Antitumor effects of a novel monoclonal antibody with high binding affinity to ganglioside GD3

Targeting Tumor Glycans for Cancer Therapy: Successes, Limitations, and Perspectives

Simple Summary

Aberrant glycosylation is a common feature of many cancers, and it plays crucial roles in tumor development and biology. Cancer progression can be regulated by several physiopathological processes controlled by glycosylation, such as cell–cell adhesion, cell–matrix interaction, epithelial-to-mesenchymal transition, tumor proliferation, invasion, and metastasis. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs), which are suitable for selective cancer targeting, as well as novel antitumor immunotherapy approaches. This review summarizes the strategies developed in cancer immunotherapy targeting TACAs, analyzing molecular and cellular mechanisms and state-of-the-art methods in clinical oncology.

Abstract

Aberrant glycosylation is a hallmark of cancer and can lead to changes that influence tumor behavior. Glycans can serve as a source of novel clinical biomarker developments, providing a set of specific targets for therapeutic intervention. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs) suitable for selective cancer-targeting therapy. The best characterized TACAs are truncated O-glycans (Tn, TF, and sialyl-Tn antigens), gangliosides (GD2, GD3, GM2, GM3, fucosyl-GM1), globo-serie glycans (Globo-H, SSEA-3, SSEA-4), Lewis antigens, and polysialic acid. In this review, we analyze strategies for cancer immunotherapy targeting TACAs, including different antibody developments, the production of vaccines, and the generation of CAR-T cells. Some approaches have been approved for clinical use, such as anti-GD2 antibodies. Moreover, in terms of the antitumor mechanisms against different TACAs, we show results of selected clinical trials, considering the horizons that have opened up as a result of recent developments in technologies used for cancer control.

Application of the Antibody-Inducing Activity of Glycosphingolipids to Human Diseases

Glycosphingolipids (GSLs) are composed of a mono-, di-, or oligosaccharide and a ceramide and function as constituents of cell membranes. Various molecular species of GSLs have been identified in mammalian cells due to differences in the structures of oligosaccharides. The oligosaccharide structure can vary depending on cell lineage, differentiation stage, and pathology; this property can be used as a cell identification marker. Furthermore, GSLs are involved in various aspects of the immune response, such as cytokine production, immune signaling, migration of immune cells, and antibody production. GSLs containing certain structures exhibit strong immunogenicity in immunized animals and promote the production of anti-GSL antibodies. By exploiting this property, it is possible to generate antibodies that recognize the fine oligosaccharide structure of specific GSLs or glycoproteins. In our study using artificially synthesized GSLs (artGSLs), we found that several structural features are correlated with the antibody-inducing activity of GSLs. Based on these findings, we designed artGSLs that efficiently induce the production of antibodies accompanied by class switching and developed several antibodies that recognize not only certain glycan structures of GSLs but also those of glycoproteins. This review comprehensively introduces the immune activities of GSLs and their application as pharmaceuticals.

Anti-proliferative and pro-apoptotic activity of GD2 ganglioside-specific monoclonal antibody 3F8 in human melanoma cells

The beneficial clinical effects of immunotherapy with GD2-specific monoclonal antibodies (mAbs) in melanoma and neuroblastoma patients have stimulated interest in characterizing the mechanisms underlying their antitumor effects. Previous studies have shown that GD2-specific mAbs mediate complement- and cell-dependent cytotoxicity and induce caspase-dependent apoptosis of tumor cells. In this study, we showed that GD2-specific mAb 3F8, which is undergoing clinical evaluation, inhibited the in vitro growth and induced apoptosis of melanoma cells. This effect was dose- and time-dependent, mediated by the interaction of mAb 3F8 combining site with GD2 ganglioside, associated with GD2 expression level on the cell surface, mAb internalization and increase of GD2 containing endosomes triggered by mAb 3F8. The induction of apoptosis by mAb 3F8 was mediated by caspase 3-, 7-, and 8-dependent pathways, downregulation of the anti-apoptotic molecules survivin and cytochrome c, and caspase 9 independent-AIF release from mitochondria. In addition, analyses of signaling pathway components demonstrated that mAb 3F8 strongly inhibited AKT and FAK activation and increased cleaved PARP expression. These results indicated that multiple mechanisms played a role in the antitumor activity of mAb 3F8 in melanoma cells. This information should provide a mechanistic basis for the optimization of the rational design of immunotherapeutic strategies in the mAb-based treatment of GD2 positive tumors.

