The authors would like to acknowledge the Baker Foundation and the Royal Children's Foundation 'Women in Science Fellowship' support of Zerina Lokmic. Andrew G. Elefanty and Edouard G. Stanley are NHMRC Senior Research Fellows. Work in their laboratories was supported by NHMRC and Stem Cells Australia.

Ethics statement: Ethical approval for collection of lymphatic malformation and foreskin tissues was obtained from the Human Research Ethics Committees at the Royal Children&#8217;s Hospital, Melbourne, Australia. Signed consent was received from patients&#8217; parents prior to surgery. Tissue samples were collected from patients diagnosed with LMs undergoing surgical procedures as part of their clinical management and patients undergoing elective circumcision. All experiments were performed in accordance with guidelines of the National Health and Medical Research Council, Australia.
1. Preparation of Cell Suspension from Foreskin and Lymphatic Malformation Tissues
<ol>
	<li>Buffers and Media Preparation.
	<ol>
		<li>Prepare complete endothelial cell media using commercially available EGM-2 MV Bullet Kit by warming EGM-2 media and gently thawing the kit components in 37 &#176;C water bath. In class II biosafety cabinet, aseptically add each component to the EGM-2 media. Once all components are added to the media, refer to this media as &#8216;complete endothelial cell media&#8217;. Use sterile 50 ml pipette to mix the contents prior to use. 
		NOTE: All steps pertaining to cell culture are performed in a class II biohazard cabinet. All solutions are stored at 4 &#176;C as per manufacturers&#8217; instructions and are warmed to room temperature prior to use. The complete endothelial cell media, cell culture buffers and enzyme solutions are warmed at 37 &#176;C for 20 min prior to use.</li>
		<li>Supplement complete endothelial cell media with 50 ng/ml VEGF-C. Aliquot the supplemented endothelial cell media into 50 ml sterile tubes and store at 4 &#176;C until use. The media is stable for at least 4 weeks when stored at 4 &#176;C.</li>
		<li>Prepare calcium and magnesium free phosphate-buffered saline (PBS) by dissolving 8.752 g NaCl, 1.416 g Na2HPO4.2H2O and 0.395 g KH2PO4 in 1,000 ml of water. Adjust pH to 7.4. Filter sterilize PBS using 0.22 &#956;m filter and store at 4 &#176;C. Prior to use add antibiotic/antimycotic solution (used at 1:100).</li>
		<li>To prepare human fibronectin, dissolve 1 mg of fibronectin in 10 ml of sterile water. Store reconstituted solution in 100 &#956;l aliquots at -20 &#176;C. On the day of use add 10 ml of sterile PBS to 100 &#956;l of fibronectin aliquot (to give a final working concentration of 10 &#956;g/ml).</li>
		<li>For the enzyme media, prepare a solution containing 0.04% Dispase II, 0.25% Collagenase II and 0.01% DNase I in sterile PBS. First, weigh dispase and collagenase, place in a sterile 50 ml tube, add the required volume of PBS and incubate for 30 min with shaking at 37 &#176;C to dissolve. Once dissolved, filter sterilize (0.22 &#956;m filter) dispase/collagenase solution in biosafety hood. Aseptically add the DNase I. Store the enzymatic solution at 37 &#176;C until use. 
		NOTE: DNase I is a commercial cell culture grade reagent available as sterile lyophilized powder.</li>
	</ol>
	</li>
</ol>
2. Preparation of Cell Suspension from Foreskin and Lymphatic Malformations
<ol>
	<li>Weigh a 50 ml tube containing 10 ml of DMEM/2% antibiotic antimycotic solution. This tube will be used for tissue collection.</li>
	<li>Following surgical removal of lymphatic malformation and foreskin tissues, aseptically add tissue specimen to the tube and transfer on ice to the cell culture laboratory.</li>
	<li>Weigh the tube containing the tissue and calculate tissue weight. Use this weight to calculate the volume of enzymatic solution needed to digest the tissue.</li>
	<li>In a Class II biosafety cabinet, use sterile forceps to transfer the tissue and media into a 100 mm tissue culture dish. Use sterile scissors to finely mince the tissue into ~1 mm3 pieces.</li>
	<li>Transfer minced tissue mixed with media into a 50 ml tube containing an additional 10 ml of sterile DMEM/2% antibiotic antimycotic solution. Mix by inversion to re-suspend the tissue. Centrifuge the sample at 300 x g for 5 min.</li>
	<li>Remove the supernatant. Based on tissue weight, add 1 ml of pre-warmed (37 &#176;C) collagenase II/DNase I/ Dispase II digestion solution per 100 mg of minced tissue. Generally, use 10 ml of enzyme solution for approximately 1 g of minced tissue.</li>
	<li>Incubate the tissue in a 37 &#176;C incubator for 20-90 min with constant shaking at 200 rpm. At the end of this period, ensure that nearly all of the tissue is digested into fine fragments. 
	NOTE: Exposure of the cells to collagenase and dispase at the time of isolation from the primary tissues influences cell survival. We have found empirically that most neonatal foreskin samples optimally require 20-30 min of digestion, whereas fibrotic lymphatic malformation samples may require 60-90 min of digestion. LM LEC yields are influenced by the amount of fibrosis present, more fibrous tissue yielding fewer cells, possibly due to deleterious effects of prolonged exposure to collagenase II and dispase II.</li>
	<li>Following digestion, transfer the tube to the biosafety cabinet and pass the digested tissue solution through a 70 &#956;m strainer placed into a sterile 50 ml tube. Using 3 ml syringe piston with rubber plunger, grind down the remaining tissue until only small traces of extracellular matrix are observed.</li>
	<li>Wash the cell strainer with a volume of endothelial cell medium equivalent to the volume of dissociating enzyme medium to recover cells stuck to sieve and to inactivate the enzymes. For example, for 2 ml of dissociating enzyme medium to digest the minced tissue, add 2 ml of endothelial cell medium to inactivate the enzymes.</li>
	<li>Centrifuge the cell solution at 300 x g for 5 min and aspirate the supernatant.&#160;R>e-suspend the cells in 10 ml of PBS. Centrifuge cells at 300 x g for 5 min, remove the supernatant then repeat cell wash twice.&#160;>Resuspend the cell pellet in 20 ml of endothelial cell medium. Count cells using trypan blue then seed 2 x 10>6 cells in 150 cm>2 flask pre-coated with fibronectin in a final volume of 20 ml of endothelial cell medium. Culture at 37 &#176;C in a 5% CO>2 in humidified air incubator.> 
	NOTE: It is expected that 75%-90% of nucleated cells survive tissue digestion as estimated by trypan blue exclusion. The initial cell count reflects all nucleated cells in the cell suspension (i.e. keratinocytes, leukocytes, macrophages, connective tissue cells and blood vessel cells). The cell count at 5-7 days reflects cells that have attached, survived and proliferated during cell culture. Coating tissue culture flasks with fibronectin also improves subsequent LEC and LM LEC survival.</li>
	<li>After overnight incubation, wash away unbound cells in three washes with PBS/1% antibiotic-antimycotic solution and add fresh endothelial cell medium. Carry out three washes to effectively remove unbound cells and red blood cells present in the flask. Change media every second day. Cells will be ~80% confluent after 5-7 days.</li>
</ol>
3. Antibody Staining of Cells for Lymphatic Endothelial Cell Surface Markers for Flow Cytometry
<ol>
	<li>After the cells have reached 80% confluence, aspirate medium and rinse cells with PBS.</li>
	<li>Detach adherent cells by incubating cells with 7 ml of cell detachment solution such as Accutase per 150 cm2 flask for 5-7 min at 37 &#176;C.</li>
	<li>Harvest detached cells, inactivate the cell detachment solution by adding 3 volumes of endothelial cell medium and transfer the cell suspension to a new sterile tube.</li>
	<li>Centrifuge the cells at 300 x g for 5 min.</li>
	<li>Aspirate supernatant and re-suspend the cells in 5 ml of PBS. Centrifuge cells at 300 x g for 5 min, remove the supernatant then repeat cell wash. Re-suspend the cells in 5 ml of PBS.</li>
	<li>Count the number of viable cells. Mix 10 &#956;l of cell suspension with 90 &#956;l of 0.4% trypan blue. Transfer 10 &#956;l of this suspension to hemocytometer for counting. 
	NOTE: The final cell yield will depend on the sample size processed. The usual cell yield per 150 cm2 flask ranges from 7 x 105 to 1.2 x 106 of viable cells.</li>
	<li>Prepare the antibody solutions for cell staining. 
	NOTE: The following dilutions were titrated for staining 1 x 106 in a staining volume of 100 &#956;l.
	<ol>
		<li>Dilute PE conjugated mouse anti human VEGFR-3 (1:50); PE-Cy7 conjugated mouse anti human conjugated CD34 (1:200); APC-conjugated mouse anti human CD31 (1:100) and Alexa 488-conjugated rat anti human PODOPLANIN (1:200) in total volume of 100 &#956;l sterile 5% FBS/PBS solution per tissue sample. Following preparation of antibody solution, keep on ice until use. Similarly prepare diluted isotype control antibody mixture to facilitate setting of flow cytometry gates.</li>
	</ol>
	</li>
	<li>To reduce nonspecific binding of the antibodies, centrifuge cells at 300 x g for 2 min, remove supernatant then suspend the cells in 100 &#956;l sterile 5% FBS/PBS solution per sample to be stained. Incubate cells on ice for 20 min at 4 &#176;C.</li>
	<li>Centrifuge cells at 300 x g for 5 min, remove supernatant then re-suspend cells in the conjugated antibody cocktail. Also stain a smaller aliquot of cells (1 x 105) in 100 &#956;l isotype control antibody mixture. Incubate cells on ice for 20 min.</li>
	<li>To remove the unbound antibody, add 2 ml of 2% FBS/PBS solution and centrifuge the cells at 300 x g for 5 min. Aspirate the supernatant and repeat the wash.</li>
	<li>Resuspend the cell pellet for the isotype control and the antibody stained sample to be sorted in 300 &#956;l of 0.5 mg/ml propidium iodide/2% FBS/PBS solution. Place tubes on ice until sorting.</li>
</ol>
4. Cell Sorting
<ol>
	<li>Use the following materials to set up the instrument; alignment beads such as commercially available fluorescent particles, phosphate-buffered saline based sheath fluid and drop delay beads, such as Accudrop fluorescent beads.</li>
	<li>Isolate the purified human LECs on a multi-parameter fluorescence-activated cell sorting instrument. Set up the instrument and align as per manufacturer&#8217;s recommendations. In addition, run single stain compensation controls with each sort to generate the compensation matrix and to thus eliminate substantial bleed through of the emission of fluorochromes such as PE into the PE-Cy channel. 
	NOTE: A higher proportion of the FACS sorted cells survive the isolation if a 100 &#956;m nozzle is used and cells are sorted into endothelial cell medium.</li>
</ol>
5. Cell Culture Post FACS Sorting
<ol>
	<li>Following sorting, centrifuge cells at 300 x g for 5 min. Aspirate the supernatant and resuspend the cells in 5-10 ml of media (depending on the flask used to seed the cell). If less than 50,000 cells are sorted, the cells are cultured in fibronectin coated 25 cm2 flask.</li>
	<li>Otherwise culture the cells in 75 cm2 fibronectin-coated flask at 37 &#176;C in a 5% CO2, air humidified incubator. Change media after 2 days. 
	NOTE: Cell media is changed every second day because prolonging the time between media changes appears to favor survival of the non-endothelial cells. We validate the lymphatic endothelial cell phenotype using immunohistochemical detection of markers: PROX-1, VEGFR-3, Podoplanin, CD34 and CD31 when the cells are first split for further expansion15.</li>
</ol>

