Monoclonal antibodies to E92, an endothelial cell surface antigen

Targeting and imaging signature caveolar molecules in lungs

A major goal of molecular medicine is to target imaging agents or therapeutic compounds to a single organ. Targeting imaging agents to a single organ could facilitate the high-resolution, in vivo imaging of molecular events. In addition, genetic and acquired diseases primary to a single organ, such as cystic fibrosis, tuberculosis, lung cancer, pulmonary fibrosis, pulmonary hypertension, and acute respiratory distress syndrome, could be specifically targeted in the lung. By targeting and concentrating imaging agents or therapeutics to the lungs, deleterious side effects can be avoided with greater efficacy at much lower dosages. Pathologic changes can be identified earlier and followed over time. In addition, therapeutics that have been abandoned due to toxicities may find renewed utility when coupled with specific targeting agents such as antibodies. To achieve these goals, distinct molecular signatures must be found for each organ or disease-state.

Prognostic value of angiogenesis in operable non-small cell lung cancer

Tumour angiogenesis is an important factor for tumour growth and metastasis. Although some recent reports suggest that microvessel counts in non-small cell lung cancer are related to a poor disease outcome, the results were not conclusive and were not compared with other molecular prognostic markers. In the present study, the vascular grade was assessed in 107 (T1,2-N0,1) operable non-small cell lung carcinomas, using the JC70 monoclonal antibody to CD31. Three vascular grades were defined with appraisal by eye and by Chalkley counting: high (Chalkley score 7-12), medium (5-6), and low (2-4). There was a significant correlation between eye appraisal and Chalkley counting (P < 0.0001). Vascular grade was not related to histology, grade, proliferation index (Ki67), or EGFR or p53 expression. Tumours from younger patients had a higher grade of angiogenesis (P = 0.05). Apart from the vascular grade, none of the other factors examined was statistically related to lymph node metastasis (P < 0.0001). A univariate analysis of survival showed that vascular grade was the most significant prognostic factor (P = 0.0004), followed by N-stage (P = 0.001). In a multivariate analysis, N-stage and vascular grade were not found to be independent prognostic factors, since they were strongly related to each other. Excluding N-stage, vascular grade was the only independent prognostic factor (P = 0.007). Kaplan-Meier survival curves showed a statistically significant worse prognosis for patients with high vascular grade, but no difference was observed between low and medium vascular grade. These data suggest that angiogenesis in operable non-small cell lung cancer is a major prognostic factor for survival and, among the parameters tested, is the only factor related to cancer cell migration to lymph nodes. The integration of vascular grading in clinical trials on adjuvant chemotherapy and/or radiotherapy could substantially contribute in defining groups of operable patients who might benefit from cytotoxic treatment.

CD31 immunoreactivity in mesenchymal neoplasms of the skin and subcutis: report of 145 cases and review of putative immunohistologic markers of endothelial differentiation

CD31 has recently been reported as a specific marker of endothelial differentiation among non-hematopoietic human neoplasms. In order to address this contention in particular regard to tumors of the skin and subcutis, the authors undertook a comparative study that surveyed 145 mesenchymal lesions. The antibodies used were directed against CD31 (clone JC/70A) and CD34 (clone My10), and these were compared with binding of Ulex europaeus I agglutinin (UEA). Proliferations that were included in the category of vascular tumors included cavernous and capillary hemangiomas (17 cases); lymphangiomas (8); epithelioid ("histiocytoid") hemangiomas (3), papillary endovascular hemangioendothelioma (1), angiosarcoma (7), and Kaposi's sarcoma of the mixed angiomatoid and spindle-cell type (17). CD31-immunoreactivity was observed in 35 of 53 vascular lesions; the neoplastic cells in a single angiosarcoma and the spindle cells in each case of Kaposi's sarcoma (KS) were not labeled. In all of the latter tumors, however, staining for CD31 was identified in the endothelia of angiomatoid areas and non-neoplastic blood vessels. These results compared favorably with those seen with anti-CD34, which decorated 36 of 53 vascular tumors--including 8 of 17 KS cases--and UEA, which bound to the neoplastic cells of 36 lesions. In contrast, all of 92 non-endothelial tumors included in this study (34 nerve sheath tumors [30 benign; 4 malignant]; 39 fibrohistiocytic neoplasms [11 benign; 28 malignant]; 9 smooth muscle tumors [6 benign; 3 malignant]; 7 glomus tumors; and 3 giant cell fibroblastomas) were negative for CD31. UEA labeled 3 non-vascular neoplasms, whereas 38 lesions of that type were CD34-positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical evaluation of vascular neoplasms

