Type I interferons regulate cytolytic activity of memory CD8(+) T cells in the lung airways during respiratory virus challenge

Dynamic landscapes and protective immunity coordinated by influenza-specific lung-resident memory CD8+ T cells revealed by intravital imaging

Lung-tissue-resident memory (TRM) CD8+ T cells are critical for heterosubtypic immunity against influenza virus (IAV) reinfection. How TRM cells surveil the lung, respond to infection, and interact with other cells remains unresolved. Here, we used IAV infection of mice in combination with intravital and static imaging to define the spatiotemporal dynamics of lung TRM cells before and after recall infection. CD69+CD103+ TRM cells preferentially localized to lung sites of prior IAV infection, where they exhibited patrolling behavior. After rechallenge, lung TRM cells formed tight clusters in an antigen-dependent manner. Transcriptomic analysis of IAV-specific TRM cells revealed the expression of several factors that regulate myeloid cell biology. In vivo rechallenge experiments demonstrated that protection elicited by TRM cells is orchestrated in part by interferon (IFN)-γ-mediated recruitment of inflammatory monocytes into the lungs. Overall, these data illustrate the dynamic landscapes of CD103+ lung TRM cells that mediate early protective immunity against IAV infection.

Time-resolved scRNA-seq reveals transcription dynamics of polarized macrophages with influenza A virus infection and antigen presentation to T cells

AbstractThroughout history, the influenza A virus has caused numerous devastating global pandemics. Macrophages, as pivotal innate immune cells, exhibit a wide range of immune functions characterized by distinct polarization states, reflecting their intricate heterogeneity. In this study, we employed the time-resolved single-cell sequencing technique coupled with metabolic RNA labelling to elucidate the dynamic transcriptional changes in distinct polarized states of bone marrow-derived macrophages (BMDMs) upon infection with the influenza A virus. Our approach not only captures the temporal dimension of transcriptional activity, which is lacking in conventional scRNA-seq methods, but also reveals that M2-polarized Arg1_macrophages is the sole state supporting successful replication of influenza A virus. Furthermore, we identified distinct antigen presentation capabilities to CD4+ T and CD8+ T cells across diverse polarized states of macrophages. Notably, the M1 phenotype, exhibited by both bone marrow-derived macrophages (BMDMs) and murine alveolar macrophages (AMs), demonstrated superior conventional and cross-presentation abilities for exogenous antigens, with a particular emphasis on cross-presentation capacity. Additionally, as CD8+ T cell differentiation progressed, M1 polarization exhibited an enhanced capacity for cross-presentation. All three phenotypes of BMDMs, including M1, demonstrated robust presentation of CD4+ regulatory T cells, while displaying limited ability to present naive CD4+ T cells. These findings offer novel insights into the immunological regulatory mechanisms governing distinct polarized states of macrophages, particularly their roles in restricting the replication of influenza A virus and modulating antigen-specific T cell responses through innate immunity.

Lasting differential gene expression of circulating CD8 T cells in chronic HCV infection with cirrhosis identifies a role for Hedgehog signaling in cellular hyperfunction

Background

The impact of chronic hepatic infection on antigen non-specific immune cells in circulation remains poorly understood. We reported lasting global hyperfunction of peripheral CD8 T cells in HCV-infected individuals with cirrhosis. Whether gene expression patterns in bulk CD8 T cells are associated with the severity of liver fibrosis in HCV infection is not known.

Methods

RNA sequencing of blood CD8 T cells from treatment naïve, HCV-infected individuals with minimal (Metavir F0-1 ≤ 7.0 kPa) or advanced fibrosis or cirrhosis (F4 ≥ 12.5 kPa), before and after direct-acting antiviral therapy, was performed. CD8 T cell function was assessed by flow cytometry.

Results

In CD8 T cells from pre-DAA patients with advanced compared to minimal fibrosis, Gene Ontology analysis and Gene Set Enrichment Analysis identified differential gene expression related to cellular function and metabolism, including upregulated Hedgehog (Hh) signaling, IFN-α, -γ, TGF-β response genes, apoptosis, apical surface pathways, phospholipase signaling, phosphatidyl-choline/inositol activity, and second-messenger-mediated signaling. In contrast, genes in pathways associated with nuclear processes, RNA transport, cytoskeletal dynamics, cMyc/E2F regulation, oxidative phosphorylation, and mTOR signaling, were reduced. Hh signaling pathway was the top featured gene set upregulated in cirrhotics, wherein hallmark genes GLI1 and PTCH1 ranked highly. Inhibition of Smo-dependent Hh signaling ablated the expression of IFN-γ and perforin in stimulated CD8 T cells from chronic HCV-infected patients with advanced compared to minimal fibrosis. CD8 T cell gene expression profiles post-DAA remained clustered with pre-DAA profiles and disparately between advanced and minimal fibrosis, suggesting a persistent perturbation of gene expression long after viral clearance.

Conclusions

This analysis of bulk CD8 T cell gene expression in chronic HCV infection suggests considerable reprogramming of the CD8 T cell pool in the cirrhotic state. Increased Hh signaling in cirrhosis may contribute to generalized CD8 T cell hyperfunction observed in chronic HCV infection. Understanding the lasting nature of immune cell dysfunction may help mitigate remaining clinical challenges after HCV clearance and more generally, improve long term outcomes for individuals with severe liver disease.

Review of the potential pharmacological role of erucic acid: a monounsaturated omega-9 fatty acid

This comprehensive review aims to provide an overview of the pharmacological properties of erucic acid (EA) and highlight areas that require further research. EA is an omega-9 fatty acid found in certain vegetable oil, such as rapeseed oil has demonstrated favourable effects in rodents, including ameliorating myocardial lipidosis (fat accumulation in the heart muscle), congestive heart disease, hepatic steatosis (fat accumulation in the liver), and memory impairments. These findings have prompted regulatory bodies to establish limits on EA content in food oils. The studies were performed on rodents and led to caution on ingesting the EA at high levels. Moreover, EA is frequently utilized as a nutritional supplement for the treatment of adrenoleukodystrophy, myocardial disease, and memory improvement. The review of the article indicated that EA improves cognitive function, has a part in Huntington's disease, interacts with peroxisome proliferator-activated receptors, inhibits elastase and thrombin, has anti-inflammatory, antioxidant, and anti-tumour properties, and inhibits influenza A virus. This article elucidates the pharmacological effects of EA, an omega-9 fatty acid.

