Lymph Node Stromal Cells Generate Antigen-Specific Regulatory T Cells and Control Autoreactive T and B Cell Responses

Rapamycin immunomodulation utilizes time-dependent alterations of lymph node architecture, leukocyte trafficking, and gut microbiome

Transplant recipients require lifelong, multimodal immunosuppression to prevent rejection by reducing alloreactive immunity. Rapamycin is known to modulate adaptive and innate immunity, but its full mechanism remains incompletely understood. We investigated the understudied effects of rapamycin on lymph node (LN) architecture, leukocyte trafficking, and gut microbiome and metabolism after 3 (early), 7 (intermediate), and 30 (late) days of rapamycin treatment. Rapamycin significantly reduced CD4+ T cells, CD8+ T cells, and Tregs in peripheral LNs, mesenteric LNs, and spleen. Rapamycin induced early proinflammation transition to protolerogenic status by modulating the LN laminin α4/α5 expression ratios (La4/La5) through LN stromal cells, laminin α5 expression, and adjustment of Treg numbers and distribution. Additionally, rapamycin shifted the Bacteroides/Firmicutes ratio and increased amino acid bioavailability in the gut lumen. These effects were evident by 7 days and became most pronounced by 30 days in naive mice, with changes as early as 3 days in allogeneic splenocyte-stimulated mice. These findings reveal what we believe to be a novel mechanism of rapamycin action through time-dependent modulation of LN architecture and gut microbiome, which orchestrates changes in immune cell trafficking, providing a framework for understanding and optimizing immunosuppressive therapies.

Regulatory T cells in solid tumor immunotherapy: effect, mechanism and clinical application

The tumor-immune response is mobilized to suppress tumorigenesis, while the immune microenvironment and lymph node microenvironment are formed gradually during tumor progression. In fact, tumor surface antigens are not easily recognized by antigen-presenting cells. So it is hard for the immune system to kill the newly formed tumor cells effectively. In a normal immune environment, immune function is always suppressed to maintain the stability of the body, and regulatory T cells play an important role in maintaining immune suppression. However, during tumorigenesis, the suppression of regulatory T cell immune functions is more likely to contribute to tumor cell proliferation and migration leading directly to tumor progression. Therefore, focusing on the role of regulatory T cells in tumor immunity could improve tumor immunotherapy outcomes in the clinic. Regulatory T cells are more mature in hematologic system tumors than in solid tumors. However, there are continuing efforts to apply regulatory T cells for immunotherapy in solid tumors. This review describes the role of regulatory T cells in solid tumor immunotherapy from the perspective of prognosis, immune microenvironment remodeling, and current clinical applications. This summary could help us better understand the mechanisms of regulatory T cells in solid tumor immunotherapy and further expand their clinical application.

Lymph node fibroblast-produced extracellular matrix shapes immune function

Lymph node (LN) fibroblastic reticular cells (FRCs) are key regulators of mammalian adaptive immune responses. Together with their deposited extracellular matrix (ECM), FRCs form a reticular network that provides mechanical strength to LNs. Furthermore, the ECM regulates various cell functions including proliferation and differentiation. The ECM is dynamically remodeled in activated LNs, thereby affecting immune cell survival and function. Although both the LN ECM and FRCs can affect immune reactivity, a link between altered LN ECM during an immune response and ECM-producing FRCs is lacking. We explore recent work on the complex interplay between FRCs, ECM, and immune cells in health and disease, and provide guidance for future research to understand the complex regulation of the adaptive immune system within LNs.

Exploring Lymph Node Stroma Ageing: Immune Implications and Future Directions

Ageing is an inevitable biological process that impacts the immune system, leading to immunosenescence and inflammaging, which contribute to increased susceptibility to infections, autoimmune diseases and cancers in individuals over the age of 65. This review focuses on the ageing of lymph node stromal cells (LNSCs), which are crucial for maintaining lymph node (LN) structure and function. Age-related changes in LNs, such as fibrosis and lipomatosis, disrupt the LN architecture and reduce immune cell recruitment and function, impairing immune responses to infections and vaccinations. The review discusses the structural and functional decline of various LNSC subsets, including fibroblastic reticular cells (FRCs), lymphatic endothelial cells (LECs) and blood endothelial cells (BECs), highlighting their roles in immune cell activation and homeostasis. Potential strategies to restore aged LNSC function, such as enhancing LNSC activation during vaccination and using senotherapeutics, are explored. Outstanding questions regarding the mechanisms of LNSC ageing and how ageing of the LN stroma might impact autoimmune disorders are also addressed. This review aims to stimulate further research into the characterisation of aged LNSCs and the development of therapeutic interventions to improve immune function in the older adults.

Spatiotemporal Cellular Dynamics of Germinal Center Reaction in Coronavirus Disease 2019 Lung-Draining Lymph Node Based on Imaging-Based Spatial Transcriptomics

Although lymph node structures may be compromised in severe SARS-CoV-2 infection, the extent and parameters of recovery in convalescing patients remain unclear. Therefore, this study aimed to elucidate the nuances of lymphoid structural recovery and their implications for immunologic memory in nonhuman primates infected with SARS-CoV-2. To do so, we utilized imaging-based spatial transcriptomics to delineate immune cell composition and tissue architecture formation in the lung-draining lymph nodes during primary infection, convalescence, and reinfection from COVID-19. We noted the establishment of a germinal center with memory B cell differentiation within lymphoid follicles during convalescence accompanied by contrasting transcriptome patterns indicative of the acquisition of follicular helper T cells versus the loss of regulatory T cells. Additionally, repopulation of germinal center-like B cells was observed in the medullary niche with accumulating plasma cells along with enhanced transcriptional expression of B cell-activating factor receptor over the course of reinfection. The spatial transcriptome atlas produced herein enhances our understanding of germinal center formation with immune cell dynamics during COVID-19 convalescence and lymphoid structural recovery with transcriptome dynamics following reinfection. These findings have the potential to inform the optimization of vaccine strategies and the development of precise therapeutic interventions in the spatial context.

Lymph nodes as gatekeepers of autoimmune diseases

Secondary lymphoid organs such as lymph nodes (LNs) are the home of peripheral tolerance mechanisms which control autoreactive T cells and prevent immune responses to self-antigen. In systemic autoimmunity, there is a clear failure of these peripheral tolerance mechanisms that leads to chronic inflammation and tissue destruction, highlighting the role for LNs as possible gatekeepers of autoimmunity. In recent years there has been a shift in research focus towards tissue sites in autoimmune diseases ranging from type 1 diabetes to rheumatoid arthritis in an effort to better characterise pathogenesis and guide diagnostic and therapeutic decisions. Although this has yielded great insight, it fails to tackle the initial break in tolerance that initiates disease progression which is most likely originating in peripheral LNs. In the majority of autoimmune diseases a preclinical phase is recognised. This is characterised by the presence of autoantibodies, which is indicative of a break in immune tolerance, and the absence of clinically apparent inflammation or tissue destruction. This review explores how our current knowledge of LNs in the preclinical and established phases of autoimmune diseases provides insight into possibly shared pathological mechanisms that drive disease progression and highlight the gaps in our knowledge that may help uncover new therapeutic avenues for intervention and prevention.

