Immunogenetic analysis of variable regions encoding AB1 and gamma-type AB2 antibodies from the NeuGc-containing ganglioside family

Monoclonal Antibody chP3R99 Reduces Subendothelial Retention of Atherogenic Lipoproteins in Insulin-Resistant Rats: Acute Treatment Versus Long-Term Protection as an Idiotypic Vaccine for Atherosclerosis

BACKGROUND

Atherosclerosis is triggered by the retention of apolipoprotein B-containing lipoproteins by proteoglycans. In addition to low-density lipoprotein, remnant lipoproteins have emerged as pivotal contributors to this pathology, particularly in the context of insulin resistance and diabetes. We have previously reported antiatherogenic properties of a monoclonal antibody (chP3R99) that recognizes sulfated glycosaminoglycans on arterial proteoglycans.

METHODS AND RESULTS

Solid-phase assays demonstrated that chP3R99 effectively blocked >50% lipoprotein binding to chondroitin sulfate and vascular extracellular matrix in vitro. The preperfusion of chP3R99 (competitive effect) resulted in specific antibody-arterial accumulation and reduced fluorescent lipoprotein retention by ~60% in insulin resistant JCR:LA-cp rats. This competitive reduction was dose dependent (25-250 μg/mL), effectively decreasing deposition of cholesterol associated with lipoproteins. In a 5-week vaccination study in insulin resistant rats with (200 μg subcutaneously, once a week), chP3R99 reduced arterial lipoprotein retention, and was associated with the production of antichondroitin sulfate antibodies (Ab3) able to accumulate in the arteries (dot-blot). Neither the intravenous inoculation of chP3R99 (4.5 mg/kg), nor the immunization with this antibody displayed adverse effects on lipid or glucose metabolism, insulin resistance, liver function, blood cell indices, or inflammation pathways in JCR:LA-cp rats.

CONCLUSIONS

Both acute (passive) and long-term administration (idiotypic cascade) of chP3R99 antibody reduced low-density lipoprotein and remnant lipoprotein interaction with proteoglycans in an insulin-resistant setting. These findings support the innovative approach of targeting proatherogenic lipoprotein retention by chP3R99 as a passive therapy or as an idiotypic vaccine for atherosclerosis.

GM3(Neu5Gc) ganglioside: an evolution fixed neoantigen for cancer immunotherapy

Numerous molecules have been considered as targets for cancer immunotherapy because of their levels of expression on tumor cells, their putative importance for tumor biology, and relative immunogenicity. In this review we focus on the ganglioside GM3(Neu5Gc), a glycosphingolipid present on the outer side of the plasma membrane of vertebrate cells. The reasons for selecting GM3(Neu5Gc) as a tumor-specific antigen and its use as a target for cancer immunotherapy are discussed, together with the development of antitumor therapies focused on this target by the Center of Molecular Immunology (CIM, Cuba).

B-CD8+ T Cell Interactions in the Anti-Idiotypic Response against a Self-Antibody

P3 is a murine, germline, IgM mAb that recognizes N-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+ T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+ T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VH region was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens.

Arresting progressive atherosclerosis by immunization with an anti-glycosaminoglycan monoclonal antibody in apolipoprotein E-deficient mice

