Potential therapeutic strategies for lymphatic metastasis

Physiologically, the lymphatic system regulates fluid volume in the interstitium and provides a conduit for immune cells to travel to lymph nodes, but pathologically, the lymphatic system serves as a primary escape route for cancer cells. Lymphatic capillaries have a thin discontinuous basement membrane, lack pericyte coverage and often contain endothelial cell gaps that can be invaded by immune cells (or tumor cells). In addition, tumor cells and stromal cells in the tumor microenvironment secrete factors that stimulate lymphangiogenesis, the growth of lymphatic endothelial cells and the sprouting of lymphatic capillaries. As a result, many tumors are surrounded by large, hyperplastic, peri-tumoral lymphatic vessels and less frequently are invaded by intra-tumoral lymphatic vessels. Carcinoma cells commonly metastasize through these lymphatic vessels to regional lymph nodes. The presence of metastatic cells in the sentinel lymph node is a prognostic indicator for many types of cancer, and the degree of dissemination determines the therapeutic course of action. Lymphangiogenesis is currently at the frontier of metastasis research. Recent strides in this field have uncovered numerous signaling pathways specific for lymphatic endothelial cells and vascular endothelial cells. This review will provide an overview of tumor lymphangiogenesis and current strategies aimed at inhibiting lymphatic metastasis. Novel therapeutic approaches that target the tumor cells as well as the vascular and lymphatic endothelial compartments are discussed.     

Expression of vascular endothelial growth factor-C and the relationship between lymphangiogenesis and lymphatic metastasis in colorectal cancer

AIM: To investigate the expression of vascular endothelial growth factor-C (VEGF-C) and the relationship between VEGF-C and lymphangiogenesis, lymph node metastasis in colorectal cancer. METHODS: Fifty six cases of colorectal cancer were selected randomly. Expression of VEGF-C was detected by immunohistochemistry, and lymphatic vessels were stained by enzyme histochemical method. RESULTS: VEGF-C expression was found in 66.7% (37/56) patients. In VEGF-C positive and negative patients, the lymphatic vessel density was 25.16+/-7.52 and 17.14+/-7.22, respectively (P<0.05). The rate of lymph node metastasis in VEGF-C positive patients (81.1%) was significantly higher than that in the negative group (42.1%). CONCLUSION: VEGF-C expression may induce lymphangiogenesis in colorectal cancer, as a result, tumor cells can entry the lymphatic vessels easily. VEGF-C may serve as a useful prognotic factor in colorectal carcinoma.     

Three-dimensional changes in lymphatic architecture around VX2 tongue cancer--dynamics of growth of cancer

Many questions remain regarding the mechanism of cervical lymph node metastasis via lymphatic vessels. We report here the three-dimensional dynamics of the lymphatic architecture around tumor during growth of implanted VX2 tongue cancer. The tongue and the deep cervical lymph nodes of rabbits were observed at 3, 7 and 10 days after transplantation of VX2 cancer cells (n = 5 in each group). Lymph node metastasis was confirmed histopathologically. Morphological changes of the collecting lymphatic vessels and lymphatic capillaries were observed, and the number and diameter of these lymphatic vessels were measured within 500 microns around the tumor using the combined method of 5'-nucleotidase (5'-Nase) staining and three-dimensional reconstruction imaging. The VX2 cells were uniformly detected in cervical lymph nodes of each rabbit of the 10-day group. The number of lymphatic capillaries and the diameters of collecting lymphatic vessels around the tumor in the 7- and 10-day groups were greater than in the 3-day group. These capillaries arose by sprouting from preexisting lymphatic vessels and showed a tree-like branching pattern. We conclude that the dynamics of the lymphatic architecture around the tumor, especially the increase in number of capillaries on preexisting lymphatic vessels outside the tumor margin, may be associated with lymph node metastasis.     

