participates in host defense and inflammatory disease. BCG given at birth can induce trained immunity as well as heterologous Th1 responses. Our results showed that BCG/FI-RSV+Al(OH)3 induced trained macrophages, TRM, specific CTL, and balanced Th cell immune memory, which contributed to inhibition of ERD and increased protection. Notably, FI-RSV+Al(OH)3 induced tolerant macrophages, while BCG/FI-RSV+Al(OH)3 prevented tolerance through promoting trained macrophages. Moreover, inhibition of ERD was attributed to trained macrophages or TRM in lungs but not memory T cells in spleens. BCG at birth as an adjuvant to regulate trained immunity and TRM may be a new strategy for developing safe and effective RSV killed vaccines for young infants.

Cancer-specific tissue-resident memory T-cells express ZNF683 in colorectal cancer

BACKGROUND

Tissue-resident memory T (Trm) cells are associated with cytotoxicity not only in viral infection and autoimmune disease pathologies but also in many cancers. Tumour-infiltrating CD103⁺ Trm cells predominantly comprise CD8 T cells that express cytotoxic activation and immune checkpoint molecules called exhausted markers. This study aimed to investigate the role of Trm in colorectal cancer (CRC) and characterise the cancer-specific Trm.

METHODS

Immunochemical staining with anti-CD8 and anti-CD103 antibodies for resected CRC tissues was used to identify the tumour-infiltrating Trm cells. The Kaplan-Meier estimator was used to evaluate the prognostic significance. Cells immune to CRC were targeted for single-cell RNA-seq analysis to characterise cancer-specific Trm cells in CRC.

RESULTS

The number of CD103⁺/CD8⁺ tumour-infiltrating lymphocytes (TILs) was a favourable prognostic and predictive factor of the overall survival and recurrence-free survival in patients with CRC. Single-cell RNA-seq analysis of 17,257 CRC-infiltrating immune cells revealed a more increased zinc finger protein 683 (ZNF683) expression in cancer Trm cells than in noncancer Trm cells and in high-infiltrating Trm cells than low-infiltrating Trm in cancer, with an upregulated T-cell receptor (TCR)- and interferon-γ (IFN-γ) signalling-related gene expression in ZNF683⁺ Trm cells.

CONCLUSIONS

The number of CD103⁺/CD8⁺ TILs is a prognostic predictive factor in CRC. In addition, we identified the ZNF683 expression as one of the candidate markers of cancer-specific Trm cells. IFN-γ and TCR signalling and ZNF683 expression are involved in Trm cell activation in tumours and are promising targets for cancer immunity regulation.

Tissue-resident, memory CD8+ T cells are effective in clearing intestinal Eimeria falciformis reinfection in mice

Eimeria, a cousin of malarial parasites, causes coccidiosis that results in huge losses in the poultry industry. Although live coccidiosis vaccines have been developed and used widely for the successful control of the disease, the mechanism underlying protective immunity remains largely unknown. Using Eimeria falciformis as a model parasite, we observed that tissue-resident memory CD8⁺ T (Trm) cells accumulated in cecal lamina propria following E. falciformis infection in mice, especially after reinfection. In convalescent mice challenged with a second infection, E. falciformis burden diminished within 48-72 h. Deep-sequencing revealed that CD8⁺ Trm cells were characterized by rapid up-regulation of effector genes encoding pro-inflammatory cytokines and cytotoxic effector molecules. While FTY720 (Fingolimod) treatment prevented the trafficking of CD8⁺ T cells in peripheral circulation and exacerbated primary E. falciformis infection, such treatment had no impact on the expansion of CD8⁺ Trm cells in convalescent mice receiving secondary infection. Adoptive transfer of cecal CD8⁺ Trm cells conferred immune protection in naïve mice, indicating that these cells provide direct and effective protection against infection. Overall, our findings not only explain a protective mechanism of live oocyst-based anti-Eimeria vaccines but also provide a valuable correlate for assessing vaccines against other protozoan diseases.

Tissue-resident memory T cells trigger rapid exudation and local antibody accumulation

Adaptive immunity is didactically partitioned into humoral and cell-mediated effector mechanisms, which may imply that each arm is separate and does not function together. Here, we report that the activation of CD8+ resident memory T cells (TRM) in nonlymphoid tissues triggers vascular permeability, which facilitates rapid distribution of serum antibodies into local tissues. TRM reactivation was associated with transcriptional upregulation of antiviral signaling pathways as well as Fc receptors and components of the complement cascade. Effects were local, but evidence is presented that TRM in brain and reproductive mucosa are both competent to induce rapid antibody exudation. TRM reactivation in the mouse female genital tract increased local concentrations of virus-specific neutralizing antibodies, including anti-vesicular stomatitis virus, and passively transferred anti-HIV antibodies. We showed that this response was sufficient to increase the efficacy of ex vivo vesicular stomatitis virus neutralization. These results indicate that CD8+ TRM antigen recognition can enhance local humoral immunity.

Single-cell profiles reveal distinctive immune response in atopic dermatitis in contrast to psoriasis

BACKGROUND

Understanding the complex orchestrated inflammation in atopic dermatitis (AD), one of the most common chronic inflammatory diseases worldwide, is essential for therapeutic approaches. However, a comparative analysis on the single-cell level of the inflammation signatures correlated with the severity is missing so far.