Glycans as targets for therapeutic antitumor antibodies

Glycans represent a vast class of molecules that modify either proteins or lipids. They exert and regulate important and complex functions in both normal and cancer cell metabolism. As such, the most immunogenic glycans have been targeted in passive and active immunotherapy in human cancer for the past 25 years but it is only recently that techniques have become available to uncover novel glycan targets. The main focus of this review article is to highlight why and how monoclonal antibodies (mAbs) recognizing glycans, and in particular the glycans expressed on glycolipids, are being used in various strategies to target and kill cancer cells. The article reports on the historical use of mAbs and on very recent progress made in antitumor therapy using the anti-GD2 mAb and the antiganglioside mAbs, anti-N-glycolylneuraminic acid mAb and anti-Lewis mAb. Anti-GD2 is showing great promise in Phase III clinical trials in adjuvant treatment of neuroblastoma. Racotumomab, an anti-idiotypic mAb mimicking N-glycolylneuraminic acid-containing gangliosides, is currently being tested in a randomized, controlled Phase II/III clinical trial. This article also presents various strategies used by different groups to develop mAbs against these naturally poorly immunogenic glycans.

Binding activities and antitumor properties of a new mouse/human chimeric antibody specific for GD2 ganglioside antigen

PURPOSE

We previously generated a mouse monoclonal antibody (mAb) specific for the tumor-associated GD2 ganglioside antigen. Here, we describe the development of a chimeric anti-GD2 mAb for more effective tumor immunotherapy.

EXPERIMENTAL DESIGN

We cloned the cDNA encoding the immunoglobulin light and heavy chains of the 60C3 anti-GD2 mAb, and constructed chimeric genes by linking the cDNA fragments of the variable regions of the murine light and heavy chains to cDNA fragments of the human kappa and gamma1 constant regions, respectively.

RESULTS

The resultant chimeric anti-GD2 mAb, c.60C3, showed identical binding affinity and specificity to that of its murine counterpart. Both c.60C3 and 60C3 were rapidly internalized by tumor cells at 37 degrees C. When human serum and human natural killer cells were used as effectors in complement-mediated cytotoxicity and antibody-dependent cell cytotoxicity, respectively, c.60C3 was more effective in killing GD2-expressing tumor cells. However, c.60C3 was ineffective at inducing cell death by apoptosis, although binding of 60C3 induced apoptotic death in vitro. In an in vivo, GD2-expressing, syngeneic tumor model, i.v. injection of c.60C3, but not of 60C3, significantly suppressed tumor growth in mice (P<0.0005).

CONCLUSION

Immune effector functions mediated by this antibody and its potentially reduced immunogenicity make chimeric c.60C3 a promising therapeutic agent against neuroectodermic tumors.

Anti-GD3 monoclonal antibody effects on lymphocytes and antibody-dependent cellular cytotoxicity

PURPOSE

Antibodies targeting GD3 gangliosides highly expressed on melanomas mediate immune effector functions in vitro and inhibit animal model melanoma tumor growth in vivo. Because GD3 is expressed also on a subpopulation of human lymphocytes, we characterized the in vitro immune effects of murine R24 and a chimeric anti-GD3 antibody (KW-2871).

DESIGN

Anti-GD3 complement-mediated (CMC) and antibody-dependent cellular cytotoxicity (ADCC) were tested against cell line Mel-624. Antibody-mediated lymphocyte expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma (IFN-gamma) was quantified. The effect of antibody and antibody-treated lymphocyte supernates on effector cell ADCC and Fc receptor expression were evaluated.

