Both VH and VL regions contribute to the antigenicity of anti-idiotypic antibody that mimics melanoma associated ganglioside GM3

Previously we developed a murine monoclonal anti-idiotype (anti-id) antibody (4C10) that mimics the melanoma-associated ganglioside antigen GM3, that is, it carries the internal image of GM3. 4C10 was made against the human monoclonal antibody (HuMAb) L612, which reacts with several types of human cancer cells, including melanoma and breast cancer. To reduce mouse components of 4C10, the constant region was replaced by a human constant domain to form the murine/human chimeric anti-id antibody TVE-1. In the present study, we sought to determine which chain (VH or VL) of the anti-id is responsible for the antigenicity of GM3. The TVE-1 VH and VL expression vectors were simultaneously transfected with either the VH or VL expression vector of a murine-human chimeric IgG antidansyl haptenic antibody, resulting in the construction of three different combinations of VH and VL chimeric antibodies. These IgG molecules were produced from the transfectomas, and their reactivity to HuMAb L612 was tested. Neither of the IgG proteins that had cross-combined the VH-VL pair showed positive results, suggesting that both heavy and light chains are required to express the antigenicity. The in vivo antigenicity of this chimeric anti-id was confirmed by skin tests in melanoma patients receiving active specific immunotherapy.

Molecular cloning of a human monoclonal antibody reactive to ganglioside GM3 antigen on human cancers

In this study we report the characterization of a human monoclonal antibody (HuMab), L612, that reacts with ganglioside GM3 and has therapeutic application for the treatment of human neoplasms, particularly melanoma. A permanent IgM-secreting Epstein-Barr virus-transformed B-cell line L612 was established. L612 HuMab bound specifically to neoplastic cell lines in culture and in tissue biopsy specimens such as melanoma, colon, breast, and lung cancer. The antibody did not bind to normal cells or biopsy tissue. HuMab L612 showed the highest reactivity to melanoma cells, particularly to those with high concentrations of GM3. Immunostaining on high-performance thin-layer chromatography plates demonstrated that L612 HuMab bound to GM3 purified from melanoma cells. Removal of the sialic acid from GM3 abolished antibody binding. HuMab L612 also reacted to GM4 purified from egg yolk, indicating that it recognizes an NeuAc alpha 2-3 galactose antigen determinant. HuMab L612 heavy and light chains were sequenced and determined to belong to the mu heavy chain variable subgroup III and kappa chain variable subgroup IV families, respectively. The studies indicate that the L612 HuMab has significant therapeutic potential for a wide variety of human cancers.

Immunocytochemical study on internalization of anti-carbohydrate monoclonal antibodies

The fate of anti-tumor monoclonal antibodies (mAbs) after binding to the cell surface is one of the important factors for application of mAbs in therapy. For mAbs to remain on the cell surface for a long time is preferable character for complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). On the other hand, quick internalization of mAbs into cytoplasm is advantageous for cytotoxic effects of toxins or cytotoxic drugs conjugated with mAbs. In this study we investigated the localization of anti-carbohydrate mAbs in vitro by immunocytochemical methods at the electron microscopic level. Anti-ganglioside GM3 mAb (mouse IgM) was localized both in cytoplasmic vesicles and on the cell surface membrane of mouse melanoma cells after incubation for 30 min at 37 degrees C. Anti-ganglioside GM2 mAb (mouse IgM), anti-ganglioside GD2 mAb (mouse IgG3) anti-ganglioside GD3 mAb (mouse IgG3) mainly existed on the cell surface of human small cell lung carcinoma cells, human neuroblastoma cells and human melanoma cells, respectively, after incubation for 30 min at 37 degrees C. On the other hand, anti-sialyl Lea mAb (mouse IgG1) was intensively incorporated into the cytoplasm of human colon tumor cells under the same conditions. Anti-ganglioside GD3 mAb and anti-sialyl Lea mAb were radiolabelled with 125Iodine and traced in in vitro culture. When the cells were incubated in the presence of the 125I-mAb for 90 min on ice, the ratio of intracellular counts to surface counts was 8/92 for anti-ganglioside GD3 mAb and 31/69 for anti-sialyl Lea mAb respectively. After the subsequent incubation for 60 min at 37 degrees C, the ratio altered to 13/87 for anti-ganglioside GD3 mAb and 54/46 for anti-sialyl Lea antigen mAb. This study suggested that internalization of anti-carbohydrate mAbs after the binding to the cell surface was different among the mAbs depending on the character of antigens. In conclusion, anti-ganglioside mAbs have beneficial characters for CDC or ADCC while anti-sialyl Lea mAb is suitable for immunoconjugates.