VEGF-C-induced lymphangiogenesis in sentinel lymph nodes promotes tumor metastasis to distant sites

The mechanisms by which tumors metastasize to sentinel and distant lymph nodes, and beyond, are poorly understood. We developed transgenic mice that overexpress vascular endothelial growth factor-C (VEGF-C) and green fluorescent protein specifically in the skin and studied the effects of chemically-induced skin carcinogenesis in this model. We found that in contrast to VEGF-A, VEGF-C does not increase the growth of primary tumors, but instead induces expansion of lymphatic networks within sentinel lymph nodes, even before the onset of metastasis. Once the metastatic cells arrived at the sentinel lymph nodes, the extent of lymphangiogenesis at these sites increased. Of importance, in mice with metastasis-containing sentinel lymph nodes, tumors that expressed VEGF-C were more likely to metastasize to additional organs, such as distal lymph nodes and lungs. No metastases were observed in distant organs in the absence of lymph node metastases. These findings indicate an important role of VEGF-C-induced lymph node lymphangiogenesis in the promotion of cancer metastasis beyond the sentinel lymph nodes. VEGF-C is therefore a good target to slow or even prevent the onset of metastasis.     

Podoplanin expression in advanced-stage gastric carcinoma and prognostic value of lymphatic microvessel density

In gastric cancer, lymph node metastasis is a major prognostic factor. Tumor lymphangiogenesis promotes metastasis in experimental models, but in human tumors data about the presence and clinical significance of lymphatic vessels in the tumor area are controversial. We investigated 70 patients with advanced-stage gastric carcinoma and the pathological examination showed 40 cases with intestinal subtype and 30 cases with diffuse subtype. Forty three from 70 cases had regional lymph node metastasis. Additional slides were stained with an antibody against podoplanin, and lymphatic microvessel density (LMVD) was evaluated in the tumoral and peritumoral areas. Lymphatic vessels were identified in tumor area in all cases and LMVD was higher in the peritumoral than in the tumor area. Podoplanin-positive vessels in tumor area were usually small, with narrow lumen. A significant correlation was found between LMVD and stage of the tumor (p<0.002) and lymph node metastasis (p<0.031), but not with the pathological subtype and grade of the tumor. We found tumor cells in the lumen of lymphatic vessels in 11 cases, whereas tumor cells expressing podoplanin were found in 4 cases of less differentiated diffuse subtype gastric carcinoma. In conclusion, our results suggest that LMVD predicts tumor stage and lymph node metastasis, and podoplanin-positive tumor cells select a subgroup of tumors with high potential of invasion and metastasis. Key words: gastric cancer, podoplanin, lymphatic microvessel density (LMVD), lymphangiogenesis, prognosis.     

Lymphatic vessels: new targets for the treatment of inflammatory diseases

The lymphatic system plays an important role in the physiological control of the tissue fluid balance and in the initiation of immune responses. Recent studies have shown that lymphangiogenesis, the growth of new lymphatic vessels and/or the expansion of existing lymphatic vessels, is a characteristic feature of acute inflammatory reactions and of chronic inflammatory diseases. In these conditions, lymphatic vessel expansion occurs at the tissue level but also within the draining lymph nodes. Surprisingly, activation of lymphatic vessel function by delivery of vascular endothelial growth factor-C exerts anti-inflammatory effects in several models of cutaneous and joint inflammation. These effects are likely mediated by enhanced drainage of extravasated fluid and inflammatory cells, but also by lymphatic vessel-mediated modulation of immune responses. Although some of the underlying mechanisms are just beginning to be identified, lymphatic vessels have emerged as important targets for the development of new therapeutic strategies to treat inflammatory conditions. In this context, it is of great interest that some of the currently used anti-inflammatory drugs also potently activate lymphatic vessels.     