IFN-λ uniquely promotes CD8 T cell immunity against SARS-CoV-2 relative to type I IFN

Optimization of protective immune responses against SARS-CoV-2 remains an urgent worldwide priority. In this regard, type III IFN (IFN-λ) restricts SARS-CoV-2 infection in vitro, and treatment with IFN-λ limits infection, inflammation, and pathogenesis in murine models. Furthermore, IFN-λ has been developed for clinical use to limit COVID-19 severity. However, whether endogenous IFN-λ signaling has an effect on SARS-CoV-2 antiviral immunity and long-term immune protection in vivo is unknown. In this study, we identified a requirement for IFN-λ signaling in promoting viral clearance and protective immune programming in SARS-CoV-2 infection of mice. Expression of both IFN and IFN-stimulated gene (ISG) in the lungs were minimally affected by the absence of IFN-λ signaling and correlated with transient increases in viral titers. We found that IFN-λ supported the generation of protective CD8 T cell responses against SARS-CoV-2 by facilitating accumulation of CD103+ DC in lung draining lymph nodes (dLN). IFN-λ signaling specifically in DCs promoted the upregulation of costimulatory molecules and the proliferation of CD8 T cells. Intriguingly, antigen-specific CD8 T cell immunity to SARS-CoV-2 was independent of type I IFN signaling, revealing a nonredundant function of IFN-λ. Overall, these studies demonstrate a critical role for IFN-λ in protective innate and adaptive immunity upon infection with SARS-CoV-2 and suggest that IFN-λ serves as an immune adjuvant to support CD8 T cell immunity.

NKT-Licensed In Vivo Dendritic Cell-Based Immunotherapy as Cellular Immunodrugs for Cancer Treatment

With the advent of new therapies, immunotherapy has gained attention as a critical modality. After the discovery of the natural killer T (NKT) cells ligand, ex vivo cultured dendritic cells (DCs) loaded with NKT ligand (especially α-galactosylceramide (α-GalCer) (DC/Gal) or ex vivo expanded NKT transfer studies were clinically examined in several institutes. To prevent tumoral immune escape, the link between innate and adaptive immunity, in situ selective targeting of DCs has been attempted; however, protocol optimization was required. As a type of DC targeting therapy that combines the benefits of invariant natural killer T (iNKT) cells, we established an all-in-one, off-the-shelf drug, named the artificial adjuvant vector cell (aAVC), which consists of the tumor antigen and the CD1d-iNKT ligand complex. Here, to our knowledge, we first demonstrate the DC/GalCer therapy and NKT transfer therapy. Next, we introduce and discuss the use of aAVC therapy not only for efficient innate and adaptive immunity induction using fully matured DC in situ but also the characterization necessary for locally reprogramming the tumor microenvironment and systemically inducing long-term memory in T cells. We also discuss how the immune network mechanism is controlled by DCs. Next, we performed the first human clinical trial using WT1 antigen-expressing aAVC against relapse and refractory acute myelogenous leukemia. Thus, we highlight the challenges of using aAVCs as prodrugs for actively energizing DCs in vivo, underpinning immunological networks, and developing strategies for providing maximal benefits for patients.

IL-27 produced during acute malaria infection regulates Plasmodium-specific memory CD4+ T cells

Malaria infection elicits both protective and pathogenic immune responses, and IL-27 is a critical cytokine that regulate effector responses during infection. Here, we identified a critical window of CD4+ T cell responses that is targeted by IL-27. Neutralization of IL-27 during acute infection with Plasmodium chabaudi expanded specific CD4+ T cells, which were maintained at high levels thereafter. In the chronic phase, Plasmodium-specific CD4+ T cells in IL-27-neutralized mice consisted mainly of CD127+ KLRG1- and CD127- KLRG1+ subpopulations that displayed distinct cytokine production, proliferative capacity, and are maintained in a manner independent of active infection. Single-cell RNA-seq analysis revealed that these CD4+ T cell subsets formed independent clusters that express unique Th1-type genes. These IL-27-neutralized mice exhibited enhanced cellular and humoral immune responses and protection. These findings demonstrate that IL-27, which is produced during the acute phase of malaria infection, inhibits the development of unique Th1 memory precursor CD4+ T cells, suggesting potential implications for the development of vaccines and other strategic interventions.

Localization, tissue biology and T cell state - implications for cancer immunotherapy

Tissue localization is a critical determinant of T cell immunity. CD8+ T cells are contact-dependent killers, which requires them to physically be within the tissue of interest to kill peptide-MHC class I-bearing target cells. Following their migration and extravasation into tissues, T cells receive many extrinsic cues from the local microenvironment, and these signals shape T cell differentiation, fate and function. Because major organ systems are variable in their functions and compositions, they apply disparate pressures on T cells to adapt to the local microenvironment. Additional complexity arises in the context of malignant lesions (either primary or metastatic), and this has made understanding the factors that dictate T cell function and longevity in tumours challenging. Moreover, T cell differentiation state influences how cues from the microenvironment are interpreted by tissue-infiltrating T cells, highlighting the importance of T cell state in the context of tissue biology. Here, we review the intertwined nature of T cell differentiation state, location, survival and function, and explain how dysfunctional T cell populations can adopt features of tissue-resident memory T cells to persist in tumours. Finally, we discuss how these factors have shaped responses to cancer immunotherapy.

Type I interferons drive MAIT cell functions against bacterial pneumonia

Mucosal-associated invariant T (MAIT) cells are abundant in the lung and contribute to host defense against infections. During bacterial infections, MAIT cell activation has been proposed to require T cell receptor (TCR)-mediated recognition of antigens derived from the riboflavin synthesis pathway presented by the antigen-presenting molecule MR1. MAIT cells can also be activated by cytokines in an MR1-independent manner, yet the contribution of MR1-dependent vs. -independent signals to MAIT cell functions in vivo remains unclear. Here, we use Klebsiella pneumoniae as a model of bacterial pneumonia and demonstrate that MAIT cell activation is independent of MR1 and primarily driven by type I interferons (IFNs). During Klebsiella infection, type I IFNs stimulate activation of murine and human MAIT cells, induce a Th1/cytotoxic transcriptional program, and modulate MAIT cell location within the lungs. Consequently, adoptive transfer or boosting of pulmonary MAIT cells protect mice from Klebsiella infection, with protection being dependent on direct type I IFN signaling on MAIT cells. These findings reveal type I IFNs as new molecular targets to manipulate MAIT cell functions during bacterial infections.

Stress promotes the infiltration of peripheral immune cells to the brain

Immune cells and the brain have a privileged interaction. Here, we report changes in the hippocampal immune microenvironment at the single cell level after stress, uncovering the tight orchestration of immune cell infiltration into the hippocampus after stress to maintain homeostasis. We show the distribution of several immune cell types in the hippocampus associated with their susceptibility or resilience to the learned helplessness paradigm in a sex- and microbiota-dependent manner using single-cell RNA sequencing and bioinformatic tools, flow cytometry, and immunofluorescence. We uncovered the presence of tissue-resident memory T cells that accumulate over time in the hippocampus of learned helpless mice, and the presence of CD74-expressing myeloid cells. These cells were found by a knockdown approach to be critical to induce resilience to learned helplessness. Altogether, these findings provide a novel overview of the neuro-immune repertoire and its impact on the landscape of the hippocampus after learned helplessness.

Tissue-resident memory T cells and lung immunopathology

Rapid reaction to microbes invading mucosal tissues is key to protect the host against disease. Respiratory tissue-resident memory T (TRM ) cells provide superior immunity against pathogen infection and/or re-infection, due to their presence at the site of pathogen entry. However, there has been emerging evidence that exuberant TRM -cell responses contribute to the development of various chronic respiratory conditions including pulmonary sequelae post-acute viral infections. In this review, we have described the characteristics of respiratory TRM cells and processes underlying their development and maintenance. We have reviewed TRM -cell protective functions against various respiratory pathogens as well as their pathological activities in chronic lung conditions including post-viral pulmonary sequelae. Furthermore, we have discussed potential mechanisms regulating the pathological activity of TRM cells and proposed therapeutic strategies to alleviate TRM -cell-mediated lung immunopathology. We hope that this review provides insights toward the development of future vaccines or interventions that can harness the superior protective abilities of TRM cells, while minimizing the potential for immunopathology, a particularly important topic in the era of coronavirus disease 2019 (COVID-19) pandemic.

