Radiogenomic markers enable risk stratification and inference of mutational pathway states in head and neck cancer.

PURPOSE: Head and neck squamous cell carcinomas (HNSCCs) are a molecularly, histologically, and clinically heterogeneous set of tumors originating from the mucosal epithelium of the oral cavity, pharynx, and larynx. This heterogeneous nature of HNSCC is one of the main contributing factors to the lack of prognostic markers for personalized treatment. The aim of this study was to develop and identify multi-omics markers capable of improved risk stratification in this highly heterogeneous patient population. METHODS: In this retrospective study, we approached this issue by establishing radiogenomics markers to identify high-risk individuals in a cohort of 127 HNSCC patients. Hybrid in vivo imaging and whole-exome sequencing were employed to identify quantitative imaging markers as well as genetic markers on pathway-level prognostic in HNSCC. We investigated the deductibility of the prognostic genetic markers using anatomical and metabolic imaging using positron emission tomography combined with computed tomography. Moreover, we used statistical and machine learning modeling to investigate whether a multi-omics approach can be used to derive prognostic markers for HNSCC. RESULTS: Radiogenomic analysis revealed a significant influence of genetic pathway alterations on imaging markers. A highly prognostic radiogenomic marker based on cellular senescence was identified. Furthermore, the radiogenomic biomarkers designed in this study vastly outperformed the prognostic value of markers derived from genetics and imaging alone. CONCLUSION: Using the identified markers, a clinically meaningful stratification of patients is possible, guiding the identification of high-risk patients and potentially aiding in the development of effective targeted therapies.

Targeting TGF beta receptor 1 in head and neck squamous cell carcinoma.

OBJECTIVES: The transforming growth factor-Beta (TGF-ß) pathway may be involved in the radioresistance of head and neck squamous cell carcinoma (HNSCC). This study analyzed TGF-ß receptor 1 (TGFBR1) expression in HNSCC patients and evaluated the antineoplastic and radiosensitizing effects of vactosertib, a novel TGFBR1 inhibitor, in vitro. MATERIALS AND METHODS: TGFBR1 expression was examined in HNSCC patients at the mRNA level in silico and the protein level by immunohistochemistry, including surgical specimens of primary tumors, matched lymph node metastasis, and recurrent disease. Furthermore, a novel small molecule TGFBR1 inhibitor was evaluated in HNSCC cell lines. Finally, an indirect coculture model using patient-derived cancer-associated fibroblasts was applied to mimic the tumor microenvironment. RESULTS: Patients with high TGFBR1 mRNA levels showed significantly worse overall survival in silico (OS, p = 0.024). At the protein level, an association between TGFBR1+ tumor and OS was observed for the subgroup with TGFBR1-stroma (p = 0.001). Those results prevailed in multivariable analysis. Inhibition of TGFBR1 showed antineoplastic effects in vitro. In combination with radiation, vactosertib showed synergistic effects. CONCLUSION: Our results indicate a high risk of death in tumorTGFBR1+ |stromaTGFBR1- expressing patients. In vitro data suggest a potential radiosensitizing effect of TGFBR1 inhibition by vactosertib.

Inhibition of beta-catenin shows therapeutic potential in head and neck squamous cell carcinoma in vitro.

Beta-catenin is known to be a vital component of the canonical Wnt signaling cascade, involved in the carcinogenesis of different solid tumors. We aimed to evaluate the effects of Beta-catenin inhibition in head and neck squamous cell carcinoma (HNSCC) in vitro. The small molecular compound MSAB was used to inhibit Wnt/Beta-catenin signaling in a human papillomavirus (HPV)-positive and HPV-negative cell line and its effects on cell proliferation, migration, colony formation, apoptosis, as well as radiosensitizing properties were assessed. Significant antineoplastic effects were observed in both cell lines. Interestingly, stronger anti-neoplastic and radiosensitizing effects were observed in the HPV-negative cell line, whereas stronger anti-migratory potential was detected in HPV-positive HNSCC cells. In conclusion, our findings suggest MSAB as a potential therapeutic agent for HNSCC. Further studies are warranted to unravel the mechanistic background of our findings.

STAT3-dependent analysis reveals PDK4 as independent predictor of recurrence in prostate cancer.

