Review: to what extent are T cells tolerant to immunoglobulin variable regions?

Idiotope-Driven T-Cell/B-Cell Collaboration-Based T-Cell Epitope Prediction Using B-Cell Receptor Repertoire Sequences in Infectious Diseases

T-cell recognition of antigen epitopes is a crucial step for the induction of adaptive immune responses, and the identification of such T-cell epitopes is, therefore, important for understanding diverse immune responses and controlling T-cell immunity. A number of bioinformatic tools exist that predict T-cell epitopes; however, many of these methods highly rely on evaluating conventional peptide presentation by major histocompatibility complex (MHC) molecules, but they ignore epitope sequences recognized by T-cell receptor (TCR). Immunogenic determinant idiotopes are present on the variable regions of immunoglobulin molecules expressed on and secreted by B-cells. In idiotope-driven T-cell/B-cell collaboration, B-cells present the idiotopes on MHC molecules for recognition by idiotope-specific T-cells. According to the idiotype network theory formulated by Niels Jerne, such idiotopes found on anti-idiotypic antibodies exhibit molecular mimicry of antigens. Here, by combining these concepts and defining the patterns of TCR-recognized epitope motifs (TREMs), we developed a T-cell epitope prediction method that identifies T-cell epitopes derived from antigen proteins by analyzing B-cell receptor (BCR) sequences. This method allowed us to identify T-cell epitopes that contain the same TREM patterns between BCR and viral antigen sequences in two different infectious diseases caused by dengue virus and SARS-CoV-2 infection. The identified epitopes were among the T-cell epitopes detected in previous studies, and T-cell stimulatory immunogenicity was confirmed. Thus, our data support this method as a powerful tool for the discovery of T-cell epitopes from BCR sequences.

Engineering therapeutic antibodies for patient safety: tackling the immunogenicity problem

Established monoclonal antibodies (mAbs) allow treatment of cancers, autoimmune diseases and other severe illnesses. Side effects either arise due to interaction with the target protein and its biology or result from of the patient's immune system reacting to the foreign protein. This immunogenic reaction against therapeutic antibodies is dependent on various factors. The presence of non-human sequences can trigger immune responses as well as chemical and post-translational modifications of the antibody. However, even fully human antibodies can induce immune response through T cell epitopes or aggregates. In this review, we briefly describe, how therapeutic antibodies can interact with the patient's immune system and summarize recent advancements in protein engineering and in silico methods to reduce immunogenicity of therapeutic monoclonal antibodies.

Advances and perspectives of dendritic cell-based active immunotherapies in follicular lymphoma

Follicular lymphoma (FL) is a remarkably immune-responsive malignancy, which is still considered incurable. As, standard immunochemotherapy is complex, toxic and not curative, improvement in FL care is now a crucial topic in hemato-oncology. Recently, we and others have shown that dendritic cell (DC)-based therapies allow a specific immune response associated with sustained lymphoma regression in a proportion of low-tumor burden FL patients. Importantly, the rate of objective clinical response (33-50%) and of sustained remission is remarkably higher compared to similar studies in solid tumors, corroborating the assumption of the immune responsiveness of FL. Our experimental intra-tumoral strategy combined injection with rituximab and interferon-α-derived dendritic cells (IFN-DC), a novel DC population particularly efficient in biasing T-helper response toward the Th1 type and in the cross-priming of CD8 + T cells. Noteworthy, intra-tumoral injection of DC is a new therapeutic option based on the assumption that following the induction of cancer-cell immunogenic death, unloaded DC would phagocytize in vivo the tumor associated antigens and give rise to a specific immune response. This approach allows the design of easy and inexpensive schedules. On the other hand, advanced and straightforward methods to produce clinical-grade antigenic formulations are currently under development. Both unloaded DC strategies and DC-vaccines are suited for combination with radiotherapy, immune checkpoint inhibitors, immunomodulators and metronomic chemotherapy. In fact, studies in animal models have already shown impressive results, while early-phase combination trials are ongoing. Here, we summarize the recent advances and the future perspectives of DC-based therapies in the treatment of FL patients.

