Functionally specialized junctions between endothelial cells of lymphatic vessels

IL-19 Is a Novel Lymphangiocrine Factor Inducing Lymphangiogenesis and Lymphatic Junctional Regulation

BACKGROUND

The lymphatic system functions by removing fluid, macromolecules, and immune cells to maintain tissue homeostasis. The structural organization of junctional protein complexes is vital to lymphatic function where initial lymphatics have permeable button junctions and collecting lymphatics have relatively impermeable zipper junctions. During inflammation, this junctional morphology appears to reverse, contributing to overall lymphatic malfunction. Little is known about the effects of immunomodulatory cytokines on lymphatic vessel formation and function during inflammation. The purpose of this study is to test the hypothesis that IL (interleukin)-19 promotes lymphangiogenesis and proper lymphatic function during inflammation.

METHODS

We used cultured human dermal lymphatic endothelial cells to determine IL-19 expression and its effects on lymphangiogenesis assays. Immunocytochemistry and electric cell-substrate impedance sensing determined effects on junctional morphology as it relates to permeability in vitro. RNA sequencing determined the effects of IL-19 on gene expression. Il19-/-Ldlr-/- double knockout mice were used to determine IL-19 effects on lymphatic function and lymphatic vessel visualization in vivo.

RESULTS

Endogenous IL-19 expression is induced by exogenous IL-19 and VEGF (vascular endothelial growth factor) C stimulation. IL-19 is lymphangiogenic, increasing human dermal lymphatic endothelial cell migration, network formation, and proliferation. IL-19 induces expression of transcription factors and permeability-associated genes. IL-19 induces rapid VE-cadherin (vascular endothelial cadherin) phosphorylation, increases permeability of human dermal lymphatic endothelial cell monolayers, and mitigates oxidized low-density lipoprotein-associated decrease in human dermal lymphatic endothelial cell permeability. In vivo, Il19-/-Ldlr-/- double knockout mice on a high-fat diet have impaired lymphatic drainage, decreased lymphatic branch points, and increased percentage of zippered junctions compared with control mice.

CONCLUSIONS

Taken together, these data show that IL-19 has potent effects on lymphatic vessel formation and function in vitro and that IL-19 regulates lymphatic drainage in vivo. IL-19 may represent an immunomodulatory cytokine with therapeutic potential for improving impaired lymphatic function consequent to inflammation.

Developing bioinspired delivery systems for enhanced tumor penetration of macromolecular drugs

Macromolecular drugs, such as proteins and nucleic acids, play a pivotal role in treating refractory diseases and hold significant promise in the growing pharmaceutical market. However, without efficient delivery systems, macromolecular drugs are highly susceptible to rapid biodegradation or systemic clearance, underscoring the need for advanced delivery strategies for clinical translation. A major challenge lies in their limited tissue penetration due to large molecular weight and size, which has recently garnered significant attention as it often leads to therapeutic failure or the emergence of resistance. In this review, we first outline the biological barriers limiting macromolecular tissue penetration, then explore the inherent permeation mechanisms of biomacromolecules in biological systems. We then highlight delivery strategies aimed at enhancing the tissue penetration of macromolecular therapeutics, with a particular focus on tissue-adaptive and tissue-remodeling delivery platforms. Finally, we provide a concise perspective on future research directions in deep tissue penetration for biomacromolecules. This review offers a comprehensive summary of recent advancements and presents critical insights into optimizing the therapeutic efficacy of macromolecular drugs.

LNPs-mediated VEGF-C mRNA delivery promotes heart repair and attenuates inflammation by stimulating lymphangiogenesis post-myocardial infarction

Myocardial infarction (MI) initiates a strong inflammatory response, leading to adverse ventricular remodeling. The reconstruction of functional lymphatic networks is indispensable for relieving myocardial edema and regulating post-infarction inflammation. However, conventional protein-based therapies and viral delivery systems aimed at promoting lymphangiogenesis in the heart have shown limited therapeutic efficacy due to their inherent limitations. In this study, a lipid nanoparticle (LNP) platform encapsulating VEGF-C mRNA was developed as a novel approach to regulate gene expression and stimulate sustained lymphatic neogenesis after MI. Intramyocardial delivery of VEGF-C mRNA-loaded LNPs significantly promoted lymphangiogenesis, reduced the infiltration of inflammatory cells, and inhibited pro-inflammatory and fibrosis-associated signaling pathways. This ultimately resulted in a substantial reduction in the fibrotic area and improved functional recovery. Our findings demonstrated that VEGF-C mRNA@LNPs repair myocardial ischemic injury by facilitating immune modulation through lymphatic neogenesis, offering a promising new therapeutic strategy with strong translational potential for treating myocardial infarction.

Meningeal lymphatic drainage: novel insights into central nervous system disease

In recent years, increasing evidence has suggested that meningeal lymphatic drainage plays a significant role in central nervous system (CNS) diseases. Studies have indicated that CNS diseases and conditions associated with meningeal lymphatic drainage dysfunction include neurodegenerative diseases, stroke, infections, traumatic brain injury, tumors, functional cranial disorders, and hydrocephalus. However, the understanding of the regulatory and damage mechanisms of meningeal lymphatics under physiological and pathological conditions is currently limited. Given the importance of a profound understanding of the interplay between meningeal lymphatic drainage and CNS diseases, this review covers seven key aspects: the development and structure of meningeal lymphatic vessels, methods for observing meningeal lymphatics, the function of meningeal lymphatics, the molecular mechanisms of meningeal lymphatic injury, the relationships between meningeal lymphatic vessels and CNS diseases, potential regulatory mechanisms of meningeal lymphatics, and conclusions and outstanding questions. We will explore the relationship between the development, structure, and function of meningeal lymphatics, review current methods for observing meningeal lymphatic vessels in both animal models and humans, and identify unresolved key points in meningeal lymphatic research. The aim of this review is to provide new directions for future research and therapeutic strategies targeting meningeal lymphatics by critically analyzing recent advancements in the field, identifying gaps in current knowledge, and proposing innovative approaches to address these gaps.

Dynamic cytoskeletal regulation of cell shape supports resilience of lymphatic endothelium

Lymphatic capillaries continuously take up interstitial fluid and adapt to resulting changes in vessel calibre1-3. The mechanisms by which the permeable monolayer of loosely connected lymphatic endothelial cells (LECs)4 maintains mechanical stability remain elusive. Here we identify dynamic cytoskeletal regulation of LEC shape, induced by isotropic stretch, as crucial for the integrity and function of dermal lymphatic capillaries. We found that the oak leaf-shaped LECs showed a spectrum of VE-cadherin-based junctional configurations at the lobular intercellular interface and a unique cytoskeletal organization, with microtubules at concave regions and F-actin at convex lobes. Multispectral and longitudinal intravital imaging of capillary LEC shape and actin revealed dynamic remodelling of cellular overlaps in vivo during homeostasis and in response to interstitial fluid volume increase. Akin to puzzle cells of the plant epidermis5,6, LEC shape was controlled by Rho GTPase CDC42-regulated cytoskeletal dynamics, enhancing monolayer stability. Moreover, cyclic isotropic stretch increased cellular overlaps and junction curvature in primary LECs. Our findings indicate that capillary LEC shape results from continuous remodelling of cellular overlaps that maintain vessel integrity while preserving permeable cell-cell contacts compatible with vessel expansion and fluid uptake. We propose a bellows-like fluid propulsion mechanism, in which fluid-induced lumen expansion and shrinkage of LEC overlaps are countered by actin-based lamellipodia-like overlap extension to aid vessel constriction.