METHODS

We applied single-cell RNA and T-cell receptor (TCR) sequencing on immune cells enriched from skin biopsies and matched blood samples of AD in comparison with psoriasis (PS) patients.

RESULTS

Clonally propagated skin-derived T cells showed disease-specific TCR motifs shared between patients which was more pronounced in PS compared to AD. The disease-specific T-cell clusters were mostly of a Th2/Th22 sub-population in AD and Th17/Tc17 in PS, and their numbers were associated with severity scores in both diseases. Herein, we provide for the first time a list that associates cell type-specific gene expression with the severity of the two most common chronic inflammatory skin diseases. Investigating the cell signatures in the patients´ PBMCs and skin stromal cells, a systemic involvement of type-3 inflammation was clearly detectable in PS circulating cells, while in AD inflammatory signatures were most pronounced in fibroblasts, pericytes, and keratinocytes. Compositional and functional analyses of myeloid cells revealed the activation of antiviral responses in macrophages in association with disease severity in both diseases.

CONCLUSION

Different disease-driving cell types and subtypes which contribute to the hallmarks of type-2 and type-3 inflammatory signatures and are associated with disease activities could be identified by single-cell RNA-seq and TCR-seq in AD and PS.

The aryl hydrocarbon receptor cell intrinsically promotes resident memory CD8+ T cell differentiation and function

The Aryl hydrocarbon receptor (Ahr) regulates the differentiation and function of CD4+ T cells; however, its cell-intrinsic role in CD8+ T cells remains elusive. Herein we show that Ahr acts as a promoter of resident memory CD8+ T cell (TRM) differentiation and function. Genetic ablation of Ahr in mouse CD8+ T cells leads to increased CD127-KLRG1+ short-lived effector cells and CD44+CD62L+ T central memory cells but reduced granzyme-B-producing CD69+CD103+ TRM cells. Genome-wide analyses reveal that Ahr suppresses the circulating while promoting the resident memory core gene program. A tumor resident polyfunctional CD8+ T cell population, revealed by single-cell RNA-seq, is diminished upon Ahr deletion, compromising anti-tumor immunity. Human intestinal intraepithelial CD8+ T cells also highly express AHR that regulates in vitro TRM differentiation and granzyme B production. Collectively, these data suggest that Ahr is an important cell-intrinsic factor for CD8+ T cell immunity.

Sepsis-induced changes in differentiation, maintenance, and function of memory CD8 T cell subsets

Formation of long-lasting memory lymphocytes is one of the foundational characteristics of adaptive immunity and the basis of many vaccination strategies. Following the rapid expansion and contraction of effector CD8 T cells, the surviving antigen (Ag)-specific cells give rise to the memory CD8 T cells that persist for a long time and are phenotypically and functionally distinct from their naïve counterparts. Significant heterogeneity exists within the memory CD8 T cell pool, as different subsets display distinct tissue localization preferences, cytotoxic ability, and proliferative capacity, but all memory CD8 T cells are equipped to mount an enhanced immune response upon Ag re-encounter. Memory CD8 T cells demonstrate numerical stability under homeostatic conditions, but sepsis causes a significant decline in the number of memory CD8 T cells and diminishes their Ag-dependent and -independent functions. Sepsis also rewires the transcriptional profile of memory CD8 T cells, which profoundly impacts memory CD8 T cell differentiation and, ultimately, the protective capacity of memory CD8 T cells upon subsequent stimulation. This review delves into different aspects of memory CD8 T cell subsets as well as the immediate and long-term impact of sepsis on memory CD8 T cell biology.

Interactions of Tissue-Resident T Cells

Resident memory T cells (TRM) are non-circulating cells that play a critical role in protection from local infections and cancers. Flow cytometric and transcriptional analyses of these cells have defined their distinct phenotypes; imaging allows study of their morphology, localization, and interactions within tissues. Here, we describe commonly used methods to generate cutaneous CD8+ TRM and to prepare skin samples for analysis, including staining of cryostat sections, epidermal sheets, and tissue whole mounts.

Lynch syndrome cancer vaccines: A roadmap for the development of precision immunoprevention strategies

