CD4+ T cells are activated in regional lymph nodes and migrate to skin to initiate lymphedema

Rituximab in non-systemic vasculitic neuropathy: a single-center experience

OBJECTIVES

This case series reports clinical features and outcome of four patients with non-systemic vasculitic neuropathy (NSVN) treated with the anti-CD20 agent rituximab.

METHODS

Clinical, electrophysiological and biopsy data were retrospectively obtained and evaluated. Only patients with pathological definite or probable NSVN were included. Extensive clinical and laboratory work-up excluded systemic vasculitis. Follow-up data for at least 12 months and up to five years is provided. Outcome of the patients was assessed using the MRC-Sum Score, Prineas Score and Neurological Symptom Score.

RESULTS

Two of four patients treated with rituximab achieved disease remission and one patient remained stable under anti-CD20 therapy after a required treatment switch due to toxic side effects of cyclophosphamide. One patient deteriorated under rituximab induction. Rituximab was well tolerated in all patients.

DISCUSSION

Anti-CD20 therapy might be an alternative in NSVN patients requiring further treatment escalation or treatment switch due to side effects of corticosteroids or cyclophosphamide.

GLP-1 receptor agonist as an effective treatment for breast cancer-related lymphedema: a case report

Introduction

Lymphedema is a major public health issue for many women undergoing breast cancer treatment. Although weight loss has been reported to be beneficial in the treatment of lymphedema, no studies to date have examined the use of GLP-1RAs for the treatment of secondary lymphedema. This case report describes a patient who experienced significant resolution of her breast cancer-related lymphedema after initiation of a GLP-1RA for weight loss.

Main symptoms and/or important clinical findings

Nine months postoperatively the patient developed arm swelling and disability. While on adjuvant chemo and hormonal therapy, her weight increased dramatically and peaked 4 years later. Corresponding to her weight gain was significant worsening of her symptoms.

The main diagnoses therapeutic interventions and outcomes

Due to adjuvant cancer-related weight gain and inability to lose weight with diet and exercise, she was referred for evaluation and diagnosed with lymphedema. The patient started treatment with a Glucagon-like peptide 1 receptor agonist and lost 24% of her body weight over the next 13 months. The improvement in her lymphedema mirrored her weight loss. Her limb volume difference dropped from 10.3% down to 3.4% and she no longer required a compression garment. Her imaging demonstrated return of lymphatic pumping and she experienced a significant improvement in quality of life, assessed by a validated lymphedema-specific patient reported outcome (PROM). She remains on hormonal therapy, no longer needs compression and is back to regular exercise without impairment.

Conclusions

GLP-1 RAs provide a potential medical option for many patients struggling with weight gain and lymphedema. We have observed by all objective measures a significant reduction in lymphedema and the elimination of compression in the case presented as a direct result of GLP-1 RA. This may also reduce a patient's BMI to the point where they become a good candidate for lymphovenous bypass or vascularized lymph node transplant when indicated.

15-Lipoxygenase promotes resolution of inflammation in lymphedema by controlling Treg cell function through IFN-β

Lymphedema (LD) is characterized by the accumulation of interstitial fluid, lipids and inflammatory cell infiltrate in the limb. Here, we find that LD tissues from women who developed LD after breast cancer exhibit an inflamed gene expression profile. Lipidomic analysis reveals decrease in specialized pro-resolving mediators (SPM) generated by the 15-lipoxygenase (15-LO) in LD. In mice, the loss of SPM is associated with an increase in apoptotic regulatory T (Treg) cell number. In addition, the selective depletion of 15-LO in the lymphatic endothelium induces an aggravation of LD that can be rescued by Treg cell adoptive transfer or ALOX15-expressing lentivector injections. Mechanistically, exogenous injections of the pro-resolving cytokine IFN-β restores both 15-LO expression and Treg cell number in a mouse model of LD. These results provide evidence that lymphatic 15-LO may represent a therapeutic target for LD by serving as a mediator of Treg cell populations to resolve inflammation.

Surgical lymphedema models in the mice hindlimb-A systematic review and quality assessment

BACKGROUND

Lymphedema constitutes a major unsolved problem in plastic surgery. To identify novel lymphedema treatments, preclinical studies are vital. The surgical mouse lymphedema model is popular and cost-effective; nonetheless, a synthesis and overview of the literature with evidence-based guidelines is needed. The aim of this review was to perform a systematic review to establish best practice and support future high-quality animal studies exploring lymphedema treatments.

METHODS

We performed a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, searching four databases (PubMed, Embase, Web of Science, and Scopus) from inception-September 2022. The Animals in Research Reporting In Vivo Experiments 2.0 (ARRIVE 2.0) guidelines were used to evaluate reporting quality. Studies claiming to surgically induce lymphedema in the hindlimb of mice were included.

RESULTS

Thirty-seven studies were included. Four main models were used. (1) Irradiation+surgery. (2) A variation of the surgery used by (1) + irradiation. (3) Surgery only (SPDF-model). (4) Surgery only (PLND-model). Remaining studies used other techniques. The most common measurement modality was the caliper. Mean quality coefficient was 0.57. Eighteen studies (49%) successfully induced sustained lymphedema. Combination of methods seemed to yield the best results, with an overrepresentation of irradiation, the removal of two lymph nodes, and the disruption of both the deep and superficial lymph vessels in the 18 studies.

CONCLUSION

Surgical mouse hindlimb lymphedema models are challenged by two related problems: (1) retaining lymphedema for an extended period, that is, establishing a (chronic) lymphedema model (2) distinguishing lymphedema from post-operative edema. Most studies failed to induce lymphedema and used error-prone measurements. We provide an overview of studies claiming to induce lymphedema and advocate improved research via five evidence-based recommendations to use: (1) a proven lymphedema model; (2) sufficient follow-up time, (3) validated measurement methods; (4) ARRIVE-guidelines; (5) contralateral hindlimb as control.

PPARγ agonist treatment reduces fibroadipose tissue in secondary lymphedema by exhausting fibroadipogenic PDGFRα+ mesenchymal cells

Secondary lymphedema occurs in up to 20% of patients after lymphadenectomy performed for the surgical management of tumors involving the breast, prostate, uterus, and skin. Patients develop progressive edema of the affected extremity due to retention of protein-rich lymphatic fluid. Despite compression therapy, patients progress to chronic lymphedema in which noncompressible fibrosis and adipose tissue are deposited within the extremity. The presence of fibrosis led to our hypothesis that rosiglitazone, a PPARγ agonist that inhibits fibrosis, would reduce fibrosis in a mouse model of secondary lymphedema after hind limb lymphadenectomy. In vivo, rosiglitazone reduced fibrosis in the hind limb after lymphadenectomy. Our findings verified that rosiglitazone reestablished the adipogenic features of TGF-β1-treated mesenchymal cells in vitro. Despite this, rosiglitazone led to a reduction in adipose tissue deposition. Single-cell RNA-Seq data obtained from human tissues and flow cytometric and histological evaluation of mouse tissues demonstrated increased presence of PDGFRα+ cells in lymphedema; human tissue analysis verified these cells have the capacity for adipogenic and fibrogenic differentiation. Upon treatment with rosiglitazone, we noted a reduction in the overall quantity of PDGFRα+ cells and LipidTOX+ cells. Our findings provide a framework for treating secondary lymphedema as a condition of fibrosis and adipose tissue deposition, both of which, paradoxically, can be prevented with a pro-adipogenic agent.

Interruption of Lymph Flow Worsens the Skin Inflammation Caused by Saprophytic Staphylococcus epidermidis

Lymphedema is often complicated by chronic inflammation, leading to fibrosis, fat deposition, and inhibition of lymphangiogenesis. This study aimed to verify whether lymphedema itself or together with commensal bacterial flora infection contributes to the severity of local inflammation. Edema was induced by interruption of the lymph flow in the rat's hind limb. Immune cell infiltrates were examined by flow cytometry and immunohistochemistry. Nine-day edema alone did not affect immune cell content in the skin but resulted in a decrease in CD4+ T helper lymphocytes and monocytes in the draining popliteal lymph nodes. In turn, local saprophytic Staphylococcus epidermidis infection of the edematous limb resulted in dense infiltrates of CD68+ macrophages and monocytes, MHC class II antigen-presenting cells, CD90+ stem cells, thymocytes, and immature B cells in the skin, accompanied by a simultaneous reduction in density of CD4+ T helper lymphocytes and monocytes, OX62+ dendritic cells, CD68+ macrophages and monocytes, HiS48+ granulocytes, CD90+ stem cells, thymocytes, and immature B cells in the draining popliteal lymph nodes. These results indicate that the combination of edema and saprophytic bacteria infection induces severe inflammation in the peripheral tissues and results in a delay of antibacterial protection processes in neighboring lymphatic organs.

