Human cytomegalovirus-specific T-cell receptor engineered for high affinity and soluble expression using mammalian cell display

T-cell receptors (TCR) have considerable potential as therapeutics and antibody-like reagents to monitor disease progression and vaccine efficacy. Whereas antibodies recognize only secreted and surface-bound proteins, TCRs recognize otherwise inaccessible disease-associated intracellular proteins when they are presented as processed peptides bound to major histocompatibility complexes (pMHC). TCRs have been primarily explored for cancer therapy applications but could also target infectious diseases such as cytomegalovirus (CMV). However, TCRs are more difficult to express and engineer than antibodies, and advanced methods are needed to enable their widespread use. Here, we engineered the human CMV-specific TCR RA14 for high-affinity and robust soluble expression. To achieve this, we adapted our previously reported mammalian display system to present TCR extracellular domains and used this to screen CDR3 libraries for clones with increased pMHC affinity. After three rounds of selection, characterized clones retained peptide specificity and activation when expressed on the surface of human Jurkat T cells. We obtained high yields of soluble, monomeric protein by fusing the TCR extracellular domains to antibody hinge and Fc constant regions, adding a stabilizing disulfide bond between the constant domains and disrupting predicted glycosylation sites. One variant exhibited 50 nm affinity for its cognate pMHC, as measured by surface plasmon resonance, and specifically stained cells presenting this pMHC. Our work has identified a human TCR with high affinity for the immunodominant CMV peptide and offers a new strategy to rapidly engineer soluble TCRs for biomedical applications.

An antibody with Fab-constant domains exchanged for a pair of CH3 domains

We have designed a complete antibody-like construct where the C_H1 and C_κ domains are exchanged for a pair of the C_H3 domains and efficient pairing of the heavy and light variable domain is achieved using “Knobs-into-Holes” strategy. This construct, composed of only naturally occurring immunoglobulin sequences without artificial linkers, expressed at a high level in mammalian cells, however exhibited low solubility. Rational mutagenesis aimed at the amino acid residues located at the interface of the variable domains and the exchanged C_H3 domains was applied to improve the biophysical properties of the molecule. The domain-exchanged construct, including variable domains of the HER2/neu specific antibody trastuzumab, was able to bind to the surface of the strongly HER2/neu positive cell line SK-BR3 4-fold weaker than trastuzumab, but could nevertheless incite a more potent response in an antibody-dependent cell cytotoxicity (ADCC) reporter assay with FcγRIIIa-overexpressing T-cells. This could be explained with a stronger binding to the FcγRIIIa. Importantly, the novel construct could mediate a specific ADCC effect with natural killer cells similar to the parental antibody.

[Correlation between macro- and micro-stability ch2 domains of human IGG2 and their biological activity. 1. Ansalysis the calorimetric and optical melting curves]

Human myeloma immunoglobulin second subclass LOM and SIN, their Fc fragment and firstly obtained hFc fragment in which there is not only low portion of the hinge region, but also its core portion (Cys-Cys-Val-Glu-Cys-Pro-Pro-Cys), have been studied by number of physical methods (scanning calorimetry, fluorescence spectroscopy, analytical centrifugation). Joint analysis of calorimetric and optical melting curves revealed that only first (low-temperature) heat absorption peak at all the melting curves corresponds to the melting of the two CH2 domains. It was shown that CH2 domains of intact IgG2 are destabilized relative to those domains in hFc and Fc fragments.

The constant region contributes to the antigenic specificity and renal pathogenicity of murine anti-DNA antibodies