Hereditary cancer syndromes (HCS) account for 5~10% of all cancer diagnosis. Lynch syndrome (LS) is one of the most common HCS, caused by germline mutations in the DNA mismatch repair (MMR) genes. Even with prospective cancer surveillance, LS is associated with up to 50% lifetime risk of colorectal, endometrial, and other cancers. While significant progress has been made in the timely identification of germline pathogenic variant carriers and monitoring and early detection of precancerous lesions, cancer-risk reduction strategies are still centered around endoscopic or surgical removal of neoplastic lesions and susceptible organs. Safe and effective cancer prevention strategies are critically needed to improve the life quality and longevity of LS and other HCS carriers. The era of precision oncology driven by recent technological advances in tumor molecular profiling and a better understanding of genetic risk factors has transformed cancer prevention approaches for at-risk individuals, including LS carriers. MMR deficiency leads to the accumulation of insertion and deletion mutations in microsatellites (MS), which are particularly prone to DNA polymerase slippage during DNA replication. Mutations in coding MS give rise to frameshift peptides (FSP) that are recognized by the immune system as neoantigens. Due to clonal evolution, LS tumors share a set of recurrent and predictable FSP neoantigens in the same and in different LS patients. Cancer vaccines composed of commonly recurring FSP neoantigens selected through prediction algorithms have been clinically evaluated in LS carriers and proven safe and immunogenic. Preclinically analogous FSP vaccines have been shown to elicit FSP-directed immune responses and exert tumor-preventive efficacy in murine models of LS. While the immunopreventive efficacy of "off-the-shelf" vaccines consisting of commonly recurring FSP antigens is currently investigated in LS clinical trials, the feasibility and utility of personalized FSP vaccines with individual HLA-restricted epitopes are being explored for more precise targeting. Here, we discuss recent advances in precision cancer immunoprevention approaches, emerging enabling technologies, research gaps, and implementation barriers toward clinical translation of risk-tailored prevention strategies for LS carriers. We will also discuss the feasibility and practicality of next-generation cancer vaccines that are based on personalized immunogenic epitopes for precision cancer immunoprevention.

Regulator of G-protein signaling 1 critically supports CD8+ TRM cell-mediated intestinal immunity

Members of the Regulator of G-protein signaling (Rgs) family regulate the extent and timing of G protein signaling by increasing the GTPase activity of Gα protein subunits. The Rgs family member Rgs1 is one of the most up-regulated genes in tissue-resident memory (T_RM) T cells when compared to their circulating T cell counterparts. Functionally, Rgs1 preferentially deactivates Gαq, and Gαi protein subunits and can therefore also attenuate chemokine receptor-mediated immune cell trafficking. The impact of Rgs1 expression on tissue-resident T cell generation, their maintenance, and the immunosurveillance of barrier tissues, however, is only incompletely understood. Here we report that Rgs1 expression is readily induced in naïve OT-I T cells in vivo following intestinal infection with Listeria monocytogenes-OVA. In bone marrow chimeras, Rgs1 ^-/- and Rgs1 ^+/+ T cells were generally present in comparable frequencies in distinct T cell subsets of the intestinal mucosa, mesenteric lymph nodes, and spleen. After intestinal infection with Listeria monocytogenes-OVA, however, OT-I Rgs1 ^+/+ T cells outnumbered the co-transferred OT-I Rgs1^{- /-} T cells in the small intestinal mucosa already early after infection. The underrepresentation of the OT-I Rgs1 ^-/- T cells persisted to become even more pronounced during the memory phase (d30 post-infection). Remarkably, upon intestinal reinfection, mice with intestinal OT-I Rgs1 ^+/+ T_RM cells were able to prevent the systemic dissemination of the pathogen more efficiently than those with OT-I Rgs1 ^-/- T_RM cells. While the underlying mechanisms are not fully elucidated yet, these data thus identify Rgs1 as a critical regulator for the generation and maintenance of tissue-resident CD8⁺ T cells as a prerequisite for efficient local immunosurveillance in barrier tissues in case of reinfections with potential pathogens.

An updated review of the immunological mechanisms of keloid scars

Keloid is a type of disfiguring pathological scarring unique to human skin. The disorder is characterized by excessive collagen deposition. Immune cell infiltration is a hallmark of both normal and pathological tissue repair. However, the immunopathological mechanisms of keloid remain unclear. Recent studies have uncovered the pivotal role of both innate and adaptive immunity in modulating the aberrant behavior of keloid fibroblasts. Several novel therapeutics attempting to restore regulation of the immune microenvironment have shown variable efficacy. We review the current understanding of keloid immunopathogenesis and highlight the potential roles of immune pathway-specific therapeutics.

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.

Tissue-resident memory T cells: The key frontier in local synovitis memory of rheumatoid arthritis

Rheumatoid arthritis (RA) is a highly disabling, systemic autoimmune disease. It presents a remarkable tendency to recur, which renders it almost impossible for patients to live without drugs. Under such circumstances, many patients have to suffer the pain of recurrent attacks as well as the side effects of long-term medication. Current therapies for RA are primarily systemic treatments without targeting the problem that RA is more likely to recur locally. Emerging studies suggest the existence of a mechanism mediating local memory during RA, which is closely related to the persistent residence of tissue-resident memory T cells (T_RM). T_RM, one of the memory T cell subsets, reside in tissues providing immediate immune protection but driving recurrent local inflammation on the other hand. The heterogeneity among synovial T_RM is unclear, with the dominated CD8⁺ T_RM observed in inflamed synovium of RA patients coming into focus. Besides local arthritis relapse, T_RM may also contribute to extra-articular organ involvement in RA due to their migration potential. Future integration of single-cell RNA sequencing (scRNA-seq) with spatial transcriptomics to explore the gene expression patterns of T_RM in both temporal dimension and spatial dimension may help us identify specific therapeutic targets. Targeting synovial T_RM to suppress local arthritis flares while using systemic therapies to prevent extra-articular organ involvement may provide a new perspective to address RA recurrence.

Allergic sensitization impairs lung resident memory CD8 T-cell response and virus clearance

BACKGROUND

Patients with asthma often suffer from frequent respiratory viral infections and reduced virus clearance. Lung resident memory T cells provide rapid protection against viral reinfections.