<ol><li>Baluk, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Functionally+specialized+junctions+between+endothelial+cells+of+lymphatic+vessels%5BTitle%5D)+AND+%22J+Exp+Med%22%5BJournal%5D)">Functionally specialized junctions between endothelial cells of lymphatic vessels.</a> J Exp Med. 204 (10), 2349-2362 (2007).</li>
<li>Yao, L. C., Baluk, P., Srinivasan, R. S., Oliver, G., McDonald, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Plasticity+of+button-like+junctions+in+the+endothelium+of+airway+lymphatics+in+development+and+inflammation%5BTitle%5D)+AND+%22Am+J+Pathol%22%5BJournal%5D)">Plasticity of button-like junctions in the endothelium of airway lymphatics in development and inflammation.</a> Am J Pathol. 180 (6), 2561-2575 (2012).</li>
<li>Zawieja, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contractile+physiology+of+lymphatics%5BTitle%5D)+AND+%22Lymphat+Res+Biol%22%5BJournal%5D)">Contractile physiology of lymphatics.</a> Lymphat Res Biol. 7 (2), 87-96 (2009).</li>
<li>Witte, M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Structure+function+relationships+in+the+lymphatic+system+and+implications+for+cancer+biology%5BTitle%5D)+AND+%22Cancer+Metastasis+Rev%22%5BJournal%5D)">Structure function relationships in the lymphatic system and implications for cancer biology.</a> Cancer Metastasis Rev. 25 (2), 159-184 (2006).</li>
<li>Andrade, M., Jacomo, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Anatomy+of+the+human+lymphatic+system%5BTitle%5D)+AND+%22Cancer+Treat+Res%22%5BJournal%5D)">Anatomy of the human lymphatic system.</a> Cancer Treat Res. 135, 55-77 (2007).</li>
<li>Kumar, V., Abbas, A. K., Aster, J. C., Ch Fausto, N. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aKumar%2C+V+%22Cotran+Pathologic+Basis+of+Disease.+43-78%22">Cotran Pathologic Basis of Disease. 43-78</a>. 2, Elsevier Saunders. Robbins. (2009).</li>
<li>Shayan, R., Achen, M. G., Stacker, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Lymphatic+vessels+in+cancer+metastasis%3A+bridging+the+gaps%5BTitle%5D)+AND+%22Carcinogenesis%22%5BJournal%5D)">Lymphatic vessels in cancer metastasis: bridging the gaps.</a> Carcinogenesis. 27 (9), 1729-1738 (2006).</li>
<li><a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22Mulliken+%26+Young%27s+Vascular+Anomalies+Hemangiomas+and%22">Mulliken & Young's Vascular Anomalies Hemangiomas and</a>. , University Press. Oxford. 1059-1076 (2013).</li>
<li><a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22Mulliken+%26+Young%27s+Vascular+Anomalies+Hemangiomas%22">Mulliken & Young's Vascular Anomalies Hemangiomas</a>. 14, University Press. Oxford. 562-594 (2013).</li>
<li>Bellini, C., Hennekam, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Clinical+disorders+of+primary+malfunctioning+of+the+lymphatic+system%5BTitle%5D)+AND+%22Adv+Anat+Embryol+Cell+Biol%22%5BJournal%5D)">Clinical disorders of primary malfunctioning of the lymphatic system.</a> Adv Anat Embryol Cell Biol. 214, 187-204 (2014).</li>
<li>Schook, C. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Primary+lymphedema%3A+clinical+features+and+management+in+138+pediatric+patients%5BTitle%5D)+AND+%22Plast+Reconstr+Surg%22%5BJournal%5D)">Primary lymphedema: clinical features and management in 138 pediatric patients.</a> Plast Reconstr Surg. 127 (6), 2419-2431 (2011).</li>
<li>Brouillard, P., Boon, L., Vikkula, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Genetics+of+lymphatic+anomalies%5BTitle%5D)+AND+%22J+Clin+Invest%22%5BJournal%5D)">Genetics of lymphatic anomalies.</a> J Clin Invest. 124 (3), 898-904 (2014).</li>
<li><a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((for+the+Study+of+Vascular+Anomalies+%28ISSVA%29+classification%5BTitle%5D)+AND+%22Available+from%3A+http%3A%2F%2Fwww.issva.org%2Fclassification.com%22%5BJournal%5D)">for the Study of Vascular Anomalies (ISSVA) classification.</a> Available from: http://www.issva.org/classification.com. , (2014).</li>
<li>Croteau, S. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Kaposiform+lymphangiomatosis%3A+a+distinct+aggressive+lymphatic+anomaly%5BTitle%5D)+AND+%22J+Pediatr%22%5BJournal%5D)">Kaposiform lymphangiomatosis: a distinct aggressive lymphatic anomaly.</a> J Pediatr. 164 (2), 383-388 (2014).</li>
<li>Lokmic, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Isolation+of+human+lymphatic+malformation+endothelial+cells%2C+their+in+vitro+characterization+and+in+vivo+survival+in+a+mouse+xenograft+model%5BTitle%5D)+AND+%22Angiogenesis%22%5BJournal%5D)">Isolation of human lymphatic malformation endothelial cells, their in vitro characterization and in vivo survival in a mouse xenograft model.</a> Angiogenesis. 17 (1), 1-15 (2014).</li>
<li>Smith, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Lymphatic+malformations%5BTitle%5D)+AND+%22Lymphat+Res+Biol%22%5BJournal%5D)">Lymphatic malformations.</a> Lymphat Res Biol. 2 (1), 25-31 (2004).</li>
<li>Chen, E. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Similar+histologic+features+and+immunohistochemical+staining+in+microcystic+and+macrocystic+lymphatic+malformations%5BTitle%5D)+AND+%22Lymphat+Res+Biol%22%5BJournal%5D)">Similar histologic features and immunohistochemical staining in microcystic and macrocystic lymphatic malformations.</a> Lymphat Res Biol. 7 (2), 75-80 (2009).</li>
