Lymph node fibroblastic reticular cells in health and disease

Single-cell omics in inflammatory bowel disease: recent insights and future clinical applications

Inflammatory bowel diseases (IBDs), which include ulcerative colitis (UC) and Crohn's disease (CD), are chronic conditions characterised by inflammation of the intestinal tract. Alterations in virtually all intestinal cell types, including immune, epithelial and stromal cells, have been described in these diseases. The study of IBD has historically relied on bulk transcriptomics, but this method averages signals across diverse cell types, limiting insights. Single-cell omic technologies overcome the intrinsic limitations of bulk analysis and reveal the complexity of multicellular tissues at a cell-by-cell resolution. Within healthy and inflamed intestinal tissues, single-cell omics, particularly single-cell RNA sequencing, have contributed to uncovering novel cell types and cell functions linked to disease activity or the development of complications. Collectively, these results help identify therapeutic targets in difficult-to-treat complications such as fibrostenosis, creeping fat accumulation, perianal fistulae or inflammation of the pouch. More recently, single-cell omics have gradually been adopted in studies to understand therapeutic responses, identify mechanisms of drug failure and potentially develop predictors with clinical utility. Although these are early days, such studies lay the groundwork for the implementation in clinical practice of new technologies in diagnostics, monitoring and prediction of disease prognosis. With this review, we aim to provide a comprehensive survey of the studies that have applied single-cell omics to the study of UC or CD, and offer our perspective on the main findings these studies contribute. Finally, we discuss the limitations and potential benefits that the integration of single-cell omics into clinical practice and drug development could offer.

Single cell and spatial analysis of immune-hot and immune-cold tumours identifies fibroblast subtypes associated with distinct immunological niches and positive immunotherapy response

Cancer-associated Fibroblasts (CAFs) have emerged as critical regulators of anti-tumour immunity, with both beneficial and detrimental properties that remain poorly characterised. To investigate this, we performed single-cell and spatial transcriptomic analysis, comparing head & neck squamous cell carcinoma (HNSCC) subgroups, which although heterogenous, can be considered broadly immune-hot and immune-cold (human papillomavirus [HPV]+ve and HPV-ve tumours respectively). This identified six fibroblast subpopulations, including two with immunomodulatory gene expression profiles (IL-11 + inflammatory [i]CAF and CCL19 + fibroblastic reticular cell [FRC]-like). IL-11 + iCAF were spatially associated with inflammatory monocytes and regulated in vitro through synergistic activation of canonical NF-κB signalling by IL-1β and TNF-α. FRC-like were enriched in immune-hot HPV+ve tumours, associated with CD4 + T-cells and B-cells in tertiary lymphoid structures and regulated through non-canonical NF-κB signalling via lymphotoxin. Pan-cancer analysis revealed several 'iCAF' subgroups present in both normal and cancer tissues; IL11 + iCAF were found in cancers from the gastrointestinal (GI) tract and transcriptomically distinct from iCAFs previously described in pancreatic and breast cancers with greater inflammatory properties; FRC-like fibroblasts were present at low frequencies in all tumour types, and were associated with significantly better survival in patients receiving checkpoint immunotherapy. This work clarifies and expands current literature on immunomodulatory CAFs, highlighting links with important immunological niches.

Molecular and spatial analysis of tertiary lymphoid structures in Sjogren's syndrome

Tertiary lymphoid structures play important roles in autoimmune and non-autoimmune conditions. While many of the molecular mechanisms involved in tertiary lymphoid structure formation have been identified, the cellular sources and temporal and spatial relationship remain unknown. Here we use combine single-cell RNA-sequencing, spatial transcriptomics and proteomics of minor salivary glands of patients with Sjogren's disease and Sicca Syndrome, with ex-vivo functional studies to construct a cellular and spatial map of key components involved in the formation and function of tertiary lymphoid structures. We confirm the presence of a fibroblast cell state and identify a pericyte/mural cell state with potential immunological functions. The identification of cellular properties associated with these structures and the molecular and functional interactions identified by this analysis may provide key therapeutic cues for tertiary lymphoid structures associated conditions in autoimmunity and cancer.

Engineered human lymph node stroma model for examining interstitial fluid flow and T cell egress

The lymph node (LN) performs essential roles in immunosurveillance throughout the body. Developing in vitro models of this key tissue is of great importance to enhancing physiological relevance in immunoengineering. The LN consists of stromal populations and immune cells, which are highly organized and bathed in constant interstitial flow. The stroma, notably the fibroblastic reticular cells (FRCs) and the lymphatic endothelial cells (LECs), play crucial roles in guiding T cell migration and are known to be sensitive to fluid flow. During inflammation, interstitial fluid flow rates drastically increase in the LN. It is unknown how these altered flow rates impact crosstalk and cell behavior in the LN, and most existing in vitro models focus on the interactions between T cells, B cells, and dendritic cells rather than with the stroma. To address this gap, we developed a human engineered model of the LN stroma consisting of FRC-laden hydrogel above a monolayer of LECs in a tissue culture insert with gravity-driven interstitial flow. We found that FRCs had enhanced coverage and proliferation in response to high flow rates, while LECs experienced decreased barrier integrity. We added CD4+ and CD8+ T cells and found that their egress was significantly decreased in the presence of interstitial flow, regardless of magnitude. Interestingly, 3.0 µm/s flow, but not 0.8 µm/s flow, correlated with enhanced inflammatory cytokine secretion in the LN stroma. Overall, we demonstrate that interstitial flow is an essential consideration in the lymph node for modulating LN stroma morphology, T cell migration, and inflammation.

Lymphomas in 3D and 4D spaces

The cellular compartments in the lymph node form dynamic networks, enabling coordinated innate and adaptive immunological responses. This compartmentalization of the lymph node into subcompartments, such as the T and B zones, has been proven to be beneficial. The study of lymph node microarchitecture has yielded new insights into a range of fields, including anatomy, pathology and biological processes. This review focuses on three-dimensional (3D) and four-dimensional (4D) investigations of human lymph nodes, with a particular emphasis on comparisons with data obtained from mice. It will discuss the findings of 3D/4D investigations of human lymph nodes. The investigation of the immune system in 3D space and time offers numerous advantages over the analysis of thin tissue sections. It provides data that is not visible in two-dimensional (2D) representations. A comparison of volumes, surfaces, cell speeds, cell contact numbers, contact duration times, morphologies and other variables can be made in the context of immune responses and lymphomas. The evaluation of data, the application of statistics and the use of machine learning have all been demonstrated to be valuable. In conditions of reactivity and neoplasia, T cells are the fastest-moving cells. In contrast, B cells show slower movement and higher turning angles in reactive lymphoid tissue and lymphomas. Even slower than B cells are reticulum cells, like follicular dendritic reticulum cells (FDC) of the B zones and macrophages. Fast T cells are especially found in Hodgkin lymphomas and mantle cell lymphomas. Contact times between T and B cells differ between different lymphoma types and may prove useful in defining lymphomas. 4D technologies, which evaluate living tissue slices, are suitable for use in testing checkpoint blockers (such as nivolumab) and other therapeutic drugs or cells. Following incubation with nivolumab, the duration of contacts between CD4-positive T cells and CD30-positive Hodgkin-Reed-Sternberg cells was documented. The preliminary data indicate that 3D and 4D experiments in hematopathology may facilitate new insights into diagnostics, biology, and clinical applications, including the development of new lymphoma classifications.

