CD69 acts downstream of interferon-alpha/beta to inhibit S1P1 and lymphocyte egress from lymphoid organs

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

Dual targeting of lymphocyte homing and retention through α4β7 and αEβ7 inhibition in inflammatory bowel disease

Anti-integrins are therapeutically effective for inflammatory bowel disease, yet the relative contribution of α4β7 and αEβ7 to gut lymphocyte trafficking is not fully elucidated. Here, we evaluate the effect of α4β7 and αEβ7 blockade using a combination of murine models of gut trafficking and longitudinal gene expression analysis in etrolizumab-treated patients with Crohn's disease (CD). Dual blockade of α4β7 and αEβ7 reduces CD8+ T cell accumulation in the gut to a greater extent than blockade of either integrin alone. Anti-αEβ7 reduces epithelial:T cell interactions and promotes egress of activated T cells from the mucosa into lymphatics. Inflammatory gene expression is greater in human intestinal αEβ7+ T cells. Etrolizumab-treated patients with CD display a treatment-specific reduction in inflammatory and cytotoxic intraepithelial lymphocytes (IEL) genes. Concurrent blockade of α4β7 and αEβ7 promotes reduction of cytotoxic IELs and inflammatory T cells in the gut mucosa through a stepwise inhibition of intestinal tissue entry and retention.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

The role of lymphatics in intestinal inflammation

The lymphatic vasculature returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays a major role in lipid absorption and immune cell trafficking. Lymphatic vascular defects have been revealed in inflammatory diseases, Crohn's disease, obesity, cardiovascular disease, hypertension, atherosclerosis, and Alzheimer's disease. In this review, we discuss lymphatic structure and function within the gut, such as dietary lipid absorption, the transport of antigens and immune cells to lymph nodes, peripheral tolerance, and lymphocyte migration from secondary lymphoid tissues to the lymphatics and the immune systems. We also discuss the potential roles of these lymphatics on the pathophysiology of inflammatory bowel disease and as new targets for therapeutic management.

T cells selectively filter oscillatory signals on the minutes timescale

T cells experience complex temporal patterns of stimulus via receptor-ligand-binding interactions with surrounding cells. From these temporal patterns, T cells are able to pick out antigenic signals while establishing self-tolerance. Although features such as duration of antigen binding have been examined, our understanding of how T cells interpret signals with different frequencies or temporal stimulation patterns is relatively unexplored. We engineered T cells to respond to light as a stimulus by building an optogenetically controlled chimeric antigen receptor (optoCAR). We discovered that T cells respond to minute-scale oscillations of activation signal by stimulating optoCAR T cells with tunable pulse trains of light. Systematically scanning signal oscillation period from 1 to 150 min revealed that expression of CD69, a T cell activation marker, reached a local minimum at a period of ∼25 min (corresponding to 5 to 15 min pulse widths). A combination of inhibitors and genetic knockouts suggest that this frequency filtering mechanism lies downstream of the Erk signaling branch of the T cell response network and may involve a negative feedback loop that diminishes Erk activity. The timescale of CD69 filtering corresponds with the duration of T cell encounters with self-peptide-presenting APCs observed via intravital imaging in mice, indicating a potential functional role for temporal filtering in vivo. This study illustrates that the T cell signaling machinery is tuned to temporally filter and interpret time-variant input signals in discriminatory ways.

Motility Matters: How CD8+ T-Cell Trafficking Influences Effector and Memory Cell Differentiation

Immunological memory is a hallmark of adaptive immunity that confers long-lasting protection from reinfections. Memory CD8⁺ T cells provide protection by actively scanning for their cognate antigen and migrating into inflamed tissues. Trafficking patterns of CD8⁺ T cells are also a major determinant of cell fate outcomes during differentiation into effector and memory cell states. CD8⁺ T-cell trafficking must therefore be dynamically and tightly regulated to ensure that CD8⁺ T cells arrive at the correct locations and differentiate to acquire appropriate effector functions. This review aims to discuss the importance of CD8⁺ T-cell trafficking patterns in regulating effector and memory differentiation, maintenance, and reactivation.

Emerging role of Tissue Resident Memory T cells in vitiligo: From pathogenesis to therapeutics

Vitiligo is an acquired depigmenting disorder which affects both skin and mucous membranes and autoimmunity has been strongly suggested to play a role in loss of melanocytes. The recurrence of skin macules at the same sites where they were observed prior to the treatment, suggests the existence of Tissue Resident Memory T cells (TRMs) that persist within the skin or peripheral tissues with a longer survivability. Emerging studies have shown that reactivation of these skin TRMs results into autoreactive TRM cells in various autoimmune diseases including vitiligo. This review focuses on different subsets (CD8⁺ TRMs and CD4⁺ TRMs) of TRM cells, their retention and survivability in the skin along with their pathomechanisms leading to melanocyte death and progression of vitiligo. In addition, the review describes the TRM cells as potential targets for developing effective therapeutics of vitiligo.

Multi-Omics Integrative Bioinformatics Analyses Reveal Long Non-coding RNA Modulates Genomic Integrity via Competing Endogenous RNA Mechanism and Serves as Novel Biomarkers for Overall Survival in Lung Adenocarcinoma

Long non-coding RNA (lncRNA) plays a crucial role in modulating genome instability, immune characteristics, and cancer progression, within which genome instability was identified as a critical regulator in tumorigenesis and tumor progression. However, the existing accounts fail to detail the regulatory role of genome instability in lung adenocarcinoma (LUAD). We explored the clinical value of genome instability-related lncRNA in LUAD with multi-omics bioinformatics analysis. We extracted the key genome instability-related and LUAD-related gene modules using weighted gene co-expression network analysis (WGCNA) and established a competing endogenous RNA (ceRNA) network using four lncRNAs (LINC01224, LINC00346, TRPM2-AS, and CASC9) and seven target mRNAs (CCNF, PKMYT1, GCH1, TK1, PSAT1, ADAM33, and DDX11). We found that LINC01224 is primarily located in the cytoplasm and that LINC00346 and TRPM2-AS are primarily located in the nucleus (CASC9 unknown). We found that all 11 genes were positively related to tumor mutational burden and involve drug resistance, cancer stemness, and tumor microenvironment infiltration. Additionally, an eight-lncRNA genome instability-related lncRNA signature was established and validated, predicting the overall survival and immunotherapy outcomes in LUAD. To conclude, we discovered that sponging microRNA, genome instability-related lncRNA functions as ceRNA, modulating genomic integrity. This research provides clinical references for LUAD immunotherapy and prognosis and interprets a potential genome instability-related ceRNA regulatory network in which LINC01224-miR-485-5p/miR-29c-3p-CCNF-RRM2 and LINC01224-miR485-5p-PKMYT1-CDK1 axes were the most promising pathways. However, the potential mechanisms underlying our findings still need biological validation through in vitro and in vivo experiments.