<li>Norgall, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Elevated+expression+of+VEGFR-3+in+lymphatic+endothelial+cells+from+lymphangiomas%5BTitle%5D)+AND+%22BMC+cancer%22%5BJournal%5D)">Elevated expression of VEGFR-3 in lymphatic endothelial cells from lymphangiomas.</a> BMC cancer. 7 (2), 75-80 (2007).</li>
<li>Garzon, M. C., Huang, J. T., Enjolras, O., Frieden, I. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vascular+malformations%5BTitle%5D)+AND+%22Part+I.+J+Am+Acad+Dermatol%22%5BJournal%5D)">Vascular malformations.</a> Part I. J Am Acad Dermatol. 56 (3), 353-370 (2007).</li>
<li>Osborn, A., Dickie, P., Adams, D., Dickie, B. 20th International workshop on Vascular Anomalies. ISSVA. , Melbourne, Australia. (2014).</li>
<li>Baluk, P., McDonald, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Markers+for+microscopic+imaging+of+lymphangiogenesis+and+angiogenesis%5BTitle%5D)+AND+%22Ann+N+Y+Acad+Sci%22%5BJournal%5D)">Markers for microscopic imaging of lymphangiogenesis and angiogenesis.</a> Ann N Y Acad Sci. 1131, 1-12 (2008).</li>
<li>Lokmic, Z., Mitchell, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Engineering+the+microcirculation.+Tissue+engineering%5BTitle%5D)+AND+%22Part+B%2C+Reviews%22%5BJournal%5D)">Engineering the microcirculation. Tissue engineering.</a> Part B, Reviews. 14 (1), 87-103 (2008).</li>
<li>Lokmic, Z., Mitchell, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Visualisation+and+stereological+assessment+of+blood+and+lymphatic+vessels%5BTitle%5D)+AND+%22Histol+Histopathol%22%5BJournal%5D)">Visualisation and stereological assessment of blood and lymphatic vessels.</a> Histol Histopathol. 26 (6), 781-796 (2011).</li>
<li>Hagerling, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+novel+multistep+mechanism+for+initial+lymphangiogenesis+in+mouse+embryos+based+on+ultramicroscopy%5BTitle%5D)+AND+%22EMBO+J%22%5BJournal%5D)">A novel multistep mechanism for initial lymphangiogenesis in mouse embryos based on ultramicroscopy.</a> EMBO J. 32 (5), 629-644 (2013).</li>
<li>Pollmann, C., Hagerling, R., Kiefer, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Visualization+of+lymphatic+vessel+development%2C+growth%2C+and+function%5BTitle%5D)+AND+%22Adv+Anat+Embryol+Cell+Biol%22%5BJournal%5D)">Visualization of lymphatic vessel development, growth, and function.</a> Adv Anat Embryol Cell Biol. 214, 167-186 (2014).</li>
<li>Breiteneder-Geleff, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Angiosarcomas+express+mixed+endothelial+phenotypes+of+blood+and+lymphatic+capillaries%3A+podoplanin+as+a+specific+marker+for+lymphatic+endothelium%5BTitle%5D)+AND+%22Am+J+Pathol%22%5BJournal%5D)">Angiosarcomas express mixed endothelial phenotypes of blood and lymphatic capillaries: podoplanin as a specific marker for lymphatic endothelium.</a> Am J Pathol. 154 (2), 385-394 (1999).</li>
<li>Kaipainen, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Expression+of+the+fms-like+tyrosine+kinase+4+gene+becomes+restricted+to+lymphatic+endothelium+during+development%5BTitle%5D)+AND+%22Proc+Natl+Acad+Sci+U+S+A%22%5BJournal%5D)">Expression of the fms-like tyrosine kinase 4 gene becomes restricted to lymphatic endothelium during development.</a> Proc Natl Acad Sci U S A. 92 (8), 3566-3570 (1995).</li>
<li>Schacht, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((T1alpha%2Fpodoplanin+deficiency+disrupts+normal+lymphatic+vasculature+formation+and+causes+lymphedema%5BTitle%5D)+AND+%22EMBO+J%22%5BJournal%5D)">T1alpha/podoplanin deficiency disrupts normal lymphatic vasculature formation and causes lymphedema.</a> EMBO J. 22 (14), 3546-3556 (2003).</li>
<li>Kriehuber, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Isolation+and+characterization+of+dermal+lymphatic+and+blood+endothelial+cells+reveal+stable+and+functionally+specialized+cell+lineages%5BTitle%5D)+AND+%22J+Exp+Med%22%5BJournal%5D)">Isolation and characterization of dermal lymphatic and blood endothelial cells reveal stable and functionally specialized cell lineages.</a> J Exp Med. 194 (6), 797-808 (2001).</li>
<li>Florez-Vargas, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Comparative+analysis+of+D2-40+and+LYVE-1+immunostaiing+in+lymphatic+malformations%5BTitle%5D)+AND+%22Lymphology%22%5BJournal%5D)">Comparative analysis of D2-40 and LYVE-1 immunostaiing in lymphatic malformations.</a> Lymphology. 41 (3), 103-110 (2008).</li>
<li>Makinen, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((PDZ+interaction+site+in+ephrinB2+is+required+for+the+remodeling+of+lymphatic+vasculature%5BTitle%5D)+AND+%22Genes+Dev%22%5BJournal%5D)">PDZ interaction site in ephrinB2 is required for the remodeling of lymphatic vasculature.</a> Genes Dev. 19 (3), 397-410 (2005).</li>
<li>Connell, F. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Analysis+of+coding+regions+of+VEGFR3+and+VEGFRC+in+Milroy+disese+and+other+primary+lymphoedemas%5BTitle%5D)+AND+%22Hum+Genet%22%5BJournal%5D)">Analysis of coding regions of VEGFR3 and VEGFRC in Milroy disese and other primary lymphoedemas.</a> Hum Genet. 124 (6), 625-631 (2009).</li>
</ol>