Single-cell RNA sequencing of OSCC primary tumors and lymph nodes reveals distinct origin and phenotype of fibroblasts

Desmoplasia in fibroblasts within metastatic lymph nodes (MLNs) serves as an indicator of extranodal extension (ENE), which led mortality in oral squamous cell carcinoma (OSCC). However, systematic studies on fibroblasts in MLNs are lacking. Therefore, this study characterized the differences in phenotype, function, and origin of fibroblasts between primary tumors (PTs) and lymph nodes (LNs) in OSCC. We generated single-cell maps of PTs and paired MLNs and draining LNs from three OSCC patients. The transcriptomic atlas, pseudotime analysis, intercellular communication networks and enrichment analysis of the single cells were characterized. Phenotype and function heterogeneity of fibroblast cells between PTs and MLNs were further verified in vitro. Among 44,052 fibroblasts, we identified two distinct subpopulations of cancer-associated myofibroblastic cells (mCAFs): RGS4+ mCAF1 and COMP + mCAF2. Notably, they exhibited distinct distributions, with mCAF1 predominantly localized in the PTs and mCAF2 in the MLNs. Moreover, pseudotime analysis revealed their distinct origins: mCAF1 originated from inherent normal myofibroblastic cells in the PT, whereas mCAF2 originated from fibroblastic reticular cells in the LNs. Further functional experiments using primary fibroblasts revealed that, compared to mCAF1, mCAF2 in MLNs exhibited weaker crosstalk with immune cells but enhanced extracellular matrix activity, which is closely linked to ENE formation in OSCC. Additionally, we identified two fibroblast subgroups in a transforming state, indicating a potential epithelial-mesenchymal transition. Our research offers profound insights into the heterogeneity of fibroblasts between the PT and MLN in OSCC, serving as an essential resource for future drug discovery endeavors.

Mechanisms of lymph node metastasis: An extracellular vesicle perspective

In several solid tumors such as breast cancer, prostate cancer, colorectal cancer or melanoma, tumor draining lymph nodes are the earliest tissues where colonization by tumor cells is detected. Lymph nodes act as sentinels of metastatic dissemination, the deadliest phase of tumor progression. Besides hematogenous dissemination, lymphatic spread of tumor cells has been demonstrated, adding more complexity to the mechanisms involved in metastasis. A network of blood and lymphatic vessels surrounds tumors providing routes for tumor soluble factors to mediate regional and long-distance effects. Additionally, extracellular vesicles (EVs), particularly small EVs/exosomes, have been shown to circulate through the blood and lymph, favoring the formation of pre-metastatic niches in the tumor-draining lymph nodes (TDLNs) and distant organs. In this review, we present an overview of the relevance of lymph node metastasis, the structural and immune changes occurring in TDLNs during tumor progression, and how extracellular vesicles contribute to modulating some of these alterations while promoting the formation of lymph node pre-metastatic niches.

Role of estrogen signaling in fibroblastic reticular cells for innate and adaptive immune responses in antigen-induced arthritis

Women are more prone to develop rheumatoid arthritis, with peak incidence occurring around menopause. Estrogen has major effects on the immune system and is protective against arthritis. We have previously shown that treatment with estrogen inhibits inflammation and joint destruction in murine models of arthritis, although the mechanisms involved remain unclear. Fibroblastic reticular cells (FRCs) are specialized stromal cells that generate the three-dimensional structure of lymph nodes (LNs). FRCs are vital for coordinating immune responses from within LNs and are characterized by the expression of the chemokine CCL19, which attracts immune cells. The aim of this study was to determine whether the influence of estrogen on innate and adaptive immune cells in arthritis is mediated by estrogen signaling in FRCs. Conditional knockout mice lacking estrogen receptor α (ERα) in CCL19-expressing cells (Ccl19-CreERαfl/fl) were generated and tested. Ccl19-CreERαfl/fl mice and littermate controls were ovariectomized, treated with vehicle or estradiol and subjected to the 28-day-long antigen-induced arthritis model to enable analyses of differentiated T- and B-cell populations and innate cells in LNs by flow cytometry. The results reveal that while the response to estradiol treatment in numbers of FRCs per LN is significantly reduced in mice lacking ERα in FRCs, estrogen does not inhibit joint inflammation or markedly affect immune responses in this arthritis model. Thus, this study validates the Ccl19-CreERαfl/fl strain for studying estrogen signaling in FRCs within inflammatory diseases, although the chosen arthritis model is deemed unsuitable for addressing this question.

Human lymph node fibroblastic reticular cells maintain heterogeneous characteristics in culture

Fibroblastic reticular cells (FRCs) are mesenchymal stromal cells in human lymph nodes (LNs) playing a pivotal role in adaptive immunity. Several FRC subsets have been identified, yet it remains to be elucidated if their heterogeneity is maintained upon culture. Here, we established a protocol to preserve and culture FRCs from human LNs and characterized their phenotypic profile in fresh LN suspensions and upon culture using multispectral flow cytometry. We found nine FRC subsets in fresh human LNs, independent of donor, of which four persisted in culture throughout several passages. Interestingly, the historically FRC-defining marker podoplanin (PDPN) was not present on all FRC subsets. Therefore, we propose that CD45negCD31neg human FRCs are not restricted by PDPN expression, as we found CD90, BST1, and CD146/MCAM to be more widely expressed. Together, our data provide insight into FRC heterogeneity in human LNs, enabling further investigation into the function of individual FRC subsets.

Mechanisms of antibody mediated immunity - Distinct in early life

Immune responses in early life are characterized by a failure to robustly generate long-lasting protective responses against many common pathogens or upon vaccination. This is associated with a reduced ability to generate T-cell dependent high affinity antibodies. This review highlights the differences in T-cell dependent antibody responses observed between infants and adults, in particular focussing on the alterations in immune cell function that lead to reduced T follicular helper cell-B cell crosstalk within germinal centres in early life. Understanding the distinct functional characteristics of early life humoral immunity, and how these are regulated, will be critical in guiding age-appropriate immunological interventions in the very young.

Development and organization of omental milky spots

The milky spots in omentum are atypical lymphoid tissues that play a pivotal role in regulating immune responses in the peritoneal cavity. The milky spots act as central hubs for collecting antigens and particles from the peritoneal cavity, regulating lymphocyte trafficking, promoting the differentiation and self-renewal of immune cells, and supporting the local germinal centre response. In addition, the milky spots exhibit unique developmental characteristics that combine the features of secondary and tertiary lymphoid tissues. These structures are innately programmed to form during foetal development; however, they can also be formed postnatally in response to peritoneal irritation such as inflammation, infection, obesity, or tumour metastasis. In this review, I discuss emerging perspectives on homeostatic development and organization of the milky spots.

CCL19-Positive Lymph Node Stromal Cells Govern the Onset of Inflammatory Arthritis via Tropomyosin Receptor Kinase

OBJECTIVE

The study objective was to assess the role of CCL19+ lymph node stromal cells of the joint-draining popliteal lymph node (pLN) for the development of arthritis.

METHODS

CCL19+ lymph node stromal cells were spatiotemporally depleted for five days in the pLN before the onset of collagen-induced arthritis (CIA) using Ccl19-Cre × iDTR mice. In addition, therapeutic treatment with recombinant CCL19-immunoglobulin G (IgG), locally injected in the footpad, was used to confirm the results. RNA sequencing of lymph node stromal cells combined with T cell coculture assays using tropomyosin receptor kinase (Trk) family inhibitors together with in vivo local pLN small interfering RNA (siRNA) treatments were used to elucidate the pathway by which CCL19+ lymph node stromal cells initiate the onset of arthritis.

RESULTS

Spatiotemporal depletion of CCL19+ lymph node stromal cells prevented disease onset in CIA mice. These inhibitory effects could be mimicked by local CCL19-IgG treatment. The messenger RNA sequencing analyses showed that CCL19+ lymph node stromal cells down-regulated the expression of the tropomyosin receptor kinase A (TrkA) just before disease onset. Blocking TrkA in lymph node stromal cells led to increased T cell proliferation in in vitro coculture assays. Similar effects were observed with the pan-Trk inhibitor larotrectinib in cocultures of lymph node stromal cells of patients with rheumatoid arthritis and T cells. Finally, local pLN treatment with TrkA inhibitor and TrkA siRNA led to exacerbated arthritis scores.

CONCLUSION

CCL19+ lymph node stromal cells are crucially involved in the development of inflammatory arthritis. Therefore, targeting of CCL19+ lymph node stromal cells via TRK could provide a tool to prevent arthritis.