Atherogenesis is associated with the early retention of low-density lipoproteins (LDL) in the arterial intima by interaction with glycosaminoglycan (GAG)-side chains of proteoglycans. Retained LDL undergo reactive oxygen species-mediated oxidation. Oxidized LDL trigger oxidative stress (OS) and inflammation, contributing to atherosclerosis development. Recently, we reported the preventive anti-atherogenic properties of the chimeric mouse/human monoclonal antibody (mAb) chP3R99-LALA, which were related to the induction of anti-chondroitin sulfate antibody response able to inhibit chondroitin sulfate dependent LDL-enhanced oxidation. In the present work, we aimed at further investigating the impact of chP3R99-LALA mAb vaccination on progressive atherosclerosis in apolipoprotein E-deficient mice (apoE(-/-)) fed with a high-fat high-cholesterol diet receiving 5 doses (50 µg) of the antibody subcutaneously, when ~5% of the aortic area was covered by lesions. Therapeutic immunization with chP3R99-LALA mAb halted atherosclerotic lesions progression. In addition, aortic OS was modulated, as shown by a significant (p<0.05) reduction of lipid and protein oxidation, preservation of antioxidant enzymes activity and reduced glutathione, together with a decrease of nitric oxide levels. chP3R99-LALA mAb immunization also regulated aortic NF-κB activation, diminishing the proinflammatory IL1-β and TNF-α gene expression as well as the infiltration of macrophages into the arterial wall. The therapeutic immunization of apoE(-/-) with progressive atheromas and persistent hypercholesterolemia using chP3R99-LALA mAb arrested further development of lesions, accompanied by a decrease of aortic OS and NF-κB-regulated pro-inflammatory cytokine gene expression. These results contribute to broaden the potential use of this anti-GAG antibody-based immunotherapy as a novel approach to target atherosclerosis at different phases of progression.

Antibody recognition of carbohydrate epitopes†

Carbohydrate antigens are valuable as components of vaccines for bacterial infectious agents and human immunodeficiency virus (HIV), and for generating immunotherapeutics against cancer. The crystal structures of anti-carbohydrate antibodies in complex with antigen reveal the key features of antigen recognition and provide information that can guide the design of vaccines, particularly synthetic ones. This review summarizes structural features of anti-carbohydrate antibodies to over 20 antigens, based on six categories of glyco-antigen: (i) the glycan shield of HIV glycoproteins; (ii) tumor epitopes; (iii) glycolipids and blood group A antigen; (iv) internal epitopes of bacterial lipopolysaccharides; (v) terminal epitopes on polysaccharides and oligosaccharides, including a group of antibodies to Kdo-containing Chlamydia epitopes; and (vi) linear homopolysaccharides.

Induction of anti-anti-idiotype antibodies against sulfated glycosaminoglycans reduces atherosclerosis in apolipoprotein E-deficient mice

OBJECTIVE

The pathogenesis of atherosclerosis is associated with the early retention of low-density lipoproteins that are trapped in the extracellular matrix of the arterial intima by interaction with glycosaminoglycan side chains of proteoglycans. Mutant mouse/human chimeric antibodies of the murine monoclonal antibody P3, which react with N-glycolyl-containing gangliosides and sulfated glycosaminoglycans, were tested for their potentially antiatherogenic properties through the induction of an idiotypic antibody network that may specifically interfere with the binding of low-density lipoproteins to proteoglycan side chains, low-density lipoprotein modification, and foam cell formation.

METHODS AND RESULTS

Apolipoprotein E-deficient mice fed a high-fat, high-cholesterol diet received 5 to 6 doses of chP3R99 or chP3S98 mutant antibodies, showing high and low reactivity, respectively, against their respective antigens. Both chimeric antibodies elicited an immunodominant anti-idiotypic response in the absence of adjuvant. A striking (40%-43%) reduction (P<0.01) in total lesion areas was observed in 18-week-old mice immunized with chP3R99, but not chP3S98, compared with PBS-treated mice. The antiatherosclerotic effect was associated with increased mice sera reactivity against heparin and sulfated glycosaminoglycans, including chondroitin and dermatan sulfate. In addition, purified IgG from chP3R99-immunized mice blocked the retention of apolipoprotein B-containing lipoproteins within the arterial wall of apolipoprotein E(-/-) mice.

CONCLUSIONS

The present study supports use of active immunization and the mounting of an idiotypic antibody network response against glycosaminoglycans as a novel approach to target atherosclerosis.