Accumulation of high level of pp60c-srcN is an early event during GM3-antibody mediated differentiation of neuro-2a neuroblastoma cells

Neuro-2a neuroblastoma cells, when differentiated via a cAMP-dependent pathway by treatment with anti-GM3 monoclonal antibody, accumulated a high level of pp60c-src protein and pp60c-src kinase activity just before the onset of neurite formation. The specific kinase activity of the accumulated c-src protein was found to be comparable to that of normal cerebellar neurons, but was about 6- to 8-fold higher than that of normal astrocytes. These results, and migrations of peptide fragments in the SDS-polyacrylamide gels after V8 proteolysis, strongly indicate the accumulation of the neuron-specific isoform of the c-src protein (pp60c-srcN) in the GM3 antibody-treated Neuro-2a cells. Similar high levels of pp60c-src protein and pp60c-src kinase activity were observed in the Neuro-2a cells differentiated via a cAMP-dependent pathway by treatment with dibutyryl cAMP, but not in the same cell line when differentiated via a cAMP-independent pathway with 5-bromo-2'-deoxyuridine. These results demonstrate that the accumulation of high levels of the neuron-specific isoform of the pp60c-src protein (pp60c-srcN) in the Neuro-2a neuroblastoma cells depends on the specific signal transduction pathway involved during the differentiation of these cells.

GM3 as a target of anti-lymphocytic ganglioside antibodies in AIDS patients

IgG antibodies reacting with the GM3-comigrating band extracted from pooled AIDS lymphocytes were detected in 33.3% of AIDS patients sera, in 8% of asymptomatic anti-HIV-positive subjects, in none of the sera obtained from asymptomatic anti-HIV-negative drug abusers, from patients with acute B and chronic C hepatitis, and from healthy donors. All positive sera reacted selectively with the GM3-comigrating band obtained from AIDS lymphocytes but not with the corresponding band from normal lymphocytes. The lymphocytic ganglioside autoantigen was revealed as GM3. In addition, two main data were shown: (a) AIDS lymphocytes have an increased concentration of GM3 and (b) the ceramide of AIDS lymphocytic GM3 has a different percentual composition of fatty acids in contrast to control cells. It is suggested that these quantitative and qualitative changes might be responsible for the appearance of circulating anti-lymphocytic GM3 antibodies.

Selection of a mutant cell line based on differential expression of glycosphingolipid, utilizing anti-lactosylceramide antibody and complement

A mouse mammary carcinoma mutant cell line showing a characteristic alteration of glycosphingolipid (GSL) composition, but with unchanged protein glycosylation pattern, was isolated. Parent cell line FM3A/F28-7 is characterized by the predominance of lactosylceramide (LacCer) and virtual absence of more complex GSLs. Mutant cell line FUA169 was isolated after treatment of F28-7 cells with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine and incubation with anti-LacCer monoclonal antibody T5A7 and complement. FUA169 cells were characterized by a dramatic reduction in LacCer and by the presence of a major ganglioside identified as GM3. They also showed high activity of CMP-sialic acid:LacCer 2,3-sialosyltransferase, whereas F28-7 cells had no detectable activity of this enzyme. In contrast to the difference in GSL pattern, F28-7 and FUA169 showed identical protein glycosylation patterns, as evidenced by "Western blotting" with various lectins and surface labeling with galactose oxidase/NaB3H4 and periodate/NaB3H4. Thus, FUA169 is identified as a glycosylation mutant with regard to GM3 expression and will be useful for studies of the functional role of GM3. Growth of FUA169 cells, relative to F28-7 cells, showed greater temperature sensitivity and greater inhibitability based on restriction of growth factors, particularly insulin.