Comprehensive immune landscape of lung-resident memory CD8+ T cells after influenza infection and reinfection in a mouse model

Background

Resident phenotypic memory CD8⁺ T cells are crucial for immune defense against pathogens. However, little is known about the potential transitions and regulation mechanisms of their function after influenza virus infection and reinfection. In this study, we utilized integrated transcriptome data and in vivo experiments to investigate the key characteristics behind it.

Methods

Two single-cell RNA sequencing (scRNA-seq) datasets of lung CD8⁺ T cells and one RNA-seq dataset of lung tissue after infection or reinfection were included. After Seurat procedures classifying CD8⁺ T subsets, the scCODE algorithm was used to identify the differentially expressed genes for GSVA, GO, and KEGG pathway enrichment. Monocle 3 and CellChat were used to infer pseudotime cell trajectory and cell interactions. The ssGSEA method was used to estimate the relative proportions of immune cells. The findings were confirmed with a mouse model via flow cytometry and RT-PCR analysis.

Results

Our study refined the landscape of CD8⁺ T-cell subsets in the lung, showing that CD8⁺ Trm cells accumulated in the lung within 14 days after influenza infection. The classical CD8⁺ Trm cells co-expressed a high level of CD49a and even maintained 90 days after primary infection. The ratio of CD8⁺ Trm cells decreased 1 day after influenza reinfection, which may be parallel with their potential transition into effector types, as observed in trajectory inference analysis. KEGG analysis suggested that PD-L1 expression and PD-1 checkpoint pathway were upregulated in CD8⁺ Trm cells on day 14 after infection. GO and GSVA analyses revealed that PI3K-Akt-mTOR and type I interferon signaling pathways were enriched in CD8⁺ Tem and Trm cells after reinfection. Additionally, CCL signaling pathways were involved in cell interaction between CD8⁺ Trm cells and other cells, with Ccl4-Ccr5 and Ccl5-Ccr5 ligand/receptor pairs being important between CD8⁺ Trm and other memory subsets after infection and reinfection.

Conclusion

Our data suggest that resident memory CD8⁺ T cells with CD49a co-expression account for a large proportion after influenza infection, and they can be rapidly reactivated against reinfection. Function differences exist in CD8⁺ Trm and Tem cells after influenza infection and reinfection. Ccl5-Ccr5 ligand/receptor pair is important in cell interactions between CD8⁺ Trm and other subsets.

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.

Vitamin D and COVID-19: where are we now?

The pandemic caused by the SARS-CoV-2 virus has triggered great interest in the search for the pathophysiological mechanisms of COVID-19 and its associated hyperinflammatory state. The presence of prognostic factors such as diabetes, cardiovascular disease, hypertension, obesity, and age influence the expression of the disease's clinical severity. Other elements, such as 25-hydroxyvitamin D (25(OH)D3) concentrations, are currently being studied. Various studies, mostly observational, have sought to demonstrate whether there is truly a relationship between 25(OH)D3 levels and the acquisition and/or severity of the disease. The objective of this study was to carry out a review of the current data that associate vitamin D status with the acquisition, evolution, and/or severity of infection by the SARS-CoV-2 virus and to assess whether prevention through vitamin D supplementation can prevent infection and/or improve the evolution once acquired. Vitamin D system has an immunomodulatory function and plays a significant role in various bacterial and viral infections. The immune function of vitamin D is explained in part by the presence of its receptor (VDR) and its activating enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) in immune cells. The vitamin D, VDR, and Retinoid X Receptor complex allows the transcription of genes with antimicrobial activities, such as cathelicidins and defensins. COVID-19 characteristically presents a marked hyperimmune state, with the release of proinflammatory cytokines such as IL-6, TNF-α, and IL-1β. Thus, there are biological factors linking vitamin D to the cytokine storm, which can herald some of the most severe consequences of COVID-19, such as acute respiratory distress syndrome. Hypovitaminosis D is widespread worldwide, so the prevention of COVID-19 through vitamin D supplementation is being considered as a possible therapeutic strategy easy to implement. However, more-quality studies and well-designed randomized clinical trials are needed to address this relevant question.

Severe respiratory viral infections: T-cell functions diverging from immunity to inflammation

Respiratory viral infections such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV) trigger distinct clinical outcomes defined by immunity-based viral clearance or disease associated with exaggerated and prolonged inflammation. The important role of T cells in shaping both antiviral immunity and inflammation has revived interest in understanding the host-pathogen interactions that lead to the diverse functions of T cells in respiratory viral infections. Inborn deficiencies and acquired insufficiency in immunity can prolong infection and shift the immune response towards exacerbated inflammation, which results from persistent innate immune activation and bystander T-cell activation that is nonspecific to the pathogen but is often driven by cytokines. This review discusses how virus variants, exposure doses, routes of infection, host genetics, and immune history can modulate the activation and function of T cells, thus influencing clinical outcomes. Knowledge of virus-host interaction can inform strategies to prevent immune dysfunction in respiratory viral infection and help in the treatment of associated diseases.

Innate-like bystander-activated CD38+ HLA-DR+ CD8+ T cells play a pathogenic role in patients with chronic hepatitis C

BACKGROUND AND AIMS

HCV-specific T cells are few and exhausted in patients with chronic hepatitis C (CHC). Whether these T cells are responsible for the liver damage and fibrosis is still debated. However, cluster of differentiation 38-positive (CD38⁺ ) human leukocyte antigen DR-positive (HLA-DR⁺ ) CD8⁺ T cells are regarded as bystander CD8⁺ T cells that cause liver injury in acute hepatitis. We propose that these innate CD8⁺ T cells play a pathogenic role in CHC.

METHODS

Lymphocytes from peripheral blood were obtained from 108 patients with CHC and 43 healthy subjects. Immunophenotyping, functional assays, T-cell receptor (TCR) repertoire, and cytotoxic assay of CD38⁺ HLA-DR⁺ CD8⁺ T cells were studied.

RESULTS

The percentage of CD38⁺ HLA-DR⁺ CD8⁺ T cells increased significantly in patients with CHC. These cells expressed higher levels of effector memory and proinflammatory chemokine molecules and showed higher interferon-γ production than CD38^- HLA-DR^- CD8 T cells. They were largely composed of non-HCV-specific CD8⁺ T cells as assessed by HLA-A2-restricted pentamers and next-generation sequencing analysis of the TCR repertoire. In addition, these CD38⁺ HLA-DR⁺ CD8⁺ T cells had strong cytotoxicity, which could be inhibited by anti-DNAX accessory molecule 1, anti-NKG2 family member D, and anti-natural killer NKp30 antibodies. Lastly, the percentage of CD38⁺ HLA-DR⁺ CD8⁺ T cells was significantly associated with liver injury and fibrosis and decreased significantly along with serum alanine aminotransferase normalization after successful direct-acting antiviral treatment.

