Human high molecular weight-melanoma-associated antigen (HMW-MAA): a melanoma cell surface chondroitin sulfate proteoglycan (MSCP) with biological and clinical significance

The lack of effective conventional therapies for the treatment of advanced stage melanoma has stimulated interest in the application of novel strategies for the treatment of patients with malignant melanoma. Because of its expression in a large percentage of melanoma lesions and its restricted distribution in normal tissues, the high molecular weight-melanoma-associated antigen (HMW-MAA), also known as the melanoma chondroitin sulfate proteoglycan (MCSP), has been used to implement immunotherapy of melanoma. The potential clinical relevance of HMW-MAA/MCSP has stimulated investigations to characterize its structural properties and biological function in melanoma cells. Over the last 10 years, the field of HMW-MAA/MCSP research has seen tremendous growth. Specifically, a significant amount of information has been accumulated regarding (1) the structural characteristics of the HMW-MAA/MCSP, (2) its role in the biology of melanoma cells, and (3) the potential molecular mechanisms underlying the association between HMW-MAA/MCSP-specific immunity and survival prolongation in melanoma patients immunized with HMW-MAA/MCSP mimics. In this review, we summarize the characteristics of the HMW-MAA/MCSP in terms of its structure, antigenic profile, tissue distribution, and similarities with its counterparts in other animal species. Additionally, we discuss the role the HMW-MAA/MCSP plays in melanoma cell biology with emphasis on the recently identified signal transduction pathways triggered by the HMW-MAA/MCSP. Finally, we discuss the potential molecular mechanisms underlying the beneficial effect of anti-HMW-MAA/MCSP antibodies on the clinical course of the disease in patients with melanoma.     

Idiotypic cascade in the human high molecular weight melanoma-associated antigen system: Fine specificity and idiotypic profile of anti-anti-idiotypic monoclonal antibodies

The mouse anti-idiotypic (anti-id) monoclonal antibody (mAb) MK2–23 bears the internal image of the determinant defined by the syngeneic immunizing anti-human high molecular weight melanoma-associated antigen (HMW-MAA) mAb 763.74, since it induces anti-HMW-MAA antibodies in syngeneic and xenogeneic hosts. To dissect the humoral immune response induced by mAb MK2–23 at the clonal level, 1351 hybridomas were generated from a BALB/c mouse immunized with mAb MK2–23. Serological and immunochemical assays showed that the anti-anti-idiotypic (anti-anti-id) mAb GH827, GH1002 and GH1081 react only with the immunizing anti-id mAb MK2–23 and that the anti-anti-id mAb GH149, GH368, GH464, GH518, GH586, GH704, GH786 and GH1151 react with both mAb MK2–23 and HMW-MAA. The eight HMW-MAA binding anti-anti-id mAb resembled mAb 763.74 in their reactivity patterns with a panel of cell lines, although the extent of reactivity was lower. Staining of surgically removed melanoma lesions detected subtle differences in the reactivity patterns of the eight HMW-MAA binding anti-anti-id mAb. This finding in conjunction with the differential ability of the eight anti-anti-id mAb to inhibit the binding of anti-HMW-MAA mAb 763.74 to melanoma cells and to mAb MK2–23 and with the different avidity of the binding to mAb MK2–23 suggest diversity in the fine specificity of the eight HMW-MAA binding anti-anti-id mAb. Like mAb 763.74, the eight HMW-MAA binding anti-anti-id mAb express the idiotopes recognized by the anti-id mAb MK2–23 and MK2-120. In contrast, the three anti-anti-id mAb GH827, GH1002 and GH1081, which do not bind HMW-MAA binding anti-anti-id mAb to the antibodies elicited by the membrane-bound HMW-MAA corroborates the validity of the use of anti-id mAb MK2-23 as an immunogen to implement active specific immunotherapy in patients with malignant melanoma.     

Differential expression of markers for endothelial cells, pericytes, and basal lamina in the microvasculature of tumors and granulation tissue.