A biliary immune landscape map of primary sclerosing cholangitis reveals a dominant network of neutrophils and tissue-resident T cells

The human biliary system, a mucosal barrier tissue connecting the liver and intestine, is an organ often affected by serious inflammatory and malignant diseases. Although these diseases are linked to immunological processes, the biliary system represents an unexplored immunological niche. By combining endoscopy-guided sampling of the biliary tree with a high-dimensional analysis approach, comprehensive mapping of the human biliary immunological landscape in patients with primary sclerosing cholangitis (PSC), a severe biliary inflammatory disease, was conducted. Major differences in immune cell composition in bile ducts compared to blood were revealed. Furthermore, biliary inflammation in patients with PSC was characterized by high presence of neutrophils and T cells as compared to control individuals without PSC. The biliary T cells displayed a CD103⁺CD69⁺ effector memory phenotype, a combined gut and liver homing profile, and produced interleukin-17 (IL-17) and IL-22. Biliary neutrophil infiltration in PSC associated with CXCL8, possibly produced by resident T cells, and CXCL16 was linked to the enrichment of T cells. This study uncovers the immunological niche of human bile ducts, defines a local immune network between neutrophils and biliary-resident T cells in PSC, and provides a resource for future studies of the immune responses in biliary disorders.

Healthy and Patient Type 2 Innate Lymphoid Cells are Differently Affected by in vitro Culture Conditions

Background

Type 2 innate lymphoid cells (ILC2s) have emerged as key players in the development of type 2 driven diseases such as allergy and asthma. Due to their low number in the circulation, in vitro expansion is needed to unravel their mechanisms of action.

Purpose

The aim of this study is to assess the impact of different culture conditions and address whether the method of expansion may distinctly affect healthy donor or patient-derived ILC2s.

Methods

Here, we described the impact of six different culture conditions on the proliferation, phenotype and function of human ILC2s freshly obtained from healthy donors (healthy ILC2s) and allergic patients (patient ILC2s).

Results

We showed that the cytokine cocktail or the PHA induced the highest proliferation of healthy ILC2s and patient ILC2s, respectively. We observed that the stromal cells OP9, used as ILC2 feeders, did not boost their proliferation, but impaired the activation marker expression and the function of patient ILC2s. Furthermore, we demonstrated that the culture conditions differently impacted the activation state of c-Kit^high and c-Kit^low ILC2s, in both healthy donors and allergic patients. Last, we also observed that ILC2s expanded only with IL-2 and IL-7 were the most prone to secrete IL-5 and IL-13 upon IL-33 stimulation. In contrast, in patients, the addition of OP9 cells during the expansion restrained their type 2 cytokine secretory functions.

Conclusion

This report highlights that culture conditions distinctly impacted on the healthy or patient ILC2 behavior, with important consequences for their study in disease settings.

Immunological Approaches to the Treatment of New Coronavirus Infection (Review)

The pandemic of the new coronavirus infection (COVID-19) caused by the SARS-CoV-2 virus has spread all over the world. The large amount of information that appears every day requires comprehension and systematization. The immunological aspects of the virus-host interaction are the core issues in the effective treatment and prevention of COVID-19' development. The review analyzes the known pathways of the viral invasion and evasion, the mechanisms of the cytokine storm, endothelial damage, and hypercoagulability associated with SARS-CoV-2 infection. Clinical data from previous SARS and MERS epidemics is discussed here. We also address the therapeutic approaches based on the basic knowledge of immune response and the blood cells' immune functions, as well as the ways to reduce their hyperactivation. The use of interferon therapy, anti-inflammatory therapy, anti-cytokine therapy, neutralizing antibodies, convalescent plasma, and mesenchymal stem cells, as well as prophylactic vaccines, is discussed.

Protective function and durability of mouse lymph node-resident memory CD8+ T cells

Protective lung tissue-resident memory CD8⁺T cells (Trm) form after influenza A virus (IAV) infection. We show that IAV infection of mice generates CD69⁺CD103⁺and other memory CD8⁺T cell populations in lung-draining mediastinal lymph nodes (mLNs) from circulating naive or memory CD8⁺T cells. Repeated antigen exposure, mimicking seasonal IAV infections, generates quaternary memory (4M) CD8⁺T cells that protect mLN from viral infection better than 1M CD8⁺T cells. Better protection by 4M CD8⁺T cells associates with enhanced granzyme A/B expression and stable maintenance of mLN CD69⁺CD103⁺4M CD8⁺T cells, vs the steady decline of CD69⁺CD103⁺1M CD8⁺T cells, paralleling the durability of protective CD69⁺CD103⁺4M vs 1M in the lung after IAV infection. Coordinated upregulation in canonical Trm-associated genes occurs in circulating 4M vs 1M populations without the enrichment of canonical downregulated Trm genes. Thus, repeated antigen exposure arms circulating memory CD8⁺T cells with enhanced capacity to form long-lived populations of Trm that enhance control of viral infections of the mLN.