Immunohistochemistry is of proven value in the evaluation of cutaneous vascular neoplasms. Nonetheless, the lack of sensitivity and specificity demonstrated by some endothelial markers requires that a panel of antibodies to other lineage-related determinants be applied in this context. Compared with electron microscopy, enzyme-linked antibody techniques can be applied in a cost-effective manner, with a satisfactory diagnostic result in most cases. The efficacy of these methods will likely improve as more sensitive and specific markers of endothelial differentiation are characterized. For the time being, the exclusion of non-endothelial proliferations remains an important aspect of the differential diagnosis of vascular tumors.

JC70: a new monoclonal antibody that detects vascular endothelium associated antigen on routinely processed tissue sections

A new monoclonal antibody, JC70, raised against a membrane preparation from a spleen affected by hairy cell leukaemia, recognises a membrane bound glycoprotein identical with that of the CD31 group of monoclonal antibodies. The antibody stains a fixation resistant epitope on endothelial cells in benign and malignant conditions in a wide variety of paraffin wax embedded tissue. JC70 stained malignant endothelial cells in 10 angiosarcomas with more consistency than monoclonal or polyclonal antibodies to factor VIII related antigen (FVIII-Rag). In four cases of Kaposi's sarcoma the antibody stained malignant endothelial cells but not spindle cells. It is concluded that antibody JC70 is of value for studying benign and malignant human vascular disorders in routinely processed tissue.

A human endothelial cell-restricted, externally disposed plasmalemmal protein enriched in intercellular junctions

We have raised an mAb to a previously undescribed 135-kD externally disposed integral membrane protein that is enriched in the intercellular junctional domain of cultured human umbilical vein endothelial cells. This protein localizes at the appositional surfaces of cells as they become confluent and is stably expressed in the junctional zones of confluent monolayers. This protein is expressed in situ on continuous endothelia of all blood vessels in all human tissues examined. Moreover, this protein, as determined by mAb immunocytochemistry, is not expressed by any other cell type. This protein may mediate endothelial-specific functions restricted to the intercellular domain. It may also serve as a unique cell surface marker for the identification and purification of human endothelial cells.

Monoclonal antibody-defined human endothelial antigens as vascular markers

A review is given of human endothelial antigens recognized by monoclonal antibodies and used as vascular markers. These antigens can be classified tentatively into two categories that partly overlap: 1) differentiation markers and 2) antigens involved in specific cellular functions. Monoclonal antibodies recognizing endothelial differentiation markers reacting with all types of human endothelium can be regarded as constitutive endothelial markers. Other differentiation markers have a restricted distribution that is associated with a subtype of endothelium. Although sensitivity of the markers is high in general, specificity for endothelium is not absolute, based on distribution studies in tissues or in cell lines. With the exception of PAL-E and EN-3/EN-4, it is not clear from the literature whether the antibodies also react with lymphatic endothelium. Immunohistochemical examination of other species indicate that only BW 200 is restricted to humans. Immunoelectron microscopy of microvascular cells in tissue specimens has revealed that the monoclonal antibodies recognizing differentiation antigens show different subcellular distribution patterns. PAL-E and BW 200 react with the luminal endothelial surface, in a local and diffuse pattern, respectively. Anti-Von Willebrand factor (i.e., Factor VIII-related ag) antibodies react with Weibel-Palade bodies but also with subendothelial structures. Applications of immunohistochemistry using monoclonal antibodies in diagnostic pathology include assessment of vascular invasion by cancer cells, and identification of endothelial neoplasms and related disorders. Because anti-Factor VIII-related antigen and BW 200 are applicable on formaldehyde-fixed and paraplast-embedded tissue, they are most suitable for histodiagnostic application. Immunohistochemistry using monoclonal antibodies recognizing endothelial antigens involved in specific cellular functions also may contribute to pathobiologic research on the characterization of blood-tissue barriers, e.g., in the tumor vascular bed.