OBJECTIVE

Because the development of resident memory T cells relies on the lung microenvironment, we investigated the impact of allergen sensitization on the development of virus-specific lung resident memory T cells and viral clearance.

METHODS

Mice were sensitized with house dust mite extract followed by priming with X47 and a subsequent secondary influenza infection. Antiviral memory T-cell response and protection to viral infection was assessed before and after secondary influenza infection, respectively. Gene set variation analysis was performed on data sets from the U-BIOPRED asthma cohort using an IFN-γ-induced epithelial cell signature and a tissue resident memory T-cell signature.

RESULTS

Viral loads were higher in lungs of sensitized compared with nonsensitized mice after secondary infection, indicating reduced virus clearance. X47 priming induced fewer antiviral lung resident memory CD8 T cells and resulted in lower pulmonary IFN-γ levels in the lungs of sensitized as compared with nonsensitized mice. Using data from the U-BIOPRED cohort, we found that patients with enrichment of epithelial IFN-γ-induced genes in nasal brushings and bronchial biopsies were also enriched in resident memory T-cell-associated genes, had more epithelial CD8 T cells, and reported significantly fewer exacerbations.

CONCLUSIONS

The allergen-sensitized lung microenvironment interferes with the formation of antiviral resident memory CD8 T cells in lungs and virus clearance. Defective antiviral memory response might contribute to increased susceptibility of patients with asthma to viral exacerbations.

Secondary infections rejuvenate the intestinal CD103 + tissue-resident memory T cell pool

Resident T lymphocytes (T RM ) protect tissues during pathogen reexposure. Although T RM phenotype and restricted migratory pattern are established, we have a limited understanding of their response kinetics, stability, and turnover during reinfections. Such characterizations have been restricted by the absence of in vivo fate-mapping systems. We generated two mouse models, one to stably mark CD103 + T cells (a marker of T RM cells) and the other to specifically deplete CD103 − T cells. Using these models, we observed that intestinal CD103 + T cells became activated during viral or bacterial reinfection, remained organ-confined, and retained their original phenotype but failed to reexpand. Instead, the population was largely rejuvenated by CD103 + T cells formed de novo during reinfections. This pattern remained unchanged upon deletion of antigen-specific circulating T cells, indicating that the lack of expansion was not due to competition with circulating subsets. Thus, although intestinal CD103 + resident T cells survived long term without antigen, they lacked the ability of classical memory T cells to reexpand. This indicated that CD103 + T cell populations could not autonomously maintain themselves. Instead, their numbers were sustained during reinfection via de novo formation from CD103 − precursors. Moreover, in contrast to CD103 - cells, which require antigen plus inflammation for their activation, CD103 + T RM became fully activated follwing exposure to inflammation alone. Together, our data indicate that primary CD103 + resident memory T cells lack secondary expansion potential and require CD103 − precursors for their long-term maintenance.

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.

A molecular signature of lung-resident CD8+ T cells elicited by subunit vaccination

Natural infection as well as vaccination with live or attenuated viruses elicit tissue resident, CD8⁺ memory T cell (Trm) response. Trm cells so elicited act quickly upon reencounter with the priming agent to protect the host. These Trm cells express a unique molecular signature driven by the master regulators-Runx3 and Hobit. We previously reported that intranasal instillation of a subunit vaccine in a prime boost vaccination regimen installed quick-acting, CD8⁺ Trm cells in the lungs that protected against lethal vaccinia virus challenge. It remains unexplored whether CD8⁺ Trm responses so elicited are driven by a similar molecular signature as those elicited by microbes in a real infection or by live, attenuated pathogens in conventional vaccination. We found that distinct molecular signatures distinguished subunit vaccine-elicited lung interstitial CD8⁺ Trm cells from subunit vaccine-elicited CD8⁺ effector memory and splenic memory T cells. Nonetheless, the transcriptome signature of subunit vaccine elicited CD8⁺ Trm resembled those elicited by virus infection or vaccination. Clues to the basis of tissue residence and function of vaccine specific CD8⁺ Trm cells were found in transcripts that code for chemokines and chemokine receptors, purinergic receptors, and adhesins when compared to CD8⁺ effector and splenic memory T cells. Our findings inform the utility of protein-based subunit vaccination for installing CD8⁺ Trm cells in the lungs to protect against respiratory infectious diseases that plague humankind.

Human T lymphocytes at tumor sites

CD4⁺ and CD8⁺ T lymphocytes mediate most of the adaptive immune response against tumors. Naïve T lymphocytes specific for tumor antigens are primed in lymph nodes by dendritic cells. Upon activation, antigen-specific T cells proliferate and differentiate into effector cells that migrate out of peripheral blood into tumor sites in an attempt to eliminate cancer cells. After accomplishing their function, most effector T cells die in the tissue, while a small fraction of antigen-specific T cells persist as long-lived memory cells, circulating between peripheral blood and lymphoid tissues, to generate enhanced immune responses when re-encountering the same antigen. A subset of memory T cells, called resident memory T (T_RM) cells, stably resides in non-lymphoid peripheral tissues and may provide rapid immunity independently of T cells recruited from blood. Being adapted to the tissue microenvironment, T_RM cells are potentially endowed with the best features to protect against the reemergence of cancer cells. However, when tumors give clinical manifestation, it means that tumor cells have evaded immune surveillance, including that of T_RM cells. Here, we review the current knowledge as to how T_RM cells are generated during an immune response and then maintained in non-lymphoid tissues. We then focus on what is known about the role of CD4⁺ and CD8⁺ T_RM cells in antitumor immunity and their possible contribution to the efficacy of immunotherapy. Finally, we highlight some open questions in the field and discuss how new technologies may help in addressing them.