Hepatic draining lymph nodes in human liver transplant: Implications in alloimmunity and tolerance

BACKGROUND

Hepatic draining lymph nodes (HDLN) are implicated in allograft alloimmunity and tolerance. In contrast to experimental work, the role of HDLNs in human liver transplant (LT) is unknown due to lack of relevant clinical tissue.

METHODS

During LT, the porta hepatis was dissected near the liver hilum during native hepatectomy. The HDLN in this region was taken prior to reperfusion (prereperfusion). Following complete reperfusion with recipient portal venous blood, hepatic arterial inflow into the allograft was established. As the recipient's common hepatic artery was fully mobilized, its HDLNs were removed and submitted to pathology (postreperfusion).

RESULTS

Of 37 LTs performed between January 1, 2021, and July 9, 2022, 20 had both pre- and postreperfusion HDLNs archived (Group A); 11 had only postreperfusion HDLNs archived (Group B), and 6 had no archived HDLNs (Group C). Removing and archiving HDLNs did not increase operative times or transfusion requirements. For groups A, B, and C, mean (SD) warm ischemic times were 25.2 (2.0), 25.3 (3.2), and 28.3 (6.2) minutes, respectively (P > .05); operating times were 3.9 (0.7), 6.9 (7.8), and 7.9 (7.1) hours, respectively (A vs C, P = .017; C vs B, P > .05); and units of transfused packed red blood cells were 8.0 (3.8), 11.1 (10.3), and 12.2 (7.6), respectively (P > .05).

CONCLUSION

We describe an approach for clinical archiving of HDLNs obtained within the operative field during orthotopic LT in humans. Availability of relevant HDLNs is essential for investigations of primary immune responses potentially important in allograft alloimmunity and tolerance.

Differential proteins from EVs identification based on tandem mass tags analysis and effect of Treg-derived EVs on T-lymphocytes in COPD patients

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a widespread respiratory disease. This study examines extracellular vesicles (EVs) and proteins contained in EVs in COPD.

METHODS

Blood samples were collected from 40 COPD patients and 10 health controls. Cytokines including IFN-γ, TNF-α, IL-1β, IL-6, IL-8, and IL-17, were measured by ELISA. Small EVs samples were extracted from plasma and identified by transmission electron microscope (TEM), nanoparticle tracking analysis (NTA), and Western blot. Protein components contained in EVs were analyzed by Tandem Mass Tags (TMT) to identify differential proteins. Treg-derived EV was extracted and added to isolated CD8+, Treg, and Th17 subsets to assess its effect on T-lymphocytes.

RESULTS

ELISA revealed higher levels of all cytokines and flow cytometry suggested a higher proportion of Treg and Th17 cells in COPD patients. After identification, TMT analysis identified 207 unique protein components, including five potential COPD biomarkers: BTRC, TRIM28, CD209, NCOA3, and SSR3. Flow cytometry revealed that Treg-derived EVs inhibited differentiation into CD8+, CD4+, and Th17 cells.

CONCLUSION

The study shows that cytokines, T-lymphocyte subsets differences in COPD and Treg-derived EVs influence T-lymphocyte differentiation. Identified biomarkers may assist in understanding COPD pathogenesis, prognosis, and therapy. The study contributes to COPD biomarker research.

Fibril-Guided Three-Dimensional Assembly of Human Fibroblastic Reticular Cells

Fibroblastic reticular cells (FRCs) are stromal cells (SCs) that can be isolated from lymph node (LN) biopsies. Studies have shown that these nonhematopoietic cells have the capacity to shape and regulate adaptive immunity and can become a form of personalized cell therapy. Successful translational efforts, however, require the cells to be formulated as injectable units, with their native architecture preserved. The intrinsic reticular organization of FRCs, however, is lost in the monolayer cultures. Organizing FRCs into three-dimensional (3D) clusters would recapitulate their structural and functional attributes. Herein, we report a scaffolding method based on the self-assembling peptide (SAP) EAKII biotinylated at the N-terminus (EAKbt). Cross-linking with avidin transformed the EAKbt fibrils into a dense network of coacervates. The combined forces of fibrillization and bioaffinity interactions in the cross-linked EAKbt likely drove the cells into a cohesive 3D reticula. This facile method of generating clustered FRCs (clFRCs) can be completed within 10 days. In vitro clFRCs attracted the infiltration of T cells and rendered an immunosuppressive milieu in the cocultures. These results demonstrate the potential of clFRCs as a method for stromal cell delivery.

Drug-Resistance Biomarkers in Patient-Derived Colorectal Cancer Organoid and Fibroblast Co-Culture System

Colorectal cancer, the third most commonly occurring tumor worldwide, poses challenges owing to its high mortality rate and persistent drug resistance in metastatic cases. We investigated the tumor microenvironment, emphasizing the role of cancer-associated fibroblasts in the progression and chemoresistance of colorectal cancer. We used an indirect co-culture system comprising colorectal cancer organoids and cancer-associated fibroblasts to simulate the tumor microenvironment. Immunofluorescence staining validated the characteristics of both organoids and fibroblasts, showing high expression of epithelial cell markers (EPCAM), colon cancer markers (CK20), proliferation markers (KI67), and fibroblast markers (VIM, SMA). Transcriptome profiling was conducted after treatment with anticancer drugs, such as 5-fluorouracil and oxaliplatin, to identify chemoresistance-related genes. Changes in gene expression in the co-cultured colorectal cancer organoids following anticancer drug treatment, compared to monocultured organoids, particularly in pathways related to interferon-alpha/beta signaling and major histocompatibility complex class II protein complex assembly, were identified. These two gene groups potentially mediate drug resistance associated with JAK/STAT signaling. The interaction between colorectal cancer organoids and fibroblasts crucially modulates the expression of genes related to drug resistance. These findings suggest that the interaction between colorectal cancer organoids and fibroblasts significantly influences gene expression related to drug resistance, highlighting potential biomarkers and therapeutic targets for overcoming chemoresistance. Enhanced understanding of the interactions between cancer cells and their microenvironment can lead to advancements in personalized medical research..

Therapeutic targeting of DNA methylation alterations in cancer

DNA methylation is a critical component of gene regulation and plays an important role in the development of cancer. Hypermethylation of tumor suppressor genes and silencing of DNA repair pathways facilitate uncontrolled cell growth and synergize with oncogenic mutations to perpetuate cancer phenotypes. Additionally, aberrant DNA methylation hinders immune responses crucial for antitumor immunity. Thus, inhibiting dysregulated DNA methylation is a promising cancer therapy. Pharmacologic inhibition of DNA methylation reactivates silenced tumor suppressors and bolster immune responses through induction of viral mimicry. Now, with the advent of immunotherapies and discovery of the immune-modulatory effects of DNA methylation inhibitors, there is great interest in understanding how targeting DNA methylation in combination with other therapies can enhance antitumor immunity. Here, we describe the role of aberrant DNA methylation in cancer and mechanisms by which it promotes tumorigenesis and modulates immune responses. Finally, we review the initial discoveries and ongoing efforts to target DNA methylation as a cancer therapeutic.