RESULTS

R24 and KW-2871 antibodies mediated CMC and ADCC to the Mel-624 cell line. R24 induced potent lymphocyte proliferation and enhanced lymphocyte RNA expression of IL-4 (2-4 logs), IL-10, and IFN-gamma (> 10-fold). KW-2871 induced no lymphocyte proliferation and had minimal effects on lymphokine expression (< 5-fold). Preincubation of effector cells with either antibody inhibited ADCC and reduced monocyte expression of FcgammaRI and II. Supernates of effector cells preincubated with either antibody were able to inhibit ADCC.

CONCLUSIONS

R24 and KW-2871 antibody differ in their lymphocyte proliferation and lymphokine release activity but have similar inhibition of lymphocyte ADCC and FcgammaR expression in vitro.

A Phase I Study of an Anti-GD3 Monoclonal Antibody, KW-2871, in Patients with Metastatic Melanoma

PURPOSE

KW-2871 (IgG1 kappa chimeric antibody) targets GD3, which is upregulated in melanomas. We conducted a phase I trial of KW-2871 in patients with metastatic melanoma.

METHODS

Seventeen (17) patients were enrolled and received an initial test dose (10 mg/m2) intravenously. Two 2 weeks later, patients were stratified into 4 cohorts to receive 4 doses of KW-2871 (infused over 1 hour) at 2-week intervals (20, 40, 60, and 80 mg/m2). No premedications were administered for the test or first therapeutic doses.

RESULTS

Dose-limiting toxicities were Grade 3 laryngospasm and chest tightness with the initial therapeutic infusion at doses of 80 and 60 mg/m2. The maximum tolerated dose (MTD) was established at 40 mg/m2 of KW2871. The most common side-effect was urticaria (Grades 1-3) in 16 of 16 patients during an initial therapeutic infusion without premedication. The mean terminal half-life, clearance, and area under the concentration-time curve (AUC(0-t)) at a dose of 40 mg/m2 for course 1 were 146 +/- 31 hours, 28 +/- 6 ml/hour, and 1922 +/- 491 mcg*hour/mL, respectively. Anti-human chimeric antibody was not detected. Two (2) patients in the 40 mg/m2 cohort had stable disease.

CONCLUSIONS

An MTD of 40 mg/m2 without premedication was established for KW-2871, with urticaria being the most common side-effect and dose-limiting anaphylactoid infusion reactions.

Comparison of biological activity among nonfucosylated therapeutic IgG1 antibodies with three different N-linked Fc oligosaccharides: the high-mannose, hybrid, and complex types

The structure of asparagine-linked oligosaccharides attached to the antibody constant region (Fc) of human immunoglobulin G1 (IgG1) has been shown to affect the pharmacokinetics and antibody effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). However, it is still unclear how differences in the N-linked oligosaccharide structures impact the biological activities of antibodies, especially those lacking core fucose. Here, we succeeded in generating core fucose-lacking human IgG1 antibodies with three different N-linked Fc oligosaccharides, namely, a high-mannose, hybrid, and complex type, using the same producing clone, and compared their activities. Cultivation of an alpha-1,6-fucosyltransferase (FUT8) knockout Chinese hamster ovary cell line in the presence or absence of a glycosidase inhibitor (either swainsonine or kifunensine) yielded antibody production of each of the three types without contamination by the others. Two of three types of nonnaturally occurring atypical oligosaccharide IgG1, except the complex type, reduced the affinity for both human lymphocyte receptor IIIa (FcgammaRIIIa) and the C1q component of the complement, resulting in reduction of ADCC and CDC. The bulky structure of the nonreducing end of N-linked Fc oligosaccharides is considered to contribute the CDC change, whereas the structural change in the reducing end, i.e. the removal of core fucose, causes ADCC enhancement through improved FcgammaRIIIa binding. In the pharmacokinetic profile, although no significant difference of human neonatal Fc receptor (FcRn)-binding affinity was observed among the three types, the complex type showed longer serum half-lives than the other types irrespective of core fucosylation in mice, which also suggests the contribution of the nonreducing end structure. The present study provides basic information on the effects of core fucose-lacking N-linked Fc oligosaccharides on antibody biological activities.