Tissue resident memory T cells- A new benchmark for the induction of vaccine-induced mucosal immunity

Historically, the gold-standard benchmark for vaccine immunogenicity has been the induction of neutralizing antibodies detectable in the serum of peripheral blood. However, in recent years there has been a new appreciation for the mucosa as an important site for vaccine induced immunity. As a point of first contact, the mucosal tissue represents a major site of immune based detection and restriction of pathogen entry and dissemination. Tissue resident memory T cells (Trm) are one of the critical cell types involved in this early detection and restriction of mucosal pathogens. Following tissue-specific infection or vaccination, Trm lodge themselves within tissues and can perform rapid sensing and alarm functions to control local re-infections, in an effort that has been defined as important for restriction of a number of respiratory pathogens including influenza and respiratory syncytial virus. Despite this characterized importance, only minor attention has been paid to the importance of Trm as a benchmark for vaccine immunogenicity. The purpose of this review is to highlight the functions of Trm with particular emphasis on respiratory infections, and to suggest the inclusion of Trm elicitation as a benchmark for vaccine immunogenicity in animal models, and where possible, human samples.

Non-cytotoxic functions of CD8 T cells: “repentance of a serial killer”

Cytotoxic CD8 T cells (CTLs) are classically described as the “serial killers” of the immune system, where they play a pivotal role in protective immunity against a wide spectrum of pathogens and tumors. Ironically, they are critical drivers of transplant rejection and autoimmune diseases, a scenario very similar to the famous novel “The strange case of Dr. Jekyll and Mr. Hyde”. Until recently, it has not been well-appreciated whether CTLs can also acquire non-cytotoxic functions in health and disease. Several investigations into this question revealed their non-cytotoxic functions through interactions with various immune and non-immune cells. In this review, we will establish a new classification for CD8 T cell functions including cytotoxic and non-cytotoxic. Further, we will discuss this novel concept and speculate on how these functions could contribute to homeostasis of the immune system as well as immunological responses in transplantation, cancer, and autoimmune diseases.

The evolving role of tissue-resident memory T cells in infections and cancer

Resident memory T cells (TRM) form a distinct type of T memory cells that stably resides in tissues. TRM form an integral part of the immune sensing network and have the ability to control local immune homeostasis and participate in immune responses mediated by pathogens, cancer, and possibly autoantigens during autoimmunity. TRM express residence gene signatures, functional properties of both memory and effector cells, and remarkable plasticity. TRM have a well-established role in pathogen immunity, whereas their role in antitumor immune responses and immunotherapy is currently evolving. As TRM form the most abundant T memory cell population in nonlymphoid tissues, they are attractive targets for therapeutic exploitation. Here, we provide a concise review of the development and physiological role of CD8+ TRM, their involvement in diseases, and their potential therapeutic exploitation.

Pulmonary resident memory T cells in respiratory virus infection and their inspiration on therapeutic strategies

The immune system generates memory cells on infection with a virus for the first time. These memory cells play an essential role in protection against reinfection. Tissue-resident memory T (TRM) cells can be generated in situ once attacked by pathogens. TRM cells dominate the defense mechanism during early stages of reinfection and have gradually become one of the most popular focuses in recent years. Here, we mainly reviewed the development and regulation of various TRM cell signaling pathways in the respiratory tract. Moreover, we explored the protective roles of TRM cells in immune response against various respiratory viruses, such as Respiratory Syncytial Virus (RSV) and influenza. The complex roles of TRM cells against SARS-CoV-2 infection are also discussed. Current evidence supports the therapeutic strategies targeting TRM cells, providing more possibilities for treatment. Rational utilization of TRM cells for therapeutics is vital for defense against respiratory viruses.

Runx3 drives a CD8+ T cell tissue residency program that is absent in CD4+ T cells

Tissue-resident memory T cells (TRM cells) provide rapid and superior control of localized infections. While the transcription factor Runx3 is a critical regulator of CD8+ T cell tissue residency, its expression is repressed in CD4+ T cells. Here, we show that, as a direct consequence of this Runx3-deficiency, CD4+ TRM cells lacked the transforming growth factor (TGF)-β-responsive transcriptional network that underpins the tissue residency of epithelial CD8+ TRM cells. While CD4+ TRM cell formation required Runx1, this, along with the modest expression of Runx3 in CD4+ TRM cells, was insufficient to engage the TGF-β-driven residency program. Ectopic expression of Runx3 in CD4+ T cells incited this TGF-β-transcriptional network to promote prolonged survival, decreased tissue egress, a microanatomical redistribution towards epithelial layers and enhanced effector functionality. Thus, our results reveal distinct programming of tissue residency in CD8+ and CD4+ TRM cell subsets that is attributable to divergent Runx3 activity.