Lymphatic vessels in the age of cancer immunotherapy

Lymphatic transport maintains homeostatic health and is necessary for immune surveillance, and yet lymphatic growth is often associated with solid tumour development and dissemination. Although tumour-associated lymphatic remodelling and growth were initially presumed to simply expand a passive route for regional metastasis, emerging research puts lymphatic vessels and their active transport at the interface of metastasis, tumour-associated inflammation and systemic immune surveillance. Here, we discuss active mechanisms through which lymphatic vessels shape their transport function to influence peripheral tissue immunity and the current understanding of how tumour-associated lymphatic vessels may both augment and disrupt antitumour immune surveillance. We end by looking forward to emerging areas of interest in the field of cancer immunotherapy in which lymphatic vessels and their transport function are likely key players: the formation of tertiary lymphoid structures, immune surveillance in the central nervous system, the microbiome, obesity and ageing. The lessons learnt support a working framework that defines the lymphatic system as a key determinant of both local and systemic inflammatory networks and thereby a crucial player in the response to cancer immunotherapy.

Regulation of autoimmune-mediated neuroinflammation by endothelial cells

The CNS has traditionally been considered an immune-privileged organ, but recent studies have identified a plethora of immune cells in the choroid plexus, meninges, perivascular spaces, and cribriform plate. Although those immune cells are crucial for the maintenance of CNS homeostasis and for neural protection against infections, they can lead to neuroinflammation in some circumstances. The blood and the lymphatic vasculatures exhibit distinct structural and molecular features depending on their location in the CNS, greatly influencing the compartmentalization and the nature of CNS immune responses. In this review, we discuss how endothelial cells regulate the migration and the functions of T cells in the CNS both at steady-state and in murine models of neuroinflammation, with a special focus on the anatomical, cellular, and molecular mechanisms implicated in EAE.

The follicular dendritic cell: At the germinal center of autoimmunity?

Autoimmune diseases strain healthcare systems worldwide as their incidence rises, and current treatments put patients at risk for infections. An increased understanding of autoimmune diseases is required to develop targeted therapies that do not impair normal immune function. Many autoimmune diseases present with autoantibodies, which drive local or systemic inflammation. This indicates the presence of autoreactive B cells that have escaped tolerance. An important step in the development of autoreactive B cells is the germinal center (GC) reaction, where they undergo affinity maturation toward cognate self-antigen. Follicular dendritic cells (FDCs) perform the essential task of antigen presentation to B cells during the affinity maturation process. However, in recent years, it has become clear that FDCs play a much more active role in regulation of GC processes. Here, we evaluate the biology of FDCs in the context of autoimmune disease, with the goal of informing future therapeutic strategies.

Draining Lymph Nodes in Human Kidney Pancreas Transplant: Potential Implications in Alloimmunity and Tolerance

BACKGROUND

Draining lymph nodes (DLNs) are implicated in alloimmunity and tolerance regulation. The role of DLNs in human organ transplant is unknown due to the lack of relevant clinical tissues.

METHODS

During a combined kidney and pancreas transplant, the distal vena cava and both right and left common and external iliac vessels were mobilized and exposed. Draining lymph nodes along these vessels were removed sequentially and archived before the pancreas transplant. Similarly, the DLNs along the left iliac vessels were removed and archived before implantation of the kidney allograft.

RESULTS

Among 13 patients undergoing kidney and pancreas transplants, 6 had pre- and postreperfusion DLNs clinically archived. The remaining 7 either had only prereperfusion DLNs archived or none. Clinical archiving of DLNs did not alter operative times or parameters.

CONCLUSION

This study describes an approach for clinical archiving of DLNs obtained within the operative field during combined kidney-pancreas transplant in humans. The availability of relevant DLNs is essential for investigating fundamental initial primary immune responses potentially important in allograft alloimmunity and tolerance.

Chikungunya virus infection disrupts lymph node lymphatic endothelial cell composition and function via MARCO

Infection with chikungunya virus (CHIKV) causes disruption of draining lymph node (dLN) organization, including paracortical relocalization of B cells, loss of the B cell-T cell border, and lymphocyte depletion that is associated with infiltration of the LN with inflammatory myeloid cells. Here, we find that during the first 24 h of infection, CHIKV RNA accumulates in MARCO-expressing lymphatic endothelial cells (LECs) in both the floor and medullary LN sinuses. The accumulation of viral RNA in the LN was associated with a switch to an antiviral and inflammatory gene expression program across LN stromal cells, and this inflammatory response, including recruitment of myeloid cells to the LN, was accelerated by CHIKV-MARCO interactions. As CHIKV infection progressed, both floor and medullary LECs diminished in number, suggesting further functional impairment of the LN by infection. Consistent with this idea, we find that antigen acquisition by LECs, a key function of LN LECs during infection and immunization, was reduced during pathogenic CHIKV infection.

Systems immunology of regulatory T cells: can one circuit explain it all?

Regulatory T (Treg) cells play vital roles in immune homeostasis and response, including discrimination between self- and non-self-antigens, containment of immunopathology, and inflammation resolution. These diverse functions are orchestrated by cellular circuits involving Tregs and other cell types across space and time. Despite dramatic progress in our understanding of Treg biology, a quantitative framework capturing how Treg-containing circuits give rise to these diverse functions is lacking. Here, we propose that different facets of Treg function can be interpreted as distinct operating regimes of the same underlying circuit. We discuss how a systems immunology approach, involving quantitative experiments, computational modeling, and machine learning, can advance our understanding of Treg function, and help identify general operating and design principles underlying immune regulation.

Cancer cell plasticity and MHC-II-mediated immune tolerance promote breast cancer metastasis to lymph nodes

Tumor-draining lymph nodes (TDLNs) are important for tumor antigen-specific T cell generation and effective anticancer immune responses. However, TDLNs are often the primary site of metastasis, causing immune suppression and worse outcomes. Through cross-species single-cell RNA-Seq analysis, we identified features defining cancer cell heterogeneity, plasticity, and immune evasion during breast cancer progression and lymph node metastasis (LNM). A subset of cancer cells in the lymph nodes exhibited elevated MHC class II (MHC-II) gene expression in both mice and humans. MHC-II+ cancer cells lacked costimulatory molecule expression, leading to regulatory T cell (Treg) expansion and fewer CD4+ effector T cells in TDLNs. Genetic knockout of MHC-II reduced LNM and Treg expansion, while overexpression of the MHC-II transactivator, Ciita, worsened LNM and caused excessive Treg expansion. These findings demonstrate that cancer cell MHC-II expression promotes metastasis and immune evasion in TDLNs.