The angiostatic protein 16K human prolactin significantly prevents tumor-induced lymphangiogenesis by affecting lymphatic endothelial cells

The 16-kDa angiostatic N-terminal fragment of human prolactin (16K hPRL) has been reported to be a new potent anticancer compound. This protein has already proven its efficiency in several mouse tumor models in which it prevented tumor-induced angiogenesis and delayed tumor growth. In addition to angiogenesis, tumors also stimulate the formation of lymphatic vessels, which contribute to tumor cell dissemination and metastasis. However, the role of 16K hPRL in tumor-induced lymphangiogenesis has never been investigated. We establish in vitro that 16K hPRL induces apoptosis and inhibits proliferation, migration, and tube formation of human dermal lymphatic microvascular endothelial cells. In addition, in a B16F10 melanoma mouse model, we found a decreased number of lymphatic vessels in the primary tumor and in the sentinel lymph nodes after 16K hPRL treatment. This decrease is accompanied by a significant diminished expression of lymphangiogenic markers in primary tumors and sentinel lymph nodes as determined by quantitative RT-PCR. These results suggest, for the first time, that 16K hPRL is a lymphangiostatic as well as an angiostatic agent with antitumor properties.     

Molecular Mechanisms of Lymphangiogenesis

Although the process of vascular development has been well documented, little is understood about lymphatic vasculature formation, despite its importance in normal and pathologic conditions. The dysfunction or abnormal growth of lymphatic vessels is associated with lymphedema and cancer metastasis. The recent discovery of lymphangiogenic growth factors vascular endothelial growth factor (VEGF)-C and VEGF-D and of their receptor, VEGFR-3, on lymphatic endothelial cells has started to provide an understanding of the molecular mechanisms of lymphangiogenesis. In addition, other genes that participate in the specification of lymphatic endothelial cells and the modulation of lymphatic vascular development have been identified. The capacity to induce or inhibit lymphangiogenesis by the manipulation of such molecules offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders. This review describes the main players in lymphangiogenesis that have been identified so far and the attempts to shed some light on the mysteries surrounding this process.     

Blockade of vascular endothelial growth factor receptor-3 signaling inhibits fibroblast growth factor-2-induced lymphangiogenesis in mouse cornea

Vascular endothelial growth factor receptor-3 (VEGFR-3) is a major mediator of lymphangiogenesis. Recently, VEGFR-3 ligands, VEGF-C, and VEGF-D were reported to promote tumor lymphangiogenesis and lymphatic metastasis, and these processes were inhibited by blocking of the VEGFR-3-signaling pathway. Here, we have adapted the mouse corneal angiogenesis assay to study potential lymphangiogenic factors and inhibitors. Immunohistochemical analysis with lymphatic endothelial markers showed that VEGF-C induces lymphatic as well as blood vessel growth in the cornea. By contrast, VEGF induced angiogenesis but not lymphangiogenesis. Fibroblast growth factor-2 (FGF-2) stimulated both lymphangiogenesis and angiogenesis. FGF-2 up-regulated VEGF-C expression in vascular endothelial and perivascular cells. Furthermore, administration of blocking anti-VEGFR-3 antibodies inhibited the FGF-2-induced lymphangiogenesis. These findings show that VEGFR-3 can mediate lymphangiogenesis induced by other growth factors. Because increased expression of FGF-2 and VEGF-C has been associated with lymphatic metastasis, our results provide a potential strategy for the inhibition of lymphatic metastasis in cancer therapy.     

Interstitial flow as a guide for lymphangiogenesis

The lymphatic system is important in tissue fluid balance regulation, immune cell trafficking, edema, and cancer metastasis, yet very little is known about the sequence of events that initiate and coordinate lymphangiogenesis. Here, we characterize the process of lymphatic regeneration by uniquely correlating interstitial fluid flow and lymphatic endothelial cell migration with lymphatic function. A new model of skin regeneration using a collagen implant in a mouse tail has been developed, and it shows that (1) interstitial fluid channels form before lymphatic endothelial cell organization and (2) lymphatic cell migration, vascular endothelial growth factor-C expression, and lymphatic capillary network organization are initiated primarily in the direction of lymph flow. These data suggest that interstitial fluid channeling precedes and may even direct lymphangiogenesis (in contrast to blood angiogenesis, in which fluid flow proceeds only after the vessel develops); thus, a novel and robust model is introduced for correlating molecular events with functionality in lymphangiogenesis.     