Anti-GM3-lactam monoclonal antibodies of the IgG type recognize natural GM3-ganglioside lactone but not GM3-ganglioside

Immunization of mice with a synthetic GM3-lactam-BSA (bovine serum albumin) conjugate (designed to emulate the corresponding natural GM3-lactone conjugate), followed by fusion of splenocytes with myeloma cells, gave rise to more than 300 monoclonal hybridomas producing antibodies to GM3-lactam-BSA, which did not react with Glc-BSA and BSA. Eight antibody clones were randomly chosen from the positive 300 hybridomas. The eight clones, all belonging to the IgG class, were unreactive against GM3-ganglioside, whereas two antibodies (P5-1 and P5-3, both IgG1, kappa) reacted with GM3-ganglioside lactone. Binding of these two antibodies to the GM3-lactam-BSA conjugate was inhibited by soluble glycosides of GM2-, GM3-, and GM4-lactam and by GM3- and GM4-lactam, respectively, but not by Gb3 or asialo-GM1 and GM2-saccharides. A third antibody (P3; IgG2b, kappa) was inhibited by GM2-, GM3-, and GM4-lactam, but did not recognize GM3-ganglioside lactone.

Differentiation of Neuro-2a neuroblastoma cells by an antibody to GM3 ganglioside

A monoclonal antibody against GM3 ganglioside (GM3Ab) was found to trigger differentiation of Neuro-2a cells in culture. The differentiation of Neuro-2a cells by GM3Ab was accompanied by increased levels of intracellular serotonin and amino acid neurotransmitters viz. aspartate, glutamate, glutamine, glycine and taurine. Further study indicated that the increase in the serotonin level was not due to a higher rate of serotonin synthesis but rather to a higher rate of active transport of serotonin from the medium. Studies on the cell surface gangliosides revealed that unlike the proliferating cells, the GM3Ab-mediated differentiated cells contained higher gangliosides in addition to GM3 and GM2 gangliosides. Analysis of total cellular proteins indicated the appearance of a 25 kDa protein, pI 5.4, in the GM3Ab-treated cells--a small amount of this protein was observed in dibutyryl cAMP (Bt2cAMP)-treated cells, however, the protein was totally absent in the 5-bromo-2'-deoxyuridine (BrdU)-treated cells. Investigation of the mode of action of GM3Ab indicated that the cellular differentiation was due to increased cAMP accumulation resulting from an increase in the adenylate cyclase activity. Further studies with different agents affecting protein kinase C (PKC) activity and direct assay of PKC ruled out the possibility that GM3Ab mediated its effect via PKC. This GM3Ab-induced differentiation could be inhibited by protein kinase A (PKA) inhibitor, H8, but could not be inhibited by sphingosine, an inhibitor of PKC. Pertussis toxin could mimic the effect of GM3Ab, suggesting that GM3Ab caused the elevation in the adenylate cyclase activity by reducing the Gi-protein inhibition of the adenylate cyclase. The data suggests that GM3Ab, after interaction with cell surface GM3, elevated intracellular cAMP level by withdrawing the inhibitory effect of some undefined factor(s) present in culture medium which normally keeps adenylate cyclase activity low through activation of Gi-protein.