Tissue fibroblasts are versatile immune regulators: An evaluation of their impact on the aging process

Fibroblasts are abundant stromal cells which not only control the integrity of extracellular matrix (ECM) but also act as immune regulators. It is known that the structural cells within tissues can establish an organ-specific immunity expressing many immune-related genes and closely interact with immune cells. In fact, fibroblasts can modify their immune properties to display both pro-inflammatory and immunosuppressive activities in a context-dependent manner. After acute insults, fibroblasts promote tissue inflammation although they concurrently recruit immunosuppressive cells to enhance the resolution of inflammation. In chronic pathological states, tissue fibroblasts, especially senescent fibroblasts, can display many pro-inflammatory and immunosuppressive properties and stimulate the activities of different immunosuppressive cells. In return, immunosuppressive cells, such as M2 macrophages and myeloid-derived suppressor cells (MDSC), evoke an excessive conversion of fibroblasts into myofibroblasts, thus aggravating the severity of tissue fibrosis. Single-cell transcriptome studies on fibroblasts isolated from aged tissues have confirmed that tissue fibroblasts express many genes coding for cytokines, chemokines, and complement factors, whereas they lose some fibrogenic properties. The versatile immune properties of fibroblasts and their close cooperation with immune cells indicate that tissue fibroblasts have a crucial role in the aging process and age-related diseases.

Activation of TLR9 signaling suppresses the immunomodulating functions of CD55lo fibroblastic reticular cells during bacterial peritonitis

Fibroblastic reticular cells (FRCs) are a subpopulation of stromal cells modulating the immune environments in health and disease. We have previously shown that activation of TLR9 signaling in FRC in fat-associated lymphoid clusters (FALC) regulate peritoneal immunity via suppressing immune cell recruitment and peritoneal resident macrophage (PRM) retention. However, FRCs are heterogeneous across tissues and organs. The functions of each FRC subset and the regulation of TLR9 in distinct FRC subsets are unknown. Here, we confirmed that specific deletion of TLR9 in FRC improved bacterial clearance and survival during peritoneal infection. Furthermore, using single-cell RNA sequencing, we found two subsets of FRCs (CD55hi and CD55lo) in the mesenteric FALC. The CD55hi FRCs were enriched in gene expression related to extracellular matrix formation. The CD55lo FRCs were enriched in gene expression related to immune response. Interestingly, we found that TLR9 is dominantly expressed in the CD55lo subset. Activation of TLR9 signaling suppressed proliferation, cytokine production, and retinoid metabolism in the CD55lo FRC, but not CD55hi FRC. Notably, we found that adoptive transfer of Tlr9 -/-CD55lo FRC from mesenteric FALC more effectively improved the survival during peritonitis compared with WT-FRC or Tlr9 -/-CD55hi FRC. Furthermore, we identified CD55hi and CD55lo subsets in human adipose tissue-derived FRC and confirmed the suppressive effect of TLR9 on the proliferation and cytokine production in the CD55lo subset. Therefore, inhibition of TLR9 in the CD55lo FRCs from adipose tissue could be a useful strategy to improve the therapeutic efficacy of FRC-based therapy for peritonitis.

Lymph Node-on-Chip Technology: Cutting-Edge Advances in Immune Microenvironment Simulation

Organ-on-a-chip technology is attracting growing interest across various domains as a crucial platform for drug screening and testing and is set to play a significant role in precision medicine research. Lymph nodes, being intricately structured organs essential for the body's adaptive immune responses to antigens and foreign particles, are pivotal in assessing the immunotoxicity of novel pharmaceuticals. Significant progress has been made in research on the structure and function of the lymphatic system. However, there is still an urgent need to develop prospective tools and techniques to delve deeper into its role in various diseases' pathological and physiological processes and to develop corresponding immunotherapeutic therapies. Organ chips can accurately reproduce the specific functional areas in lymph nodes to better simulate the complex microstructure of lymph nodes and the interactions between different immune cells, which is convenient for studying specific biological processes. This paper reviews existing lymph node chips and their design approaches. It discusses the applications of the above systems in modeling immune cell motility, cell-cell interactions, vaccine responses, drug testing, and cancer research. Finally, we summarize the challenges that current research faces in terms of structure, cell source, and extracellular matrix simulation of lymph nodes, and we provide an outlook on the future direction of integrated immune system chips.

C-C Chemokine 21-Expressing T-cell Zone Fibroblastic Reticular Cells, Abundant in Lymph Nodes, Are Absent in Cancer Lymphoid Stroma

Cancer tissue generally possesses an immunosuppressive microenvironment. However, some cancers are associated with lymphoid stroma (i.e., a widely developed tertiary lymphoid structure). The T-cell zone (paracortex) of secondary lymphoid organs, particularly lymph nodes, is characterized by an abundance of T-cell zone fibroblastic reticular cells (TCZ-FRCs) that express C-C motif chemokine ligand 21 (CCL21) and smooth muscle actin (SMA). We analyzed the presence of TCZ-FRCs in 30 cases of carcinomas with lymphoid stroma of the breast, stomach, colon, tongue, and skin. Immunohistochemistry corroborated the abundance of CCL21+ SMA+ TCZ-FRCs in the normal lymph nodes. In sharp contrast, all 30 carcinomas with lymphoid stroma displayed no CCL21+ SMA+ TCZ-FRCs despite the affluence of T cells. Real-time reverse transcription polymerase chain reaction confirmed a marked decrease in the messenger ribonucleic acid expression of CCL21 and its receptor C-C motif chemokine receptor 7 in cancer lymphoid stroma compared to that in lymph nodes. Next, we analyzed the T cell phenotypes. The cancer lymphoid stroma demonstrated an abundance of CD3+ CD62L- memory-type T cells, in contrast to the presence of CD3+ CD62L+ naïve- and central memory T cells in the T cell zone of lymphoid tissues. Our data demonstrated the following: 1) Cancer lymphoid stroma lacked TCZ-FRCs with abundance of more activated T cells than in lymph nodes and 2) these were common phenomena in cancer lymphoid stroma irrespective of the histological types and organs involved.

Spatiotemporal architecture of immune cells and cancer-associated fibroblasts in high-grade serous ovarian carcinoma

High-grade serous ovarian carcinoma (HGSOC), the deadliest form of ovarian cancer, is typically diagnosed after it has metastasized and often relapses after standard-of-care platinum-based chemotherapy, likely due to advanced tumor stage, heterogeneity, and immune evasion and tumor-promoting signaling from the tumor microenvironment. To understand how spatial heterogeneity contributes to HGSOC progression and early relapse, we profiled an HGSOC tissue microarray of patient-matched longitudinal samples from 42 patients. We found spatial patterns associated with early relapse, including changes in T cell localization, malformed tertiary lymphoid structure (TLS)-like aggregates, and increased podoplanin-positive cancer-associated fibroblasts (CAFs). Using spatial features to compartmentalize the tissue, we found that plasma cells distribute in two different compartments associated with TLS-like aggregates and CAFs, and these distinct microenvironments may account for the conflicting reports about the role of plasma cells in HGSOC prognosis.

The immunoregulatory roles of non-haematopoietic cells in the kidney

The deposition of immune complexes, activation of complement and infiltration of the kidney by cells of the adaptive and innate immune systems have long been considered responsible for the induction of kidney damage in autoimmune, alloimmune and other inflammatory kidney diseases. However, emerging findings have highlighted the contribution of resident immune cells and of immune molecules expressed by kidney-resident parenchymal cells to disease processes. Several types of kidney parenchymal cells seem to express a variety of immune molecules with a distinct topographic distribution, which may reflect the exposure of these cells to different pathogenic threats or microenvironments. A growing body of literature suggests that these cells can stimulate the infiltration of immune cells that provide protection against infections or contribute to inflammation - a process that is also regulated by draining kidney lymph nodes. Moreover, components of the immune system, such as autoantibodies, cytokines and immune cells, can influence the metabolic profile of kidney parenchymal cells in the kidney, highlighting the importance of crosstalk in pathogenic processes. The development of targeted nanomedicine approaches that modulate the immune response or control inflammation and damage directly within the kidney has the potential to eliminate the need for systemically acting drugs.

