A robust in vitro model for trans-lymphatic endothelial migration

MRI Detection of Lymph Node Metastasis through Molecular Targeting of C-C Chemokine Receptor Type 2 and Monocyte Hitchhiking

Biopsy is the clinical standard for diagnosing lymph node (LN) metastasis, but it is invasive and poses significant risk to patient health. Magnetic resonance imaging (MRI) has been utilized as a noninvasive alternative but is limited by low sensitivity, with only ∼35% of LN metastases detected, as clinical contrast agents cannot discriminate between healthy and metastatic LNs due to nonspecific accumulation. Nanoparticles targeted to the C-C chemokine receptor 2 (CCR2), a biomarker highly expressed in metastatic LNs, have the potential to guide the delivery of contrast agents, improving the sensitivity of MRI. Additionally, cancer cells in metastatic LNs produce monocyte chemotactic protein 1 (MCP1), which binds to CCR2+ inflammatory monocytes and stimulates their migration. Thus, the molecular targeting of CCR2 may enable nanoparticle hitchhiking onto monocytes, providing an additional mechanism for metastatic LN targeting and early detection. Hence, we developed micelles incorporating gadolinium (Gd) and peptides derived from the CCR2-binding motif of MCP1 (MCP1-Gd) and evaluated the potential of MCP1-Gd to detect LN metastasis. When incubated with migrating monocytes in vitro, MCP1-Gd transport across lymphatic endothelium increased 2-fold relative to nontargeting controls. After administration into mouse models with initial LN metastasis and recurrent LN metastasis, MCP1-Gd detected metastatic LNs by increasing MRI signal by 30-50% relative to healthy LNs. Furthermore, LN targeting was dependent on monocyte hitchhiking, as monocyte depletion decreased accumulation by >70%. Herein, we present a nanoparticle contrast agent for MRI detection of LN metastasis mediated by CCR2-targeting and demonstrate the potential of monocyte hitchhiking for enhanced nanoparticle delivery.

Immunity-on-a-Chip: Integration of Immune Components into the Scheme of Organ-on-a-Chip Systems

Studying the immune system in vitro aims to understand how, when, and where the immune cells migrate/differentiate and respond to the various triggering events and the decision points along the immune response journey. It becomes evident that organ-on-a-chip (OOC) technology has a superior capability to recapitulate the cell-cell and tissue-tissue interaction in the body, with a great potential to provide tools for tracking the paracrine signaling with high spatial-temporal precision and implementing in situ real-time, non-destructive detection assays, therefore, enabling extraction of mechanistic information rather than phenotypic information. However, despite the rapid development in this technology, integration of the immune system into OOC devices stays among the least navigated tasks, with immune cells still the major missing components in the developed models. This is mainly due to the complexity of the immune system and the reductionist methodology of the OOC modules. Dedicated research in this field is demanded to establish the understanding of mechanism-based disease endotypes rather than phenotypes. Herein, we systemically present a synthesis of the state-of-the-art of immune-cantered OOC technology. We comprehensively outlined what is achieved and identified the technology gaps emphasizing the missing components required to establish immune-competent OOCs and bridge these gaps.

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.

In Vitro Models of Blood and Lymphatic Vessels-Connecting Tissues and Immunity

Blood and lymphatic vessels are regulators of physiological processes, including oxygenation and fluid transport. Both vessels are ubiquitous throughout the body and are critical for sustaining tissue homeostasis. The complexity of each vessel's processes has limited the understanding of exactly how the vessels maintain their functions. Both vessels have been shown to be involved in the pathogenesis of many diseases, including cancer metastasis, and it is crucial to probe further specific mechanisms involved. In vitro models are developed to better understand blood and lymphatic physiological functions and their mechanisms. In this review, blood and lymphatic in vitro model systems, including 2D and 3D designs made using Transwells, microfluidic devices, organoid cultures, and various other methods, are described. Models studying endothelial cell-extracellular matrix interactions, endothelial barrier properties, transendothelial transport and cell migration, lymph/angiogenesis, vascular inflammation, and endothelial-cancer cell interactions are particularly focused. While the field has made significant progress in modeling and understanding lymphatic and blood vasculature, more models that include coculture of multiple cell types, complex extracellular matrix, and 3D morphologies, particularly for models mimicking disease states, will help further the understanding of the role of blood and lymphatic vasculature in health and disease.

