Immunoglobulin class switch of anti-ganglioside monoclonal antibody from IgM to IgG

Production and characterization of monoclonal antibodies specific to lactotriaosylceramide

We have established hybridoma cell lines producing monoclonal antibodies (mAbs) directed to N-acetylglucosaminylβ1-3galactose (GlcNAcβ1-3Gal) residue by immunizing BALB/c mice with lactotriaosylceramide (Lc(3)Cer). These obtained hybridoma cells, specific to Lc(3)Cer, were dual immunoglobulin (Ig)-producing cells which secreted both IgM and IgG molecules as antibodies. The established mAbs are able to react with not only Lc(3)Cer but also GlcNAcβ1-3-terminal glycosphingolipids (GSLs) despite branching or lactosamine chain lengths and human transferrin with terminal GlcNAc residues. Comparison of the variable regions of the cloned IgM and IgG by reversed transcription-polymerase chain reaction analysis confirmed that the variable regions determine the specificity, the other amino acids are conserved, and these mAbs are encoded by J558 and Vκ-21family genes. Furthermore, we have analyzed the expression of GSLs with GlcNAcβ1-3 epitope in acute leukemia cell lines and mouse fetal tissues using these mAbs, in which antigens were distributed comparatively. These mAbs are useful for studying the precise distribution of GlcNAcβ1-3Gal-terminating GSL expression in tissues as well as for detecting GSLs carrying terminal GlcNAcβ1-3Gal carbohydrate structure.

Antibodies against tumor cell glycolipids and proteins, but not mucins, mediate complement-dependent cytotoxicity

One of several effector mechanisms thought to contribute to Ab efficacy against cancer is complement-dependent cytotoxicity (CDC). Serological analysis of a series of clinical trials conducted over a 10-year period suggested that six vaccines containing different glycolipids induced Abs mediating CDC whereas four vaccines containing carbohydrate or peptide epitopes carried almost exclusively by mucin molecules induced Abs that did not mediate CDC. To explore this further, we have now compared cell surface reactivity using flow cytometry assays (FACS), complement-fixing ability, and CDC activity of a panel of mAbs and immune sera from these trials on the same two tumor cell lines. Abs against glycolipids GM2, globo H and Lewis Y, protein KSA (epithelial cell adhesion molecule, also known as EpCAM) and mucin Ags Tn, sialylated Tn, Thomsen Friedenreich (TF), and MUC1 all reacted comparably by FACS with tumor cells expressing these Ags. Compared with the strong complement binding and CDC with Abs against glycolipids and KSA, complement binding was diminished with Abs against mucin Ags and no CDC was detected. A major difference between these two groups of Ags is proximity to the cell membrane. Glycolipids and globular glycoproteins extend less than 100 A from the cell membrane while mucins extend up to 5000 A. Although complement activation at sites remote from the cell membrane has long been known as a mechanism for resistance from complement lysis in bacteria, it is identified here for the first time as a factor which may contribute to resistance from CDC against cancer cells.

In vitro system for immunoglobulin class switching using BHK cells transfected with murine recombinant CD40 ligand

To develop an in vitro system for mouse immunoglobulin (Ig) class switching, the expression vector of murine CD40 ligand (CD40L) which is expressed on T cells was transfected to BHK cells. By using culture plates coated with the BHK cells expressing the recombinant CD40L, Ig class switching of splenic B cells was examined. The CD40L mRNA was cloned from splenic T cells of BALB/mice activated with anti-CD3 antibody in vitro. As the No.593 base in the open reading frame sequence of the CD40L from BALB/c spleen differed from T to G, when compared with the known sequence from C57BL/6, one of the BALB/c-derived clones was reconstructed to the known CD40L by site-directed mutagenesis. Splenic B cells from BALB/c were induced secretion of Ig isotypes, IgM, IgG1 and IgE when cultured on two types of BHK cells, the transfected BHK cells with a CD40L clone from BALB/c and the transfected BHK cells with the reconstructed CD40L clone, in the presence of IL-4. However, when splenic B cells from C57BL/6 were cultured on the same systems, the B cells produced Ig isotypes, IgM, IgG1, IgG2a, IgG2b, IgG3 and IgE. In the similar experiments using the transfected BHK cells with a empty vector and the normal BHK cells, none of B cells produced any Ig isotypes other than IgM. These results indicate that Ig class switching of murine B cells can be induced by using these two types of CD40L-expressing BHK cells in vitro.

Relationship of glycosyltransferases and mRNA levels to ganglioside expression in neuroblastoma and melanoma cells

Most human neuroblastoma tumors are characterized by the high expression of GD2 (or GD2 and/or GM2) gangliosides, whereas melanomas characteristically express GD3 ganglioside. The molecular basis for these patterns was investigated by examining the relationship between ganglioside levels, glycosyltransferase (GM2/GD2 synthase and GD3 synthase) activity, and corresponding mRNA levels in a panel of human neuroblastoma and melanoma cell lines. In general, the ganglioside patterns could be explained by the levels of the transferases and their mRNA, indicating control at the level of transcription. A key role was noted for GD3 synthase. Notably, it was found that neuroblastoma cell lines with high GD2 ganglioside levels had low levels of GD3, its synthase, and mRNA for the enzyme even though this step provides the substrate for GD2 synthesis. The key role for GD3 synthase was also examined by stably transfecting GD3 synthase cDNA into a neuroblastoma cell line (SH-SY5Y) not expressing GD3 and GD2. The resulting cell line had high levels of GD2 ganglioside and altered morphology and growth characteristics.