Advancing Lung Immunology Research: An Official American Thoracic Society Workshop Report

The mammalian airways and lungs are exposed to a myriad of inhaled particulate matter, allergens, and pathogens. The immune system plays an essential role in protecting the host from respiratory pathogens, but a dysregulated immune response during respiratory infection can impair pathogen clearance and lead to immunopathology. Furthermore, inappropriate immunity to inhaled antigens can lead to pulmonary diseases. A complex network of epithelial, neural, stromal, and immune cells has evolved to sense and respond to inhaled antigens, including the decision to promote tolerance versus a rapid, robust, and targeted immune response. Although there has been great progress in understanding the mechanisms governing immunity to respiratory pathogens and aeroantigens, we are only beginning to develop an integrated understanding of the cellular networks governing tissue immunity within the lungs and how it changes after inflammation and over the human life course. An integrated model of airway and lung immunity will be necessary to improve mucosal vaccine design as well as prevent and treat acute and chronic inflammatory pulmonary diseases. Given the importance of immunology in pulmonary research, the American Thoracic Society convened a working group to highlight central areas of investigation to advance the science of lung immunology and improve human health.

Activated-memory T cells influence naïve T cell fate: a noncytotoxic function of human CD8 T cells

T cells are endowed with the capacity to sense their environment including other T cells around them. They do so to set their numbers and activation thresholds. This form of regulation has been well-studied within a given T cell population - i.e., within the naïve or memory pool; however, less is known about the cross-talk between T cell subsets. Here, we tested whether memory T cells interact with and influence surrounding naïve T cells. We report that human naïve CD8 T cells (T_N) undergo phenotypic and transcriptional changes in the presence of autologous activated-memory CD8 T cells (T_Mem). Following in vitro co-culture with activated central memory cells (T_CM), ~3% of the T_N acquired activation/memory canonical markers (CD45RO and CD95) in an MHC-I dependent-fashion. Using scRNA-seq, we also observed that ~3% of the T_N acquired an activated/memory signature, while ~84% developed a unique activated transcriptional profile hybrid between naïve and activated memory. Pseudotime trajectory analysis provided further evidence that T_N with an activated/memory or hybrid phenotype were derived from T_N. Our data reveal a non-cytotoxic function of T_Mem with potential to activate autologous T_N into the activated/memory pool. These findings may have implications for host-protection and autoimmunity that arises after vaccination, infection or transplantation.

Phenotypic and Immunometabolic Aspects on Stem Cell Memory and Resident Memory CD8+ T Cells

The immune system, smartly and surprisingly, saves the exposure of a particular pathogen in its memory and reacts to the pathogen very rapidly, preventing serious diseases.

Immunologists have long been fascinated by understanding the ability to recall and respond faster and more vigorously to a pathogen, known as “memory”.

T-cell populations can be better described by using more sophisticated techniques to define phenotype, transcriptional and epigenetic signatures and metabolic pathways (single-cell resolution), which uncovered the heterogeneity of the memory T-compartment. Phenotype, effector functions, maintenance, and metabolic pathways help identify these different subsets. Here, we examine recent developments in the characterization of the heterogeneity of the memory T cell compartment. In particular, we focus on the emerging role of CD8+ TRM and TSCM cells, providing evidence on how their immunometabolism or modulation can play a vital role in their generation and maintenance in chronic conditions such as infections or autoimmune diseases.

Tissue-Resident Memory CD4+ T Cells Play a Dominant Role in the Initiation of Antitumor Immunity

Tumor immunology has been studied extensively. Tumor immunology-based cancer immunotherapy has become one of the most promising approaches for cancer treatment. However, one of the fundamental aspects of tumor immunology-the initiation of antitumor immunity-is not fully understood. Compared to that of CD8⁺ T cells, the effect of CD4⁺ T cells on antitumor immunity has not been fully appreciated. Using a gene knockout mouse model, the mice of which are deficient in the TCRα repertoire, specifically lacking invariant NKT and mucosal-associated invariant T cells, we found that the deficiency in TCRα repertoire diversity did not affect the antitumor immunity, at least to B16BL6 melanoma and EO771 breast cancer. However, after acquiring thymocytes or splenocytes from wild-type mice, these knockout mice exhibited greatly enhanced and long-lasting antitumor immunity. This enhanced antitumor immunity depended on CD4⁺ T cells, especially CD4⁺ tissue-resident memory T (T_RM) cells, but not invariant NKT or CD8⁺ T cells. We also present evidence that CD4⁺ T_RM cells initiate antitumor immunity through IFN-γ, and the process is dependent on NK cells. The CD4⁺ T_RM/NK axis appears to control tumor formation and development by eliminating tumor cells and modulating the tumor microenvironment. Taken together, our results demonstrated that CD4⁺ T_RM cells play a dominant role in the initiation of antitumor immunity.