The structure and function of the tumor microvasculature is of great interest for cancer biology, diagnosis, and therapy. The distribution of endothelial cells, pericytes, and basal lamina in tumors is not well documented. In this study, the authors investigated the distribution of markers for these different components in a series of malignant human tumors and in human granulation tissue, both situations with extensive angiogenesis. Their results show a striking heterogeneity in the expression of markers for pericytes and endothelial cells between different tumors, but also within a single tumor lesion. To be able to distinguish between these two adjacent cell types decisively, all marker studies were carried out both on the light and the electron microscopical level and compared with staining results in granulation tissue of cutaneous wounds in healthy volunteers and of decubitus lesions. In granulation tissue of decubitus lesions, well-defined zones with increasing levels of maturation can be delineated. It was found that antibodies recognizing von Willebrand factor often failed to stain the tumor capillaries. Of the pericyte markers, alpha-smooth muscle actin was only locally expressed by pericytes in the tumor vasculature, whereas the high-molecular-weight melanoma-associated antigen, a chondroitin sulfate proteoglycan, stained the microvasculature broadly. Staining of the basal lamina components collagen type IV and laminin was, within the tumor, not restricted to the microvasculature. From their findings the authors conclude that 1) for the visualization of the tumor vasculature, antibodies recognizing endothelial markers, especially monoclonal antibodies PAL-E and BMA 120, are preferable to those recognizing pericytes or basal lamina; 2) within the microvasculature of tumors and granulation tissue, a heterogeneity of expression of endothelial and pericyte markers is observed; 3) during the formation of granulation tissue, all three microvascular components can be demonstrated already in the histologically earliest stage, suggesting not only an involvement of endothelial cells but also of pericytes and basal lamina in the initial steps of angiogenesis in wound healing.     

Induction of alpha-smooth muscle actin expression in cultured human brain pericytes by transforming growth factor-beta 1.

Pericytes are cells localized at the abluminal side of the microvascular endothelium and completely enveloped by a basement membrane. Pericytes have close contact with endothelial cells and are probably involved in the regulation of endothelial cell functions. Previous studies suggested a role for pericytes in microvascular proliferation in tumors. To study this cell type, we isolated human brain pericytes from microvessel segments derived from autopsy brain tissue. These cells were characterized in vitro using a panel of monoclonal antibodies. Human brain pericytes were reactive with monoclonal antibodies directed against the high molecular weight-melanoma associated antigen and intercellular adhesion molecule-1, but only a minority of the cells expressed alpha-smooth muscle actin (alpha-SMA, 0 to 10%) or vascular cell adhesion molecule-1 (10 to 50%). In histologically normal human brain microvessels in situ, pericytes consistently lacked staining for these four markers. Tissue with microvascular proliferation, however, showed a marked pericyte staining for both alpha-SMA and high molecular weight-melanoma associated antigen. The expression of alpha-SMA in vitro could be slightly up-regulated by incubation with serum-containing medium. An increase in alpha-SMA expression up to 40% of the total cell population was seen when pericytes were treated with transforming growth factor-beta 1, whereas basic fibroblast growth factor slightly inhibited alpha-SMA expression. Incubation with other factors (platelet-derived growth factor-AA, heparin, interferon-gamma, tumor necrosis factor-alpha) had no effect on the alpha-SMA expression at all. Transforming growth factor-beta 1 thus induces smooth muscle-like differentiation in pericytes in vitro and might play a role in the activation of pericytes during angiogenesis in vivo.     

Gene products of the HLA-D region in normal and malignant tissues of nonlymphoid origin

Indirect immunofluorescence staining with monoclonal antibodies has shown a differential distribution of HLA-DR, DQ, and DP antigens in normal tissues of nonlymphoid origin. The distribution of HLA-DP antigens is similar to that of HLA-DR antigens, while that of HLA-DQ antigens is more restricted. Malignant transformation of cells of nonlymphoid origin may be associated with the appearance of the gene products of the HLA-D region. HLA-DR antigens appear more frequently than the other two types of HLA class II antigens and HLA-DP antigens more frequently than HLA-DQ antigens. Differential expression of the gene products of the HLA-D region was also found in autologous metastases removed from different anatomic sites from patients with melanoma. The HLA class II phenotype of surgically removed malignant lesions did not correlate with the degree of differentiation of tumor cells and/or with the expression and/or cellular distribution of HLA class I antigens. Furthermore, in melanoma lesions, no relationship was found between the HLA class II phenotype and the expression of 3 membrane bound and 1 cytoplasmic melanoma associated antigen recognized by monoclonal antibodies. The functional significance and the practical implications of the differential expression of the gene products of the HLA-D region by tumor cells are discussed.     