The Bone Marrow as Sanctuary for Plasma Cells and Memory T-Cells: Implications for Adaptive Immunity and Vaccinology

The bone marrow (BM) is key to protective immunological memory because it harbors a major fraction of the body’s plasma cells, memory CD4+ and memory CD8+ T-cells. Despite its paramount significance for the human immune system, many aspects of how the BM enables decade-long immunity against pathogens are still poorly understood. In this review, we discuss the relationship between BM survival niches and long-lasting humoral immunity, how intrinsic and extrinsic factors define memory cell longevity and show that the BM is also capable of adopting many responsibilities of a secondary lymphoid organ. Additionally, with more and more data on the differentiation and maintenance of memory T-cells and plasma cells upon vaccination in humans being reported, we discuss what factors determine the establishment of long-lasting immunological memory in the BM and what we can learn for vaccination technologies and antigen design. Finally, using these insights, we touch on how this holistic understanding of the BM is necessary for the development of modern and efficient vaccines against the pandemic SARS-CoV-2.

Maintenance of quiescent immune memory in the bone marrow

The adaptive immune system has the important ability to generate and maintain a memory for antigens once encountered. Recent progress in understanding the organization of immunological memory has challenged the established paradigm of maintenance of memory by restless, circulating, and "homeostatically" proliferating lymphocytes. Among other tissues, the bone marrow has emerged as a preferred resting place for memory lymphocytes providing both local and systemic long-term protection. Why the bone marrow? There, mesenchymal stromal cells provide a privileged environment for quiescent memory B and T lymphocytes, the protagonists of secondary immune reactions, and for memory plasma cells providing persistent humoral immunity. In this review, we discuss the dedicated role of the bone marrow for the maintenance of memory lymphocytes and its implications for immunological memory.

Robust CD8+ T-cell proliferation and diversification after mogamulizumab in patients with adult T-cell leukemia-lymphoma

Skin-related adverse events (AEs) occur frequently in adult T-cell leukemia-lymphoma (ATL) patients treated with mogamulizumab, a humanized anti-CCR4 monoclonal antibody. This study was undertaken to elucidate the mechanisms of mogamulizumab-induced skin-related AEs. We analyzed the T-cell receptor β chain repertoire in ATL patients' peripheral blood mononuclear cells (PBMCs) before and after mogamulizumab. Skin-related AEs were present in 16 patients and were absent in 8 patients. Additionally, we included 11 patients before and after chemotherapy without mogamulizumab. Immune-related gene expression in PBMCs before and after mogamulizumab was also assessed (n = 24). Mogamulizumab treatment resulted in CCR4+ T-cell depletion, and the consequent lymphopenia provoked homeostatic CD8+ T-cell proliferation, as evidenced by increased expressions of CD8B and CD8A, which were significantly greater in patients with skin-related AEs than in those without them. We hypothesize that proliferation is driven by the engagement of self-antigens, including skin-related antigens, in the face of regulatory T-cell depletion. Together with the observed activated antigen presentation function, this resulted in T-cell diversification that was significantly greater in patients with skin-related AEs than in those without. We found that the CD8+ T cells that proliferated and diversified after mogamulizumab treatment were almost entirely newly emerged clones. There was an inverse relationship between the degree of CCR4+ T-cell depletion and increased CD8+ T-cell proliferation and diversification. Thus, lymphocyte-depleting mogamulizumab treatment provokes homeostatic CD8+ T-cell proliferation predominantly of newly emerging clones, some of which could have important roles in the pathogenesis of mogamulizumab-induced skin-related AEs.

CD8+ T cell self-tolerance permits responsiveness but limits tissue damage

Self-specific CD8⁺T cells can escape clonal deletion, but the properties and capabilities of such cells in a physiological setting are unclear. We characterized polyclonal CD8⁺ T cells specific for the melanocyte antigen tyrosinase-related protein 2 (Trp2) in mice expressing or lacking this enzyme (due to deficiency in Dct, which encodes Trp2). Phenotypic and gene expression profiles of pre-immune Trp2/K^b-specific cells were similar; the size of this population was only slightly reduced in wild-type (WT) compared to Dct-deficient (Dct^-/-) mice. Despite comparable initial responses to Trp2 immunization, WT Trp2/K^b-specific cells showed blunted expansion and less readily differentiated into a CD25⁺proliferative population. Functional self-tolerance clearly emerged when assessing immunopathology: adoptively transferred WT Trp2/K^b-specific cells mediated vitiligo much less efficiently. Hence, CD8⁺ T cell self-specificity is poorly predicted by precursor frequency, phenotype, or even initial responsiveness, while deficient activation-induced CD25 expression and other gene expression characteristics may help to identify functionally tolerant cells.

COVID-19 in Immunosuppressed Children

Following the spread of the SARS-CoV-2 infection and coronavirus disease 2019 (COVID-19) to a global pandemic, concerns have arisen for the disease impact in at-risk populations, especially in immunocompromised hosts. On the other hand, clinical studies have clarified that the COVID-19 clinical burden is mostly due to over-inflammation and immune-mediated multiorgan injury. This has led to downsizing the role of immunosuppression as a determinant of outcome, and early reports confirm the hypothesis that patients undergoing immunosuppressive treatments do not have an increased risk of severe COVID-19 with respect to the general population. Intriguingly, SARS-CoV-2 natural reservoirs, such as bats and mice, have evolved mechanisms of tolerance involving selection of genes optimizing viral clearance through interferon type I and III responses and also dampening inflammasome response and cytokine expression. Children exhibit resistance to COVID-19 severe manifestations, and age-related features in innate and adaptive response possibly explaining this difference are discussed. A competent recognition by the innate immune system and controlled pro-inflammatory signaling seem to be the pillars of an effective response and the premise for pathogen clearance in SARS-CoV-2 infection. Immunosuppression-if not associated with other elements of fragility-do not represent per se an obstacle to this competent/tolerant phenotype in children. Several reports confirm that children receiving immunosuppressive medications have similar clinical involvement and outcomes as the pediatric general population, indicating that maintenance treatments should not be interrupted in suspect or confirmed SARS-CoV-2 infection.

