Analysis of the individual contributions of immunoglobulin heavy and light chains to the binding of antigen using cell transfection and plasmon resonance analysis

Identification of antigen-specific B cell receptor sequences using public repertoire analysis

High-throughput sequencing allows detailed study of the BCR repertoire postimmunization, but it remains unclear to what extent the de novo identification of Ag-specific sequences from the total BCR repertoire is possible. A conjugate vaccine containing Haemophilus influenzae type b (Hib) and group C meningococcal polysaccharides, as well as tetanus toxoid (TT), was used to investigate the BCR repertoire of adult humans following immunization and to test the hypothesis that public or convergent repertoire analysis could identify Ag-specific sequences. A number of Ag-specific BCR sequences have been reported for Hib and TT, which made a vaccine containing these two Ags an ideal immunological stimulus. Analysis of identical CDR3 amino acid sequences that were shared by individuals in the postvaccine repertoire identified a number of known Hib-specific sequences but only one previously described TT sequence. The extension of this analysis to nonidentical, but highly similar, CDR3 amino acid sequences revealed a number of other TT-related sequences. The anti-Hib avidity index postvaccination strongly correlated with the relative frequency of Hib-specific sequences, indicating that the postvaccination public BCR repertoire may be related to more conventional measures of immunogenicity correlating with disease protection. Analysis of public BCR repertoire provided evidence of convergent BCR evolution in individuals exposed to the same Ags. If this finding is confirmed, the public repertoire could be used for rapid and direct identification of protective Ag-specific BCR sequences from peripheral blood.

Heavy-light chain interrelations of MS-associated immunoglobulins probed by deep sequencing and rational variation

The mechanisms triggering most of autoimmune diseases are still obscure. Autoreactive B cells play a crucial role in the development of such pathologies and, in particular, production of autoantibodies of different specificities. The combination of deep-sequencing technology with functional studies of antibodies selected from highly representative immunoglobulin combinatorial libraries may provide unique information on specific features in the repertoires of autoreactive B cells. Here, we have analyzed cross-combinations of the variable regions of human immunoglobulins against the myelin basic protein (MBP) previously selected from a multiple sclerosis (MS)-related scFv phage-display library. On the other hand, we have performed deep sequencing of the sublibraries of scFvs against MBP, Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1), and myelin oligodendrocyte glycoprotein (MOG). Bioinformatics analysis of sequencing data and surface plasmon resonance (SPR) studies have shown that it is the variable fragments of antibody heavy chains that mainly determine both the affinity of antibodies to the parent autoantigen and their cross-reactivity. It is suggested that LMP1-cross-reactive anti-myelin autoantibodies contain heavy chains encoded by certain germline gene segments, which may be a hallmark of the EBV-specific B cell subpopulation involved in MS triggering.

Antigen binding characteristics of immunoglobulin free light chains: crosslinking by antigen is essential to induce allergic inflammation

Beside the production of complete immunoglobulins IgG, IgE, IgA, IgM and IgD, consisting of tetrameric heterodimers of immunoglobulin heavy and light chains, B cells also secrete immunoglobulin free light chains (Ig-fLC). Previous studies showed that Ig-fLCs are able to induce immediate hypersensitivity reactions. It is apparent that recognition and binding of antigen are crucial steps in the onset of these inflammatory responses. In this study, the binding characteristics of Ig-fLC to antigen were further investigated using various biochemical approaches. In addition, we investigated whether antigen-mediated crosslinking of Ig-fLC is required to initiate allergic skin inflammation in vivo. Our study shows that binding of Ig-fLCs to antigen can be measured with different experimental setups. Surface plasmon resonance analysis showed real-time antigen binding characteristics. Specific antigen binding by Ig-fLCs was further detected using immunoblotting and ELISA. Using the ELISA-based assay, a binding affinity of 76.9±3.8 nM was determined for TNP-specific Ig-fLC. Antigen-induced ear swelling in mice passively sensitized with trinitrophenol-specific Ig-fLC was inhibited when multivalent antigen was combined with excess of monovalent antigen during challenge. We conclude that Ig-fLCs are able to interact with antigen, a prerequisite for antigen-specific cellular activation. In analogy to antigen-specific Fc receptor-induced mast cell activation, crosslinking of Ig-fLCs is necessary to initiate a local allergic response.