CD4+ T Cells in the Blood of MS Patients Respond to Predicted Epitopes From B cell Receptors Found in Spinal Fluid

B cells are important pathogenic players in multiple sclerosis (MS), but their exact role is not known. We have previously demonstrated that B cells from cerebrospinal fluid (CSF) of MS patients can activate T cells that specifically recognize antigenic determinants (idiotopes) from their B cell receptors (BCRs). The aim of this study was to evaluate whether in silico prediction models could identify antigenic idiotopes of immunoglobulin heavy-chain variable (IGHV) transcriptomes in MS patients. We utilized a previously assembled dataset of CSF IGHV repertoires from MS patients. To guide selection of potential antigenic idiotopes, we used in silico predicted HLA-DR affinity, endosomal processing, as well as transcript frequency from nine MS patients. Idiotopes with predicted low affinity and low likelihood of cathepsins cleavage were inert controls. Peripheral blood mononuclear cells from these patients were stimulated with the selected idiotope peptides in presence of anti-CD40 for 12 h. T cells were then labeled for activation status with anti-CD154 antibodies and CD3+CD4+ T cells phenotyped as memory (CD45RO+) or naïve (CD45RO-), with potential for brain migration (CXCR3 and/or CCR6 expression). Anti-CD14 and -CD8 were utilized to exclude monocytes and CD8+ T cells. Unstimulated cells or insulin peptides were negative controls, and EBNA-1 peptides or CD3/CD28 beads were positive controls. The mean proportion of responding memory CD4+ T cells from all nine MS patients was significantly higher for idiotope peptides with predicted high HLA-DR affinity and high likelihood of cathepsin cleavage, than toward predicted inert peptides. Responses were mainly observed toward peptides affiliated with the CDR3 region. Activated memory CD4+ T cells expressed the chemokine receptor CCR6, affiliated with a Th17 phenotype and allowing passage into the central nervous system (CNS). This in vitro study suggests that that antigenic properties of BCR idiotopes can be identified in silico using HLA affinity and endosomal processing predictions. It further indicates that MS patients have a memory T cell repertoire capable of recognizing frequent BCR idiotopes found in endogenous CSF, and that these T cells express chemokine receptors allowing them to reach the CSF B cells expressing these idiotopes.

Human Cysteine Cathepsins Degrade Immunoglobulin G In Vitro in a Predictable Manner

Cysteine cathepsins are critical components of the adaptive immune system involved in the generation of epitopes for presentation on human leukocyte antigen (HLA) molecules and have been implicated in degradation of autoantigens. Immunoglobulin variable regions with somatic mutations and random complementarity region 3 amino acid composition are inherently immunogenic. T cell reactivity towards immunoglobulin variable regions has been investigated in relation to specific diseases, as well as reactivity to therapeutic monoclonal antibodies. Yet, how the immunoglobulins, or the B cell receptors, are processed in endolysosomal compartments of professional antigen presenting cells has not been described in detail. Here we present in silico and in vitro experimental evidence suggesting that cysteine cathepsins S, L and B may have important roles in generating peptides fitting HLA class II molecules, capable of being presented to T cells, from monoclonal antibodies as well as from central nervous system proteins including a well described autoantigen. By combining neural net models with in vitro proteomics experiments, we further suggest how such degradation can be predicted, how it fits with available cellular models, and that it is immunoglobulin heavy chain variable family dependent. These findings are relevant for biotherapeutic drug design as well as to understand disease development. We also suggest how these tools can be improved, including improved machine learning methodology.

Anti-PD1 'SHR-1210' aberrantly targets pro-angiogenic receptors and this polyspecificity can be ablated by paratope refinement