The Function of T Cell Immunity in Lymphedema: A Comprehensive Review

Lymphedema is a debilitating disease characterized by extremity edema, fibroadipose deposition, impaired lymphangiogenesis, and dysfunctional lymphatics, often with lymphatic injury secondary to the treatment of malignancies. Emerging evidence has shown that immune dysfunction regulated by T cells plays a pivotal role in development of lymphedema. Specifically, Th1, Th2, Treg, and Th17 cells have been identified as critical regulators of pathological changes in lymphedema. In this review, our aim is to provide an overview of the current understanding of the roles of CD4+ T cells, including Th1, Th2, Treg, and Th17 subsets, in the progression of lymphedema and to discuss associated therapies targeting T cell inflammation for management of lymphedema.

YAP1/Piezo1 involve in the dynamic changes of lymphatic vessels in UVR-induced photoaging progress to squamous cell carcinoma

BACKGROUND

UV-induced cutaneous squamous cell carcinoma (cSCC) is one of the most common skin cancers. The constant alterations of the lymphatic-centered immune microenvironment are essential in transforming from photoaging to cSCC. Studying the mechanism will be beneficial for new targets exploration to the early prediction of cSCC.

AIMS

To investigate the dynamic changes and mechanism of the lymphatic-centered immune microenvironment in transforming from photoaging to cSCC induced by ultraviolet irradiation (UVR).

METHODS

TIMER2.0 was used to analyze whether YAP1/VEGFC signaling pathway is involved in lymphangiogenesis in head and neck squamous cell carcinoma (HNSCC). Meanwhile, lymphatic-centered immune microenvironments alterations and the related cumulative survival time were also analyzed. With the accumulated UVR, skin photoaging developed and gradually progressed into actinic keratosis and cSCC on SKH-1 hairless mice. The skin lymphatic-centered immune microenvironment was evaluated at the 0th, 8th, 12th, 16-18th, and 20-24th week of UVR. Skin phenotype was assessed using optical coherence tomography (OCT) and skin image. H&E and Masson's trichrome staining evaluated epidermis and dermis. The structure of lymphatic vessels (LVs), blood vessels, and different types of T cells were evaluated by immunohistochemistry staining. The expression of Piezo1 whose deletion in adult lymphatics led to substantial valve degeneration, VE-cadherin that maintained the permeability of LVs, and YAP1 were evaluated by immunohistochemistry staining as well. Besides, the drainage function of LVs was assessed by Evans Blue assay in vivo.

RESULTS

The lymphatic function and immune cell infiltration underwent adaptive changes under continuous UVR. TIMER2.0 analysis indicated that VEGFC genes high expressed in HNSCC. YAP1 gene expression was positive correlated with VEGFC in HNSCC. LV density increased in human cSCC. More LVs in HNSCC were beneficial to prolong the survival time. VEGFC gene overexpression was positive correlated to CD8+T cell infiltration. More CD8A+T cells and CD8B+T cell infiltration in HNSCC extended survival time. When YAP1 gene overexpression and high infiltration of endothelial cells took place simultaneously might prolong the survival time of HNSCC patients. And high infiltration of CD8+T cells prolonged the survival time as well. In animal studies, UVR-induced eight weeks (photoaging) and 16-18 weeks (precancerous) were two turning points. The density of LVs in UV-8w was the least. When photoaged skin developed into AK lesions (UV-16-18w), LV slightly exceeded healthy skin and proliferated sharply in cSCC (UV-20-24w). YAP1 expression was almost consistent with LV but rose after the photoaging stage. The drainage of cSCC mice induced by UVR was better than that of photoaged skin and worse than that of health skin. The dynamic alterations of LVs number, Piezo1 expression, and collagen might be reasons for it. The expression of Piezo1 was in the highest point after 8 weeks of UVR, then gradually descended to the platform. The total T cells increased slowly, but the infiltration of CD4+T cells increased, and CD8+T cells decreased after eight weeks of UVR. The CD8+T cells and CD4+T cells increased sharply in UV-16-18w and UV-20-24w groups.

CONCLUSION

The lymphatic-centered immune microenvironment underwent adaptive changes under continuous UVR via regulating YAP1/VEGFC and Piezo1. During the formation of cSCC, there are two turning points, eight weeks (photoaging) and 16-18 weeks (precancerous). YAP1, Piezo1, LVs, and immune cells constantly changed with the skin state induced by UVR. According to these changes the process of cSCC can be identified in advance and intervene timely.

Abnormal Lymphatic Sphingosine-1-Phosphate Signaling Aggravates Lymphatic Dysfunction and Tissue Inflammation

BACKGROUND

Lymphedema is a global health problem with no effective drug treatment. Enhanced T-cell immunity and abnormal lymphatic endothelial cell (LEC) signaling are promising therapeutic targets for this condition. Sphingosine-1-phosphate (S1P) mediates a key signaling pathway required for normal LEC function, and altered S1P signaling in LECs could lead to lymphatic disease and pathogenic T-cell activation. Characterizing this biology is relevant for developing much needed therapies.

METHODS

Human and mouse lymphedema was studied. Lymphedema was induced in mice by surgically ligating the tail lymphatics. Lymphedematous dermal tissue was assessed for S1P signaling. To verify the role of altered S1P signaling effects in lymphatic cells, LEC-specific S1pr1-deficient (S1pr1LECKO) mice were generated. Disease progression was quantified by tail-volumetric and -histopathologic measurements over time. LECs from mice and humans, with S1P signaling inhibition, were then cocultured with CD4 T cells, followed by an analysis of CD4 T-cell activation and pathway signaling. Last, animals were treated with a monoclonal antibody specific to P-selectin to assess its efficacy in reducing lymphedema and T-cell activation.

RESULTS

Human and experimental lymphedema tissues exhibited decreased LEC S1P signaling through S1P receptor 1 (S1PR1). LEC S1pr1 loss-of-function exacerbated lymphatic vascular insufficiency, tail swelling, and increased CD4 T-cell infiltration in mouse lymphedema. LECs, isolated from S1pr1LECKO mice and cocultured with CD4 T cells, resulted in augmented lymphocyte differentiation. Inhibiting S1PR1 signaling in human dermal LECs promoted T-helper type 1 and 2 (Th1 and Th2) cell differentiation through direct cell contact with lymphocytes. Human dermal LECs with dampened S1P signaling exhibited enhanced P-selectin, an important cell adhesion molecule expressed on activated vascular cells. In vitro, P-selectin blockade reduced the activation and differentiation of Th cells cocultured with shS1PR1-treated human dermal LECs. P-selectin-directed antibody treatment improved tail swelling and reduced Th1/Th2 immune responses in mouse lymphedema.

CONCLUSIONS

This study suggests that reduction of the LEC S1P signaling aggravates lymphedema by enhancing LEC adhesion and amplifying pathogenic CD4 T-cell responses. P-selectin inhibitors are suggested as a possible treatment for this pervasive condition.

Substance P promote macrophage M2 polarization to attenuate secondary lymphedema by regulating NF-kB/NLRP3 signaling pathway

Secondary lymphedema often occurs after filariasis, trauma, lymph node dissection and radiation therapy, which is manifested by infiltration of inflammatory cells and fibrosis formation in pathologically. Substance P is a widely used neuropeptide in the field of tissue repair, while the regenerative potential of the substance P has not been proven in the secondary lymphedema. In this study, animal model of secondary lymphedema was constructed by excising the skin and subcutaneous lymphatic network in the tail of mice, and the degree of swelling in the tail of mice was evaluated after 6 weeks under the treatment with substance P. Immunofluorescence staining was also performed to assess immune cell infiltration, subcutaneous fibrosis and lymphangiogenesis. The results revealed that substance P significantly alleviated post-surgical lymphedema in mice. Furthermore, we found that substance P promoted macrophages M2 polarization, a process associated with downregulation of the NF-kB/NLRP3 pathway. After application of disodium clodronate (macrophage scavenger, CLO), the positive effect of substance P in lymphedema is significantly inhibited. In vitro experiments, we further demonstrated the polarizing effect of substance P on bone marrow-derived macrophages (BMDMs), while substance P inhibited the activation of the NF-kB/NLRP3 pathway in BMDMs after the treatment of lipopolysaccharide (LPS). In addition, polarized macrophages were demonstrated to promote the proliferation, tube-forming and migratory functions of human lymphatic endothelial cells (hLEC). In conclusion, our study provides preliminary evidence that substance P alleviates secondary lymphedema by promoting macrophage M2 polarization, and this therapeutic effect may be associated with downregulation of the NF-kB/NLRP3 pathway.