An Overview of Tissue-Resident Memory T Cells in the Intestine: From Physiological Functions to Pathological Mechanisms

The human intestine contains a complex network of innate and adaptive immune cells that provide protective immunity. The dysfunction of this network may cause various chronic diseases. A large number of T cells in the human intestine have been identified as tissue-resident memory T cells (TRM). TRM are present in the peripheral tissues, and they do not recirculate through the blood. It is known that TRM provide rapid immune responses at the frontline of pathogen invasion. Recent evidence also suggests that these cells play a role in tumor surveillance and the pathogenesis of autoimmune diseases. In this review, we discuss the general features of intestinal TRM together with their role in intestinal infection, colorectal cancer (CRC), and inflammatory bowel disease (IBD).

Corneal tissue-resident memory T cells form a unique immune compartment at the ocular surface

The eye is considered immune privileged such that immune responses are dampened to protect vision. As the most anterior compartment of the eye, the cornea is exposed to pathogens and can mount immune responses that recruit effector T cells. However, presence of immune memory in the cornea is not defined. Here, we use intravital 2-photon microscopy to examine T cell responses in the cornea in mice. We show that recruitment of CD8⁺ T cells in response to ocular virus infection results in the formation of tissue-resident memory T (T_RM) cells. Motile corneal T_RM cells patrol the cornea and rapidly respond in situ to antigen rechallenge. CD103⁺ T_RM cell generation requires antigen and transforming growth factor β. In vivo imaging in humans also reveals highly motile cells that patrol the healthy cornea. Our study finds that T_RM cells form in the cornea where they can provide local protective immunity.

Towards Understanding the Lymph Node Response to Skin Infection with Saprophytic Staphylococcus epidermidis

In individuals with lymphedema, diabetic foot, or other diseases, infections with saprophytes are common. The response of major cell subpopulations in the draining lymph nodes to skin infection with Staphylococcus epidermidis was assessed using the rat model. After massive subepidermal infection, a cytometric evaluation showed an increase in cytotoxic and helper T lymphocytes and major subpopulations of the innate immune response. Three weeks later, signs of inflammation reduction with an increase in the content of memory T helper lymphocytes and effector memory T cytotoxic lymphocytes were observed. After skin re-infection, a rapid response of cytotoxic, helper, and memory T lymphocytes, memory B lymphocytes and plasmablasts, and macrophages was detected. In addition, a reduction in the number of naïve B lymphocytes, activated MHC class II+ cells, and some cells of the innate immune system was observed. T regulatory lymphocyte response after the initial and secondary S. epidermidis skin infection was not detected. The morphometric evaluation showed significant changes in the main cell subpopulations in each functional zone of the node and then confirmed the efficient elimination of the administered antigen, as evidenced by the observations on day 28. Notably, after re-infection, the cellular response did not exceed the level after the initial infection and was reduced in many cell subpopulations. Understanding how the lymph nodes eliminate S. epidermidis can provide valuable insights into creating immunological therapies against infections with saprophytes.

Tissue-resident memory CD8+ T cells cooperate with CD4+ T cells to drive compartmentalized immunopathology in the CNS

In chronic inflammatory diseases of the central nervous system (CNS), immune cells persisting behind the blood-brain barrier are supposed to promulgate local tissue destruction. The drivers of such compartmentalized inflammation remain unclear, but tissue-resident memory T cells (T_RM) represent a potentially important cellular player in this process. Here, we investigated whether resting CD8⁺ T_RM persisting after cleared infection with attenuated lymphocytic choriomeningitis virus (LCMV) can initiate immune responses directed against cognate self-antigen in the CNS. We demonstrated that time-delayed conditional expression of the LCMV glycoprotein as neo-self-antigen by glia cells reactivated CD8⁺ T_RM. Subsequently, CD8⁺ T_RM expanded and initiated CNS inflammation and immunopathology in an organ-autonomous manner independently of circulating CD8⁺ T cells. However, in the absence of CD4⁺ T cells, TCF-1⁺ CD8⁺ T_RM failed to expand and differentiate into terminal effectors. Similarly, in human demyelinating CNS autoimmune lesions, we found CD8⁺ T cells expressing TCF-1 that predominantly exhibited a T_RM-like phenotype. Together, our study provides evidence for CD8⁺ T_RM-driven CNS immunopathology and sheds light on why inflammatory processes may evade current immunomodulatory treatments in chronic autoimmune CNS conditions.

Tissue resident memory T cells inhabit the deep human conjunctiva

Mucosal linings of the body, including the conjunctiva, are enriched in tissue-resident memory T cells (T_RMs) whose defining feature is their continual tissue protection that does not rely on migration to lymphoid organs to elicit immune responses. Hitherto, conjunctival T_RMs have only been identified in the superficial epithelium. This work aims to develop a more complete understanding of the conjunctival immunological capacity by investigating the presence of T_RMs within the deeper, more stable layers of the healthy human conjunctiva. Using immunofluorescence microscopy and antibodies against CD3, CD4, CD69 and HLA-DR on bulbar conjunctival biopsies obtained from 7 healthy adults (age range = 32-77 years; females = 4), we identified CD69⁺T_RM subsets in all layers of the human conjunctiva: the superficial epithelium, the basal epithelium, the adenoid, and the fibrous layers. Interestingly, the adenoid layer showed significantly higher densities of both CD4 and CD8 T_RMs when compared to the fibrous layer and conjunctival epithelia. Additionally, CD4 T_RMs predominated significantly over CD8 T_RMs in the adenoid layer. The abundance of deep conjunctival CD69⁺T_RMs within the healthy human may suggest the presence of defence mechanisms capable of inducing long-term immunogenic memory. Understanding this spatial distribution of conjunctival CD69⁺T_RMs is essential to improving mucosal vaccine design.