Isolation, characterization, and long-term cultivation of porcine and murine cerebral capillary endothelial cells

We present a simple method for isolation and long-term cultivation of porcine and murine cerebral capillary endothelial cells (cEC). Two major points are made. First, that the "characteristic" morphology of the endothelial cells depends mainly on the presence of endothelial cell growth factors in the culture medium and second, that the identification of the cells as endothelial cells requires a special lectin instead of criteria used for large vessel endothelial cells, such as factor VIII staining or LDL uptake. Pure cerebral capillaries were isolated by means of a series of centrifugation steps; endothelial cells were released by collagenase treatment and cultivated on plastic petri dishes, which proved to be better for cell attachment than collagen or gelatin coating. The microvascular cells were cultivated in either the presence or absence of growth factors. Medium 199 + 10% FCS produced mainly spindle-shaped cells, growing in the "hills and valleys" pattern, which, if not passaged for weeks, showed three dimensional tubular structures. Cells of the "cobblestone" phenotype were promoted in medium 199 + 10% FCS, enriched with endothelial cell growth supplement (ECGS) and heparin (referred to as complete medium). These cells retained their phenotype for months and could be passaged up to 35 times till now. If ECGS and heparin were omitted from these cultures, the cells became elongated and resembled smooth muscle cells. This effect was reversible when the cells were transferred to complete medium. With cEC, cloned by limiting dilution, we noticed this reversal phenomenon as well. We used several markers to characterize the microvascular cells and could show that the lectin of Bandeiraea simplicifolia is a highly reliable marker for endothelial cells and that the monoclonal antibody alpha-sm-1 (anti-smooth muscle cell actin) is excellent for determining smooth muscle cells.

Hemangioma with Kaposi's sarcoma-like features: report of two cases

We describe two children with vascular neoplasms that resembled Kaposi's sarcoma in places. Both presented with intraabdominal masses and severe thrombocytopenia. At autopsy the tumors extensively infiltrated the peritoneum and retroperitoneum and surrounded or invaded numerous organs including the kidneys, pancreas, adrenal glands, gastrointestinal tract, mesentery, and lymph nodes in both cases, and spleen or bone marrow in one case each. The neoplasms were histologically identical and displayed two patterns: dilated vascular spaces (angiomatous areas) lined by flat endothelial-like cells and areas of spindle cells forming slitlike vascular spaces similar to those described in Kaposi's sarcoma. Tumor cells in both cases expressed markers for endothelial cells. The clinical and histologic character of these neoplasms differentiates them from Kaposi's sarcoma, hemangioendothelioma, and from conventional juvenile hemangioma.

Differential expression of cell surface glycoproteins on various organ-derived microvascular endothelia and endothelial cell cultures

Glycoproteins expressed on the luminal surfaces of microvascular endothelium derived from various murine organs were analyzed and compared with those expressed by cultured vascular endothelial cells. Cell-surface vascular proteins were radiolabeled in situ via intracardiac perfusion with lactoperoxidase/Na125I. Autoradiography confirmed that the radiolabel was restricted to the vessel lumen in most tissues. Controls contained 125I-labeled serum proteins to identify adsorbed serum components. Glycoproteins were analyzed by western enzyme-linked lectin analysis using detergent extracts of 125I-labeled microvessels isolated from different organs. The western transfers were probed with a panel of lectin-peroxidase conjugates to determine differences in protein glycosylation. The same transfers were also screened for exposed 125I-labeled cell-surface proteins by autoradiography. This dual analysis detected glycoprotein patterns unique for each organ. At least seven major proteins (Mr approximately 180 K, 130 K, 95 K, 80 K, 75 K, 60 K, 12 K) were common to microvessels derived from each organ; however, certain glycoproteins appeared to be expressed differentially in particular organs. For example, a Mr approximately 135 K WGA-binding glycoprotein was detected in brain microvessels, whereas another WGA-binding glycoprotein of Mr approximately 40 K was detected only in kidney. In lung microvessels, a Mr approximately 140 K WGA binding glycoprotein and a Mr approximately 55 K RCA-I-binding galactoprotein were expressed preferentially, and liver microvessels displayed Mr approximately 220 K protein and a Mr approximately 35 K PNA-binding galactoprotein. The cell-surface-iodinated protein profiles from in situ labeled microvessels were similar to profiles derived from cultured bovine aortic endothelial cells and several short-term endothelial cell cultures isolated from different organs. The results from this study suggest that organ-associated endothelia express glycoprotein fingerprints unique to each organ.

Monoclonal antibody to human endothelial cell surface internalization and liposome delivery in cell culture

A monoclonal antibody (mAb), E25, is described that binds to the surface of cultured human endothelial cells. Upon binding E25 is rapidly internalized and digested intracellularly. Selective liposome targeting to the surface of the cells is performed using a biotinylated E25 antibody and an avidin-biotin system. Up to 30% of the cell-adherent liposomal lipid is internalized.