[Studies on Hanganutziu-Deicher antibodies in renal diseases]

H-D antibodies which were known as antibodies detectable in patients with serum sickness have recently been detected in renal diseases. We attempted to detect IgG, IgA and IgM antibodies to N-glycolyl GM3, among other H-D antibodies, by ELISA in various renal diseases and found increased IgM antibody in mesangial proliferative glomerulonephritis, membranoproliferative glomerulonephritis, IgA nephropathy, minimal change nephrotic syndrome and Henoch-Schönlein purpura nephritis (HSPN), elevated IgA antibody in IgA nephropathy and HSPN and raised IgG antibody in IgA nephropathy. In 2 cases of IgA nephropathy, there was noted a good correlation between clinical course and anti-N-glycolyl GM3 antibody titers. Measurement by ELISA of IgG antibody to cytomegalovirus (CMV) seemed as one of immune pathogenetic factors of IgA nephropathy showed a high positive rate for this antibody of IgA nephropathy patients and a positive correlation between the antibody and anti-N-glycolyl GM3 antibody. The key molecule of H-D antigens is N-glycolyl neuraminic acid (NGNA) and this sialic acid does not normally exist in humans. One can surmise, therefore, that in those renal diseases in which there was noted an elevation of anti-N-glycolyl GM3 antibody, this antigen is formed or generated by some unknown mechanism. In other words, it may be that humans are not entirely negative for H-D antigens but have a minimum inherent antigenicity and a potential capacity to synthesize these antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoreactivity of leukemic lymphoblasts of T-cell and B-cell precursor origin with monoclonal anti-GD3 and anti-GM3 antibodies

The glycosphingolipids GD3, GM3, and alpha 2, 3-sialosylparagloboside (SPG) are major gangliosides of lymphoid leukemia cells. The reactivity of two monoclonal anti-ganglioside antibodies, an anti-GD3 (R24) and an antibody cross-reactive to GM3 and SPG (M2590), to blasts of patients with T-cell acute lymphoblastic leukemia (ALL) and B-cell precursor ALL (pre-B-ALL), were compared using indirect immunofluorescence and flow cytometry. Results from 23 patients with T-ALL and eight with pre-B-ALL yielded four subclasses of T-ALL and two subclasses of pre-B-ALL. Blasts from most of the patients with T-ALL were R24+M2590- whereas most of the patients with pre-B-ALL were R24-M2590-. Seven of 23 patients with T-ALL had ganglioside immunophenotypes similar to that of pre-B-ALL, i.e. R24-M2590- or R24-M2590+. These subclasses could not be further characterized by additional cell surface immunophenotypic markers or by gene (immunoglobulin and T-cell receptor) rearrangement analysis. The ratio R24/M2590 was less than 1.0 in all patients with pre-B-ALL, and was greater than 1.0 in all patients with T-ALL who were R24 positive, but was not useful in characterizing the double negative T-ALL subclass. To assess whether cryptogenicity of gangliosides due to cell surface protein could account for the low binding of either R24 or M2590, blasts were treated with trypsin before antibody analysis. Whereas the binding of R24 was unchanged after trypsin treatment, binding of M2590 was increased in a number of samples, particularly in those samples which were originally M2590-positive. The results show that comparative staining of T-ALL and pre-B-ALL cells with both anti-GD3 and anti-GM3/SPG antibodies results in a further subclassification of ALL and provides a quantitative assessment of the expression of tumor-associated gangliosides on the blasts of this disease.

Autoreactive T-cell clones which suppress cytotoxic T cell responses

Autoreactive T-cell clones (Thy 1+, CD4+, CD3+) which suppress generation of cytotoxic T lymphocytes (CTL) were established in long-term in vitro culture by stimulation with GM3-liposomes or soluble melanoma (B16) antigen composed of GM3. The T-cell receptors (TCR) of two representative clones analyzed used the same TCR alpha- and V13+ beta-chains. The clones produce only interferon gamma(IFN-gamma) but not interleukins (IL)2 and 4, despite their CD4+ phenotype, suggesting that they are not a typical TH1 or TH2 type. The clones are effectively stimulated by IFN-gamma treated (I-Ab/GM3+) B16 melanoma or I-Ab-transfected GM3+ L cells, but not by GM3-/I-Ab mutant melanoma, EL 4, or I-Ad/k-transfected L cells. This strongly suggested the involvement of GM3/class II in T-cell recognition. Antigen specificity was required for stimulation of the clones. However, once stimulated, they suppressed CTL generation in an antigen non-specific fashion. As class II+ B16 melanoma cells effectively function as antigen-presenting cells to stimulate the autoreactive suppressor T cell (Ts) clones of this type, this negative circuit between class II+ tumor cells and IFN-gamma-producing Ts would be a possible mechanism whereby tumor cells could escape the immune system.