S100A4-dependent glycolysis promotes lymphatic vessel sprouting in tumor

Tumor-induced lymphangiogenesis promotes the formation of new lymphatic vessels, contributing to lymph nodes (LNs) metastasis of tumor cells in both mice and humans. Vessel sprouting appears to be a critical step in this process. However, how lymphatic vessels sprout during tumor lymphangiogenesis is not well-established. Here, we report that S100A4 expressed in lymphatic endothelial cells (LECs) promotes lymphatic vessel sprouting in a growing tumor by regulating glycolysis. In mice, the loss of S100A4 in a whole body (S100A4^-/-), or specifically in LECs (S100A4^ΔLYVE1) leads to impaired tumor lymphangiogenesis and disrupted metastasis of tumor cells to sentinel LNs. Using a 3D spheroid sprouting assay, we found that S100A4 in LECs was required for the lymphatic vessel sprouting. Further investigations revealed that S100A4 was essential for the position and motility of tip cells, where it activated AMPK-dependent glycolysis during lymphatic sprouting. In addition, the expression of S100A4 in LECs was upregulated under hypoxic conditions. These results suggest that S100A4 is a novel regulator of tumor-induced lymphangiogenesis. Targeting S100A4 in LECs may be a potential therapeutic strategy for lymphatic tumor metastasis.

New evidence for dietary fatty acids in the neutrophil traffic between the bone marrow and the peripheral blood

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SFAs but not MUFAs boosted neutrophils both in bone marrow and blood.

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SFAs were strong inducers of bone marrow neutrophil apoptosis and inflammation.

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CXCL2-CXCR2 axis engaged in fatty-acid-mediated navigation of neutrophils.

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Fatty-acid-dependent neutrophilia occurred in a postprandial model.

Chronic administration of a high-fat diet in mice has been established to influence the generation and trafficking of immune cells such as neutrophils in the bone marrow, the dysregulation of which may contribute to a wide range of diseases. However, no studies have tested the hypothesis that a short-term, high-fat diet could early modulate the neutrophil release from bone marrow at fasting and at postprandial in response to a high-fat meal challenge, and that the predominant type of fatty acids in dietary fats could play a role in both context conditions. Based on these premises, we aimed to establish the effects of different fats [butter, enriched in saturated fatty acids (SFAs), olive oil, enriched in monounsaturated fatty acids (MUFAs), and olive oil supplemented with eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids] on neutrophil navigation from bone marrow to blood in mice. The analysis of cellular models for mechanistic understanding and of postprandial blood samples from healthy volunteers for translational purposes was assessed. The results revealed a powerful effect of dietary SFAs in promotion the neutrophil traffic from bone marrow to blood via the CXCL2-CXCR2 axis. Dietary SFAs, but not MUFAs or EPA and DHA, were also associated with increased neutrophil apoptosis and bone marrow inflammation. Similar dietary fatty-acid-induced postprandial neutrophilia was observed in otherwise healthy humans. Therefore, dietary MUFAs might preserve bone marrow health and proper migration of bone marrow neutrophils early in the course of high-fat diets even after the intake of high-fat meals.

PD-L1 signaling selectively regulates T cell lymphatic transendothelial migration

Programmed death-1 (PD-1) and its ligand PD-L1 are checkpoint molecules which regulate immune responses. Little is known about their functions in T cell migration and there are contradictory data about their roles in regulatory T cell (Treg) function. Here we show activated Tregs and CD4 effector T cells (Teffs) use PD-1/PD-L1 and CD80/PD-L1, respectively, to regulate transendothelial migration across lymphatic endothelial cells (LECs). Antibody blockade of Treg PD-1, Teff CD80 (the alternative ligand for PD-L1), or LEC PD-L1 impairs Treg or Teff migration in vitro and in vivo. PD-1/PD-L1 signals through PI3K/Akt and ERK to regulate zipper junctional VE-cadherin, and through NFκB-p65 to up-regulate VCAM-1 expression on LECs. CD80/PD-L1 signaling up-regulates VCAM-1 through ERK and NFκB-p65. PD-1 and CD80 blockade reduces tumor egress of PD-1high fragile Tregs and Teffs into draining lymph nodes, respectively, and promotes tumor regression. These data provide roles for PD-L1 in cell migration and immune regulation.