Affinity for DNA and cross-reactivity with renal antigens are associated with enhanced renal pathogenicity of lupus autoantibodies. In addition, certain IgG subclasses are enriched in nephritic kidneys, suggesting that isotype may determine the outcome of antibody binding to renal antigens. To investigate if the isotype of DNA antibodies affects renal pathogenicity by influencing antigen binding, we derived IgM, IgG1, IgG2b and IgG2a forms of the PL9-11 antibody (IgG3 anti-DNA) by in vitro class switching or PCR cloning. The affinity and specificity of PL9-11 antibodies for nuclear and renal antigens were analyzed using ELISA, Western blotting, surface plasmon resonance (SPR), binding to mesangial cells, and glomerular proteome arrays. Renal deposition and pathogenicity were assayed in mice injected with PL9-11 hybridomas. We found that PL9-11 and its isotype-switched variants had differential binding to DNA and chromatin (IgG3>IgG2a>IgG1>IgG2b>IgM) by direct and competition ELISA, and SPR. In contrast, in binding to laminin and collagen IV the IgG2a isotype actually had the highest affinity. Differences in affinity of PL9-11 antibodies for renal antigens were mirrored in analysis of specificity for glomeruli, and were associated with significant differences in renal pathogenicity in vivo and survival. Our novel findings indicate that the constant region plays an important role in the nephritogenicity of antibodies to DNA by affecting immunoglobulin affinity and specificity. Increased binding to multiple glomerular and/or nuclear antigens may contribute to the renal pathogenicity of anti-DNA antibodies of the IgG2a and IgG3 isotype. Finally, class switch recombination may be another mechanism by which B cell autoreactivity is generated.

A method for rapid, ligation-independent reformatting of recombinant monoclonal antibodies

Recombinant monoclonal antibodies currently dominate the protein biologics marketplace. The path from target antigen discovery and screening, to a recombinant therapeutic antibody can be time-consuming and laborious. We describe a set of expression vectors, termed mAbXpress, that enable rapid and sequence-independent insertion of antibody variable regions into human constant region backbones. This method takes advantage of the In Fusion cloning system from Clontech, which allows ligation-free, high-efficiency insertion of the variable region cassette without the addition of extraneous amino acids. These modular vectors simplify the antibody reformatting process during the preliminary evaluation of therapeutic or diagnostic candidates. The resulting constructs can be used directly for transient or amplifiable, stable expression in mammalian cells. The effectiveness of this method was demonstrated by the creation of a functional, fully human anti-human CD83 monoclonal antibody.

Channel catfish soluble FcmuR binds conserved linear epitopes present on Cmu3 and Cmu4

A linear epitope on catfish IgM has been identified as the docking site for the catfish soluble FcmuR (IpFcRI). Western blot analyses and latex bead binding assays identified the consensus octapeptide motif FxCxVxHE located at the second cysteine that forms the intrachain disulfide bond of the catfish Cmu3 and Cmu4 immunolglobulin (Ig) domains as the IpFcRI binding sites. Furthermore, molecular modeling of catfish Cmu3 and Cmu4 confirmed that the octapeptide in both of these domains is accessible for IpFcRI interactions. In addition, since this octapeptide motif is also found in other vertebrate Ig domains, IpFcRI binding to Ig heavy (H) and light (L) chains from rainbow trout, chicken, mouse, rabbit, and goat were examined by Western blot analyses and latex bead binding assays. IpFcRI readily bound reduced rainbow trout (Igmu), chicken (Ignu), mouse (Igmu, Iggamma1, Iggamma2a, Iggamma2b, and Igalpha), rabbit (Igmu and Iggamma) and goat (Iggamma) IgH chains, and mouse Igkappa and Iglambda, and chicken Iglambda IgL chains. IpFcRI also bound mouse IgM, IgA and IgG subclasses when examined under native conditions.

Sequence and characterization of the Ig heavy chain constant and partial variable region of the mouse strain 129S1

Although the entire mouse genome has been sequenced, there remain challenges concerning the elucidation of particular complex and polymorphic genomic loci. In the murine Igh locus, different haplotypes exist in different inbred mouse strains. For example, the Igh(b) haplotype sequence of the Mouse Genome Project strain C57BL/6 differs considerably from the Igh(a) haplotype of BALB/c, which has been widely used in the analyses of Ab responses. We have sequenced and annotated the 3' half of the Igh(a) locus of 129S1/SvImJ, covering the C(H) region and approximately half of the V(H) region. This sequence comprises 128 V(H) genes, of which 49 are judged to be functional. The comparison of the Igh(a) sequence with the homologous Igh(b) region from C57BL/6 revealed two major expansions in the germline repertoire of Igh(a). In addition, we found smaller haplotype-specific differences like the duplication of five V(H) genes in the Igh(a) locus. We generated a V(H) allele table by comparing the individual V(H) genes of both haplotypes. Surprisingly, the number and position of D(H) genes in the 129S1 strain differs not only from the sequence of C57BL/6 but also from the map published for BALB/c. Taken together, the contiguous genomic sequence of the 3' part of the Igh(a) locus allows a detailed view of the recent evolution of this highly dynamic locus in the mouse.