Acquisition of optimal TFH cell function is defined by specific molecular, positional, and TCR dynamic signatures

The development of follicular helper CD4 T (TFH) cells is a dynamic process resulting in a heterogenous pool of TFH subsets. However, the cellular and molecular determinants of this heterogeneity and the possible mechanistic links between them is not clear. We found that human TFH differentiation is associated with significant changes in phenotypic, chemokine, functional, metabolic and transcriptional profile. Furthermore, this differentiation was associated with distinct positioning to follicular proliferating B cells. Single-cell T cell receptor (TCR) clonotype analysis indicated the transitioning toward PD-1^hiCD57^hi phenotype. Furthermore, the differentiation of TFH cells was associated with significant reduction in TCR level and drastic changes in immunological synapse formation. TFH synapse lacks a tight cSMAC (central supra molecular activation Cluster) but displays the TCR in peripheral microclusters, which are potentially advantageous in the ability of germinal center (GC) B cells to receive necessary help. Our data reveal significant aspects of human TFH heterogeneity and suggest that the PD-1^hiCD57^hi TFH cells, in particular, are endowed with distinctive programming and spatial positioning for optimal GC B cell help.

In Sickness and in Health: The Immunological Roles of the Lymphatic System

The lymphatic system plays crucial roles in immunity far beyond those of simply providing conduits for leukocytes and antigens in lymph fluid. Endothelial cells within this vasculature are distinct and highly specialized to perform roles based upon their location. Afferent lymphatic capillaries have unique intercellular junctions for efficient uptake of fluid and macromolecules, while expressing chemotactic and adhesion molecules that permit selective trafficking of specific immune cell subsets. Moreover, in response to events within peripheral tissue such as inflammation or infection, soluble factors from lymphatic endothelial cells exert “remote control” to modulate leukocyte migration across high endothelial venules from the blood to lymph nodes draining the tissue. These immune hubs are highly organized and perfectly arrayed to survey antigens from peripheral tissue while optimizing encounters between antigen-presenting cells and cognate lymphocytes. Furthermore, subsets of lymphatic endothelial cells exhibit differences in gene expression relating to specific functions and locality within the lymph node, facilitating both innate and acquired immune responses through antigen presentation, lymph node remodeling and regulation of leukocyte entry and exit. This review details the immune cell subsets in afferent and efferent lymph, and explores the mechanisms by which endothelial cells of the lymphatic system regulate such trafficking, for immune surveillance and tolerance during steady-state conditions, and in response to infection, acute and chronic inflammation, and subsequent resolution.

TGF-β: Many Paths to CD103+ CD8 T Cell Residency

CD8 tissue-resident memory T (T_RM) cells primarily reside in nonlymphoid tissues without recirculating and provide front-line protective immunity against infections and cancers. CD8 T_RM cells can be generally divided into CD69⁺ CD103⁻ T_RM cells (referred to as CD103⁻ T_RM cells) and CD69⁺ CD103⁺ T_RM cells (referred to as CD103⁺ T_RM cells). TGF-β plays a critical role in the development and maintenance of CD103⁺ CD8 T_RM cells. In this review, we summarize the current understanding of tissue-specific activation of TGF-β mediated by integrins and how it contributes to CD103⁺ CD8 T_RM cell development and maintenance. Furthermore, we discuss the underlying mechanisms utilized by TGF-β to regulate the development and maintenance of CD103⁺ CD8 T_RM cells. Overall, this review highlights the importance of TGF-β in regulating this unique subset of memory CD8 T cells that may shed light on improving vaccine design to target this population.

Tissue-Resident Memory-Like CD8+ T Cells Exhibit Heterogeneous Characteristics in Tuberculous Pleural Effusion

Tissue-resident memory T (TRM) cells are well known to play critical roles in peripheral tissues during virus infection and tumor immunology. Our previous studies indicated that CD69+CD4+ and CD69+CD8+ T cells in tuberculous pleural effusion (TPE) were antigen-specific memory T cells. However, the phenotypical and functional characteristics of CD8+ TRM cells in tuberculosis remain unknown. We found that CD103+CD8+ T cells were the predominant subset of CD103+ lymphocytes in TPE; both CD103 and CD69 expressed on memory CD8+ T cells from TPE were significantly increased compared with those from paired peripheral blood. Phenotypically, CD103+CD69+ and CD103+CD69-CD8+ T cells expressed higher levels of CD45RO than CD103-CD69+CD8+ T cells did; CD103+CD69-CD8+ T cells highly expressed CD27, CD127, and CD62L and some chemokine receptors. We further compared the functional differences among the four distinct CD45RO+CD8+ T subsets identified by CD103 and CD69 expression. In consist with our published results, CD69+CD8+ T cells, but not CD103+CD8+, produced high levels of IFN-γ after treatment with BCG in the presence of BFA. Nevertheless, CD103-CD69+ and CD103+CD69+ memory CD8+ T cells expressed higher levels of Granzyme B, while CD103+CD69- memory CD8+ T cells were characterized as a possibly immunosuppressive subset by highly expressing CTLA-4, CD25, and FoxP3. Furthermore, TGF-β extremely increased CD103 expression but not CD69 in vitro. Together, CD103+CD8+ T cells form the predominant subset of CD103+ lymphocytes in TPE; CD103 and CD69 expression defines distinct CD8+ TRM-like subsets exhibiting phenotypical and functional heterogeneity. Our findings provide an important theoretical basis to optimize and evaluate new tuberculosis vaccines.

Plasmacytoid dendritic cells have divergent effects on HIV infection of initial target cells and induce a pro-retention phenotype

Although HIV infection inhibits interferon responses in its target cells in vitro, interferon signatures can be detected in vivo soon after sexual transmission, mainly attributed to plasmacytoid dendritic cells (pDCs). In this study, we examined the physiological contributions of pDCs to early HIV acquisition using coculture models of pDCs with myeloid DCs, macrophages and the resting central, transitional and effector memory CD4 T cell subsets. pDCs impacted infection in a cell-specific manner. In myeloid cells, HIV infection was decreased via antiviral effects, cell maturation and downregulation of CCR5 expression. In contrast, in resting memory CD4 T cells, pDCs induced a subset-specific increase in intracellular HIV p24 protein expression without any activation or increase in CCR5 expression, as measured by flow cytometry. This increase was due to reactivation rather than enhanced viral spread, as blocking HIV entry via CCR5 did not alter the increased intracellular p24 expression. Furthermore, the load and proportion of cells expressing HIV DNA were restricted in the presence of pDCs while reverse transcriptase and p24 ELISA assays showed no increase in particle associated reverse transcriptase or extracellular p24 production. In addition, pDCs also markedly induced the expression of CD69 on infected CD4 T cells and other markers of CD4 T cell tissue retention. These phenotypic changes showed marked parallels with resident memory CD4 T cells isolated from anogenital tissue using enzymatic digestion. Production of IFNα by pDCs was the main driving factor for all these results. Thus, pDCs may reduce HIV spread during initial mucosal acquisition by inhibiting replication in myeloid cells while reactivating latent virus in resting memory CD4 T cells and retaining them for immune clearance.