The absence of fucose but not the presence of galactose or bisecting N-acetylglucosamine of human IgG1 complex-type oligosaccharides shows the critical role of enhancing antibody-dependent cellular cytotoxicity

An anti-human interleukin 5 receptor (hIL-5R) humanized immunoglobulin G1 (IgG1) and an anti-CD20 chimeric IgG1 produced by rat hybridoma YB2/0 cell lines showed more than 50-fold higher antibody-dependent cellular cytotoxicity (ADCC) using purified human peripheral blood mononuclear cells as effector than those produced by Chinese hamster ovary (CHO) cell lines. Monosaccharide composition and oligosaccharide profiling analysis showed that low fucose (Fuc) content of complex-type oligosaccharides was characteristic in YB2/0-produced IgG1s compared with high Fuc content of CHO-produced IgG1s. YB2/0-produced anti-hIL-5R IgG1 was subjected to Lens culinaris aggulutin affinity column and fractionated based on the contents of Fuc. The lower Fuc IgG1 had higher ADCC than the IgG1 before separation. In contrast, the content of bisecting GlcNAc of the IgG1 affected ADCC much less than that of Fuc. In addition, the correlation between Gal and ADCC was not observed. When the combined effect of Fuc and bisecting GlcNAc was examined in anti-CD20 IgG1, only a severalfold increase of ADCC was observed by the addition of GlcNAc to highly fucosylated IgG1. Quantitative PCR analysis indicated that YB2/0 cells had lower expression level of FUT8 mRNA, which codes alpha1,6-fucosyltransferase, than CHO cells. Overexpression of FUT8 mRNA in YB2/0 cells led to an increase of fucosylated oligosaccharides and decrease of ADCC of the IgG1. These results indicate that the lack of fucosylation of IgG1 has the most critical role in enhancement of ADCC, although several reports have suggested the importance of Gal or bisecting GlcNAc and provide important information to produce the effective therapeutic antibody.

Specific targeting, biodistribution, and lack of immunogenicity of chimeric anti-GD3 monoclonal antibody KM871 in patients with metastatic melanoma: results of a phase I trial

PURPOSE

KM871 is a chimeric monoclonal antibody against the ganglioside antigen GD3, which is highly expressed on melanoma cells. We conducted an open-label, dose escalation phase I trial of KM871 in patients with metastatic melanoma.

PATIENTS AND METHODS

Seventeen patients were entered onto one of five dose levels (1, 5, 10, 20, and 40 mg/m2). Patients received three infusions of KM871 at 2-week intervals, with the first infusion of KM871 trace-labeled with indium-111 (111In) to enable assessment of biodistribution in vivo. Biopsies of metastatic melanoma sites were performed on days 7 to 10.

RESULTS

Fifteen of 17 patients completed a cycle of three infusions of KM871. No dose-limiting toxicity was observed during the trial; the maximum-tolerated dose was therefore not reached. Three patients (at the 1-, 5-, and 40-mg/m2 dose levels) developed pain and/or erythema at tumor sites consistent with an inflammatory response. No normal tissue uptake of 111In-KM871 was observed, and tumor uptake of 111In-KM871 was observed in all lesions greater than 1.5 cm (tumor biopsy 111KM871 uptake results: range, 0.001% to 0.026% injected dose/g). The ratio of maximum tumor to normal tissue was 15:1. Pharmacokinetic analysis revealed a 111In-KM871 terminal half-life of 7.68 +/- 2.94 days. One patient had a clinical partial response that lasted 11 months. There was no serologic evidence of human antichimeric antibody in any patient, including one patient who received 16 infusions over a 12-month period.

CONCLUSION

This study is the first to demonstrate the biodistribution and specific targeting of an anti-GD3 antibody to metastatic melanoma in patients. The long half-life and lack of immunogenicity of KM871 makes this antibody an attractive potential therapy for patients with metastatic melanoma.