P3 mAb: An Immunogenic Anti-NeuGcGM3 Antibody with Unusual Immunoregulatory Properties

P3 is a murine IgM mAb that recognize N-glycosylated gangliosides, sulfatides, and antigens expressed in melanoma, breast, and lung human tumors. This antibody has the ability to trigger an IgG antibody response in the syngeneic BALB/c model, even when it is administered in the absence of adjuvant or carrier protein. The mechanism by which the P3 mAb, a self-immunoglobulin, induce this immune response in the absence of co-stimulatory or classical danger signals is still unknown. In the present paper we show that the high immunogenicity of P3 mAb depends not only on CD4 but also on CD8⁺ T cells, since the depletion of CD8⁺ or CD4⁺ T cells led to the loss of P3 mAb immunogenicity in the syngeneic model. Furthermore, the immunization with P3 mAb enhanced the recovery of the CD8⁺ T cell population in mice treated with an anti-CD8a antibody. Additionally, the immunization with P3 mAb restored the capacity of immunosuppressed mice to reject allogeneic tumors, a mechanism mediated by the action of CD8⁺ T cells. Finally, in mice with cyclophosphamide induced lymphopenia, the administration of P3 mAb accelerated the recovery of both CD4⁺ and CD8⁺ T cells. These results show new possibilities for B and CD8⁺ T cells interactions during the immune response elicited by a self-protein. Furthermore they point to P3 mAb as a potential interesting candidate for the treatment of immunosuppressed patients.

Lonely killers: effector cell- and complement-independent non-proapoptotic cytotoxic antibodies inducing membrane lesions

The majority of the most effective monoclonal antibodies (mAbs) currently in the clinics bind to cancer or immune cells. Classic mechanisms of cell killing by therapeutic mAbs include antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity and induction of apoptosis by engagement of specific cell ligands. A few reports have described mAbs whose cytotoxic activity is Fc-independent and that do not induce the morphological and biochemical changes associated with the apoptosis-type of cell death. Even fewer works describe mAbs able to directly induce membrane lesions. Here, we discuss the available data on those molecules and their cell killing activity, with particular attention to the case of a mAb specific for the tumor-associated N-glycolyl (Neu5Gc)-GM3 ganglioside (GM3(Neu5Gc)). Some similarities are found in the cell death pathways triggered by these mAbs, but data are not abundant. We conclude that the usefulness of mAbs with a direct cytotoxic activity for immunotherapeutic strategies deserves deeper research.

Anti-idiotypic antibody mimicking a T-antigen-specific lectin inhibits human epithelial tumor cell proliferation

Cancer-associated mucins show frequent alterations of oligosaccharide chain profile. Terminal structures may be deleted, thereby exposing normally 'cryptic' structures such as Tn (GalNAcα-O-Ser/Thr) and T antigen (Galβ1-3GalNAcα-O-Ser/Thr). Overexpression of these commonly hidden glycoforms, and reduced level of naturally occurring anti-T or anti-Tn antibodies, is associated with epithelial tumor progression and aggressiveness. The lectin from the common edible mushroom Agaricus bisporus (ABL) shows high affinity binding to T antigen, and reversible noncytotoxic inhibitory effect on epithelial tumor cell proliferation. The aim of this study was to induce immune response with tumor-associated glycan specificity and biological activity similar to those of ABL. An anti-idiotypic (Id) antibody strategy was developed using ABL as first template. ABL was purified by affinity chromatography and assayed as immunogen in rabbit. Rabbit IgG was purified from anti-ABL serum using a protein G column, and specific anti-ABL IgG was obtained by affinity chromatography using immobilized ABL. Affinity-purified anti-ABL IgG contained an antibody fraction that recognizes the carbohydrate-binding site of ABL. This IgG was used as immunogen in mouse to yield anti-Id antibody recognizing tumor-associated glycans such as Tn and T antigen. Competitive assays showed that α-anomeric GalNAc is the main binding subsite of anti-Id antibody in glycan recognition. Anti-Id antibody bound human epithelial tumor cells, as shown by cell enzyme-linked immunosorbent assay and immunofluorescence. Anti-Id antibody raised by immunization with affinity-purified anti-ABL IgG had antiproliferative effect on human epithelial tumor cells through apoptosis induction similar to that of ABL. The anti-Id immune response developed here has potential application in cancer therapy.