The authors have nothing to disclose.

LECs play an important role in maintaining fluid homeostasis, immune response to foreign antigens and absorption and transport of some nutrients. LEC homeostasis can be affected by disease processes such as bacterial infections and tumor metastasis, but LECs can also develop somatic mutations that result in formation of dysfunctional lymphatic vessels and significant morbidity for affected patients. To gain more understanding of lymphatic malformation etiology through in vivo implantation and ex vivo experimentation, and discover new treatment options, we first developed an LEC isolation method based on magnetic bead selection strategy using CD34NegCD31Pos selection strategy15. However, the resulting cultures often contained cells other than endothelial cells that were difficult to remove. Subsequently, the method was refined by using FACS to sort LECs that express CD34LowCD31PosVEGR3PosPODOPLANINPos phenotype. This approach resulted in relatively homogenous LEC cultures containing &#60;0.5% of non- CD34LowCD31PosVEGR3PosPODOPLANINPos cells on post-sorting check. In practical terms, the advantage of sorting cells by FACS is that reduction of non- LECs presence to &#60;0.5%. Cultured LECs and LM LECs have a typical cobblestone morphology and become senescent around passage 13.
In this study we have described a flow cytometry based protocol for the isolation and culture of highly enriched LECs from normal and abnormal tissues based on their expression of a suite of cell surface markers (CD34LowCD31PosVEGR3PosPODOPLANINPos). Cells were sorted from primary tissues following 5-7 days of in vitro expansion, a step that resulted in substantial enrichment of LEC compared to their frequency in tissues at the time of isolation. During surgery we obtain tissues ranging from several micrograms to tens of grams in weight. This tissue can vary greatly in its composition with respect to volume of lymphatic malformation vessels present, tissue scarring and presence of lymphatic malformation cyst thrombi. All these components will influence how many cells can be isolated from the diseased tissue. Hence the starting cell number can range from few thousand cells to several million cells. Similarly, this will influence the composition of the cell suspension and starting cell numbers meaning that the number of sorted cells will also differ from one sample to another.
The frequency of LECs in unsorted foreskin samples following 5-7 days in culture ranges from 0.52% to 4.7%, whereas LM LECs range from 0.8% to 12.43%. The LEC cultures comprised &#62;99% CD34LowCD31PosVEGR3PosPODOPLANINPos cells after post-sorting re-analysis and maintained a typical cobblestone morphology in culture until senescence at passage ~13 without overgrowth by non-endothelial elements.
It is necessary to expand cells ex&#160;vivo following initial tissue digestion and sorting because the yield of either foreskin or lymphatic malformation cells is generally low. Thus, the prior expansion of lymphatic endothelial cells in vitro allows the generation of the ~2x106 cells needed to seed a mouse chamber. This requires an in vitro expansion stage of 5-7 days. While we accept that cell culture may induce phenotypic changes in the primary cells, we have shown that these cultured cells retain their capacity to form lymphatic malformation-like structures in a mouse xenograft model15.
There are several critical steps within the protocol that determine the degree of success when sorting cells by FACS. The most critical step is the time of exposure of the cells to collagenase and dispase during isolation from the primary tissues as described in step 2.7. This is not only influenced by the amount and type of tissue present but also by the batch of enzymes used. In addition, fluorescently labelled antibodies used to characterize the cell populations need to be titrated and preferably monoclonal. We tested several different cell detachment solutions such as trypsin/EDTA, EDTA, TrypLE Select and cell detachment solution. We found that EDTA had to be used for a prolonged period of time to detach cells and residual cell clumps often remained. In contrast, single cell suspensions were generated within 3-5 minutes of incubation in Trypsin/EDTA, cell detachment solution and TrypLE Select. We found no substantial difference in the expression of CD31, CD34, Podoplanin and VEGFR-3 following treatment with any of the enzyme solutions. Single stained samples should also be done with every sorting experiment to ensure that fluorochrome emission spectra do not overlap and therefore give incorrect readings. These critical steps also constitute steps where modifications to the cell protocol might be required or troubleshooting during the flow cytometry sorting.
When compared to our previously published magnetic bead isolation of LECs 15, the advantage of isolating LECs by FACS includes the following: more rapid isolation of cells with high purity and identification of discrete cell subsets and rare populations within a heterogeneous sample. The major limitations of FACS-based LEC and LM LEC isolation revolves around limited number of cells available for validation following cell sorting results. In addition, while every attempt is made to standardize our assays and instrument set-up, these same parameters may not necessarily be reproducible in other laboratories. Therefore, some variability in the results may occur. In addition, one of the issues that lymphatic biologists face is the absence of cell specific markers that would differentiate between initial capillary LEC markers and collecting capillary LEC markers. At this stage, we have not yet identified LEC markers that would distinguish between healthy LECs and LM LECs. Since lymphatic malformation tissue also contains normal-looking lymphatic vessels (Figure 1A), the resulting CD34LowCD31PosVEGR3PosPODOPLANINPos will contain a proportion of normal LECs as well as those of the diseased phenotype. Future studies examining LEC and LM LEC gene expression and proteomics may be able to direct us towards more specific LM LEC markers that could distinguish LM LECs from LECs in the same tissue.
In the future, we expect to utilize FACS and these new LEC markers in attempt to identify rare subsets of LEC populations both in foreskin and lymphatic malformations. This would allow us to isolate these cell populations and study their role in the development of the lymphatic vascular system and lymphatic malformations.
Isolating LECs and LM LECs based on CD34LowCD31PosVEGR3PosPODOPLANINPos significantly reduced non-endothelial cell contamination. Furthermore, the FACS technology allows us to separate LECs into subtypes based on the expression of CD31, PODOPLANIN and VEGFR-3 cell surface markers and to understand this in the context of cell lineage development. For diseased LECs, this allows for cell-specific studies that will shed further light on genes causing LEC diseases and LEC capacity to respond to various cell stimuli in vitro and in animal xenograft models.