Immunoglobulin double isotype-producing hybridomas isolated from an autoimmune (NZB x NZW)F1 mouse

In the sera of (NZB x NZW)F1 (B/W) mice that develop a lupus-like syndrome, increased levels of IgG antibodies (Ab) reacting with TNP have been detected before the appearance of IgG anti-DNA Ab and clinical symptoms. A single injection of trinitrophenyl-bovine serum albumin (TNP/BSA) in physiological saline into a young B/W mouse (3 months old), followed by fusion of its splenocytes 3 days later, gave rise to hybridomas simultaneously secreting IgM and IgG Ab with anti-TNP reactivity. Both mu and gamma chains were detected in culture supernatants by ELISA, and double isotype-producing cells were labeled by immunofluorescence. Molecular analysis of two of these double isotype-producing hybridomas showed the presence of mRNA coding for both mu and gamma chains of Ig, and this gamma mRNA could be translated in vitro into a gamma heavy (H) chain. Comparison of the H chain variable-region sequences of IgM and IgG revealed 100% homology between mu and gamma V(H) genes in one clone, while mu and gamma V(H) genes showed only 80% homology in the other clone. Both clones produced a single kappa light (L) chain. These two hybridomas, isolated from a B/W mouse, thus represent two different mechanisms of double isotype expression: the first one corresponds to an IgM to IgG switch, while the second one reflects a lack of allelic exclusion.

Selection of tumor antigens as targets for immune attack using immunohistochemistry: I. Focus on gangliosides

Understanding the distribution of tumor-associated antigens on cancers and normal tissues is essential for selection of targets for cancer immunotherapy. Seven carbohydrate antigens, potential targets for immunotherapy, were studied using a panel of well-characterized MAbs by immunohistochemistry on cryostat-cut tissue sections of 13 types of cancers and 18 normal tissues. GD2 and GD3 were present on most cancers of neuroectodermal origin and GD2 was also present on B cell lymphomas. 9-O-acetyl-GD3 was detected only on melanoma while fucosyl GM1 was detected only on small cell lung cancers (SCLC). Surprisingly, GM2 was strongly expressed on all tested tumors, including cancers of neuroectodermal origin and cancers of epithelial origin. Polysialic acid was primarily expressed on SCLC and neuroblastomas. Globo H was present on most cancers of epithelial origin. These antigens were also identified in normal tissues. Fucosyl GM1 was not expressed significantly on any of the normal tissues analyzed. GD3, GD2, GM2 and polysialic acid were detected in normal brain to varying degrees. GM2 and Globo H were expressed on the luminal surface of epithelia of a variety of organs. The unexpected expression of GM2 on a broad range of cancers and normal epithelial tissues was confirmed by loss after methanol fixation and by immune thin layer chromatography.

Selection of tumor antigens as targets for immune attack using immunohistochemistry: I. Focus on gangliosides

Understanding the distribution of tumor-associated antigens on cancers and normal tissues is essential for selection of targets for cancer immunotherapy. Seven carbohydrate antigens, potential targets for immunotherapy, were studied using a panel of well-characterized MAbs by immunohistochemistry on cryostat-cut tissue sections of 13 types of cancers and 18 normal tissues. GD2 and GD3 were present on most cancers of neuroectodermal origin and GD2 was also present on B cell lymphomas. 9-O-acetyl-GD3 was detected only on melanoma while fucosyl GM1 was detected only on small cell lung cancers (SCLC). Surprisingly, GM2 was strongly expressed on all tested tumors, including cancers of neuroectodermal origin and cancers of epithelial origin. Polysialic acid was primarily expressed on SCLC and neuroblastomas. Globo H was present on most cancers of epithelial origin. These antigens were also identified in normal tissues. Fucosyl GM1 was not expressed significantly on any of the normal tissues analyzed. GD3, GD2, GM2 and polysialic acid were detected in normal brain to varying degrees. GM2 and Globo H were expressed on the luminal surface of epithelia of a variety of organs. The unexpected expression of GM2 on a broad range of cancers and normal epithelial tissues was confirmed by loss after methanol fixation and by immune thin layer chromatography.

A method for monoclonal antibody isotype switching: anti-CD60 VH expression in a heavy chain-deficient hybridoma variant

Alteration of monoclonal antibody isotype is desirable for a variety of purposes, including obtaining an improved reagent for investigative or therapeutic use. A variety of approaches for isotype switching, particularly from IgM to various IgG subclasses, have been described. Antibodies that recognize carbohydrate determinants on glycoproteins, glycolipids, or polysaccharides are generally of the IgM isotype. This includes all available antibodies to the human CD60 antigen, a determinant with cell coactivating properties described on a subset of T lymphocytes and on other cell types. In this report a new method for monoclonal antibody isotype switching is presented. A plasmid containing the VH regions of anti-CD60 linked to C gamma 1 was transfected into a spontaneously arising variant of the CD60 hybridoma that produced kappa light chain but no heavy chain. This transfected hybridoma line maintains stable production of useful quantities of IgG1 monoclonal anti-CD60 in vitro and in vivo.