Survey of Hanganutziu and Deicher antibodies in operated patients

The appearance of Hanganutziu and Deicher (HD) antibody in the sera of patients suffering from various diseases, including malignancies of some organs and liver disorders, was investigated by enzyme-linked immunosorbent assay using N-glycolylneuraminyl-lactosylceramide (HD3) and 4-O-acetyl-HD3 as the antigenic molecules. More than 25% of sera from patients suffering from malignancies, cholelithiasis and liver cirrhosis had HD antibody, whereas none of 41 sera from healthy persons had HD antibody. The percentage of HD antibody-positive patients was similar in stages I, II and III of gastric cancer and recurrence cases. Antibody titers of the positive patients in each stage were also not different from those in each other stage. These results indicated that HD antigenic expression on cancerous tissue is not dependent on the cancerous malignancy. The HD antibody level was elevated after surgical removal of cancerous tissues in 5 of 6 patients examined, indicating that tumor growth absorbed the serum antibody. Serum antibody against 4-O-acetyl-HD3 was detected independently of HD3 antibody in some cases; however, in most cases, correlation between the two antibody titers was observed.

Anti-idiotype monoclonal antibody carrying the internal image of ganglioside GM3

Murine anti-idiotype monoclonal antibodies were generated against a human IgM monoclonal antibody (L612) that recognizes ganglioside GM3 on human melanoma. Hybridomas secreting antibodies that bound specifically to L612 were selected by enzyme-linked immunosorbent assay using L612 and three negative control human IgMs, including monoclonal anti-GM2 and anti-GD2 antibodies, as well as purified serum IgM, as antigen sources. GM3-binding inhibition and cell-binding inhibition assays were used to identify seven anti-idiotype monoclonal antibodies that recognized determinants located within the antigen-combining sites of L612. To determine whether these anti-idiotype monoclonal antibodies possessed the internal image of the original antigen, we immunized syngeneic BALB/c mice with one of the anti-idiotype monoclonal antibodies, 4C10, coupled with keyhole limpet hemocyanin. Sera from the immunized mice reacted strongly with an antigen-positive M12 melanoma cell line and with purified GM3. Because L612 detects and kills melanoma tumor cells in vitro and in vivo in the presence of complement without affecting normal tissues, anti-idiotype monoclonal antibodies carrying the internal image of GM3 may be an effective tool for active specific immunotherapy in patients with melanoma.

Murine monoclonal anti-idiotype antibody (alpha) as a probe to detect human monoclonal antibody bound to human tumor tissues

A new immunohistochemical assay was developed for the detection of human monoclonal antibody (HuMAb) bound to human biopsied tumor tissues. A murine anti-idiotype monoclonal antibody, alpha type, 18C6 (IgGl), was raised against an IgM HuMAb, L612, defining a tumor-associated ganglioside antigen (GM3) and used as a probe in a three step cell-binding assay (HuMAb + anti-id + biotinylated anti-mouse Ig). Anti-id 18C6 has an exclusive binding specificity for HuMAb L612, but does not interfere with the binding of L612 to antigen positive melanoma cell lines or to a purified antigen, GM3. The applicability of 18C6 in the three step cell-binding assay was tested first using a melanoma cell line, UCLASO-M12. L612 bound to M12 cells was specifically detected by 18C6 without any background reactivity in ELISA. When this assay was compared with the standard two-step cell-binding assay (HuMAb + peroxidase-conjugated anti-human IgM) using various cultured tumor cell lines, parallel reactivity was observed. The three-step cell-binding assay was then applied to various fresh-frozen human tumor sections. Positive reactivity was demonstrated on various histologic types of human tumor tissues: primary melanoma (10/10), metastatic melanoma (4/4), nevus (10/10), lung cancer (3/6), breast cancer (2/6), and colon cancer (1/1). Adjacent normal tissues were unstained. Control experiments included the cell-binding assay with L612 alone, 18C6 alone. L612 + unrelated mouse IgG, and unrelated IgM HuMAb (L72) + 18C6; but biotinylated anti-mouse IgG did not react with these control preparations. The results indicate that anti-id 18C6 is a highly specific probe to assess the expression of the ganglioside antigenic epitope recognized by the L612 HuMAb on biopsied human tumor tissues.