A major function of the lymphatic vascular system is to absorb lymph, an excess interstitial fluid containing lipids, proteins and cellular components, and conduct it to the blood venous system. A network of lymphatic capillaries directs lymph to the lymph nodes where it is screened for presence of foreign antigens, an important process in immune surveillance and deployment of white blood cells to neutralize foreign antigens.
The uni-directional lymphatic system starts in tissues with the initial lymphatic capillary, a unique structure with a discontinuous single layer of thin-walled flat endothelial cells with specialized cell junctions that permit lymph entry1,2. These capillaries are attached to the neighboring connective tissue matrix via anchoring filaments to prevent vessel collapse in presence of increased interstitial pressure3. The initial lymphatic capillaries empty into collecting lymphatic capillaries that coalesce into larger lymphatic vessels or veins. In comparison to initial lymphatic capillary vessels, collecting lymphatic vessels have thicker vessel walls, paired lymphatic valves and are encased by a discontinuous basement membrane in which a few smooth muscle cells are embedded4. Coordinated opening and closure of lymphatic valves and contraction of smooth muscle cells facilitates flow of lymph3. In humans, the lymphatic veins from various regions of the body join to form lymphatic trunks which merge to form two lymphatic ducts: the thoracic duct and the right lymphatic duct. The thoracic duct drains lymph from the left side of the body and from the right side below the chest while the right lymphatic duct drains lymph from the right arm and right side of the head, neck, and thorax. Both ducts conduct lymph into the subclavian veins in the neck5.
Disorders of the lymphatic system are broadly grouped into acquired and congenital (Table 1). Examples of acquired conditions are lymphangitis and secondary lymphedema. Lymphangitis is an inflammation of a lymphatic vessel due to bacterial infection. The affected lymphatics dilate and fill with exudate containing polymorphonuclear cells. In skin, these lymphatics are visible as red, painful subcutaneous streaks often accompanied by enlargement of the associated draining lymph node (lymphadenitis)6. Secondary lymphedema arises as a consequence of damage or obstruction to the lymphatic vessel or lymph node obstruction. This leads to chronic progressive swelling due to accumulation of lymph distal to the damage or obstruction. In developed countries, secondary lymphedema is most commonly associated with malignancy where metastasizing tumors obstruct lymphatic vessels or regional lymph nodes, or as a consequence of anti-cancer therapy following surgical removal of lymph nodes, post-irradiation fibrosis and post-inflammatory thrombosis and scarring7. In other parts of the world, secondary lymphedema may be secondary to lymphatic obstruction caused by parasitic worms such as Wuchereria bancrofti6.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td colspan="4">Disorders of Lymphatic Vascular System</td>
		</tr>
		<tr>
			<td>Acquired</td>
			<td colspan="3">Congenital</td>
		</tr>
		<tr>
			<td rowspan="3">Lymphadenitis 
			Secondary lymphedema</td>
			<td>Primary Lymphedema10</td>
			<td>Sporadic Lymphatic Malformations13</td>
			<td>Lymphatic Malformations Associated with Syndromes13</td>
		</tr>
		<tr>
			<td rowspan="2">e.g. 
			Milroy Syndrome 
			Meige Syndrome</td>
			<td>Simple: 
			Lymphatic malformations</td>
			<td rowspan="2">e.g. 
			Klippel-Tranaunay Syndrome 
			Parks Weber Syndrome 
			Sturge-Weber Syndrome</td>
		</tr>
		<tr>
			<td>Combined: 
			Capillary-lymphatic malformations 
			Capillary-lymphatic-venous malformation 
			Capillary-lymphatic-arteriovenous malformation 
			Capillary-lymphatic venous-arteriovenous malformation</td>
		</tr>
	</tbody>
</table>
Table 1. Overview of the disorders of lymphatic vascular system.
Congenital disorders of the lymphatic system include primary (idiopathic) lymphedema thought to be caused by genetic mutations, lymphangiectasia and anomalies of the lymphatic system8,9. Primary lymphedema can be sporadic presumably caused by de novo mutations, or inherited. Lymphatic disorders can also be isolated or comprise part of a more generalized syndrome10. In the pediatric population, 97% of lymphedema is sporadic with abnormalities in lymphatic vessel structure that impair regional lymph drainage11. Milroy disease is an example of primary lymphedema caused by mutation in the VEGFR-3 gene evident at birth or soon after12. Although mostly familial condition, the Milroy disease can also be identified in infants without family history of Milroy disease32. The severity of any lymphedema is dependent on the amount of lymph production and ability to transport lymph back to venous circulation6.
Based on clinical presentation and in situ endothelial cell proliferation, anomalies of the lymphatic system are classified as lymphatic tumors or lymphatic malformations13. Kaposiform lymphangiomatosis is an example of an LEC tumor14. Lymphatic malformations are thought to arise during embryonic development and grow in proportion to the child15,16. They rarely regress but can remain asymptomatic until trauma or infection precipitates rapid growth leading to clinical complications. The orderly structure of lymphatic network and conduction of lymph from the tissue to venous circulation described above is perturbed in lymphatic malformations which consist of localized collections of abnormal cystic structures filled with lymphatic fluid. While there is no clinical or experimental evidence that these cystic vessels are connected to the lymphatic circulation or that they contain functional lymphatic valves, their lymphatic identity is confirmed by expression of range of lymphatic cell markers such as PODOPLANIN, CD31, Lymphatic Vessel Endothelial Receptor 1 (LYVE-1), Prospero homeobox protein 1 (PROX-1) and VEGFR-315,17,18. These cystic structures can be either small (microcystic) or large (macrocystic), but most lymphatic malformations contain both microcystic and macrocystic components (Figure 1)16. Following surgery, injection sclerotherapy and/or radiofrequency ablation the lymphatic malformations often reoccur.
<img alt="Figure 1" src="/files/ftp_upload/52691/52691fig1highres.jpg" width="700" /> 
Figure 1. Morphology of human lymphatic vessels and lymphatic malformations. Normal human lymphatic (A) and lymphatic malformation vessels (B and C) labelled with antibody to PODOPLANIN (brown label, arrow). Human lymphatic malformation vessels are characterized by marked dilation and considerable variation in lumen size. These localized abnormal cystic structures can be either small (microcystic, *) (B) or large (macrocystic, #) (C). Most lymphatic malformations contain both microcystic and macrocystic components. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52691/52691fig1highres.jpg" target="_blank">Please click here to view a larger version of the figure.</a>
Some investigators have suggested that lymphatic malformations represent a developmental disorder of lymphatic vasculature in which the LECs do not have abnormal growth potential but instead have failed to connect to the normal circulation19. However, we have found that the LM LECs proliferate faster and are more resistant to apoptosis than foreskin LECs15 suggesting that there is a primary defect in the LM LECs. When LM LECs are implanted in a mouse xenograft model, they form structures reminiscent of lymphatic malformations15. This supports a hypothesis that lymphatic malformations may be caused by one or more somatic mutations arising in LM LECs during fetal development. Indeed, recent reports have identified one such mutation in the p110&#945; catalytic subunit of Phosphoinositide-3-Kinase (PIK3CA) gene20.
Given the advances in DNA sequencing technology, relevant mutations could be more readily identified in isolated LM LECs, guiding future studies of these conditions. The isolation of viable LECs would facilitate comparisons between abnormal and normal LECs in assays such as migration, proliferation, tube forming ability and survival in response to reduced nutrient availability or pro-apoptotic agents15. Isolated LECs would further enable us to perform cell-specific gene expression and proteomic studies, to delineate new LEC subpopulations and discover novel pharmacological agents suitable for clinical management of lymphatic malformations.
We have previously published a LEC isolation method based on magnetic bead separation of LECs from neonatal foreskin and lymphatic malformations15. We reported a strategy of separating normal and diseased LECs from vascular endothelial cells based on the absence of CD34 expression, followed by subjecting CD34Neg cell fraction to positive selection for CD31. However, this method was hampered by the presence of residual non-endothelial cells. This was independent of removing epidermis prior to subsequent connective tissue digestion. These contaminants generally proliferated more rapidly and thus eventually overgrew the endothelial cell cultures despite subsequent attempts to repeat LEC isolation. Indeed, an initial contamination of non-endothelial cells as low as 2% to 5% was sufficient to overwhelm the LEC population15. This prompted us to explore fluorescently activated cell sorting method as an option to improve LEC cell yield and purity. In addition, we used multi-parameter sorting to enhance the specificity of the LEC populations, adding VEGFR-3 and PODOPLANIN to the selection markers to identify CD34LowCD31PosVEGFR-3PosPODOPLANINPos LECs.
The rationale for selecting these markers was based on the reports that while LECs and blood vascular endothelial cells have many cell surface markers in common such as CD31, LECs show phenotypic variation in their expression of CD34, PODOPLANIN and VEGFR-3 cell surface marker when compared to blood vascular endothelial cells21-23. CD31 is a 130 kDa transmembrane glycoprotein also known as platelet endothelial cell adhesion molecule 1 (PECAM-1). It is considered to be a pan-endothelial cell marker since it is expressed on all types of blood and lymphatic vessels21,24,25. CD34 is 110-kDa transmembrane glycoprotein present on most hematopoietic progenitor and stem cells, vascular endothelial cells and some lymphatic vessels26.
VEGFR-3, the receptor for vascular endothelial growth factors C and D, is initially present on the developing veins in the mouse embryo, but following lymphatic specification regulated by the transcription factors SRY-related HMG-box (SOX)-18, chicken ovalbumin upstream promoter transcription factor 2 (COUPTF-II) and PROX-1, VEGFR-3 venous expression is lost and it becomes restricted to embryonic LECs25,27. PODOPLANIN, a 38 kDa membrane mucoprotein, is first noted on lymphatic vessels at approximately embryonic day 11 (~E11.0) of mouse embryonic development 28 and whilst it is strongly expressed by microvascular lymphatic vessels, PODOPLANIN expression by macrocystic lymphatic endothelium in lymphatic malformations is more variable15. Flow cytometry experiments suggest that at least some CD34HighCD31Pos endothelial cells express the lymphatic marker PODOPLANIN29. Although systematic evaluation of LYVE-1 and PODOPLANIN staining in human lymphatic malformations showed that both are effective at staining lymphatic malformation endothelium30, in normal tissues, LYVE-1 was reported to be strongly present in the initial lymphatic capillary endothelium but reduced and even absent in the collecting lymphatic endothelium31. As our aim is to isolate both the initial and collecting lymphatic endothelial cells we have opted not to use LYVE-1 as part of our cell selection strategy. Finally, the decision to employ these markers was also based on the availability of antibodies that are used diagnostically for labelling lymphatic vessels for microscopic imaging, a feature that would permit correlation between flow cytometry and immunofluorescent studies.
This article will describe the tissue digestion method, cell staining and FACS settings required for successful isolation of CD34LowCD31PosVEGFR-3PosPODOPLANINPos LECs as well as CD34HighCD31PosVEGFR-3PosPODOPLANINPos endothelial cells from foreskin and lymphatic malformation tissue.

