Growth factor therapy and lymph node graft for lymphedema

Review of treatment strategies after lymphadenectomy: From molecular therapeutics to immediate microsurgical lymphatic reconstruction

OBJECTIVE

Lymphedema is a common complication of cancer treatment, such as lymphadenectomy and radiation therapy. It is a debilitating condition with pathologic tissue changes that hinder effective curative treatment and jeopardize patients' quality of life. Various attempts to prevent the development of lymphedema have been made, with improvements in the incidence of the pathology. However, it is still prevalent among survivors of cancer. In this paper, we review both molecular therapeutics and immediate surgical lymphatic reconstruction as treatment strategies after lymphadenectomy. Specifically, we discuss pro-lymphangiogenic molecules that have proved efficient in animal models of lymphedema and clinical trials, and review currently available microsurgical techniques of immediate lymphatic reconstruction.

METHODS

A literature search was conducted in PubMed, Embase, Cochrane Library, and Google Scholar through May 2022. Searches were done separately for molecular therapeutics and microsurgical techniques for immediate lymphatic reconstruction. Search terms used for (1) non-surgical methods include 'lymphangiogenesis,' 'lymphedema,' 'growth factor,' and 'gene therapy.' Search terms used for (2) surgical methods include 'lymphedema,' 'lymph node excision,' 'lymphatic vessels,' 'primary prevention,' and 'microsurgery.'

RESULTS

Various pro-lymphangiogenic factors with therapeutic potential include VEGF-C, VEGF-D, HGF, bFGF, PDGF, IGF, Retinoic acid, Ang-1, S1P, TLR4, and IL-8. Microsurgical lymphatic reconstruction for prevention of secondary lymphedema includes lymphovenous anastomosis, vascularized lymph node flap transfer, and lymph-interpositional flap transfer, with promising clinical outcomes.

CONCLUSIONS

With growing knowledge of the lymphangiogenic pathway and lymphedema pathology and advances in microsurgical techniques to restore lymphatic channels, molecular and surgical approaches may represent a promising method for primary prevention of lymphedema.

Therapeutic Lymphangiogenesis Is a Promising Strategy for Secondary Lymphedema

Secondary lymphedema is caused by lymphatic insufficiency (lymphatic drainage failure) following lymph node dissection during the surgical treatment or radiation therapy of breast or pelvic cancer. The clinical problems associated with lymphedema are reduced quality of life in terms of appearance and function, as well as the development of skin ulcers, recurrent pain, and infection. Currently, countermeasures against lymphedema are mainly physical therapy such as lymphatic massage, elastic stockings, and skin care, and there is no effective and fundamental treatment with a highly recommended grade. Therefore, there is a need for the development of a fundamental novel treatment for intractable lymphedema. Therapeutic lymphangiogenesis, which has been attracting attention in recent years, is a treatment concept that reconstructs the fragmented lymphatic network to recover lymphatic vessel function and is revolutionary to be a fundamental cure. This review focuses on the translational research of therapeutic lymphangiogenesis for lymphedema and outlines the current status and prospects in the development of therapeutic applications.

Utilization of Vascular Endothelial Growth Factor-C156S in Therapeutic Lymphangiogenesis: A Systematic Review

Background: Vascular endothelial growth factor (VEGF) C156S is an engineering variant of VEGF-C that has the potential to promote lymphangiogenesis, activating on VEGF receptor (VEGFR) 3, without promoting angiogenesis (i.e., not acting on VEGFR-2). We conducted a systematic review of publications assessing the use of this growth factor in lymphedema treatment. We hypothesized that VEGF-C156S specificity for VEGFR-3 was an important differential for the lymphangiogenesis promoted by it. Methods and Results: We conducted a comprehensive systematic review of the published literature on PubMed/Medline, Embase, and Cochrane Clinical Answers. Eligibility criteria included articles reporting data on the use of VEGF-C156S in lymphedema treatment. We excluded articles that investigated physiology action of VEGF-C156S and articles that focused on other therapies. From 304 potential articles found in the literature, four studies fulfilled the study eligibility criteria. To date, all studies about this growth factor have been experimental. The effect of VEGF-C156 on lymph node transfer was investigated in half of the experiments. Interestingly, delivery of VEGF-C156S was mostly performed through viral gene transfer, but injection (subcutaneously or intravenously) of it as a protein (liposomal or nonliposomal) was also investigated by one author to assess drug bioavailability. Conclusions: Although authors reported promotion of lymphangiogenesis, VEGF-C156S was correlated with lymphatic hyperplasia or nonstatistically significant lymphangiogenesis compared with controls. Scientific evidence about the use of VEGF-C156S in lymphedema treatment is still limited. However, authors have shown that its lymphangiogenic effect is inferior to VEGF-C.