Intra-abdominal transplantation of PLGA/PCL/M13 phage electrospun scaffold induces self-assembly of lymphoid tissue-like structure

Lymphoid organs are the main structural components of the immune system. In the current research, the mixture of poly lactic-co-glycolic acid (PLGA), polycaprolactone (PCL), and M13 phage or its RGD-modified form was used in the construction of a fibrillar scaffold using the electrospinning method. The constructs were transplanted intra-abdominally and examined for the formation of lymphoid-like tissues at different time intervals. The confocal and scanning electron microscopy demonstrate that M13 phage-containing scaffolds provide a suitable environment for lymph node-isolated fibroblasts. Morphological analysis demonstrate the formation of lymph node-like tissues in the M13 phage-containing scaffolds after transplantation. Histological analysis confirm both blood and lymph angiogenesis in the implanted construct and migration of inflammatory cells to the M13 phage-containing scaffolds. In addition, flow cytometry and immunohistochemistry analysis showed the homing and compartmentalization of dendritic cells (DCs), B and T lymphocytes within the PLGA/PCL/M13 phage-RGD based scaffolds and similar to what is seen in the mouse lymphoid tissues. It seems that the application of M13 phage could improve the generation of functional lymphoid tissues in the electrospun scaffolds and could be used for lymphoid tissue regeneration.

Whole-body cellular mapping in mouse using standard IgG antibodies

Whole-body imaging techniques play a vital role in exploring the interplay of physiological systems in maintaining health and driving disease. We introduce wildDISCO, a new approach for whole-body immunolabeling, optical clearing and imaging in mice, circumventing the need for transgenic reporter animals or nanobody labeling and so overcoming existing technical limitations. We identified heptakis(2,6-di-O-methyl)-β-cyclodextrin as a potent enhancer of cholesterol extraction and membrane permeabilization, enabling deep, homogeneous penetration of standard antibodies without aggregation. WildDISCO facilitates imaging of peripheral nervous systems, lymphatic vessels and immune cells in whole mice at cellular resolution by labeling diverse endogenous proteins. Additionally, we examined rare proliferating cells and the effects of biological perturbations, as demonstrated in germ-free mice. We applied wildDISCO to map tertiary lymphoid structures in the context of breast cancer, considering both primary tumor and metastases throughout the mouse body. An atlas of high-resolution images showcasing mouse nervous, lymphatic and vascular systems is accessible at http://discotechnologies.org/wildDISCO/atlas/index.php .

Rapid Generation of hPSC-Derived High Endothelial Venule Organoids with In Vivo Ectopic Lymphoid Tissue Capabilities

Bioengineering strategies for the fabrication of implantable lymphoid structures mimicking lymph nodes (LNs) and tertiary lymphoid structures (TLS) could amplify the adaptive immune response for therapeutic applications such as cancer immunotherapy. No method to date has resulted in the consistent formation of high endothelial venules (HEVs), which is the specialized vasculature responsible for naïve T cell recruitment and education in both LNs and TLS. Here orthogonal induced differentiation of human pluripotent stem cells carrying a regulatable ETV2 allele is used to rapidly and efficiently induce endothelial differentiation. Assembly of embryoid bodies combining primitive inducible endothelial cells and primary human LN fibroblastic reticular cells results in the formation of HEV-like structures that can aggregate into 3D organoids (HEVOs). Upon transplantation into immunodeficient mice, HEVOs successfully engraft and form lymphatic structures that recruit both antigen-presenting cells and adoptively-transferred lymphocytes, therefore displaying basic TLS capabilities. The results further show that functionally, HEVOs can organize an immune response and promote anti-tumor activity by adoptively-transferred T lymphocytes. Collectively, the experimental approaches represent an innovative and scalable proof-of-concept strategy for the fabrication of bioengineered TLS that can be deployed in vivo to enhance adaptive immune responses.

Lymph node-biomimetic scaffold boosts CAR-T therapy against solid tumor

The limited infiltration and persistence of chimeric antigen receptor (CAR)-T cells is primarily responsible for their treatment deficits in solid tumors. Here, we present a three-dimensional scaffold, inspired by the physiological process of T-cell proliferation in lymph nodes. This scaffold gathers the function of loading, delivery, activation and expansion for CAR-T cells to enhance their therapeutic effects on solid tumors. This porous device is made from poly(lactic-co-glycolic acid) by a microfluidic technique with the modification of T-cell stimulatory signals, including anti-CD3, anti-CD28 antibodies, as well as cytokines. This scaffold fosters a 50-fold CAR-T cell expansion in vitro and a 15-fold cell expansion in vivo. Particularly, it maintains long-lasting expansion of CAR-T cells for up to 30 days in a cervical tumor model and significantly inhibits the tumor growth. This biomimetic delivery strategy provides a versatile platform of cell delivery and activation for CAR-T cells in treating solid tumors.

Leptin Receptor Deficiency Impairs Lymph Node Development and Adaptive Immune Response

Activation and clonal expansion of the Ag-specific adaptive immune response in the draining lymph node is essential to clearing influenza A virus infections. Activation sufficient for virus clearance is dependent on the lymph node's architectural organization that is maintained by stromal cells, chiefly fibroblastic reticular cells. During an analysis of influenza A virus clearance in leptin receptor knockout (DB/DB) mice, we observed that the DB/DB mice have markedly reduced numbers of lymph node fibroblastic reticular cells at the steady state. The reduction in lymph node fibroblastic reticular cells resulted in abnormal lymph node organization and diminished numbers of adaptive immune cells in the lymph nodes under homeostatic conditions. As a consequence, the DB/DB mice were impaired in their ability to generate an effective influenza-specific adaptive immune response, which prevented virus clearance. Using leptin receptor mutant mice with point mutations at distinct signaling sites in the leptin receptor, we were able to link the leptin receptor's signaling domain tyrosine 985, which does not contribute to obesity, to lymph node fibroblastic reticular cell development and function. These results demonstrate a novel role for leptin receptor signaling in regulating lymph node development in a manner that is crucial to the generation of Ag-specific adaptive immune responses.

Multi-omic profiling of follicular lymphoma reveals changes in tissue architecture and enhanced stromal remodeling in high-risk patients

Follicular lymphoma (FL) is a generally incurable malignancy that evolves from developmentally blocked germinal center (GC) B cells. To promote survival and immune escape, tumor B cells undergo significant genetic changes and extensively remodel the lymphoid microenvironment. Dynamic interactions between tumor B cells and the tumor microenvironment (TME) are hypothesized to contribute to the broad spectrum of clinical behaviors observed among FL patients. Despite the urgent need, existing clinical tools do not reliably predict disease behavior. Using a multi-modal strategy, we examined cell-intrinsic and -extrinsic factors governing progression and therapeutic outcomes in FL patients enrolled onto a prospective clinical trial. By leveraging the strengths of each platform, we identify several tumor-specific features and microenvironmental patterns enriched in individuals who experience early relapse, the most high-risk FL patients. These features include stromal desmoplasia and changes to the follicular growth pattern present 20 months before first progression and first relapse.

Tertiary lymphoid structures in cancer: immune mechanisms and clinical implications

Cancer is a major cause of death globally, and traditional treatments often have limited efficacy and adverse effects. Immunotherapy has shown promise in various malignancies but is less effective in tumors with low immunogenicity or immunosuppressive microenvironment, especially sarcomas. Tertiary lymphoid structures (TLSs) have been associated with a favorable response to immunotherapy and improved survival in cancer patients. However, the immunological mechanisms and clinical significance of TLS in malignant tumors are not fully understood. In this review, we elucidate the composition, neogenesis, and immune characteristics of TLS in tumors, as well as the inflammatory response in cancer development. An in-depth discussion of the unique immune characteristics of TLSs in lung cancer, breast cancer, melanoma, and soft tissue sarcomas will be presented. Additionally, the therapeutic implications of TLS, including its role as a marker of therapeutic response and prognosis, and strategies to promote TLS formation and maturation will be explored. Overall, we aim to provide a comprehensive understanding of the role of TLS in the tumor immune microenvironment and suggest potential interventions for cancer treatment.