CONCLUSIONS

The TCR-independent, cytokine-responsive bystander CD38⁺ HLA-DR⁺ CD8⁺ T cells are strongly cytotoxic and play a pathogenic role in patients with CHC.

Targeting PARP11 to avert immunosuppression and improve CAR T therapy in solid tumors

Evasion of antitumor immunity and resistance to therapies in solid tumors are aided by an immunosuppressive tumor microenvironment (TME). We found that TME factors, such as regulatory T cells and adenosine, downregulated type I interferon receptor IFNAR1 on CD8⁺ cytotoxic T lymphocytes (CTLs). These events relied upon poly-ADP ribose polymerase-11 (PARP11), which was induced in intratumoral CTLs and acted as a key regulator of the immunosuppressive TME. Ablation of PARP11 prevented loss of IFNAR1, increased CTL tumoricidal activity and inhibited tumor growth in an IFNAR1-dependent manner. Accordingly, genetic or pharmacologic inactivation of PARP11 augmented the therapeutic benefits of chimeric antigen receptor T cells. Chimeric antigen receptor CTLs engineered to inactivate PARP11 demonstrated a superior efficacy against solid tumors. These findings highlight the role of PARP11 in the immunosuppressive TME and provide a proof of principle for targeting this pathway to optimize immune therapies.

Vitamin D Regulation of Immune Function

PURPOSE OF REVIEW

To review the mechanisms by which vitamin D and its metabolites regulate the immune system to facilitate the ability of the body to prevent and/or treat SARS-CoV2 and other respiratory infections and encourage further research into the role that vitamin D supplementation plays in preventing/treating such infections.

RECENT FINDINGS

Vitamin D deficiency is associated with an increased risk of SARS-CoV2 and other respiratory infections. Clinical trials in general demonstrate that correction of vitamin D deficiency reduces the risk of hospitalization, ICU admission, and death from SARS-CoV2 infection. The airway epithelium and alveolar macrophages express the enzyme, CYP27B1, that produces the active metabolite of vitamin D, 1,25(OH)2D, and the vitamin D receptor, VDR. Vitamin D and its metabolites promote the innate immune response, which provides the first line of defense against viral and bacterial infections while restricting the adaptive immune response, which if unchecked promotes the inflammatory response leading to the acute respiratory distress syndrome and death. The rationale for treating vitamin D deficiency to reduce the risk of SARS-CoV2 infection and supplementing patients with vitamin D early in the course of SARS-CoV2 infection rests primarily on the ability of vitamin D metabolites to promote an effective immune response to the infection.

Mucosal viral infection induces a regulatory T cell activation phenotype distinct from tissue residency in mouse and human tissues

Regulatory T cells (Tregs) mediate immune homeostasis, yet also facilitate nuanced immune responses during infection, balancing pathogen control while limiting host inflammation. Recent studies have identified Treg populations in non-lymphoid tissues that are phenotypically distinct from Tregs in lymphoid tissues (LT), including performance of location-dependent roles. Mucosal tissues serve as critical barriers to microbes while performing unique physiologic functions, so we sought to identify distinct phenotypical and functional aspects of mucosal Tregs in the female reproductive tract. In healthy human and mouse vaginal mucosa, we found that Tregs are highly activated compared to blood or LT Tregs. To determine if this phenotype reflects acute activation or a general signature of vaginal tract (VT)-residency, we infected mice with HSV-2 to discover that VT Tregs express granzyme-B (GzmB) and acquire a VT Treg signature distinct from baseline. To determine the mechanisms that drive GzmB expression, we performed ex vivo assays to reveal that a combination of type-I interferons and interleukin-2 is sufficient for GzmB expression. Together, we highlight that VT Tregs are activated at steady state and become further activated in response to infection; thus, they may exert robust control of local immune responses, which could have implications for mucosal vaccine design.

Functional, transcriptional, and microbial shifts associated with healthy pulmonary aging in rhesus macaques

Older individuals are at increased risk of developing severe respiratory infections. However, our understanding of the impact of aging on the respiratory tract remains limited as samples from healthy humans are challenging to obtain and results can be confounded by variables such as smoking and diet. Here, we carry out a comprehensive cross-sectional study (n = 34 adult, n = 49 aged) to define the consequences of aging on the lung using the rhesus macaque model. Pulmonary function testing establishes similar age and sex differences as humans. Additionally, we report increased abundance of alveolar and infiltrating macrophages and a concomitant decrease in T cells were in aged animals. scRNAseq reveals shifts from GRZMB to IFN expressing CD8⁺ T cells in the lungs. These data provide insight into age-related changes in the lungs’ functional, microbial, and immunological landscape that explain increased prevalence and severity of respiratory diseases in the elderly.

Rhoades et al. describe age-associated functional, microbial, and immunological changes in the lung using the rhesus macaque model. These data will support further studies aimed at designing and testing interventions to mitigate the impact of age-associated shifts in the lung environment to reduce age-related pulmonary disease in the elderly.

IFITM3 Is Upregulated Characteristically in IL-15-Mediated Bystander-Activated CD8+ T Cells during Influenza Infection

In bystander activation, pre-existing memory CD8⁺ T cells unrelated to the infecting microbes are activated by cytokines without cognate Ags. The detailed mechanisms and unique gene signature of bystander activation remain to be elucidated. In this study, we investigated bystander activation of OT-1 memory cells in a mouse model of influenza infection. We found that OT-1 memory cells are activated with upregulation of granzyme B and IFN-γ, during PR8 (A/Puerto Rico/8/1934) infection, and IL-15 is a critical cytokine for bystander activation. In transcriptomic analysis, the IFN-induced gene signature was upregulated in bystander-activated OT-1 memory cells during PR8 infection but not in the presence of TCR stimulation. Among the IFN-induced genes, upregulation of IFN-induced transmembrane protein 3 (IFITM3) distinguished bystander-activated OT-1 memory cells from TCR-activated OT-1 memory cells. Therefore, we reveal that bystander-activated memory CD8⁺ T cells have a unique transcriptomic feature compared with TCR-activated memory CD8⁺ T cells. In particular, IFITM3 upregulation can be used as a marker of bystander-activated memory CD8⁺ T cells at early infection.

Vitamin D regulation of immune function during covid-19

Covid-19 has to date infected a confirmed 275 million people with 5.4 million, now dead, with the count rising every day. Although the virus, SARS-CoV2, causing Covid-19 infects many cells in the body, its infection of the upper and lower respiratory tract (upper airway epithelia and pulmonary alveolar pneumocytes and macrophages) causing what is now called a cytokine storm in the lungs is the major cause of morbidity and mortality. This results from a dysregulation of the innate immune system with an outpouring of proinflammatory cytokines and chemokines leading to abnormal activation of the adaptive immune pathway. Airway epithelia constitutively expresses CYP27B1, the enzyme producing the active vitamin D metabolite, 1,25(OH)2D, and the vitamin D receptor (VDR) for which 1,25(OH)2D is the ligand. Pulmonary alveolar macrophages, on the other hand, are induced to express both CYP27B1 and VDR by various pathogens including viruses and cytokines released from infected epithelia and other immune cells. Although not demonstrated for corona viruses like SARS-CoV2, for other viruses and other respiratory pathogens activation of innate immunity leading to increased local 1,25(OH)2D production has been shown to enhance viral neutralization and clearance while modulating the subsequent proinflammatory response. Whether such will be the case for SARS-CoV2 remains to be seen, but is currently being proposed and investigated. This mini review will discuss some of the mechanisms by which vitamin D may help reduce morbidity and mortality in this devastating pandemic.