Three-dimensional changes in lymphatic architecture around VX2 tongue cancer--dynamic changes after administration of antiangiogenic agent

We examined the three-dimensional changes of the lymphatic architecture in the rabbit VX2 tongue cancer model after administration of an antiangiogenic agent, TNP-470. TNP-470 at 30 mg/kg was administered via the auricular vein to the rabbit four times every other day from 3 days after transplantation of the tumor. The tongue and both sides of deep cervical lymph nodes of rabbit were observed at 10 days after transplantation. Lymph node metastasis was confirmed histopathologically. Morphological changes of collecting lymphatic vessels and lymphatic capillaries were observed, and the number and diameter of lymphatic vessels within 500 microm around the tumor were measured using the combined method with 5'-nucleotidase staining and three-dimensional reconstruction imaging. Tumor growth and lymph node metastasis were suppressed by administration of TNP-470. In the TNP-treatment group, the mean number of lymphatic capillaries was significantly fewer than in the control group. The mean diameter of collecting lymphatic vessels was significantly smaller than in the control group. In conclusion, our results suggest that cancer cell invasion into the lymphatics is probably decreased by inhibiting not only the growth of tumor but also new formation of lymphatic capillaries around the tumor by administration of TNP-470.     

PI3Kα activates integrin α4β1 to establish a metastatic niche in lymph nodes

Lymph nodes are initial sites of tumor metastasis, yet whether the lymph node microenvironment actively promotes tumor metastasis remains unknown. We show here that VEGF-C/PI3Kα-driven remodeling of lymph nodes promotes tumor metastasis by activating integrin α4β1 on lymph node lymphatic endothelium. Activated integrin α4β1 promotes expansion of the lymphatic endothelium in lymph nodes and serves as an adhesive ligand that captures vascular cell adhesion molecule 1 (VCAM-1)⁺ metastatic tumor cells, thereby promoting lymph node metastasis. Experimental induction of α4β1 expression in lymph nodes is sufficient to promote tumor cell adhesion to lymphatic endothelium and lymph node metastasis in vivo, whereas genetic or pharmacological blockade of integrin α4β1 or VCAM-1 inhibits it. As lymph node metastases accurately predict poor disease outcome, and integrin α4β1 is a biomarker of lymphatic endothelium in tumor-draining lymph nodes from animals and patients, these results indicate that targeting integrin α4β1 or VCAM to inhibit the interactions of tumor cells with the lymph node microenvironment may be an effective strategy to suppress tumor metastasis.Tumor metastases are a leading cause of cancer-related mortality and morbidity, and both tumor cell intrinsic and extrinsic factors promote metastasis (1–4). Metastatic spread occurs primarily via lymphatic and hematogenous routes, and the presence of metastases in tumor draining lymph nodes is an accurate predictor of poor outcome in many types of tumors (5, 6). To further refine therapy for cancer patients, studies that define the mechanisms that promote tumor metastasis to lymph nodes could lead to novel therapeutic regimens that could improve clinical outcomes for cancer patients.In primary tumors, lymphangiogenesis, the growth of new lymphatic vessels, is strongly correlated with lymph node and distant metastasis. Increased expression of the lymphangiogenic factors VEGF-A, VEGF-C, or VEGF-D in tumors correlates closely with increased incidence of regional lymph node metastases in both humans and animals (7–9). Accordingly, systemic administration of antagonists of the VEGF-C receptor, VEGF-R3, blocked primary tumor lymphangiogenesis and metastasis (10–12).VEGF-C stimulates the expression of integrin α4β1, which promotes lymphatic endothelial cell (LEC) adhesion and invasion, leading to tumor-associated lymphangiogenesis (13). VEGF-C–mediated signaling stimulates LEC invasion and survival during lymphangiogenesis, as VEGF-R3 activates PI3K/v-akt murine thymoma viral oncogene homolog 1 (Akt) and mammalian target of rapamycin (mTOR) signaling pathways (14, 15). VEGF–VEGF-R3 signaling thus plays an important role in tumor lymphangiogenesis.Lymphangiogenesis occurs not only with primary tumors but also in tumor draining lymph nodes, where it is associated with increased tumor metastasis (16–18). However, it is unclear whether lymph node lymphangiogenesis plays an independent role in promoting tumor metastasis. Here we present the unique findings that integrin α4β1 is a biomarker of tumor-draining lymph nodes in animals and patients and that lymph node metastases depend on PI3Kα-mediated α4β1 activation in lymph node lymphatic endothelium. Once activated, α4β1 promotes lymph node lymphangiogenesis and facilitates adhesion of VCAM-1⁺ metastatic tumor cells within lymph nodes, thereby promoting tumor spread.     