TGF-β Signaling Prevents MHC Class II-Expressing Lymphatic Endothelial Cells from Reactivating Human Allogenic Memory CD4+ T Cells

Lymphatic endothelial cells (LECs) express MHC class II (MHC-II) upon IFN-γ stimulation, yet recent evidence suggests that LECs cannot activate naive or memory CD4+ T cells. In this article, we show that IFN-γ-activated human dermal LECs can robustly reactivate allogeneic human memory CD4+ T cells (hCD4+ TMs), but only when TGF-β signaling is inhibited. We found that in addition to upregulating MHC-II, IFN-γ also induces LECs to upregulate glycoprotein A repetitions predominant, which anchors latent TGF-β to the membrane and potentially inhibits T cell activation. Indeed, hCD4+ TM proliferation was substantially increased when LEC-CD4+ TM cultures were treated with a TGF-β receptor type 1 inhibitor or when glycoprotein A repetitions predominant expression was silenced in LECs. Reactivated hCD4+ TMs were characterized by their proliferation, CD25 expression, and cytokine secretion. CD4+ TM reactivation was dependent on LEC expression of MHC-II, confirming direct TCR engagement. Although CD80 and CD86 were not detected on LECs, the costimulatory molecules OX40L and ICOSL were upregulated upon cytokine stimulation; however, blocking these did not affect CD4+ TM reactivation by LECs. Finally, we found that human dermal LECs also supported the maintenance of Foxp3-expressing hCD4+ TMs independently of IFN-γ-induced MHC-II. Together, these results demonstrate a role for LECs in directly modulating CD4+ TM reactivation under inflammatory conditions and point to LEC-expressed TGF-β as a negative regulator of this activation.

Amphiregulin couples IL1RL1+ regulatory T cells and cancer-associated fibroblasts to impede antitumor immunity

Regulatory T (Treg) cells and cancer-associated fibroblasts (CAFs) jointly promote tumor immune tolerance and tumorigenesis. The molecular apparatus that drives Treg cell and CAF coordination in the tumor microenvironment (TME) remains elusive. Interleukin 33 (IL-33) has been shown to enhance fibrosis and IL1RL1+ Treg cell accumulation during tumorigenesis and tissue repair. We demonstrated that IL1RL1 signaling in Treg cells greatly dampened the antitumor activity of both IL-33 and PD-1 blockade. Whole tumor single-cell RNA sequencing (scRNA-seq) analysis and blockade experiments revealed that the amphiregulin (AREG)-epidermal growth factor receptor (EGFR) axis mediated cross-talk between IL1RL1+ Treg cells and CAFs. We further demonstrated that the AREG/EGFR axis enables Treg cells to promote a profibrotic and immunosuppressive functional state of CAFs. Moreover, AREG mAbs and IL-33 concertedly inhibited tumor growth. Our study reveals a previously unidentified AREG/EGFR-mediated Treg/CAF coupling that controls the bifurcation of fibroblast functional states and is a critical barrier for cancer immunotherapy.

The multifaceted roles of CD4+ T cells and MHC class II in cancer surveillance

CD4⁺ T cells exhibit diverse functions in cancer surveillance. Concordantly, single-cell transcriptional analyses have revealed several distinct CD4⁺ T-cell differentiation states in tumours, including cytotoxic and regulatory subsets associated with favourable or unfavourable outcomes, respectively. These transcriptional states are determined and further shaped by dynamic interactions of CD4⁺ T cells with different types of immune cells, stromal cells and cancer cells. Therefore, we discuss the cellular networks in the tumour microenvironment (TME) that either promote or impede CD4⁺ T-cell cancer surveillance. We consider antigen/Major histocompatibility complexclass-II (MHC-II)-dependent interactions of CD4⁺ T cells with both professional antigen-presenting cells and cancer cells, the latter of which can directly express MHC-II, at least in some tumours. Additionally, we examine recent single-cell RNA sequencing studies that have shed light on the phenotype and functions of cancer-specific CD4⁺ T cells in human tumours.

The advent of immune stimulating CAFs in cancer

The theory that cancer-associated fibroblasts (CAFs) are immunosuppressive cells has prevailed throughout the past decade. However, recent high-throughput, high-resolution mesenchyme-directed single-cell studies have harnessed computational advances to functionally characterize cell states, highlighting the existence of immunostimulatory CAFs. Our group and others have uncovered and experimentally substantiated key functions of cancer antigen-presenting CAFs in T cell immunity, both in vitro and in vivo, refuting the conventional assumption that CAFs impede adaptive immune rejection of tumours. In this Perspective, I unify the follicular and non-follicular, non-endothelial stroma of tumours under the 'peripheral adaptive immune mesenchyme' framework and position subsets of CAFs as direct positive regulators of the adaptive immune system. Building on the understanding of cancer antigen presentation by CAFs and the second touch hypothesis, which postulates that full T cell polarization requires interaction with antigen-presenting cells in the non-lymphoid tissue where the antigen resides, I re-design the 'cancer-immunity cycle' to incorporate intratumoural activation of cancer-specific CD4⁺ T cells. Lastly, a road map to therapeutic harnessing of immunostimulatory CAF states is proposed.

Crosstalk between fibroblasts and T cells in immune networks

Fibroblasts are primarily considered as cells that support organ structures and are currently receiving attention for their roles in regulating immune responses in health and disease. Fibroblasts are assigned distinct phenotypes and functions in different organs owing to their diverse origins and functions. Their roles in the immune system are multifaceted, ranging from supporting homeostasis to inducing or suppressing inflammatory responses of immune cells. As a major component of immune cells, T cells are responsible for adaptive immune responses and are involved in the exacerbation or alleviation of various inflammatory diseases. In this review, we discuss the mechanisms by which fibroblasts regulate immune responses by interacting with T cells in host health and diseases, as well as their potential as advanced therapeutic targets.

Lymphoid stromal cells - potential implications for the pathogenesis of CVID

Non-hematopoietic lymphoid stromal cells (LSC) maintain lymph node architecture and form niches allowing the migration, activation, and survival of immune cells. Depending on their localization in the lymph node, these cells display heterogeneous properties and secrete various factors supporting the different activities of the adaptive immune response. LSCs participate in the transport of antigen from the afferent lymph as well as in its delivery into the T and B cell zones and organize cell migration via niche-specific chemokines. While marginal reticular cells (MRC) are equipped for initial B-cell priming and T zone reticular cells (TRC) provide the matrix for T cell-dendritic cell interactions within the paracortex, germinal centers (GC) only form when both T- and B cells successfully interact at the T-B border and migrate within the B-cell follicle containing the follicular dendritic cell (FDC) network. Unlike most other LSCs, FDCs are capable of presenting antigen via complement receptors to B cells, which then differentiate within this niche and in proximity to T follicular helper (T_FH) cells into memory and plasma cells. LSCs are also implicated in maintenance of peripheral immune tolerance. In mice, TRCs induce the alternative induction of regulatory T cells instead of T_FH cells by presenting tissue-restricted self-antigens to naïve CD4 T cells via MHC-II expression. This review explores potential implications of our current knowledge of LSC populations regarding the pathogenesis of humoral immunodeficiency and autoimmunity in patients with autoimmune disorders or common variable immunodeficiency (CVID), the most common form of primary immunodeficiency in humans.