Temporal changes in T cell subsets and expansion of cytotoxic CD4+ T cells in the lungs in severe COVID-19

Many studies have been performed in severe COVID-19 on immune cells in the circulation and on cells obtained by bronchoalveolar lavage. Most studies have tended to provide relative information rather than a quantitative view, and it is a combination of approaches by various groups that is helping the field build a picture of the mechanisms that drive severe lung disease. Approaches employed to date have not revealed information on lung parenchymal T cell subsets in severe COVID-19. Therefore, we sought to examine early and late T cell subset alterations in the lungs and draining lymph nodes in severe COVID-19 using a rapid autopsy protocol and quantitative imaging approaches. Here, we have established that cytotoxic CD4+ T cells (CD4 + CTLs) increase in the lungs, draining lymph nodes and blood as COVID-19 progresses. CD4 + CTLs are prominently expanded in the lung parenchyma in severe COVID-19. In contrast CD8+ T cells are not prominent, exhibit increased PD-1 expression, and no obvious increase is seen in the number of Granzyme B+ CD8+ T cells in the lung parenchyma in severe COVID-19. Based on quantitative evidence for re-activation in the lung milieu, CD4 + CTLs may be as likely to drive viral clearance as CD8+ T cells and may also be contributors to lung inflammation and eventually to fibrosis in severe COVID-19.

Setd2 determines distinct properties of intestinal ILC3 subsets to regulate intestinal immunity

Subsets of group 3 innate lymphoid cells (ILC3s) are heterogeneous in development and function and play differential roles in intestinal immunity. Histone modifications are involved in the fate commitment of immune cells, including ILC3s. Here, we report that deletion of Setd2, histone H3K36 methyltransferase, in ILC3s results in increased generation of NKp46⁺ILC3s with enhanced cytotoxic signatures and tumor-suppressive capacity. Meanwhile, Rag1^-/-Rorc^CreSetd2^flox/flox mice have fewer CCR6⁺ILC3s and less defective solitary intestinal lymphoid tissue formation, accompanied by reduced granulocyte-macrophage colony-stimulating factor (GM-CSF) production by NKp46^-ILC3s and decreased CD11b⁺CD103⁺ dendritic cell accumulation. The deficiency of Setd2^-/-NKp46^-ILC3s may contribute to disturbed RORγt⁺Treg homeostasis and intestinal inflammation in Rag1^-/-Rorc^CreSetd2^flox/flox mice upon T cell reconstitution. Setd2 regulates genome accessibility imprinting gene mRNA expression, with a more profound effect on NKp46⁺ILC3s than NKp46^-ILC3s. Therefore, Setd2 determines distinct chromatin status and transcriptomic programs of ILC3 subsets to affect their function and intestinal immunity.

Type I interferons and MAVS signaling are necessary for tissue resident memory CD8+ T cell responses to RSV infection

Respiratory syncytial virus (RSV) can cause bronchiolitis and viral pneumonia in young children and the elderly. Lack of vaccines and recurrence of RSV infection indicate the difficulty in eliciting protective memory immune responses. Tissue resident memory T cells (TRM) can confer protection from pathogen re-infection and, in human experimental RSV infection, the presence of lung CD8+ TRM cells correlates with a better outcome. However, the requirements for generating and maintaining lung TRM cells during RSV infection are not fully understood. Here, we use mouse models to assess the impact of innate immune response determinants in the generation and subsequent expansion of the TRM cell pool during RSV infection. We show that CD8+ TRM cells expand independently from systemic CD8+ T cells after RSV re-infection. Re-infected MAVS and MyD88/TRIF deficient mice, lacking key components involved in innate immune recognition of RSV and induction of type I interferons (IFN-α/β), display impaired expansion of CD8+ TRM cells and reduction in antigen specific production of granzyme B and IFN-γ. IFN-α treatment of MAVS deficient mice during primary RSV infection restored TRM cell expansion upon re-challenge but failed to recover TRM cell functionality. Our data reveal how innate immunity, including the axis controlling type I IFN induction, instructs and regulates CD8+ TRM cell responses to RSV infection, suggesting possible mechanisms for therapeutic intervention.

Shaping the Innate Immune Response Through Post-Transcriptional Regulation of Gene Expression Mediated by RNA-Binding Proteins

Innate immunity is the frontline of defense against infections and tissue damage. It is a fast and semi-specific response involving a myriad of processes essential for protecting the organism. These reactions promote the clearance of danger by activating, among others, an inflammatory response, the complement cascade and by recruiting the adaptive immunity. Any disequilibrium in this functional balance can lead to either inflammation-mediated tissue damage or defense inefficiency. A dynamic and coordinated gene expression program lies at the heart of the innate immune response. This expression program varies depending on the cell-type and the specific danger signal encountered by the cell and involves multiple layers of regulation. While these are achieved mainly via transcriptional control of gene expression, numerous post-transcriptional regulatory pathways involving RNA-binding proteins (RBPs) and other effectors play a critical role in its fine-tuning. Alternative splicing, translational control and mRNA stability have been shown to be tightly regulated during the innate immune response and participate in modulating gene expression in a global or gene specific manner. More recently, microRNAs assisting RBPs and post-transcriptional modification of RNA bases are also emerging as essential players of the innate immune process. In this review, we highlight the numerous roles played by specific RNA-binding effectors in mediating post-transcriptional control of gene expression to shape innate immunity.

Significance of bystander T cell activation in microbial infection

During microbial infection, pre-existing memory CD8⁺ T cells that are not specific for the infecting pathogens can be activated by cytokines without cognate antigens, termed bystander activation. Studies in mouse models and human patients demonstrate bystander activation of memory CD8⁺ T cells, which exerts either protective or detrimental effects on the host, depending on the infection model or disease. Research has elucidated mechanisms underlying the bystander activation of CD8⁺ T cells in terms of the responsible cytokines and the effector mechanisms of bystander-activated CD8⁺ T cells. In this Review, we describe the history of research on bystander CD8⁺ T cell activation as well as evidence of bystander activation. We also discuss the mechanisms and immunopathological roles of bystander activation in various microbial infections.