Coexpression of VEGF-C and Cox-2 in Human Colorectal Cancer and its Association With Lymph Node Metastasis

Purpose Several lines of experimental evidence indicated that over-expression of vascular endothelial growth factor-C and cyclooxygenase-2 genes promotes angiogenesis and lymphangiogenesis, both of which are essential for the growth and spreading of tumor cells. This study was designed to evaluate the coexpression of vascular endothelial growth factor-C and cyclooxygenase-2 in human colorectal carcinoma to determine their relationships and correlations with lymph node metastasis and prognosis. Methods Tissue samples of primary tumors and metastatic lymph nodes from 150 patients undergoing intentionally curative surgical resections for colorectal adenocarcinoma were immunohistochemically examined for vascular endothelial growth factor-C, cyclooxygenase-2, and CD34 expressions. Then, we analyzed their relationships and correlations with clinicopathologic findings and patients' survival time. Results The positivity rate of vascular endothelial growth factor-C and cyclooxygenase-2 in the primary tumor was 68 and 72.7 percent, respectively, and in the metastatic lymph nodes was 93.3 and 80 percent, respectively. A significant correlation was found between the expression scores of vascular endothelial growth factor-C and cyclooxygenase-2 (P < 0.0001), and both also were correlated to microvessels density and several clinicopathologic parameters, including primary tumor size, lymph node metastasis, lymphatic invasion, and TNM stage. Patients with vascular endothelial growth factor-C-positive and/or cyclooxygenase-2-positive tumors had a significant shorter survival time than those with negative tumors did. However, in a multivariate analysis, only cyclooxygenase-2 expression was recognized as an independent prognostic factor (P = 0.0412; relative risk ratio, 3.067; 95 percent confidence interval, 1.046–8.994). Conclusions These data show that in human colorectal carcinoma, vascular endothelial growth factor-C and cyclooxygenase-2 are coexpressed and significantly associated with lymph node metastasis and prognosis. Supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan. Presented at the meeting of the Japan Society of Clinical Oncology, Kyoto, Japan, October 27 to 29, 2004.     

Relationship of mast cell density with lymphangiogenesis and prognostic parameters in breast carcinoma

In many cancers, mast cell density (MCD) in the tumor microenvironment is associated with tumor progression and, to a greater extent, angiogenesis. Our study was designed to investigate the correlation between MCD, tumor lymphangiogenesis, and several well-established prognostic parameters in breast cancer. One hundred and four cases of invasive breast carcinoma diagnosed in our clinic between 2007 and 2011 were included. Mast cells and lymphatic vessels were stained with toluidine blue and D2-40, respectively, and their densities were calculated in various areas of tumors and lymph nodes. The variables of MCD and lymphatic vessel density (LVD) were compared using prognostic parameters as well as with each other. As tumor size and volume increased, MCD increased comparably in metastatic lymph nodes; intratumoral and peritumoral LVD also increased. Lymphovascular invasion, lymphatic invasion, perineural invasion, and estrogen receptor positivity were positively related to intratumoral MCD. The relationship between peritumoral MCD and nontumoral breast tissue MCD was statistically significant. Stage was correlated with MCD in metastatic lymph nodes. Metastatic lymph node MCD and intratumoral MCD were also significantly related. Stage, lymphatic invasion, perineural invasion, lymphovascular invasion, and metastatic lymph node MCD were all correlated with intratumoral and/or peritumoral LVD. As nuclear grade increased, intratumoral LVD became higher. In breast carcinoma, MCD, depending on its location, was related to several prognostic parameters. Notably, mast cells may have at least some effect on lymphangiogenesis, which appears to be a predictor of tumor progression.     