Lower Metabolic Potential and Impaired Metabolic Flexibility in Human Lymph Node Stromal Cells from Patients with Rheumatoid Arthritis

Cellular metabolism is important for determining cell function and shaping immune responses. Studies have shown a crucial role for stromal cells in steering proper immune responses in the lymph node microenvironment. These lymph node stromal cells (LNSCs) tightly regulate immune tolerance. We hypothesize that malfunctioning LNSCs create a microenvironment in which normal immune responses are not properly controlled, possibly leading to the development of autoimmune diseases such as rheumatoid arthritis (RA). Therefore, we set out to determine their metabolic profile during health and systemic autoimmunity. We included autoantibody positive individuals at risk of developing RA (RA-risk individuals), RA patients and healthy volunteers. All study subjects underwent lymph node biopsy sampling. Mitochondrial function in cultured LNSCs was assessed by quantitative PCR, flow cytometry, Seahorse and oleate oxidation assays. Overall, mitochondrial respiration was lower in RA(-risk) LNSCs compared with healthy LNSCs, while metabolic potential was only lower in RA LNSCs. To maintain basal mitochondrial respiration, all LNSCs were mostly dependent on fatty acid oxidation. However, RA(-risk) LNSCs were also dependent on glutamine oxidation. Finally, we showed that RA LNSCs have impaired metabolic flexibility. Our results show that the metabolic landscape of LNSCs is not only altered during established disease, but partly already in individuals at risk of developing RA. Future studies are needed to investigate the impact of restoring metabolic capacity in LNSC-mediated immunomodulation and disease progression.

Fibroblastic reticular cells mitigate acute GvHD via MHCII-dependent maintenance of regulatory T cells

Acute graft versus host disease (aGvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT) inflicted by alloreactive T cells primed in secondary lymphoid organs (SLOs) and subsequent damage to aGvHD target tissues. In recent years, Treg transfer and/or expansion has emerged as a promising therapy to modulate aGvHD. However, cellular niches essential for fostering Tregs to prevent aGvHD have not been explored. Here, we tested whether and to what extent MHC class II (MHCII) expressed on Ccl19+ fibroblastic reticular cells (FRCs) shape the donor CD4+ T cell response during aGvHD. Animals lacking MHCII expression on Ccl19-Cre-expressing FRCs (MHCIIΔCcl19) showed aberrant CD4+ T cell activation in the effector phase, resulting in exacerbated aGvHD that was associated with significantly reduced expansion of Foxp3+ Tregs and invariant NK T (iNKT) cells. Skewed Treg maintenance in MHCIIΔCcl19 mice resulted in loss of protection from aGvHD provided by adoptively transferred donor Tregs. In contrast, although FRCs upregulated costimulatory surface receptors, and although they degraded and processed exogenous antigens after myeloablative irradiation, FRCs were dispensable to activate alloreactive CD4+ T cells in 2 mouse models of aGvHD. In summary, these data reveal an immunoprotective, MHCII-mediated function of FRC niches in secondary lymphoid organs (SLOs) after allo-HCT and highlight a framework of cellular and molecular interactions that regulate CD4+ T cell alloimmunity.

Lymphatic vessels in cancer

The lymphatic system, composed of initial and collecting lymphatic vessels as well as lymph nodes that are present in almost every tissue of the human body, acts as an essential transport system for fluids, biomolecules and cells between peripheral tissues and the central circulation. Consequently, it is required for normal body physiology but is also involved in the pathogenesis of various diseases, most notably cancer. The important role of tumor-associated lymphatic vessels and lymphangiogenesis in the formation of lymph node metastasis has been elucidated during the last two decades, whereas the underlying mechanisms and the relation between lymphatic and peripheral organ dissemination of cancer cells are incompletely understood. Lymphatic vessels are also important for tumor-host communication, relaying molecular information from a primary or metastatic tumor to regional lymph nodes and the circulatory system. Beyond antigen transport, lymphatic endothelial cells, particularly those residing in lymph node sinuses, have recently been recognized as direct regulators of tumor immunity and immunotherapy responsiveness, presenting tumor antigens and expressing several immune-modulatory signals including PD-L1. In this review, we summarize recent discoveries in this rapidly evolving field and highlight strategies and challenges of therapeutic targeting of lymphatic vessels or specific lymphatic functions in cancer patients.

Radioresistant cells initiate lymphocyte-dependent lung inflammation and IFNγ-dependent mortality in STING gain-of-function mice

Pediatric patients with constitutively active mutations in the cytosolic double-stranded-DNA-sensing adaptor STING develop an autoinflammatory syndrome known as STING-associated vasculopathy with onset in infancy (SAVI). SAVI patients have elevated interferon-stimulated gene expression and suffer from interstitial lung disease (ILD) with lymphocyte predominate bronchus-associated lymphoid tissue (BALT). Mice harboring SAVI mutations (STING V154M [VM]) that recapitulate human disease also develop lymphocyte-rich BALT. Ablation of either T or B lymphocytes prolongs the survival of SAVI mice, but lung immune aggregates persist, indicating that T cells and B cells can independently be recruited as BALT. VM T cells produced IFNγ, and IFNγR deficiency prolonged the survival of SAVI mice; however, T-cell-dependent recruitment of infiltrating myeloid cells to the lung was IFNγ independent. Lethally irradiated VM recipients fully reconstituted with wild type bone-marrow-derived cells still developed ILD, pointing to a critical role for VM-expressing radioresistant parenchymal and/or stromal cells in the recruitment and activation of pathogenic lymphocytes. We identified lung endothelial cells as radioresistant cells that express STING. Transcriptional analysis of VM endothelial cells revealed up-regulation of chemokines, proinflammatory cytokines, and genes associated with antigen presentation. Together, our data show that VM-expressing radioresistant cells play a key role in the initiation of lung disease in VM mice and provide insights for the treatment of SAVI patients, with implications for ILD associated with other connective tissue disorders.

Canonical and Non-Canonical Functions of the Autophagy Machinery in MHC Restricted Antigen Presentation

Macroautophagy delivers cytoplasmic constituents for lysosomal degradation. Since major histocompatibility complex (MHC) class II molecules sample peptides after lysosomal degradation for presentation to CD4+ T cells, it was originally described that these peptides can also originate from macroautophagy substrates. In recent years it has become clear that in addition to this canonical function of the macroautophagy machinery during MHC class II restricted antigen presentation at least parts of this machinery are also used to regulate phagocytosis of antigens, degradation of MHC class I molecules, and unconventional secretion of antigens in extracellular vesicles, including virus particles. This review discusses how both canonical and non-canonical functions of the macroautophagy machinery influence antigen presentation on MHC class I and II molecules to CD8+ and CD4+ T cells. A better understanding of the molecular mechanisms by which the macroautophagy machinery is distributed between its canonical and non-canonical functions should allow targeting of antigens to these different pathways to influence MHC restricted presentation during vaccination against infectious diseases and tumors.

The Influence of Different Types of Diabetes on Vascular Complications

The final outcome of diabetes is chronic complications, of which vascular complications are the most serious, which is the main cause of death for diabetic patients and the direct cause of the increase in the cost of diabetes. Type 1 and type 2 diabetes are the main types of diabetes, and their pathogenesis is completely different. Type 1 diabetes is caused by genetics and immunity to destroy a large number of β cells, and insulin secretion is absolutely insufficient, which is more prone to microvascular complications. Type 2 diabetes is dominated by insulin resistance, leading to atherosclerosis, which is more likely to progress to macrovascular complications. This article explores the pathogenesis of two types of diabetes, analyzes the pathogenesis of different vascular complications, and tries to explain the different trends in the progression of different types of diabetes to vascular complications, in order to better prevent diabetes and its vascular complications.