Understanding the Lymphatic System: Tissue-on-Chip Modeling

The lymphatic vasculature plays critical roles in maintaining fluid homeostasis, transporting lipid, and facilitating immune surveillance. A growing body of work has identified lymphatic dysfunction as contributing to the severity of myriad diseases and to systemic inflammation, as well as modulating drug responses. Here, we review efforts to reconstruct lymphatic vessels in vitro toward establishing humanized, functional models to advance understanding of lymphatic biology and pathophysiology. We first review lymphatic endothelial cell biology and the biophysical lymphatic microenvironment, with a focus on features that are unique to the lymphatics and that have been used as design parameters for lymphatic-on-chip devices. We then discuss the state of the art for recapitulating lymphatic function in vitro, and we acknowledge limitations and challenges to current approaches. Finally, we discuss opportunities and the need for further development of microphysiological lymphatic systems to bridge the gap in model systems between lymphatic cell culture and animal physiology.

[Anatomy and physiology of the lymph system : What clinicians should know]

The lymphatic vessels are a unidirectional, centripetal system that collects interstitial fluid from tissues and organs, directing it into the venous system. The lymphatic vessels can be categorized into four types: initial lymphatic vessels, precollectors, collectors, and lymphatic trunks. Initial lymphatic vessels comprise interconnected networks characterized by larger mash sizes compared to blood capillaries and are lined with a specialized endothelium. They have interendothelial openings that allow exchange with the surrounding tissue. These vessels also have characteristic markers such as VEGFR‑3, podoplanin, and LYVE‑1. Precollectors have smooth muscle cells that are still arranged irregularly and parietal valves that promote centripetal lymph flow. Collectors have also valves and a continuous layer of spirally arranged muscle fibers that allow the vessels to pulse and contract. This contraction causes the lymph to be transported from one lymphangion to the next. Lymphatic trunks form the next section and often flow into the thoracic duct, which opens into the venous system. Lymph nodes are situated along the course of the collectors and trunks and serve as filter centers to intercept pathogens and increase the colloid osmotic pressure of the lymph. They are organized into groups with a specific structure with cortex, medulla, and embedded B and T lymphocytes. The central lymphatic system transports lymph through segmental connections and anastomoses. The thoracic duct empties into the left venous angle and collects also other lymphatic truncs. The thoracic duct's developmental history and variations occasionally lead to anatomical anomalies.

Differential biomarker expression of blood and lymphatic vasculature in multi-organ-chips

Since the blood and lymphatic endothelium regulates homeostasis and inflammation during health and disease, establishment of vascularized Organ-on-Chip platforms with blood and lymphatic endothelial cells (BEC/LEC) is a pre-requisite to further advance the field of tissue engineering. Here, we aimed to determine whether characteristics of BECs and LECs cultured under flow in a multi-organ-chip (MOC) are influenced by shear stress or inflammation. Dermis-derived primary BECs and LECs were used to endothelialize a MOC followed by culture for up to 14 days at lymphatic and blood flow rates. Under blood flow, both cell types changed morphology, aligned in flow direction, and showed close cell-cell contacts as in in vivo blood vasculature. Under lymphatic flow, neither BEC nor LEC aligned, and both showed a cobblestone-appearance with limited intercellular contacts similar to lymphatics. Cells retained their cell type-specific phenotype and cytokine secretion profiles. CCL21 expression in LECs was rescued by flow, but diminished again with TNFα exposure, together with the LEC-specific markers PROX1 and TFF3. Homeostatic cytokine secretion was higher in BECs, but the response to TNFα was more pronounced in LECs. Results indicate that BEC and LEC phenotype and cytokine secretion is mostly an intrinsic property with only morphology and CCL21 being influenced by flow.

Lymphatic collection and cell isolation from mouse models for multiomic profiling

Premetastatic cancer cells often spread from the primary lesion through the lymphatic vasculature and, clinically, the presence or absence of lymph node metastases impacts treatment decisions. However, little is known about cancer progression via the lymphatic system or of the effect that the lymphatic environment has on cancer progression. This is due, in part, to the technical challenge of studying lymphatic vessels and collecting lymph fluid. Here we provide a step-by-step procedure to collect both lymph and tumor-draining lymph in mouse models of cancer metastasis. This protocol has been adapted from established methods of lymph collection and was developed specifically for the collection of lymph from tumors. The approach involves the use of mice bearing melanoma or breast cancer orthotopic tumors. After euthanasia, the cisterna chyli and the tumor are exposed and viewed using a stereo microscope. Then, a glass cannula connected to a 1 mL syringe is inserted directly into the cisterna chyli or the tumor-draining lymphatics for collection of pure lymph. These lymph samples can be used to analyze the lymph-derived cancer cells using highly sensitive multiomics approaches to investigate the impact of the lymph environment during cancer metastasis. The procedure requires 2 h per mouse to complete and is suitable for users with minimal expertise in small animal handling and use of microsurgical tools under a stereo microscope.

Regulatory T cell and endothelial cell crosstalk

Regulatory T (Treg) cells have a central role in the maintenance of immune surveillance and tolerance. They can migrate from lymphoid organs to blood and then into tissues and egress from tissues into draining lymph nodes. Specialized endothelial cells of blood and lymphatic vessels are the key gatekeepers for these processes. Treg cells that transmigrate across single-cell layers of endothelial cells engage in bidirectional crosstalk with these cells and regulate vascular permeability by promoting structural modifications of blood and lymphatic endothelial cells. In turn, blood and lymphatic endothelial cells can modulate Treg cell recirculation and residency. Here, we discuss recent insights into the cellular and molecular mechanisms of the crosstalk between Treg cells and endothelial cells and explore potential therapeutic strategies to target these interactions in autoimmunity, transplantation and cancer.

Multifaceted Role of Notch Signaling in Vascular Health and Diseases

Notch signaling is evolutionarily conserved from Drosophila to mammals and it functions as an essential modulator of vascular growth and development by directing endothelial cell specification, proliferation, migration, arteriovenous differentiation, inflammation, and apoptosis. The interplay between Notch and other signaling pathways plays a homeostatic role by modulating multiple vascular functions, including permeability regulation, angiogenesis, and vascular remodeling. This review explores current knowledge on Notch signaling in vascular development, homeostasis, and disease. It also discusses recent developments in understanding how endothelial Notch signaling affects vascular inflammation via cytokines or aberrant shear stress in endothelial cells while addressing the reciprocal relationship between Notch signaling and inflammation.

Structure and unusual binding mechanism of the hyaluronan receptor LYVE-1 mediating leucocyte entry to lymphatics

Immune surveillance involves the continual migration of antigen-scavenging immune cells from the tissues to downstream lymph nodes via lymphatic vessels. To enable such passage, cells first dock with the lymphatic entry receptor LYVE-1 on the outer surface of endothelium, using their endogenous hyaluronan glycocalyx, anchored by a second hyaluronan receptor, CD44. Why the process should require two different hyaluronan receptors and by which specific mechanism the LYVE-1•hyaluronan interaction enables lymphatic entry is however unknown. Here we describe the crystal structures and binding mechanics of murine and human LYVE-1•hyaluronan complexes. These reveal a highly unusual, sliding mode of ligand interaction, quite unlike the conventional sticking mode of CD44, in which the receptor grabs free hyaluronan chain-ends and winds them in through conformational re-arrangements in a deep binding cleft, lubricated by a layer of structured waters. Our findings explain the mode of action of a dedicated lymphatic entry receptor and define a distinct, low tack adhesive interaction that enables migrating immune cells to slide through endothelial junctions with minimal resistance, while clinging onto their hyaluronan glycocalyx for essential downstream functions.