Monoclonal anti-programmed cell death 1 (PD1) antibodies are successful cancer therapeutics, but it is not well understood why individual antibodies should have idiosyncratic side-effects. As the humanized antibody SHR-1210 causes capillary hemangioma in patients, a unique toxicity amongst anti-PD1 antibodies, we performed human receptor proteome screening to identify nonspecific interactions that might drive angiogenesis. This screen identified that SHR-1210 mediated aberrant, but highly selective, low affinity binding to human receptors such as vascular endothelial growth factor receptor 2 (VEGFR2), frizzled class receptor 5 and UL16 binding protein 2 (ULBP2). SHR-1210 was found to be a potent agonist of human VEGFR2, which may thereby drive hemangioma development via vascular endothelial cell activation. The v-domains of SHR-1210's progenitor murine monoclonal antibody 'Mab005' also exhibited off-target binding and agonism of VEGFR2, proving that the polyspecificity was mediated by the original mouse complementarity-determining regions (CDRs), and had survived the humanization process. Molecular remodelling of SHR-1210 by combinatorial CDR mutagenesis led to deimmunization, normalization of binding affinity to human and cynomolgus PD1, and increased potency in PD1/PD-L1 blockade. Importantly, CDR optimization also ablated all off-target binding, rendering the resulting antibodies fully PD1-specific. As the majority of changes to the paratope were found in the light chain CDRs, the germlining of this domain drove the ablation of off-target binding. The combination of receptor proteome screening and optimization of the antibody binding interface therefore succeeded in generating novel, higher-potency, specificity-enhanced therapeutic IgGs from a single, clinically sub-optimal progenitor. This study showed that highly-specific off-target binding events might be an under-appreciated phenomenon in therapeutic antibody development, but that these unwanted properties can be fully ameliorated by paratope refinement.

In Silico Prediction Analysis of Idiotope-Driven T-B Cell Collaboration in Multiple Sclerosis

Memory B cells acting as antigen-presenting cells are believed to be important in multiple sclerosis (MS), but the antigen they present remains unknown. We hypothesized that B cells may activate CD4⁺ T cells in the central nervous system of MS patients by presenting idiotopes from their own immunoglobulin variable regions on human leukocyte antigen (HLA) class II molecules. Here, we use bioinformatics prediction analysis of B cell immunoglobulin variable regions from 11 MS patients and 6 controls with other inflammatory neurological disorders (OINDs), to assess whether the prerequisites for such idiotope-driven T–B cell collaboration are present. Our findings indicate that idiotopes from the complementarity determining region (CDR) 3 of MS patients on average have high predicted affinities for disease associated HLA-DRB1*15:01 molecules and are predicted to be endosomally processed by cathepsin S and L in positions that allows such HLA binding to occur. Additionally, complementarity determining region 3 sequences from cerebrospinal fluid (CSF) B cells from MS patients contain on average more rare T cell-exposed motifs that could potentially escape tolerance and stimulate CD4⁺ T cells than CSF B cells from OIND patients. Many of these features were associated with preferential use of the IGHV4 gene family by CSF B cells from MS patients. This is the first study to combine high-throughput sequencing of patient immune repertoires with large-scale prediction analysis and provides key indicators for future in vitro and in vivo analyses.

Tregitopes and impaired antigen presentation: Drivers of the immunomodulatory effects of IVIg?

Introduction

Although intravenous immunoglobulin (IVIg) is commonly used in the clinic to treat various autoimmune and severe inflammatory diseases, the mode of action is not fully elucidated. This work investigates two proposed mechanisms: (1) the potential role of regulatory T‐cell epitopes (Tregitopes) from the constant domain of IgG in the immunosuppressive function of IVIg; and (2) a potential impact of IVIg on the ability of antigen presenting cells (APCs) to present peptides.

Methods and Results

Investigation of the HLA class II peptide repertoire from IVIg‐loaded dendritic cells (DCs) via MHC‐associated peptide proteomics (MAPPs) revealed that numerous IgG‐derived peptides were strongly presented along the antibody sequence. Surprisingly, Tregitopes 167 and 289 did not show efficient natural presentation although they both bound to HLA class II when directly loaded as “naked” peptides on human DCs. In addition, both Tregitopes could not reproduce the inhibitory effect of IVIg in a human in vitro T‐cell proliferation assay as well as in vivo in mice. MAPPs data demonstrate that presentation of peptides from several antigens remained unchanged even when competed with high doses of IVIg, in both human and mouse.

Conclusion

These data suggest that the effects mediated by IVIg are not caused by Tregitopes nor by impaired antigen presentation.

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.