Promoting alpha-secretase cleavage of beta-amyloid with engineered proteolytic antibody fragments

Deposition of beta-amyloid (A beta) is considered as an important early event in the pathogenesis of Alzheimer's Disease (AD), and reduction of A beta levels by various therapeutic approaches is actively being pursued. A potentially non-inflammatory approach to facilitate clearance and reduce toxicity is to hydrolyze A beta at its alpha-secretase site. We have previously identified a light chain fragment, mk18, with alpha-secretase-like catalytic activity, producing the 1-16 and 17-40 amino acid fragments of A beta 40 as primary products, although hydrolysis is also observed following other lysine and arginine residues. To improve the specific activity of the recombinant antibody by affinity maturation, we constructed a single chain variable fragment (scFv) library containing a randomized CDR3 heavy chain region. A biotinylated covalently reactive analog mimicking alpha-secretase site cleavage was synthesized, immobilized on streptavidin beads, and used to select yeast surface expressed scFvs with increased specificity for A beta. After two rounds of selection against the analog, yeast cells were individually screened for proteolytic activity towards an internally quenched fluorogenic substrate that contains the alpha-secretase site of A beta. From 750 clones screened, the two clones with the highest increase in proteolytic activity compared to the parent mk18 were selected for further study. Kinetic analyses using purified soluble scFvs showed a 3- and 6-fold increase in catalytic activity (k(cat)/K(M)) toward the synthetic A beta substrate compared to the original scFv primarily due to an expected decrease in K(M) rather than an increase in k(cat). This affinity maturation strategy can be used to select for scFvs with increased catalytic specificity for A beta. These proteolytic scFvs have potential therapeutic applications for AD by decreasing soluble A beta levels in vivo.

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.

Regulatable systemic production of monoclonal antibodies by in vivo muscle electroporation

The clinical application of monoclonal antibodies (mAbs) potentially concerns a wide range of diseases including, among others, viral infections, cancer and autoimmune diseases. Although intravenous infusion appears to be the simplest and most obvious mode of administration, it is very often not applicable to long-term treatments because of the restrictive cost of mAbs certified for human use and the side effects associated with injection of massive doses of antibodies. Gene/cell therapies designed for sustained and, possibly, regulatable in vivo production and systemic delivery of mAbs might permit to advantageously replace it. We have already shown that several such approaches allow month- to year-long ectopic antibody production by non-B cells in living organisms. Those include grafting of ex vivo genetically modified cells of various types, in vivo adenoviral gene transfer and implantation of encapsulated antibody-producing cells. Because intramuscular electrotransfer of naked DNA has already been used for in vivo production of a variety of proteins, we have wanted to test whether it could be adapted to that of ectopic mAbs as well. We report here that this is actually the case since both long-term and regulatable production of an ectopic mAb could be obtained in the mouse taken as a model animal. Although serum antibody concentrations obtained were relatively low, these data are encouraging in the perspective of future therapeutical applications of this technology in mAb-based immunotherapies, especially in developing countries where cost-effective and easily implementable technologies would be required for large-scale applications in the context of severe chronic viral diseases such as HIV and HCV infections.

Monoclonal antibody 667 recognizes the variable region A motif of the ecotropic retrovirus CasBrE envelope glycoprotein and inhibits Env binding to the viral receptor

Monoclonal antibody (MAb) 667 is a neutralizing mouse monoclonal antibody recognizing the envelope glycoprotein (Env) of the ecotropic neurotropic murine retrovirus CasBrE but not that of other murine retroviruses. Since 667 can be used for preclinical studies of antiviral gene therapy as well as for studying the early events of retroviral infection, we have cloned its cDNAs and molecularly characterized it in detail. Spot technique-based experiments showed that 667 recognizes a linear epitope of 12 amino acids located in the variable region A of the receptor binding domain. Alanine scanning experiments showed that six amino acids within the epitope are critical for MAb binding. One of them, D(57), is not present in any other murine retroviral Env, which suggests a critical role for this residue in the selectivity of 667. MAb 667 heavy- and light-chain cDNAs were functionally characterized by transient transfection into Cos-7 cells. Enzyme-linked immunosorbent assays and Biacore studies showed that the specificities as well as the antigen-binding thermodynamic and kinetic properties of the recombinant 667 MAb (r667) produced by Cos-7 cells and those of the parental hybridoma-produced MAb (h667) were similar. However, h667 was shown to contain contaminating retroviral and/or retrovirus-like particles which interfere with both viral binding and neutralization experiments. These contaminants could successfully be removed by a stringent purification protocol. Importantly, this purified 667 could completely prevent retrovirus binding to target cells and was as efficient as the r667 MAb produced by transfected Cos-7 cells in neutralization assays. In conclusion, this study shows that the primary mechanism of virus neutralization by MAb 667 is the blocking of the retroviral receptor binding domain of CasBrE Env. In addition, the findings of this study constitute a warning against the direct use of hybridoma cell culture supernatants for studying the initial events of retroviral cell infection as well as for carrying out in vivo neutralization experiments and suggest that either recombinant antibodies or highly purified antibodies are preferable for these purposes.