<table><tbody><tr><td>DMEM</td><td>Life Technologies (Gibco)</td><td>11965-092</td><td>Used to collect tissue samples from the operating theatre.</td></tr><tr><td>EGM-2 MV Bullet Kit</td><td>Lonza</td><td>CC-3202</td><td>EGM-2 MV Bullet Kit contains 500 ml of EBM-2 media and human EGF, hydrocortisone, gentamycin (GA-1000), fetal bovine serum (FBS), VEGF, human FGF-b, R&lt;sup&gt;3&lt;/sup&gt;-IGF-1 and ascorbic acid.</td></tr><tr><td>VEGF-C</td><td>R&amp;amp;D Systems</td><td>2179-VC-025</td><td>Complete endothelial cell media is supplemented with 50 ng/ml VEGF-C</td></tr><tr><td>Antibiotic-antimycotic solution (100x)</td><td>Life Technologies (Gibco)</td><td>15240-062</td><td>This solution contains 10,000&amp;nbsp;U/ml of penicillin, 10,000&amp;nbsp;mg/ml of streptomycin and 25&amp;nbsp;mg/ml of Fungizone antimycotic. Use at 1:100 dilution.</td></tr><tr><td>Fibronectin from human plasma</td><td>Sigma-Aldrich</td><td>F2006</td><td>Used at 10 mg/ml concentrations. It can be re-used for up to 1 month if kept at 4&amp;nbsp;&amp;#176;C and maintained sterile. Use 7&amp;nbsp;ml to coat 150 cm&lt;sup&gt;2&lt;/sup&gt; flask.</td></tr><tr><td>StemPro Accutase Cell dissociation reagent</td><td>Life Technologies (Gibco)</td><td>A11105-01</td><td>StemPro&amp;reg;Accutase&amp;reg; is used at 0.05 ml per cm&lt;sup&gt;2&lt;/sup&gt; to cover the entire surface area of the flask. Using lesser volumes may result in incomplete cell detachment.</td></tr><tr><td>0.4% Trypan Blue dye</td><td>Life Technologies (Gibco)</td><td>15250-061</td><td>Used as a viability stain.</td></tr><tr><td>Dispase II</td><td>Roche Applied Biosciences</td><td>4942078001</td><td>Used at 0.04%</td></tr><tr><td>Collagenase II</td><td>Worthington Lab</td><td>4176</td><td>Used at 0.25%</td></tr><tr><td>DNase I</td><td>Roche Applied Biosciences</td><td>11284932001</td><td>Used at 0.01%</td></tr><tr><td>70 mm nylon cell strainers</td><td>BD Falcon</td><td>352350</td><td></td></tr><tr><td colspan="4">[header]</td></tr><tr><td>PE-conjugated VEGFR-3 clone 9D9F9, clone WM59</td><td>BioLegend</td><td>356204</td><td>Used at 1:50 dilution</td></tr><tr><td>PE-Cy7-conjugated CD34, clone 581</td><td>BioLegend</td><td>343516</td><td>Used at 1:200 dilution</td></tr><tr><td>APC-conjugated mouse anti human CD31, clone WM59</td><td>BioLegend</td><td>303116,</td><td>Used at 1:100 dilution</td></tr><tr><td>Alexa 488-conjugated rat anti human Podoplanin, clone NC-80.</td><td>BioLegend</td><td>337006</td><td>Used at 1:200 dilution</td></tr><tr><td>PE-conjugated mouse IgG1, k isotype, clone MOPC-21</td><td>BioLegend</td><td>400112</td><td>Used at 1:50 dilution</td></tr><tr><td>PE-Cy7-conjugated mouse IgG1, k isotype, clone MOPC-21</td><td>BioLegend</td><td>400126</td><td>Used at 1:200 dilution</td></tr><tr><td>APC-conjugated mouse IgG1, k isotype, clone MOPC-21</td><td>BioLegend</td><td>400120</td><td>Used at 1:100 dilution</td></tr><tr><td>Alexa 488-conjugated mouse IgG2a, k isotype, clone RATK2758</td><td>BioLegend</td><td>400525</td><td>Used at 1:200 dilution</td></tr></tbody></table>

isolation of human lymphatic endothelial cells by multi-parameter fluorescence-activated cell sorting

Lymphatic system disorders such as primary lymphedema, lymphatic malformations and lymphatic tumors are rare conditions that cause significant morbidity but little is known about their biology. Isolating highly pure human lymphatic endothelial cells (LECs) from diseased and healthy tissue would facilitate studies of the lymphatic endothelium at genetic, molecular and cellular levels. It is anticipated that these investigations may reveal targets for new therapies that may change the clinical management of these conditions. A protocol describing the isolation of human foreskin LECs and lymphatic malformation lymphatic endothelial cells (LM LECs) is presented. To obtain a single cell suspension tissue was minced and enzymatically treated using dispase II and collagenase II. The resulting single cell suspension was then labelled with antibodies to cluster of differentiation (CD) markers CD34, CD31, Vascular Endothelial Growth Factor-3 (VEGFR-3) and PODOPLANIN. Stained viable cells were sorted on a fluorescently activated cell sorter (FACS) to separate the CD34LowCD31PosVEGFR-3PosPODOPLANINPos LM LEC population from other endothelial and non-endothelial cells. The sorted LM LECs were cultured and expanded on fibronectin-coated flasks for further experimental use.

Following initial tissue digestion, after 24 hours in culture of unfractionated samples, distinct endothelial cell colonies can be observed (Figure 2A) together with fibroblast-like cells and smooth muscle cells. Following sorting and after 24 hours in cell culture, the CD34LowCD31PosVEGFR-3PosPodoplaninPos cells attach and show typical cobblestone morphology (Figure 2B and C). Using the FACS method described above, we are able to purify cells up to 99.8% purity and distinguish them from CD34HighCD31PosVEGFR-3PosPodoplaninPos endothelial cells. Representative results of gating strategy and sorting are presented in Figure 3. This has resolved the issues experienced when using magnetic-bead isolation method. To date, we have passaged these cells up to passage 13. After this passage, the LM LECs and foreskin LECs start to senescence, accompanied by morphological changes and reduced cell division.
<img alt="Figure 2" src="/files/ftp_upload/52691/52691fig2.jpg" /> 
Figure 2. Foreskin LECs and LM-LEC. Twenty-four hours after enzymatic digestion, unsorted cells contain both endothelial (arrow) and non-endothelial cells (A). Following CD34LowCD31Pos VEGFR-3PosPodoplaninPos FACS cell isolation, foreskin LECs (B) and LM-LECs (C) are devoid of non-endothelial cells and maintain cobblestone morphology. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52691/52691fig2large.jpg" target="_blank">Please click here to view a larger version of the figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/52691/52691fig3.jpg" /> 
Figure 3. Fluorescence-activated cell sorting gating strategies for cell sorting of vascular and lymphatic endothelial cells. (A) Live cells are first gated on CD34 and CD31 expression, followed by VEGFR-3 and PODOPLANIN gating to sort vascular (B) and lymphatic endothelial (C) cells respectively. (D) Re-analysis of sorted CD34HighCD31PosVEGFR-3PosPODOPLANINPos cells shows &#62;98% vascular endothelial cell phenotype. (E) LEC cells sorted on CD34LowCD31PosVEGFR-3PosPODOPLANINPos phenotype are also &#62;98% pure. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/52691/52691fig3highres.jpg" target="_blank">Please click here to view a larger version of the figure.</a>

Watch this Scientific Journal Video about Isolation of Human Lymphatic Endothelial Cells by Multi-parameter Fluorescence-activated Cell Sorting at JoVE.com

Isolation of Human Lymphatic Endothelial Cells by Multi-parameter Fluorescence-activated Cell Sorting

The goal of this protocol is to isolate lymphatic endothelial cells lining human lymphatic malformation cyst-like vessels and foreskins using fluorescence-activated cell sorting (FACS). Subsequent cell culturing and expansion of these cells permits a new level of experimental sophistication for genetic, proteomic, functional and cell differentiation studies.

Lymphatic system disorders such as primary lymphedema, lymphatic malformations and lymphatic tumors are rare conditions that cause significant morbidity ...

isolation-human-lymphatic-endothelial-cells-multi-parameter

Nanyang Technological University

Research

JoVE Journal

Medicine

14.3K Views.  The Royal Children&#146;s Hospital.  Het doel van dit protocol is om lymfatische endotheelcellen voering de menselijke lymfatische misvorming cyste-achtige schepen en voorhuiden met fluorescentie-geactiveerde celsortering (FACS) te isoleren. Latere cel kweken en uitbreiding van deze cellen maakt een nieuw niveau van experimentele verfijning voor genetische, proteomics, functioneel en celdifferentiatie studies. 

Video: Isolation of Human Lymphatic Endothelial Cells by Multi-parameter Fluorescence-activated Cell Sorting

Isolation of Murine Lymph Node Stromal Cells

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and differentiation of lymphocytes. Various stromal cell subsets have been identified by the expression of the adhesion molecule CD31 and glycoprotein podoplanin (gp38), T zone reticular cells or fibroblastic reticular cells, lymphatic endothelial cells, blood endothelial cells and FRC-like pericytes within the double negative cell population. For all populations different functions are described including, separation and lining of different compartments, attraction of and interaction with different cell types, filtration of the draining fluidics and contraction of the lymphatic vessels. In the last years, different groups have described an additional role of stromal cells in orchestrating and regulating cytotoxic T cell responses potentially dangerous for the host. 
Lymph nodes are complex structures with many different cell types and therefore require a appropriate procedure for isolation of the desired cell populations. Currently, protocols for the isolation of lymph node stromal cells rely on enzymatic digestion with varying incubation times; however, stromal cells and their surface molecules are sensitive to these enzymes, which results in loss of surface marker expression and cell death. Here a short enzymatic digestion protocol combined with automated mechanical disruption to obtain viable single cells suspension of lymph node stromal cells maintaining their surface molecule expression is proposed.

Isolation of lymph node stromal cells is a multistep procedure including enzymatic digestion and mechanical disaggregation to obtain fibroblastic reticular cells, lymphatic and blood endothelial cells. In the described procedure, a short digestion is combined with automated mechanical disaggregation to minimize surface marker degradation of viable lymph node stromal cells.

Secondary lymphoid organs including lymph nodes are composed of stromal cells that provide a structural environment for homeostasis, activation and ...