Density-dependent expression of ganglioside GM3 by human skin fibroblasts in an all-or-none fashion, as a possible modulator of cell growth in vitro

The expression of GM3 in human skin fibroblasts (cell type MF II) was investigated biochemically and immunochemically by means of the monoclonal antibody M2590. A cell density-related increase in total gangliosides (about threefold) and especially in GM3 (about sixfold) was found upon attainment of confluency. Immunostaining with mAb M2590 revealed that in preconfluent cultures GM3 is expressed by only a few cells in an all-or-none fashion. The portion of GM3-expressing cells increases in parallel with cell density. In confluent cultures, which are growth-arrested by contact inhibition, all cells are intensely stained by mAb M2590, indicating a high content of GM3 in the plasma membrane. These data suggest that increased cellular M2590 binding is due to an increased GM3 content rather than to an altered conformation or arrangement in the cell membrane. GM3-expressing cells usually show a broad, flat morphology, like that of cells in the resting state (G1/G0-phase) of the cell cycle. The M2590 staining on these cells appear as clusters, orientated along straight lines and indicating an ordered distribution of GM3 in the plasma membrane. A dose-dependent inhibition of cell growth by addition of exogenous gangliosides supports the possible involvement of these glycosphingolipids in the regulation of cell growth.

Induction of mouse anti-melanoma cytotoxic and suppressor T cells in vitro by an artificial antigen, GM3-lactone

We investigated the ability of GM3-lactone liposomes to induce anti-melanoma T cell responses in mice. GM3-lactone liposomes, like murine B16 melanoma cells, induced anti-melanoma cytotoxic T cells (CTL) and also suppressor T cells (Ts). A small dose of GM3-lactone (0.0003 micrograms/ml) was enough to generate CTL in the in vitro primary response, whereas relatively large amounts of the antigen (0.03-0.3 microgram/ml) were required for anti-melanoma Ts induction. As the epitope for anti-melanoma Ts is NeuAc but not NeuGc residue on GM3, and anti-melanoma CTL are effectively induced by either GM3(NeuAc) or GM3(NeuGc)-lactone liposomes, GM3(NeuGc)-lactone or GM3(NeuGc) liposomes have potent activity as an artificial melanoma antigen to induce anti-melanoma CTL in vitro.

[Ganglioside GM3 derivatives and their immunomodulating effect]

The derivatives of ganglioside GM3-NeuLacCer. NeuLacSph and NeuAcLacSphAc-were obtained and their immunomodulating properties studied. These substances are shown to inhibit lymphocyte blast-transformation independently of their ceramide structure. On the contrary, the stimulation by the above GM3-derivatives of Con A-induced T-suppressor activity depends significantly on the structure of their ceramide moiety.