Prostate cancer (PCa) has a broad spectrum of clinical behavior; hence, biomarkers are urgently needed for risk stratification. Here, we aim to find potential biomarkers for risk stratification, by utilizing a gene co-expression network of transcriptomics data in addition to laser-microdissected proteomics from human and murine prostate FFPE samples. We show up-regulation of oxidative phosphorylation (OXPHOS) in PCa on the transcriptomic level and up-regulation of the TCA cycle/OXPHOS on the proteomic level, which is inversely correlated to STAT3 expression. We hereby identify gene expression of pyruvate dehydrogenase kinase 4 (PDK4), a key regulator of the TCA cycle, as a promising independent prognostic marker in PCa. PDK4 predicts disease recurrence independent of diagnostic risk factors such as grading, staging, and PSA level. Therefore, low PDK4 is a promising marker for PCa with dismal prognosis.

Expression of inhibitors of apoptosis proteins in salivary gland adenoid cystic carcinoma: XIAP is an independent marker of impaired cause-specific survival.

OBJECTIVES: Inhibitors of apoptosis proteins are crucial to carcinogenesis since their expression results in evasion of apoptosis. Overexpression of inhibitors of apoptosis has repeatedly been associated with resistance to treatment and poor prognosis in various cancers. The role of inhibitors of apoptosis in adenoid cystic carcinoma of the salivary gland is still unclear. The aim of this study was to investigate the expression of inhibitors of apoptosis and their potential prognostic value in adenoid cystic carcinoma. DESIGN, SETTING AND PARTICIPANTS: Forty-nine patients, diagnosed with adenoid cystic carcinoma of the salivary gland between 1996 and 2016, were retrospectively included in this study. The expression of cIAP1, cIAP2, XIAP, Birc6, Livin and Survivin was assessed using immunohistochemistry, and their association of survival and prognosis was evaluated during a median follow-up of 6.4 years. MAIN OUTCOME MEASURE: Cause-specific survival and recurrence-free survival rates. RESULTS: XIAP, cIAP2, Livin and nuclear Survivin showed high expression levels in adenoid cystic carcinoma in most patients. There was no significant association of cIAP1, cIAP2, Livin, Birc6 and Survivin with outcome. However, high XIAP expression was associated with worse cause-specific survival and worse response to radiotherapy and proved to be an independent marker in multivariable analysis. CONCLUSION: Our data indicate that high expression of XIAP may be used as a prognosticator for poor survival and poor response to radiotherapy in adenoid cystic carcinoma patients.

DNA Repair Cofactors ATMIN and NBS1 Are Required to Suppress T Cell Activation.

Proper development of the immune system is an intricate process dependent on many factors, including an intact DNA damage response. The DNA double-strand break signaling kinase ATM and its cofactor NBS1 are required during T cell development and for the maintenance of genomic stability. The role of a second ATM cofactor, ATMIN (also known as ASCIZ) in T cells is much less clear, and whether ATMIN and NBS1 function in synergy in T cells is unknown. Here, we investigate the roles of ATMIN and NBS1, either alone or in combination, using murine models. We show loss of NBS1 led to a developmental block at the double-positive stage of T cell development, as well as reduced TCRα recombination, that was unexpectedly neither exacerbated nor alleviated by concomitant loss of ATMIN. In contrast, loss of both ATMIN and NBS1 enhanced DNA damage that drove spontaneous peripheral T cell hyperactivation, proliferation as well as excessive production of proinflammatory cytokines and chemokines, leading to a highly inflammatory environment. Intriguingly, the disease causing T cells were largely proficient for both ATMIN and NBS1. In vivo this resulted in severe intestinal inflammation, colitis and premature death. Our findings reveal a novel model for an intestinal bowel disease phenotype that occurs upon combined loss of the DNA repair cofactors ATMIN and NBS1.

ß-CATENIN is a positive prognostic marker for HPV-positive head and neck squamous cell carcinoma.

PURPOSE: The evolutionary-conserved Wnt/ß-CATENIN (WBC) pathway has been implicated in the pathogenesis of different solid malignant tumors. We evaluated the prognostic relevance of ß-CATENIN, a pivotal mediator of WBC activation, in patients with human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC). METHODS: We analyzed if patients with HPV-positive HNSCC from the "The Cancer Genome Atlas" (TCGA cohort, n = 41) can be stratified based on their CTNNB1 mRNA expression. Moreover, in a tissue microarray (TMA) of primary tumor sections from HPV-positive HNSCC patients treated in a tertiary academic center (in-house cohort, n = 31), we evaluated the prognostic relevance of ß-CATENIN expression on protein level. RESULTS: In silico mining of CTNNB1 expression in HPV-positive HNSCC revealed that high CTNNB1 expression was linked to better overall survival (OS, p = 0.062). Moreover, high ß-CATENIN expression was significantly associated with a better OS in our in-house cohort (p = 0.035). CONCLUSION: Based on these findings, we postulate that ß-CATENIN expression could serve (potentially in conjunction with other WBC pathway members) as a marker for better survival outcomes in patients with HPV-positive HNSCC. However, it is evident that future studies on bigger cohorts are warranted.