Analysis of CD4+ T-helper-associated hub gene signature and immune dysregulation via RNA-sequencing data in a mouse tail model of lymphedema

Background

T-helper cells play an essential role in the progression of lymphedema. This study aimed to explore the biological significance of T-helper cell-associated genes (THAGs) in a mouse tail model of lymphedema by RNA-sequencing (RNA-seq) data.

Methods

The expression profiles of a murine model of secondary lymphedema were obtained from European Nucleotide Archive (ENA) database. Differentially expressed genes (DEGs) were screened and the enrichment analysis of DEGs was conducted. THAGs were constructed by crossing the T-helper-related gene sets obtained from Molecular Signatures Database with DEGs. Protein-protein interaction (PPI) network analysis was utilized to establish T-helper-associated hub genes (THAHGs). Single-sample gene set enrichment analysis (ssGSEA) was employed to decipher differences in immune cell infiltration. The correlation between THAHGs and immune infiltration was calculated by Pearson correlation analysis. Receiver operating characteristic (ROC) curves of THAHGs were drawn to evaluate their diagnostic properties. Additionally, potential drugs and upstream transcription factors (TFs) were predicted based on THAHGs.

Results

Enrichment analysis showed that lymphedematous tissue presented higher activation of biological process (BP) of T-helper 1 (Th1), T-helper 2 (Th2), T-helper 17 (Th17). The immune infiltration analysis further calculated that the relative immune abundance of follicular B cells, memory B cells, M1 macrophage, and CD4+ Tm cells was significantly elevated while the relative immune abundance of neutrophils and plasma cells were down-regulated in lymphedema. We established a list of THAHGs consisting of eight hub genes, compassing Cd4, Foxp3, Irf4, Ccr6, Il12rb1, Batf, Il1b, Cd74. THAHGs were shown to be significantly interrelated and related to immune infiltration by Pearson correlation analysis. ROC curves showcased that the area under curve (AUC) values of THAHGs were larger than 0.70. Gata3 was the most potential TF and thalidomide might be the immunoregulatory drug for lymphedema based on THAHGs.

Conclusions

Biological pathways associated with T-helpers were significantly enriched in mouse lymphedema tissue. The relative immune infiltration abundance of M1 macrophage, CD4+ Tm cells, and T-helper cells was higher in the lymphedema group. Besides, we identified the THAHGs containing eight genes, namely, Cd4, Foxp3, Irf4, Ccr6, Il12rb1, Batf, Il1b, and Cd74. The THAHGs were closely correlated with immune infiltration results and with good diagnostic properties.

The emerging importance of lymphatics in health and disease: an NIH workshop report

The lymphatic system (LS) is composed of lymphoid organs and a network of vessels that transport interstitial fluid, antigens, lipids, cholesterol, immune cells, and other materials in the body. Abnormal development or malfunction of the LS has been shown to play a key role in the pathophysiology of many disease states. Thus, improved understanding of the anatomical and molecular characteristics of the LS may provide approaches for disease prevention or treatment. Recent advances harnessing single-cell technologies, clinical imaging, discovery of biomarkers, and computational tools have led to the development of strategies to study the LS. This Review summarizes the outcomes of the NIH workshop entitled "Yet to be Charted: Lymphatic System in Health and Disease," held in September 2022, with emphasis on major areas for advancement. International experts showcased the current state of knowledge regarding the LS and highlighted remaining challenges and opportunities to advance the field.

Ovol1/2 loss-induced epidermal defects elicit skin immune activation and alter global metabolism

Skin epidermis constitutes the outer permeability barrier that protects the body from dehydration, heat loss, and myriad external assaults. Mechanisms that maintain barrier integrity in constantly challenged adult skin and how epidermal dysregulation shapes the local immune microenvironment and whole-body metabolism remain poorly understood. Here, we demonstrate that inducible and simultaneous ablation of transcription factor-encoding Ovol1 and Ovol2 in adult epidermis results in barrier dysregulation through impacting epithelial-mesenchymal plasticity and inflammatory gene expression. We find that aberrant skin immune activation then ensues, featuring Langerhans cell mobilization and T cell responses, and leading to elevated levels of secreted inflammatory factors in circulation. Finally, we identify failure to gain body weight and accumulate body fat as long-term consequences of epidermal-specific Ovol1/2 loss and show that these global metabolic changes along with the skin barrier/immune defects are partially rescued by immunosuppressant dexamethasone. Collectively, our study reveals key regulators of adult barrier maintenance and suggests a causal connection between epidermal dysregulation and whole-body metabolism that is in part mediated through aberrant immune activation.

Topical captopril: a promising treatment for secondary lymphedema

Transforming growth factor-beta 1 (TGF-β1)-mediated tissue fibrosis is an important regulator of lymphatic dysfunction in secondary lymphedema. However, TGF-β1 targeting can cause toxicity and autoimmune complications, limiting clinical utility. Angiotensin II (Ang II) modulates intracellular TGF-β1 signaling, and inhibition of Ang II production using angiotensin-converting enzyme (ACE) inhibitors, such as captopril, has antifibrotic efficacy in some pathological settings. Therefore, we analyzed the expression of ACE and Ang II in clinical lymphedema biopsy specimens from patients with unilateral breast cancer-related lymphedema (BCRL) and mouse models, and found that cutaneous ACE expression is increased in lymphedematous tissues. Furthermore, topical captopril decreases fibrosis, activation of intracellular TGF-β1 signaling pathways, inflammation, and swelling in mouse models of lymphedema. Captopril treatment also improves lymphatic function and immune cell trafficking by increasing collecting lymphatic pumping. Our results show that the renin-angiotensin system in the skin plays an important role in the regulation of fibrosis in lymphedema, and inhibition of this signaling pathway may hold merit for treating lymphedema.

Peripheral T cell profiling reveals downregulated exhaustion marker and increased diversity in lymphedema post-lymphatic venous anastomosis

Lymphedema is a progressive condition accompanying cellulitis and angiosarcoma, suggesting its association with immune dysfunction. Lymphatic venous anastomosis (LVA) can provide relief from cellulitis and angiosarcoma. However, the immune status of peripheral T cells during lymphedema and post-LVA remains poorly understood. Using peripheral blood T cells from lymphedema, post-LVA, and healthy controls (HCs), we compared the profile of T cell subsets and T cell receptor (TCR) diversity. PD-1⁺ Tim-3 ⁺ expression was downregulated in post-LVA compared with lymphedema. IFN-γ levels in CD4⁺PD-1⁺ T cells and IL-17A levels in CD4⁺ T cells were downregulated in post-LVA compared with lymphedema. TCR diversity was decreased in lymphedema compared with HCs; such TCR skewing was drastically improved in post-LVA. T cells in lymphedema were associated with exhaustion, inflammation, and diminished diversity, which were relieved post-LVA. The results provide insights into the peripheral T cell population in lymphedema and highlight the immune modulatory importance of LVA.

Abnormal lymphatic S1P signaling aggravates lymphatic dysfunction and tissue inflammation

BACKGROUND

Lymphedema is a global health problem with no effective drug treatment. Enhanced T cell immunity and abnormal lymphatic endothelial cell (LEC) signaling are promising therapeutic targets for this condition. Sphingosine-1-phosphate (S1P) mediates a key signaling pathway required for normal LEC function, and altered S1P signaling in LECs could lead to lymphatic disease and pathogenic T cell activation. Characterizing this biology is relevant for developing much-needed therapies.

METHODS

Human and mouse lymphedema was studied. Lymphedema was induced in mice by surgically ligating the tail lymphatics. Lymphedematous dermal tissue was assessed for S1P signaling. To verify the role of altered S1P signaling effects in lymphatic cells, LEC-specific S1pr1 -deficient ( S1pr1 LECKO ) mice were generated. Disease progression was quantified by tail-volumetric and -histopathological measurements over time. LECs from mice and humans, with S1P signaling inhibition, were then co-cultured with CD4 T cells, followed by an analysis of CD4 T cell activation and pathway signaling. Finally, animals were treated with a monoclonal antibody specific to P-selectin to assess its efficacy in reducing lymphedema and T cell activation.