The immunoglobulin heavy chain constant region affects kinetic and thermodynamic parameters of antibody variable region interactions with antigen

A central dogma in immunology is that antibody specificity is a function of the variable (V) region. However serological analysis of IgG(1), IgG(2a), and IgG(2b) switch variants of murine monoclonal antibody (mAb) 3E5 IgG(3) with identical V domains revealed apparent specificity differences for Cryptococcus neoformans glucuronoxylomannan (GXM). Kinetic and thermodynamic binding properties of mAbs 3E5 to a 12-mer peptide mimetic of GXM revealed differences in the affinity of these mAbs for a monovalent ligand, a result that implied that the constant (C) region affects the secondary structure of the antigen binding site, thus accounting for variations in specificity. Structural models of mAbs 3E5 suggested that isotype-related differences in binding resulted from amino acid sequence polymorphisms in the C region. This study implies that isotype switching is another mechanism for generating diversity in antigen binding and that isotype restriction of certain antibody responses may reflect structural constraints imposed by C region on V region binding. Furthermore, isotype affected the polyreactivity of V region identical antibodies, implying a role for C region in determining self-reactivity.

IL-21 Has a Pathogenic Role in a Lupus-Prone Mouse Model and Its Blockade with IL-21R.Fc Reduces Disease Progression

Systemic lupus erythematosus is a complex autoimmune disease characterized by dysregulated interactions between autoreactive T and B lymphocytes and the development of anti-nuclear Abs. The recently described pleiotropic cytokine IL-21 has been shown to regulate B cell differentiation and function. IL-21 is produced by activated T lymphocytes and its interactions with IL-21R are required for isotype switching and differentiation of B cells into Ab-secreting cells. In this report, we studied the impact of blocking IL-21 on disease in the lupus-prone MRL-Fas(lpr) mouse model. Mice treated for 10 wk with IL-21R.Fc fusion protein had reduced proteinuria, fewer IgG glomerular deposits, no glomerular basement membrane thickening, reduced levels of circulating dsDNA autoantibodies and total sera IgG1 and IgG2a, and reduced skin lesions and lymphadenopathy, compared with control mice. Also, treatment with IL-21R.Fc resulted in a reduced number of splenic T lymphocytes and altered splenic B lymphocyte ex vivo function. Our data show for the first time that IL-21 has a pathogenic role in the MRL-Fas(lpr) lupus model by impacting B cell function and regulating the production of pathogenic autoantibodies. From a clinical standpoint, these results suggest that blocking IL-21 in systemic lupus erythematosus patients may represent a promising novel therapeutic approach.

Reversible contraction by looping of the Tcra and Tcrb loci in rearranging thymocytes

Reversible contraction of immunoglobulin loci juxtaposes the variable (V) genes next to the (diversity)-joining-constant ((D)JC) gene domain, thus facilitating V-(D)J recombination. Here we show that the T cell receptor beta (Tcrb) and T cell receptor alphadelta (Tcra-Tcrd) loci also underwent long-range interactions by looping in double-negative and double-positive thymocytes, respectively. Contraction of the Tcrb and Tcra loci occurred in rearranging thymocytes and was reversed at the next developmental stage. Decontraction of the Tcrb locus probably prevented further V(beta)-DJ(beta) rearrangements in double-positive thymocytes by separating the V(beta) genes from the DJC(beta) domain. In most double-negative cells, one Tcrb allele was recruited to pericentromeric heterochromatin. Such allelic positioning may facilitate asynchronous V(beta)-DJ(beta) recombination. Hence, pericentromeric recruitment and locus 'decontraction' seem to contribute to the initiation and maintenance of allelic exclusion at the Tcrb locus.