Mechanics of Lymphatic Pumping and Lymphatic Function

The lymphatic system plays a crucial role in maintaining tissue fluid balance, immune surveillance, and the transport of lipids and macromolecules. Lymph is absorbed by initial lymphatics and then driven through lymph nodes and to the blood circulation by the contraction of collecting lymphatic vessels. Intraluminal valves in collecting lymphatic vessels ensure the unidirectional flow of lymph centrally. The lymphatic muscle cells that invest in collecting lymphatic vessels impart energy to propel lymph against hydrostatic pressure gradients and gravity. A variety of mechanical and biochemical stimuli modulate the contractile activity of lymphatic vessels. This review focuses on the recent advances in our understanding of the mechanisms involved in regulating and collecting lymphatic vessel pumping in normal tissues and the association between lymphatic pumping, infection, inflammatory disease states, and lymphedema.

Lymphatic transport in anti-tumor immunity and metastasis

Although lymphatic vessels (LVs) are present in many tumors, their importance in cancer has long been underestimated. In contrast to the well-studied tumor-associated blood vessels, LVs were previously considered to function as passive conduits for tumor metastasis. However, emerging evidence over the last two decades has shed light on their critical role in locally shaping the tumor microenvironment (TME). Here we review the involvement of LVs in tumor progression, metastasis, and modulation of anti-tumor immune response.

A MPET2-mPBPK model for subcutaneous injection of biotherapeutics with different molecular weights: From local scale to whole-body scale

BACKGROUND AND OBJECTIVE

Subcutaneous injection of biotherapeutics has attracted considerable attention in the pharmaceutical industry. However, there is limited understanding of the mechanisms underlying the absorption of drugs with different molecular weights and the delivery of drugs from the injection site to the targeted tissue.

METHODS

We propose the MPET2-mPBPK model to address this issue. This multiscale model couples the MPET2 model, which describes subcutaneous injection at the local tissue scale from a biomechanical view, with a post-injection absorption model at injection site and a minimal physiologically-based pharmacokinetic (mPBPK) model at whole-body scale. Utilizing the principles of tissue biomechanics and fluid dynamics, the local MPET2 model provides solutions that account for tissue deformation and drug absorption in local blood vessels and initial lymphatic vessels during injection. Additionally, we introduce a model accounting for the molecular weight effect on the absorption by blood vessels, and a nonlinear model accounting for the absorption in lymphatic vessels. The post-injection model predicts drug absorption in local blood vessels and initial lymphatic vessels, which are integrated into the whole-body mPBPK model to describe the pharmacokinetic behaviors of the absorbed drug in the circulatory and lymphatic system.

RESULTS

We establish a numerical model which links the biomechanical process of subcutaneous injection at local tissue scale and the pharmacokinetic behaviors of injected biotherapeutics at whole-body scale. With the help of the model, we propose an explicit relationship between the reflection coefficient and the molecular weight and predict the bioavalibility of biotherapeutics with varying molecular weights via subcutaneous injection.

CONCLUSION

The considered drug absorption mechanisms enable us to study the differences in local drug absorption and whole-body drug distribution with varying molecular weights. This model enhances the understanding of drug absorption mechanisms and transport routes in the circulatory system for drugs of different molecular weights, and holds the potential to facilitate the application of computational modeling to drug formulation.

Simultaneous Presentation of Swimming-Induced Pulmonary Edema in a Set of Monozygotic Twin Elite Maritime Warfare Candidates: A Novel Case Report

Swimming-induced pulmonary edema (SIPE) is an incompletely understood condition that is often seen in U.S. special operations candidates participating in maritime qualification training courses. We present a case of two monozygotic twins with the simultaneous onset of acute respiratory distress during a crucible event of a maritime assessment and selection course. Subsequent pulmonary ultrasonography in both candidates showed wedge-shaped hyperechoic lines (B-lines) extending from the pleural interface into the interstitium. Chest radiography of both candidates revealed bilateral asymmetric hazy opacities consistent with SIPE. Both candidates recovered with supportive measures but were medically removed from training. Given the near-identical exposures of the candidates to the same ambient and water temperatures, duration of water submersion, magnitude of physical stressors, and viral colonization, this case study suggests that there may be underlying genetic factors, in addition to environmental factors, that predispose individuals to developing SIPE. Further benchtop and clinical research must be performed to identify potential genetic polymorphisms that contribute to the development of SIPE and to investigate safe interventions that address the underlying etiologies of SIPE pathophysiology.

Viral Infection and Dissemination Through the Lymphatic System

Many viruses induce viremia (virus in the blood) and disseminate throughout the body via the bloodstream from the initial infection site. However, viruses must often pass through the lymphatic system to reach the blood. The lymphatic system comprises a network of vessels distinct from blood vessels, along with interconnected lymph nodes (LNs). The complex network has become increasingly appreciated as a crucial host factor that contributes to both the spread and control of viral infections. Viruses can enter the lymphatics as free virions or along with migratory cells. Once virions arrive in the LN, sinus-resident macrophages remove infectious virus from the lymph. Depending on the virus, macrophages can eliminate infection or propagate the virus. A virus released from an LN is eventually deposited into the blood. This unique pathway highlights LNs as targets for viral infection control and for modulation of antiviral response development. Here, we review the lymphatic system and viruses that disseminate through this network. We discuss infection of the LN, the generation of adaptive antiviral immunity, and current knowledge of protection within the infected node. We conclude by sharing insights from ongoing efforts to optimize lymphatic targeting by vaccines and pharmaceuticals. Understanding the lymphatic system's role during viral infection enhances our knowledge of antiviral immunity and virus-host interactions and reveals potential targets for next-generation therapies.

Listeria monocytogenes use multiple mechanisms to disseminate from the intestinal lamina propria to the mesenteric lymph nodes

Listeria monocytogenes are facultative intracellular bacterial pathogens that cause foodborne disease in humans. The bacteria can use the surface protein InlA to invade intestinal epithelial cells or transcytose across M cells in the gut, but it is not well understood how the bacteria traffic from the underlying lamina propria to the draining mesenteric lymph nodes (MLN). Previous studies indicated that L. monocytogenes associated with both monocytes and dendritic cells in the intestinal lamina propria. We show here that CCR2-/- mice had a significant reduction in Ly6Chi monocytes in the MLN but no change in bacterial burden following foodborne infection; thus, dissemination of L. monocytogenes associated with monocytes is not required for colonization of the MLN. To block CCR7-mediated trafficking of dendritic cells from the lamina propria, we treated mice with anti-VEGFR3 antibody (clone AFL4) prior to and during infection but did not see a change in dendritic numbers in the MLN as had been previously reported with other anti-VEGFR3-specific antibodies. However, increasing the number of circulating dendritic cells by treating mice with rFlt3L resulted in a significant increase in L. monocytogenes in the lymph nodes that drain the small intestine and the spleen. Whole-mount fluorescent microscopy of lymphatic vessels following ligated loop infection revealed both free-floating L. monocytogenes and cell-associated bacteria within lymphatic vessels. Together, these results suggest that L. monocytogenes can use multiple, redundant mechanisms to disseminate from the gut tissue to the MLN.

IMPORTANCE

Consumption of the foodborne bacterial pathogen Listeria monocytogenes results in a wide spectrum of human disease from mild self-limiting gastroenteritis to life-threatening infections of the bloodstream, brain, and placenta. It is not well understood how the bacteria migrate from the intestines to the draining mesenteric lymph nodes, which are thought to serve as the last barrier to prevent systemic infections. Results presented here reveal multiple redundant mechanisms L. monocytogenes can use to disseminate from the ileum or colon to the mesenteric lymph nodes.