IFNs constitute one of the first and most important innate immune controls to restrict initial viral replication and spread. As HIV has evolved mechanisms to block IFN-I induction in its target cells, but not in infiltrating pDCs, understanding how pDCs influence HIV infection of target cells upon initial transmission is critical to prevent or control initial infection. Therefore, we modelled the early events occurring immediately as HIV enters the human genital mucosa. We showed that IFNα secreting pDC compensated for HIV inhibition of IFN-I production in its target cells in two different ways: i) reduced infection in DCs and macrophages which would limit viral spread to resident or newly infiltrating memory CD4 T cells; ii) reactivation of latent HIV in all subsets of resting memory CD4 T cell subsets, accompanied by limited viral spread, upregulation of MHC-I and induction of a tissue retention phenotype. The increased HIV protein, MHC-I expression and retention may enhance exposure to CD8 T cell surveillance. This model suggests that IFNα reactivation of latent HIV combined with adoptive immunotherapy using CD8 T cells or those expressing chimeric antigen receptors (CAR) could provide a novel ‘kick and kill’ approach to eradicate HIV reservoirs.

Central human B cell tolerance manifests with a distinctive cell phenotype and is enforced via CXCR4 signaling in hu-mice

Central B cell tolerance, the process restricting the development of many newly generated autoreactive B cells, has been intensely investigated in mouse cells while studies in humans have been hampered by the inability to phenotypically distinguish autoreactive and nonautoreactive immature B cell clones and the difficulty in accessing fresh human bone marrow samples. Using a human immune system mouse model in which all human Igκ⁺ B cells undergo central tolerance, we discovered that human autoreactive immature B cells exhibit a distinctive phenotype that includes lower activation of ERK and differential expression of CD69, CD81, CXCR4, and other glycoproteins. Human B cells exhibiting these characteristics were observed in fresh human bone marrow tissue biopsy specimens, although differences in marker expression were smaller than in the humanized mouse model. Furthermore, the expression of these markers was slightly altered in autoreactive B cells of humanized mice engrafted with some human immune systems genetically predisposed to autoimmunity. Finally, by treating mice and human immune system mice with a pharmacologic antagonist, we show that signaling by CXCR4 is necessary to prevent both human and mouse autoreactive B cell clones from egressing the bone marrow, indicating that CXCR4 functionally contributes to central B cell tolerance.

B cell intrinsic expression of IFNλ receptor suppresses the acute humoral immune response to experimental blood-stage malaria

Antibodies play a critical protective role in the host response to blood-stage malaria infection. The role of cytokines in shaping the antibody response to blood-stage malaria is unclear. Interferon lambda (IFNλ), a type III interferon, is a cytokine produced early during blood-stage malaria infection that has an unknown physiological role during malaria infection. We demonstrate that B cell-intrinsic IFNλ signals suppress the acute antibody response, acute plasmablast response, and impede acute parasite clearance during a primary blood-stage malaria infection. Our findings demonstrate a previously unappreciated role for B cell intrinsic IFNλ-signaling in the initiation of the humoral immune response in the host response to experimental malaria.

Immunological memory in rheumatic inflammation - a roadblock to tolerance induction

Why do we still have no cure for chronic inflammatory diseases? One reason could be that current therapies are based on the assumption that chronic inflammation is driven by persistent 'acute' immune reactions. Here we discuss a paradigm shift by suggesting that beyond these reactions, chronic inflammation is driven by imprinted, pathogenic 'memory' cells of the immune system. This rationale is based on the observation that in patients with chronic inflammatory rheumatic diseases refractory to conventional immunosuppressive therapies, therapy-free remission can be achieved by resetting the immune system; that is, by ablating immune cells and regenerating the immune system from stem cells. The success of this approach identifies antigen-experienced and imprinted immune cells as essential and sufficient drivers of inflammation. The 'dark side' of immunological memory primarily involves memory plasma cells secreting pathogenic antibodies and memory T lymphocytes secreting pathogenic cytokines and chemokines, but can also involve cells of innate immunity. New therapeutic strategies should address the persistence of these memory cells. Selective targeting of pathogenic immune memory cells could be based on their specificity, which is challenging, or on their lifestyle, which differs from that of protective immune memory cells, in particular for pathogenic T lymphocytes. The adaptations of such pathogenic memory cells to chronic inflammation offers entirely new therapeutic options for their selective ablation and the regeneration of immunological tolerance.

Extensive activation, tissue trafficking, turnover and functional impairment of NK cells in COVID-19 patients at disease onset associates with subsequent disease severity

The SARS-CoV-2 infection causes severe respiratory involvement (COVID-19) in 5-20% of patients through initial immune derangement, followed by intense cytokine production and vascular leakage. Evidence of immune involvement point to the participation of T, B, and NK cells in the lack of control of virus replication leading to COVID-19. NK cells contribute to early phases of virus control and to the regulation of adaptive responses. The precise mechanism of NK cell dysregulation is poorly understood, with little information on tissue margination or turnover. We investigated these aspects by multiparameter flow cytometry in a cohort of 28 patients hospitalized with early COVID-19. Relevant decreases in CD56brightCD16+/- NK subsets were detected, with a shift of circulating NK cells toward more mature CD56dimCD16+KIR+NKG2A+ and "memory" KIR+CD57+CD85j+ cells with increased inhibitory NKG2A and KIR molecules. Impaired cytotoxicity and IFN-γ production were associated with conserved expression of natural cytotoxicity receptors and perforin. Moreover, intense NK cell activation with increased HLA-DR and CD69 expression was associated with the circulation of CD69+CD103+ CXCR6+ tissue-resident NK cells and of CD34+DNAM-1brightCXCR4+ inflammatory precursors to mature functional NK cells. Severe disease trajectories were directly associated with the proportion of CD34+DNAM-1brightCXCR4+ precursors and inversely associated with the proportion of NKG2D+ and of CD103+ NK cells. Intense NK cell activation and trafficking to and from tissues occurs early in COVID-19, and is associated with subsequent disease progression, providing an insight into the mechanism of clinical deterioration. Strategies to positively manipulate tissue-resident NK cell responses may provide advantages to future therapeutic and vaccine approaches.