Bioinspired 3D microprinted cell scaffolds: Integration of graph theory to recapitulate complex network wiring in lymph nodes

Physical networks are ubiquitous in nature, but many of them possess a complex organizational structure that is difficult to recapitulate in artificial systems. This is especially the case in biomedical and tissue engineering, where the microstructural details of 3D cell scaffolds are important. Studies of biological networks-such as fibroblastic reticular cell (FRC) networks-have revealed the crucial role of network topology in a range of biological functions. However, cell scaffolds are rarely analyzed, or designed, using graph theory. To understand how networks affect adhered cells, 3D culture platforms capturing the complex topological properties of biologically relevant networks would be needed. In this work, we took inspiration from the small-world organization (high clustering and low path length) of FRC networks to design cell scaffolds. An algorithmic toolset was created to generate the networks and process them to improve their 3D printability. We employed tools from graph theory to show that the networks were small-world (omega factor, ω = -0.10 ± 0.02; small-world propensity, SWP = 0.74 ± 0.01). 3D microprinting was employed to physicalize networks as scaffolds, which supported the survival of FRCs. This work, therefore, represents a bioinspired, graph theory-driven approach to control the networks of microscale cell niches.

Modeling the crosstalk between malignant B cells and their microenvironment in B-cell lymphomas: challenges and opportunities

B-cell lymphomas are a group of heterogeneous neoplasms resulting from the clonal expansion of mature B cells arrested at various stages of differentiation. Specifically, two lymphoma subtypes arise from germinal centers (GCs), namely follicular lymphoma (FL) and GC B-cell diffuse large B-cell lymphoma (GCB-DLBCL). In addition to recent advances in describing the genetic landscape of FL and GCB-DLBCL, tumor microenvironment (TME) has progressively emerged as a central determinant of early lymphomagenesis, subclonal evolution, and late progression/transformation. The lymphoma-supportive niche integrates a dynamic and coordinated network of immune and stromal cells defining microarchitecture and mechanical constraints and regulating tumor cell migration, survival, proliferation, and immune escape. Several questions are still unsolved regarding the interplay between lymphoma B cells and their TME, including the mechanisms supporting these bidirectional interactions, the impact of the kinetic and spatial heterogeneity of the tumor niche on B-cell heterogeneity, and how individual genetic alterations can trigger both B-cell intrinsic and B-cell extrinsic signals driving the reprogramming of non-malignant cells. Finally, it is not clear whether these interactions might promote resistance to treatment or, conversely, offer valuable therapeutic opportunities. A major challenge in addressing these questions is the lack of relevant models integrating tumor cells with specific genetic hits, non-malignant cells with adequate functional properties and organization, extracellular matrix, and biomechanical forces. We propose here an overview of the 3D in vitro models, xenograft approaches, and genetically-engineered mouse models recently developed to study GC B-cell lymphomas with a specific focus on the pros and cons of each strategy in understanding B-cell lymphomagenesis and evaluating new therapeutic strategies.

Disorganization of secondary lymphoid organs and dyscoordination of chemokine secretion as key contributors to immune aging

Aging is characterized by progressive loss of organ and tissue function, and the immune system is no exception to that inevitable principle. Of all the age-related changes in the body, reduction of the size of, and naïve T (Tn) cell output from, the thymus occurs earliest, being prominent already before or by the time of puberty. Therefore, to preserve immunity against new infections, over much of their lives, vertebrates dominantly rely on peripheral maintenance of the Tn cell pool in the secondary lymphoid organs (SLO). However, SLO structure and function subsequently also deteriorate with aging. Several recent studies have made a convincing case that this deterioration is of major importance to the erosion of protective immunity in the last third of life. Specifically, the SLO were found to accumulate multiple degenerative changes with aging. Importantly, the results from adoptive transfer and parabiosis studies teach us that the old microenvironment is the limiting factor for protective immunity in old mice. In this review, we discuss the extent, mechanisms, and potential role of stromal cell aging in the age-related alteration of T cell homeostatic maintenance and immune function decline. We use that discussion to frame the potential strategies to correct the SLO stromal aging defects - in the context of other immune rejuvenation approaches, - to improve functional immune responses and protective immunity in older adults.

Deciphering the localization and trajectory of human natural killer cell development

Innate immune cells represent the first line of cellular immunity, comprised of both circulating and tissue-resident natural killer cells and innate lymphoid cells. These innate lymphocytes arise from a common CD34+ progenitor that differentiates into mature natural killer cells and innate lymphoid cells. The successive stages in natural killer cell maturation are characterized by increased lineage restriction and changes to phenotype and function. Mechanisms of human natural killer cell development have not been fully elucidated, especially the role of signals that drive the spatial localization and maturation of natural killer cells. Cytokines, extracellular matrix components, and chemokines provide maturation signals and influence the trafficking of natural killer cell progenitors to peripheral sites of differentiation. Here we present the latest advances in our understanding of natural killer and innate lymphoid cell development in peripheral sites, including secondary lymphoid tissues (i.e. tonsil). Recent work in the field has provided a model for the spatial distribution of natural killer cell and innate lymphoid cell developmental intermediates in tissue and generated further insights into the developmental niche. In support of this model, future studies using multifaceted approaches seek to fully map the developmental trajectory of human natural killer cells and innate lymphoid cells in secondary lymphoid tissues.

Cancer cell-derived extracellular vesicles drive pre-metastatic niche formation of lymph node via IFNGR1/JAK1/STAT1-activated-PD-L1 expression on FRCs in head and neck cancer

OBJECTIVE

The aim of this study is to evaluate the role of FRCs regulated by cancer cell-derived extracellular vesicles (CEVs) played in pre-metastatic niche (PMN) formation of lymph node (LN).

MATERIALS AND METHODS

The FRCs in sixty fresh cervical LNs from 20 patients were evaluated by flow cytometric analysis. Cells in LN with or without metastasis were analyzed by single-cell RNA sequencing (scRNA-seq). CEVs were isolated from the culture supernatant of primarily cultured cancer cells and cocultured with FRCs. Mass Spectrometry was used to identify LN metastasis related protein in CEVs. The activation of IFNGR1/JAK1/STAT1-activated-PD-L1 pathway in FRCs was detected by western blotting. FRCs were co-cultured with CD8+ T lymphocytes to confirm the cytotoxicity assay of FRCs.

RESULTS

The proportion of fibroblastic reticular cells (FRCs) was significantly higher in micro-metastatic LN in head and neck squamous cell carcinoma patients (HNSCC, p < 0.05) and scRNA-seq analysis further showed a high focus of extracellular vesicles-related pathway on FRCs in LN with metastasis (p < 0.05). Interferon gamma receptor 1 (IFNGR1) in CEVs can be engulfed by FRCs and promote PD-L1 expression on FRCs via JAK1-STAT1 pathway, resulting in an increased CD8+ T cell exhaustion.

CONCLUSION

IFNGR1, originated from cancer cell-derived extracellular vesicles, promote PD-L1 expression on FRCs and subsequent CD8+ T cell exhaustion via JAK1-STAT1 activation, which facilitate pre-metastatic niche formation and tumor metastasis in sentinel lymph node in HNSCC.

Mapping human natural killer cell development in pediatric tonsil by imaging mass cytometry and high-resolution microscopy

Natural killer (NK) cells develop from CD34+ progenitors in a stage-specific manner defined by changes in cell surface receptor expression and function. Secondary lymphoid tissues, including tonsil, are sites of human NK cell development. Here we present new insights into human NK cell development in pediatric tonsil using cyclic immunofluorescence and imaging mass cytometry. We show that NK cell subset localization and interactions are dependent on NK cell developmental stage and tissue residency. NK cell progenitors are found in the interfollicular domain in proximity to cytokine-expressing stromal cells that promote proliferation and maturation. Mature NK cells are primarily found in the T-cell rich parafollicular domain engaging in cell-cell interactions that differ depending on their stage and tissue residency. The presence of local inflammation results in changes in NK cell interactions, abundance, and localization. This study provides the first comprehensive atlas of human NK cell development in secondary lymphoid tissue.