Targeting Wnt/Beta-Catenin Signaling in HPV-Positive Head and Neck Squamous Cell Carcinoma.

Wnt/Beta-Catenin signaling is involved in the carcinogenesis of different solid malignant tumors. The interaction of Creb-binding protein (CBP) with Beta-Catenin is a pivotal component of the Wnt/Beta-Catenin signaling pathway. The first aim of this study was to evaluate the association of CBP expression with survival in patients with human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC). Second, the in vitro effects of the inhibition of CBP/Beta-Catenin interaction were analyzed. In particular, the effects of ICG-001, an inhibitor of CBP/Beta-Catenin interaction, on proliferation, cell death, modulation of Wnt/Beta-Catenin target expression, and cell migration were examined in vitro. High CBP expression is significantly associated with better survival on mRNA and protein levels. Furthermore, we observed cytotoxic as well as anti-migratory effects of ICG-001. These effects were particularly more potent in the HPV-positive than in the -negative cell line. Mechanistically, ICG-001 treatment induced apoptosis and led to a downregulation of CBP, c-MYC, and Cyclin D1 in HPV-positive cells, indicating inhibition of Wnt/Beta-Catenin signaling. In conclusion, high CBP expression is observed in HPV-positive HNSCC patients with a good prognosis, and ICG-001 showed a promising antineoplastic potential, particularly in HPV-positive HNSCC cells. Therefore, ICG-001 may potentially become an essential component of treatment de-escalation regimens for HPV-positive HNSCC. Further studies are warranted for additional assessment of the mechanistic background of our in vitro findings.

Protein Expression of Folate Receptor Alpha in Adenoid Cystic Carcinoma of the Head and Neck.

Purpose: Folate receptor alpha (FRα) is overexpressed in various cancer entities while expression in normal tissue is limited. Thus, FRα is an attractive target in cancer therapy. Currently, various therapeutic and diagnostic approaches are under investigation in clinical trials. The aim of this study was to assess the expression and clinical relevance of FRα in adenoid cystic carcinoma of the head and neck. Patients and Methods: In this retrospective cohort study, 43 patients with adenoid cystic carcinoma (ACC) of the head and neck were included. FRα expression was analyzed in tumor tissue and tumor-free margin in a tissue microarray using immunohistochemical staining. Protein levels were correlated with clinical parameters. Results: FRα staining was positive in 47% of ACC patients. The tumor-free margin was positive in 22%. Patients with positive tumor tissue showed positive margin staining in 55%. FRα expression was not associated with the clinical parameters (sex, age, staging, grading, perineural invasion, lymphovascular invasion). Conclusion: FRα expression is common in ACC of the head and neck. Therefore, FRα should be further evaluated as a therapeutic target in ACC.

Transcription factors CP2 and YY1 as prognostic markers in head and neck squamous cell carcinoma: analysis of The Cancer Genome Atlas and a second independent cohort.

PURPOSE: The transcription factors YY1 and CP2 have been associated with tumor promotion and suppression in various cancers. Recently, simultaneous expression of both markers was correlated with negative prognosis in cancer. The aim of this study was to explore the expression of YY1 and CP2 in head and neck squamous cell carcinoma (HNSCC) patients and their association with survival. METHODS: First, we analyzed mRNA expression and copy number variations (CNVs) of YY1 and CP2 using "The Cancer Genome Atlas" (TCGA) with 510 HNSCC patients. Secondly, protein expression was investigated via immunohistochemistry in 102 patients, who were treated in the Vienna General Hospital, utilizing a tissue microarray. RESULTS: The median follow-up was 2.9 years (1.8-4.6) for the TCGA cohort and 10.3 years (6.5-12.8) for the inhouse tissue micro-array (TMA) cohort. The median overall survival of the TCGA cohort was decreased for patients with a high YY1 mRNA expression (4.0 vs. 5.7 years, p = 0.030, corr. p = 0.180) and high YY1-CNV (3.53 vs. 5.4 years, p = 0.0355, corr. p = 0.213). Furthermore, patients with a combined high expression of YY1 and CP2 mRNA showed a worse survival (3.5 vs. 5.4 years, p = 0.003, corr. p = 0.018). The mortality rate of patients with co-expression of YY1 and CP2 mRNA was twice as high compared to patients with low expression of one or both (HR 1.99, 95% CI 1.11-3.58, p = 0.021). Protein expression of nuclear YY1 and CP2 showed no association with disease outcome in our inhouse cohort. CONCLUSION: Our data indicate that simultaneous expression of YY1 and CP2 mRNA is associated with shorter overall survival. Thus, combined high mRNA expression might be a suitable prognostic marker for risk stratification in HNSCC patients. However, since we could not validate this finding at genomic or protein level, we hypothesize that unknown underlying mechanisms which regulate mRNA transcription of YY1 and CP2 are the actual culprits leading to a worse survival.