Predictive monitoring and therapeutic immune biomarkers in the management of clinical complications of COVID-19

The coronavirus disease-2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), appears with a wide spectrum of mild-to-critical clinical complications. Many clinical and experimental findings suggest the role of inflammatory mechanisms in the immunopathology of COVID-19. Hence, cellular and molecular mediators of the immune system can be potential targets for predicting, monitoring, and treating the progressive complications of COVID-19. In this review, we assess the latest cellular and molecular data on the immunopathology of COVID-19 according to the pathological evidence (e.g., mucus and surfactants), dysregulations of pro- and anti-inflammatory mediators (e.g., cytokines and chemokines), and impairments of innate and acquired immune system functions (e.g., mononuclear cells, neutrophils and antibodies). Furthermore, we determine the significance of immune biomarkers for predicting, monitoring, and treating the progressive complications of COVID-19. We also discuss the clinical importance of recent immune biomarkers in COVID-19, and at the end of each section, recent clinical trials in immune biomarkers for COVID-19 are mentioned.

Antigen-Specific Tissue-Resident Memory T Cells in the Respiratory System Were Generated following Intranasal Vaccination of Mice with BCG

Tissue-resident memory T cells (T_RM) are different from effector memory T cells (T_EM) and central memory T cells (T_CM) and contribute to the protective immunity against local challenges. Currently, we found that CD4⁺ and CD8⁺ T_RM cells in the nasal mucosa, trachea, lungs, and lavage fluids were heterogeneous on the expression of CD69 and CD103 as well as the production of cytokines including IFN-γ, IL-2, and TNF-α. After intranasal vaccination of mice with BCG, respiratory tissues expressed higher levels of the chemokine CXCL16 and T_RM cells expressed CXCR6 to CXCL16. In addition, antigen-specific CD4⁺ and CD8⁺ T_RM cells expressed cytokines following the stimulation with BCG and persisted in the nasal mucosa, trachea, and lungs for more than a hundred days. At the same time, mice were infected intranasally with live BCG and the results showed that vaccinated mice cleared up live BCG faster than nonvaccinated mice in the respiratory system. Taken together, our data demonstrated that intranasal vaccination of mice with BCG could induce antigen-specific CD4⁺ and CD8⁺ T_RM cells in the respiratory system and have the ability to provide protection against pulmonary reinfection.

Rapid Isolation of Functional ex vivo Human Skin Tissue-Resident Memory T Lymphocytes

Studies in animal models have shown that skin tissue-resident memory T (T_RM) cells provide enhanced and immediate effector function at the site of infection. However, analyses of skin T_RM cells in humans have been hindered by the lack of an optimized isolation protocol. Here, we present a combinatorial strategy-the 6-h collagenase IV digestion and gentle tissue dissociation – for rapid and efficient isolation of skin T_RM cells with skin tissue-specific immune features. In comparison with paired blood circulating memory T cells, these ex vivo isolated skin T cells express typical T_RM cell markers and display higher polyfunctional properties. Moreover, these isolated cells can also be assessed for longer periods of time in ex vivo cultures. Thus, the optimized isolation protocol provides a valuable tool for further understanding of human skin T_RM cells, especially for direct comparison with peripheral blood T cells at the same sample collection time.

Discipline in Stages: Regulating CD8+ Resident Memory T Cells

Resident memory CD8⁺ T (T_RM) cells are a lymphocyte lineage distinct from circulating memory CD8⁺ T cells. T_RM lodge within peripheral tissues and secondary lymphoid organs where they provide rapid, local protection from pathogens and control tumor growth. However, dysregulation of CD8⁺ T_RM formation and/or activation may contribute to the pathogenesis of autoimmune diseases. Intrinsic mechanisms, including transcriptional networks and inhibitory checkpoint receptors control T_RM differentiation and response. Additionally, extrinsic stimuli such as cytokines, cognate antigen, fatty acids, and damage signals regulate T_RM formation, maintenance, and expansion. In this review, we will summarize knowledge of CD8⁺ T_RM generation and highlight mechanisms that regulate the persistence and responses of heterogeneous T_RM populations in different tissues and distinct microenvironments.

Natural Killer Cell Integrins and Their Functions in Tissue Residency

Integrins are transmembrane receptors associated with adhesion and migration and are often highly differentially expressed receptors amongst natural killer cell subsets in microenvironments. Tissue resident natural killer cells are frequently defined by their differential integrin expression compared to other NK cell subsets, and integrins can further localize tissue resident NK cells to tissue microenvironments. As such, integrins play important roles in both the phenotypic and functional identity of NK cell subsets. Here we review the expression of integrin subtypes on NK cells and NK cell subsets with the goal of better understanding how integrin selection can dictate tissue residency and mediate function from the nanoscale to the tissue environment.

T cell responses to Chlamydia

Chlamydia trachomatis is the most commonly reported sexually transmitted infection in the United States. The high prevalence of infection and lack of a vaccine indicate a critical knowledge gap surrounding the host's response to infection and how to effectively generate protective immunity. The immune response to C. trachomatis is complex, with cells of the adaptive immune system playing a crucial role in bacterial clearance. Here, we discuss the CD4+ and CD8+ T cell response to Chlamydia, the importance of antigen specificity and the role of memory T cells during the recall response. Ultimately, a deeper understanding of protective immune responses is necessary to develop a vaccine that prevents the inflammatory diseases associated with Chlamydia infection.