RESULTS

Human and experimental lymphedema tissues exhibited decreased LEC S1P signaling through S1PR1. LEC S1pr1 loss-of-function exacerbated lymphatic vascular insufficiency, tail swelling, and increased CD4 T cell infiltration in mouse lymphedema. LECs, isolated from S1pr1 LECKO mice and co-cultured with CD4 T cells, resulted in augmented lymphocyte differentiation. Inhibiting S1PR1 signaling in human dermal LECs (HDLECs) promoted T helper type 1 and 2 (Th1 and Th2) cell differentiation through direct cell contact with lymphocytes. HDLECs with dampened S1P signaling exhibited enhanced P-selectin, an important cell adhesion molecule expressed on activated vascular cells. In vitro , P-selectin blockade reduced the activation and differentiation of Th cells co-cultured with sh S1PR1 -treated HDLECs. P-selectin-directed antibody treatment improved tail swelling and reduced Th1/Th2 immune responses in mouse lymphedema.

CONCLUSION

This study suggests that reduction of the LEC S1P signaling aggravates lymphedema by enhancing LEC adhesion and amplifying pathogenic CD4 T cell responses. P-selectin inhibitors are suggested as a possible treatment for this pervasive condition.

Clinical Perspective

What is New?: Lymphatic-specific S1pr1 deletion exacerbates lymphatic vessel malfunction and Th1/Th2 immune responses during lymphedema pathogenesis. S1pr1 -deficient LECs directly induce Th1/Th2 cell differentiation and decrease anti-inflammatory Treg populations. Peripheral dermal LECs affect CD4 T cell immune responses through direct cell contact.LEC P-selectin, regulated by S1PR1 signaling, affects CD4 T cell activation and differentiation.P-selectin blockade improves lymphedema tail swelling and decreases Th1/Th2 population in the diseased skin.What Are the Clinical Implications?: S1P/S1PR1 signaling in LECs regulates inflammation in lymphedema tissue.S1PR1 expression levels on LECs may be a useful biomarker for assessing predisposition to lymphatic disease, such as at-risk women undergoing mastectomyP-selectin Inhibitors may be effective for certain forms of lymphedema.

The Future of Lymphedema: Potential Therapeutic Targets for Treatment

Purpose of Review

This review aims to summarize the current knowledge regarding the pharmacological interventions studied in both experimental and clinical trials for secondary lymphedema.

Recent Findings

Lymphedema is a progressive disease that results in tissue swelling, pain, and functional disability. The most common cause of secondary lymphedema in developed countries is an iatrogenic injury to the lymphatic system during cancer treatment. Despite its high incidence and severe sequelae, lymphedema is usually treated with palliative options such as compression and physical therapy. However, recent studies on the pathophysiology of lymphedema have explored pharmacological treatments in preclinical and early phase clinical trials.

Summary

Many potential treatment options for lymphedema have been explored throughout the past two decades including systemic agents and topical approaches to decrease the potential toxicity of systemic treatment. Treatment strategies including lymphangiogenic factors, anti-inflammatory agents, and anti-fibrotic therapies may be used independently or in conjunction with surgical approaches.

Trametinib-Induced Epidermal Thinning Accelerates a Mouse Model of Junctional Epidermolysis Bullosa

Junctional epidermolysis bullosa (JEB) patients experience skin and epithelial fragility due to a pathological deficiency in genes associated with epidermal adhesion. Disease severity ranges from post-natal lethality to localized skin involvement with persistent blistering followed by granulation tissue formation and atrophic scarring. We evaluated the potential of utilizing Trametinib, an MEK inhibitor previously shown to target fibrosis, with and without the documented EB-anti-fibrotic Losartan for reducing disease severity in a mouse model of JEB; Lamc2^jeb mice. We found that Trametinib treatment accelerated disease onset and decreased epidermal thickness, which was in large part ameliorated by Losartan treatment. Interestingly, a range of disease severity was observed in Trametinib-treated animals that tracked with epidermal thickness; those animals grouped with higher disease severity had thinner epidermis. To examine if the difference in severity was related to inflammation, we conducted immunohistochemistry for the immune cell markers CD3, CD4, CD8, and CD45 as well as the fibrotic marker αSMA in mouse ears. We used a positive pixel algorithm to analyze the resulting images and demonstrated that Trametinib caused a non-significant reduction in CD4 expression that inversely tracked with increased fibrotic severity. With the addition of Losartan to Trametinib, CD4 expression was similar to control. Together, these data suggest that Trametinib causes a reduction in both epidermal proliferation and immune cell infiltration/proliferation, with concurrent acceleration of skin fragility, while Losartan counteracts Trametinib's adverse effects in a mouse model of JEB.

Lymphatic-draining nanoparticles deliver Bay K8644 payload to lymphatic vessels and enhance their pumping function

Dysfunction of collecting lymphatic vessel pumping is associated with an array of pathologies. S-(-)-Bay K8644 (BayK), a small-molecule agonist of L-type calcium channels, improves vessel contractility ex vivo but has been left unexplored in vivo because of poor lymphatic access and risk of deleterious off-target effects. When formulated within lymph-draining nanoparticles (NPs), BayK acutely improved lymphatic vessel function, effects not seen from treatment with BayK in its free form. By preventing rapid drug access to the circulation, NP formulation also reduced BayK's dose-limiting side effects. When applied to a mouse model of lymphedema, treatment with BayK formulated in lymph-draining NPs, but not free BayK, improved pumping pressure generated by intact lymphatic vessels and tissue remodeling associated with the pathology. This work reveals the utility of a lymph-targeting NP platform to pharmacologically enhance lymphatic pumping in vivo and highlights a promising approach to treating lymphatic dysfunction.

The Vicious Circle of Stasis, Inflammation, and Fibrosis in Lymphedema

SUMMARY

Lymphedema is a progressive disease of the lymphatic system arising from impaired lymphatic drainage, accumulation of interstitial fluid, and fibroadipose deposition. Secondary lymphedema resulting from cancer treatment is the most common form of the disease in developed countries, affecting 15% to 40% of patients with breast cancer after lymph node dissection. Despite recent advances in microsurgery, outcomes remain variable and, in some cases, inadequate. Thus, development of novel treatment strategies is an important goal. Research over the past decade suggests that lymphatic injury initiates a chronic inflammatory response that regulates the pathophysiology of lymphedema. T-cell inflammation plays a key role in this response. In this review, the authors highlight the cellular and molecular mechanisms of lymphedema and discuss promising preclinical therapies.

Keratinocytes coordinate inflammatory responses and regulate development of secondary lymphedema

Epidermal changes are histological hallmarks of secondary lymphedema, but it is unknown if keratinocytes contribute to its pathophysiology. Using clinical lymphedema specimens and mouse models, we show that keratinocytes play a primary role in lymphedema development by producing T-helper 2 (Th2) -inducing cytokines. Specifically, we find that keratinocyte proliferation and expression of protease-activated receptor 2 (PAR2) are early responses following lymphatic injury and regulate the expression of Th2-inducing cytokines, migration of Langerhans cells, and skin infiltration of Th2-differentiated T cells. Furthermore, inhibition of PAR2 activation with a small molecule inhibitor or the proliferation inhibitor teriflunomide (TF) prevents activation of keratinocytes stimulated with lymphedema fluid. Finally, topical TF is highly effective for decreasing swelling, fibrosis, and inflammation in a preclinical mouse model. Our findings suggest that lymphedema is a chronic inflammatory skin disease, and topically targeting keratinocyte activation may be a clinically effective therapy for this condition.

Acquired lymphedema: Molecular contributors and future directions for developing intervention strategies

Lymphedema is a debilitating chronic disease that mostly develops as an adverse reaction to cancer treatment modalities such as chemotherapy, surgery, and radiotherapy. Lymphedema also appears to be a deteriorating consequence of roundworm infections, as best represented by filariasis. According to its origin, lymphedema is classified as primary lymphedema and acquired lymphedema. The latter is an acquired condition that, hitherto, received a considerably low attention owing to the less number of fatal cases been reported. Notably, despite the low mortality rate in lymphedema, it has been widely reported to reduce the disease-free survival and thus the quality of life of affected patients. Hence, in this review, we focused on acquired lymphedema and orchestration of molecular interplays associated with either stimulation or inhibition of lymphedema development that were, in vast majority, clearly depicted in animal models with their specific and distinct technical approaches. We also discussed some recent progress made in phytochemical-based anti-lymphedema intervention strategies and the specific mechanisms underlying their anti-lymphedema properties. This review is crucial to understand not only the comprehensive aspects of the disease but also the future directions of the intervention strategies that can address the quality of life of affected patients rather than alleviating apparent symptoms only.

