Characterization of a human melanoma-associated ganglioside antigen defined by a monoclonal antibody, 4.2

A monoclonal IgM antibody, 4.2, reacting with a surface antigen expressed on most human melanomas (Yeh, M.-I., Hellström, I., Abe, K., Hakomori, S., and Hellström, K. E. (1982) Int. J. Cancer, 29, 269-275) was shown to be directed to a ganglioside with the carbohydrate structure NeuAc alpha 2 leads to 8NeuAc alpha 2 leads to 3Gal beta 1 leads to 4Glc beta 1 leads to 1Cer. The carbohydrate structure, established by enzymatic degradation and methylation analysis with mass spectrometry, is identical with that of brain GD3 ganglioside, but its ceramide is characterized by a predominance of longer chain fatty acids, in contrast to brain GD3 that has mainly C18:0 fatty acid. The antibody did not react with various other gangliosides, including those having the same terminal sugar sequence (NeuAc alpha 2 leads to 8NeuAc alpha 2 leads to 3Gal) as GD3, such as GT1a and GQ1b. Its specificity is therefore restricted to the NeuAc alpha 2 leads to 8NeuAc alpha 2 leads to 3Gal beta 1 leads to 4Glc leads to Cer sequence, including the innermost sugar, Glc residue.

A cell-surface antigen which is present in the ganglioside fraction and shared by human melanomas

We have raised a hybridoma, 4.2, which forms an IgM antibody to an antigen expressed on cultivated cells from most human melanomas, more infrequently on cells from other human tumors, and very weakly on cultivated fibroblasts, T cells and B cells. The antigen can be detected in biopsy material of human melanoma and, in smaller amounts, in fresh samples of normal human lung and kidney. Preliminary biochemical characterization indicates that it is associated with the ganglioside fraction. We feel that the antigen (referred to as 4.2) has a sufficient degree of tumor specificity to be rated as a human melanoma-associated antigen.

Clonal variation in expression of a human melanoma antigen defined by a monoclonal antibody

Previous work established 3 monoclonal mouse antibodies, 3.1, 3.2, and 3.3, which define an antigenic determinant that is expressed by a human melanoma, M1804, and, in smaller amounts, by another melanoma, M1801. In the present study we first investigated the expression of this determinant, which we refer to as 3.1, by cells from different melanomas, using membrane immunofluorescence techniques. We found that some tumors, such as M1801, appeared to be mixtures of cells that varied in their expression of 3.1. Clones were established from cultures of M1801 and M1804, and their expression of 3.1 was studied by a variety of serologic techniques, including membrane immunofluorescence, complement-dependent cytotoxicity, and absorption. Some of the clones expressed determinant 3.1, and others did not. By recloning a late passage of a 3.1-positive clone from M1801, a negative subclone was established, proving that 3.1-positive cells can yield 3.1-negative progeny. A clone that had lost 3.1 was tested and found to still express p97, an antigen defined by a different monoclonal antibody. We conclude that since some melanomas are heterogeneous with respect to the expression of antigenic determinant 3.1, and since 3.1 negative progeny can be derived from 3.1-positive cells, there is the potential for selection of 3.1-negative cells. The implications of this, for antigenic determinant 3.1 and possibly for other tumor antigens, must be taken into account when considering using monoclonal antibodies for tumor therapy.

Clonal variation in expression of a human melanoma antigen defined by a monoclonal antibody

Previous work established 3 monoclonal mouse antibodies, 3.1, 3.2, and 3.3, which define an antigenic determinant that is expressed by a human melanoma, M1804, and, in smaller amounts, by another melanoma, M1801. In the present study we first investigated the expression of this determinant, which we refer to as 3.1, by cells from different melanomas, using membrane immunofluorescence techniques. We found that some tumors, such as M1801, appeared to be mixtures of cells that varied in their expression of 3.1. Clones were established from cultures of M1801 and M1804, and their expression of 3.1 was studied by a variety of serologic techniques, including membrane immunofluorescence, complement-dependent cytotoxicity, and absorption. Some of the clones expressed determinant 3.1, and others did not. By recloning a late passage of a 3.1-positive clone from M1801, a negative subclone was established, proving that 3.1-positive cells can yield 3.1-negative progeny. A clone that had lost 3.1 was tested and found to still express p97, an antigen defined by a different monoclonal antibody. We conclude that since some melanomas are heterogeneous with respect to the expression of antigenic determinant 3.1, and since 3.1 negative progeny can be derived from 3.1-positive cells, there is the potential for selection of 3.1-negative cells. The implications of this, for antigenic determinant 3.1 and possibly for other tumor antigens, must be taken into account when considering using monoclonal antibodies for tumor therapy.

Lymphocyte-dependent antibodies to antigen 3.1, a cell-surface antigen expressed by a subgroup of human melanomas

Previous work from our laboratory has led to the isolation of a monoclonal IgG2a mouse antibody, 3.2, which is specific for an antigen, 3.1, that is strongest expressed by a group of human melanomas. We have no demonstrated that this antibody can mediate antibody-dependent cellular cytotoxicity (ADCC) to human melanoma cells expressing antigen 3., and that lymphocytes from human peripheral blood can be used as the source of K cells. A monoclonal IgG1 antibody, 3.1, to the same determinant of antigen 3.1 gave only weak and inconsistent ADCC.

Identification of a cell surface protein, p97, in human melanomas and certain other neoplasms

BALB/c mice were immunized with a human melanoma cell line, SK-MEL 28, and their spleen cells were fused with mouse NS-1 myeloma cells. Hybrid cells were tested in an indirect 125I-labeled protein A assay for production of antibodies that bound to surface antigens of SK-MEL 28 melanoma cells but not to autologous skin fibroblasts. One hybridoma, designated 4.1, had the required specificity. It was cloned and grown in mice as an ascites tumor. The monoclonal IgG1 antibody produced by the hybridoma was purified from the ascites fluid and labeled with 125I. The labeled antibody bound, at significant levels, to approximately 90% of the melanomas tested and to approximately 55% of other tumor cells, but not to three B-lymphoblastoid cell lines or to cultivated fibroblasts from 15 donors. Immunoprecipitation and sodium dodecyl sulfate gel electrophoresis were used to detect the target antigen in 125I-labeled cell membranes of both cultivated cells and tumor biopsy samples. A protein with a molecular weight of 97,000 was identified. This protein, designated p97, was present in both cultured cells and biopsy material from melanomas and certain other tumors, but it was not detected in eight different samples of normal adult epithelial or mesenchymal tissues obtained from five donors.

Cell surface antigens of human melanoma identified by monoclonal antibody

Mouse NS-1 myeloma cells were fused with spleen cells from mice that had been immunized with cells from a human melanoma, M1804. Hybrid cells were grown in selective medium and tested for production of antibody to surface antigens of M1804 cells. Three hybrids that produced antibodies that bound to the melanoma cells but not to autologous skin fibroblasts were cloned. Antibodies produced by two of the clones were cytotoxic to M1804 cells in the presence of rabbit complement. Extensive specificity tests showed that the antibodies produced by the clones bound strongly only to M1804 cells; significant, although weaker, binding occurred with 2 of 11 allogeneic melanomas. Apart from weak binding of the antibody produced by one of the clones to a breast carcinoma, binding assays of five carcinomas, one sarcoma, and fibroblasts from 17 individuals were negative, as were cytotoxic tests of 10 lymphoblastoid cell lines and peripheral blood lymphocytes from 68 normal donors and 12 chronic lymphocytic leukemia patients. This suggests that we have identified one or more determinants of a melanoma-associated antigen(s), whose expression is limited to a small proportion of melanomas.