Augmented Binary Substitution: Single-pass CDR germ-lining and stabilization of therapeutic antibodies

Although humanized antibodies have been highly successful in the clinic, all current humanization techniques have potential limitations, such as: reliance on rodent hosts, immunogenicity due to high non-germ-line amino acid content, v-domain destabilization, expression and formulation issues. This study presents a technology that generates stable, soluble, ultrahumanized antibodies via single-step complementarity-determining region (CDR) germ-lining. For three antibodies from three separate key immune host species, binary substitution CDR cassettes were inserted into preferred human frameworks to form libraries in which only the parental or human germ-line destination residue was encoded at each position. The CDR-H3 in each case was also augmented with 1 ± 1 random substitution per clone. Each library was then screened for clones with restored antigen binding capacity. Lead ultrahumanized clones demonstrated high stability, with affinity and specificity equivalent to, or better than, the parental IgG. Critically, this was mainly achieved on germ-line frameworks by simultaneously subtracting up to 19 redundant non-germ-line residues in the CDRs. This process significantly lowered non-germ-line sequence content, minimized immunogenicity risk in the final molecules and provided a heat map for the essential non-germ-line CDR residue content of each antibody. The ABS technology therefore fully optimizes the clinical potential of antibodies from rodents and alternative immune hosts, rendering them indistinguishable from fully human in a simple, single-pass process.

Extensive T-Cell Epitope Repertoire Sharing among Human Proteome, Gastrointestinal Microbiome, and Pathogenic Bacteria: Implications for the Definition of Self

T-cell receptor binding to MHC-bound peptides plays a key role in discrimination between self and non-self. Only a subset, typically a pentamer, of amino acids in a MHC-bound peptide form the motif exposed to the T-cell receptor. We categorize and compare the T-cell exposed amino acid motif repertoire of the total proteomes of two groups of bacteria, comprising pathogens and gastrointestinal microbiome organisms, with the human proteome and immunoglobulins. Given the maximum 20⁵, or 3.2 million of such motifs that bind T-cell receptors, there is considerable overlap in motif usage. We show that the human proteome, exclusive of immunoglobulins, only comprises three quarters of the possible motifs, of which 65.3% are also present in both composite bacterial proteomes. Very few motifs are unique to the human proteome. Immunoglobulin variable regions carry a broad diversity of T-cell exposed motifs (TCEMs) that provides a stratified random sample of the motifs found in pathogens, microbiome, and the human proteome. Individual bacterial genera and species vary in the content of immunoglobulin and human proteome matched motifs that they carry. Mycobacteria and Burkholderia spp carry a particularly high content of such matched motifs. Some bacteria retain a unique motif signature and motif sharing pattern with the human proteome. The implication is that distinguishing self from non-self does not depend on individual TCEMs, but on a complex and dynamic overlay of signals wherein the same TCEM may play different roles in different organisms, and the frequency with which a particular TCEM appears influences its effect. The patterns observed provide clues to bacterial immune evasion and to strategies for intervention, including vaccine design. The breadth and distinct frequency patterns of the immunoglobulin-derived peptides suggest a role of immunoglobulins in maintaining a broadly responsive T-cell repertoire.

Antibody humanization by structure-based computational protein design

Antibodies derived from non-human sources must be modified for therapeutic use so as to mitigate undesirable immune responses. While complementarity-determining region (CDR) grafting-based humanization techniques have been successfully applied in many cases, it remains challenging to maintain the desired stability and antigen binding affinity upon grafting. We developed an alternative humanization approach called CoDAH ("Computationally-Driven Antibody Humanization") in which computational protein design methods directly select sets of amino acids to incorporate from human germline sequences to increase humanness while maintaining structural stability. Retrospective studies show that CoDAH is able to identify variants deemed beneficial according to both humanness and structural stability criteria, even for targets lacking crystal structures. Prospective application to TZ47, a murine anti-human B7H6 antibody, demonstrates the approach. Four diverse humanized variants were designed, and all possible unique VH/VL combinations were produced as full-length IgG1 antibodies. Soluble and cell surface expressed antigen binding assays showed that 75% (6 of 8) of the computationally designed VH/VL variants were successfully expressed and competed with the murine TZ47 for binding to B7H6 antigen. Furthermore, 4 of the 6 bound with an estimated KD within an order of magnitude of the original TZ47 antibody. In contrast, a traditional CDR-grafted variant could not be expressed. These results suggest that the computational protein design approach described here can be used to efficiently generate functional humanized antibodies and provide humanized templates for further affinity maturation.