Doxycycline for the treatment of breast cancer-related lymphedema

Purpose: Secondary lymphedema is a common complication of cancer treatment for which no effective drug treatments yet exist. Level I clinical data suggests that doxycycline is effective for treating filariasis-induced lymphedema, in which it decreases tissue edema and skin abnormalities; however, this treatment has not been tested for cancer-related lymphedema. Over the past year, we used doxycycline in an off-label manner in patients with breast cancer-related secondary lymphedema. The purpose of this report was to retrospectively analyze the efficacy of this treatment. Methods: Patients who presented to our lymphedema clinic between January 2021 and January 2022 were evaluated, and barring allergies or contraindications to doxycycline treatment, were counseled on the off-label use of this treatment. Patients who wished to proceed were treated with doxycycline (200 mg given orally once daily) for 6 weeks. After IRB approval of this study, lymphedema outcomes were retrospectively reviewed. Results: Seventeen patients with a mean follow-up of 17.0 ± 13.2 weeks were identified in our retrospective review. Although doxycycline treatment had no significant effect on relative limb volume change or L-Dex scores, we found a significant improvement in patient-reported quality of life. Analysis of patient responses to the Lymphedema Life Impact Scale showed a significant improvement in the total impairment score due to improvements in the physical and psychological well-being subscales (p = 0.03, p = 0.03, p = 0.04, respectively). Conclusion: This small, retrospective study did not show significant improvements in limb volume or L-Dex scores in patients with breast cancer-related lymphedema treated with doxycycline. However, our patients reported improvements in quality-of-life measures using a validated lymphedema patient-reported outcome instrument. Our results suggest that doxycycline may be of use in patients with breast cancer-related lymphedema; however, larger and more rigorous studies are needed.

Enhancement of Lymphangiogenesis by Human Mesenchymal Stem Cell Sheet

Preparation of human mesenchymal stem cell (hMSC) suspension for lymphedema treatment relies on conventional enzymatic digestion methods, which severely disrupts cell-cell and cell-extracellular matrix (ECM) connections, and drastically impairs cell retention and engraftment after transplantation. The objective of the present study is to evaluate the ability of hMSC-secreted ECM to augment lymphangiogenesis by using an in vitro coculturing model of hMSC sheets with lymphatic endothelial cells (LECs) and an in vivo mouse tail lymphedema model. Results demonstrate that the hMSC-secreted ECM augments the formation of lymphatic capillary-like structure by a factor of 1.2-3.6 relative to the hMSC control group, by serving as a prolymphangiogenic growth factor reservoir and facilitating cell regenerative activities. hMSC-derived ECM enhances MMP-2 mediated matrix remodeling, increases the synthesis of collagen IV and laminin, and promotes lymphatic microvessel-like structure formation. The injection of rat MSC sheet fragments into a mouse tail lymphedema model confirms the benefits of the hMSC-derived ECM by stimulating lymphangiogenesis and wound closure.

Current Advancements in Animal Models of Postsurgical Lymphedema: A Systematic Review

Significance: Secondary lymphedema is a debilitating disease caused by lymphatic dysfunction characterized by chronic swelling, dysregulated inflammation, disfigurement, and compromised wound healing. Since there is no effective cure, animal model systems that support basic science research into the mechanisms of secondary lymphedema are critical to advancing the field. Recent Advances: Over the last decade, lymphatic research has led to the improvement of existing animal lymphedema models and the establishment of new models. Although an ideal model does not exist, it is important to consider the strengths and limitations of currently available options. In a systematic review adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we present recent developments in the field of animal lymphedema models and provide a concise comparison of ease, cost, reliability, and clinical translatability. Critical Issues: The incidence of secondary lymphedema is increasing, and there is no gold standard of treatment or cure for secondary lymphedema. Future Directions: As we iterate and create animal models that more closely characterize human lymphedema, we can achieve a deeper understanding of the pathophysiology and potentially develop effective therapeutics for patients.

Emerging Anti-Inflammatory Pharmacotherapy and Cell-Based Therapy for Lymphedema

Secondary lymphedema is a common complication of lymph node dissection or radiation therapy for cancer treatment. Conventional therapies such as compression sleeve therapy, complete decongestive physiotherapy, and surgical therapies decrease edema; however, they are not curative because they cannot modulate the pathophysiology of lymphedema. Recent advances reveal that the activation and accumulation of CD4+ T cells are key in the development of lymphedema. Based on this pathophysiology, the efficacy of pharmacotherapy (tacrolimus, anti-IL-4/IL-13 antibody, or fingolimod) and cell-based therapy for lymphedema has been demonstrated in animal models and pilot studies. In addition, mesenchymal stem/stromal cells (MSCs) have attracted attention as candidates for cell-based lymphedema therapy because they improve symptoms and decrease edema volume in the long term with no serious adverse effects in pilot studies. Furthermore, MSC transplantation promotes functional lymphatic regeneration and improves the microenvironment in animal models. In this review, we focus on inflammatory cells involved in the pathogenesis of lymphedema and discuss the efficacy and challenges of pharmacotherapy and cell-based therapies for lymphedema.

Current Understanding of Pathological Mechanisms of Lymphedema

Significance: Lymphedema is a common disease that affects hundreds of millions of people worldwide with significant financial and social burdens. Despite increasing prevalence and associated morbidities, the mainstay treatment of lymphedema is largely palliative without an effective cure due to incomplete understanding of the disease. Recent Advances: Recent studies have described key histological and pathological processes that contribute to the progression of lymphedema, including lymphatic stasis, inflammation, adipose tissue deposition, and fibrosis. This review aims to highlight cellular and molecular mechanisms involved in each of these pathological processes. Critical Issues: Despite recent advances in the understanding of the pathophysiology of lymphedema, cellular and molecular mechanisms underlying the disease remains elusive due to its complex nature. Future Directions: Additional research is needed to gain a better insight into the cellular and molecular mechanisms underlying the pathophysiology of lymphedema, which will guide the development of therapeutic strategies that target specific pathology of the disease.

Blocking prostanoid receptors switches on multiple immune responses and cascades of inflammatory signaling against larval stages in snail fever

Schistosomiasis, also known as snail fever or bilharziasis, is a worm infection caused by trematode called schistosomes that affects humans and animals worldwide. Schistosomiasis endemically exists in developing countries. Inflammatory responses elicited in the early phase of infection represent the rate limiting step for parasite migration and pathogenesis and could be a valuable target for therapeutic interventions. Prostaglandin E2 (PGE2) and interleukin (IL)-10 were found to be differentially affected in case of immune-modulation studies and cytokine analysis of hosts infected with either normal or radiation-attenuated parasite (RA) which switches off the development of an effective immune response against the migrating parasite in the early phase of schistosomiasis. Normal parasites induce predominantly a T helper 2 (Th2)-type cytokine response (IL-4 and IL-5) which is essential for parasite survival; here, we discuss in detail the downstream effects and cascades of inflammatory signaling of PGE2 and IL10 induced by normal parasites and the effect of blocking PGE2 receptors. We suggest that by selectively constraining the production of PGE2 during vaccination or therapy of susceptible persons or infected patients of schistosomiasis, this would boost IL-12 and reduce IL-10 production leading to a polarization toward the anti-worm Thl cytokine synthesis (IL-2 and Interferon (IFN)-γ).

Structural and Functional Changes in Aged Skin Lymphatic Vessels

Lymphatic structure and function play a critical role in fluid transport, antigen delivery, and immune homeostasis. A dysfunctional lymphatic system is associated with chronic low-grade inflammation of peripheral tissues, poor immune responses, and recurrent infections, which are also hallmarks of aging pathology. Previous studies have shown that aging impairs lymphatic structure and function in a variety of organ systems, including the intestines and central nervous system. However, previous studies are mostly limited to qualitative analysis of lymphatic structural changes and quantification of intestinal collecting vessel contractile function. It is not clear whether decreased lymphatic function contributes to pathological conditions related to aging, nor how it affects the skin immune microenvironment. Further, the effects of aging on skin initial and collecting lymphatic vessels, dendritic cell (DC) migration, cutaneous lymphatic pumping, and VEGFR-3 signaling in lymphatic endothelial cells (LECs) have not been quantitatively analyzed. Here, using fluorescent immunohistochemistry and flow cytometry, we confirm that aging decreases skin initial and collecting lymphatic vessel density. Indocyanine green (ICG) lymphangiography and DC migration assays confirm that aging decreases both fluid pumping and cell migration via lymphatic vessels. At the cellular level, aging causes decreased VEGFR-3 signaling, leading to increased LEC apoptosis and senescence. Finally, we determined that aging causes decreased lymphatic production of chemokines and alters LEC expression of junctional and adhesion molecules. This in turn leads to increased peri-lymphatic inflammation and nitrosative stress that might contribute to aging pathology in a feed-forward manner. Taken together, our study, in addition to quantitatively corroborating previous findings, suggests diverse mechanisms that contribute to lymphatic dysfunction in aging that in turn exacerbate the pathology of aging in a feed-forward manner.