Infection, inflammation and thrombosis: a review of potential mechanisms mediating arterial thrombosis associated with influenza and severe acute respiratory syndrome coronavirus 2

Thrombosis has long been reported as a potentially deadly complication of respiratory viral infections and has recently received much attention during the global coronavirus disease 2019 pandemic. Increased risk of myocardial infarction has been reported during active infections with respiratory viruses, including influenza and severe acute respiratory syndrome coronavirus 2, which persists even after the virus has cleared. These clinical observations suggest an ongoing interaction between these respiratory viruses with the host's coagulation and immune systems that is initiated at the time of infection but may continue long after the virus has been cleared. In this review, we discuss the epidemiology of viral-associated myocardial infarction, highlight recent clinical studies supporting a causal connection, and detail how the virus' interaction with the host's coagulation and immune systems can potentially mediate arterial thrombosis.

Potentiating Lung Mucosal Immunity Through Intranasal Vaccination

Yearly administration of influenza vaccines is our best available tool for controlling influenza virus spread. However, both practical and immunological factors sometimes result in sub-optimal vaccine efficacy. The call for improved, or even universal, influenza vaccines within the field has led to development of pre-clinical and clinical vaccine candidates that aim to address limitations of current influenza vaccine approaches. Here, we consider the route of immunization as a critical factor in eliciting tissue resident memory (Trm) populations that are not a target of current licensed intramuscular vaccines. Intranasal vaccination has the potential to boost tissue resident B and T cell populations that reside within specific niches of the upper and lower respiratory tract. Within these niches, Trm cells are poised to respond rapidly to pathogen re-encounter by nature of their anatomic localization and their ability to rapidly deliver anti-pathogen effector functions. Unique features of mucosal immunity in the upper and lower respiratory tracts suggest that antigen localized to these regions is required for the elicitation of protective B and T cell immunity at these sites and will need to be considered as an important attribute of a rationally designed intranasal vaccine. Finally, we discuss outstanding questions and areas of future inquiry in the field of lung mucosal immunity.

Functional roles of graft-infiltrating lymphocytes during early-phase post-transplantation in mouse cardiac transplantation models

Immunological behavior of graft-infiltrating lymphocytes (GILs) determines the graft fate (i.e., rejection or acceptance). Nevertheless, the functional alloreactivity and the phenotype of GILs at various times during the early post-transplantation phase have not been fully elucidated. We examined the immunological activities of early-phase GILs using a murine model of cardiac transplantation. GILs from 120-h allografts, but not 72-h allografts, showed robust activation and produced proinflammatory cytokines. In particular, a significant increase in CD69⁺ T-bet⁺ Nur77⁺ T cells was detected in 120-h allografts. Furthermore, isolated GILs were used to reconstitute BALB/c Rag2^-/- γc^-/- (BRG) mice. BRG mice reconstituted with 120-h GILs displayed donor-specific immune reactivity and rejected donor strain cardiac allografts; conversely, 72-h GILs exhibited weak anti-donor reactivity and did not reject allografts. These findings were confirmed by re-transplantation of cardiac allografts into BRG mice at 72-h post-transplantation. Re-transplanted allografts continued to function for >100 days, despite the presence of CD3⁺ GILs. In conclusion, the immunological behavior of GILs considerably differs over time during the early post-transplantation phase. A better understanding of the functional role of early-phase GILs may clarify the fate determination process in the graft-site microenvironment.

Toward a universal influenza virus vaccine: Some cytokines may fulfill the request

The influenza virus annually causes widespread damages to the health and economy of the global community. Vaccination is currently the most crucial strategy in reducing the number of patients. Genetic variations, the high diversity of pandemic viruses, and zoonoses make it challenging to select suitable strains for annual vaccine production. If new pandemic viruses emerge, it will take a long time to produce a vaccine according to the new strains. In the present study, intending to develop a universal influenza vaccine, new bicistronic DNA vaccines were developed that expressed NP or NPm antigen with one of modified IL-18/ IL-17A/ IL-22 cytokine adjuvants. NPm is a mutant form of the antigen that has the ability for cytoplasmic accumulation. In order to investigate and differentiate the role of each of the components of Th1, Th2, Th17, and Treg cellular immune systems in the performance of vaccines, Treg competent and Treg suppressed mouse groups were used. Mice were vaccinated with Foxp3-FC immunogen to produce Treg suppressed mouse groups. The potential of the vaccines to stimulate the immune system was assessed by IFN-γ/IL-17A Dual FluoroSpot. The vaccine's ability to induce humoral immune response was determined by measuring IgG1, IgG2a, and IgA-specific antibodies against the antigen. Kinetics of Th1, Th2, and Th17 cellular immune responses after vaccination, were assessed by evaluating the expression changes of IL-17A, IFN-γ, IL-18, IL-22, IL-4, and IL-2 cytokines by semi-quantitative real-time RT-PCR. To assess the vaccines' ability to induce heterosubtypic immunity, challenge tests with homologous and heterologous viruses were performed and then the virus titer was measured in the lungs of animals. Evaluation of the data obtained from this study showed that the DNA-vaccines coding NPm have more ability to induces a potent cross-cellular immune response and protective immunity than DNA-vaccines coding NP. Although the use of IL-18/ IL-17A/ IL-22 genetic adjuvants enhanced immune responses and protective immunity, Administration of NPm in combination with modified IL-18 (Igk-mIL18-IgFC) induced the most effective immunity in Treg competent mice group.

Resident memory CD8+ T cells in regional lymph nodes mediate immunity to metastatic melanoma

The nature of the anti-tumor immune response changes as primary tumors progress and metastasize. We investigated the role of resident memory (Trm) and circulating memory (Tcirm) cells in anti-tumor responses at metastatic locations using a mouse model of melanoma-associated vitiligo. We found that the transcriptional characteristics of tumor-specific CD8+ T cells were defined by the tissue of occupancy. Parabiosis revealed that tumor-specific Trm and Tcirm compartments persisted throughout visceral organs, but Trm cells dominated lymph nodes (LNs). Single-cell RNA-sequencing profiles of Trm cells in LN and skin were distinct, and T cell clonotypes that occupied both tissues were overwhelmingly maintained as Trm in LNs. Whereas Tcirm cells prevented melanoma growth in the lungs, Trm afforded long-lived protection against melanoma seeding in LNs. Expanded Trm populations were also present in melanoma-involved LNs from patients, and their transcriptional signature predicted better survival. Thus, tumor-specific Trm cells persist in LNs, restricting metastatic cancer.

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.

Immunoregulatory Functions of Interferons During Genital HSV-2 Infection

Herpes simplex virus type 2 (HSV-2) infection is one of the most prevalent sexually transmitted infections that disproportionately impacts women worldwide. Currently, there are no vaccines or curative treatments, resulting in life-long infection. The mucosal environment of the female reproductive tract (FRT) is home to a complex array of local immune defenses that must be carefully coordinated to protect against genital HSV-2 infection, while preventing excessive inflammation to prevent disease symptoms. Crucial to the defense against HSV-2 infection in the FRT are three classes of highly related and integrated cytokines, type I, II, and III interferons (IFN). These three classes of cytokines control HSV-2 infection and reduce tissue damage through a combination of directly inhibiting viral replication, as well as regulating the function of resident immune cells. In this review, we will examine how interferons are induced and their critical role in how they shape the local immune response to HSV-2 infection in the FRT.