Frequency Patterns of T-Cell Exposed Amino Acid Motifs in Immunoglobulin Heavy Chain Peptides Presented by MHCs

Immunoglobulins are highly diverse protein sequences that are processed and presented to T-cells by B-cells and other antigen presenting cells. We examined a large dataset of immunoglobulin heavy chain variable regions (IGHV) to assess the diversity of T-cell exposed motifs (TCEMs). TCEM comprise those amino acids in a MHC-bound peptide, which face outwards, surrounded by the MHC histotope, and which engage the T-cell receptor. Within IGHV there is a distinct pattern of predicted MHC class II binding and a very high frequency of re-use of the TCEMs. The re-use frequency indicates that only a limited number of different cognate T-cells are required to engage many different clonal B-cells. The amino acids in each outward-facing TCEM are intercalated with the amino acids of inward-facing MHC groove-exposed motifs (GEM). Different GEM may have differing, allele-specific, MHC binding affinities. The intercalation of TCEM and GEM in a peptide allows for a vast combinatorial repertoire of epitopes, each eliciting a different response. Outcome of T-cell receptor binding is determined by overall signal strength, which is a function of the number of responding T-cells and the duration of engagement. Hence, the frequency of TCEM re-use appears to be an important determinant of whether a T-cell response is stimulatory or suppressive. The frequency distribution of TCEMs implies that somatic hypermutation is followed by T-cell clonal expansion that develops along repeated pathways. The observations of TCEM and GEM derived from immunoglobulins suggest a relatively simple, yet powerful, mechanism to correlate T-cell polyspecificity, through re-use of TCEMs, with a very high degree of specificity achieved by combination with a diversity of GEMs. The frequency profile of TCEMs also points to an economical mechanism for maintaining T-cell memory, recall, and self-discrimination based on an endogenously generated profile of motifs.

Targeted DNA vaccines eliciting crossreactive anti-idiotypic antibody responses against human B cell malignancies in mice

BACKGROUND

Therapeutic idiotypic (Id) vaccination is an experimental treatment for selected B cell malignancies. A broader use of Id-based vaccination, however, is hampered by the complexity and costs due to the individualized production of protein vaccines. These limitations may be overcome by targeted DNA vaccines encoding stereotyped immunoglobulin V regions of B cell malignancies. We have here investigated whether such vaccines might elicit cross-reactive immune responses thus offering the possibility to immunize subsets of patients with the same vaccine.

METHODS

Fusion vaccines targeting patient Id to mouse Major Histocompatibility Complex (MHC) class II molecules (chimeric mouse/human) or chemokine receptors (fully human) on antigen-presenting cells (APC) were genetically constructed for two Chronic Lymphocytic Leukemia (CLL) patients and one prototypic stereotyped B-cell receptor (BCR) commonly expressed by Hepatitis C Virus (HCV)-associated Non Hodgkin Lymphoma (NHL). The A20 murine B lymphoma cells were engineered to express prototypic HCV-associated B cell lymphoma BCR. Anti-Id antibody responses were studied against stereotyped and non-stereotyped BCRs on CLL patients' cells as well as transfected A20 cells.

RESULTS

DNA vaccination of mice with Id vaccines that target APC elicited increased amounts of antibodies specific for the patient's Id as compared with non targeted control vaccines. Anti-Id antibodies cross-reacted between CLL cells with closely related BCR. A20 cells engineered to express patients' V regions were not tumorigenic in mice, preventing tumor challenge experiments.

CONCLUSIONS

These findings provide experimental support for use of APC-targeted fusion Id DNA vaccines for the treatment of B cell lymphoma and CLL that express stereotyped BCRs.

Self-tolerance in a minimal model of the idiotypic network

We consider the problem of self-tolerance in the frame of a minimalistic model of the idiotypic network. A node of this network represents a population of B-lymphocytes of the same idiotype, which is encoded by a bit string. The links of the network connect nodes with (nearly) complementary strings. The population of a node survives if the number of occupied neighbors is not too small and not too large. There is an influx of lymphocytes with random idiotype from the bone marrow. Previous investigations have shown that this system evolves toward highly organized architectures, where the nodes can be classified into groups according to their statistical properties. The building principles of these architectures can be analytically described and the statistical results of simulations agree very well with results of a modular mean-field theory. In this paper, we present simulation results for the case that one or several nodes, playing the role of self, are permanently occupied. These self nodes influence their linked neighbors, the autoreactive clones, but are themselves not affected by idiotypic interactions. We observe that the group structure of the architecture is very similar to the case without self antigen, but organized such that the neighbors of the self are only weakly occupied, thus providing self-tolerance. We also treat this situation in mean-field theory, which give results in good agreement with data from simulation. The model supports the view that autoreactive clones, which naturally occur also in healthy organisms are controlled by anti-idiotypic interactions, and could be helpful to understand network aspects of autoimmune disorders.