Treg tissue stability depends on lymphotoxin beta-receptor- and adenosine-receptor-driven lymphatic endothelial cell responses

Regulatory T cell (Treg) lymphatic migration is required for resolving inflammation and prolonging allograft survival. Focusing on Treg interactions with lymphatic endothelial cells (LECs), we dissect mechanisms and functional consequences of Treg transendothelial migration (TEM). Using three genetic mouse models of pancreatic islet transplantation, we show that Treg lymphotoxin (LT) αβ and LEC LTβ receptor (LTβR) signaling are required for efficient Treg migration and suppressive function to prolong allograft survival. Inhibition of LT signaling increases Treg conversion to Foxp3loCD25lo exTregs. In a transwell-based model of TEM across polarized LECs, non-migrated Tregs become exTregs. Such conversion is regulated by LTβR nuclear factor κB (NF-κB) signaling in LECs, which increases interleukin-6 (IL-6) production and drives exTreg conversion. Migrating Tregs are ectonucleotidase CD39hi and resist exTreg conversion in an adenosine-receptor-2A-dependent fashion. Human Tregs migrating across human LECs behave similarly. These molecular interactions can be targeted for therapeutic manipulation of immunity and suppression.

Lipoxins modulate neutrophil oxidative burst, integrin expression and lymphatic transmigration differentially in human health and atherosclerosis

Dysregulated chronic inflammation plays a crucial role in the pathophysiology of atherosclerosis and may be a result of impaired resolution. Thus, restoring levels of specialized pro‐resolving mediators (SPMs) to promote the resolution of inflammation has been proposed as a therapeutic strategy for patients with atherosclerosis, in addition to standard clinical care. Herein, we evaluated the effects of the SPM lipids, lipoxin A₄ (LXA₄) and lipoxin B₄ (LXB₄), on neutrophils isolated from patients with atherosclerosis compared with healthy controls. Patients displayed altered endogenous SPM production, and we demonstrated that lipoxin treatment in whole blood from atherosclerosis patients attenuates neutrophil oxidative burst, a key contributor to atherosclerotic development. We found the opposite effect in neutrophils from healthy controls, indicating a potential mechanism whereby lipoxins aid the endogenous neutrophil function in health but reduce its excessive activation in disease. We also demonstrated that lipoxins attenuated upregulation of the high‐affinity conformation of the CD11b/CD18 integrin, which plays a central role in clot activation and atherosclerosis. Finally, LXB₄ enhanced lymphatic transmigration of human neutrophils isolated from patients with atherosclerosis. This finding is noteworthy, as impaired lymphatic function is now recognized as an important contributor to atherosclerosis. Although both lipoxins modulated neutrophil function, LXB₄ displayed more potent effects than LXA₄ in humans. This study highlights the therapeutic potential of lipoxins in atherosclerotic disease and demonstrates that the effect of these SPMs may be specifically tailored to the need of the individual.

Lymphatic Reconstruction in Kidney Allograft Aggravates Chronic Rejection by Promoting Alloantigen Presentation

Chronic rejection of the renal allograft remains a major cause of graft loss. Here, we demonstrated that the remodeling of lymphatic vessels (LVs) after their broken during transplantation contributes to the antigen presenting and lymph nodes activating. Our studies observed a rebuilt of interrupted lymph draining one week after mouse kidney transplantation, involving preexisting lymphatic endothelial cells (LECs) from both the donor and recipient. These expanding LVs also release C-C chemokine ligand 21 (CCL21) and recruit CCR7⁺ cells, mainly dendritic cells (DCs), toward lymph nodes and spleen, evoking the adaptive response. This rejection could be relieved by LYVE-1 specific LVs knockout or CCR7 migration inhibition in mouse model. Moreover, in retrospective analysis, posttransplant patients exhibiting higher area density of LVs presented with lower eGFR, severe serum creatinine and proteinuria, and greater interstitial fibrosis. These results reveal a rebuilt pathway for alloantigen trafficking and lymphocytes activation, providing strategies to alleviate chronic transplantation rejection.

