Novel cross-reactive anti-idiotype antibodies with properties close to the human intravenous immunoglobulin (IVIg)

Non-classical binding of a polyreactive α-type anti-idiotypic antibody to B cells

Detailed information on the immunological relevance of α-type anti-idiotypic antibodies is lacking after more than 30 years since Jerne postulated his Idiotypic Network Theory. The B7Y33 mutant is a mouse-human chimeric version of the B7 MAb, a polyreactive α-type anti-idiotypic antibody, generated against an anti-GM2 ganglioside IgM Ab1 antibody. It retained the unusual self-binding activity and multispecificity of the parental murine antibody, being able to recognize several anti-ganglioside IgM antibodies as well as non-immunoglobulin antigens. Previous work with the murine B7 MAb suggested that this antibody might have immunoregulatory properties, and therefore we investigated the possible interaction of B7Y33 with immune cells. We found that B7Y33 binds to human and murine B lymphocytes. Inhibition assays using flow cytometry indicated that this antibody is capable of binding the Fc γ receptor II (FcγRII). The recognition of FcγRII-expressing K562, Raji and Daudi human cell lines, together with the capability of inhibiting the binding of an anti-human FcγRII antibody to these cells, suggest that B7Y33 interacts with both the FcγRIIa and FcγRIIb isoforms. We evaluated the contribution to the binding of different surface-exposed residues at the top of the heavy chain variable region (VH) CDR loops through the construction of mutants with substitutions in the three conventional VH CDRs (HCDRs) and the "HCDR4", located in the framework 3 (HFR3). In addition, we assessed the involvement of the Fc region by performing key mutations in the CH2 domain. Furthermore, chimeric hybrid molecules were obtained by combining the B7Y33 heavy chain with unrelated light chains. Our results indicate that the multispecificity and self-binding properties of B7Y33 are not linked to its recognition of B lineage cells, and that this phenomenon occurs in a non-classical way with the participation of both the variable and constant regions of the antibody. Two possible models for this interaction are proposed, with B7Y33 binding to two FcγRIIb molecules through the Fc and Fv regions, or simultaneously to FcγRIIb and another unknown antigen on B cells. The FcγRIIb has recently received great attention as an attractive target for therapies directed to B lymphocytes. The recognition of peripheral B lymphocytes from B cell chronic lymphocytic leukemia (B-CLL) patients by B7Y33 suggests its potential application for the treatment of B cell malignancies.

B7 and 34B7 Monoclonal Antibodies: A Theoretical Approach to the Molecular Basis of Immunoglobulin Cross-Reactive Antibodies

Neonatal natural antibodies (NAbs) are characterized by their high degree of idiotypic cross reactivity, together with some restrictions in the genetic mechanisms of variable region diversity. We report here the immunogenetic analysis of two anti-idiotype antibodies (B7 and 34B7 monoclonal antibodies [MAbs]), which are also polyreactive as NAbs. Evidence of a process of somatic mutations were found for heavy and light chain variable regions of both antibodies. A phylogenetic analysis of the V(H)J558 family showed that the immunoglobulin cross-reactivity displayed by B7 and 34B7 MAbs is not restricted to a particular subgroup of this family. Moreover, we identified amino acid motifs in the CDR H1 and H2 of B7 and 34B7 MAbs that are also present in high proportion in immunoglobulin cross-reactive antibodies (ICRA) reported in the Kabat database. We propose that these regions are involved in ICRA activity.

Analyzing the "degree of humanness" of antibody sequences

Genetically engineered mouse antibodies are now commonly in clinical use. However, their development is limited because the human immune system tends to regard them as foreign and this triggers an immune response. The solution is to make engineered antibodies appear more human. Here, we propose a method to assess the "degree of humanness" of antibody sequences providing a tool that may contribute to predictions of antigenicity. We analyzed sequences of antibodies belonging to various chains/classes in human and mouse. Our analysis of metrics based on percentage sequence identity between antibody sequences shows distinct differences between human and mouse sequences. Based on mean sequence identity and standard deviation, we calculated Z-scores for data sets of antibody sequences extracted from the Kabat database. We applied the analysis to a set of humanized and chimeric antibodies and to human germline sequences. We conclude that this approach may aid in the selection of more suitable mouse variable domains for antibody engineering to render them more human but in general, we find that typicality of a sequence compared with the expressed human repertoire is not well correlated with antigenicity. We have provided a Web server allowing humanness to be assigned for a sequence.