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.

In Vitro, In Vivo, and In Silico Models of Lymphangiogenesis in Solid Malignancies

Lymphangiogenesis (LA) is the formation of new lymphatic vessels by lymphatic endothelial cells (LECs) sprouting from pre-existing lymphatic vessels. It is increasingly recognized as being involved in many diseases, such as in cancer and secondary lymphedema, which most often results from cancer treatments. For some cancers, excessive LA is associated with cancer progression and metastatic dissemination to the lymph nodes (LNs) through lymphatic vessels. The study of LA through in vitro, in vivo, and, more recently, in silico models is of paramount importance in providing novel insights and identifying the key molecular actors in the biological dysregulation of this process under pathological conditions. In this review, the different biological (in vitro and in vivo) models of LA, especially in a cancer context, are explained and discussed, highlighting their principal modeled features as well as their advantages and drawbacks. Imaging techniques of the lymphatics, complementary or even essential to in vivo models, are also clarified and allow the establishment of the link with computational approaches. In silico models are introduced, theoretically described, and illustrated with examples specific to the lymphatic system and the LA. Together, these models constitute a toolbox allowing the LA research to be brought to the next level.

Use of Vascular Endothelial Growth Factor-D As a Targeted Therapy in Lymphedema Treatment: A Comprehensive Literature Review

Background: Lymphangiogenic growth factors, such as vascular endothelial growth factor (VEGF)-D, are subjects of interest in studies of targeted therapies in lymphedema treatment. Methods and Results: We conducted a systematic review assessing the use of VEGF-D as a targeted therapy in lymphedema treatment. We hypothesized that VEGF-D was a promising therapy to induce lymphangiogenesis. Our search yielded 90 studies in the literature, but only 4 articles fulfilled our study eligibility criteria, and they were all experimental studies using viral gene transfer. The majority of the studies were conducted on small animals (mice) and investigated the effects of VEGF-D on lymph node transfer. All authors agreed about VEGF-D's lymphangiogenic potential, but they noticed that VEGF-C induced a superior lymphangiogenesis, and one study noticed that VEGF-D induced seroma. Conclusions: The publications assessing the use of VEGF-D as a targeted therapy in lymphedema treatment were able to demonstrate its lymphangiogenic potential. Nonetheless, further studies are still necessary to investigate VEGF-D's efficacy and safety in lymphedema treatment on patients.

Lymphatic Tissue Engineering: A Further Step for Successful Lymphedema Treatment

BACKGROUND

 Secondary lymphedema, caused by oncologic surgery, radiation, and chemotherapy, is one of the most relevant, nononcological complications affecting cancer survivors. Severe functional deficits can result in impairing quality of life and a societal burden related to increased treatment costs. Often, conservative treatments are not sufficient to alleviate lymphedema or to prevent stage progression of the disease, as they do not address the underlying etiology that is the disruption of lymphatic pathways. In recent years, lymphatic surgery approaches were revolutionized by advances in microsurgical technique. Currently, lymphedema can effectively be treated by procedures such as lymphovenous anastomosis (LVA) and lymph node transfer (LNT). However, not all patients have suitable lymphatic vessels, and lymph node harvesting is associated with risks. In addition, some data have revealed nonresponders to the microsurgical techniques.

METHODS

 A literature review was performed to evaluate the value of lymphatic tissue engineering for plastic surgeons and to give an overview of the achievements, challenges, and goals of the field.

RESULTS

 While certain challenges exist, including cell harvesting, nutrient supply, biocompatibility, and hydrostatic properties, it is possible and desirable to engineer lymph nodes and lymphatic vessels. The path toward clinical translation is considered more complex for LNTs secondary to the complex microarchitecture and pending final mechanistic clarification, while LVA is more straight forward.

CONCLUSION

 Lymphatic tissue engineering has the potential to be the next step for microsurgical treatment of secondary lymphedema. Current and future researches are necessary to optimize this clinical paradigm shift for improved surgical treatment of lymphedema.