Temporal changes in pathology and viral RNA distribution in guinea pigs following separate infection with two New World Arenaviruses

Numerous arenaviruses have been identified throughout the Americas and a subset of these viruses cause viral hemorrhagic fever in humans. This study compared the pathology and viral RNA distribution in Hartley guinea pigs challenged with two human-disease causing New World arenaviruses, Junin virus (JUNV) or Guanarito virus (GTOV). Histopathologic analysis and RNA in situ hybridization revealed similar pathology and viral RNA distribution for both groups of animals challenged with either JUNV or GTOV on days 3, 7, 10 and 12 post exposure (PE). Gross lesions were first observed on day 7 and primarily involved the lungs and liver. The most severe histologic lesions occurred in the lymph nodes, spleen, and thymus and included lymphoid depletion and necrosis which increased in severity over time. Extensive necrosis was also observed in the bone marrow on day 12. Minimal to mild inflammation with and without necrosis was observed in the choroid plexus of the brain, choroid of the eye, intestinal tract, lung and adrenal gland. Significant liver lesions were rare, consisting predominantly of hepatocyte vacuolation. Viral RNA labeling was identified in nearly all organs examined, was often extensive in certain organs and generally increased over time starting on day 7. Our data demonstrate the guinea pig may serve as a useful model to study New World arenavirus infection in humans and for the evaluation and development of medical countermeasures.

Fibroblastic reticular cells provide a supportive niche for lymph node-resident macrophages

The lymph node (LN) is home to resident macrophage populations that are essential for immune function and homeostasis, but key factors controlling this niche are undefined. Here, we show that fibroblastic reticular cells (FRCs) are an essential component of the LN macrophage niche. Genetic ablation of FRCs caused rapid loss of macrophages and monocytes from LNs across two in vivo models. Macrophages co-localized with FRCs in human LNs, and murine single-cell RNA-sequencing revealed that FRC subsets broadly expressed master macrophage regulator CSF1. Functional assays containing purified FRCs and monocytes showed that CSF1R signaling was sufficient to support macrophage development. These effects were conserved between mouse and human systems. These data indicate an important role for FRCs in maintaining the LN parenchymal macrophage niche.

Proteome analysis, bioinformatic prediction and experimental evidence revealed immune response down-regulation function for serum-starved human fibroblasts

Emerging evidence indicates that fibroblasts play pivotal roles in immunoregulation by producing various proteins under health and disease states. In the present study, for the first time, we compared the proteomes of serum-starved human skin fibroblasts and peripheral blood mononuclear cells (PBMCs) using Nano-LC-ESI-tandem mass spectrometry. This analysis contributes to a better understanding of the underlying molecular mechanisms of chronic inflammation and cancer, which are intrinsically accompanied by growth factor deficiency.The proteomes of starved fibroblasts and PBMCs consisted of 307 and 294 proteins, respectively, which are involved in lymphocyte migration, complement activation, inflammation, acute phase response, and immune regulation. Starved fibroblasts predominantly produced extracellular matrix-related proteins such as collagen/collagenase, while PBMCs produced focal adhesion-related proteins like beta-parvin and vinculin which are involved in lymphocyte migration. PBMCs produced a more diverse set of inflammatory molecules like heat shock proteins, while fibroblasts produced human leukocytes antigen-G and -E that are known as main immunomodulatory molecules. Fifty-four proteins were commonly found in both proteomes, including serum albumin, amyloid-beta, heat shock cognate 71 kDa, and complement C3. GeneMANIA bioinformatic tool predicted 418 functions for PBMCs, including reactive oxygen species metabolic processes and 241 functions for starved fibroblasts such as antigen processing and presentation including non-classical MHC -Ib pathway, and negative regulation of the immune response. Protein-protein interactions network analysis indicated the immunosuppressive function for starved fibroblasts-derived human leucocytes antigen-G and -E. Moreover, in an in vitro model of allogeneic transplantation, the immunosuppressive activity of starved fibroblasts was experimentally documented.

Conclusion

Under serum starvation-induced metabolic stress, both PBMCs and fibroblasts produced molecules like heat shock proteins and amyloid-beta, which can have pathogenic roles in auto-inflammatory diseases such as rheumatoid arthritis, type 1 diabetes mellitus, systemic lupus erythematosus, aging, and cancer. However, starved fibroblasts showed immunosuppressive activity in an in vitro model of allogeneic transplantation, suggesting their potential to modify such adverse reactions by down-regulating the immune system.

A tessellated lymphoid network provides whole-body T cell surveillance in zebrafish

Homeostatic trafficking to lymph nodes allows T cells to efficiently survey the host for cognate antigen. Nonmammalian jawed vertebrates lack lymph nodes but maintain diverse T cell pools. Here, we exploit in vivo imaging of transparent zebrafish to investigate how T cells organize and survey for antigen in an animal devoid of lymph nodes. We find that naïve-like T cells in zebrafish organize into a previously undescribed whole-body lymphoid network that supports streaming migration and coordinated trafficking through the host. This network has the cellular hallmarks of a mammalian lymph node, including naïve T cells and CCR7-ligand expressing nonhematopoietic cells, and facilitates rapid collective migration. During infection, T cells transition to a random walk that supports antigen-presenting cell interactions and subsequent activation. Our results reveal that T cells can toggle between collective migration and individual random walks to prioritize either large-scale trafficking or antigen search in situ. This lymphoid network thus facilitates whole-body T cell trafficking and antigen surveillance in the absence of a lymph node system.

New tools for immunologists: models of lymph node function from cells to tissues

The lymph node is a highly structured organ that mediates the body's adaptive immune response to antigens and other foreign particles. Central to its function is the distinct spatial assortment of lymphocytes and stromal cells, as well as chemokines that drive the signaling cascades which underpin immune responses. Investigations of lymph node biology were historically explored in vivo in animal models, using technologies that were breakthroughs in their time such as immunofluorescence with monoclonal antibodies, genetic reporters, in vivo two-photon imaging, and, more recently spatial biology techniques. However, new approaches are needed to enable tests of cell behavior and spatiotemporal dynamics under well controlled experimental perturbation, particularly for human immunity. This review presents a suite of technologies, comprising in vitro, ex vivo and in silico models, developed to study the lymph node or its components. We discuss the use of these tools to model cell behaviors in increasing order of complexity, from cell motility, to cell-cell interactions, to organ-level functions such as vaccination. Next, we identify current challenges regarding cell sourcing and culture, real time measurements of lymph node behavior in vivo and tool development for analysis and control of engineered cultures. Finally, we propose new research directions and offer our perspective on the future of this rapidly growing field. We anticipate that this review will be especially beneficial to immunologists looking to expand their toolkit for probing lymph node structure and function.

Aldh1a2 + fibroblastic reticular cells regulate lymphocyte recruitment in omental milky spots

Lymphoid clusters in visceral adipose tissue omentum, known as milky spots, play a central role in the immunological defense in the abdomen. Milky spots exhibit hybrid nature between secondary lymph organs and ectopic lymphoid tissues, yet their development and maturation mechanisms are poorly understood. Here, we identified a subset of fibroblastic reticular cells (FRCs) that are uniquely present in omental milky spots. These FRCs were characterized by the expression of retinoic acid-converting enzyme, Aldh1a2, and endothelial cell marker, Tie2, in addition to canonical FRC-associated genes. Diphtheria toxin-mediated ablation of Aldh1a2+ FRCs resulted in the alteration in milky spot structure with a significant reduction in size and cellularity. Mechanistically, Aldh1a2+ FRCs regulated the display of chemokine CXCL12 on high endothelial venules (HEVs), which recruit blood-borne lymphocytes from circulation. We further found that Aldh1a2+ FRCs are required for the maintenance of peritoneal lymphocyte composition. These results illustrate the homeostatic roles of FRCs in the formation of non-classical lymphoid tissues.