Immunocytochemical distribution of a breast carcinoma associated glycoprotein identified by monoclonal antibodies.

A glycoprotein, BCA-225 (Mr 225,000-250,000), has been identified in cells and spent medium of clone 11 T47D breast carcinoma cells by three murine monoclonal antibodies, CU18, CU26, and CU46. The antigen was localized in paraffin sections of 167/178 (94%) Bouin's-fixed human breast carcinoma tissues and few other carcinomas (1/8 lung [squamous], 4/4 uterine cervix) in an intracellular pattern, whereas an apical or glycocalyx distribution was seen in several normal tissues, benign lesions, and malignant tumors. Although the immunocytochemical staining patterns observed with these antibodies have many similarities to those described with other previously reported monoclonal antibodies, notable differences include the lack of reactivity of CU18, CU26, and CU46 with lactating mammary gland and with gastrointestinal malignancies. BCA-225 binds to wheat germ lectin, not to concanavalin A, but monoclonal antibody binding does not appear to involve the carbohydrate component of the molecule. The frequency of the immunocytochemical detection of BCA-225 in breast carcinomas and its restricted distribution in other human tissues suggest considerable clinical potential for this antigen and its corresponding monoclonal antibodies.     

AMINOPEPTIDASE A IS A CONSTITUENT OF ACTIVATED PERICYTES IN ANGIOGENESIS

Monoclonal antibody (MAb) RC38 recognizes a human renal antigen of 160 kD recently identified as human aminopeptidase A (APA; EC 3.4.11.7). This ectoenzyme is able to hydrolyse selectively N-terminal glutamyl and aspartyl residues from oligopeptides. By enzyme histochemistry, APA activity has also been localized in the microvessels of all organs in animals and man. The purpose of this study was to investigate the distribution of human APA as recognized by MAb RC38 in the microvasculature of normal human tissues and pathological conditions associated with neovascularization. Unexpectedly, in normal tissues vascular staining with MAb RC38 was generally weak and often absent, while in tumours, granulation tissue, and chronic synovitis, marked microvascular staining was demonstrated. By immuno-electron microscopy, the antigen was found on the cell membrane of activated pericytes and their processes in the tumour vasculature. RC38 expression could not be detected on cultured human endothelial cells or pericytes. These observations suggest that pericyte expression of a subtype of APA (as recognized by MAb RC38) is markedly enhanced in the vasculature of tumours and wound healing tissue as compared with normal resting tissues. This provides further evidence of the altered state of pericytes in these conditions. Pericyte APA may be involved in the metabolism of biologically active oligopeptides during neovascularization, supporting a regulatory role of pericytes in this process. In addition, MAb RC38 may be useful as a marker of pericyte activation in tissue sections.     

Novel monoclonal antibodies defining epitope of human cytokeratin 18 molecule

Two monoclonal antibodies, DA7 and DC10, were obtained from fusions of mouse myeloma cells with splenic lymphocytes from mice immunized with human breast cancer cells of PMC 42 line. The indirect immunofluorescence studies performed on established tumor cell lines together with immunoperoxidase staining of normal human tissues showed that the components reacting with the antibodies were cytokeratins. Positive reaction was noted in all epithelia derived cultured cells and in all simple epithelial tissues known to express keratin 18. Immunoblotting performed on various cytoskeletal preparations demonstrated strong staining of a single band with a mobility corresponding to that of cytokeratin 18 (45 kD). The negative immunoperoxidase reaction found in different epithelial tissues of seven animal species suggests that both antibodies are specific for human keratin 18. It was shown that DA7 and DC10 antibodies exhibited strong reaction in paraffin embedded tissues fixed in either methacarn or standard formalin. These characteristics predetermine both antibodies as suitable reagents for the specialized histopathological work.     