Bridging Insights From Lymph Node and Synovium Studies in Early Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease of unknown etiology characterized by inflammation of the peripheral synovial joints leading to pannus formation and bone destruction. Rheumatoid Factor (RF) and anti-citrullinated protein antibodies (ACPA) are present years before clinical manifestations and are indicative of a break in tolerance that precedes chronic inflammation. The majority of studies investigating disease pathogenesis focus on the synovial joint as target site of inflammation while few studies explore the initial break in peripheral tolerance which occurs within secondary lymphoid organs such as lymph nodes. If explored during the earliest phases of RA, lymph node research may provide innovative drug targets for disease modulation or prevention. RA research largely centers on the role and origin of lymphocytes, such as pro-inflammatory T cells and macrophages that infiltrate the joint, as well as growing efforts to determine the role of stromal cells within the synovium. It is therefore important to explore these cell types also within the lymph node as a number of mouse studies suggest a prominent immunomodulatory role for lymph node stromal cells. Synovium and proximal peripheral lymph nodes should be investigated in conjunction with one another to gain understanding of the immunological processes driving RA progression from systemic autoimmunity toward synovial inflammation. This perspective seeks to provide an overview of current literature concerning the immunological changes present within lymph nodes and synovium during early RA. It will also propose areas that warrant further exploration with the aim to uncover novel targets to prevent disease progression.

Tissue-specific Tregs in cancer metastasis: opportunities for precision immunotherapy

Decades of advancements in immuno-oncology have enabled the development of current immunotherapies, which provide long-term treatment responses in certain metastatic cancer patients. However, cures remain infrequent, and most patients ultimately succumb to treatment-refractory metastatic disease. Recent insights suggest that tumors at certain organ sites exhibit distinctive response patterns to immunotherapy and can even reduce antitumor immunity within anatomically distant tumors, suggesting the activation of tissue-specific immune tolerogenic mechanisms in some cases of therapy resistance. Specialized immune cells known as regulatory T cells (Tregs) are present within all tissues in the body and coordinate the suppression of excessive immune activation to curb autoimmunity and maintain immune homeostasis. Despite the high volume of research on Tregs, the findings have failed to reconcile tissue-specific Treg functions in organs, such as tolerance, tissue repair, and regeneration, with their suppression of local and systemic tumor immunity in the context of immunotherapy resistance. To improve the understanding of how the tissue-specific functions of Tregs impact cancer immunotherapy, we review the specialized role of Tregs in clinically common and challenging organ sites of cancer metastasis, highlight research that describes Treg impacts on tissue-specific and systemic immune regulation in the context of immunotherapy, and summarize ongoing work reporting clinically feasible strategies that combine the specific targeting of Tregs with systemic cancer immunotherapy. Improved knowledge of Tregs in the framework of their tissue-specific biology and clinical sites of organ metastasis will enable more precise targeting of immunotherapy and have profound implications for treating patients with metastatic cancer.

Induction of Foxp3 and activation of Tregs by HSP gp96 for treatment of autoimmune diseases

Upregulation and stabilization of Foxp3 expression in Tregs are essential for regulating Treg function and immune homeostasis. In this study, gp96 immunization showed obvious therapeutic effects in a Lyn^–/– mouse model of systemic lupus erythematosus. Moreover, gp96 alleviated the initiation and progression of MOG-induced experimental autoimmune encephalomyelitis. Immunization of gp96 increased Treg frequency, expansion, and suppressive function. Gene expression profiling identified the NF-κB family member p65 and c-Rel as the key transcription factors for enhanced Foxp3 expression in Treg by gp96. Mutant gp96 within its Toll-like receptor (TLR) binding domain, TLR2 knockout mice, and mice with cell-specific deletion of MyD88, were used to demonstrate that gp96 activated Tregs and induced Foxp3 expression via a TLR2-MyD88-mediated NF-κB signaling pathway. Taken together, these results show that gp96 immunization restricted antibody-induced and Th-induced autoimmune diseases by integrating Treg expansion and activation, indicating its potential clinical usefulness against autoimmune diseases.

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SLE symptoms in Lyn^–/– mice are ameliorated by gp96 immunization

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Tregs expanded by gp96 provide potential in suppressing Th-mediated EAE

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Gp96 promotes Treg proliferation, stability, and suppressive function

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Gp96 binds to and activates Treg in a TLR2-MyD88-NF-кB-Foxp3 pathway

Imaging leukocyte migration through afferent lymphatics

Afferent lymphatics mediate the transport of antigen and leukocytes, especially of dendritic cells (DCs) and T cells, from peripheral tissues to draining lymph nodes (dLNs). As such they play important roles in the induction and regulation of adaptive immunity. Over the past 15 years, great advances in our understanding of leukocyte trafficking through afferent lymphatics have been made through time‐lapse imaging studies performed in tissue explants and in vivo, allowing to visualize this process with cellular resolution. Intravital imaging has revealed that intralymphatic leukocytes continue to actively migrate once they have entered into lymphatic capillaries, as a consequence of the low flow conditions present in this compartment. In fact, leukocytes spend considerable time migrating, patrolling and interacting with the lymphatic endothelium or with other intralymphatic leukocytes within lymphatic capillaries. Cells typically only start to detach once they arrive in downstream‐located collecting vessels, where vessel contractions contribute to enhanced lymph flow. In this review, we will introduce the biology of afferent lymphatic vessels and report on the presumed significance of DC and T cell migration via this route. We will specifically highlight how time‐lapse imaging has contributed to the current model of lymphatic trafficking and the emerging notion that ‐ besides transport – lymphatic capillaries exert additional roles in immune modulation.

Lymph Node-Targeted Synthetically Glycosylated Antigen Leads to Antigen-Specific Immunological Tolerance

Inverse vaccines that tolerogenically target antigens to antigen-presenting cells (APCs) offer promise in prevention of immunity to allergens and protein drugs and treatment of autoimmunity. We have previously shown that targeting hepatic APCs through intravenous injection of synthetically glycosylated antigen leads to effective induction of antigen-specific immunological tolerance. Here, we demonstrate that targeting these glycoconjugates to lymph node (LN) APCs under homeostatic conditions leads to local and increased accumulation in the LNs compared to unmodified antigen and induces a tolerogenic state both locally and systemically. Subcutaneous administration directs the polymeric glycoconjugate to the draining LN, where the glycoconjugated antigen generates robust antigen-specific CD4+ and CD8+ T cell tolerance and hypo-responsiveness to antigenic challenge via a number of mechanisms, including clonal deletion, anergy of activated T cells, and expansion of regulatory T cells. Lag-3 up-regulation on CD4+ and CD8+ T cells represents an essential mechanism of suppression. Additionally, presentation of antigen released from the glycoconjugate to naïve T cells is mediated mainly by LN-resident CD8+ and CD11b+ dendritic cells. Thus, here we demonstrate that antigen targeting via synthetic glycosylation to impart affinity for APC scavenger receptors generates tolerance when LN dendritic cells are the cellular target.

Lymph node stromal cells: subsets and functions in health and disease

Lymph nodes (LNs) aid the interaction between lymphocytes and antigen-presenting cells, resulting in adequate and prolonged adaptive immune responses. LN stromal cells (LNSCs) are crucially involved in steering adaptive immune responses at different levels. Most knowledge on LNSCs has been obtained from mouse studies, and few studies indicate similarities with their human counterparts. Recent advances in single-cell technologies have revealed significant LNSC heterogeneity among different subsets with potential selective functions in immunity. This review provides an overview of current knowledge of LNSCs based on human and murine studies describing the role of these cells in health and disease.