Biased dA/dT somatic hypermutation as regulated by the heavy chain intronic iEmu enhancer and 3'Ealpha enhancers in human lymphoblastoid B cells

Somatic hypermutation (SHM) in immunoglobulin gene (Ig) variable (V) regions is critical for the maturation of the antibody response. It is dependent on the expression of activation-induced cytidine deaminase (AID) and translesion DNA polymerases in germinal center B cells as well as Ig V transcription, as regulated by the Ig heavy chain (H) intronic enhancer (iEmu) and the 3' enhancer (3'Ealpha) region. We analyzed the role of these cis elements in SHM by stably transfecting Ramos human lymphoblastoid B cells with a rearranged human IgH chain VD (diversity) J (joining) DNA construct containing a V(H) promoter at the 5' end and C(H)1 and C(H)2 exons of Cgamma1 at the 3' end. In this construct, mutations preferentially targeted dA/dT basepairs in the RGYW/WRCY hotspot. Most of the dA/dT mutations and accompanying dC/dG mutations were transitions. Deletion of iEmu resulted in decreased SHM which could be partially restored by insertion of the IgH hs1,2 enhancer. Other two 3'Ealpha enhancers, hs3-hs4, did not significantly increase the mutation frequency, but further strengthened the dA/dT bias. The frequency and spectrum of the mutations were independent of the genomic integration of the transgene or V gene transcription level. Thus, we have established a novel in vitro system to analyze SHM and identify the role of multiple cis-regulatory elements in regulating dA/dT biased SHM. This model system will be useful to further address the role of other cis-regulating elements and recruited trans-acting factors in expressing the modalities of SHM.

Inducible DNA breaks in Ig S regions are dependent on AID and UNG

Class switch recombination (CSR) occurs by an intrachromosomal deletion whereby the IgM constant region gene (Cμ) is replaced by a downstream constant region gene. This unique recombination event involves formation of double-strand breaks (DSBs) in immunoglobulin switch (S) regions, and requires activation-induced cytidine deaminase (AID), which converts cytosines to uracils. Repair of the uracils is proposed to lead to DNA breaks required for recombination. Uracil DNA glycosylase (UNG) is required for most CSR activity although its role is disputed. Here we use ligation-mediated PCR to detect DSBs in S regions in splenic B cells undergoing CSR. We find that the kinetics of DSB induction corresponds with AID expression, and that DSBs are AID- and UNG-dependent and occur preferentially at G:C basepairs in WRC/GYW AID hotspots. Our results indicate that AID attacks cytosines on both DNA strands, and staggered breaks are processed to blunt DSBs at the initiating ss break sites. We propose a model to explain the types of end-processing events observed.

Fucose removal from complex-type oligosaccharide enhances the antibody-dependent cellular cytotoxicity of single-gene-encoded antibody comprising a single-chain antibody linked the antibody constant region

Fucose removal from complex-type oligosaccharide of human IgG1-type antibody results in a great enhancement of antibody-dependent cellular cytotoxicity (ADCC). The aim of this study was to clarify the effect of fucose removal on effector functions of a single-gene-encoded antibody with an scFv used as the binding domain. We generated both a fucose-negative anti-tumor associated glycoprotein (TAG)-72 scFv-Fc using alpha-1,6-fucosyltransferase knock-out CHO cells and a highly fucosylated scFv-Fc from parental CHO cells. Expression, assembly and antigen binding activity of the scFv-Fcs were not influenced by fucose removal. The scFv-Fc lacking fucose exhibited significantly more potent FcgammaRIIIa binding and ADCC compared to highly fucosylated scFv-Fc. These results prove that ADCC enhancement by fucose-removal is effective in not only whole IgG1, but also scFv-Fc, and thus increases the potential of Fc-fusion proteins as therapeutic candidates.