Density of GM3 with normal primary structure determines mouse melanoma antigenicity; a new concept of tumor antigen

We attempted to induce anti-melanoma cytotoxic T cells (CTL) and suppressor T cells (Ts) inhibiting CTL generation by using liposomes carrying various densities of GM3 as tumor antigens. We found that liposomes carrying 6-16 mol% of GM3 with normal primary structure successfully generated anti-melanoma CTL and suppressor T cells, while liposomes with GM3 outside this range had little or no such activity. Anti-melanoma CTL induced by GM3(NeuGc)-liposomes belonged to CD4-/CD8- double-negative CD3+ CTL while GM3(NeuAc)-liposomes induced two types of T cells, CD4+ T cells and double-negative I-J positive T cells which mediated inhibition of the induction of anti-melanoma CTL responses. These cell types were the same as those induced by mitomycin C-treated melanoma cells for CTL induction and soluble melanoma antigen for Ts generation. The results clearly demonstrate that even GM3 with normal primary structure can, at a certain density, generate melanoma antigenicity.

Campylobacter pylori colonization factor shows specificity for lactosylceramide sulfate and GM3 ganglioside

The specificity of Campylobacter pylori cell surface lectin, a presumptive colonization factor, was investigated using various sulfated and sialic acid containing glycolipids. C. pylori cells, cultured from human antral mucosal biopsies, were incubated with intact and modified glycolipid preparations and examined for agglutination inhibition of human erythrocytes. Titration data revealed that the inhibitory activity was highest with lactosylceramide sulfate and GM3 ganglioside, while galactosylceramide sulfate GM1, GD1a and GD1b gangliosides were less effective. A strong inhibitory activity towards C. pylori hemagglutin was also observed with an antiulcer agent, sucralfate. The inhibitory effect of both types of glycolipids was abolished by the removal of sialic acid and sulfate ester groups, thus indicating that sulfated and sialic acid containing glycolipids with terminal lactosyl moieties serve as mucosal receptors for colonization of gastric epithelium by C. pylori.

Monoclonal antibody MACG1 distinguishes between different molecular species of the ganglioside GM3

The present study investigates the chemical structure of a ganglioside, detected by monoclonal antibody (MAb) MacG1, which reacts with intracytoplasmic granules of tumor-infiltrating macrophages. The results obtained by enzymatic hydrolysis and fast-atom bombardment-mass spectrometry reveal that MAb MacG1 reacts with a subcomponent of the ganglioside GM3 found in melanoma and bovine brain. MAb MacG1 might be a powerful tool to distinguish among GM3 species and could help to define their possibly different biological functions.

Use of biotinylated antibody for the assay of Hanganutziu-Deicher antibodies and antigens in fluids and tissues from cancer patients

An improved enzyme-linked immunosorbent assay (ELISA) for detection of heterophile Hanganutziu-Deicher (HD) antibodies and antigens, which are frequently detected in sera and/or cancerous tissues from patients with various cancers was developed using biotinylated chicken anti-GM3(NeuGc) antibody and avidin-horseradish peroxidase conjugate. The N-glycolylneuraminyllactosyl-ceramide, GM3(NeuGc) ganglioside was purified from horse erythrocyte membranes. The ELISA procedure required 300 ng GM3(NeuGc) antigen to coat plastic microtiter plates and 190 ng biotinylated antibody per well to give optimum product formation. The technique could detect 6 ng antigen in tissue homogenate as compared to 0.6 ng of the pure compound by inhibition. Chicken anti-GM3(NeuGc) antibody quantitatively inhibited the biotinylated antibody, however, this procedure was not suitable to quantify lower affinity HD antibody in patient sera. Immunostaining specific for HD antigen-positive cells, in tissue sections was by 4 micrograms/ml biotinylated antibody and 200 dilution of Avidin-biotinylated peroxidase complex reagent using pig intestine and lymph node as positive tissues and chicken intestine and lung as negative tissues.