Lymph Node Stromal Cell-Intrinsic MHC Class II Expression Promotes MHC Class I-Restricted CD8 T Cell Lineage Conversion to Regulatory CD4 T Cells

MHC class I (MHC-I)-restricted CD4⁺ T cells have long been discovered in the natural repertoire of healthy humans as well as patients with autoimmune diseases or cancer, but the exact origin of these cells remains to be fully characterized. In mouse models, mature peripheral CD8⁺ T cells have the potential to convert to CD4⁺ T cells in the mesenteric lymph nodes. This conversion can produce a unique population of MHC-I-restricted CD4⁺ T cells including Foxp3⁺ regulatory T cells termed MHC-I-restricted CD4⁺Foxp3⁺ T (CI-T_reg) cells. In this study we examined the cellular and molecular elements that promote CD8-to-CD4 lineage conversion and the development of CI-T_reg cells in mice. Using adoptive transfer and bone marrow chimera experiments, we found that the differentiation of CI-T_reg cells was driven by lymph node stromal cell (LNSC)-intrinsic MHC-II expression as opposed to transcytosis of MHC-II from bone marrow-derived APCs. The lineage conversion was accompanied by Runx3 versus ThPOK transcriptional switch. This finding of a new role for LNSCs in vivo led us to develop an efficient tissue culture method using LNSCs to generate and expand CI-T_reg cells in vitro. CI-T_reg cells expanded in vitro with LNSCs effectively suppressed inflammatory tissue damage caused by pathogenic CD4⁺ T cells in mouse models of colitis. This study identified a novel role of MHC-II expressed by LNSCs in immune regulation and the potential utilization of LNSCs to generate novel subsets of immune regulatory cells for therapeutic applications.

The lymphatic vasculature: An active and dynamic player in cancer progression

The lymphatic vasculature has been widely described and explored for its key functions in fluid homeostasis and in the organization and modulation of the immune response. Besides transporting immune cells, lymphatic vessels play relevant roles in tumor growth and tumor cell dissemination. Cancer cells that have invaded into afferent lymphatics are propagated to tumor‐draining lymph nodes (LNs), which represent an important hub for metastatic cell arrest and growth, immune modulation, and secondary dissemination to distant sites. In recent years many studies have reported new mechanisms by which the lymphatic vasculature affects cancer progression, ranging from induction of lymphangiogenesis to metastatic niche preconditioning or immune modulation. In this review, we provide an up‐to‐date description of lymphatic organization and function in peripheral tissues and in LNs and the changes induced to this system by tumor growth and progression. We will specifically focus on the reported interactions that occur between tumor cells and lymphatic endothelial cells (LECs), as well as on interactions between immune cells and LECs, both in the tumor microenvironment and in tumor‐draining LNs. Moreover, the most recent prognostic and therapeutic implications of lymphatics in cancer will be reported and discussed in light of the new immune‐modulatory roles that have been ascribed to LECs.

Lymph node fibroblastic reticular cells steer immune responses

Lymph nodes (LNs), where immune responses are initiated, are organized into distinctive compartments by fibroblastic reticular cells (FRCs). FRCs imprint immune responses by supporting LN architecture, recruiting immune cells, coordinating immune cell crosstalk, and presenting antigens. Recent high-resolution transcriptional and histological analyses have enriched our knowledge of LN FRC genetic and spatial heterogeneities. Here, we summarize updated anatomic, phenotypic, and functional identities of FRC subsets, delve into topological and transcriptional remodeling of FRCs in inflammation, and illustrate the crosstalk between FRCs and immune cells. Discussing FRC functions in immunity and tolerance, we highlight state-of-the-art FRC-based therapeutic approaches for maintaining physiological homeostasis, steering protective immunity, inducing transplantation tolerance, and treating diverse immune-related diseases.

MHC Class II Antigen Presentation by Lymphatic Endothelial Cells in Tumors Promotes Intratumoral Regulatory T cell-Suppressive Functions

Several solid malignancies trigger lymphangiogenesis, facilitating metastasis. Tumor-associated lymphatic vessels significantly contribute to the generation of an immunosuppressive tumor microenvironment (TME). Here, we have investigated the ability of tumoral lymphatic endothelial cells (LEC) to function as MHC class II-restricted antigen-presenting cells in the regulation of antitumor immunity. Using murine models of lymphangiogenic tumors engrafted under the skin, we have shown that tumoral LECs upregulate MHC class II and the MHC class II antigen-processing machinery, and that they promote regulatory T-cell (Treg) expansion ex vivo. In mice with LEC-restricted lack of MHC class II expression, tumor growth was severely impaired, whereas tumor-infiltrating effector T cells were increased. Reduction of tumor growth and reinvigoration of tumor-specific T-cell responses both resulted from alterations of the tumor-infiltrating Treg transcriptome and phenotype. Treg-suppressive functions were profoundly altered in tumors lacking MHC class II in LECs. No difference in effector T-cell responses or Treg phenotype and functions was observed in tumor-draining lymph nodes, indicating that MHC class II-restricted antigen presentation by LECs was required locally in the TME to confer potent suppressive functions to Tregs. Altogether, our study suggests that MHC class II-restricted antigen-presenting tumoral LECs function as a local brake, dampening T cell-mediated antitumor immunity and promoting intratumoral Treg-suppressive functions.

Type II alveolar cell MHCII improves respiratory viral disease outcomes while exhibiting limited antigen presentation

Type II alveolar cells (AT2s) are critical for basic respiratory homeostasis and tissue repair after lung injury. Prior studies indicate that AT2s also express major histocompatibility complex class II (MHCII) molecules, but how MHCII expression by AT2s is regulated and how it contributes to host defense remain unclear. Here we show that AT2s express high levels of MHCII independent of conventional inflammatory stimuli, and that selective loss of MHCII from AT2s in mice results in modest worsening of respiratory virus disease following influenza and Sendai virus infections. We also find that AT2s exhibit MHCII presentation capacity that is substantially limited compared to professional antigen presenting cells. The combination of constitutive MHCII expression and restrained antigen presentation may position AT2s to contribute to lung adaptive immune responses in a measured fashion, without over-amplifying damaging inflammation.

Stromal Cells Underlining the Paths From Autoimmunity, Inflammation to Cancer With Roles Beyond Structural and Nutritional Support

Stromal cells provide structural support and nutrients in secondary lymphoid organs and non-lymphoid tissues. However, accumulating evidence suggests that a complex relationship exists between stromal cells and immune cells. Interactions between immune cells and stromal cells have been shown to influence the pathology of both autoimmunity and cancer. This review examines the heterogeneity of stromal cells within the lymph node and non-lymphoid tissues during both homeostatic and inflammatory conditions, in particular autoimmunity and cancer, with the goal of better understanding the complex and apparently paradoxical relationship between these two classes of diseases. The review surveys potential novel mechanisms involving the interactions between stromal cells and immune cells which may contribute to the development, pathology and underlying connection between autoimmunity and cancer, including potential pathways from autoimmune inflammation to either “hot” or “cold” tumors. These interactions may provide some insights to explain the rising incidence of both autoimmunity and cancer in young women in industrialized countries and have the potential to be exploited in the development of new interventions for preventions and treatments of both autoimmune diseases and cancer.