The Ugly Duckling Turned to Swan: A Change in Perception of Bystander-Activated Memory CD8 T Cells

Memory T cells (T_mem) rapidly mount Ag-specific responses during pathogen reencounter. However, T_mem also respond to inflammatory cues in the absence of an activating TCR signal, a phenomenon termed bystander activation. Although bystander activation was first described over 20 years ago, the physiological relevance and the consequences of T cell bystander activation have only become more evident in recent years. In this review, we discuss the scenarios that trigger CD8 T_mem bystander activation including acute and chronic infections that are either systemic or localized, as well as evidence for bystander CD8 T_mem within tumors and following vaccination. We summarize the possible consequences of bystander activation for the T cell itself, the subsequent immune response, and the host. We highlight when T cell bystander activation appears to benefit or harm the host and briefly discuss our current knowledge gaps regarding regulatory signals that can control bystander activation.

Risk factors for adverse outcomes of COVID-19 patients: Possible basis for diverse responses to the novel coronavirus SARS-CoV-2

Severe coronavirus disease 2019 (COVID-19) caused by the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) is characterized by an unpredictable disease course, with variable presentations of different organ systems. The clinical manifestations of COVID-19 are highly variable ranging from mild presentations to severe, life-threatening symptoms and the wide individual variability may be due to the broad heterogeneity in the underlying pathologies. There is no doubt that early management may have a major influence on the outcome. This led the scientists to search for ways to monitor disease progression or to predict outcomes in COVID-19. Although it is not yet possible to predict who will progress to the severe forms or in what time, numerous prospective and longitudinal studies represent the evidence for determining the potential immunological risk factors of COVID-19 critical disease and death. The kinetics and breadth of immune responses during COVID-19 appear to follow a trend which is consistent to the predominant pathological alterations. Recent publications have used these biomarkers to help identify patients who will develop the severe acute COVID-19. Of particular interest is the relationship between the kinetics of peripheral leukocytes and clinical progress of the disease in COVID-19. Although research is ongoing in this area, we present details about the current status of the evaluation. Understanding of the COVID-19 related alterations of the innate and adaptive immune responses may help to promote the vaccine development and immunological interventions.

Induction of T Cell Senescence by Cytokine Induced Bystander Activation

As people around the world continue to live longer, maintaining a good quality of life is of increasing importance. The COVID-19 pandemic revealed that the elderly are disproportionally vulnerable to infectious diseases and Immunosenescence plays a critical role in that. An ageing immune system influences the conventional activity of T cells which are at the forefront of eliminating harmful foreign antigens. With ageing, unconventional end-stage T cells, that exhibit a senescent phenotype, amass. These senescent T cells deviate from T cell receptor (TCR) signaling toward natural killer (NK) activity. The transition toward innate immune cell function from these adaptor T cells impacts antigen specificity, contributing to increased susceptibility of infection in the elderly. The mechanism by which senescent T cells arise remains largely unclear however in this review we investigate the part that bystander activation plays in driving the change in function of T cells with age. Cytokine-induced bystander activation may offer a plausible explanation for the induction of NK-like activity and senescence in T cells. Further understanding of these specific NK-like senescent T cells allows us to identify the benefits and detriments of these cells in health and disease which can be utilized or regulated, respectively. This review discusses the dynamic of senescent T cells in adopting NK-like T cells and the implications that has in an infectious disease context, predominately in the elderly.

Relevance of vitamin D3 in COVID-19 infection

SARS-CoV-2 virus, the main culprit for COVID-19 disaster, has triggered a gust of curiosity both in the mechanism of action of this infection as well as potential risk factors for disease generation and regimentation. The prime focus of the present review, which is basically a narrative one, is in utilizing the current concepts of vitamin D₃ as an agent with myriad functions, one of them being immunocompetence and a promising weapon for both innate and adaptive immunity against COVID-19 infection. Some of the manifestations of SARS-CoV-2 virus such as Acute Respiratory Distress Syndrome (ARDS) overlap with the pathophysiological effects that are overcome due to already established role of vitamin D₃ e.g., amelioration of cytokine outburst. Additionally, the cardiovascular complications due to COVID-19 infection may also be connected to vitamin D₃ levels and the activity of its active forms. Eventually, we summarise the clinical, observational and epidemiological data of the respiratory diseases including COVID-19 disease and try to bring its association with the potential role of vitamin D₃, in particular, the activity of its active forms, circulating levels and its supplementation, against dissemination of this disease.

Rhinovirus-induced Human Lung Tissue Responses Mimic COPD and Asthma Gene Signatures

Human rhinovirus (RV) is a major risk factor for chronic obstructive pulmonary disease (COPD) and asthma exacerbations. The exploration of RV pathogenesis has been hampered by a lack of disease-relevant model systems. We performed a detailed characterization of host responses to RV infection in human lung tissue ex vivo and investigated whether these responses are disease relevant for patients with COPD and asthma. In addition, impact of the viral replication inhibitor rupintrivir was evaluated. Human precision-cut lung slices (PCLS) were infected with RV1B with or without rupintrivir. At Days 1 and 3 after infection, RV tissue localization, tissue viability, and viral load were determined. To characterize host responses to infection, mediator and whole genome analyses were performed. RV successfully replicated in PCLS airway epithelial cells and induced both antiviral and proinflammatory cytokines such as IFNα2a, CXCL10, CXCL11, IFN-γ, TNFα, and CCL5. Genomic analyses revealed that RV not only induced antiviral immune responses but also triggered changes in epithelial cell–associated pathways. Strikingly, the RV response in PCLS was reflective of gene expression changes described in patients with COPD and asthma. Although RV-induced host immune responses were abrogated by rupintrivir, RV-triggered epithelial processes were largely refractory to antiviral treatment. Detailed analysis of RV-infected human PCLS and comparison with gene signatures of patients with COPD and asthma revealed that the human RV PCLS model represents disease-relevant biological mechanisms that can be partially inhibited by a well-known antiviral compound and provide an outstanding opportunity to evaluate novel therapeutics.

Post-transcriptional control of T-cell cytokine production: Implications for cancer therapy

As part of the adaptive immune system, T cells are vital for the eradication of infected and malignantly transformed cells. To perform their protective function, T cells produce effector molecules that are either directly cytotoxic, such as granzymes, perforin, interferon-γ and tumour necrosis factor α, or attract and stimulate (immune) cells, such as interleukin-2. As these molecules can also induce immunopathology, tight control of their production is required. Indeed, inflammatory cytokine production is regulated on multiple levels. Firstly, locus accessibility and transcription factor availability and activity determine the amount of mRNA produced. Secondly, post-transcriptional mechanisms, influencing mRNA splicing/codon usage, stability, decay, localization and translation rate subsequently determine the amount of protein that is produced. In the immune suppressive environments of tumours, T cells gradually lose the capacity to produce effector molecules, resulting in tumour immune escape. Recently, the role of post-transcriptional regulation in fine-tuning T-cell effector function has become more appreciated. Furthermore, several groups have shown that exhausted or dysfunctional T cells from cancer patients or murine models possess mRNA for inflammatory mediators, but fail to produce effector molecules, hinting that post-transcriptional events also play a role in hampering tumour-infiltrating lymphocyte effector function. Here, the post-transcriptional regulatory events governing T-cell cytokine production are reviewed, with a specific focus on the importance of post-transcriptional regulation in anti-tumour responses. Furthermore, potential approaches to circumvent tumour-mediated dampening of T-cell effector function through the (dis)engagement of post-transcriptional events are explored, such as CRISPR/Cas9-mediated genome editing or chimeric antigen receptors.