Cardiac lymphatics: state of the art

PURPOSE OF REVIEW

The beneficial role of cardiac lymphatics in health and disease has begun to be recognized, with both preclinical and clinical evidence demonstrating that lymphangiogenesis is activated in cardiovascular diseases. This review aims to summarize our current understanding of the regulation and impact of cardiac lymphatic remodeling during development and in adult life, highlighting emerging concepts regarding distinguishing traits of cardiac lymphatic endothelial cells (LEC).

RECENT FINDINGS

Genetic lineage-tracing and clonal analyses have revealed that a proportion of cardiac LECs originate from nonvenous sources. Further, these sources may vary between different regions of the heart, and could translate to differences in LEC sensitivity to molecular regulators. Several therapeutic approaches have been applied to investigate how lymphatics contribute to resolution of myocardial edema and inflammation in cardiovascular diseases. From these studies have emerged novel insights, notably concerning the cross-talk between lymphatics and cardiac interstitial cells, especially immune cells.

SUMMARY

Recent years have witnessed a significant expansion in our knowledge of the molecular characteristics and regulation of cardiac lymphatics. The current body of work is in support of critical contributions of cardiac lymphatics to maintain both fluid and immune homeostasis in the heart.

Pathogenic Tconvs promote inflammatory macrophage polarization through GM‐CSF and exacerbate abdominal aortic aneurysm formation

Abdominal aortic aneurysms (AAAs) elicit massive inflammatory leukocyte recruitment to the aorta. CD4⁺ T cells, which include regulatory T cells (Tregs) and conventional T cells (Tconvs), are involved in the progression of AAA. Tregs have been reported to limit AAA formation. However, the function and phenotype of the Tconvs found in AAAs remain poorly understood. We characterized aortic Tconvs by bulk RNA sequencing and discovered that Tconvs in aortic aneurysm highly expressed Cxcr6 and Csf2. Herein, we determined that the CXCR6/CXCL16 signaling axis controlled the recruitment of Tconvs to aortic aneurysms. Deficiency of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), encoded by Csf2, markedly inhibited AAA formation and led to a decrease of inflammatory monocytes, due to a reduction of CCL2 expression. Conversely, the exogenous administration of GM‐CSF exacerbated inflammatory monocyte infiltration by upregulating CCL2 expression, resulting in worsened AAA formation. Mechanistically, GM‐CSF upregulated the expression of interferon regulatory factor 5 to promote M1‐like macrophage differentiation in aortic aneurysms. Importantly, we also demonstrated that the GM‐CSF produced by Tconvs enhanced the polarization of M1‐like macrophages and exacerbated AAA formation. Our findings revealed that GM‐CSF, which was predominantly derived from Tconvs in aortic aneurysms, played a pathogenic role in the progression of AAAs and may represent a potential target for AAA treatment.

Heparin-induced thrombocytopenia and thrombosis in primary lymphedema patients who underwent vascularized lymph node transplantations

BACKGROUND

Heparin-induced thrombocytopenia and thrombosis (HITT) may result in microsurgical flap failure. This study investigated the outcomes of HITT in primary lymphedema patients who underwent vascularized lymph node transplantations (VLNT).

METHODS

Between 2012 and 2019, primary lymphedema patients who underwent VLNTs were retrospectively included. The 4Ts score was used to categorize patients into HITT (scores of 5-7) and non-HITT (score < 5) groups. Outcome evaluations included the re-exploration rate, success rate, circumferential differences, cellulitis episodes, and Lymphedema Specific Quality of Life Questionnaire (LYMQoL) scores.

RESULTS

Twenty-six and 15 patients with 31 and 16 VLNTs were included in the HITT and non-HITT groups, respectively. The HITT group had significantly greater first, second and third re-exploration rates of 38.7% (12/31), 25.7% (8/31), and 6.5% (2/31) than the non-HITT group (6.3%, 0%, and 0%, all p < 0.01), respectively. The platelet counts significantly decreased by 21.0% in the HITT group compared with the non-HITT group (14%) on postoperative Day one (p < 0.01) with a cutoff value of 17% and AUC = 0.88.

CONCLUSIONS

HITT may cause a high re-exploration rate of VLNTs in primary lymphedema patients. The 17% reduction in platelets on postoperative day one was an early sign for detecting HITT.

Pharmacological Treatment of Secondary Lymphedema

Lymphedema is a chronic disease that results in swelling and decreased function due to abnormal lymphatic fluid clearance and chronic inflammation. In Western countries, lymphedema most commonly develops following an iatrogenic injury to the lymphatic system during cancer treatment. It is estimated that as many as 10 million patients suffer from lymphedema in the United States alone. Current treatments for lymphedema are palliative in nature, relying on compression garments and physical therapy to decrease interstitial fluid accumulation in the affected extremity. However, recent discoveries have increased the hopes of therapeutic interventions that may promote lymphatic regeneration and function. The purpose of this review is to summarize current experimental pharmacological strategies in the treatment of lymphedema.

Lymphatic Collecting Vessels in Health and Disease: A Review of Histopathological Modifications in Lymphedema

Secondary lymphedema of the extremities affects millions of people in the world as a common side effect of oncological treatments with heavy impact on every day life of patients and on the health care system. One of the surgical techniques for lymphedema treatment is the creation of a local connection between lymphatic vessels and veins, facilitating drainage of lymphatic fluid into the circulatory system. Successful results, however, rely on using a functional vessel for the anastomosis, and vessel function, in turn, depends on its structure. The structure of lymphatic collecting vessels changes with the progression of lymphedema. They appear initially dilated by excess interstitial fluid entered at capillary level. The number of lymphatic smooth muscle cells in their media then increases in the attempt to overcome the impaired drainage. When lymphatic muscle cells hyperplasia occurs at the expenses of the lumen, vessel patency decreases hampering lymph flow. Finally, collagen fiber accumulation leads to complete occlusion of the lumen rendering the vessel unfit to conduct lymph. Different types of vessels may coexist in the same patient but usually the distal part of the limb contains less affected vessels that are more likely to perform efficient lymphatic–venular anastomosis. Here we review the structure of the lymphatic collecting vessels in health and in lymphedema, focusing on the histopathological changes of the lymphatic vessel wall based on the observations on segments of the vessels used for lymphatic–venular anastomoses.

Pilot Study of Anti-Th2 Immunotherapy for the Treatment of Breast Cancer-Related Upper Extremity Lymphedema

Recent studies suggest that Th2 cells play a key role in the pathology of secondary lymphedema by elaborating cytokines such as IL4 and IL13. The aim of this study was to test the efficacy of QBX258, a monoclonal IL4/IL13 neutralizing antibody, in women with breast cancer-related lymphedema (BCRL). We enrolled nine women with unilateral stage I/II BCRL and treated them once monthly with intravenous infusions of QBX258 for 4 months. We measured limb volumes, bioimpedance, and skin tonometry, and analyzed the quality of life (QOL) using a validated lymphedema questionnaire (Upper Limb Lymphedema 27, ULL-27) before treatment, immediately after treatment, and 4 months following treatment withdrawal. We also obtained 5 mm skin biopsies from the normal and lymphedematous limbs before and after treatment. Treatment was well-tolerated; however, one patient with a history of cellulitis developed cellulitis during the trial and was excluded from further analysis. We found no differences in limb volumes or bioimpedance measurements after drug treatment. However, QBX258 treatment improved skin stiffness (p < 0.001) and improved QOL measurements (Physical p < 0.05, Social p = 0.01). These improvements returned to baseline after treatment withdrawal. Histologically, treatment decreased epidermal thickness, the number of proliferating keratinocytes, type III collagen deposition, infiltration of mast cells, and the expression of Th2-inducing cytokines in the lymphedematous skin. Our limited study suggests that immunotherapy against Th2 cytokines may improve skin changes and QOL of women with BCRL. This treatment appears to be less effective for decreasing limb volumes; however, additional studies are needed.