MB1, a quail leukocyte-endothelium antigen: partial characterization of the cell surface and secreted forms in cultured endothelial cells

We describe here conditions allowing the selective growth in culture of embryonic capillary endothelial cells from quail yolk sac. Such cultures were set up to characterize an antigen present on the endothelial cell surface and to study whether it was secreted in the culture medium. This antigen, MB1, was previously evidenced by a monoclonal antibody raised to quail IgM heavy chain. It is present at the surface of all endothelial and hemopoietic cells (except mature erythrocytes) starting from the hemangioblast, the early mesodermal precursor of blood and vascular endothelial cells. The MB1 epitope is also found on quail plasma molecules of 80 and 125-200 kDa. By immunoprecipitation of either surface or metabolically labeled endothelial cellular material, we have chemically characterized MB1-bearing components as glycoproteins of apparent molecular mass ranging from 80 to 200 kDa and provided evidence for their release into the culture medium. This is consistent with the hypothesis that, in the quail, vascular endothelium participates in the secretion of the alpha-MB1-positive plasmatic components.

A monoclonal antibody reacting with endothelial cells of budding vessels in tumors and inflammatory tissues, and non-reactive with normal adult tissues

This report describes a monoclonal antibody (MAb) generated by immunization of mice with cell suspensions of capillary-rich fragments of mammary carcinomas. The antibody (EN 7/44) belongs to the IgM class and detects a 30.5 kDa antigen which is found in the cytoplasm of human placental and umbilical vein-endothelial cells (HUVEC) and on the surface of tumor endothelium. Using indirect immunofluorescence and immunoperoxidase techniques, we did not find the MAb in peripheral blood cells or in any human cell lines tested, nor in endothelial cells from normal, nonproliferating adult tissues. Positively staining endothelium was found in the placenta, the umbilical vein and in proliferating normal tissues (intestine). Positive endothelial cells were found in acute inflammatory reactions and in tumors. In the latter, the strongest reactions were seen in newly formed budding capillaries, which were identified by their reactivity with Ulex europaeus I-lectin and antibodies against F VIII-RAG. In tumor tissues, large vessels could be positively stained with the EN 7/44 antigen, in contrast to inflammatory tissues. It is concluded that endothelial cells at the tip of a budding capillary express distinct phenotypic characteristics.

Lymphatic and blood vessel invasion in breast carcinoma: a useful prognostic indicator?

Recent studies have presented compelling evidence to support the prognostic importance of peritumoral lymphatic and blood vessel invasion in breast cancer. This parameter appears to be particularly valuable in the hands of pathologists who are experienced in diseases of the breast and who have developed standardized criteria and expertise in their recognition. However, its application is seriously hampered by various factors, especially interobserver and intraobserver differences in interpretation. A more uniform and objective approach, such as the use of immunohistochemical techniques, may be helpful in overcoming these obstacles. This may render lymphatic and blood vessel invasion a reliably reproducible indicator that a practicing pathologist can utilize to recognize high-risk patients and recommend appropriate therapy. The extension of this approach to evaluate neoplasms of other organs--such as malignant melanomas and thyroid, uterine, and cervical carcinomas--should also be explored.

In situ labelling of vascular endothelium with fluorescent acetylated low density lipoprotein

Acetylated low density lipoprotein is metabolized by a receptor-mediated process in endothelial cells. We have used the lipoprotein labelled with the fluorescent probe 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate to localize endothelial cells lining blood vessels. Following intravenous injection of the labelled lipoprotein, the vascular sinusoids and all other hepatic blood vessels were clearly labelled in cryostat sections of mouse liver. The endothelium of other organs such as brain, kidney, and testis was also brightly labelled. In addition, the lipoprotein was used to label the endothelium of bovine aorta, the vasculature in the chick chorioallantoic membrane, and the vessels in a growing murine melanoma. These results demonstrate that the fluorescent-labelled lipoprotein can be used for in situ labelling of the endothelium from large as well as small blood vessels in a variety of species.