Prognostic Relevance of Thyroid-Hormone-Associated Proteins in Adenoid Cystic Carcinoma of the Head and Neck.

The proteins sodium iodide symporter (NIS), µ-crystallin (CRYM), and thyroid hormone receptor beta (THRB) have been associated with prognosis in various cancer entities. While NIS and THRB may serve as possible therapeutic targets, the role of CRYM in cancer is still unclear. Protein levels of 44 patients with adenoid cystic carcinoma of the head and neck were analyzed using immunohistochemistry and correlated with clinicopathological data and outcome. NIS was positive in 72%, CRYM was positive in 55%, and THRB was positive in 39% of the patients. CRYM-positive adenoid cystic carcinomas were associated with a better cause-specific survival. Thus, our data indicate that CRYM might be a suitable positive prognostic marker in adenoid cystic carcinoma of the head and neck. Furthermore, expression of NIS was present in most patients and therefore evaluation of the use of radioiodine treatment is recommended.

YAP/TAZ inhibition reduces metastatic potential of Ewing sarcoma cells.

Ewing sarcoma (EwS) is a highly metastatic bone cancer characterized by the ETS fusion oncoprotein EWS-FLI1. EwS cells are phenotypically highly plastic and switch between functionally distinct cell states dependent on EWS-FLI1 fluctuations. Whereas EWS-FLI1high cells proliferate, EWS-FLI1low cells are migratory and invasive. Recently, we reported activation of MRTFB and TEAD, effectors of RhoA and Hippo signalling, upon low EWS-FLI1, orchestrating key steps of the EwS migratory gene expression program. TEAD and its co-activators YAP and TAZ are commonly overexpressed in cancer, providing attractive therapeutic targets. We find TAZ levels to increase in the migratory EWS-FLI1low state and to associate with adverse prognosis in EwS patients. We tested the effects of the potent YAP/TAZ/TEAD complex inhibitor verteporfin on EwS cell migration in vitro and on metastasis in vivo. Verteporfin suppressed expression of EWS-FLI1 regulated cytoskeletal genes involved in actin signalling to the extracellular matrix, effectively blocked F-actin and focal-adhesion assembly and inhibited EwS cell migration at submicromolar concentrations. In a mouse EwS xenograft model, verteporfin treatment reduced relapses at the surgical site and delayed lung metastasis. These data suggest that YAP/TAZ pathway inhibition may prevent EwS cell dissemination and metastasis, justifying further preclinical development of YAP/TAZ inhibitors for EwS treatment.

Super-enhancer-based identification of a BATF3/IL-2R-module reveals vulnerabilities in anaplastic large cell lymphoma.

Anaplastic large cell lymphoma (ALCL), an aggressive CD30-positive T-cell lymphoma, comprises systemic anaplastic lymphoma kinase (ALK)-positive, and ALK-negative, primary cutaneous and breast implant-associated ALCL. Prognosis of some ALCL subgroups is still unsatisfactory, and already in second line effective treatment options are lacking. To identify genes defining ALCL cell state and dependencies, we here characterize super-enhancer regions by genome-wide H3K27ac ChIP-seq. In addition to known ALCL key regulators, the AP-1-member BATF3 and IL-2 receptor (IL2R)-components are among the top hits. Specific and high-level IL2R expression in ALCL correlates with BATF3 expression. Confirming a regulatory link, IL-2R-expression decreases following BATF3 knockout, and BATF3 is recruited to IL2R regulatory regions. Functionally, IL-2, IL-15 and Neo-2/15, a hyper-stable IL-2/IL-15 mimic, accelerate ALCL growth and activate STAT1, STAT5 and ERK1/2. In line, strong IL-2Rα-expression in ALCL patients is linked to more aggressive clinical presentation. Finally, an IL-2Rα-targeting antibody-drug conjugate efficiently kills ALCL cells in vitro and in vivo. Our results highlight the importance of the BATF3/IL-2R-module for ALCL biology and identify IL-2Rα-targeting as a promising treatment strategy for ALCL.