Transport functions of intestinal lymphatic vessels

Lymphatic vessels are crucial for fluid absorption and the transport of peripheral immune cells to lymph nodes. However, in the small intestine, the lymphatic fluid is rich in diet-derived lipids incorporated into chylomicrons and gut-specific immune cells. Thus, intestinal lymphatic vessels have evolved to handle these unique cargoes and are critical for systemic dietary lipid delivery and metabolism. This Review covers mechanisms of lipid absorption from epithelial cells to the lymphatics as well as unique features of the gut microenvironment that affect these functions. Moreover, we discuss details of the intestinal lymphatics in gut immune cell trafficking and insights into the role of inter-organ communication. Lastly, we highlight the particularities of fat absorption that can be harnessed for efficient lipid-soluble drug distribution for novel therapies, including the ability of chylomicron-associated drugs to bypass first-pass liver metabolism for systemic delivery. In all, this Review will help to promote an understanding of intestinal lymphatic-systemic interactions to guide future research directions.

Complementary Strategies to Identify Differentially Expressed Genes in the Choroid Plexus of Patients with Progressive Multiple Sclerosis

Multiple sclerosis (MS) is a neurological disease causing myelin and axon damage through inflammatory and autoimmune processes. Despite affecting millions worldwide, understanding its genetic pathways remains limited. The choroid plexus (ChP) has been studied in neurodegenerative processes and diseases like MS due to its dysregulation, yet its role in MS pathophysiology remains unclear. Our work re-evaluates the ChP transcriptome in progressive MS patients and compares gene expression profiles using diverse methodological strategies. Samples from patient and healthy control RNASeq sequencing of brain tissue from post-mortem patients (GEO: GSE137619) were used. After an evaluation and quality control of these data, they had their transcripts mapped and quantified against the reference transcriptome GRCh38/hg38 of Homo sapiens using three strategies to identify differentially expressed genes in progressive MS patients. Functional analysis of genes revealed their involvement in immune processes, cell adhesion and migration, hormonal actions, amino acid transport, chemokines, metals, and signaling pathways. Our findings can offer valuable insights for progressive MS therapies, suggesting specific genes influence immune cell recruitment and potential ChP microenvironment changes. Combining complementary approaches maximizes literature coverage, facilitating a deeper understanding of the biological context in progressive MS.

A Rapidly Synthesized, Ultrasmall Silver Nanocluster for Near-Infrared-II Imaging and Metabolic Studies

Near-infrared-II (NIR-II) imaging has emerged as a powerful technique for high-resolution visualization of deep anatomical features, benefiting from minimized autofluorescence, diminished optical scattering, and absorption of tissue. However, the current synthesis of NIR-II nanoprobes is a time-consuming, labor-intensive process with low yields, highlighting the need for an efficient and rapid synthesis approach instead. Herein, we report DNA-templated silver nanoclusters (Ag NCs) with NIR-II emission that can be rapidly synthesized via a simple one-spot process within 2 min. The Ag NCs are about 1.6 nm in size, making it easy for them to enter into the capillaries of muscle tissue. In vivo NIR-II imaging results indicate that the Ag NCs we designed are promising probes for studying the metabolic pathways of nanoprobes after intramuscular injection. Therefore, it is expected that Ag NCs with ultrafast room temperature synthesis, excellent NIR-II emission, and ultrasmall size will be ideal probes for biological applications.

Unveiling the Mysteries of the Blood-brain Barrier: The Problem of the Brain/spinal Pharmacotherapy

The most critical issue impeding the development of innovative cerebrospinal medications is the blood-brain barrier (BBB). The BBB limits the ability of most medications to penetrate the brain to the CNS. The BBB structure and functions are summarized, with the physical barrier generated by endothelial tight junctions and the transport barrier formed by transporters within the membrane and vesicular processes. The functions of connected cells, particularly the end feet of astrocytic glial cells, microglia, and pericytes, are described. The drugs that cross the blood brain barrier are explained below along with their mechanisms. Some of the associated conditions and problems are given.

Models of Hydration Dependent Lymphatic Opening, Interstitial Fluid Flows and Ambipolar Diffusion

OBJECTIVE

A theoretical understanding of fluid exchange and the role of initial lymph formation in tissues through mathematical/physical modeling is lacking.

METHODS

Here, we present three models for tissues rich in negative fixed charges due to glycosaminoglycans interacting with the extracellular matrix.

RESULTS

We first model a lymphatic opening mechanism at relevant hydrations of the interstitium. At each hydration affecting tissue strain, two equations coupled in time are developed and solved with the new lymphatic opening and particle draining mechanism. The lymphatic opening mechanism is then included in a new model of interstitial fluid and macromolecular flow where the influence of different exclusion and available volumes for charged and neutral particles are quantified. For therapeutic interactions with cells, essential differences are found between electrically charged and neutral therapeutic substances. The interstitial fluid hydrostatic pressure gradient and flow are expressed through an extended Darcy equation, derived using similar methods as in kinetic theory of dense gases and fluid flows. Finally, a model for ambipolar diffusion of electrically charged macromolecules in tissue is developed.

CONCLUSIONS

Our study will inform transport of charged and neutral macromolecules between the vasculature, interstitium, and the lymphatic system, thus having implications for tissue uptake of therapeutic agents.

Advances in molecular imaging and targeted therapeutics for lymph node metastasis in cancer: a comprehensive review

Lymph node metastasis is a critical indicator of cancer progression, profoundly affecting diagnosis, staging, and treatment decisions. This review article delves into the recent advancements in molecular imaging techniques for lymph nodes, which are pivotal for the early detection and staging of cancer. It provides detailed insights into how these techniques are used to visualize and quantify metastatic cancer cells, resident immune cells, and other molecular markers within lymph nodes. Furthermore, the review highlights the development of innovative, lymph node-targeted therapeutic strategies, which represent a significant shift towards more precise and effective cancer treatments. By examining cutting-edge research and emerging technologies, this review offers a comprehensive overview of the current and potential impact of lymph node-centric approaches on cancer diagnosis, staging, and therapy. Through its exploration of these topics, the review aims to illuminate the increasingly sophisticated landscape of cancer management strategies focused on lymph node assessment and intervention.

In Vivo Delivery Processes and Development Strategies of Lipid Nanoparticles

Lipid nanoparticles (LNPs) represent an advanced and highly efficient delivery system for RNA molecules, demonstrating exceptional biocompatibility and remarkable delivery efficiency. This is evidenced by the clinical authorization of three LNP formulations: Patisiran, BNT162b2, and mRNA-1273. To further maximize the efficacy of RNA-based therapy, it is imperative to develop more potent LNP delivery systems that can effectively protect inherently unstable and negatively charged RNA molecules from degradation by nucleases, while facilitating their cellular uptake into target cells. Therefore, this review presents feasible strategies commonly employed for the development of efficient LNP delivery systems. The strategies encompass combinatorial chemistry for large-scale synthesis of ionizable lipids, rational design strategy of ionizable lipids, functional molecules-derived lipid molecules, the optimization of LNP formulations, and the adjustment of particle size and charge property of LNPs. Prior to introducing these developing strategies, in vivo delivery processes of LNPs, a crucial determinant influencing the clinical translation of LNP formulations, is described to better understand how to develop LNP delivery systems.