Short-term molecular and cellular effects of ischemia/reperfusion on vascularized lymph node flaps in rats

Vascularized lymph node (VLN) transfer is an emerging strategy to re-establish lymphatic drainage in chronic lymphedema. However, the biological processes underlying lymph node integration remain elusive. This study introduces an experimental approach facilitating the analysis of short-term molecular and cellular effects of ischemia/reperfusion on VLN flaps. Lymph node flaps were dissected pedicled on the lateral thoracic vessels in 44 Lewis rats. VLN flaps were exposed to 45 or 120 minutes ischemia by in situ clamping of the vascular pedicle with subsequent reperfusion for 24 hours. Flaps not exposed to ischemia/reperfusion served as controls. Lymph nodes and the perinodal adipose tissue were separately analyzed by Western blot for the expression of lymphangiogenic and angiogenic growth factors. Moreover, morphology, microvessel density, proliferation, apoptosis and immune cell infiltration of VLN flaps were further assessed by histology and immunohistochemistry. Ischemia for 120 minutes was associated with a markedly reduced cellularity of lymph nodes but not of the perinodal adipose tissue. In line with this, ischemic lymph nodes exhibited a significantly lower microvessel density and an increased expression of VEGF-D and VEGF-A. However, VEGF-C expression was not upregulated. In contrast, analyses of the perinodal adipose tissue revealed a more subtle decrease of microvessel density, while only the expression of VEGF-D was increased. Moreover, after 120 minutes ischemia, lymph nodes but not the perinodal adipose tissue exhibited significantly higher numbers of proliferating and apoptotic cells as well as infiltrated macrophages and neutrophilic granulocytes compared with non-ischemic flaps. Taken together, lymph nodes of VLN flaps are highly susceptible to ischemia/reperfusion injury. In contrast, the perinodal adipose tissue is less prone to ischemia/reperfusion injury.

Anatomical Theories of the Pathophysiology of Cancer-Related Lymphoedema

Lymphoedema is a well-known concern for cancer survivors. A crucial issue in lymphoedema is that we cannot predict who will be affected, and onset can occur many years after initial cancer treatment. The variability of time between cancer treatment and lymphoedema onset is an unexplained mystery. Retrospective cohort studies have investigated the risk factors for lymphoedema development, with extensive surgery and the combination of radiation and surgery identified as common high-risk factors. However, these studies could not predict lymphoedema risk in each individual patient in the early stages, nor could they explain the timing of onset. The study of anatomy is one promising tool to help shed light on the pathophysiology of lymphoedema. While the lymphatic system is the area least investigated in the field of anatomical science, some studies have described anatomical changes in the lymphatic system after lymph node dissection. Clinical imaging studies in lymphangiography, lymphoscintigraphy and indocyanine green (ICG) fluorescent lymphography have reported post-operative anatomical changes in the lymphatic system, including dermal backflow, lymphangiogenesis and creation of alternative pathways via the deep and torso lymphatics, demonstrating that such dynamic anatomical changes contribute to the maintenance of lymphatic drainage pathways. This article presents a descriptive review of the anatomical and imaging studies of the lymphatic system in the normal and post-operative conditions and attempts to answer the questions of why some people develop lymphoedema after cancer and some do not, and what causes the variability in lymphoedema onset timing.

Use of Gene Transfer Vectors in Lymphedema Treatment: A Systematic Review

Different delivery mechanisms have been proposed in the literature for targeted therapies in the treatment of lymphedema. They vary from simple and direct injection to sophisticated induction of gene expression in a targeted tissue. We conducted a systematic review of publications assessing the use of viral vectors for gene transfer in lymphedema treatment. We hypothesized that viral vectors are an effective way to deliver targeted therapy in lymphedema treatment. We conducted a comprehensive systematic review of the published literature on targeted therapies associated with lymphedema surgery using the PubMed database. Eligibility criteria excluded papers that reported use of viral vectors for other medical conditions. Abstracts, presentations, reviews, meta-analyses, and non-English language articles were also excluded. From 21 potential articles found in the literature, fourteen fulfilled study eligibility criteria. Positive outcomes in terms of lymphangiogenesis were seen. The viral vectors used included adenovirus and recombinant adeno-associated virus. Most of the genes expressed were growth factors, but expression of dominant-negative transforming growth factor-β1 receptor-II or Prox1 was also proposed. Five studies targeted genetic expression on lymphedema tissue, five on transplanted lymph nodes, two on skeletal muscle, and one on adipose-derived stem cells. Publications assessing use of viral vectors for gene transfer in lymphedema treatment demonstrated that it is an effective mechanism of delivering targeted therapies. However, to date, all studies were experimental and further studies must be performed before translating these therapies into clinical practice.