AF1q Expression Associates with CD44 and STAT3 and Impairs Overall Survival in Adenoid Cystic Carcinoma of the Head and Neck.

Salivary gland malignancies of the head and neck form a heterogeneous group. Adenoid cystic carcinomas are an aggressive entity of salivary gland malignancies characterized by frequent distant metastases and poor response to radio- and chemotherapy. AF1Q is a MLL fusion partner, which can activate Wnt and STAT3 signaling. Recently, overexpression of AF1q has been identified as a poor prognosticator in patients of different malignancies. A total of 46 patients with adenoid cystic carcinoma were immunohistochemically evaluated for expression of AF1q and clinical outcome was analyzed in this context. Additionally, STAT3 and the Wnt downstream target CD44 were investigated and correlated with AF1q. AF1q was overexpressed in 52.2%. Overexpression of AF1q was associated with poorer overall survival (p = 0.03). Additionally, lymph node metastases and solid tumor parts were more frequently observed in AF1qhigh patients (p = 0.07 and 0.05, respectively). AF1q did not influence the occurrence of distant metastases. Expression of AF1q was associated with higher levels of STAT3 and CD44 (p = 0.003 and 0.006, respectively). AF1q is a novel prognostic marker for poor overall survival in adenoid cystic carcinoma patients. The deleterious effects on survival may be a result of promotion of the STAT3 and Wnt pathway.

Correction: Dependency on the TYK2/STAT1/MCL1 axis in anaplastic large cell lymphoma.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Lymphatic precollectors contain a novel, specialized subpopulation of podoplanin low, CCL27-expressing lymphatic endothelial cells.

Expression of the lymphoendothelial marker membrane mucoprotein podoplanin (podo) distinguishes endothelial cells of both blood and lymphatic lineages. We have previously discovered two distinct subpopulations of lymphatic endothelial cells (LECs) in human skin that were defined by their cell surface densities of podoplanin and were designated LEC podo-low and LEC podo-high. LEC podo-low is restricted to lymphatic precollector vessels that originate from initial LEC podo-high-containing lymphatic capillaries and selectively express several pro-inflammatory factors. In addition to the chemokine receptor protein Duffy blood group antigen receptor for chemokines, these factors include the constitutively expressed chemokine CCL27, which is responsible for the accumulation of pathogenic CCR10+ T lymphocytes in human inflammatory skin diseases. In this study, we report that CCR10+ T cells accumulate preferentially both around and within CCL27+ LEC podo-low precollector vessels in skin biopsies of human inflammatory disease. In transmigration assays, isolated CCR10+ T lymphocytes are chemotactically attracted by LEC podo-low in a CCL27-dependent fashion, but not by LEC podo-high. These observations indicate that LEC podo-low-containing precollector vessels constitute a specialized segment of the initial lymphatic microvasculature, and we hypothesize that these LEC podo-low-containing vessels are involved in the trafficking of CCR10+ T cells during skin inflammation.

Overexpression of LAPTM4B-35 is a negative prognostic factor in head and neck squamous cell carcinoma.

Overexpression of LAPTM4B-35 (lysosomal-associated transmembrane protein 4ß-35) is associated with a poor prognosis in numerous malignant tumours. Expression patterns and effects of LAPTM4B-35 on head and neck squamous cell carcinomas (HNSCC) are unknown. The aim of this study was to investigate the prognostic relevance of LAPTM4B-35 in HNSCC. Tissue microarrays were constructed with primary tumours and associated lymph node metastases isolated from 127 patients. The expression of LAPTM4B-35 was investigated by immunohistochemistry and the results were correlated with survival data. LAPTM4B-35 in the primary tumour was highly expressed in 47.2% of the patients (60/127). LAPTM4B-35 expression was significantly associated with tumour stage. Moreover, overexpression of LAPTM4B-35 correlated with a significantly worse disease-free survival (10.23 years vs. not reached) and a higher recurrence rate (40.7% vs. 25%). High expression of LAPTM4B-35 in lymph node metastasis was found in 29.2% of cases. In 19.4% of cases, high LAPTM4B-35 expression was observed in both the primary tumour and corresponding lymph node metastases. In conclusion, our data indicates that overexpression of LAPTM4B-35 is associated with poor prognosis and may therefore serve as a new prognostic marker in HNSCC.