Biochemical and mechanical signals in the lymphatic vasculature

Lymphatic vasculature is an integral part of the cardiovascular system where it maintains interstitial fluid balance. Additionally, lymphatic vasculature regulates lipid assimilation and inflammatory response. Lymphatic vasculature is composed of lymphatic capillaries, collecting lymphatic vessels and valves that function in synergy to absorb and transport fluid against gravitational and pressure gradients. Defects in lymphatic vessels or valves leads to fluid accumulation in tissues (lymphedema), chylous ascites, chylothorax, metabolic disorders and inflammation. The past three decades of research has identified numerous molecules that are necessary for the stepwise development of lymphatic vasculature. However, approaches to treat lymphatic disorders are still limited to massages and compression bandages. Hence, better understanding of the mechanisms that regulate lymphatic vascular development and function is urgently needed to develop efficient therapies. Recent research has linked mechanical signals such as shear stress and matrix stiffness with biochemical pathways that regulate lymphatic vessel growth, patterning and maturation and valve formation. The goal of this review article is to highlight these innovative developments and speculate on unanswered questions.

Multiplexed gene expression analysis of HLA class II-associated podoconiosis implicates chronic immune activation in its pathogenesis

Background

Podoconiosis is a tropical lymphoedema of the leg resulting from barefoot exposure to irritant volcanic soils. Approximately 4 million people are affected, mainly in African highland regions. The pathogenesis of this neglected tropical disease is still largely unknown, although HLA class II (HLAII) polymorphisms are associated with the disease.

Methods

NanoString technology was used to assess expression of 579 immune-related genes in formalin-fixed and paraffin-embedded lymph node archival samples from podoconiosis patients and unaffected controls.

Results

Forty-eight genes were upregulated and 21 downregulated in podoconiosis samples compared with controls. Gene ontology analysis showed differentially expressed genes to be closely related to major histocompatibility complex protein, cytokine and TNF receptor binding genes. Pathway enrichment analysis revealed involvement of lymphocyte activation, adaptive immunity, cytokine signalling, antigen processing and the IL-12 pathways.

Conclusions

This exploratory study reports a multiplex gene expression analysis in podoconiosis and shows upregulation of pro-inflammatory transcripts compatible with the notion of local, chronic immune activation in this HLAII-associated disease. Implicated pathways will inform future research into podoconiosis immunopathogenesis.

Afferent Lymphatic Transport and Peripheral Tissue Immunity

Lymphatic vessels provide an anatomical framework for immune surveillance and adaptive immune responses. Although appreciated as the route for Ag and dendritic cell transport, peripheral lymphatic vessels are often not considered active players in immune surveillance. Lymphatic vessels, however, integrate contextual cues that directly regulate transport, including changes in intrinsic pumping and capillary remodeling, and express a dynamic repertoire of inflammatory chemokines and adhesion molecules that facilitates leukocyte egress out of inflamed tissue. These mechanisms together contribute to the course of peripheral tissue immunity. In this review, we focus on context-dependent mechanisms that regulate fluid and cellular transport out of peripheral nonlymphoid tissues to provide a framework for understanding the effects of afferent lymphatic transport on immune surveillance, peripheral tissue inflammation, and adaptive immunity.

The Kinetics of Lymphatic Dysfunction and Leukocyte Expansion in the Draining Lymph Node during LTB4 Antagonism in a Mouse Model of Lymphedema

The mechanisms of lymphedema development are not well understood, but emerging evidence highlights the crucial role the immune system plays in driving its progression. It is well known that lymphatic function deteriorates as lymphedema progresses; however, the connection between this progressive loss of function and the immune-driven changes that characterize the disease has not been well established. In this study, we assess changes in leukocyte populations in lymph nodes within the lymphatic drainage basin of the tissue injury site (draining lymph nodes, dLNs) using a mouse tail model of lymphedema in which a pair of draining collecting vessels are left intact. We additionally quantify lymphatic pump function using established near infrared (NIR) lymphatic imaging methods and lymph-draining nanoparticles (NPs) synthesized and employed by our team for lymphatic tissue drug delivery applications to measure lymphatic transport to and resulting NP accumulation within dLNs associated with swelling following surgery. When applied to assess the effects of the anti-inflammatory drug bestatin, which has been previously shown to be a possible treatment for lymphedema, we find lymph-draining NP accumulation within dLNs and lymphatic function to increase as lymphedema progresses, but no significant effect on leukocyte populations in dLNs or tail swelling. These results suggest that ameliorating this loss of lymphatic function is not sufficient to reverse swelling in this surgically induced disease model that better recapitulates the extent of lymphatic injury seen in human lymphedema. It also suggests that loss of lymphatic function during lymphedema may be driven by immune-mediated mechanisms coordinated in dLNs. Our work indicates that addressing both lymphatic vessel dysfunction and immune cell expansion within dLNs may be required to prevent or reverse lymphedema when partial lymphatic function is sustained.

Ionic-Liquid-Based Safe Adjuvants

Adjuvants play a critical role in the design and development of novel vaccines. Despite extensive research, only a handful of vaccine adjuvants have been approved for human use. Currently used adjuvants are mostly composed of components that are non-native to the human body, such as aluminum salt, bacterial lipids, or foreign genomic material. Here, a new ionic-liquid-based adjuvant is explored, synthesized using two metabolites of the body, choline and lactic acid (ChoLa). ChoLa distributes the antigen efficiently upon injection, maintains antigen integrity, enhances immune infiltration at the injection site, and leads to a potent immune response against the antigen. Thus, it can serve as a promising safe adjuvant platform that can help to protect against pandemics and future infectious threats.

Lymphatic Valves and Lymph Flow in Cancer-Related Lymphedema

Lymphedema is a complex disease caused by the accumulation of fluid in the tissues resulting from a dysfunctional or damaged lymphatic vasculature. In developed countries, lymphedema most commonly occurs as a result of cancer treatment. Initially, impaired lymph flow causes edema, but over time this results in inflammation, fibrotic and fatty tissue deposition, limited mobility, and bacterial infections that can lead to sepsis. While chronically impaired lymph flow is generally believed to be the instigating factor, little is known about what pathophysiological changes occur in the lymphatic vessels to inhibit lymph flow. Lymphatic vessels not only regulate lymph flow through a variety of physiologic mechanisms, but also respond to lymph flow itself. One of the fascinating ways that lymphatic vessels respond to flow is by growing bicuspid valves that close to prevent the backward movement of lymph. However, lymphatic valves have not been investigated in cancer-related lymphedema patients, even though the mutations that cause congenital lymphedema regulate genes involved in valve development. Here, we review current knowledge of the regulation of lymphatic function and development by lymph flow, including newly identified genetic regulators of lymphatic valves, and provide evidence for lymphatic valve involvement in cancer-related lymphedema.

Evidence of stage progression in a novel, validated fluorescence-navigated and microsurgical-assisted secondary lymphedema rodent model

Secondary lymphedema (SL)is a frequent and devastating complication of modern oncological therapy and filarial infections. A lack of a reliable preclinical model to investigate the underlying mechanism of clinical stage progression has limited the development of new therapeutic strategies. Current first line treatment has shown to be merely symptomatic and relies on lifetime use of compression garments and decongestive physiotherapy. In this study, we present the development of a secondary lymphedema model in 35 rats using pre- and intraoperative fluorescence-guided mapping of the lymphatics and microsurgical induction. In contrast to the few models reported so far, we decided to avoid the use of radiation for lymphedema induction. It turned out, that the model is nearly free of complications and capable of generating a statistically significant limb volume increase by water displacement measurements, sustained for at least 48 days. A translational, accurate lymphatic dysfunction was visualized by a novel VIS-NIR X-ray ICG-Clearance-Capacity imaging technology. For the first-time SL stage progression was validated by characteristic histological alterations, such as subdermal mast cell infiltration, adipose tissue deposition, and fibrosis by increased skin collagen content. Immunofluorescence confocal microscopy analysis suggested that stage progression is related to the presence of a characteristic α SMA+/HSP-47+/vimentin+ fibroblast subpopulation phenotype. These findings demonstrate that the in-vivo model is a reliable and clinically relevant SL model for the development of further secondary lymphedema therapeutic strategies and the analysis of the veiled molecular mechanisms of lymphatic dysfunction.