Targeted DNA vaccines for enhanced induction of idiotype-specific B and T cells

Background: Idiotypes (Id) are antigenic determinants localized in variable (V) regions of Ig. Id-specific T and B cells (antibodies) play a role in immunotherapy of Id⁺ tumors. However, vaccine strategies that enhance Id-specific responses are needed. Methods: Id⁺ single-chain fragment variable (scFv) from multiple myelomas and B cell lymphomas were prepared in a fusion format that bivalently target surface molecules on antigen-presenting cells (APC). APC-specific targeting units were either scFv from APC-specific mAb (anti-MHC II, anti-CD40) or chemokines (MIP-1α, RANTES). Homodimeric Id-vaccines were injected intramuscularly or intradermally as plasmids in mice, combined with electroporation. Results: (i) Transfected cells secreted plasmid-encoded Id⁺ fusion proteins to extracellular fluid followed by binding of vaccine molecules to APC. (ii) Targeted vaccine molecules increased Id-specific B and T cell responses. (iii) Bivalency and xenogeneic sequences both contributed to enhanced responses. (iv) Targeted Id DNA vaccines induced tumor resistance against challenges with Id⁺ tumors. (v) Human MIP-1α targeting units enhanced Id-specific responses in mice, due to a cross reaction with murine chemokine receptors. Thus, targeted vaccines designed for humans can be quality tested in mice. (vi) Human Id⁺ scFv from four multiple myeloma patients were inserted into the vaccine format and were successfully tested in mice. (vii) Human MIP-1α vaccine proteins enhanced human T cell responses in vitro. (viii) A hypothetical model for how the APC-targeted vaccine molecules enhance Id-specific T and B cells is presented. Conclusion: Targeted DNA Id-vaccines show promising results in preclinical studies, paving the way for testing in patients.

Immunoglobulin class switching appears to be regulated by B-cell antigen receptor-specific T-cell action

Antigen affinity is commonly viewed as the driving force behind the selection for dominant clonotypes that can occur during the T-cell-dependent processes of class switch recombination (CSR) and immune maturation. To test this view, we analyzed the variable gene repertoires of natural monoclonal antibodies to the hapten 2-phenyloxazolone (phOx) as well as those generated after phOx protein carrier-induced thymus-dependent or Ficoll-induced thymus-independent antigen stimulation. In contrast to expectations, the extent of IgM heterogeneity proved similar and many IgM from these three populations exhibited similar or even greater affinities than the classic Ox1 clonotype that dominates only after CSR among primary and memory IgG. The population of clones that were selected during CSR exhibited a reduced VH/VL repertoire that was enriched for variable domains with shorter and more uniform CDR-H3 lengths and almost completely stripped of variable domains encoded by the large VH1 family. Thus, contrary to the current paradigm, T-cell-dependent clonal selection during CSR appeared to select for VH family and CDR-H3 loop content even when the affinity provided by alternative clones exhibited similar to increased affinity for antigen.

Protective role of anti-idiotypic antibodies in autoimmunity--lessons for type 1 diabetes