Targeted Therapies in Surgical Treatment of Lymphedema: A Systematic Review

Although physiologic surgeries for lymphedema (i.e., lymphovenous bypass, vascularized lymph node transplantation) are becoming well established, unpredictable outcomes have still been reported in some studies. Therefore, authors have investigated ways to improve these surgery outcomes. The goal of our study was to conduct a comprehensive systematic review of targeted therapy administration in the surgical treatment of lymphedema. We conducted a comprehensive systematic review of the published literature on targeted therapies associated with lymphedema surgery using the PubMed database. Eligibility criteria excluded papers that reported surgical treatment of lymphedema without the use of targeted therapies and also papers describing targeted therapies in nonsurgical treatment of lymphedema. Abstracts, presentations, reviews, and meta-analyses were also excluded. Extracted data included the year of study, country, lymphedema model, surgical technique, targeted therapy agent, therapy delivery, findings, and outcomes. From 823 potential papers found in the literature, 10 studies fulfilled the eligibility criteria. All papers were experimental, and most of them on small animal model (7/10). Different targeted therapies were proposed, but all of them were associated with lymph node transplantation. The most common targeted therapy proposed mechanism was growth factor delivery (8/10). However, one paper used adipose-stem cell, and one paper proposed the use of sterile inflammation. The pooled publications assessing targeted therapy administration in the surgical treatment of lymphedema demonstrate encouraging data for positive outcomes. To date, all studies were experimental and related to lymph node transfer.

Lymphatic and blood systems: Identical or fraternal twins?

Blood and lymphatic systems work in close collaboration to ensure their respective physiological functions. The lymphatic vessel network is being extensively studied, but has been overlooked as compared to the blood vasculature mainly due to the problematic discrimination of lymphatic vessels from the blood ones. This issue has been fortunately resolved in the past decade leading to the emergence of a huge amount of data in lymphatic biology revealing many shared features with the blood vasculature. However, this likeliness between the two vascular systems may lead to a simplistic view of lymphatics and a direct transcription of what is known for the blood system to the lymphatic one, thereby neglecting the lymphatic specificities. In this context, this review aims to clarify the main differences between the two vascular systems focusing on recently discovered lymphatic features.

Modulation of Immunity by Lymphatic Dysfunction in Lymphedema

The debilitating condition known as secondary lymphedema frequently occurs after lymphadenectomy and/or radiotherapy for the treatment of cancer. These therapies can damage lymphatic vessels leading to edema, fibrosis, inflammation and dysregulated adipogenesis, which result in profound swelling of an affected limb. Importantly, lymphedema patients often exhibit impaired immune function which predisposes them to a variety of infections. It is known that lymphadenectomy can compromise the acquisition of adaptive immune responses and antibody production; however the cellular mechanisms involved are poorly understood. Here we discuss recent progress in revealing the cellular and molecular mechanisms underlying poor immune function in secondary lymphedema, which has indicated a key role for regulatory T cells in immunosuppression in this disease. Furthermore, the interaction of CD4⁺ T cells and macrophages has been shown to play a role in driving proliferation of lymphatic endothelial cells and aberrant lymphangiogenesis, which contribute to interstitial fluid accumulation in lymphedema. These new insights into the interplay between lymphatic vessels and the immune system in lymphedema will likely provide opportunities for novel therapeutic approaches designed to improve clinical outcomes in this problematic disease.

Evans Blue Dye: A Revisit of Its Applications in Biomedicine

Evans blue (EB) dye has owned a long history as a biological dye and diagnostic agent since its first staining application by Herbert McLean Evans in 1914. Due to its high water solubility and slow excretion, as well as its tight binding to serum albumin, EB has been widely used in biomedicine, including its use in estimating blood volume and vascular permeability, detecting lymph nodes, and localizing the tumor lesions. Recently, a series of EB derivatives have been labeled with PET isotopes and can be used as theranostics with a broad potential due to their improved half-life in the blood and reduced release. Some of EB derivatives have even been used in translational applications in clinics. In addition, a novel necrosis-avid feature of EB has recently been reported in some preclinical animal studies. Given all these interesting and important advances in EB study, a comprehensive revisiting of EB has been made in its biomedical applications in the review.