PTX3 is expressed in terminal lymphatics and shapes their organization and function

Introduction

The lymphatic system is a multifaceted regulator of tissue homeostasis and an integral part of immune responses. Previous studies had shown that subsets of lymphatic endothelial cells (LEC) express PTX3, an essential component of humoral innate immunity and tissue homeostasis.

Methods

In the present study using whole-mount imaging and image-based morphometric quantifications, Ptx3-targeted mice and in vivo functional analysis, we investigated the involvement of PTX3 in shaping and function of the lymphatic vasculature.

Results

We found that PTX3 is localized in the extracellular matrix (ECM) surrounding human and murine lymphatic vessels (LV). In murine tissues, PTX3 was localized in the ECM close to LV terminals and sprouting. Ptx3-deficient mice showed LV abnormalities in the colon submucosa and diaphragm, including a disorganized pattern and hyperplasia of initial LV capillaries associated with altered distribution of tight junction-associated molecules. Mice with LEC-restricted PTX3 gene inactivation showed morphological and organization abnormalities similar to those observed in Ptx3-deficient animals. Ptx3-deficient mice showed defective fluid drainage from footpads and defective dendritic cell (DC) trafficking.

Discussion

Thus, PTX3 is strategically localized in the ECM of specialized LV, playing an essential role in their structural organization and immunological function.

Molecules That Have Rarely Been Studied in Lymphatic Endothelial Cells

A number of standard molecules are used for the molecular and histological characterization of lymphatic endothelial cells (LECs), including lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), Podoplanin (D2-40), VEGFR3, Prospero homeobox protein 1 (PROX1), and CD31. The number of molecules whose mutations cause lymphatic malformations or primary congenital lymphedema is considerable, but the majority of these diseases have not yet been characterized at the molecular level. Therefore, there is still considerable scope for molecular and functional studies of the lymphatic vasculature. Using RNASeq, we have previously characterized lymphatic endothelial cells (LECs) under normoxic and hypoxic conditions. We used this information to compare it with immunohistochemical data. We carried out some of the immunohistology ourselves, and systematically studied the Human Protein Atlas, a cell and tissue database based in Sweden. Here we describe molecules that are expressed at RNA and protein levels in LECs, hoping to stimulate future functional studies of these molecules.

From foes to friends: rethinking the role of lymph nodes in prostate cancer

Clinically localized prostate cancer is often treated with radical prostatectomy combined with pelvic lymph node dissection. Data suggest that lymph node dissection does improve disease staging, but its therapeutic value has often been debated, with few studies showing that lymph node removal directly improves oncological outcomes; however, lymph nodes are an important first site of antigen recognition and immune system activation and the success of many currently used immunological therapies hinges on this dogma. Evidence, particularly in the preclinical setting, has demonstrated that the success of immune checkpoint inhibitors is dampened by the removal of tumour-draining lymph nodes. Thus, whether lymph nodes are truly 'foes' or whether they are actually 'friends' in oncological care is an important idea to discuss.

Overview of Lymphatic Muscle Cells in Development, Physiology, and Disease

Lymphatic muscle cells (LMCs) are indispensable for proper functioning of the lymphatic system, as they provide the driving force for lymph transport. Recent studies have advanced our understanding of the molecular mechanisms that regulate LMCs, which control rhythmic contraction and vessel tone of lymphatic vessels-traits also found in cardiac and vascular smooth muscle. In this review, we discuss the molecular pathways that orchestrate LMC-mediated contractility and summarize current knowledge about their developmental origin, which may shed light on the distinct contractile characteristics of LMCs. Further, we highlight the growing evidence implicating LMC dysregulation in the pathogenesis of lymphedema and other diseases related to lymphatic vessel dysfunction. Given the limited number and efficacy of existing therapies to treat lymphedema, LMCs present a promising focus for identifying novel therapeutic targets aimed at improving lymphatic vessel contractility. Here, we discuss LMCs in health and disease, as well as therapeutic strategies aimed at targeting them to improve lymphatic vessel function.

The right lymphatic duct: basic anatomy and clinical relevance

The anatomical variability of the thoracic duct and the right lymphatic duct predisposes them to inadvertent damage following head and neck surgery thereby leading to chyle leak which is an uncommon complication with potentially significant associated morbidity. Although chyle leak is predominately associated with left-sided neck surgery, it also occurs as a complication of the right-sided neck dissection. Variable figures concerning chyle leakage after right-sided neck dissections were reported, ranging from 0 per cent to higher prevalences such as 14%, 24%, 33% and 60% of total cases of chyle leakages associated with neck surgery. The right-sided complications may implicate the right lymphatic duct and right-sided terminations of the thoracic duct into the venous system which occur in about 1-6% of humans. Other clinically relevant conditions involving the right-sided major lymphatic vessels include chyle leaks following right anterior cervical spine surgery, cysts of the right lymphatic duct and dilatation of the right lymphatic duct in the setting of recurrent cervical swelling. This article presents a review of the literature concerning the basic anatomy and the clinical relevance of the right lymphatic duct and the right-sided terminations of the thoracic duct into the venous circulation.

Pharmacokinetic differences between subcutaneous injection and intradermal microneedle delivery of protein therapeutics

Protein therapeutics are essential in the treatment of various diseases, but most of them require parenteral administration. Since intravenous and subcutaneous injections are associated with discomfort and pain, other routes have been investigated including intradermal microneedle delivery. Microneedles are shorter than hypodermic needles and therefore minimize contact with pain receptors in deeper skin layers. But the differences in anatomical and physiological characteristics of dermis and subcutis can potentially result in varying protein penetration through the skin, absorption, and metabolism. This review summarizes pharmacokinetic studies that compare the administration of protein therapeutics by subcutaneous injections and different types of microneedles intradermally including hollow, dissolvable, coated, and hydrogel-forming microneedles. Across animal and human studies, hollow microneedle delivery resulted in quicker and higher peak plasma levels of proteins and comparable bioavailability to subcutaneous injections potentially due to the extensive network of lymphatic and blood vessels in the dermis. In case of dissolvable and coated microneedles, drug release kinetics depend on component materials. The dissolution of polymer excipients can slow the release and permeation of protein therapeutics at the administration site and thereby delay absorption. The understanding of drug penetration through different skin layers, its absorption into blood capillaries or lymphatics, and dermal metabolism remains limited. Additionally, the effects of these processes on the differences in pharmacokinetic profiles of proteins following intradermal microneedle administration are not well understood. Greater insights are required for the development of the next generation of intradermal microneedle biotherapeutics.

The role of ferroptosis resistance in lymph-associated tumour metastasis

Tumour metastasis is a crucial factor in determining clinically challenging tumours. In this respect, the lymphatic system may act as potential entry portals for tumour metastasis, whilst, clinical detection of tumour-infiltrated lymph nodes also indicates poorer prognosis and higher metastatic risk. Whether tumour cells gain ferroptosis resistance in lymph that make them exhibit a stronger propensity for lymphatic dissemination compared to hematogenous spread might be a breakthrough for elucidating lymph-associated tumour metastasis. This review discusses how the lymphatic system endows tumour cells with ferroptosis resistance character, which makes them more propensity for lymph node pre-metastasis and distant metastasis through lymphatic circulation. Comprehensively considering the distinct structure and property of lymph and the unique metabolic characteristics of tumours, all of the lymphatic vessels, intestinal lymph and lymph nodes collectively manipulate an intricate interaction with the hematogenous system and afford substances exchange with tumour cells and extracellular vesicles, upon which make a ferroptosis resistant microenvironment for subsequent metastasis in distant organs and lymph nodes.