Go with the flow: modeling unique biological flows in engineered in vitro platforms

Interest in recapitulating in vivo phenomena in vitro using organ-on-a-chip technology has grown rapidly and with it, attention to the types of fluid flow experienced in the body has followed suit. These platforms offer distinct advantages over in vivo models with regards to human relevance, cost, and control of inputs (e.g., controlled manipulation of biomechanical cues from fluid perfusion). Given the critical role biophysical forces play in several tissues and organs, it is therefore imperative that engineered in vitro platforms capture the complex, unique flow profiles experienced in the body that are intimately tied with organ function. In this review, we outline the complex and unique flow regimes experienced by three different organ systems: blood vasculature, lymphatic vasculature, and the intestinal system. We highlight current state-of-the-art platforms that strive to replicate physiological flows within engineered tissues while introducing potential limitations in current approaches.

Molecular tracking devices quantify antigen distribution and archiving in the murine lymph node

The detection of foreign antigens in vivo has relied on fluorescent conjugation or indirect read-outs such as antigen presentation. In our studies, we found that these widely used techniques had several technical limitations that have precluded a complete picture of antigen trafficking or retention across lymph node cell types. To address these limitations, we developed a 'molecular tracking device' to follow the distribution, acquisition, and retention of antigen in the lymph node. Utilizing an antigen conjugated to a nuclease-resistant DNA tag, acting as a combined antigen-adjuvant conjugate, and single-cell mRNA sequencing, we quantified antigen abundance in the lymph node. Variable antigen levels enabled the identification of caveolar endocytosis as a mechanism of antigen acquisition or retention in lymphatic endothelial cells. Thus, these molecular tracking devices enable new approaches to study dynamic tissue dissemination of antigen-adjuvant conjugates and identify new mechanisms of antigen acquisition and retention at cellular resolution in vivo.

Bioengineered in vitro models of leukocyte-vascular interactions

Leukocytes continuously circulate our body through the blood and lymphatic vessels. To survey invaders or abnormalities and defend our body against them, blood-circulating leukocytes migrate from the blood vessels into the interstitial tissue space (leukocyte extravasation) and exit the interstitial tissue space through draining lymphatic vessels (leukocyte intravasation). In the process of leukocyte trafficking, leukocytes recognize and respond to multiple biophysical and biochemical cues in these vascular microenvironments to determine adequate migration and adhesion pathways. As leukocyte trafficking is an essential part of the immune system and is involved in numerous immune diseases and related immunotherapies, researchers have attempted to identify the key biophysical and biochemical factors that might be responsible for leukocyte migration, adhesion, and trafficking. Although intravital live imaging of in vivo animal models has been remarkably advanced and utilized, bioengineered in vitro models that recapitulate complicated in vivo vascular structure and microenvironments are needed to better understand leukocyte trafficking since these in vitro models better allow for spatiotemporal analyses of leukocyte behaviors, decoupling of interdependent biological factors, better controlling of experimental parameters, reproducible experiments, and quantitative cellular analyses. This review discusses bioengineered in vitro model systems that are developed to study leukocyte interactions with complex microenvironments of blood and lymphatic vessels. This review focuses on the emerging concepts and methods in generating relevant biophysical and biochemical cues. Finally, the review concludes with expert perspectives on the future research directions for investigating leukocyte and vascular biology using the in vitro models.

Regulatory T Cells Condition Lymphatic Endothelia for Enhanced Transendothelial Migration

Regulatory T cells (Tregs) express high levels of cell surface lymphotoxin alpha beta (LTα1β2) to activate the LT beta receptor (LTβR) on the lymphatic endothelial cells (LECs), modulating LEC adhesion molecules, intercellular junctions, and chemokines. We demonstrate a role for Tregs through this pathway to condition the permissiveness of lymphatic endothelia for transendothelial migration (TEM), thus gating leukocyte traffic. Human Tregs share the same property with murine Tregs. Activation of TLR2 on Tregs during inflammation specifically augments LTα1β2-LTβR signaling, which further enhances the permissiveness of LECs to facilitate TEM. The conditioning of endothelia may promote the resolution of inflammation by directing leukocytes out of tissues to lymphatic vessels and draining lymph nodes (dLNs). Thus, Tregs interact with lymphatic endothelia under homeostasis and inflammation and dictate endothelial permissiveness and gating mechanisms for subsequent leukocyte migration through endothelial barriers.