[GM3 ganglioside as melanoma specific antigen and its biological function]

We have shown that a syngenic monoclonal antibody, M2590, established after immunization of C57BL/6 mice with B16 melanoma cells, recognized GM3 (NeuAc) ganglioside. Although GM3 is widely distributed among various normal cells and tissues, the antibody did not react with them. However, it reacted exclusively with melanoma cells from mouse, hamster and human. Preliminary experiments suggested that proteins and lipids as well as GM3 density on B16 cells are involved in the reactivity of GM3 with the antibody. Then, we investigated the biological function of the melanoma antigen, which was secreted from B16 cells into the culture medium. This soluble antigen was shown to suppress the positive immune responses by inhibiting CTL activity in the effector phase and by induction of specific suppressor T cells (Ts) that block CTL generation in the induction phase. Liposomes containing GM3 (NeuAc) but not GM3 (NeuGc) can effectively induce the melanoma specific Ts as did the soluble antigen. The results indicated the tumor cells can escape from host-immune system by stimulating the repertoire of Ts for self-antigen, GM3. To understand the biological role of GM3, we have established mutant clones of no-expressor of GM3 recognized by M2590. The clones were found to have lower attachment to laminin and type IV collagen and poor ability of lung metastasis.

Absence of a stratum corneum antigen in disorders of epidermal cell proliferation: detection with an anti-ganglioside GM3 antibody

We have investigated the distribution of ganglioside GM3 in normal skin with 8G9D8, a monoclonal antibody against GM3, and found binding to the stratum corneum. By electron microscopy, strong deposition of antibody was seen at the corneocyte envelope/"plasma membrane" region. Significantly decreased to absent binding to the stratum corneum was shown in a variety of disorders of excessive keratinocyte proliferation, including squamous cell carcinomas, psoriasis, and bullous and non-bullous forms of congenital ichthyosiform erythrodermas, as well as in the hyperplastic cornoid lamellae of porokeratosis. The 8G9D8 antibody recognizes the carbohydrate sequence N-acetylneuraminic acid alpha 2----3 galactose beta 1----4 glucose (or N-acetylglucosamine). Thus, in addition to ganglioside GM3, 8G9D8 may bind to glycoproteins or another glycolipid of the stratum corneum with a shared carbohydrate sequence. The carbohydrate sequence recognized by 8G9D8, whether attached to an epidermal glycoprotein or glycolipid, may prove to be important in keratinocyte proliferation and differentiation.

Immunosuppressive activity of human neuroblastoma tumor gangliosides

Gangliosides are shed in substantial amounts by some tumors, including human neuroblastoma, and these molecules modulate experimental tumor formation in vivo. We now demonstrate that neuroblastoma tumor gangliosides have potent immunoregulatory activity. Gangliosides of every one of 17 tumors studied were highly inhibitory for the normal in vitro human lymphoproliferative responses to the soluble antigen, tetanus toxoid; 30 nmol ganglioside/ml caused 43% to greater than 99% inhibition and the mean concentration causing 50% inhibition was only 17.3 nmol/ml. Furthermore, gangliosides isolated from clinically more aggressive tumors (Stage III or IV) were up to twice as immunosuppressive as those of the generally less aggressive tumors (Stage I or II) (p less than 0.05). Taken together with the lack of immunosuppressive activity of normal plasma gangliosides, the potent activity of neuroblastoma gangliosides supports the hypothesis that one mechanism by which these shed molecules may act to enhance tumor formation in vivo is through abrogation of the host cellular immune response at the site of tumor formation.

Involvement of the acyl chain of ceramide in carbohydrate recognition by an anti-glycolipid monoclonal antibody: the case of an anti-melanoma antibody, M2590, to GM3-ganglioside

The effect of the chain length of the fatty acid residue of the ceramide moiety of ganglioside GM3 on the binding ability of monoclonal antibody M2590, which is specific for the carbohydrate structure of GM3-ganglioside, was examined by means of a direct binding assay on thin layer chromatography plates (TLC immunostaining) and a quantitative enzyme-linked immunosorbent assay (ELISA). Derivatives of GM3 with a long fatty acid chain reacted with the M2590 antibody, but those with a short fatty acid chain showed no reaction in either assay system. These results suggested that the acyl fatty acid moiety of the ganglioside played an important role in the formation or maintenance of the antigenic structure of the carbohydrate moiety of the ganglioside.