Reactivity of monoclonal antibody (mAb) GD9 with a cytoplasmic antigen preserved in formalin-fixed, paraffin-embedded gastrointestinal tumors

In order to develop monoclonal antibodies to tumor associated antigens which are preserved in formalin-fixed, paraffin-embedded tissues, BALB/c mice were immunized with a formalin-fixed paraffin-embedded melanoma lesion. One of the resulting monoclonal antibodies, monoclonal antibody (mAb) GD9, stained formalin-fixed, paraffin-embedded melanoma lesions. When tested with a large panel of normal tissues from adults and from two fetuses of 4 and 16 week gestation and of benign and malignant tumors of different embryological origin, the mAb GD9 stained normal small bowel mucosa, areas of gastric intestinal metaplasia, the 6 pancreatic carcinoid tumors tested and a high percentage of gastrointestinal tumors. In the latter group, the reactivity with well differentiated tumors was higher than with poorly differentiated ones. Furthermore, the percentage of malignant cells stained by mAb GD9 in differentiated tumors was higher than in poorly differentiated ones. In the latter, the staining was diffuse and granular, while in the former, the staining was located in the cytoplasm close to the glandular lumen. The reactivity of mAb GD9 with colon carcinomas did not correlate with the Duke's staging and with the clinical course of the disease. The results of the immunohistochemical staining of normal tissues and benign and malignant lesions suggest that the specificity of mAb GD9 is different from that of previously described monoclonal antibodies which recognize tumor associated antigens expressed by tumors of the gastrointestinal tract.     

CA 50 and CA 19-9 antigen expression in normal, hyperplastic, and neoplastic thyroid tissue

The occurrence of the tumor-associated carbohydrate antigens defined by the monoclonal antibodies (moabs) C 50 and 19-9 has been studied by immunoperoxidase staining of formalin-fixed and paraffin-embedded tissue specimens from normal, hyperplastic, adenomatous, and carcinomatous thyroid tissues. Epithelial expression of these antigens was observed neither in normal nor in hyperplastic thyroid tissue. The antigens were expressed in only 1 of 26 follicular adenomas and the staining in this case was weak and restricted to a few cells. In contrast, the expression of this antigens is marked and progressive in carcinomatous tissues. A high proportion, 48 of 52 papillary carcinomas demonstrated C 50 reactivity, whereas 25 of these tumors expressed the CA 19-9 antigen. Of 25 follicular carcinomas, 15 gave a positive staining for the CA 50 and 6 for the CA 19-9 antigen. CA 50 antigen expression was still detected in tumor cells lacking the CA 19-9 antigen and C 50 reactive material was found in all tissue specimens from medullary carcinomas tested, whereas CA 19-9 antigen staining was consistently negative. This indicates that the moab C 50 which reacts, like the moab 19-9, with the sialylated Lewisa (Lea) blood group determinant also binds to other antigens apart from the sialylated Lea in CA 19-9 antigen negative tumor cells. Although, the functional significance of CA 50 and CA 19-9 antigen expression remains to be investigated, these results suggest that the demonstration of these antigens could provide additional differential diagnostic parameters for the characterization of hyperplastic and neoplastic lesions of the thyroid gland. Further clinical studies will show whether these carbohydrate antigens are useful serum markers for the monitoring of thyroid carcinomas.     

Immunohistochemical and biochemical characterization of the mucin-type tumor associated antigen TAG-12 by monoclonal antibody 7A9.