LN-Derived Fibroblastic Reticular Cells and Their Impact on T Cell Response—A Systematic Review

Fibroblastic reticular cells (FRCs), usually found and isolated from the T cell zone of lymph nodes, have recently been described as much more than simple structural cells. Originally, these cells were described to form a conduit system called the “reticular fiber network” and for being responsible for transferring the lymph fluid drained from tissues through afferent lymphatic vessels to the T cell zone. However, nowadays, these cells are described as being capable of secreting several cytokines and chemokines and possessing the ability to interfere with the immune response, improving it, and also controlling lymphocyte proliferation. Here, we performed a systematic review of the several methods employed to investigate the mechanisms used by fibroblastic reticular cells to control the immune response, as well as their ability in determining the fate of T cells. We searched articles indexed and published in the last five years, between 2016 and 2020, in PubMed, Scopus, and Cochrane, following the PRISMA guidelines. We found 175 articles published in the literature using our searching strategies, but only 24 articles fulfilled our inclusion criteria and are discussed here. Other articles important in the built knowledge of FRCs were included in the introduction and discussion. The studies selected for this review used different strategies in order to access the contribution of FRCs to different mechanisms involved in the immune response: 21% evaluated viral infection in this context, 13% used a model of autoimmunity, 8% used a model of GvHD or cancer, 4% used a model of Ischemic-reperfusion injury (IRI). Another four studies just targeted a particular signaling pathway, such as MHC II expression, FRC microvesicles, FRC secretion of IL-15, FRC network, or ablation of the lysophosphatidic acid (LPA)-producing ectoenzyme autotaxin. In conclusion, our review shows the strategies used by several studies to isolate and culture fibroblastic reticular cells, the models chosen by each one, and dissects their main findings and implications in homeostasis and disease.

Tertiary Lymphoid Structures: Diversity in Their Development, Composition, and Role

Lymph node stromal cells coordinate the adaptive immune response in secondary lymphoid organs, providing both a structural matrix and soluble factors that regulate survival and migration of immune cells, ultimately promoting Ag encounter. In several inflamed tissues, resident fibroblasts can acquire lymphoid-stroma properties and drive the formation of ectopic aggregates of immune cells, named tertiary lymphoid structures (TLSs). Mature TLSs are functional sites for the development of adaptive responses and, consequently, when present, can have an impact in both autoimmunity and cancer conditions. In this review, we go over recent findings concerning both lymph node stromal cells and TLSs function and formation and further describe what is currently known about their role in disease, particularly their potential in tolerance.

LN-Derived Fibroblastic Reticular Cells and Their Impact on T Cell Response-A Systematic Review

Fibroblastic reticular cells (FRCs), usually found and isolated from the T cell zone of lymph nodes, have recently been described as much more than simple structural cells. Originally, these cells were described to form a conduit system called the “reticular fiber network” and for being responsible for transferring the lymph fluid drained from tissues through afferent lymphatic vessels to the T cell zone. However, nowadays, these cells are described as being capable of secreting several cytokines and chemokines and possessing the ability to interfere with the immune response, improving it, and also controlling lymphocyte proliferation. Here, we performed a systematic review of the several methods employed to investigate the mechanisms used by fibroblastic reticular cells to control the immune response, as well as their ability in determining the fate of T cells. We searched articles indexed and published in the last five years, between 2016 and 2020, in PubMed, Scopus, and Cochrane, following the PRISMA guidelines. We found 175 articles published in the literature using our searching strategies, but only 24 articles fulfilled our inclusion criteria and are discussed here. Other articles important in the built knowledge of FRCs were included in the introduction and discussion. The studies selected for this review used different strategies in order to access the contribution of FRCs to different mechanisms involved in the immune response: 21% evaluated viral infection in this context, 13% used a model of autoimmunity, 8% used a model of GvHD or cancer, 4% used a model of Ischemic-reperfusion injury (IRI). Another four studies just targeted a particular signaling pathway, such as MHC II expression, FRC microvesicles, FRC secretion of IL-15, FRC network, or ablation of the lysophosphatidic acid (LPA)-producing ectoenzyme autotaxin. In conclusion, our review shows the strategies used by several studies to isolate and culture fibroblastic reticular cells, the models chosen by each one, and dissects their main findings and implications in homeostasis and disease.

Macroautophagy in lymphatic endothelial cells inhibits T cell-mediated autoimmunity

Lymphatic endothelial cells (LECs) present peripheral tissue antigens to induce T cell tolerance. In addition, LECs are the main source of sphingosine-1-phosphate (S1P), promoting naive T cell survival and effector T cell exit from lymph nodes (LNs). Autophagy is a physiological process essential for cellular homeostasis. We investigated whether autophagy in LECs modulates T cell activation in experimental arthritis. Whereas genetic abrogation of autophagy in LECs does not alter immune homeostasis, it induces alterations of the regulatory T cell (T reg cell) population in LNs from arthritic mice, which might be linked to MHCII-mediated antigen presentation by LECs. Furthermore, inflammation-induced autophagy in LECs promotes the degradation of Sphingosine kinase 1 (SphK1), resulting in decreased S1P production. Consequently, in arthritic mice lacking autophagy in LECs, pathogenic Th17 cell migration toward LEC-derived S1P gradients and egress from LNs are enhanced, as well as infiltration of inflamed joints, resulting in exacerbated arthritis. Our results highlight the autophagy pathway as an important regulator of LEC immunomodulatory functions in inflammatory conditions.

Progression of Metastasis through Lymphatic System

Lymph nodes are the most common sites of metastasis in cancer patients. Nodal disease status provides great prognostic power, but how lymph node metastases should be treated is under debate. Thus, it is important to understand the mechanisms by which lymph node metastases progress and how they can be targeted to provide therapeutic benefits. In this review, we focus on delineating the process of cancer cell migration to and through lymphatic vessels, survival in draining lymph nodes and further spread to other distant organs. In addition, emerging molecular targets and potential strategies to inhibit lymph node metastasis are discussed.

Conversations that count: Cellular interactions that drive T cell fate

The relationship between the extrinsic environment and the internal transcriptional network is circular. Naive T cells first engage with antigen‐presenting cells to set transcriptional differentiation networks in motion. In turn, this regulates specific chemokine receptors that direct migration into distinct lymph node niches. Movement into these regions brings newly activated T cells into contact with accessory cells and cytokines that reinforce the differentiation programming to specify T cell function. We and others have observed similarities in the transcriptional networks that specify both CD4+ T follicular helper (T_FH) cells and CD8+ central memory stem‐like (T_SCM) cells. Here, we compare and contrast the current knowledge for these shared differentiation programs, compared to their effector counterparts, CD4+ T‐helper 1 (T_H1) and CD8+ short‐lived effector (T_SLEC) cells. Understanding the interplay between cellular interactions and transcriptional programming is essential to harness T cell differentiation that is fit for purpose; to stimulate potent T cell effector function for the elimination of chronic infection and cancer; or to amplify the formation of humoral immunity and longevity of cellular memory to prevent infectious diseases.