Intestinal Lymphatic Biology, Drug Delivery, and Therapeutics: Current Status and Future Directions

Historically, the intestinal lymphatics were considered passive conduits for fluids, immune cells, dietary lipids, lipid soluble vitamins, and lipophilic drugs. Studies of intestinal lymphatic drug delivery in the late 20th century focused primarily on the drugs' physicochemical properties, especially high lipophilicity, that resulted in intestinal lymphatic transport. More recent discoveries have changed our traditional view by demonstrating that the lymphatics are active, plastic, and tissue-specific players in a range of biological and pathological processes, including within the intestine. These findings have, in turn, inspired exploration of lymph-specific therapies for a range of diseases, as well as the development of more sophisticated strategies to actively deliver drugs or vaccines to the intestinal lymph, including a range of nanotechnologies, lipid prodrugs, and lipid-conjugated materials that "hitchhike" onto lymphatic transport pathways. With the increasing development of novel therapeutics such as biologics, there has been interest in whether these therapeutics are absorbed and transported through intestinal lymph after oral administration. Here we review the current state of understanding of the anatomy and physiology of the gastrointestinal lymphatic system in health and disease, with a focus on aspects relevant to drug delivery. We summarize the current state-of-the-art approaches to deliver drugs and quantify their uptake into the intestinal lymphatic system. Finally, and excitingly, we discuss recent examples of significant pharmacokinetic and therapeutic benefits achieved via intestinal lymphatic drug delivery. We also propose approaches to advance the development and clinical application of intestinal lymphatic delivery strategies in the future. SIGNIFICANCE STATEMENT: This comprehensive review details the understanding of the anatomy and physiology of the intestinal lymphatic system in health and disease, with a focus on aspects relevant to drug delivery. It highlights current state-of-the-art approaches to deliver drugs to the intestinal lymphatics and the shift toward the use of these strategies to achieve pharmacokinetic and therapeutic benefits for patients.

The Lymphatic Highway: How Lymphatics Drive Lung Health and Disease

The pulmonary lymphatic system has emerged as a critical regulator of lung homeostasis and a key contributor to the pathogenesis of respiratory diseases. As the primary conduit responsible for maintaining fluid balance and facilitating immune cell trafficking, the integrity of lymphatic vessels is essential for preserving normal pulmonary structure and function. Lymphatic abnormalities manifest across a broad spectrum of pulmonary disorders, underscoring their significance in respiratory health and disease. This review provides an overview of pulmonary lymphatic biology and delves into the involvement of lymphatics in four major lung diseases: chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), asthma, and lung transplant rejection. We examine how lymphatic abnormalities manifest in each of these conditions and investigate the mechanisms through which lymphatic remodeling and dysfunction contribute to disease progression. Furthermore, we explore the therapeutic potential of targeting the lymphatic system to ameliorate these debilitating respiratory conditions. Despite the current knowledge, several crucial questions remain unanswered, such as the spatial and temporal dynamics of lymphatic changes, the molecular crosstalk between lymphatics and the lung microenvironment, and the distinction between protective versus detrimental lymphatic phenotypes. Unraveling these mysteries holds the promise of identifying novel molecular regulators, characterizing lymphatic endothelial phenotypes, and uncovering bioactive mediators. By harnessing this knowledge, we can pave the way for the development of innovative disease-modifying therapies targeting the lymphatic highway in lung disorders.

Photodynamic opening of the blood-brain barrier affects meningeal lymphatics and the brain's drainage in healthy male mice

Here, we present the new vascular effects of photodynamic therapy (PDT) with 5-aminolevulinic acid (5-ALA). PDT with 5-ALA induces a leakage of both the meningeal and cerebral blood vessels. The extravasation of photo-excited 5-ALA from the leaky blood vessels into the meninges causes photo-damage of the meningeal lymphatics (MLVs) leading to a dramatic reducing the MLV network and brain's drainage. The PDT-induced impairment of lymphatic regulation of brain's drainage can lead to excessive accumulation of fluids in brain tissues, which is important to consider in the PDT therapy for brain diseases as s possible side effect of PDT with 5-ALA.

Lymphangiogenesis: novel strategies to promote cutaneous wound healing

The cutaneous lymphatic system regulates tissue inflammation, fluid balance and immunological responses. Lymphangiogenesis or lymphatic dysfunction may lead to lymphedema, immune deficiency, chronic inflammation etc. Tissue regeneration and healing depend on angiogenesis and lymphangiogenesis during wound healing. Tissue oedema and chronic inflammation can slow wound healing due to impaired lymphangiogenesis or lymphatic dysfunction. For example, impaired lymphangiogenesis or lymphatic dysfunction has been detected in nonhealing wounds such as diabetic ulcers, venous ulcers and bedsores. This review summarizes the structure and function of the cutaneous lymphatic vessel system and lymphangiogenesis in wounds. Furthermore, we review wound lymphangiogenesis processes and remodelling, especially the influence of the inflammatory phase. Finally, we outline how to control lymphangiogenesis to promote wound healing, assess the possibility of targeting lymphangiogenesis as a novel treatment strategy for chronic wounds and provide an analysis of the possible problems that need to be addressed.

Microfluidic device reveals new insights into impairment of neutrophil transmigration in patients with sepsis

Neutrophils need to migrate through tight tissue spaces to eliminate pathogens, but their movement is often hindered by their large and stiff nuclei. Neutrophil migration is impaired in sepsis patients, but it is unclear whether this defect is related to the deformability of their nuclei. Herein, we designed microfluidic devices with micron-scale narrow slits to simulate biological barriers. This setup allowed us to observe and record neutrophil movement and nuclear deformation in real-time. We also developed a method for morphological analysis to quantify nucleus deformation in numerous individual cells. Our studies showed that neutrophils from healthy individuals could adjust their nuclear shape to squeeze through these constrictions, whereas those from sepsis patients demonstrated less flexibility. Neutrophils with rigid nuclei struggled to pass through narrow gaps and were more likely to rupture under pressure. These findings suggest that the migration defects of neutrophils observed in sepsis may be attributed to the inability of neutrophils to deform their nuclei, highlighting the crucial role of microfluidic technologies in offering new insights into migration defects under pathological conditions.

The role of vascular and lymphatic networks in bone and joint homeostasis and pathology

The vascular and lymphatic systems are integral to maintaining skeletal homeostasis and responding to pathological conditions in bone and joint tissues. This review explores the interplay between blood vessels and lymphatic vessels in bones and joints, focusing on their roles in homeostasis, regeneration, and disease progression. Type H blood vessels, characterized by high expression of CD31 and endomucin, are crucial for coupling angiogenesis with osteogenesis, thus supporting bone homeostasis and repair. These vessels facilitate nutrient delivery and waste removal, and their dysfunction can lead to conditions such as ischemia and arthritis. Recent discoveries have highlighted the presence and significance of lymphatic vessels within bone tissue, challenging the traditional view that bones are devoid of lymphatics. Lymphatic vessels contribute to interstitial fluid regulation, immune cell trafficking, and tissue repair through lymphangiocrine signaling. The pathological alterations in these networks are closely linked to inflammatory joint diseases, emphasizing the need for further research into their co-regulatory mechanisms. This comprehensive review summarizes the current understanding of the structural and functional aspects of vascular and lymphatic networks in bone and joint tissues, their roles in homeostasis, and the implications of their dysfunction in disease. By elucidating the dynamic interactions between these systems, we aim to enhance the understanding of their contributions to skeletal health and disease, potentially informing the development of targeted therapeutic strategies.