不同转移潜能的小鼠肝癌淋巴道转移和淋巴管生成的研究

目的探讨小鼠淋巴道高、低转移潜能的肝癌细胞的体内淋巴道转移状况和淋巴管生成对淋巴道转移的影响。方法将淋巴道高、低转移潜能的肝癌细胞接种于Balb／C小鼠，观察成瘤及转移情况，对肿瘤组织进行淋巴管染色，观察淋巴管生成情况。另取高、低转移潜能的细胞株进行体外淋巴管生成实验并进行小鼠肿瘤转移基因芯片检测，对血管内皮细胞生长因子C、D（VEGF—C、D）进行半定量逆转录聚合酶链反应及实时定量聚合酶链反应分析。结果高，低转移细胞在小鼠髂总动脉旁、肾门淋巴结的转移差异有统计学意义（P=0．0l8）。高转移潜能组诱导淋巴管生成的数量大于低转移组和对照组（P=0．032）。高转移组的CD44、E-cadherin．HER2／neu、H—Ras．VEGF—C的表达均高于低转移组，nm23A．nm23-E4、pl6ink4a、CD61等均低于低转移组。半定量逆转录聚合酶链反应表明，高转移组vEGF—C高于低转移组，VEGF—D低于低转移组。实时定量聚合酶链反应分析高转移组的VEGF—D分泌显著小于低转移组，vEGF—C／VEGF—D在高转移组明显高于低转移组。结论肝癌的淋巴道转移与淋巴管生成有关，VEGF—C、D相关基因表达的改变影响淋巴管生成。VEGF—C／VEGF—D比值可能是有效判断并影响肝癌淋巴道转移潜能的指标之一。     

肿瘤抗淋巴管生成研究进展

肿瘤转移是癌症患者的主要死因之一,淋巴管转移是肿瘤转移的重要途径,研究发现VEGF-C/VEGF-D/VEGFR-3与肿瘤淋巴管生成、肿瘤转移、肿瘤预后密切相关.大量的研究证实VEGF-C/VEGF-D/VEGFR-3信号传导轴在调节肿瘤淋巴管生成中起主导作用,临床病理研究也显示VEGF-C/VEGF-D/VEGFR-...     

The relationship between tumors and the lymphatics: what more is there to know?

Ten years ago the relationship between tumors and the lymphatic system was perceived to be rather passive. Since then, the dramatic increase in our understanding of the molecular biology of lymphatic endothelial cells and the regulation of lymphangiogenesis has revealed that tumors can actively interact with the lymphatics by inducing lymphangiogenesis. In turn, this interaction promotes the entry of tumor cells into the lymphatic vasculature and their subsequent transport to regional lymph nodes, a process that stimulates the formation of metastases. Tumor-induced lymphangiogenesis has thus emerged as an important new target in the fight against metastatic cancer. Nevertheless, there is still much to be learned about the relationship between tumors and the lymphatics that will have important ramifications for the design of clinical trials aimed at the application of anti-lymphangiogenesis therapies in the management of cancer. This Lymphangiogenesis Review focuses on these issues.     