CD4 T cell sphingosine 1-phosphate receptor (S1PR)1 and S1PR4 and endothelial S1PR2 regulate afferent lymphatic migration

Sphingosine 1-phosphate (S1P) and S1P receptors (S1PRs) regulate migration of lymphocytes out of thymus to blood and lymph nodes (LNs) to efferent lymph, whereas their role in other tissue sites is not known. Here, we investigated the question of how these molecules regulate leukocyte migration from tissues through afferent lymphatics to draining LNs (dLNs). S1P, but not other chemokines, selectively enhanced human and murine CD4 T cell migration across lymphatic endothelial cells (LECs). T cell S1PR1 and S1PR4, and LEC S1PR2, were required for migration across LECs and into lymphatic vessels and dLNs. S1PR1 and S1PR4 differentially regulated T cell motility and vascular cell adhesion molecule-1 (VCAM-1) binding. S1PR2 regulated LEC layer structure, permeability, and expression of the junction molecules VE-cadherin, occludin, and zonulin-1 through the ERK pathway. S1PR2 facilitated T cell transcellular migration through VCAM-1 expression and recruitment of T cells to LEC migration sites. These results demonstrated distinct roles for S1PRs in comodulating T cell and LEC functions in migration and suggest previously unknown levels of regulation of leukocytes and endothelial cells during homeostasis and immunity.

Engineered fluidic systems to understand lymphatic cancer metastasis

The majority of all cancers metastasize initially through the lymphatic system. Despite this, the mechanisms of lymphogenous metastasis remain poorly understood and understudied compared to hematogenous metastasis. Over the past few decades, microfluidic devices have been used to model pathophysiological processes and drug interactions in numerous contexts. These devices carry many advantages over traditional 2D in vitro systems, allowing for better replication of in vivo microenvironments. This review highlights prominent fluidic devices used to model the stages of cancer metastasis via the lymphatic system, specifically within lymphangiogenesis, vessel permeability, tumor cell chemotaxis, transendothelial migration, lymphatic circulation, and micrometastases within the lymph nodes. In addition, we present perspectives for the future roles that microfluidics might play within these settings and beyond.

Metastasis in Pancreatic Ductal Adenocarcinoma: Current Standing and Methodologies

Pancreatic ductal adenocarcinoma is an extremely aggressive disease with a high metastatic potential. Most patients are diagnosed with metastatic disease, at which the five-year survival rate is only 3%. A better understanding of the mechanisms that drive metastasis is imperative for the development of better therapeutic interventions. Here, we take the reader through our current knowledge of the parameters that support metastatic progression in pancreatic ductal adenocarcinoma, and the experimental models that are at our disposal to study this process. We also describe the advantages and limitations of these models to study the different aspects of metastatic dissemination.

Granulomatous Inflammation in Tuberculosis and Sarcoidosis: Does the Lymphatic System Contribute to Disease?

A striking and unexplained feature of granulomatous inflammation is its anatomical association with the lymphatic system. Accumulating evidence suggests that lymphatic tracks and granulomas may alter the function of each other. The formation of new lymphatics, or lymphangiogenesis, is an adaptive response to tumor formation, infection, and wound healing. Granulomas also may induce lymphangiogenesis which, through a variety of mechanisms, could contribute to disease outcomes in tuberculosis and sarcoidosis. On the other hand, alterations in lymph node function and lymphatic draining may be primary events which attenuate the risk and severity of granulomatous inflammation. This review begins with an introduction of granulomatous inflammation and the lymphatic system. A role of the lymphatic system in tuberculosis and sarcoidosis is then hypothesized. With a focus on lymphangiogenesis in these diseases, and on the potential for this process to promote dissemination, parallels are established with the well-established role of lymphangiogenesis in tumor biology.