Immunology and Infection

Lymphocyte Isolation from Human Skin for Phenotypic Analysis and Ex Vivo Cell Culture

Human skin has an important barrier function and contains various immune cells that contribute to tissue homeostasis and protection from pathogens. As the skin is relatively easy to access, it provides an ideal platform to study peripheral immune regulatory mechanisms. Immune resident cells in healthy skin conduct immunosurveillance, but also play an important role in the development of inflammatory skin disorders, such as psoriasis. Despite emerging insights, our understanding of the biology underlying various inflammatory skin diseases is still limited. There is a need for good quality (single) cell populations isolated from biopsied skin samples. So far, isolation procedures have been seriously hampered by a lack of obtaining a sufficient number of viable cells. Isolation and subsequent analysis have also been affected by the loss of immune cell lineage markers, due to the mechanical and chemical stress caused by the current dissociation procedures to obtain single cell suspension. Here, we describe a modified method to isolate T cells from both healthy and involved psoriatic human skin by combining mechanical skin dissociation using an automated tissue dissociator and collagenase treatment. This methodology preserves expression of most immune lineage markers such as CD4, CD8, Foxp3 and CD11c upon the preparation of single cell suspensions. Examples of successful CD4+ T cell isolation and subsequent phenotypic and functional analysis are shown.

Lymphocyte Isolation from Human Skin for Phenotypic Analysis and Ex Vivo Cell Culture

We describe a protocol to efficiently isolate skin resident T cells from human skin biopsies. This protocol yields sufficient numbers of viable human skin resident lymphocytes for flow cytometric analysis and ex vivo culture.

Human skin has an important barrier function and contains various immune cells that contribute to tissue homeostasis and protection from pathogens. As the ...

Isolation of Murine Retinal Endothelial Cells for Next-Generation Sequencing

Recent improvements in next-generation sequencing have advanced researchers&#39; knowledge of molecular and cellular biology, with several studies revealing novel paradigms in vascular biology. Applying these methods to models of vascular development requires the optimization of cell isolation techniques from embryonic and postnatal tissues. Cell yield, viability, and purity all need to be maximal to obtain accurate and reproducible results from next-generation sequencing approaches. The neonatal mouse retinal vascularization model is used by researchers to study mechanisms of vascular development. Researchers have used this model to investigate mechanisms of angiogenesis and arterial-venous fate specification during blood vessel formation and maturation. Applying next-generation sequencing techniques to study the retinal vascular development model requires optimization of a method for the isolation of retinal endothelial cells that maximizes cell yield, viability, and purity. This protocol describes a method for murine retinal tissue isolation, digestion, and purification using fluorescence-activated cell sorting (FACS). The results indicate that the FACS-purified CD31+/CD45- endothelial cell population is highly enriched for endothelial cell gene expression and exhibits no change in viability for 60 min post-FACS. Included are representative results of next-generation sequencing approaches on endothelial cells isolated using this method, including bulk RNA sequencing and single-cell RNA sequencing, demonstrating that this method for retinal endothelial cell isolation is compatible with next-generation sequencing applications. This method of retinal endothelial cell isolation will allow for advanced sequencing techniques to reveal novel mechanisms of vascular development.

This protocol describes a method for the isolation of murine postnatal retinal endothelial cells optimized for cell yield, purity, and viability. These cells are suitable for next-generation sequencing approaches.

Recent improvements in next-generation sequencing have advanced researchers&#39; knowledge of molecular and cellular biology, with several studies ...

Developmental Biology

Isolating Lymphocytes from the Mouse Small Intestinal Immune System

The intestinal immune system plays an essential role in maintaining the barrier function of the gastrointestinal tract by generating tolerant responses to dietary antigens and commensal bacteria while mounting effective immune responses to enteropathogenic microbes. In addition, it has become clear that local intestinal immunity has a profound impact on distant and systemic immunity. Therefore, it is important to study how an intestinal immune response is induced and what the immunologic outcome of the response is. Here, a detailed protocol is described for the isolation of lymphocytes from small intestine inductive sites like the gut-associated lymphoid tissue Peyer&#39;s patches and the draining mesenteric lymph nodes and effector sites like the lamina propria and the intestinal epithelium. This technique ensures isolation of a large numbers of lymphocytes from small intestinal tissues with optimal purity and viability and minimal cross compartmental contamination within acceptable time constraints. The technical capability to isolate lymphocytes and other immune cells from intestinal tissues enables the understanding of immune responses to gastrointestinal infections, cancers, and inflammatory diseases.

Here we describe a detailed protocol for the isolation of lymphocytes from the inductive sites including the gut-associated lymphoid tissue Peyer&#39;s patches and the draining mesenteric lymph nodes, and the effector sites including the lamina propria and the intestinal epithelium of the small intestinal immune system.

The intestinal immune system plays an essential role in maintaining the barrier function of the gastrointestinal tract by generating tolerant responses to ...

Digestion of the Murine Liver for a Flow Cytometric Analysis of Lymphatic Endothelial Cells

Within the liver, lymphatic vessels are found within the portal triad, and their described function is to remove interstitial fluid from the liver to the lymph nodes where cellular debris and antigens can be surveyed. We are very interested in understanding how the lymphatic vasculature might be involved in inflammation and immune cell function within the liver. However, very little has been published establishing digestion protocols for the isolation of lymphatic endothelial cells (LECs) from the liver or specific markers that can be used to evaluate liver LECs on a per cell basis. Therefore, we optimized a method for the digestion and staining of the liver in order to evaluate the LEC population in the liver. We are confident that the method outlined here will be useful for the identification and isolation of LECs from the liver and will strengthen our understanding of how LECs respond to the liver microenvironment.

The goal of this protocol is to identify lymphatic endothelial cell populations within the liver using described markers. We utilize collagenase IV and DNase and a gentle mincing of tissue, combined with flow cytometry, to identify a distinct population of lymphatic endothelial cells.

Within the liver, lymphatic vessels are found within the portal triad, and their described function is to remove interstitial fluid from the liver to the ...

Isolation of Uterine Innate Lymphoid Cells for Analysis by Flow Cytometry

Described here is a simple method to isolate and phenotype mouse group 1 uterine innate lymphoid cells (g1 uILCs) from individual pregnant uterus by flow cytometry. The protocol describes how to set up time mating to obtain multiple synchronous dams, the mechanical and enzymatic digestion of the pregnant uterus, the staining of single-cell suspensions, and a FACS strategy to phenotype and discriminate g1 uILCs. Although this method inevitably loses the spatial information of cellular distribution within the tissue, the protocol has been successfully applied to determine uILC heterogeneity, their response to maternal and foetal factors affecting pregnancy, their gene expression profile, and their functions.

This is a method to isolate uterine lymphoid cells from both pregnant and non-pregnant mice. This method can be used for multiple downstream applications such as FACS phenotyping, cell sorting, functional assays, RNA-seq, and proteomics. The protocol here demonstrates how to phenotype group 1 uterine innate lymphoid cells by flow cytometry.

Described here is a simple method to isolate and phenotype mouse group 1 uterine innate lymphoid cells (g1 uILCs) from individual pregnant uterus by flow ...

Isolating Malignant and Non-Malignant B Cells from lck:eGFP Zebrafish

Zebrafish (Danio rerio) are a powerful model to study lymphocyte development. Like mammals, D. rerio possess an adaptive immune system that includes B and T lymphocytes. Studies of zebrafish lymphopoiesis are difficult because antibodies recognizing D. rerio cell surface markers are generally not available, complicating isolation and characterization of different lymphocyte populations, including B-lineage cells. Transgenic lines with lineage-specific fluorophore expression are often used to circumvent this challenge. The transgenic lck:eGFP line has been used to study D. rerio T cell development, and has also been utilized to model T cell development and acute lymphoblastic leukemia (T-ALL). Although lck:eGFP fish have been widely used to analyze the T-lineage, they have not been used to study B cells. Recently, we discovered that many zebrafish B cells also express lck, albeit at lower levels. Consequently, lck:eGFP B cells likewise express low levels of GFP. Based on this finding, we developed a protocol to purify B-lineage cells from lck:eGFP zebrafish, which we report here. Our method describes how to utilize a fluorescent-activated cell sorter (FACS) to purify B cells from lck:eGFP fish or related lines, such as double-transgenic rag2:hMYC; lck:eGFP fish. In these lines, B cells, particularly immature B cells, express GFP at low but detectable levels, allowing them to be distinguished from T cells, which express GFP highly. B cells can be isolated from marrow, thymus, spleen, blood, or other tissues. This protocol provides a new method to purify D. rerio B cells, enabling studies focused on topics like B cell development and B lymphocyte malignancies.