Opposing effects of T cell receptor signal strength on CD4 T cells responding to acute versus chronic viral infection

A hallmark of adaptive immunity is CD4 T cells’ ability to differentiate into specialized effectors. A long-standing question is whether T cell receptor (TCR) signal strength can dominantly instruct the development of Th1 and T follicular helper (Tfh) cells across distinct infectious contexts. We characterized the differentiation of murine CD4 TCR transgenic T cells responding to altered peptide ligand lymphocytic choriomeningitis viruses (LCMV) derived from acute and chronic parental strains. We found that TCR signal strength exerts opposite and hierarchical effects on the balance of Th1 and Tfh cells responding to acute versus persistent infection. TCR signal strength correlates positively with Th1 generation during acute but negatively during chronic infection. Weakly activated T cells express lower levels of markers associated with chronic T cell stimulation and may resist functional inactivation. We anticipate that the panel of recombinant viruses described herein will be valuable for investigating a wide range of CD4 T cell responses.

Monocyte-derived S1P in the lymph node regulates immune responses

The lipid chemoattractant sphingosine 1-phosphate (S1P) guides cells from the low-S1P environment of tissues into the high-S1P environment of circulatory fluids(1). Notably, S1P directs T cell exit from lymph nodes (LN), where T cells are initially activated, into lymph, from which T cells reach blood and ultimately inflamed tissues(1). T cells follow S1P gradients primarily using S1P receptor 1 (S1PR1)(1). While recent work has described how S1P gradients are established at steady-state, little is known about S1P distribution in disease, or about how changing S1P levels may affect immune responses. Here, we find that S1P concentrations increase in LN during an immune response. Hematopoietic cells, including inflammatory monocytes (iMo), are an important source of this S1P, an unexpected finding as endothelial cells provide lymph S1P(1). iMo require the early activation marker CD69 to supply this S1P, in part because CD69 expression is associated with reduced levels of S1pr5. CD69 acts as a “stand-your-ground” signal, keeping immune cells at a site of inflammation by regulating both S1P receptors and S1P gradients. Finally, increased S1P prolongs T cell residence time in LN, and exacerbates the severity of experimental autoimmune encephalomyelitis. This finding suggests the hypothesis that LN residence time regulates T cell differentiation, and points to novel uses of drugs targeting S1P signaling.

COVID-19: Immunology, Immunopathogenesis and Potential Therapies

The Coronavirus Disease-2019 (COVID-19) imposed public health emergency and affected millions of people around the globe. As of January 2021, 100 million confirmed cases of COVID-19 along with more than 2 million deaths were reported worldwide. SARS-CoV-2 infection causes excessive production of pro-inflammatory cytokines thereby leading to the development of "Cytokine Storm Syndrome." This condition results in uncontrollable inflammation that further imposes multiple-organ-failure eventually leading to death. SARS-CoV-2 induces unrestrained innate immune response and impairs adaptive immune responses thereby causing tissue damage. Thus, understanding the foremost features and evolution of innate and adaptive immunity to SARS-CoV-2 is crucial in anticipating COVID-19 outcomes and in developing effective strategies to control the viral spread. In the present review, we exhaustively discuss the sequential key immunological events that occur during SARS-CoV-2 infection and are involved in the immunopathogenesis of COVID-19. In addition to this, we also highlight various therapeutic options already in use such as immunosuppressive drugs, plasma therapy and intravenous immunoglobulins along with various novel potent therapeutic options that should be considered in managing COVID-19 infection such as traditional medicines and probiotics.

Long-Term Liver Expression of an Apolipoprotein A-I Mimetic Peptide Attenuates Interferon-Alpha-Induced Inflammation and Promotes Antiviral Activity

Apolipoprotein A-I mimetic peptides are amphipathic alpha-helix peptides that display similar functions to apolipoprotein A-I. Preclinical and clinical studies have demonstrated the safety and efficacy of apolipoprotein A-I mimetic peptides in multiple indications associated with inflammatory processes. In this study, we evaluated the effect of the long-term expression of L37pA in the liver by an adeno-associated virus (AAV-L37pA) on the expression of an adeno-associated virus encoding interferon-alpha (AAV-IFNα). Long-term IFNα expression in the liver leads to lethal hematological toxicity one month after AAV administration. Concomitant administration of AAV-L37pA prevented the lethal toxicity since the IFNα expression was reduced one month after AAV administration. To identify the mechanism of action of L37pA, a genomic and proteomic analysis was performed 15 days after AAV administration when a similar level of IFNα and interferon-stimulated genes were observed in mice treated with AAV-IFNα alone and in mice treated with AAV-IFNα and AAV-L37pA. The coexpression of the apolipoprotein A-I mimetic peptide L37pA with IFNα modulated the gene expression program of IFNα, inducing a significant reduction in inflammatory pathways affecting pathogen-associated molecular patterns receptor, dendritic cells, NK cells and Th1 immune response. The proteomic analysis confirmed the impact of the L37pA activity on several inflammatory pathways and indicated an activation of LXR/RXR and PPPARα/γ nuclear receptors. Thus, long-term expression of L37pA induces an anti-inflammatory effect in the liver that allows silencing of IFNα expression mediated by an adeno-associated virus.

Organ-Specific Surveillance and Long-Term Residency Strategies Adapted by Tissue-Resident Memory CD8+ T Cells

Tissue-resident CD8⁺ T cells (CD8⁺ T_RM) populate lymphoid and non-lymphoid tissues after infections as first line of defense against re-emerging pathogens. To achieve host protection, CD8⁺ T_RM have developed surveillance strategies that combine dynamic interrogation of pMHC complexes on local stromal and hematopoietic cells with long-term residency. Factors mediating CD8⁺ T_RM residency include CD69, a surface receptor opposing the egress-promoting S1P1, CD49a, a collagen-binding integrin, and CD103, which binds E-cadherin on epithelial cells. Moreover, the topography of the tissues of residency may influence T_RM retention and surveillance strategies. Here, we provide a brief summary of these factors to examine how CD8⁺ T_RM reconcile constant migratory behavior with their long-term commitment to local microenvironments, with a focus on epithelial barrier organs and exocrine glands with mixed connective-epithelial tissue composition.