Circulating autoantibodies to beta cell antigens are present in the majority of patients with Type 1 diabetes. These autoantibodies can be detected before and at time of clinical diagnosis of disease. Although the role of autoantibodies in the pathogenesis of the disease is debated, their presence indicates a dysregulation of the humoral immune response. Mechanisms regulating autoantibodies in Type 1 diabetes are not well understood. In contrast, in other autoimmune diseases there is acceptance that autoantibodies are regulated not only by antigen but also by other antibodies that bind to the antigen-binding site of these autoantibodies (anti-idiotypic antibodies). The proposed purpose of this network is to maintain an equilibrium between autoantibodies and their anti-idiotypic antibodies, preventing autoimmunity, while allowing a robust response to exogenous antigen. Anti-idiotypic antibodies regulate both autoantibody binding and their levels by a) neutralizing autoantibodies, and b) inhibiting the secretion of autoantibodies. Because it has been proposed that the B lymphocytes that produce autoantibodies function as autoantigen presenting cells, inhibiting their binding to autoantigen by anti-idiotypic antibodies may prevent development of autoimmune disease. This hypothesis is supported by the presence of anti-idiotypic antibodies in healthy individuals and in patients in remission from autoimmune diseases, and by the lack of anti-idiotypic antibodies during active disease. We recently reported the presence of autoantibodies to glutamate decarboxylase in the majority of healthy individuals, where their binding to autoantigen is prevented by anti-idiotypic antibodies. These anti-idiotypic antibodies are absent at clinical diagnosis of Type 1 diabetes, revealing the presence of autoantibodies. Type 1 diabetes (T1D) is an autoimmune disease characterized by the dysfunction and destruction of insulin-producing beta cells by autoreactive T cells. Although much progress has been made towards understanding the respective roles of effector and regulatory T cells in this beta cell destruction, the development of autoantibodies to beta cell proteins is widely considered simply a by-product of the autoimmune destruction of the beta cells, rather than having an active role in the pathogenesis. This view is starting to change based on increasing recognition that autoantibodies can have defined roles in other autoimmune diseases, and the emergence of new data on their role in T1D. This exploration of the role of autoantibodies in autoimmune disease has been spurred, in part, by increasing recognition that development of autoimmune diseases is influenced by regulatory antibodies (anti-idiotypic antibodies) directed against the unique binding site of autoantibodies. This review provides an overview of the development and function of these anti-idiotypic antibodies, and present evidence supporting their role in the development of autoimmune diseases. Finally, we conclude this review with a model of the events that may cause loss of anti-idiotypic antibodies and the implications for the development of T1D.

Targeted idiotype-fusion DNA vaccines for human multiple myeloma: preclinical testing

OBJECTIVES

  A homodimeric fusion DNA vaccine targeting idiotype (Id) to antigen-presenting cells (APC) induced robust tumor protection in a mouse model of multiple myeloma (MM). Similar Id vaccine molecules were generated for four patients with MM with three main objectives: (i) do the vaccine molecules induce bona fide anti-Id immune responses in mice? (ii) does targeting of the vaccine molecules to APC enhance immune responses? (iii) can anti-Id antibodies, generated as by-product in vaccinated mice, be used to establish sensitive assays for complete remission (CR) prior to patient vaccination?

METHODS

  Chimeric vaccine molecules targeting patient Id to mouse major histocompatibility complex (MHC) class II molecules were genetically constructed for four patients with MM.

RESULTS

  DNA vaccination of mice with chimeric vaccines targeting patient Id to mouse MHC class II molecules elicited antibodies specific for the patient's myeloma protein. Targeting MHC class II greatly enhanced anti-Id responses. Mouse anti-Id antibodies were used to establish myeloma protein-specific enzyme-linked immunosorbent assays (ELISAs) that were between 75 and 1500 times more sensitive than conventional serum protein electrophoresis and immunofixation.

CONCLUSIONS

  These results pave the way for testing targeted DNA Id vaccines in patients in CR. Id- and patient-specific ELISA could be established affording evaluation of CR depth beyond current serological methods.

Upfront immunization with autologous recombinant idiotype Fab fragment without prior cytoreduction in indolent B-cell lymphoma

Idiotype vaccination for follicular lymphoma is primarily being developed as remission consolidation after chemotherapy. We investigated idiotype vaccination as primary intervention for treatment-naive indolent B-cell lymphoma and in a separate cohort as remission consolidation after chemotherapy to assess immunization-induced immune responses in relation to progression-free survival (German Clinical Trials Register, DRKS00000227). Twenty-one patients in each cohort received 6 intradermal injections of adjuvanted recombinant idiotype Fab fragment (FabId); 76% of patients in both groups developed anti-idiotype antibodies and/or cellular immunity as measured by enzyme-linked immunosorbent assay and interferon-γ ELISpot. In treatment-naive patients, only cellular responses correlated with superior progression-free survival (P < .002) and durable objective remissions (P = .04). Immunization-induced T cells recognized hypermutated or complementarity-determining region 3 epitopes. After remission consolidation immunization, induction of anti-idiotype antibodies correlated with progression-free survival. Low B-cell counts after rituximab therapy predicted for failure to develop anti-idiotype antibodies. These results are similar to published trials showing an association of humoral immunity with control of residual lymphoma. In contrast, effective immunity against untreated lymphoma appears to be dependent on idiotype-specific T cells. Sustained remissions in patients with vaccination-induced cellular immunity suggest clinical benefit and warrant a randomized comparison of this vaccine with expectant management for asymptomatic follicular lymphoma.