S1PR1 regulates the quiescence of lymphatic vessels by inhibiting laminar shear stress-dependent VEGF-C signaling

During the growth of lymphatic vessels (lymphangiogenesis), lymphatic endothelial cells (LECs) at the growing front sprout by forming filopodia. Those tip cells are not exposed to circulating lymph, as they are not lumenized. In contrast, LECs that trail the growing front are exposed to shear stress, become quiescent, and remodel into stable vessels. The mechanisms that coordinate the opposed activities of lymphatic sprouting and maturation remain poorly understood. Here, we show that the canonical tip cell marker Delta-like 4 (DLL4) promotes sprouting lymphangiogenesis by enhancing VEGF-C/VEGF receptor 3 (VEGFR3) signaling. However, in lumenized lymphatic vessels, laminar shear stress (LSS) inhibits the expression of DLL4, as well as additional tip cell markers. Paradoxically, LSS also upregulates VEGF-C/VEGFR3 signaling in LECs, but sphingosine 1-phosphate receptor 1 (S1PR1) activity antagonizes LSS-mediated VEGF-C signaling to promote lymphatic vascular quiescence. Correspondingly, S1pr1 loss in LECs induced lymphatic vascular hypersprouting and hyperbranching, which could be rescued by reducing Vegfr3 gene dosage in vivo. In addition, S1PR1 regulates lymphatic vessel maturation by inhibiting RhoA activity to promote membrane localization of the tight junction molecule claudin-5. Our findings suggest a potentially new paradigm in which LSS induces quiescence and promotes the survival of LECs by downregulating DLL4 and enhancing VEGF-C signaling, respectively. S1PR1 dampens LSS/VEGF-C signaling, thereby preventing sprouting from quiescent lymphatic vessels. These results also highlight the distinct roles that S1PR1 and DLL4 play in LECs when compared with their known roles in the blood vasculature.

Histopathologic Features of Lymphedema: A Molecular Review

An estimated 5 million people in the United States are affected by secondary lymphedema, with most cases attributed to malignancies or malignancy-related treatments. The pathogenesis of secondary lymphedema has historically been attributed to lymphatic injury or dysfunction; however, recent studies illustrate the complexity of lymphedema as a disease process in which many of its clinical features such as inflammation, fibrosis, adipogenesis, and recurrent infections contribute to on-going lymphatic dysfunction in a vicious cycle. Investigations into the molecular underpinning of these features further our understanding of the pathophysiology of this disease and suggests new therapeutics.

Mouse tail models of secondary lymphedema: fibrosis gradually worsens and is irreversible

Although the mouse tail model of secondary lymphedema has been widely used in research, our knowledge regarding some of the characteristic changes in this model is lacking. Therefore, in the current study, we aimed to identify pathologic changes after surgery. Tail lymphedema was created in C57BL/6J mice by disconnecting both superficial and deep lymphatic vessels. The surgery resulted in chronic edema formation with the proliferation of subcutaneous adipose tissue, deposition of fibrotic tissue, and gradual increase in CD4⁺ T lymphocyte infiltration. Furthermore, dramatic expansion and an increased number of lymphatic vessels were observed postoperatively. Lymphatic reflux was established at least 8 weeks after surgery, as evidenced by staining of the scar from the surgical excision. In addition, tissue fibrosis was irreversible, although CD4⁺ T cell infiltration, tail swelling, and subcutaneous adipose hyperplasia were alleviated over time. We also show that necrosis could be effectively avoided by paying attention to several details in the modeling process. As animal models play a key role in exploring the pathophysiology of disease, our findings provide strong support for the study of lymphedema. The irreversibility of fibrosis suggests the importance of treating lymphedema by preventing fibrosis development.

An intravital window to image the colon in real time

Intravital microscopy is a powerful technique to observe dynamic processes with single-cell resolution in live animals. No intravital window has been developed for imaging the colon due to its anatomic location and motility, although the colon is a key organ where the majority of microbiota reside and common diseases such as inflammatory bowel disease, functional gastrointestinal disorders, and colon cancer occur. Here we describe an intravital murine colonic window with a stabilizing ferromagnetic scaffold for chronic imaging, minimizing motion artifacts while maximizing long-term survival by preventing colonic obstruction. Using this setup, we image fluorescently-labeled stem cells, bacteria, and immune cells in live animal colons. Furthermore, we image nerve activity via calcium imaging in real time to demonstrate that electrical sacral nerve stimulation can activate colonic enteric neurons. The simple implantable apparatus enables visualization of live processes in the colon, which will open the window to a broad range of studies.

Performing intravital imaging of the colon in mouse models is challenging due to the colon’s anatomic location and motility. Here, the authors develop a murine colonic window for intravital chronic imaging that maximises long-term animal survival and minimises motion artefacts.

Development and Themes of Diagnostic and Treatment Procedures for Secondary Leg Lymphedema in Patients with Gynecologic Cancers

Patients with leg lymphedema sometimes suffer under constraint feeling leg heaviness and pain, requiring lifelong treatment and psychosocial support after surgeries or radiation therapies for gynecologic cancers. We herein review the current issues (a review of the relevant literature) associated with recently developed diagnostic procedures and treatments for secondary leg lymphedema, and discuss how to better manage leg lymphedema. Among the currently available diagnostic tools, indocyanine green lymphography (ICG-LG) can detect dermal lymph backflow in asymptomatic legs at stage 0. Therefore, ICG-LG is considered the most sensitive and useful tool. At symptomatic stage ≥1, ultrasonography, magnetic resonance imaging-lymphography/computed tomography-lymphography (MRI-LG/CT-LG) and lymphosintiography are also useful. For the treatment of lymphedema, complex decongestive physiotherapy (CDP) including manual lymphatic drainage (MLD), compression therapy, exercise and skin care, is generally performed. In recent years, CDP has often required effective multi-layer lymph edema bandaging (MLLB) or advanced pneumatic compression devices (APCDs). If CDP is not effective, microsurgical procedures can be performed. At stage 1–2, when lymphaticovenous anastomosis (LVA) is performed, lymphaticovenous side-to-side anastomosis (LVSEA) is principally recommended. At stage 2–3, vascularized lymph node transfer (VLNT) is useful. These ingenious procedures can help maintain the patient’s quality of life (QOL) but unfortunately cannot cure lymphedema. The most important concern is the prevention of secondary lymphedema, which is achieved through approaches such as skin care, weight control, gentle limb exercises, avoiding sun and heat, and elevation of the affected leg.

Fibrosis and secondary lymphedema: chicken or egg?

Secondary lymphedema is a common complication of cancer treatment resulting in progressive fibroadipose tissue deposition, increased risk of infections, and, in rare cases, secondary malignancies. Until recently, the pathophysiology of secondary lymphedema was thought to be related to impaired collateral lymphatic formation after surgical injury. However, more recent studies have shown that chronic inflammation-induced fibrosis plays a key role in the pathophysiology of this disease. In this review, we will discuss the evidence supporting this hypothesis and summarize recent publications demonstrating that lymphatic injury activates chronic immune responses that promote fibrosis and lymphatic leakiness, decrease collecting lymphatic pumping, and impair collateral lymphatic formation. We will review how chronic mixed T-helper cell inflammatory reactions regulate this process and how this response may be used to design novel therapies for lymphedema.

T helper 2 differentiation is necessary for development of lymphedema

T cells infiltrating lymphedematous tissues have a mixed T helper 1 (Th1) and Th2 differentiation profile. Treatment with neutralizing antibodies targeting cytokines that promote Th2 differentiation (interleukin 4 [IL-4] and IL-13) decreases the severity of lymphedema in preclinical models, suggesting that Th2 cells play a key role in the pathology of this disease. However, these previous studies do not address the contribution of Th1 cells and it remains unknown if IL-4 and IL-3 blockade acts primarily on T cells or decreases the pathological changes of lymphedema by other mechanisms. Therefore, this study sought to analyze the effect of lymphatic injury in transgenic mice with mutations that cause defects in Th1 and Th2 cell generation (T-bet knockout or T-betKO and STAT6 knockout or STAT6KO mice, respectively). Using both the mouse tail and popliteal lymph node dissection models of lymphedema, we show that Th2-deficient (STAT6KO) mice are protected from developing lymphedema, have decreased fibrosis, increased collateral vessel formation, and preserved collecting lymphatic vessel pumping function. In contrast, mice with defective Th1 cell generation (T-betKO) develop disease with the same severity as wild-type controls. Taken together, our results suggest that Th2 differentiation is necessary for development of lymphedema following lymphatic injury and that Th1 differentiation does not significantly contribute to the pathology of the disease. Such findings are important as immunotherapy directed at Th2 cells has been found to be effective in well-studied Th2-mediated diseases such as asthma and atopic dermatitis and may therefore be similarly useful for lymphedema management.