Skin as a potential organ for ectopic monoclonal antibody production

The therapeutic potential of monoclonal antibodies for treating a variety of severe or life-threatening diseases is high. Although intravenous infusion appears the simplest and most obvious mode of administration, it is not applicable to many long-term treatments. It might be advantageously replaced by gene/cell therapies, however, rendering treatments cost-effective and eliminating the short- and long-term side-effects associated with injection of massive doses of antibodies. We have tested whether skin can potentially be used as an organ for production and systemic delivery of ectopic antibodies. Normal human primary keratinocytes were shown to be capable of synthesis and secretion of a model monoclonal antibody directed against human thyroglobulin upon retroviral gene transduction in vitro. Neo- epidermis reconstructed in vitro, either in cell culture inserts or on dermal substrates, from such modified keratinocytes also produced the monoclonal antibody. Interestingly, the latter could cross the epidermis basal layer and be released in culture fluids. Finally, grafting of epidermis reconstituted in vitro on dermal substrates to SCID mice permitted sustained monoclonal antibody delivery into the bloodstream to be achieved. Our data thus show that genetically engineered keratinocytes can potentially be used for genetic antibody-based immunotherapies. They also indicate that proteins as big as 150 kDa, after release by engineered keratinocytes into skin intercellular spaces, can migrate to the general circulation, which is potentially important for a number of other gene-based therapies.

Sustained systemic delivery of monoclonal antibodies by genetically modified skin fibroblasts

In vivo production and systemic delivery of therapeutic antibodies by engineered cells might advantageously replace injection of purified antibodies for treating a variety of life-threatening diseases, including cancer, acquired immunodeficiency syndrome, and autoimmune diseases. We report here that skin fibroblasts retrovirally transduced to express immunoglobulin genes can be used for sustained long-term systemic delivery of cloned antibodies in immunocompetent mice. Importantly, no anti- idiotypic response against the ectopically expressed model antibody used in this study was observed. This supports the notion that skin fibroblasts can potentially be used in antibody-based gene/cell therapy protocols without inducing any adverse immune response in treated individuals.

Diversity in the CDR3 region of V(H) is sufficient for most antibody specificities

All rearranging antigen receptor genes have one or two highly diverse complementarity determining regions (CDRs) among the six that typically form the ligand binding surface. We report here that, in the case of antibodies, diversity at one of these regions, CDR3 of the V(H) domain, is sufficient to permit otherwise identical IgM molecules to distinguish between a variety of hapten and protein antigens. Furthermore, we find that somatic mutation can allow such antibodies to achieve surprisingly high affinities. These results are consistent with a model in which the highly diverse CDR3 loops are the key determinant of specificity in antigen recognition in both T cell receptors (TCR) and antibodies, whereas the germline-encoded CDR1 and CDR2 sequences are much more cross-reactive.

Affinity of recombinant antibody and antibody fragment binding to human thyroglobulin: potential applications in gene therapy

Recombinant antibodies and antibody fragments are currently being produced. They can be used in vitro for the structural study of antigen-antibody interactions for instance, but their in vivo production may have applications for gene therapy of certain cancers and severe viral diseases and in developing new animal models of autoimmune disease. We report here these two types of applications using a recombinant antihuman thyroglobulin (hTg) antibody.

Dissection of an antibody paratope into peptides discloses the idiotope recognized by the cognate anti-idiotypic antibody

Using methods of parallel synthesis, the complete amino acid sequence of an Ab 1 antibody (Tg 10, an anti-human thyroglobulin monoclonal antibody) was made in the form of a set of 100 synthetic overlapping peptides. This set of immobilized peptides was allowed to react with the cognate Ab2 (AI 10, a highly purified rabbit anti-idiotypic polyclonal antibody to Tg 10). A dominant peptide idiotope, INTFSGVPTYA, was thus mapped, which corresponds mainly to the CDR2 region from the V(H) domain of the Tg 10 mAb. A synthetic peptide replica of this idiotope was found to bind to AI 10 with an affinity (K(D) in the 10(-8) M range, as measured using BIACORE technology) which represents a significant part of the affinity of the complete Tg 10 antibody (K(D) in the 10(-9) M range). The synthetic peptide also elicited anti-idiotypic antibodies in rabbits that recognized specifically the Ab1 antibody in an Ab1- and antigen-inhibitable manner. The peptide idiotope was further characterized chemically by the identification of residues important for binding to the Ab2 and by modelization of its structure. Our approach makes it readily possible to map and characterize functional, continuous-type idiotopes that could be further used to manipulate the immune response by peptide technologies.