Control of the specificity of T cell-mediated anti-idiotype immunity by natural regulatory T cells

The idiotypes of B cell lymphomas represent tumor-specific antigens. T cell responses induced by idiotype vaccination in vivo are directed predominantly against CDR peptides, whereas in vitro T cells also recognize framework-derived epitopes. To investigate the mechanisms regulating the specificity of idiotype-specific T cells, BALB/c or B10.D2 mice were immunized with mature dendritic cells loaded with H-2K^d-restricted peptides from influenza hemagglutinin, or from shared (J region) or unique (CDR3) structures of the A20 lymphoma idiotype. Antigen-specific T cells were induced in vivo by the CDR3 and influenza epitopes, but not by the J peptide. Gene expression profiling of splenic regulatory T cells revealed vaccination-induced Treg activation and proliferation. Treg activity involved J epitope-dependent IL-10 secretion and functional suppression of peptide-specific effector T cells. Vaccination-induced in vivo proliferation of transgenic hemagglutinin-specific T cells was suppressed by co-immunization with the J peptide and was restored in CD25-depleted animals. In conclusion, Treg induced by a shared idiotype epitope can systemically suppress T cell responses against idiotype-derived and immunodominant foreign epitopes in vivo. The results imply that tumor vaccines should avoid epitopes expressed by normal cells in the draining lymph node to achieve optimal anti-tumor efficacy.

Comparative analysis of predicted HLA binding of immunoglobulin idiotype sequences indicates T cell-mediated immunosurveillance in follicular lymphoma

Active immunization with the idiotype of follicular lymphoma induces tumor-specific immunity. T cells induced in vivo by idiotype vaccination recognize human leukocyte antigen (HLA)--restricted hypervariable but not conserved idiotype peptides. We hypothesized that idiotype-directed T-cell immunity occurs naturally and performed a reverse immunology analysis of idiotype HLA binding in 39 follicular lymphoma patients. For every idiotype, the sum of HLA-A or -B binding scores of the 20 highest-scoring peptides was calculated for all 39 HLA types through the BIMAS algorithm. The idiotype sum score of every patient's lymphoma was compared on the respective patient's HLA type to the mean of the sum scores of the remaining 38 idiotypes. Autologous idiotypes had lower immunogenicity than allogeneic idiotypes. Differential immunogenicity resided predominantly in all 3 complementarity-determining regions rather than in framework peptides. Idiotype immunogenicity was not changed by somatic hypermutation. These findings indicate T cell-mediated immunosurveillance of follicular lymphoma directed specifically against individual idiotype epitopes.

The immunogenicity of humanized and fully human antibodies: residual immunogenicity resides in the CDR regions

Monoclonal antibodies represent an attractive therapeutic tool as they are highly specific for their targets, convey effector functions and enjoy robust manufacturing procedures. Humanization of murine monoclonal antibodies has vastly improved their in vivo tolerability. Humanization, the replacement of mouse constant regions and V framework regions for human sequences, results in a significantly less immunogenic product. However, some humanized and even fully human sequence-derived antibody molecules still carry immunological risk. To more fully understand the immunologic potential of humanized and human antibodies, we analyzed CD4(+) helper T cell epitopes in a set of eight humanized antibodies. The antibodies studied represented a number of different VH and VL family members carrying unique CDR regions. In spite of these differences, CD4(+) T cell epitopes were found only in CDR-sequence containing regions. We were able to incorporate up to two amino acid modifications in a single epitope that reduced the immunogenic potential while retaining full biologic function. We propose that immunogenicity will always be present in some antibody molecules due to the nature of the antigen-specific combining sites. A consequence of this result is modifications to reduce immunogenicity will be centered on the affinity-determining regions. Modifications to CDR regions can be designed that reduce the immunogenic potential while maintaining the bioactivity of the antibody molecule.