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.

Imaging viral infection in vivo to gain unique perspectives on cellular antiviral immunity

The past decade has seen near continual global public health crises caused by emerging viral infections. Extraordinary increases in our knowledge of the mechanisms underlying successful antiviral immune responses in animal models and during human infection have accompanied these viral outbreaks. Keeping pace with the rapidly advancing field of viral immunology, innovations in microscopy have afforded a previously unseen view of viral infection occurring in real-time in living animals. Here, we review the contribution of intravital imaging to our understanding of cell-mediated immune responses to viral infections, with a particular focus on studies that visualize the antiviral effector cells responding to infection as well as virus-infected cells. We discuss methods to visualize viral infection in vivo using intravital microscopy (IVM) and significant findings arising through the application of IVM to viral infection. Collectively, these works underscore the importance of developing a comprehensive spatial understanding of the relationships between immune effectors and virus-infected cells and how this has enabled unique discoveries about virus/host interactions and antiviral effector cell biology.

T-cell subsets in the skin and their role in inflammatory skin disorders

T lymphocytes (T cells) are major players of the adaptive immune response. Naive T cells are primed in the presence of cytokines, leading to polarization into distinct T-cell subsets with specific functions. These subsets are classified based on their T-cell receptor profile, expression of transcription factors, surface cytokine and chemokine receptors, and their cytokine production, which together determine their specific function. This review provides an overview of the various T-cell subsets and their function in several inflammatory skin disorders ranging from allergic inflammation to skin tumors. Moreover, we highlight similarities of T-cell responses across different skin disorders, demonstrating the presence of similar and opposing functions for the different T-cell subsets. Finally, we discuss the effects of currently available and promising therapeutic approaches to harness T cells in inflammatory skin diseases for which efficacy next to unwanted side effects provide new insights into the pathophysiology of skin disorders.

Prompt Antiviral Action of Pulmonary CD8+ TRM Cells Is Mediated by Rapid IFN-γ Induction and Its Downstream ISGs in the Lung

Growing lines of evidence supported the importance of CD8+ lung tissue resident memory T (TRM) cells in protection against respiratory viruses, exemplified by influenza A virus. However, the underlying in vivo mechanism remains largely undetermined. Here, we used mouse infection models to dissect in vivo cross-protective activity of lung CD8+ TRM cells. By simultaneously interrogating transcriptional dynamics in lung CD8+ TRM cells and surrounding tissues during the early course of infection, we demonstrated that lung CD8+ TRM cells react to antigen re-exposure within hours, manifested by IFN-γ upregulation, and a tissue-wide interferon-stimulated gene (ISG) program is subsequently elicited. Using antibody-mediated IFN-γ neutralization and IFN-γ receptor knockout mice, we could show that the induction of several important antiviral ISGs required IFN-γ signaling, so did the suppression of key inflammatory cytokines. Interestingly, there were also examples of ISGs unaffected in the absence of IFN-γ activity. Collectively, focusing on in situ characterization of lung CD8+ TRM cells during very early stage of infection, a critical period of host antiviral defense that has been poorly investigated, our studies highlight that these cells, once triggered by antigen re-exposure, are programmed to produce IFN-γ expeditiously to promote a lung-wide antiviral response for effective virus control.

CD8+ tissue-resident memory T cells recruit neutrophils that are essential for flare-ups in contact dermatitis

BACKGROUND

Allergic contact dermatitis (ACD) is classically described as a delayed-type hypersensitivity reaction. However, patients often experience flare-ups characterized by itching erythema, edema, and often vesicles occurring within hours after re-exposure of previously sensitized skin to the specific contact allergen. Recent studies have indicated that skin-resident memory T (T_RM ) cells play a central role in ACD. However, the pathogenic role of T_RM cells in allergen-induced flare-ups is not known.

METHODS

By the use of various mouse models and cell depletion protocols, we investigated the role of epidermal T_RM cells in flare-up reactions to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene. The inflammatory response was measured by changes in ear thickness, and the cellular composition in epidermis was determined by flow cytometry and confocal microscopy. Finally, adaptive transfer and inhibitors were used to determine the role of T_RM cells, neutrophils, and CXCL1/CXCL2 in the response.

RESULTS

We show that CD8⁺ T_RM cells initiate massive infiltration of neutrophils in the epidermis within 12 h after re-exposure to the contact allergen. Depletion of neutrophils before re-exposure to the allergen abrogated the flare-up reactions. Furthermore, we demonstrate that CD8⁺ T_RM cells mediate neutrophil recruitment by inducing CXCL1 and CXCL2 production in the skin, and that blockage of the C-X-C chemokine receptor type 1 and 2 inhibits flare-up reactions and neutrophil infiltration.

CONCLUSION

As the first, we show that epidermal CD8⁺ T_RM cells cause ACD flare-ups by rapid recruitment of neutrophils to the epidermis.