Biology of Vascular Endothelial Growth Factor C in the Morphogenesis of Lymphatic Vessels

Because virtually all tissues contain blood vessels, the importance of hemevascularization has been long recognized in regenerative medicine and tissue engineering. However, the lymphatic vasculature has only recently become a subject of interest. Central to the task of growing a lymphatic network are lymphatic endothelial cells (LECs), which constitute the innermost layer of all lymphatic vessels. The central molecule that directs proliferation and migration of LECs during embryogenesis is vascular endothelial growth factor C (VEGF-C). VEGF-C is therefore an important ingredient for LEC culture and attempts to (re)generate lymphatic vessels and networks. During its biosynthesis VEGF-C undergoes a stepwise proteolytic processing, during which its properties and affinities for its interaction partners change. Many of these fundamental aspects of VEGF-C biosynthesis have only recently been uncovered. So far, most—if not all—applications of VEGF-C do not discriminate between different forms of VEGF-C. However, for lymphatic regeneration and engineering purposes, it appears mandatory to understand these differences, since they relate, e.g., to important aspects such as biodistribution and receptor activation potential. In this review, we discuss the molecular biology of VEGF-C as it relates to the growth of LECs and lymphatic vessels. However, the properties of VEGF-C are similarly relevant for the cardiovascular system, since both old and recent data show that VEGF-C can have a profound effect on the blood vasculature.

New and Emerging Treatments for Lymphedema

Although nonoperative and operative treatments for lymphedema (LE) are well established, these procedures typically provide only partial relief from limb swelling, functional impairment, and the risk of cellulitis. The lack of a cure for LE, however, is due to an incomplete understanding of the underlying pathophysiological mechanisms, and current research efforts are focusing on elucidating these processes to provide new, targeted therapies for this prevalent disease for which there is no cure. This article reviews the current literature regarding the pathophysiological mechanisms that underlie LE, as well as new and emerging therapies for the condition.

Targeting lymphatic function as a novel therapeutic intervention for rheumatoid arthritis

Although clinical outcomes for patients with rheumatoid arthritis (RA) have greatly improved with the use of biologic and conventional DMARDs, approximately 40% of patients do not achieve primary clinical outcomes in randomized trials, and only a small proportion achieve lasting remission. Over the past decade, studies in murine models point to the critical role of the lymphatic system in the pathogenesis and therapy of inflammatory-erosive arthritis, presumably by the removal of catabolic factors, cytokines and inflammatory cells from the inflamed synovium. Murine studies demonstrate that lymphatic drainage increases at the onset of inflammatory-erosive arthritis but, as inflammation progresses to a more chronic phase, lymphatic clearance declines and both structural and cellular changes are observed in the draining lymph node. Specifically, chronic damage to the lymphatic vessel from persistent inflammation results in loss of lymphatic vessel contraction followed by lymph node collapse, reduced lymphatic drainage, and ultimately severe synovitis and joint erosion. Notably, clinical pilot studies in patients with RA report lymph node changes following treatment, and thus draining lymphatic vessels and nodes could represent a potential biomarker of arthritis activity and response to therapy. Most importantly, targeting lymphatics represents an innovative strategy for therapeutic intervention for RA.

Donor-Site Lymphedema Following Lymph Node Transfer for Breast Cancer-Related Lymphedema: A Systematic Review of the Literature

Abstracts Background: Among current surgical options used for treating breast cancer-related lymphedema (BCRL), autologous lymph node transfer (ALNT) is shown to provide favorable results. However, postoperative donor-site lymphedema (DSL), following the lymphatic flap harvesting from the groin area, has already been reported. Our aim is to summarize the recent literature for evidence of DSL following an ALNT for BCRL.