Insulin-like growth factors 1 and 2 induce lymphangiogenesis in vivo

Lymphangiogenesis is an important process that contributes to the spread of cancer. Here we show that insulin-like growth factors 1 (IGF-1) and 2 (IGF-2) induce lymphangiogenesis in vivo. In a mouse cornea assay, IGF-1 and IGF-2 induce lymphangiogenesis as detected with LYVE-1, a specific marker for lymphatic endothelium. Interestingly, IGF-1-induced lymphangiogenesis could not be blocked by a soluble vascular endothelial growth factor receptor 3, suggesting that the vascular endothelial growth factor receptor 3-signaling pathway is not required for IGF-induced lymphangiogenesis. In vitro, IGF-1 and IGF-2 significantly stimulated proliferation and migration of primary lymphatic endothelial cells. IGF-1 and IGF-2 induced phosphorylation of intracellular signaling components, such as Akt, Src, and extracellular signal-regulated kinase in lymphatic endothelial cells. Immunohistochemistry, RT-PCR, and Affymetrix GeneChip microarray analysis showed that the receptors for IGFs are present in lymphatic endothelium. Together, our findings suggest that IGFs might act as direct lymphangiogenic factors, although any indirect roles in the induction of lymphangiogenesis cannot be excluded. Because members of the IGF ligand and receptor families are widely expressed in various types of solid tumors, our findings suggest that these factors are likely to contribute to lymphatic metastasis.     

Optimization and regeneration kinetics of lymphatic-specific photodynamic therapy in the mouse dermis

Lymphatic vessels transport fluid, antigens, and immune cells to the lymph nodes to orchestrate adaptive immunity and maintain peripheral tolerance. Lymphangiogenesis has been associated with inflammation, cancer metastasis, autoimmunity, tolerance and transplant rejection, and thus, targeted lymphatic ablation is a potential therapeutic strategy for treating or preventing such events. Here we define conditions that lead to specific and local closure of the lymphatic vasculature using photodynamic therapy (PDT). Lymphatic-specific PDT was performed by irradiation of the photosensitizer verteporfin that effectively accumulates within collecting lymphatic vessels after local intradermal injection. We found that anti-lymphatic PDT induced necrosis of endothelial cells and pericytes, which preceded the functional occlusion of lymphatic collectors. This was specific to lymphatic vessels at low verteporfin dose, while higher doses also affected local blood vessels. In contrast, light dose (fluence) did not affect blood vessel perfusion, but did affect regeneration time of occluded lymphatic vessels. Lymphatic vessels eventually regenerated by recanalization of blocked collectors, with a characteristic hyperplasia of peri-lymphatic smooth muscle cells. The restoration of lymphatic function occurred with minimal remodeling of non-lymphatic tissue. Thus, anti-lymphatic PDT allows control of lymphatic ablation and regeneration by alteration of light fluence and photosensitizer dose.     

LYVE-1 expression on high endothelial venules (HEVs) of lymph nodes

LYVE-1 (lymphatic endothelium hyaluronan receptor) has been identified as a powerful marker for lymphatic endothelium. Apart from lymphatic endothelium, LYVE-1 is expressed in normal liver blood sinusoids, spleen endothelium and activated tissue macrophages. LYVE-1 has not been detected in blood vascular endothelium with the exception of blood vessels in the lung. High endothelial venules (HEVs) belong to the vascular compartment of lymph nodes. They are the major site of entry for circulating lymphocytes into the node. HEVs are characterized by cuboidal endothelial cells, the existence of discontinuous junctions between these endothelial cells, and the presence of large numbers of lymphocytes within their walls. 40 paraffin-embedded lymph node biopsy specimens from newly diagnosed patients with non-Hodgkin lymphoma were evaluated as well as 10 lymph node biopsy specimens from adult patients with reactive lymphadenitis, and 10 normal, non-metastatic lymph nodes obtained from adult patients during cancer surgery served as controls. Samples were fixed in 10% buffered formalin, paraffin embedded, and stained with hematoxylin and eosin for histopathological evaluation. Sections were also evaluated with mouse monoclonal antibodies against LYVE-1 and CD34, and expression of both LYVE-1 and CD34 was demonstrated in HEVs. LYVE-1 expression was also found on the endothelial cells of the lymphatic sinus and in reticular cells in the lymph nodes.