Harnessing liver-resident memory T cells for protection against malaria

INTRODUCTION

Tissue-resident memory T cells (T_RM cells) are powerful mediators of protracted adaptive immunity to infection in peripheral organs. Harnessing T_RM cells through vaccination hence promises unprecedented potential for protection against infection. A paramount example of this is malaria, a major infectious disease for which immunity through traditional vaccination strategies remains challenging. Liver T_RM cells appear to be highly protective against malaria, and recent developments in our knowledge of the biology of these cells have defined promising, novel strategies for their induction.

AREAS COVERED

Here, we describe the path that led to the discovery of T_RM cells and discuss the importance of liver T_RM cells in immunity against Plasmodium spp. infection; we summarize current knowledge on T_RM cell biology and discuss the current state and potential of T_RM-based vaccination against malaria.

EXPERT OPINION

T_RM based vaccination has emerged as a promising means to achieve efficient protection against malaria. Recent advances provide a solid basis for continuing the development of this area of research. Deeper understanding of the mechanisms that mediate T_RM formation and maintenance and identification of immunogenic and protective target epitopes suitable for human vaccination remain the main challenges for translation of these discoveries.

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.

Balancing Inflammation and Central Nervous System Homeostasis: T Cell Receptor Signaling in Antiviral Brain TRM Formation and Function

Tissue-resident memory (T_RM) CD8 T cells provide early frontline defense against regional pathogen reencounter. CD8 T_RM are predominantly parked in nonlymphoid tissues and do not circulate. In addition to this anatomic difference, T_RM are transcriptionally and phenotypically distinct from central-memory T cells (T_CM) and effector-memory T cells (T_EM). Moreover, T_RM differ phenotypically, functionally, and transcriptionally across barrier tissues (e.g., gastrointestinal tract, respiratory tract, urogenital tract, and skin) and in non-barrier organs (e.g., brain, liver, kidney). In the brain, T_RM are governed by a contextual milieu that balances T_RM activation and preservation of essential post-mitotic neurons. Factors contributing to the development and maintenance of brain T_RM, of which T cell receptor (TCR) signal strength and duration is a central determinant, vary depending on the infectious agent and modulation of TCR signaling by inhibitory markers that quell potentially pathogenic inflammation. This review will explore our current understanding of the context-dependent factors that drive the acquisition of brain (b)T_RM phenotype and function, and discuss the contribution of T_RM to promoting protective immune responses in situ while maintaining tissue homeostasis.

Rotavirus infection causes mesenteric lymph node hypertrophy independently of type I interferon or TNF-α in mice

Lymphoid organ hypertrophy is a characteristic feature of acute infection and is considered to enable efficient induction of adaptive immune responses. Accordingly, oral infection with rotavirus induced a robust increase in cellularity in the mesenteric LNs, whose kinetics correlated with viral load and was caused by halted lymphocyte egress and increased recruitment of cells without altered cellular proliferation. Lymphocyte sequestration and mesenteric LN hypertrophy were independent of type 1 IFN receptor signaling or the continuous presence of TNF-α. Our results support previous findings that adaptive immunity toward rotavirus is initiated primarily in the mesenteric LNs and show that type I IFN or TNF-α are not required to coordinate the events involved in the LN response.

The Shaping of a B Cell Pool Maximally Responsive to Infections

B cell subsets differ in development, tissue distribution, and mechanisms of activation. In response to infections, however, all can differentiate into extrafollicular plasmablasts that rapidly provide highly protective antibodies, indicating that these plasmablasts are the main humoral immune response effectors. Yet, the effectiveness of this response type depends on the presence of antigen-specific precursors in the circulating mature B cell pool, a pool that is generated initially through the stochastic processes of B cell receptor assembly. Importantly, germinal centers then mold the repertoire of this B cell pool to be increasingly responsive to pathogens by generating a broad array of antimicrobial memory B cells that act as highly effective precursors of extrafollicular plasmablasts. Such B cell repertoire molding occurs in two ways: continuously via the chronic germinal centers of mucosal lymphoid tissues, driven by the presence of the microbiome, and via de novo generated germinal centers following acute infections. For effectively evaluating humoral immunity as a correlate of immune protection, it might be critical to measure memory B cell pools in addition to antibody titers.

Pulmonary MTBVAC vaccination induces immune signatures previously correlated with prevention of tuberculosis infection

To fight tuberculosis, better vaccination strategies are needed. Live attenuated Mycobacterium tuberculosis-derived vaccine, MTBVAC, is a promising candidate in the pipeline, proven to be safe and immunogenic in humans so far. Independent studies have shown that pulmonary mucosal delivery of Bacillus Calmette-Guérin (BCG), the only tuberculosis (TB) vaccine available today, confers superior protection over standard intradermal immunization. Here we demonstrate that mucosal MTBVAC is well tolerated, eliciting polyfunctional T helper type 17 cells, interleukin-10, and immunoglobulins in the airway and yielding a broader antigenic profile than BCG in rhesus macaques. Beyond our previous work, we show that local immunoglobulins, induced by MTBVAC and BCG, bind to M. tuberculosis and enhance pathogen uptake. Furthermore, after pulmonary vaccination, but not M. tuberculosis infection, local T cells expressed high levels of mucosal homing and tissue residency markers. Our data show that pulmonary MTBVAC administration has the potential to enhance its efficacy and justifies further exploration of mucosal vaccination strategies in preclinical efficacy studies.

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

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

A noninflammatory mRNA vaccine for treatment of experimental autoimmune encephalomyelitis

The ability to control autoreactive T cells without inducing systemic immune suppression is the major goal for treatment of autoimmune diseases. The key challenge is the safe and efficient delivery of pharmaceutically well-defined antigens in a noninflammatory context. Here, we show that systemic delivery of nanoparticle-formulated 1 methylpseudouridine-modified messenger RNA (m1Ψ mRNA) coding for disease-related autoantigens results in antigen presentation on splenic CD11c+ antigen-presenting cells in the absence of costimulatory signals. In several mouse models of multiple sclerosis, the disease is suppressed by treatment with such m1Ψ mRNA. The treatment effect is associated with a reduction of effector T cells and the development of regulatory T cell (Treg cell) populations. Notably, these Treg cells execute strong bystander immunosuppression and thus improve disease induced by cognate and noncognate autoantigens.