Proximity interactome of lymphatic VE-cadherin reveals mechanisms of junctional remodeling and reelin secretion

The adhesion receptor vascular endothelial (VE)-cadherin transduces an array of signals that modulate crucial lymphatic cell behaviors including permeability and cytoskeletal remodeling. Consequently, VE-cadherin must interact with a multitude of intracellular proteins to exert these functions. Yet, the full protein interactome of VE-cadherin in endothelial cells remains a mystery. Here, we use proximity proteomics to illuminate how the VE-cadherin interactome changes during junctional reorganization from dis-continuous to continuous junctions, triggered by the lymphangiogenic factor adrenomedullin. These analyses identified interactors that reveal roles for ADP ribosylation factor 6 (ARF6) and the exocyst complex in VE-cadherin trafficking and recycling. We also identify a requisite role for VE-cadherin in the in vitro and in vivo control of secretion of reelin-a lymphangiocrine glycoprotein with recently appreciated roles in governing heart development and injury repair. This VE-cadherin protein interactome shines light on mechanisms that control adherens junction remodeling and secretion from lymphatic endothelial cells.

Characterization of Photo-Crosslinked Methacrylated Type I Collagen as a Platform to Investigate the Lymphatic Endothelial Cell Response

Despite chronic fibrosis occurring in many pathological conditions, few in vitro studies examine how fibrosis impacts lymphatic endothelial cell (LEC) behavior. This study examined stiffening profiles of PhotoCol®-commercially available methacrylated type I collagen-photo-crosslinked with the photoinitiators: Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), Irgacure 2959 (IRG), and Ruthenium/Sodium Persulfate (Ru/SPS) prior to evaluating PhotoCol® permeability and LEC response to PhotoCol® at stiffnesses representing normal and fibrotic tissues. Ru/SPS produced the highest stiffness (~6 kilopascal (kPa)) for photo-crosslinked PhotoCol®, but stiffness did not change with burst light exposures (30 and 90 s). The collagen fibril area fraction increased, and dextran permeability (40 kilodalton (kDa)) decreased with photo-crosslinking, showing the impact of photo-crosslinking on microstructure and molecular transport. Human dermal LECs on softer, uncrosslinked PhotoCol® (~0.5 kPa) appeared smaller with less prominent vascular endothelial (VE)-cadherin (cell-cell junction) expression compared to LECs on stiffer PhotoCol® (~6 kPa), which had increased cell size, border irregularity, and VE-cadherin thickness (junction zippering) that is consistent with LEC morphology in fibrotic tissues. Our quantitative morphological analysis demonstrates our ability to produce LECs with a fibrotic phenotype, and the overall study shows that PhotoCol® with Ru/SPS provides the necessary physical properties to systematically study LEC responses related to capillary growth and function under fibrotic conditions.

Cardiac Lymphatics and Therapeutic Prospects in Cardiovascular Disease: New Perspectives and Hopes

The lymphatic system is the same reticular fluid system as the circulatory system found throughout the body in vascularized tissues. Lymphatic vessels are low-pressure, blind-ended tubular structures that play a crucial role in maintaining tissue fluid homeostasis, immune cell transport, and lipid absorption. The heart also has an extensive lymphatic network, and as research on cardiac lymphatics has progressed in recent years, more and more studies have found that cardiac lymphangiogenesis may ameliorate certain cardiovascular diseases, and therefore stimulation of cardiac lymphangiogenesis may be an important tool in the future treatment of cardiovascular diseases. This article briefly reviews the development and function of cardiac lymphatic vessels, the interaction of cardiac lymphatic vessels with cardiovascular diseases (including atrial fibrillation, coronary atherosclerosis, and heart failure), and finally discusses the therapeutic potential of targeted cardiac lymphatic therapy for cardiovascular diseases.

A multi-scale numerical study of monoclonal antibodies uptake by initial lymphatics after subcutaneous injection

This paper studies the transport of monoclonal antibodies through skin tissue and initial lymphatics, which impacts the pharmacokinetics of monoclonal antibodies. Our model integrates a macroscale representation of the entire skin tissue with a mesoscale model that focuses on the papillary dermis layer. Our results indicate that it takes hours for the drugs to disperse from the injection site to the papillary dermis before entering the initial lymphatics. Additionally, we observe an inhomogeneous drug distribution in the interstitial space of the papillary dermis, with higher drug concentrations near initial lymphatics and lower concentrations near blood capillaries. To validate our model, we compare our numerical simulation results with experimental data, finding a good alignment. Our parametric studies on the drug molecule properties and injection parameters suggest that a higher diffusion coefficient increases the transport and uptake rate while binding slows down these processes. Furthermore, shallower injection depths lead to faster lymphatic uptake, whereas the size of the injection plume has a minor effect on the uptake rate. These findings advance our understanding of drug transport and lymphatic absorption after subcutaneous injection, offering valuable insights for optimizing drug delivery strategies and the design of biotherapeutics.

Lymphatic system regulation of anti-cancer immunity and metastasis

Cancer dissemination to lymph nodes (LN) is associated with a worse prognosis, increased incidence of distant metastases and reduced response to therapy. The LN microenvironment puts selective pressure on cancer cells, creating cells that can survive in LN as well as providing survival advantages for distant metastatic spread. Additionally, the presence of cancer cells leads to an immunosuppressive LN microenvironment, favoring the evasion of anti-cancer immune surveillance. However, recent studies have also characterized previously unrecognized roles for tumor-draining lymph nodes (TDLNs) in cancer immunotherapy response, including acting as a reservoir for pre-exhausted CD8+ T cells and stem-like CD8+ T cells. In this review, we will discuss the spread of cancer cells through the lymphatic system, the roles of TDLNs in metastasis and anti-cancer immune responses, and the therapeutic opportunities and challenges in targeting LN metastasis.

Lymphatic trafficking of immune cells and insights for cancer metastasis

Most cancers and in particular carcinomas metastasise via the lymphatics to draining lymph nodes from where they can potentially achieve systemic dissemination by invasion of high endothelial blood venules (HEVs) in the paracortex [1, 2]. Currently however, the mechanisms by which tumours invade and migrate within the lymphatics are incompletely understood, although it seems likely they exploit at least some of the normal physiological mechanisms used by immune cells to access lymphatic capillaries and traffic to draining lymph nodes in the course of immune surveillance, immune modulation and the resolution of inflammation [3, 4]. Typically these include directional guidance via chemotaxis, haptotaxis and durotaxis, adhesion to the vessel surface via receptors including integrins, and junctional re-modelling by MMPs (Matrix MetalloProteinases) and ADAMs (A Disintegrin And Metalloproteinases) [5-7]. This short review focusses on a newly emerging mechanism for lymphatic entry that involves the large polysaccharide hyaluronan (HA) and its key lymphatic and immune cell receptors respectively LYVE-1 (Lymphatic Vessel Endothelial receptor) and CD44, and outlines recent work which indicates this axis may also be used by some tumours to aid nodal metastasis.