METHODS AND RESULTS

A PubMed bibliographic search was performed for published studies evaluating donor-site complications following LNT in BCRL patients. We recorded demographic data of the patients, the type of flap used, the follow-up, the donor-site morbidity, and the diagnostic tests performed pre- and postoperatively. Statistical analysis was conducted to document any correlation between the incidence of DSL and the abovementioned recorded parameters. According to our results, 11 studies met the inclusion criteria. From a total of 189 patients, three cases with DSL of the lower limb were reported (1.6%). No statistically significant correlations were found.

CONCLUSION

ALNT has become increasingly popular and is considered an effective surgical option for treating BCRL of the upper limb. Although the incidence of postoperative DSL is low, insufficient data on patients' demographics, surgical details, and postoperative assessment do not allow extracting significant correlations. Meticulous technique of lymph node harvesting should be seriously considered to further minimize this infrequent but debilitating complication.

Effectiveness of acupuncture for breast cancer related lymphedema: protocol for a single-blind, sham-controlled, randomized, multicenter trial

BACKGROUND

Although various treatments for breast cancer related lymphedema exist, there is still a need for a more effective and convenient approach. Pilot studies and our clinical observations suggested that acupuncture may be a potential option. This study aims to verify the effectiveness of acupuncture on BCRL and evaluate its safety using a rigorously designed trial.

METHODS/DESIGN

Women who are clinically diagnosed as unilateral BCRL, with a 10% to 40% increase in volume compared to the unaffected arm, will be recruited. Following baseline assessment, participants will be randomized to either the real acupuncture group or sham-acupuncture group at a ratio of 1:1, and given a standard real acupuncture or sham-acupuncture treatment accordingly on both arms followed by the same usual care of decongestive therapy. Volume measurements of both arms will be performed for every participant after each treatment. Data collected at baseline and the last session will be used to calculate the primary outcome and secondary outcomes. Other data will be exploited for interim analyses and trial monitoring. The primary outcome is the absolute reduced limb volume ratio. Secondary outcomes are incidence of adverse events and change in quality of life. A t test or non-parameter test will be used to compare the difference between two groups, and assess the overall effectiveness of acupuncture using the SPSS software (version 12).

DISCUSSION

This study will help expand our knowledge about the effectiveness of acupuncture on BCRL, and how acupuncture might be used in the management of this condition. Acupuncture may be a promising complement or alternative to conventional lymphedema treatment methods, if its effectiveness is confirmed.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02803736 (Registered on October 31, 2016).

Animal Models of Secondary Lymphedema: New Approaches in the Search for Therapeutic Options

Secondary lymphedema is still a worldwide problem. Symptomatic approaches to lymphedema therapy have been mainly used, with complete decongestive therapy as the cornerstone. Due to a lack of regenerative therapy, researchers have established various animal models to obtain insights into pathomechanisms and to reveal the best therapeutic option. Since the first reproducible and reliable animal model of lymphedema was reported in dogs, the technique of circumferential excision of lymphatic tissue has been translated mainly to rodents to induce secondary lymphedema. In these models, various promising pharmacological and surgical approaches have been investigated to improve secondary lymphedema therapy. Imaging modalities are crucial to detect the extent of lymphatic dysfunction and decide the best therapy. The gold standard of lymphoscintigraphy is currently limited by poor spatial resolution and lack of quantification. Animal models could help to bridge a gap in improving morphological correlation and quantifying lymphatic functionality. This review summarizes the animal models used in lymphatic research and focuses on new therapeutic options and requirements for imaging modalities to visualize the lymphatic system.

Differential Receptor Binding and Regulatory Mechanisms for the Lymphangiogenic Growth Factors Vascular Endothelial Growth Factor (VEGF)-C and -D