Quantitative single molecule analysis of podoplanin clustering in fibroblastic reticular cells uncovers CD44 function

Upon initial immune challenge, dendritic cells (DCs) migrate to lymph nodes and interact with fibroblastic reticular cells (FRCs) via C-type lectin-like receptor 2 (CLEC-2). CLEC-2 binds to the membrane glycoprotein podoplanin (PDPN) on FRCs, inhibiting actomyosin contractility through the FRC network and permitting lymph node expansion. The hyaluronic acid receptor CD44 is known to be required for FRCs to respond to DCs but the mechanism of action is not fully elucidated. Here, we use DNA-PAINT, a quantitative single molecule super-resolution technique, to visualize and quantify how PDPN clustering is regulated in the plasma membrane of FRCs. Our results indicate that CLEC-2 interaction leads to the formation of large PDPN clusters (i.e. more than 12 proteins per cluster) in a CD44-dependent manner. These results suggest that CD44 expression is required to stabilize large pools of PDPN at the membrane of FRCs upon CLEC-2 interaction, revealing the molecular mechanism through which CD44 facilitates cellular crosstalk between FRCs and DCs.

The cervical lymph node contributes to peripheral inflammation related to Parkinson's disease

BACKGROUND

Peripheral inflammation is an important feature of Parkinson's disease (PD). However, if and how CNS pathology is involved in the peripheral inflammation in PD remains to be fully investigated. Recently, the existence of meningeal lymphatics and its involvement in draining cerebral spinal fluid (CSF) to the cervical lymph node has been discovered. It is known that meningeal lymphatic dysfunction exists in idiopathic PD. The deep cervical lymph node (dCLN) substantially contributes to the drainage of the meningeal lymphatics. In addition, one of the lymphatics draining components, CSF, contains abundant α-synuclein (α-syn), a protein critically involved in PD pathogenesis and neuroinflammation. Thus, we began with exploring the possible structural and functional alterations of the dCLN in a PD mouse model (A53T mice) and investigated the role of pathological α-syn in peripheral inflammation and its potential underlying molecular mechanisms.

METHODS

In this study, the transgenic mice (prnp-SNCA*A53T) which specifically overexpressed A53T mutant α-syn in CNS were employed as the PD animal model. Immunofluorescent and Hematoxylin and eosin staining were used to evaluate structure of dCLN. Inflammation in dCLNs as well as in bone-marrow-derived macrophages (BMDMs) was assessed quantitatively by measuring the mRNA and protein levels of typical inflammatory cytokines (including IL-1β, IL-6 and TNF-α). Intra-cisterna magna injection, flow cytometric sorting and electrochemiluminescence immunoassays were applied to investigate the lymphatic drainage of α-syn from the CNS. RNA-seq and Western blot were used to explore how pathological α-syn mediated the inflammation in PD mice.

RESULTS

The results unequivocally revealed substantially enlarged dCLNs, along with slow lymphatic flow, and increased inflammation in the dCLNs of A53T mice. Oligomeric α-syn drained from CSF potently activated macrophages in the dCLN via endoplasmic reticulum (ER) stress. Notably, inhibition of ER stress effectively suppressed peripheral inflammation in PD mice.

CONCLUSIONS

Our findings indicate that lymph node enlargement is closely related to macrophage activation, induced by meningeal lymphatics draining oligomeric α-syn, and contributes to the peripheral inflammation in PD. In addition, ER stress is a potential therapeutic target to ameliorate PD pathogenesis.

Spleen fibroblastic reticular cell-derived acetylcholine promotes lipid metabolism to drive autoreactive B cell responses

Autoreactive B cell responses are essential for the development of systemic lupus erythematosus (SLE). Fibroblastic reticular cells (FRCs) are known to construct lymphoid compartments and regulate immune functions. Here, we identify spleen FRC-derived acetylcholine (ACh) as a key factor that controls autoreactive B cell responses in SLE. In SLE, CD36-mediated lipid uptake leads to enhanced mitochondrial oxidative phosphorylation in B cells. Accordingly, the inhibition of fatty acid oxidation results in reduced autoreactive B cell responses and ameliorated diseases in lupus mice. Ablation of CD36 in B cells impairs lipid uptake and differentiation of autoreactive B cells during autoimmune induction. Mechanistically, spleen FRC-derived ACh promotes lipid influx and generation of autoreactive B cells through CD36. Together, our data uncover a novel function of spleen FRCs in lipid metabolism and B cell differentiation, placing spleen FRC-derived ACh in a key position in promoting autoreactive B cells in SLE.

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.

Melanocortin therapies to resolve fibroblast-mediated diseases

Stromal cells have emerged as central drivers in multiple and diverse diseases, and consequently, as potential new cellular targets for the development of novel therapeutic strategies. In this review we revise the main roles of fibroblasts, not only as structural cells but also as players and regulators of immune responses. Important aspects like fibroblast heterogeneity, functional specialization and cellular plasticity are also discussed as well as the implications that these aspects may have in disease and in the design of novel therapeutics. An extensive revision of the actions of fibroblasts on different conditions uncovers the existence of numerous diseases in which this cell type plays a pathogenic role, either due to an exacerbation of their 'structural' side, or a dysregulation of their 'immune side'. In both cases, opportunities for the development of innovative therapeutic approaches exist. In this regard, here we revise the existing evidence pointing at the melanocortin pathway as a potential new strategy for the treatment and management of diseases mediated by aberrantly activated fibroblasts, including scleroderma or rheumatoid arthritis. This evidence derives from studies involving models of in vitro primary fibroblasts, in vivo models of disease as well as ongoing human clinical trials. Melanocortin drugs, which are pro-resolving mediators, have shown ability to reduce collagen deposition, activation of myofibroblasts, reduction of pro-inflammatory mediators and reduced scar formation. Here we also discuss existing challenges, both in approaching fibroblasts as therapeutic targets, and in the development of novel melanocortin drug candidates, that may help advance the field and deliver new medicines for the management of diseases with high medical needs.

A tessellated lymphoid network provides whole-body T cell surveillance in zebrafish

Homeostatic trafficking to lymph nodes allows T cells to efficiently survey the host for cognate antigen. Non-mammalian jawed vertebrates lack lymph nodes but maintain similarly diverse T cell pools. Here, we exploit in vivo imaging of transparent zebrafish to investigate how T cells organize and survey for antigen in an animal devoid of lymph nodes. We find that naïve-like T cells in zebrafish organize into a previously undescribed whole-body lymphoid network that supports streaming migration and coordinated trafficking through the host. This network has the cellular hallmarks of a mammalian lymph node, including naïve T cells and CCR7-ligand expressing non-hematopoietic cells, and facilitates rapid collective migration. During infection, T cells transition to a random walk that supports antigen presenting cell interactions and subsequent activation. Our results reveal that T cells can toggle between collective migration and individual random walks to prioritize either large-scale trafficking or antigen search in situ . This novel lymphoid network thus facilitates whole-body T cell trafficking and antigen surveillance in the absence of a lymph node system.

Significance Statement

In mammals, lymph nodes play a critical role in the initiation of adaptive immune responses by providing a dedicated place for T cells to scan antigen-presenting cells. Birds, reptiles, amphibians, and fish all maintain diverse repertoires of T cells but lack lymph nodes, raising questions about how adaptive immunity functions in lower jawed vertebrates. Here, we describe a novel network of lymphocytes in zebrafish that supports whole-body T cell trafficking and provides a site for antigen search, mirroring the function of mammalian lymph nodes. Within this network, T cells can prioritize large-scale trafficking or antigen scanning by toggling between two distinct modes of migration. This network provides valuable insights into the evolution of adaptive immunity.