Crystal structure of an anti-ganglioside antibody, and modelling of the functional mimicry of its NeuGc-GM3 antigen by an anti-idiotypic antibody

N-Glycolylated (NeuGc) gangliosides are tumor-specific antigens and as such represent attractive targets for cancer immunotherapy. The chimeric antibody chP3 selectively recognizes a broad variety of NeuGc gangliosides, showing no cross-reactivity to the highly similar N-acetylated (NeuAc) gangliosides that are common cellular antigens in humans. Here, we report the crystal structure of the chP3 Fab and its computer-docking model with the trisaccharide NeuGcalpha3Galbeta4Glcbeta, which represents the carbohydrate moiety of the tumor-antigen NeuGc-GM3. The interaction involves only the heavy chain of the chP3 antibody. The modelled complex is consistent with all available experimental data and shows good surface complementarity. The negatively charged sialic acid residue NeuGc is buried in a pocket flanked by two arginine residues, VH Arg31 and VH Arg100A. We have further investigated the interaction of chP3 with its anti-idiotypic antibody, 1E10 (also known as Racotumomab), currently in clinical trials as a cancer vaccine. While many of the chP3 residues predicted to interact with the NeuGc ganglioside also feature prominently in the modelled complex of chP3 and 1E10, we do not observe structural mimicry. Rather, we suspect that the anti-idiotype 1E10 may serve as an imprint of the structural characteristics of the chP3 idiotype and, consequently, give rise to antibodies with P3-like properties upon immunization.

Gangliosides, Ab1 and Ab2 antibodies

This report is focused on the molecular basis for the interaction of a monoclonal antibody (mAb) and its anti-idiotypic mAb. P3 mAb (Ab1) recognizes N-glycolyl-gangliosides, and 1E10 mAb is one of its anti-idiotypic mAbs (Ab2). Chimeric versions of both antibodies retained their specificity. Charged residues in their H-CDRs, particularly H-CDR3, were considered to play a major role in their binding and immunogenic properties. P3 mAb has the unusual property of generating a strong antibody response in syngeneic mice, even when it is administered in saline. We selected phagotopes from a 12mer peptide library displayed on filamentous phage to characterize amino acid motifs recognized by these antibodies. The peptides were enriched in charged amino acids similar to those present in P3 and 1E10 mAb H-CDR3. We also report the construction of four mutants of the P3 antibody, where arginine residues in the heavy chain CDRs were substituted by serine residues, and the characterization of their interaction with 1E10 mAb and GM3(NeuGc) ganglioside, as well as their immunogenic properties in Balb/c mice. H-CDR1 R31 residue appears to have a central role in P3 mAb reactivity and antigenicity. H-CDR3 R100a residue seems to be more involved in the immunogenicity of the P3 idiotype.

Monoclonal MOG-reactive autoantibody from progressive EAE has the characteristics of a natural antibody

A.SW mice sensitized with myelin oligodendrocyte glycoprotein (MOG)92-106 is an animal model for progressive multiple sclerosis (MS). We isolated MOG-reactive monoclonal antibodies that were immunoglobulin (Ig)M and polyreactive, similar to natural autoantibodies. Upon analysis of the variable (V) light chains and the diversity (D) and joining (J) regions of V heavy chains, we found they were identical to germ line Vkappa19/28, Jkappa5, DFL16.1e and JH4, respectively. The sequence of the VH region had 99.7% and 100% identity at the nucleotide and amino acid levels, respectively, compared with the germ line encoded antibody, P3, of the Q52 family. Although A strain mice have been reported to have an insertion in BAFF-R, the receptor for BAFF (B cell activation factor from the tumor necrosis factor family), which could explain our results, A.SW mice have no mutations in BAFF-R.