Dissection and optimization of immune effector functions of humanized anti-ganglioside GM2 monoclonal antibody

A mouse/human chimeric monoclonal antibody (MAb) KM966, specific for the cell-surface tumor antigen ganglioside GM2, was humanized by the complementarity determining regions (CDRs) grafting method. Not only the amino acid residues in the CDRs but also several in the framework regions (FRs) were changed from the human to the murine residues. A humanized variant, huKM796H/Lm-28, containing eight and five amino acid alterations in variable light (VL) and variable heavy (VH) FRs, respectively, showed a 9-fold reduction in complement-dependent cytotoxicity (CDC) compared to the chimeric KM966, despite tight antigen binding and potent antibody-dependent cellular cytotoxicity (ADCC). Several additional variants were subsequently constructed to improve the CDC of the antibody. One of the variants, designated KM8969, which differs by three amino acids, exhibited a CDC within 3-fold of the chimeric KM966. In addition, humanized KM8969 bound GM2 antigen 1.25-fold more tightly than the chimeric KM966 and showed 5-fold higher ADCC than the chimeric KM966. These results clearly show that the humanized KM8969, having the optimized immune effector functions and theoretically minimal immunogenicity, is an ideal candidate to test the effectiveness of anti-GM2 MAb in human cancer therapy. Taken together, the results obtained here indicate that the ADCC and CDC of an antibody can be dissected independently via engineering of the antibody variable region.

Synthesis and HPLC analysis of enzymatically cleavable linker consisting of poly(ethylene glycol) and dipeptide for the development of immunoconjugate

A model compound of anti-tumor agent, segment B of duocarmycin derivative DU-86, was conjugated to tumor-specific antibody via a cleavable linker consisting of poly(ethylene glycol) (PEG) and dipeptide, L-alanyl-L-valine (Ala-Val), to confirm the feasibility of the linker for application to immunoconjugate. The release of segment B from the linker was evaluated by HPLC analysis. When segment B was derivatized to have an amino residue and then linked to PEG through a dipeptide, segment B was cleaved at the peptide bond by a particular enzyme, thermolysin (EC 3.4.24.4), but not by plasmin (EC 3.4.2 1.7.), indicating that certain protease specifically expressed at the tumor site would be capable of peptide-specific digestion and release of anti-tumor agent since a thermolysin-like enzyme has been reported to be expressed at many tumor cells. Furthermore, the results showing that cell extract from G361 human melanoma had an ability to digest the linker peptide while the linker was stable in normal human serum suggested the tumor-specific activation of the conjugated agent. Segment B was conjugated via the linker to murine monoclonal antibody KM641 reactive to GD3 ganglioside to form immunoconjugate and the quantitative release of segment B under the treatment with the enzyme was also confirmed. These results indicate the possibility of double targeting based on both the recognition ability of tumor specific antibody and tumor specific activation of the anti-tumor agents to enhance tumor treatment efficacy and to decrease unwanted side effects.

Treatment of neoplastic meningeal xenografts by intraventricular administration of an antiganglioside monoclonal antibody, 3F8

Leptomeningeal (LM) neoplastic metastases are painful, debilitating and inevitably lethal. Intrathecal (IT) anti-tumor antibodies may have therapeutic potential. We evaluated 3F8, an anti-G(D2) murine IgG(3) monoclonal antibody (MAb) in the treatment of human melanoma (SKMEL-1) and neuroblastoma (NMB7) xenografts in athymic rats. Both tumors were lysed efficiently in vitro by 3F8 in the presence of rat neutrophils or rat complement. Antibody-dependent cellular cytotoxicity (ADCC) was not augmented by recombinant human GM-CSF (rhGM-CSF), rhG-CSF, recombinant rat MIP-2 (rrMIP-2) or lipopolysaccharide (LPS). In vivo, continuous intraventricular administration of 3F8 and LPS prevented tumor engraftment, retarded tumor growth and eradicated 3-day-old established xenografts whereas 3F8 alone, LPS alone or F(ab)'(2) plus LPS had no or only marginal effects. Tumor establishment in brain was completely prevented in 36% of animals implanted with SKMEL-1 and 65% of animals implanted with NMB7. Twenty percent of established xenografts around the brain were eradicated but all animals had persistent tumor in the lumbosacral meninges despite treatment. Continuous intraventricular infusion of LPS produced a variable polymorphonuclear (PMN) pleocytosis that was dose-dependent. Continuous intraventricular infusion of 3F8 produced immunohistochemically detectable attachment to 86% of persistent brain deposits of tumor but <1% of spinal lumbosacral deposits. We conclude that regional therapy with anti-G(D2) MAb could target neutrophils to inhibit LM tumor growth. However, optimal activation and mobilization of neutrophils into the cerebrospinal fluid (CSF) and improved penetration of MAb to tumor sites remain critical variables.