VEGF-C and VEGF-D are secreted glycoproteins that induce angiogenesis and lymphangiogenesis in cancer, thereby promoting tumor growth and spread. They exhibit structural homology and activate VEGFR-2 and VEGFR-3, receptors on endothelial cells that signal for growth of blood vessels and lymphatics. VEGF-C and VEGF-D were thought to exhibit similar bioactivities, yet recent studies indicated distinct signaling mechanisms (e.g. tumor-derived VEGF-C promoted expression of the prostaglandin biosynthetic enzyme COX-2 in lymphatics, a response thought to facilitate metastasis via the lymphatic vasculature, whereas VEGF-D did not). Here we explore the basis of the distinct bioactivities of VEGF-D using a neutralizing antibody, peptide mapping, and mutagenesis to demonstrate that the N-terminal α-helix of mature VEGF-D (Phe⁹³–Arg¹⁰⁸) is critical for binding VEGFR-2 and VEGFR-3. Importantly, the N-terminal part of this α-helix, from Phe⁹³ to Thr⁹⁸, is required for binding VEGFR-3 but not VEGFR-2. Surprisingly, the corresponding part of the α-helix in mature VEGF-C did not influence binding to either VEGFR-2 or VEGFR-3, indicating distinct determinants of receptor binding by these growth factors. A variant of mature VEGF-D harboring a mutation in the N-terminal α-helix, D103A, exhibited enhanced potency for activating VEGFR-3, was able to promote increased COX-2 mRNA levels in lymphatic endothelial cells, and had enhanced capacity to induce lymphatic sprouting in vivo. This mutant may be useful for developing protein-based therapeutics to drive lymphangiogenesis in clinical settings, such as lymphedema. Our studies shed light on the VEGF-D structure/function relationship and provide a basis for understanding functional differences compared with VEGF-C.

Outcomes of vascularized versus non-vascularized lymph node transplant in animal models for lymphedema. Review of the literature

Lymph node transfer has been performed to treat lymphedema for several years. The goal of this procedure is to provide a bridge between the lymphatic system distal and proximal to the lymph node dissection. There is a lack of consensus about the necessity of an additional vascular anastomosis for the transplanted lymph nodes. A systematic literature search in Cochrane Library database CENTRAL, MEDLINE, and EMBASE of animal studies using lymph node transplantation with and without additional vascularization was performed in March 2016. The strategy used for the search was: (("Models, Animal"[Mesh]) AND (("Lymphedema"[Mesh]) OR "Lymph Nodes"[Mesh]) OR "Lymph Node Excision"[Mesh])) AND ((vascularized lymph node transfer) OR ((non-vascularized lymph node transfer) OR lymph node graft)). The primary outcomes were: survival of transplanted lymph node and lymphatic vessel regeneration. Sixteen studies were included. Vascularization and the use of growth factors were significantly associated with lymph node survival. Lymphatic vessels regeneration was independent from vascularization. According to the results of the current study, additional vascular anastomosis might improve the transplanted lymph node survival. Further studies in both experimental and clinical setting are needed in order to support it. J. Surg. Oncol. 2017;115:32-36. © 2016 Wiley Periodicals, Inc.

Local inhibition of elastase reduces EMILIN1 cleavage reactivating lymphatic vessel function in a mouse lymphoedema model

Lymphatic vasculature critically depends on the connections of lymphatic endothelial cells with the extracellular matrix (ECM), which are mediated by anchoring filaments (AFs). The ECM protein EMILIN1 is a component of AFs and is involved in the regulation of lymphatic vessel functions: accordingly, Emilin1^−/− mice display lymphatic vascular morphological alterations, leading to functional defects such as mild lymphoedema, lymph leakage and compromised lymph drainage. In the present study, using a mouse post-surgical tail lymphoedema model, we show that the acute phase of acquired lymphoedema correlates with EMILIN1 degradation due to neutrophil elastase (NE) released by infiltrating neutrophils. As a consequence, the intercellular junctions of lymphatic endothelial cells are weakened and drainage to regional lymph nodes is severely affected. The local administration of sivelestat, a specific NE inhibitor, prevents EMILIN1 degradation and reduces lymphoedema, restoring a normal lymphatic functionality. The finding that, in human secondary lymphoedema samples, we also detected cleaved EMILIN1 with the typical bands of an NE-dependent pattern of fragmentation establishes a rationale for a powerful strategy that targets NE inhibition. In conclusion, the attempts to block EMILIN1 degradation locally represent the basis for a novel ‘ECM’ pharmacological approach to assessing new lymphoedema treatments.

The Lymphatic System in Disease Processes and Cancer Progression

Advances in our understanding of the structure and function of the lymphatic system have made it possible to identify its role in a variety of disease processes. Because it is involved not only in fluid homeostasis but also in immune cell trafficking, the lymphatic system can mediate and ultimately alter immune responses. Our rapidly increasing knowledge of the molecular control of the lymphatic system will inevitably lead to new and effective therapies for patients with lymphatic dysfunction. In this review, we discuss the molecular and physiological control of lymphatic vessel function and explore how the lymphatic system contributes to many disease processes, including cancer and lymphedema.