Generation and characterization of an anti-idiotype monoclonal antibody related to GM3(NeuGc) ganglioside

The 14F7 monoclonal antibody (MAb), IgG1 isotype, which reacts specifically to GM3(NeuGc) ganglioside induced a specific IgG anti-idiotypic antibody (Ab2) response in syngeneic mice when it was administered coupled with KLH and in the presence of Freund's adjuvant. Spleen cells from these mice were used in somatic-cell hybridization experiments using the murine myeloma cell line P3-X63-Ag8 653 as fusion partner. An IgG1 Ab2 MAb was selected. This Ab2 MAb, called 4G9, was able to block the binding of 14F7 MAb to GM3(NeuGc) ganglioside and developed a strong IgG anti-anti-idiotypic antibody (Ab3) response, when injected into syngeneic mice. These Ab3 antibodies were characterized to bear 14F7 MAb idiotopes, but did not have the same specificity as 14F7 MAb. In the other hand, a very specific anti-NeuGc-containing ganglioside response was generated in chickens immunized with this Ab2 MAb, thus behaving, in this species as an "internal image" antibody.

Chimeric Anti-N-Glycolyl-Ganglioside and Its Anti-Idiotypic MAbs: Immunodominance of Their Variable Regions

P3 monoclonal antibody (MAb) is a murine IgM that specifically recognizes N-glycolyl (NeuGc)-gangliosides and sulfatides. It also reacts with antigens expressed in human breast tumors and melanoma. In syngeneic model, P3 MAb is able to elicit a strong anti-idiotypic (Ab2) antibody response, even in the absence of adjuvants or carrier proteins. 1E10 MAb is an anti-idiotypic antibody specific for P3 MAb that has demonstrated anti-tumoral effects in syngeneic and allogeneic animals. Here we report the construction of the human IgG(1) chimeric P3 and 1E10 antibodies, and the evaluation of the maintenance of the main properties of the murine MAbs. Chimeric P3 antibody specifically reacted with GM3(NeuGc) and GM2(NeuGc) gangliosides, and not with their acetylated variants. Also, it strongly recognized the anti-idiotypic 1E10 MAb. Chimeric 1E10 antibody specifically reacted with P3 MAb. Upon immunization of Balb/c mice with both chimeric antibodies, we were able to demonstrate the immunodominance of their variable regions. The anti-idiotypic response induced by both antibodies was strong and in most of the mice was even significantly higher than the anti-isotypic response, despite the fact that 70% of the chimeric molecule is xenogenic with respect to the animal model.

A monoclonal antibody against NeuGc-containing gangliosides contains a regulatory idiotope involved in the interaction with B and T cells

P3 (IgM-kappa) is a monoclonal antibody (mAb) reacting with N-glycolyl neuraminic acid (NeuGc)-containing gangliosides and sulfated glycolipids. To explore the nature of the idiotope defined by 1E10, we used a phage-displayed random peptide library. After three rounds of selection, seven different phagotopes were isolated. Noteworthy, all the sequences were found to bear the basic amino acid-rich motifs KPPR (3) or RRPR/K (4). This recursive selection of basic sequences by 1E10 mAb confirmed previous suggestions of the involvement of charged residues in the interaction between gamma-type Ab2 and P3 mAb. The binding of 1E10 to phage peptides representing each group was completely inhibited by P3 mAb. In addition, other Ab2 to P3 were able to recognize these peptides. Thus, phage peptides seem to be mimotopes of the idiotope recognized by anti-idiotypic antibodies in P3. Phage motifs were represented in the lineal sequence of P3's heavy chain H-CDR3 and a 14-mer peptide representing this region was able to specifically inhibit 1E10 binding to P3. Previous studies showed that P3's idiotype was autoimmunogenic and shared by antibodies with different specificities. Now, we demonstrated that P3 mAb is able to activate a network cascade involving autologous anti-idiotypic and anti-anti-idiotypic T cells. Thus, P3's idiotype fulfill the three criteria previously established to define a "regulatory idiotype". Particularly, data presented here revealed the immunodominance of the H-CDR3 of this mAb as a T cell epitope. Thus, H-CDR3 is simultaneously involved in the interaction of P3 mAb with anti-idiotypic B and T cells, behaving as a potential regulatory idiotope.