Aging and Interferons: Impacts on Inflammation and Viral Disease Outcomes

As highlighted by the COVID-19 global pandemic, elderly individuals comprise the majority of cases of severe viral infection outcomes and death. A combined inability to control viral replication and exacerbated inflammatory immune activation in elderly patients causes irreparable immune-mediated tissue pathology in response to infection. Key to these responses are type I, II, and III interferons (IFNs), which are involved in inducing an antiviral response, as well as controlling and suppressing inflammation and immunopathology. IFNs support monocyte/macrophage-stimulated immune responses that clear infection and promote their immunosuppressive functions that prevent excess inflammation and immune-mediated pathology. The timing and magnitude of IFN responses to infection are critical towards their immunoregulatory functions and ability to prevent immunopathology. Aging is associated with multiple defects in the ability of macrophages and dendritic cells to produce IFNs in response to viral infection, leading to a dysregulation of inflammatory immune responses. Understanding the implications of aging on IFN-regulated inflammation will give critical insights on how to treat and prevent severe infection in vulnerable individuals. In this review, we describe the causes of impaired IFN production in aging, and the evidence to suggest that these impairments impact the regulation of the innate and adaptive immune response to infection, thereby causing disease pathology.

Mammalian and Avian Host Cell Influenza A Restriction Factors

The threat of a new influenza pandemic is real. With past pandemics claiming millions of lives, finding new ways to combat this virus is essential. Host cells have developed a multi-modular system to detect incoming pathogens, a phenomenon called sensing. The signaling cascade triggered by sensing subsequently induces protection for themselves and their surrounding neighbors, termed interferon (IFN) response. This response induces the upregulation of hundreds of interferon-stimulated genes (ISGs), including antiviral effectors, establishing an antiviral state. As well as the antiviral proteins induced through the IFN system, cells also possess a so-called intrinsic immunity, constituted of antiviral proteins that are constitutively expressed, creating a first barrier preceding the induction of the interferon system. All these combined antiviral effectors inhibit the virus at various stages of the viral lifecycle, using a wide array of mechanisms. Here, we provide a review of mammalian and avian influenza A restriction factors, detailing their mechanism of action and in vivo relevance, when known. Understanding their mode of action might help pave the way for the development of new influenza treatments, which are absolutely required if we want to be prepared to face a new pandemic.

Immune suppressive activity of myeloid-derived suppressor cells in cancer requires inactivation of the type I interferon pathway

Myeloid-derived suppressor cells (MDSC) are pathologically activated neutrophils and monocytes with potent immune suppressive activity. These cells play an important role in accelerating tumor progression and undermining the efficacy of anti-cancer therapies. The natural mechanisms limiting MDSC activity are not well understood. Here, we present evidence that type I interferons (IFN1) receptor signaling serves as a universal mechanism that restricts acquisition of suppressive activity by these cells. Downregulation of the IFNAR1 chain of this receptor is found in MDSC from cancer patients and mouse tumor models. The decrease in IFNAR1 depends on the activation of the p38 protein kinase and is required for activation of the immune suppressive phenotype. Whereas deletion of IFNAR1 is not sufficient to convert neutrophils and monocytes to MDSC, genetic stabilization of IFNAR1 in tumor bearing mice undermines suppressive activity of MDSC and has potent antitumor effect. Stabilizing IFNAR1 using inhibitor of p38 combined with the interferon induction therapy elicits a robust anti-tumor effect. Thus, negative regulatory mechanisms of MDSC function can be exploited therapeutically.

Polymeric Pathogen-Like Particles-Based Combination Adjuvants Elicit Potent Mucosal T Cell Immunity to Influenza A Virus

Eliciting durable and protective T cell-mediated immunity in the respiratory mucosa remains a significant challenge. Polylactic-co-glycolic acid (PLGA)-based cationic pathogen-like particles (PLPs) loaded with TLR agonists mimic biophysical properties of microbes and hence, simulate pathogen-pattern recognition receptor interactions to safely and effectively stimulate innate immune responses. We generated micro particle PLPs loaded with TLR4 (glucopyranosyl lipid adjuvant, GLA) or TLR9 (CpG) agonists, and formulated them with and without a mucosal delivery enhancing carbomer-based nanoemulsion adjuvant (ADJ). These adjuvants delivered intranasally to mice elicited high numbers of influenza nucleoprotein (NP)-specific CD8+ and CD4+ effector and tissue-resident memory T cells (T_RMs) in lungs and airways. PLPs delivering TLR4 versus TLR9 agonists drove phenotypically and functionally distinct populations of effector and memory T cells. While PLPs loaded with CpG or GLA provided immunity, combining the adjuvanticity of PLP-GLA and ADJ markedly enhanced the development of airway and lung T_RMs and CD4 and CD8 T cell-dependent immunity to influenza virus. Further, balanced CD8 (Tc1/Tc17) and CD4 (Th1/Th17) recall responses were linked to effective influenza virus control. These studies provide mechanistic insights into vaccine-induced pulmonary T cell immunity and pave the way for the development of a universal influenza and SARS-CoV-2 vaccines.

Influenza-Specific Lung-Resident Memory CD8+ T Cells

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

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

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

Toll-like receptor-2/7-mediated T cell activation: An innate potential to augment CD8+ T cell cytokine production

CD8⁺ T cells are critical to combat pathogens and eradicate malignantly transformed cells. To exert their effector function and kill target cells, T cells produce copious amounts of effector molecules, including the pro-inflammatory cytokines interferon γ, tumour necrosis factor α and interleukin 2. TCR triggering alone is sufficient to induce cytokine secretion by effector and memory CD8⁺ T cells. However, T cells can also be directly activated by pathogen-derived molecules, such as through the triggering of Toll-like receptors (TLRs). TLR-mediated pathogen sensing by T cells results in the production of only interferon γ. However, in particular when the antigen load on target cells is low, or when TCR affinity to the antigen is limited, antigen-experienced T cells can benefit from costimulatory signals. TLR stimulation can also function in a costimulatory fashion to enhance TCR triggering. Combined TCR and TLR triggering enhances the proliferation, memory formation and effector function of T cells, resulting in enhanced production of interferon γ, tumour necrosis factor α and interleukin 2. Therefore, TLR ligands or the exploitation of TLR signalling could provide novel opportunities for immunotherapy approaches. In fact, CD19 CAR T cells bearing an intracellular TLR2 costimulatory domain were recently employed to treat cancer patients in a clinical trial. Here, the current knowledge regarding TLR2/7 stimulation-induced cytokine production by T cells is reviewed. Specifically, the transcriptional and post-transcriptional pathways engaged upon TLR2/7 sensing and TLR2/7 signalling are discussed. Finally, the potential uses of TLRs to enhance the anti-tumor effector function of T cells are explored.

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

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

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CD8⁺ Trm cells downregulate IL-18 receptor during differentiation

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

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

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