Immunomodulatory Effects of Intravenous Immunoglobulins as a Treatment for Autoimmune Diseases, Cancer, and Recurrent Pregnancy Loss

Intravenous immunoglobulin (IVIG) is a safe preparation, made of human plasma of thousands of healthy donors. The fascinating history of gamma globulin therapy begins in 1930 when Finland treated pneumococcal pneumonia patients with equine serum, which prolonged their survival from pneumonia. Since then, significant breakthroughs were achieved by Cohn, Bruton, Imbach, and others, whose clinical contribution to the world of medicine was of great importance. Originally IVIG was used to treat immunodeficiencies. Later on the use of IVIG extended to autoimmune diseases as well. The efficacy of IVIG has been established only in several autoimmune diseases; clinical reports of trials, series, and case reports indicate significant improvement in many more autoimmune diseases. IVIG have also showed antimetastatic effects in a variety of cancer cell lines, as well as in a few case reports. The efficiency of IVIG has also been observed in recurrent pregnancy loss (RPL), either as a result of an autoimmune disease or spontaneous. Several attempts were made to discover the immunomodulatory effects of IVIG, but it is still not fully understood. Clearly IVIG has multiple mechanisms of actions, which are thought to cooperate synergistically. One of the main mechanisms of actions of IVIG is its ability to neutralize pathogenic autoantibodies via anti-idiotypic antibodies within IVIG preparation. The ability of IVIG to neutralize pathogenic autoantibodies is of great importance in many autoimmune diseases, as well as in RPL. In cancer cell lines, IVIG modulates the immune system in a few ways, including the induction of IL-12 secretion, which consequently activates natural killer cells, and the induction of expression of proapoptotic genes only in cancer cells. Side effects from IVIG are rare and mostly mild and transient. More importantly adverse effects can be minimized by administration to a selective patient population in a proper way: slow infusion rate of 0.4 g/Kg body weight IVIG for 5 consecutive days, given in monthly cycles. The only downside of IVIG therapy is its high price. Therefore, clinicians should balance efficiency versus cost in deciding whether or not to treat certain conditions with IVIG.

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

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.

IVIg inhibits reticuloendothelial system function and ameliorates murine passive-immune thrombocytopenia independent of anti-idiotype reactivity

Although the mechanism of action of intravenous immunoglobulin (IVIg) in treating antibody-dependent thrombocytopenia remains unclear, most studies have suggested that IVIg blocks the function of Fc receptors in the reticuloendothelial system (RES) and/or the protective effect may be due to the presence of variable region-reactive (anti-idiotype) antibodies within IVIg. We evaluated the effect of IVIg on platelet counts in a murine model of passively induced immune thrombocytopenia (PIT). Although IVIg was unable to neutralize the binding of two platelet-specific monoclonal antibodies to their target antigens either in vivo or in vitro, it was able to prevent PIT as well as ameliorate pre-established PIT mediated by these antibodies. IVIg adsorbed against the antibody used to induce thrombocytopenia or endogenous murine immunoglobulin also protected against PIT, indicating that antibodies with anti-idiotype activity present in IVIg are not necessary for its effective treatment of PIT. IVIg significantly blocked the ability of the RES to clear antibody-sensitized red blood cells. F(ab')2 fragments of IVIg, which are unable to block the RES but retain the idiotypic regions, were ineffective at protecting mice from PIT. Our data suggest that IVIg exerts its rapid effect by inhibiting RES function and that anti-idiotype interactions are not required.

A murine monoclonal anti-idiotype to anti-ribosomal P antibodies: production, characterization, and use in systemic lupus erythematosus

Overt anti-ribosomal P (anti-P) autoantibodies are restricted to a subset of systemic lupus erythematosus (SLE) patients, and are potentially pathogenic. Covert anti-P are detected in all other individuals. An idiotype (Id) network is nonoperational in those with overt anti-P, whereas it is functional in all others. The aim of this study was to produce a murine monoclonal (mAb) anti-Id to characterize the anti-P Id network in SLE. BALB/c mice were immunized with F(ab')(2) fragments of IgG anti-P from a patient with a broadly cross-reactive Id. One mAb was chosen (mAb41) that reacted preferentially to the immunogen. This IgG1 mAb bound comparably in ELISAs to affinity-purified anti-P from 11 SLE patients with overt anti-P. This binding was partially inhibited with ribosomal P antigen. In contrast, it did not bind to affinity-purified control autoantibodies, nor to normal human IgG. mAb41 inhibited anti-P binding to ribosomal P antigen in immunoassays and on Jurkat cells. No change was detected in patients' anti-P antibodies over time when mAb41 was used in Id-specific ELISAs. We conclude that mAb41 is an anti-Id that recognizes a public idiotope within the antigen-combining site of anti-P antibodies. Thus, it is analogous to its human counterparts, and potentially, would modulate the pathogenicity of anti-P autoantibodies in vivo.

Antibody humanization: a case of the 'Emperor's new clothes'?

The antiglobulin response is perceived as a major problem in the clinical development of therapeutic antibodies. Successive technical developments such as chimeric, humanized and, now, fully human antibodies claim to offer improved solutions to this problem. Although there is clear evidence that chimeric antibodies are less immunogenic than murine monoclonal antibodies, little evidence exists to support claims for further improvements as a result of more elaborate humanization protocols.