Peptide models of immunological recognition: paratope dissection by multiple peptide synthesis

New approaches to obtain information about the residues of the antibody paratope involved in the interaction with antigen would be very useful to help perform rational mutagenesis of antibodies for improving sensitivity or selectivity in immunoassays. We have evaluated the possibility of dissecting the antibody paratope into large sets of short (12 residues) overlapping peptides to determine the contribution of each peptide to antigen binding. Our results show that the systematic analysis of the antigen-binding properties of heavy chain variable segment and light chain variable segment derived peptides of HyHEL-5, a model anti-lysozyme antibody, can be an experimental approach to the selection of paratope-derived peptides with antigen-binding activity. Detailed analysis of the contribution of each residue from each binding peptide permitted the identification of residues contributing to antigen binding. Of the 38 residues we identified, 22 corresponded to residues that had been shown by X-ray crystallography to be at the interface between HyHEL-5 and lysozyme. The peptide analysis we have developed is thus a way to map the subset of residues from the antibody paratope involved in antigen recognition. The same peptide approach was used to map the idiotope that an anti-idiotypic antibody recognized in the paratope of its cognate antibody.

Anti-digoxin scFv fragments expressed in bacteria and in insect cells have different antigen binding properties

A gene encoding a single-chain antibody fragment directed against digoxin (named 1C10 scFv) was cloned in two expression systems. For this purpose, a new baculovirus transfer cassette fully compatible with the procaryotic pHEN vector was constructed. Baculovirus production led to higher yield than did Escherichia coli expression. The procaryotic fragment showed variations in the fine specificity profile but an affinity constant nearly identical to that of the 1C10 Fab, whereas the eucaryotic scFv fragment had a lower affinity with a specificity profile identical to original mAb. The half-lives of the digoxin:scFv complexes and the global specificity are compatible with therapeutic use of this antibody fragment.

Systematic exploration of the antigen binding activity of synthetic peptides isolated from the variable regions of immunoglobulins

Sets of short (12 residues) cellulose-bound synthetic overlapping peptides derived from the sequences of the variable regions of the heavy and light chains of three different antibodies (an anti-thyroglobulin antibody, the HyHEL-5 anti-lysozyme antibody, and an anti-angiotensin II antibody) were used to systematically assess the antigen binding capacity of peptides from the antibody paratope outside their natural molecular context. Peptides enclosing one or several of the complementarity determining region (CDR) residues had antigen binding activity, although the most active peptides were not necessarily those bearing the greatest number of CDR residues. Several residues from the framework region, preceding or following the CDR, were found to play a role in binding. Affinity constants from 4.1 x 10(-7) to 6.7 x 10(-8) M-1 for the soluble form of 9 lysozyme-binding dodecapeptides were measured by BIAcore analysis. Alanine scanning of lysozyme-binding hexapeptides from the HyHEL-5 sequence identified 38 residues important for binding, of which 22 corresponded to residues that had been shown by x-ray crystallography to be at the interface between HyHEL-5 and lysozyme. Our results could be of interest for the rational identification of biologically active peptides derived from antibody sequences and in providing an experimental basis for mutagenesis of the antibody paratope.

In vitro and in vivo secretion of cloned antibodies by genetically modified myogenic cells

In vivo production of recombinant antibodies by engineered cells may have applications for gene therapy of certain cancers and of certain severe viral diseases. It would also permit the development of new animal models of autoimmune diseases and new approaches for in vivo ablation of specific cell types for fundamental purposes. Using gene transfer of an anti-human thyroglobulin monoclonal antibody, we show here that several cell types permitting autologous grafting of genetically engineered cells are efficiently able to secrete antibodies in vitro. Those cells include skin fibroblasts, hepatocytes, and myogenic cells. We also show that the secreted antibodies display an affinity for the antigen close to that of the parental antibody, with, however, slight differences varying according to the cell type. This indicates that the foldings of antigen combining sites of antibodies produced in B cell- and non-B cell contexts are very similar. Finally, we report that, when implanted in the forelimb of a mouse, genetically modified myogenic cells are able to secrete antibodies for at least 4 months. Taken together, our observations point to the notion that genetic modification of patient cells may be used for long-term antibody-based gene therapies.