The aging of the immune system and its implications for transplantation

By the last third of life, most mammals, including humans, exhibit a decline in immune cell numbers, immune organ structure, and immune defense of the organism, commonly known as immunosenescence. This decline leads to clinical manifestations of increased susceptibility to infections, particularly those caused by emerging and reemerging microorganisms, which can reach staggering levels-infection with SARS-CoV-2 has been 270-fold more lethal to older adults over 80 years of age, compared to their 18-39-year-old counterparts. However, while this would be expected to be beneficial to situations where hyporeactivity of the immune system may be desirable, this is not always the case. Here, we discuss the cellular and molecular underpinnings of immunosenescence as they pertain to outcomes of solid organ and hematopoietic transplantation.

Lymph Node Fibroblastic Reticular Cells Attenuate Immune Responses Through Induction of Tolerogenic Macrophages at Early Stage of Transplantation

BACKGROUND

Fibroblastic reticular cells (FRCs) are a type of stromal cells located in the T zone in secondary lymphoid organs. Previous studies showed that FRCs possess the potential to promote myeloid differentiation. We aim to investigate whether FRCs in lymph nodes (LNs) could induce tolerogenic macrophage generation and further influence T-cell immunity at an early stage of allogeneic hematopoietic stem cell transplantation (allo-HSCT).

METHODS

LNs were assayed to confirm the existence of proliferating macrophages after allo-HSCT. Ex vivo-expanded FRCs and bone marrow cells were cocultured to verify the generation of macrophages. Real-time quantitative PCR and ELISA assays were performed to observe the cytokines expressed by FRC. Transcriptome sequencing was performed to compare the difference between FRC-induced macrophages (FMs) and conventional macrophages. Mixed lymphocyte reaction and the utilization of FMs in acute graft-versus-host disease (aGVHD) mice were used to test the inhibitory function of FMs in T-cell immunity in vitro and in vivo.

RESULTS

We found a large number of proliferating macrophages near FRCs in LNs with tolerogenic phenotype under allo-HSCT conditions. Neutralizing anti-macrophage colony-stimulating factor receptor antibody abolished FMs generation in vitro. Phenotypic analysis and transcriptome sequencing suggested FMs possessed immunoinhibitory function. Mixed lymphocyte reaction proved that FMs could inhibit T-cell activation and differentiation toward Th1/Tc1 cells. Injection of FMs in aGVHD mice effectively attenuated aGVHD severity and mortality.

CONCLUSIONS

This study has revealed a novel mechanism of immune regulation through the generation of FRC-induced tolerogenic macrophages in LNs at an early stage of allo-HSCT.

Delivery of costimulatory blockade to lymph nodes promotes transplant acceptance in mice

The lymph node (LN) is the primary site of alloimmunity activation and regulation during transplantation. Here, we investigated how fibroblastic reticular cells (FRCs) facilitate the tolerance induced by anti-CD40L in a murine model of heart transplantation. We found that both the absence of LNs and FRC depletion abrogated the effect of anti-CD40L in prolonging murine heart allograft survival. Depletion of FRCs impaired homing of T cells across the high endothelial venules (HEVs) and promoted formation of alloreactive T cells in the LNs in heart-transplanted mice treated with anti-CD40L. Single-cell RNA sequencing of the LNs showed that anti-CD40L promotes a Madcam1+ FRC subset. FRCs also promoted the formation of regulatory T cells (Tregs) in vitro. Nanoparticles (NPs) containing anti-CD40L were selectively delivered to the LNs by coating them with MECA-79, which binds to peripheral node addressin (PNAd) glycoproteins expressed exclusively by HEVs. Treatment with these MECA-79-anti-CD40L-NPs markedly delayed the onset of heart allograft rejection and increased the presence of Tregs. Finally, combined MECA-79-anti-CD40L-NPs and rapamycin treatment resulted in markedly longer allograft survival than soluble anti-CD40L and rapamycin. These data demonstrate that FRCs are critical to facilitating costimulatory blockade. LN-targeted nanodelivery of anti-CD40L could effectively promote heart allograft acceptance.

Impact of interaction networks of B cells with other cells on tumorigenesis, progression and response to immunotherapy of renal cell carcinoma: A review

Ample evidence indicates that the development and progression of renal cell carcinoma (RCC) are complex pathological processes involving interactions between tumor cells, immune cells and stromal components. Tumor infiltrated immune cells determine whether tumor advancement is promoted or inhibited. Among them, infiltrated B lymphocytes are present in all stages of RCC, playing a major role in determining tumor formation and advancement, as an essential part in the tumor microenvironment (TME). Although the advent of targeted and immune therapies has remarkably improved the survival of patients with advanced RCC, few cases can achieve complete response due to drug resistance. In this review article, we intend to summary the recent studies that outline the interaction networks of B cells with other cells, discuss the role of B cells in RCC development and progression, and assess their impact on RCC immunotherapy.

The influence of three-dimensional structure on naïve T cell homeostasis and aging

A breakdown in cellular homeostasis is thought to drive naïve T cell aging, however the link between naïve T cell homeostasis and aging in humans is poorly understood. To better address this, we developed a lymphoid organoid system that maintains resting naïve T cells for more than 2 weeks, in conjunction with high CD45RA expression. Deep phenotypic characterization of naïve T cells across age identified reduced CD45RA density as a hallmark of aging. A conversion from CD45RA^high naive cells to a CD45RA^low phenotype was reproduced within our organoid system by structural breakdown, but not by stromal cell aging or reduced lymphocyte density, and mediated by alternative CD45 splicing. Together, these data suggest that external influences within the lymph node microenvironment may cause phenotypic conversion of naïve T cells in older adults.

Spatial Positioning and Matrix Programs of Cancer-Associated Fibroblasts Promote T-cell Exclusion in Human Lung Tumors

It is currently accepted that cancer-associated fibroblasts (CAF) participate in T-cell exclusion from tumor nests. To unbiasedly test this, we used single-cell RNA sequencing coupled with multiplex imaging on a large cohort of lung tumors. We identified four main CAF populations, two of which are associated with T-cell exclusion: (i) MYH11+αSMA+ CAF, which are present in early-stage tumors and form a single cell layer lining cancer aggregates, and (ii) FAP+αSMA+ CAF, which appear in more advanced tumors and organize in patches within the stroma or in multiple layers around tumor nests. Both populations orchestrate a particular structural tissue organization through dense and aligned fiber deposition compared with T cell-permissive CAF. Yet they produce distinct matrix molecules, including collagen IV (MYH11+αSMA+ CAF) and collagen XI/XII (FAP+αSMA+ CAF). Hereby, we uncovered unique molecular programs of CAF driving T-cell marginalization, whose targeting should increase immunotherapy efficacy in patients bearing T cell-excluded tumors.

SIGNIFICANCE

The cellular and molecular programs driving T-cell marginalization in solid tumors remain unclear. Here, we describe two CAF populations associated with T-cell exclusion in human lung tumors. We demonstrate the importance of pairing molecular and spatial analysis of the tumor microenvironment, a prerequisite to developing new strategies targeting T cell-excluding CAF. See related commentary by Sherman, p. 2501. This article is highlighted in the In This Issue feature, p. 2483.

Implications and Emerging Therapeutic Avenues of Inflammatory Response in HPV+ Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCC) are a heterogeneous group of malignancies which have shown exponential incidence in the last two decades especially due to human papillomavirus (HPV) infection. The HPV family comprises more than 100 types of viruses with HPV16 and HPV18 being the most prevalent strains in HNSCC. Literature data reveal that the mutation profile as well as the response to chemotherapy and radiotherapy are distinct among HPV+ versus HPV-negative tumors. Furthermore, the presence of the virus induces activation of an immune response, in particular the recruitment of specific antiviral T lymphocytes to tumor sites. These T cells when activated produce soluble factors including cytokines and chemokines capable of modifying the local immune tumor microenvironment and impact on tumor response to the treatment. In this comprehensive review we investigated current knowledge on how the presence of an HPV can modify the inflammatory response systemically and within the tumor microenvironment's immunological responses, thereby impacting on disease prognosis and survival. We highlighted the research gaps and emerging approaches necessary to discover novel immunotherapeutic targets for HPV-associated HNSCC.