Isolating Malignant and Non-Malignant B Cells from lck:eGFP Zebrafish

Transgenic lck:eGFP zebrafish express GFP highly in T lymphocytes, and have been used to study T cell development and acute lymphoblastic leukemia. This line can be used to study B cells, which express lck at lower levels. This protocol describes purification of malignant and non-malignant B cells from lck:eGFP zebrafish.

Zebrafish (Danio rerio) are a powerful model to study lymphocyte development. Like mammals, D. rerio possess an adaptive immune system that includes B and ...

Establishing In Vitro LLEC Cultures Using Magnetic Cell Selection

Harvest and Primary Culture of Leptomeningeal Lymphatic Endothelial Cells

Leptomeningeal lymphatic endothelial cells (LLECs) are a recently discovered intracranial cellular population with a unique distribution clearly distinct from peripheral lymphatic endothelial cells. Their cellular function and clinical implications remain largely unknown. Consequently, the availability of a supply of LLECs is essential for conducting functional research in vitro. However, there is currently no existing protocol for harvesting and culturing LLECs in vitro.
This study successfully harvested LLECs using a multi-step protocol, which included coating the flask with fibronectin, dissecting the leptomeninges with the assistance of a microscope, enzymatically digesting the leptomeninges to prepare a single-cell suspension, inducing the expansion of LLECs with vascular endothelial growth factor-C (VEGF-C), and selecting lymphatic vessel hyaluronic receptor-1 (LYVE-1) positive cells through magnetic-activated cell sorting (MACS). This process ultimately led to the establishment of a primary culture. The purity of the LLECs was confirmed through immunofluorescence staining and flow cytometric analysis, with a purity level exceeding 95%. This multi-step protocol has demonstrated reproducibility and feasibility, which will greatly facilitate the exploration of the cellular function and clinical implications of LLECs.

Author Spotlight: Unveiling Cellular Functions and Potential Clinical Implications of Leptomeningeal Lymphatic Endothelial Cells 

Leptomeningeal lymphatic endothelial cells (LLECs), a recently identified intracranial cell type, have poorly understood functions. This study presents a reproducible protocol for harvesting LLECs from mice and establishing in vitro primary cultures. This protocol is designed to enable researchers to delve into the cellular functions and potential clinical implications of LLECs.

Leptomeningeal lymphatic endothelial cells (LLECs) are a recently discovered intracranial cellular population with a unique distribution clearly distinct ...

Neuroscience

Isolating Endothelial Cells from Murine Dermal Lymphatic Capillaries

Murine Dermal Lymphatic Endothelial Cell Isolation

The lymphatic system participates in the regulation of immune surveillance, lipid absorption, and tissue fluid balance. The isolation of murine lymphatic endothelial cells is an important process for lymphatic research, as it allows the performance of in vitro and biochemical experiments on the isolated cells. Moreover, the development of Cre-lox technology has enabled the tissue-specific deficiency of genes that cannot be globally targeted, leading to the precise determination of their role in the studied tissues. The dissection of the role of certain genes in lymphatic physiology and pathophysiology requires the use of lymphatic-specific promoters, and thus, the experimental verification of the expression levels of the targeted genes.
Methods for efficient isolation of lymphatic endothelial cells from wild-type or transgenic mice enable the use of ex vivo and in vitro assays to study the mechanisms regulating the lymphatic functions and the identification of the expression levels of the studied proteins. We have developed, standardized and present a protocol for the efficient isolation of murine dermal lymphatic endothelial cells (DLECs) via magnetic bead purification based on LYVE-1 expression. The protocol outlined aims to equip researchers with a tool to further understand and elucidate important players of lymphatic endothelial cell functions, especially in facilities where fluorescence-activated cell sorting equipment is not available.

Author Spotlight: Magnetic Bead-Based Isolation of Murine Dermal Lymphatic Endothelial Cells

This paper describes a method for magnetic bead-based isolation of murine endothelial cells from dermal lymphatic capillaries. The isolated lymphatic endothelial cells can be used for downstream in vitro experiments and protein expression analysis.

The lymphatic system participates in the regulation of immune surveillance, lipid absorption, and tissue fluid balance. The isolation of murine lymphatic ...

Biology

Flow Cytometry and Fluorescence-Activated Cell Sorting (FACS): Isolation of Splenic B Lymphocytes

Source: Perchet Thibaut1,2,3, Meunier Sylvain1,2,3, Sophie Novault4, Rachel Golub1,2,3 
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur Institute, Paris, France 
2 INSERM U1223, Paris, France 
3 Universit&#233; Paris Diderot, Sorbonne Paris Cit&#233;, Cellule Pasteur, Paris, France 
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, Center for Translational Science, Pasteur Institute, Paris, France
The overall function of the immune system is to defend the body against infectious organisms and other invaders. White blood cells, or leukocytes, are the key players of the immune system. Upon infection, they are activated and initiate an immune response. Leukocytes can be divided into various sub-populations (e.g., myeloid cells, lymphocytes, dendritic cells) based on different parameters that can be biological, physical, and/or functional (e.g., size, granularity, and secretion). One way to characterize leukocytes is through their surface proteins, which are mainly receptors. Each leukocyte population expresses a specific combination of receptors (e.g., cytotoxic, activating, migration receptors) that can define subsets among populations. As the immune system encompasses a wide range of cell populations, it is essential to characterize them to decipher their participation in the immune response.
Flow cytometry (FC or FCM) is a widely used method for analyzing the expression of cell surface and intracellular molecules, characterizing and defining different cell types in a heterogenous cell mixture. Flow cytometers are composed of three main sub-systems: fluidics, optics, and electronics. The fluidics system transports the cells in a stream such that they pass in front of a laser one by one. The optics system consists of light sources (lasers) to illuminate the particles, optical filters to direct the resulting light, and fluorescent signals to appropriate detectors. Finally, the electronics system converts the detected light signals into electronic signals that can be processed by the computer. As an individual cell passes in front of the laser beam, it scatters light. A detector in front of the beam measures forward scatter (FS) and several detectors to the side measure side scatter (SC). The FS correlates with cell size and SC is proportional to the granularity of the cells. In this manner, cell populations can often be distinguished based on differences in their size and granularity alone.
In addition to analyzing a cell&#39;s size, shape, and complexity, flow cytometry is widely used for detecting the expression of cell surface receptors (1). This is accomplished by using fluorochrome-labelled monoclonal antibodies which bind to known cell-specific receptors. Upon excitation, these bound fluorochromes emit a light of specific wavelength, called emission wavelength, which can be detected and scored. Fluorescence measurements provide quantitative and qualitative data about fluorochrome-labeled cell surface receptors. Hematologists were first to use FC for the therapeutic follow up of immune cell populations (2). Now, it is used for a wide range of applications such as immunophenotyping, cell viability, gene expression, cell counting, and GFP analysis.
FACS (Fluorescent Activated Cell Sorter) is a specialized type of flow cytometry, which sorts a population of cells into subpopulation using fluorescent labelling. Just like conventional flow cytometry, first FS, SC, and fluorescent data are collected. Then, the machine applies a charge (negative or positive) and an electrostatic deflection system (electromagnets) facilitates the collection of charged droplets containing cells into appropriate tubes.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/10494/10494fig1.jpg" /> 
Figure 1: Schematic representation of FACS. Sample (1) is aspirated in the FACS (2) and passed in front of the laser (3). Cell fluorescence is sensed by fluorescence detectors (4). Finally, cells are incorporated in droplets and the cells of interest are deflected by deflection plates (5) and collected in a collection tube (6). The remaining cells go into the trash (7). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/10494/10494fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The sorting aspect of the FACS presents many advantages. Many tests can help understand the role of specific cells in immune system, such as analyses of gene expression like RT-qPCR, cell cycle, or cytokine secretion. However, cells should be purified upstream to obtain clear and specific results. Here, FACS comes in useful and the desired cells can be sorted with great purity, yielding highly reliable and reproducible results. FACS can also be used to sort cells based on nuclear or other intracellular staining and according to the presence, absence, and density of surface receptors. FACS is now a standard technique for the purification of subpopulations of cells and has the ability sort up to four populations simultaneously.
This lab exercise demonstrates how to isolate splenic leukocytes and then how to specifically sort B lymphoid cells from the splenic leukocyte cell mixture using FACS.

Isolation of Human Lymphatic Endothelial Cells by Multi-parameter Fluorescence-activated Cell Sorting

Samenvatting

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