Direct immobilization of gangliosides onto gold-carboxymethyldextran sensor surfaces by hydrophobic interaction: applications to antibody characterization

We describe a novel immobilization technique to investigate interactions between immobilized gangliosides (GD3, GM1, and GM2) and their respective antibodies, antibody fragments, or binding partners using an optical biosensor. Immobilization was performed by direct injection onto a carboxymethyldextran sensor chip and did not require derivatization of the sensor surface or the ganglioside. The ganglioside appeared to bind to the sensor surface by hydrophobic interaction, leaving the carbohydrate epitope available for antibody or, in the case of GM1, cholera toxin binding. The carboxyl group of the dextran chains on the sensor surface did not appear to be involved in the immobilization as evidenced by equivalent levels of immobilization following conversion of the carboxyl groups into acyl amino esters, but rather the dextran layer provided a hydrophilic coverage of the sensor chip which was essential to prevent nonspecific binding. This technique gave better reactivity and specificity for anti-ganglioside monoclonal antibodies (anti-GD3: KM871, KM641, R24; and anti-GM2: KM966) than immobilization by hydrophobic interaction onto a gold sensor surface or photoactivated cross-linking onto carboxymethydextran. This rapid immobilization procedure has facilitated detailed kinetic analysis of ganglioside/antibody interactions, with the surface remaining viable for a large number of cycles (>125). Kinetic constants were determined from the biosensor data using linear regression, nonlinear least squares and equilibrium analysis. The values of kd, ka, and KAobtained by nonlinear analysis (KAKM871 = 1.05, KM641 = 1.66, R24 = 0.14, and KM966 = 0.65 x 10(7) M-1) were essentially independent of concentration and showed good agreement with data obtained by other analytical methods.

Reversal of adriamycin resistance with chimeric anti-ganglioside GM2 antibody

Ganglioside GM2 is one of the major cell-surface gangliosides expressed in human tumors. We earlier established a mouse/human IgG1 chimeric anti-GM2 antibody, KM966, which displayed anti-tumor activity in human tumor cells both in vitro and in vivo. In this study, we have screened for changes in ganglioside expressions in several drug-resistant human cancer cell lines to examine the modulation of drug resistance by immunotherapy with anti-ganglioside antibodies. Increased GM2 expression, detected by flow cytometry and thin-layer chromatography, was observed in the SBC-3/ADM and AdrR MCF7 adriamycin-resistant cell lines, in contrast with their parental lines. In other related gangliosides, ganglioside GD2 levels in AdrR MCF7 were higher than those in MCF7 cells. We confirmed increased N-acetylgalactosaminyltransferase mRNA in adriamycin-resistant cell lines, as compared with the parental cells, by Northern-blot analysis. Moreover, to investigate the possibility of exploiting the anti-tumor activity of KM966 in order to overcome resistance to adriamycin, we investigated the antibody-dependent cell-mediated cytotoxity of human peripheral mononuclear blood cells and the complement-dependent cytotoxity of human serum with KM966 against SBC-3, SBC-3/ADM, MCF7 and AdrR MCF7. Significantly higher killing via KM966 was observed in SBC-3/ADM and AdrR MCF7 cells as compared with the parental cells. This suggests that passive immunotherapy using KM966 against human adriamycin-resistant cancer may be useful for overcoming resistance to adriamycin.