Spatially targeted chemokine exocytosis guides transmigration at lymphatic endothelial multicellular junctions

Migrating cells preferentially breach and integrate epithelial and endothelial monolayers at multicellular vertices. These sites are amenable to forces produced by the migrating cell and subsequent opening of the junctions. However, the cues that guide migrating cells to these entry portals, and eventually drive the transmigration process, are poorly understood. Here, we show that lymphatic endothelium multicellular junctions are the preferred sites of dendritic cell transmigration in both primary cell co-cultures and in mouse dermal explants. Dendritic cell guidance to multicellular junctions was dependent on the dendritic cell receptor CCR7, whose ligand, lymphatic endothelial chemokine CCL21, was exocytosed at multicellular junctions. Characterization of lymphatic endothelial secretory routes indicated Golgi-derived RAB6+ vesicles and RAB3+/27+ dense core secretory granules as intracellular CCL21 storage vesicles. Of these, RAB6+ vesicles trafficked CCL21 to the multicellular junctions, which were enriched with RAB6 docking factor ELKS (ERC1). Importantly, inhibition of RAB6 vesicle exocytosis attenuated dendritic cell transmigration. These data exemplify how spatially-restricted exocytosis of guidance cues helps to determine where dendritic cells transmigrate.

Connexin-45 is expressed in mouse lymphatic endothelium and required for lymphatic valve function

The expression and functional relevance of the gap junction molecule connexin-45 (Cx45; GJC1) in lymphatic endothelium were not previously known. We found that Cx45 was expressed widely in the endothelium of murine lymphatics, in both valve and nonvalve regions. Cell-specific deletion of Cx45, driven by a constitutive Cre line (Lyve1-Cre) or an inducible Cre line (Prox1-CreERT2), compromised the function of lymphatic valves, as assessed by physiological tests (back leak and closure) of isolated, single-valve vessel segments. The defects were comparable to those previously reported for loss of Cx43, and as with Cx43, deletion of Cx45 resulted in shortening or increased asymmetry of lymphatic valve leaflets, providing an explanation for the compromised valve function. In contrast with Cx43, lymphatic endothelial cell-specific (LEC-specific) deletion of Cx45 did not alter the number of valves in mesenteric or dermal lymphatic networks or the expression patterns of the canonical valve-associated proteins PROX1, ITGA9, or CLAUDIN5. Constitutive deletion of Cx45 from LECs resulted in increased backflow of injected tracer in popliteal networks in vivo and compromised the integrity of the LEC permeability barrier in a subset of collecting vessels. These findings provide evidence for an unexpected role of Cx45 in the development and maintenance of lymphatic valves.

In vitro throughput screening of anticancer drugs using patient-derived cell lines cultured on vascularized three-dimensional stromal tissues

The development of high-throughput anticancer drug screening methods using patient-derived cancer cell (PDC) lines that maintain their original characteristics in an in vitro three-dimensional (3D) culture system poses a significant challenge to achieving personalized cancer medicine. Because stromal tissue plays a critical role in the composition and maintenance of the cancer microenvironment, in vitro 3D-culture using reconstructed stromal tissues has attracted considerable attention. Here, a simple and unique in vitro 3D-culture method using heparin and collagen together with fibroblasts and endothelial cells to fabricate vascularized 3D-stromal tissues for in vitro culture of PDCs is reported. Whereas co-treatment with bevacizumab, a monoclonal antibody against vascular endothelial growth factor, and 5-fluorouracil significantly reduced the survival rate of 3D-cultured PDCs to 30%, separate addition of each drug did not induce comparable strong cytotoxicity, suggesting the possibility of evaluating the combined effect of anticancer drugs and angiogenesis inhibitors. Surprisingly, drug evaluation using eight PDC lines with the 3D-culture method resulted in a drug efficacy concordance rate of 75% with clinical outcomes. The model is expected to be applicable to in vitro throughput drug screening for the development of personalized cancer medicine. STATEMENT OF SIGNIFICANCE: To replicate the cancer microenvironment, we constructed a cancer-stromal tissue model in which cancer cells are placed above and inside stromal tissue with vascular network structures derived from vascular endothelial cells in fibroblast tissue using CAViTs method. Using this method, we were able to reproduce the invasion and metastasis processes of cancer cells observed in vivo. Using patient-derived cancer cells, we assessed the possibility of evaluating the combined effect with an angiogenesis inhibitor. Further, primary cancer cells also grew on the stromal tissues with the normal medium. These data suggest that the model may be useful for new in vitro drug screening and personalized cancer medicine.

Molecular pathophysiology of secondary lymphedema

Lymphedema occurs as a result of lymphatic vessel damage or obstruction, leading to the lymphatic fluid stasis, which triggers inflammation, tissue fibrosis, and adipose tissue deposition with adipocyte hypertrophy. The treatment of lymphedema is divided into conservative and surgical approaches. Among surgical treatments, methods like lymphaticovenular anastomosis and vascularized lymph node transfer are gaining attention as they focus on restoring lymphatic flow, constituting a physiologic treatment approach. Lymphatic endothelial cells form the structure of lymphatic vessels. These cells possess button-like junctions that facilitate the influx of fluid and leukocytes. Approximately 10% of interstitial fluid is connected to venous return through lymphatic capillaries. Damage to lymphatic vessels leads to lymphatic fluid stasis, resulting in the clinical condition of lymphedema through three mechanisms: Inflammation involving CD4+ T cells as the principal contributing factor, along with the effects of immune cells on the VEGF-C/VEGFR axis, consequently resulting in abnormal lymphangiogenesis; adipocyte hypertrophy and adipose tissue deposition regulated by the interaction of CCAAT/enhancer-binding protein α and peroxisome proliferator-activated receptor-γ; and tissue fibrosis initiated by the overactivity of Th2 cells, leading to the secretion of profibrotic cytokines such as IL-4, IL-13, and the growth factor TGF-β1. Surgical treatments aimed at reconstructing the lymphatic system help facilitate lymphatic fluid drainage, but their effectiveness in treating already damaged lymphatic vessels is limited. Therefore, reviewing the pathophysiology and molecular mechanisms of lymphedema is crucial to complement surgical treatments and explore novel therapeutic approaches.

Predictors of lung cancer subtypes and lymph node status in non-small-cell lung cancer: intravoxel incoherent motion parameters and extracellular volume fraction

OBJECTIVE

To determine the performance of intravoxel incoherent motion (IVIM) parameters and the extracellular volume fraction (ECV) in distinguishing between different subtypes of lung cancer and predicting lymph node metastasis (LNM) status in patients with non-small-cell lung cancer (NSCLC).

METHODS

One hundred sixteen patients with lung cancer were prospectively recruited. IVIM, native, and postcontrast T1 mapping examinations were performed, and the T1 values were measured to calculate the ECV. The differences in IVIM parameters and ECV were compared between NSCLC and small-cell lung cancer (SCLC), adenocarcinoma (Adeno-Ca) and squamous cell carcinoma (SCC), and NSCLC without and with LNM. The assessment of each parameter's diagnostic performance was based on the area under the receiver operating characteristic curve (AUC).

RESULTS

The apparent diffusion coefficient (ADC), true diffusion coefficient (D), and ECV values in SCLC were considerably lower compared with NSCLC (all p < 0.001, AUC > 0.887). The D value in SCC was substantially lower compared with Adeno-Ca (p < 0.001, AUC = 0.735). The perfusion fraction (f) and ECV values in LNM patients were markedly higher compared with those without LNM patients (p < 0.01, < 0.001, AUC > 0.708).

CONCLUSION

IVIM parameters and ECV can serve as non-invasive biomarkers for assisting in the pathological classification and LNM status assessment of lung cancer patients.

CRITICAL RELEVANCE STATEMENT

IVIM parameters and ECV demonstrated remarkable potential in distinguishing pulmonary carcinoma subtypes and predicting LNM status in NSCLC.

KEY POINTS

Lung cancer is prevalent and differentiating subtype and invasiveness determine the treatment course. True diffusion coefficient and ECV showed promise for subtyping and determining lymph node status. These parameters could serve as non-invasive biomarkers to help determine personalized treatment strategies.