Evaluation of the cancer stem cell marker DCLK1 in patients with lymph node metastases of head and neck cancer.

BACKGROUND: Lymph node metastases are frequently detected in head and neck squamous cell carcinoma (HNSCC) patients. Little is known about biomarkers expressed in lymph node metastases or their influence on clinical outcome. Doublecortin-like kinase 1 (DCLK1) is one marker that might be associated with outcome, owing to its correlation with stem cell-like characteristics. METHODS: We assessed the expression of DCLK1 in 74 postoperatively irradiated patients in histologically confirmed HNSCC lymph node metastases. Statistical analysis of the association with DCLK1 on clinical outcomes was performed. RESULTS: DCLK1 was expressed in 63.5% of our patient cohort. DCLK1(+) HNSCC patients, compared with those without DCLK1 expression, showed a significantly poorer time to recurrence. Moreover, we observed a significantly poorer time to recurrence in HPV(-) HNSCC patients, and significantly shorter overall and disease-free survival rates in HPV(-) oropharyngeal cancer patients, compared with HPV(+) patients with these cancers. HPV(+) patients showed no significant differences in survival time according to DCLK1 expression. However, recurrent disease occurred in only DCLK1(+) patients. Mulitivariate analysis showed that DCLK1 expression in lymph node metastases is an independent marker for recurrence. CONCLUSION: DCLK1 expression might be associated with poorer clinical outcomes in HNSCC patients, specifically in HPV(-) move patients. However, larger studies are required to verify our results.

Dependency on the TYK2/STAT1/MCL1 axis in anaplastic large cell lymphoma.

TYK2 is a member of the JAK family of tyrosine kinases that is involved in chromosomal translocation-induced fusion proteins found in anaplastic large cell lymphomas (ALCL) that lack rearrangements activating the anaplastic lymphoma kinase (ALK). Here we demonstrate that TYK2 is highly expressed in all cases of human ALCL, and that in a mouse model of NPM-ALK-induced lymphoma, genetic disruption of Tyk2 delays the onset of tumors and prolongs survival of the mice. Lymphomas in this model lacking Tyk2 have reduced STAT1 and STAT3 phosphorylation and reduced expression of Mcl1, a pro-survival member of the BCL2 family. These findings in mice are mirrored in human ALCL cell lines, in which TYK2 is activated by autocrine production of IL-10 and IL-22 and by interaction with specific receptors expressed by the cells. Activated TYK2 leads to STAT1 and STAT3 phosphorylation, activated expression of MCL1 and aberrant ALCL cell survival. Moreover, TYK2 inhibitors are able to induce apoptosis in ALCL cells, regardless of the presence or absence of an ALK-fusion. Thus, TYK2 is a dependency that is required for ALCL cell survival through activation of MCL1 expression. TYK2 represents an attractive drug target due to its essential enzymatic domain, and TYK2-specific inhibitors show promise as novel targeted inhibitors for ALCL.

Transcriptomal comparison of human dermal lymphatic endothelial cells ex vivo and in vitro.

The in vivo functions of lymphatic endothelial cells depend on their microenvironment, which cannot be fully reproduced in vitro. Because of technical limitations, gene expression in uncultured, "ex vivo" lymphatic endothelial cells has not been characterized at the molecular level. We combined tissue micropreparation and direct cell isolation with DNA chip experiments to identify 159 genes differentiating human lymphatic endothelial cells from blood vascular endothelial cells ex vivo. The same analysis performed with cultured primary cells revealed that only 19 genes characteristic for lymphatic endothelium ex vivo retained this property upon culture, while 27 marker genes were newly induced. In addition, a set of panendothelial genes could be recognized. The propagation of lymphatic endothelial cells in culture stimulated transcription of genes associated with cell turnover, basic metabolism, and the cytoskeleton. On the other hand, there was downregulation of genes encoding extracellular matrix components, signaling via transmembrane tyrosine kinase pathways and the chemokine (C-C) ligand 21. Direct ex vivo analysis of the lymphatic endothelial cell transcriptome is helpful for the understanding of the physiology of the lymphatic vascular system and of the pathogenesis of its diseases.