The reactivity of monoclonal antibody 7A9 with normal and neoplastic human tissues and some biochemical characteristics of the antigen (TAG-12) bound by 7A9 were evaluated. Antibody 7A9 showed broad reactivity with various carcinomas in paraffin sections. High percentages of positive tumor cells, displaying membrane and cytoplasmic staining, were noticed in adenocarcinomas of the breast (83/85), serous cystadenocarcinomas of the ovary (15/16), and lung adenocarcinomas (14/16). TAG-12 antigen was also detectable in normal adult and fetal tissues, but the reactivity of 7A9 was mainly restricted to the luminal surface of epithelial cells. For biochemical analyses, TAG-12 antigen purified from T47-D breast carcinoma cells by lectin affinity chromatography was treated with different glycosidases and proteases and analyzed by immunoblotting with 7A9. The data indicate that the antigen recognized by 7A9 is a heavily sialated mucin-type glycoprotein with a molecular weight of more than 200 KD. Similar to all other antibodies against tumor associated antigens, monoclonal antibody 7A9 is not tumor-specific but displays tissue staining patterns with a high carcinoma-to-normal ratio. The strong reactivity with the majority of tumor cells in several carcinoma types suggests that 7A9 is useful for in vitro and in vivo targeting of those tumors.     

Hyaluronectin: detection with monoclonal antibodies in human tumors

Two monoclonal IgG1 antibodies (MAbs) were raised against human brain hyaluronectin (HN) and used to characterize tumor HN. They were screened using an enzyme immunological technique (ELISA) combined with the HN property of specific binding to hyaluronic acid. They were shown to detect two different epitopes (HN1 and HN2) in human normal brain as well as in most tumors. Both HN1 and HN2 epitopes were found associated with mesenchymal benign or neoplastic proliferations (e.g. connective areas of fibroadenomas, extracellular matrix of fibrosarcomas) and with reactive connective tissue (e.g. stroma reaction of carcinomas, ground substance of gliomas). The results corresponded with those previously obtained with polyclonal rabbit antibodies and confirmed that HN is a constant marker of desmoplasia. Thus anti-HN MAbs recognize an antigen that is associated with tumor development and will be suitable for targeting.     

Equilibrium binding characteristics of monoclonal antibodies recognizing melanoma cell surface antigens

The equilibrium binding characteristics of a panel of six monoclonal antibodies (MAb) recognizing melanoma cell surface antigens (125 kdal cell surface melanoma associated glycoprotein antigen, 125kD-MAA; high molecular weight melanoma associated antigen, HMW-MAA; and a non-protein melanoma associated antigen, NP-MAA) were investigated using the cell lines SK-MEL-2, SK-MEL-5, and M21. The MAbs displayed equilibrium association constant (K) values ranging from 10(7) M-1 to 10(10) M-1 and maximum MAb binding values (Qmax) from 2 x 10(4) to 2 x 10(6) MAb molecules bound per cell. High trypsin concentrations were shown to have deleterious effects on Qmax values obtained for antibodies recognizing the 125kD-MAA, and even low trypsin concentrations affected Qmax values obtained for MAbs recognizing the HMW-MAA (although a complete linear recovery of HMW-MAA antigen was observed in 20-25 hours). Significant changes in Qmax were also noted for different cell passages. Except for MAb 43.2, little variation in K was observed when different cell lines were used. Linear Scatchard plots were obtained for all MAbs except 43.2 in which case concave down behavior was observed suggesting the existence of positive cooperativity between the binding sites of this MAb.     

Microvascular pericytes express platelet-derived growth factor-beta receptors in human healing wounds and colorectal adenocarcinoma.

The expression of platelet-derived growth factor- beta (PDGF-beta) receptors in the microvasculature of human healing wounds and colorectal adenocarcinoma was investigated. Frozen sections were subjected to double immunofluorescence staining using monoclonal antibodies (MAbs) specific for pericytes (MAb 225.28 recognizing the high-molecular weight-melanoma-associated antigen, expressed by activated pericytes during angiogenesis), endothelial cells (MAb PAL-E), laminin, as well as PDGF-beta receptors (MAb PDGFR-B2) and its ligand PDGF-B chain (MAb PDGF 007). Stained sections were analyzed by computer-aided imaging processing that allowed for a numerical quantification of the degree of colocalization of the investigated antigens. An apparent background colocalization, varying between 23 and 35%, between markers for cells not expected to co-localize was recorded. This background could be due to limitations of camera resolution, to out-of-focus fluorescence, and to interdigitations of the investigated structures. In all six tumor specimens, co-localization of PDGF-beta receptors and PAL-E was not different from the background co-localization, whereas that of PDGF-beta receptors and high-molecular weight-melanoma-associated antigen was significantly higher with mean values between 57 and 71%. Qualitatively, the same pattern was obtained in the two investigated healing wounds. PDGF-B chain did not co-localize with either PAL-E or high-molecular weight-melanoma-associated antigen, but PDGF-B chain-expressing cells were, however, frequently found juxtaposed to the microvasculature. The expression of PDGF-beta receptors on pericytes in activated microvessels and the presence of PDGF-B chain-expressing cells in close proximity to the microvasculature of healing wounds and colorectal adenocarcinoma is compatible with a role for PDGF in the physiology of the microvasculature in these conditions.     