Role of lymph node stroma and microenvironment in T cell tolerance

Lymph nodes (LNs) are at the cross roads of immunity and tolerance. These tissues are compartmentalized into specialized niche areas by lymph node stromal cells (LN SCs). LN SCs shape the LN microenvironment and guide immunological cells into different zones through establishment of a CCL19 and CCL21 gradient. Following local immunological cues, LN SCs modulate activity to support immune cell priming, activation, and fate. This review will present our current understanding of LN SC subsets roles in regulating T cell tolerance. Three major types of LN SC subsets, namely fibroblastic reticular cells, lymphatic endothelial cells, and blood endothelial cells, are discussed. These subsets serve as scaffolds to support and regulate T cell homeostasis. They contribute to tolerance by presenting peripheral tissue antigens to both CD4 and CD8 T cells. The role of LN SCs in regulating T cell migration and tolerance induction is discussed. Looking forward, recent advances in bioengineered materials and approaches to leverage LN SCs to induce T cell tolerance are highlighted, as are current clinical practices that allow for manipulation of the LN microenvironment to induce tolerance. Increased understanding of LN architecture, how different LN SCs integrate immunological cues and shape immune responses, and approaches to induce T cell tolerance will help further combat autoimmune diseases and graft rejection.

Human organotypic lymphatic vessel model elucidates microenvironment-dependent signaling and barrier function

The lymphatic system is an active player in the pathogenesis of several human diseases, including lymphedema and cancer. Relevant models are needed to advance our understanding of lymphatic biology in disease progression to improve therapy and patient outcomes. Currently, there are few 3D in vitro lymphatic models that can recapitulate the physiological structure, function, and interactions of lymphatic vessels in normal and diseased microenvironments. Here, we developed a 3D microscale lymphatic vessel (μLYMPH) system for generating human lymphatic vessels with physiological tubular structure and function. Consistent with characteristics of lymphatic vessels in vivo, the endothelium of cultured vessels was leaky with an average permeability of 1.38 × 10^-5 ± 0.29 × 10^-5 cm/s as compared to 0.68 × 10^-5 ± 0.13 × 10^-5 cm/s for blood vessels. This leakiness also resulted in higher uptake of solute by the lymphatic vessels under interstitial flow, demonstrating recapitulation of their natural draining function. The vessels secreted appropriate growth factors and inflammatory mediators. Our system identified the follistatin/activin axis as a novel pathway in lymphatic vessel maintenance and inflammation. Moreover, the μLYMPH system provided a platform for examining crosstalk between lymphatic vessels and tumor microenvironmental components, such as breast cancer-associated fibroblasts (CAFs). In co-culture with CAFs, vessel barrier function was significantly impaired by CAF-secreted IL-6, a possible pro-metastatic mechanism of lymphatic metastasis. Targeted blocking of the IL-6/IL-6R signaling pathway with an IL-6 neutralizing antibody fully rescued the vessels, demonstrating the potential of our system for screening therapeutic targets. These results collectively demonstrate the μLYMPH system as a powerful model for advancing lymphatic biology in health and disease.

Application of microscale culture technologies for studying lymphatic vessel biology

Immense progress in microscale engineering technologies has significantly expanded the capabilities of in vitro cell culture systems for reconstituting physiological microenvironments that are mediated by biomolecular gradients, fluid transport, and mechanical forces. Here, we examine the innovative approaches based on microfabricated vessels for studying lymphatic biology. To help understand the necessary design requirements for microfluidic models, we first summarize lymphatic vessel structure and function. Next, we provide an overview of the molecular and biomechanical mediators of lymphatic vessel function. Then we discuss the past achievements and new opportunities for microfluidic culture models to a broad range of applications pertaining to lymphatic vessel physiology. We emphasize the unique attributes of microfluidic systems that enable the recapitulation of multiple physicochemical cues in vitro for studying lymphatic pathophysiology. Current challenges and future outlooks of microscale technology for studying lymphatics are also discussed. Collectively, we make the assertion that further progress in the development of microscale models will continue to enrich our mechanistic understanding of lymphatic biology and physiology to help realize the promise of the lymphatic vasculature as a therapeutic target for a broad spectrum of diseases.