A new vector for the high level expression of chimeric antibodies in myeloma cells

We previously reported the expression of a mouse/human chimeric anti-ganglioside GD3 antibody, KM871 (IgG1,kappa) in mouse myeloma SP2/0 cells under the control of the ecotropic Moloney virus long terminal repeat by the co-transfection of chimeric heavy (H) and light (L) chain vectors (Shitara et al. (1993) Cancer Immunol. Immunother.). To establish an efficient and high level expression system for the chimeric antibody, we did comparative study on vector systems and host cells. An improved expression vector, named 'a tandem vector, pChi641HLGM4' was constructed, in which both of the chimeric H and L chain gene transcription units and a dihydrofolate reductase (dhfr) gene transcription unit were inserted. When two kinds of mouse myeloma cell lines, SP2/0 and P3U1, were used as host cells, frequency of the incidence of antibody-producing transfectants was markedly increased by the use of the tandem vector compared with the use of the mixture of each chimeric H vector and L chain vector. To select out appropriate host cells, transfection frequency and antibody production level were compared among SP2/0, P3U1 and rat myeloma YB2/0 cells by transfection of the tandem vector. YB2/0 cell was shown to have the highest potential in both the transfection frequency and the antibody production. Introduction of the tandem vector into YB2/0 cells and the subsequent amplification with 50-200 nM methotrexate gave rise to several clones that stably secreted 70-100 micrograms/10(6) cells per 24 h of the chimeric antibody. This productivity of the antibody is one of the highest levels which have been achieved by other investigators using transfected myeloma cells. Using this system it took only 2-3 months to establish the transfectant clones which stably produced the chimeric antibody.

Monoclonal antibody against a lactose epitope of glycosphingolipids binds to melanoma tumour cells

Mice were immunized with a neoglycoprotein consisting of a chemically modified carbohydrate moiety (reductively aminated 3'-sialyllactose) linked to human serum albumin. By this procedure an antibody response to the normally non-immunogenic carbohydrate structure was obtained. Hybridomas were established, and monoclonal antibodies were selected in ELISA based on their binding to the saccharide hapten, or to a lactosylceramide-mimicking neoglycolipid, lactose-bis-sulfone. One of the selected antibodies, 2H4, was of particular interest, since it also bound to glycolipids present on melanoma cells. FACS analysis of a panel of 14 melanoma cell lines showed that the 2H4 antibody bound to the majority of these. In frozen, non-fixed sections or paraffin sections of biopsies the monoclonal antibody 2H4 stained melanoma cells, but not tumour infiltrating lymphocytes or normal skin. Detailed immunochemical analysis of 2H4, using thin layer chromatography revealed that it recognized an internal lactose epitope in several glycosphingolipids.

A mouse/human chimeric anti-(ganglioside GD3) antibody with enhanced antitumor activities

Ganglioside GD3, which is one of the major gangliosides expressed on the cell surface of human tumors of neuroectodermal origin has been focused on as a target molecule for passive immunotherapy. We have cloned the cDNA encoding the immunoglobulin light and heavy chains of an anti-GD3 monoclonal antibody KM641 (murine IgG3, kappa), and constructed the chimeric genes by linking the cDNA fragments of the murine light and heavy variable regions to cDNA fragments of the human kappa and gamma 1 constant regions, respectively. The transfer of these cDNA constructs into SP2/0 mouse myeloma cells resulted in the production of the chimeric antibody, designated KM871, that retained specific binding activity to GD3. Indirect immunofluorescence revealed the same staining pattern for chimeric KM871 and the mouse counterpart KM641 on GD3-expressing melanoma cells. When human serum and human peripheral blood mononuclear cells were used as effectors in complement-mediated cytotoxicity and antibody-dependent cell-mediated cytotoxicity respectively, the chimeric KM871 was more effective in killing GD3-expressing tumor cells than was the mouse counterpart KM641. Intravenous injection of chimeric KM871 markedly suppressed tumor growth in nude mice. The chimeric KM871, having enhanced antitumor activities and less immunogenicity than the mouse counterpart, would be a useful agent for passive immunotherapy of human cancer.