Reactivity spectrum of 30 monoclonal antimelanoma antibodies to a panel of 28 melanoma and control cell lines

Thirty monoclonal antibodies from eight laboratories exchanged after the First Workshop on Monoclonal Antibodies to Human Melanoma held in March 1981 at NIH were tested in an antibody-binding radioimmunoassay using a panel of 28 different cell lines. This panel included 12 melanomas, three neuroblastomas, four gliomas, one retinoblastoma, four colon carcinomas, one lung carcinoma, one cervical carcinoma, one endometrial carcinoma, and one breast carcinoma. The reactivity pattern of the 30 monoclonal antibodies tested showed that none of them were directed against antigens strictly restricted to melanoma, but that several of them recognize antigenic structures preferentially expressed on melanoma cells. A large number of antibodies were found to crossreact with gliomas and neuroblastomas. Thus, they seem to recognize neuroectoderm associated differentiation antigens. Four monoclonal antibodies produced in our laboratory were further studied for the immunohistological localization of melanoma associated antigens on fresh tumor material. In a three-layer biotin-avidin-peroxidase system each antibody showed a different staining pattern with the tumor cells, suggesting that they were directed against different antigens.     

Reactivity of human trophoblast monoclonal antibodies with marmoset monkey trophoblast cultures

The aim of this study was to determine whether cultured trophoblast tissues, derived from the trophectoderm of marmoset monkey blastocysts, contain homologues of human trophoblast antigens. This is an essential prerequisite to determine whether the marmoset may be a suitable model for preclinical testing of a human antitrophoblast antigen for fertility regulation. Previously evaluated monoclonal antibodies from the Flinders University laboratory, which reacted with human trophoblast with a high degree of specificity, were tested for immunohistochemical reactivity using an immunoperoxidase detection method on both frozen and paraformaldehyde-fixed sections of the cultured marmoset monkey trophoblast. All monoclonal antibodies raised against human placenta reacted positively, when compared to controls, suggesting that human and marmoset trophoblast cells share common epitopes. The specificity of the monoclonal antibodies was investigated by determining whether there was cross-reactivity with other marmoset monkey tissues, including adrenal, spleen, kidney, liver, muscle, ovary and testis. The specificities of the monoclonal antibodies on these marmoset tissues were similar to those previously found on the corresponding human tissues. We have concluded that marmoset monkey trophoblast exhibits homologues of human trophoblast antigens. The findings also suggest that marmoset monkeys should be evaluated further as a primate model to test suitable target antigens for antitrophoblast vaccines that may be useful contragestation agents in humans.      

Expression in normal adult, fetal, and neoplastic tissues of a carbohydrate differentiation antigen recognised by antigranulocyte mouse monoclonal antibodies.

The distribution in paraffin fixed human tissues of a carbohydrate antigen defined by two monoclonal antibodies raised against human granulocytes has been studied by means of an immunoperoxidase technique. In addition to granulocytes, the antigen has been detected in adult tissues on identifiable cell types of the stomach, kidney, adrenal medulla, and brain and on the mucins of the gastrointestinal tract and other secretions. In fetal tissue, epithelial cells of the alimentary tract, lung, brain, and kidney express the antigen. Adenocarcinoma of the colon, stomach, breast, and lung are stained strongly, as are other types of lung cancer. The monoclonal antibodies give a staining pattern similar but not identical to other monoclonal antibodies raised against granulocytes or neoplastic cell lines which recognise the antigen 3-fucosyl N-acetyllactosamine. The use of antibodies against this oncofetal antigen in the study of differentiation and as tumour markers is discussed.     