Inhibition of tumor formation and metastasis by a monoclonal antibody against lymphatic vessel endothelial hyaluronan receptor 1

Although cancer metastasis is associated with poor prognosis, the mechanisms of this event, especially via lymphatic vessels, remain unclear. Lymphatic vessel endothelial hyaluronan receptor 1 (LYVE‐1) is expressed on lymphatic vessel endothelium and is considered to be a specific marker of lymphatic vessels, but it is unknown how LYVE‐1 is involved in the growth and metastasis of cancer cells. We produced rat monoclonal antibodies (mAb) recognizing the extracellular domain of mouse LYVE‐1, and investigated the roles of LYVE‐1 in tumor formation and metastasis. The mAb 38M and 64R were selected from hybridoma clones created by cell fusion between spleen cells of rats immunized with RH7777 rat hepatoma cells expressing green fluorescent protein (GFP)‐fused mouse LYVE‐1 proteins and mouse myeloma cells. Two mAb reacted with RH7777 and HEK293F human embryonic kidney cells expressing GFP‐fused mouse LYVE‐1 proteins in a GFP expression‐dependent manner, and each recognized a distinct epitope. On immunohistology, the 38M mAb specifically stained lymphatic vessels in several mouse tissues. In the wound healing assay, the 64R mAb inhibited cell migration of HEK293F cells expressing LYVE‐1 and mouse lymphatic endothelial cells (LEC), as well as tube formation by LEC. Furthermore, this mAb inhibited primary tumor formation and metastasis to lymph nodes in metastatic MDA‐MB‐231 xenograft models. This shows that LYVE‐1 is involved in primary tumor formation and metastasis, and it may be a promising molecular target for cancer therapy.

Docetaxel facilitates lymphatic-tumor crosstalk to promote lymphangiogenesis and cancer progression

Background

Infiltration into lymphatic vessels is a critical step in breast cancer metastasis. Lymphatics undergo changes that facilitate metastasis as a result of activation of the cells lining lymphatic vessels, lymphatic endothelial cells (LECs). Inhibition of activation by targeting VEGFR3 can reduce invasion toward lymphatics. To best benefit patients, this approach should be coupled with standard of care that slows tumor growth, such as chemotherapy. Little is known about how chemotherapies, like docetaxel, may influence lymphatics and conversely, how lymphatics can alter responses to therapy.

Methods

A novel 3D in vitro co-culture model of the human breast tumor microenvironment was employed to examine the contribution of LECs to tumor invasion and viability with docetaxel and anti-VEGFR3, using three cell lines, MDA-MB-231, HCC38, and HCC1806. In vivo, the 4T1 mouse model of breast carcinoma was used to examine the efficacy of combinatorial therapy with docetaxel and anti-VEGFR3 on lymph node metastasis and tumor growth. Lymphangiogenesis in these mice was analyzed by immunohistochemistry and flow cytometry. Luminex analysis was used to measure expression of lymphangiogenic cytokines.

Results

In vitro, tumor cell invasion significantly increased with docetaxel when LECs were present; this effect was attenuated by inhibition of VEGFR3. LECs reduced docetaxel-induced cell death independent of VEGFR3. In vivo, docetaxel significantly increased breast cancer metastasis to the lymph node. Docetaxel and anti-VEGFR3 combination therapy reduced lymph node and lung metastasis in 4T1 and synergized to reduce tumor growth. Docetaxel induced VEGFR3-dependent vessel enlargement, lymphangiogenesis, and expansion of the LEC population in the peritumoral microenvironment, but not tumor-free stroma. Docetaxel caused an upregulation in pro-lymphangiogenic factors including VEGFC and TNF-α in the tumor microenvironment in vivo.

Conclusions

Here we present a counter-therapeutic effect of docetaxel chemotherapy that triggers cancer cells to elicit lymphangiogenesis. In turn, lymphatics reduce cancer response to docetaxel by altering the cytokine milieu in breast cancer. These changes lead to an increase in tumor cell invasion and survival under docetaxel treatment, ultimately reducing docetaxel efficacy. These docetaxel-induced effects can be mitigated by anti-VEGFR3 therapy, resulting in a synergism between these treatments that reduces tumor growth and metastasis.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4619-8) contains supplementary material, which is available to authorized users.