Podoendin. A new cell surface protein of the podocyte and endothelium

A new cell surface protein, podoendin, has been identified in Sprague-Dawley rats, and isolated using monoclonal antibody (mAb) G4. The distribution of podoendin is restricted to the surface of glomerular podocytes, urinary surface of the parietal epithelium of Bowman's capsule, and the luminal surface of endothelial cells. The antibody does not crossreact with podocytes or endothelia of human or mice. In newborn rats, the appearance of podoendin on glomerular epithelium is attendant on podocyte differentiation during glomerulogenesis of metanephrogenic vesicles. It disappears when podocytes retract and efface foot processes in tissue culture. Thus, podoendin appears to be a cell differentiation-dependent surface protein of podocytes. Podoendin is a protein of 62 kD mobility on 5% polyacrylamide gel electrophoresis. It stains intensely with Coomassie blue, but gives negative reactions to carbohydrate (periodic acid/Schiff reaction) and polyanions (alcian blue, colloidal iron, and carbocyanine). It is distinct from the major sialoglycoprotein of podocyte fuzzy coat, podocalyxin (11). Podoendin isolated and purified from endothelium of lungs appears to be identical with that from podocytes and endothelium of kidneys. Injection of mAb G4 into left ventricle of rats resulted in intense decoration of the endothelium and podocyte surface within 30 min. The decoration persisted throughout the 3-d period of observation. This was not accompanied by complement (C3) fixation. Preliminary results showed that the rats developed moderate proteinuria (100 mg/ml protein in urine), which was associated with the presence of hyaline droplets in renal tubules, on the third day. The proteinuria was not accompanied by effacement of podocyte pedicels. There were no morphologic alterations indicating glomerular or vascular injury in the kidneys.

Characterization of an apically derived epithelial membrane glycoprotein from bovine milk, which is expressed in capillary endothelia in diverse tissues

A glycoprotein (PAS IV) of apparent Mr 76,000 was purified from bovine milk-fat-globule membrane and partially characterized. PAS IV contained mannose, galactose, and sialic acid as principal sugars (approximately 5.3% total carbohydrate [wt/wt]) and existed in milk in at least four isoelectric variants. The glycoprotein appeared to be an integral membrane protein by several criteria. PAS IV was recovered in the detergent phase of Triton X-114 extracts of milk-fat-globule membrane at room temperature. When bound to membrane, PAS IV was resistant to digestion by a number of proteinases, although after solubilization with non-ionic detergents, the protein was readily degraded. Amino acid analysis of the purified protein revealed a high percentage of amino acids with nonpolar residues. The location of PAS IV was determined in bovine tissues by using immunofluorescence techniques. In mammary tissue, PAS IV was located on both the apical surfaces of secretory epithelial cells and endothelial cells of capillaries. This glycoprotein was also detected in endothelial cells of heart, liver, spleen, pancreas, salivary gland, and small intestine. In addition to mammary epithelial cells, PAS IV was also located in certain other epithelial cells, most notably the bronchiolar epithelial cells of lung. The potential usefulness of this protein as a specific marker of capillary endothelial cells in certain tissues is discussed.

Isolation and characterization of monoclonal antibodies reactive with endothelial cells

Monoclonal antibodies were generated to antigens on cultured human umbilical vein endothelial cells. Spleen cells from BALB/c mice, immunized with low passage cultures of human umbilical vein endothelial cells, were fused with the non-secretory myeloma line, P3 x 63Ag 8.653. Hybridoma supernatants were screened for the desired immunological reactivity using ELISA binding assays. Hybridomas secreting antibodies reacting with the immunizing endothelial cells, but not with peripheral blood mononuclear cells, were cloned by limiting dilution and three stable clones were chosen for study. Further testing by ELISA revealed that each antibody displayed a unique pattern of reactivity. One antibody, 14E5, reacted with the macrophage-like cell line DHL-2, cultured macrophages derived from peripheral blood monocytes, and macrophages derived from malignant effusions. The antibody failed to react with fibroblasts or bovine endothelial cells. The second antibody, 12C6, reacted with human and primate fibroblasts and endothelial cells derived from bovine arteries, but not with mature macrophages. The third clone, 10B9, reacted only with the immunizing endothelial cells and the immature-macrophage line U-937. All three antibodies failed to react with long-term human B or T lymphoblastoid cell lines, leukemic cell lines, or murine macrophage lines. None of the antibodies reacted with a battery of human epithelial derived cell lines or primary cultures of human epithelial cells. Indirect immunofluorescence assays revealed that the antigens were expressed on the cell surface. These antibodies should prove useful as differentiation markers of human endothelial cells and in studies of endothelial cell function.