Localization of urokinase-type plasminogen activator in stromal cells in adenocarcinomas of the colon in humans.

Human colon adenocarcinomas and adjacent normal colon tissues were stained immunohistochemically with three different monoclonal antibodies and one preparation of polyclonal antibodies against each of the two plasminogen activators, uPA (urokinase type) and tPA (tissue type). The staining patterns seen with the respective sets of antibodies were identical. In all of 10 cases, staining for uPA in the normal colon tissue was confined to scattered fibroblastlike cells in the lamina propria. Other cells, including epithelial and endothelial cells, were uPA negative. All the tumor infiltrates contained many more uPA-positive cells than the normal tissues, but the staining was confined to fibroblastlike cells and endothelial cells in the tumor stroma, while no staining of the malignant epithelial cells was detected. Analysis for uPA by enzyme-linked immunosorbent assay (ELISA) in four cases showed an average uPA content of 0.15 ng uPA/mg protein in the normal colon tissues and 1.6 ng uPA/mg protein in the tumors. Tissue-type plasminogen activator immunoreactivity was confined to endothelial cells in both the normal colon tissue and in the colon carcinomas. These findings may indicate that colon cancer cells recruit stromal cells to produce uPA involved in degradation of the extracellular matrix during invasive growth.     

Paraneoplastic IgG striational autoantibodies produced by clonal thymic B cells and in serum of patients with myasthenia gravis and thymoma react with titin.

Autoantibodies with heterogeneous specificities for contractile elements of striated muscle are found in 80 to 90% of patients who have myasthenia gravis (MG) with thymoma. The stimulus for production of these paraneoplastic striational autoantibodies (StrAb) is unknown. One approach to understanding their association with MG and thymoma is to define the antigenic specificities of monoclonal StrAb secreted by B cell lines established from patients who have MG and thymoma. Here, we report the isolation from a single patient of two independent thymic B cell clones secreting StrAb of IgG isotype. In immunoblots, both StrAb bound monospecifically to an antigen of human skeletal muscle that comigrated with the high molecular weight protein, titin. The pattern of immunofluorescence staining yielded by both antibodies in cultured human muscle cells was similar to that produced by rabbit polyclonal anti-titin antibodies. Each monoclonal antibody bound to a different region of the sarcomere in stretched myofibrils; these corresponded to sites previously reported to bind murine anti-titin monoclonal antibodies. The pattern of sarcomere immunostaining produced by combining the two human monoclonal antibodies was indistinguishable from that produced by serum IgG from the patient whose thymus yielded the B cell clones. Thus, the monoclonal antibodies appear to identify two epitopes of titin that are recognized by IgG StrAb in serum. The finding that IgG anti-titin autoantibodies are restricted to serum of MG patients who have thymoma suggests that titin is a major specificity of IgG StrAb. Our additional finding that anti-titin IgG binds to striated elements in medullary myoid cells of the human thymus supports the hypothesis that StrAb represent an intrathymic B cell immune response that is initiated by autoantigens that are rendered immunogenic for helper T cells in the course of noeplastic transformation to thymoma.     

Epithelial antigens in malignant mixed Müllerian tumours of endometrium

Immunohistochemical staining of formalin fixed paraffin sections with the mouse monoclonal antibodies E29 and CAM 5.2 effectively distinguish epithelium (antigen positive) from stroma (antigen negative) in normal endometrium. These antibodies were used as epithelial markers in the study of eight malignant mixed Müllerian tumours (MMT) of endometrium and gave normal reactions with well differentiated neoplastic glands; in contrast, negative or very weak staining was observed in poorly differentiated epithelial cells, present in large numbers in three cases. Abnormal antigen-containing cells were observed in the stroma of seven MMT. In some cases these are probably due to stromal invasion by malignant epithelium but in others they may represent an early stage of epithelial differentiation in mesenchymal cells of the malignant stroma.