Immunogenicity of engineered antibodies

Administration of a therapeutic antibody can lead to an anti-antibody response (AAR). Much effort has been applied to engineering antibodies with as little as possible non-human structure to minimize such responses. Here, we review reported AAR to murine, mouse-human chimeric, and humanized antibodies. Replacement of mouse immunoglobulin constant regions with human ones effects the largest immunogenicity reduction. Humanization of variable domains effects a further decrease.

Neonatal Fc receptors discriminates and monitors the pathway of native and modified immunoglobulin G in placental endothelial cells

In the placenta, immunoglobulin G (IgG) is selectively transported from mother to fetus by a highly regulated transcellular mechanism aimed to achieve fetal humoral immunity. We questioned the role of neonatal Fc receptors (FcRn) in the traffic of IgG in human placental endothelial cells (HPEC). Cells were cultured in a double-chamber system and further exposed to IgG or Fc or to diethylpyrocarbonate-modified IgG or Fc in which the receptor recognition domain of the molecule (CH2-CH3) was altered. We provide evidence that the native IgG/Fc probes are transcytosed or recycled by HPEC, whereas the probes with the altered receptor recognition domain (which do not bind to FcRn) massively accumulate into the endocytic/lysosomal compartments. The results indicate that FcRn distinguishes between the intact and modified IgG and control their cellular traffic: native IgG is salvaged and released out of the cells, whereas modified IgG is retained and sorted to a degradative pathway. The data advance the understanding of the basic mechanism for IgG traffic in human endothelial cells, which may be exploited for the specific transport of antibodies in various immune disorders.

Dissecting MHC class II export, B cell maturation, and DM stability defects in invariant chain mutant mice

Invariant (Ii) chain loss causes defective class II export, B cell maturation, and reduced DM stability. In this study, we compare Ii chain and class II mutant mouse phenotypes to dissect these disturbances. The present results demonstrate that ER retention of alphabeta complexes, and not beta-chain aggregates, disrupts B cell development. In contrast, we fail to detect class II aggregates in Ii chain mutant thymi. Ii chain loss in NOD mice leads to defective class II export and formation of alphabeta aggregates, but in this background, downstream signals are misregulated and mature B cells develop normally. Finally, Ii chain mutant strains all display reduced levels of DM, but mice expressing either p31 or p41 alone, and class II single chain mutants, are indistinguishable from wild type. We conclude that Ii chain contributions as a DM chaperone are independent of its role during class II export. This Ii chain/DM partnership favors class II peptide loading via conventional pathway(s).

Humanization of the anti-CEA T84.66 antibody based on crystal structure data

Chimeric T84.66 (cT84.66) is a monoclonal antibody (mAb) of high specificity and affinity for the tumor-associated carcinoembryonic antigen (CEA). Radiolabeled cT84.66 has demonstrated utility in the clinic as a reagent for the radioimmunoscintigraphy and radioimmunotherapy of CEA-positive colorectal and breast malignancies. To extend the therapeutic efficacy of T84.66, humanization by complementary determining region (CDR) grafting was employed. CDR grafting is a well-established technique, though often a series of framework back-mutations is required to restore high affinity. Recently, the crystal structure of the T84.66 diabody (scFv dimer) derived from the murine T84.66 mAb was determined, facilitating the humanization process by the availability of crystal structure data for both the graft donor and graft acceptor. A search of the Protein Data Bank revealed close structural similarity (r.m.s.d. of 1.07 A) between the Fv of T84.66 and the Fv of 4D5v8, a humanized anti-p185HER2 antibody marketed as Herceptin (Trastuzumab). This resulted in two humanized versions of the T84.66 M5A and M5B mAbs that differed only in the number of murine residues present in the C-terminal half of CDR-H2. Biochemical analysis and animal biodistribution studies were conducted to evaluate the humanized mAbs. The M5A, M5B and cT84.66 mAbs showed sub-nanomolar affinity for CEA and as radiolabeled mAbs exhibited specific tumor localization in tumor bearing mice. The T84.66 M5A mAb was selected for clinical development due to a slightly higher tumor uptake and a larger content of human residues, and was renamed hT84.66. A limited-scale production and animal imaging study have demonstrated hT84.66's ability to support clinical trials. Planned clinical trials will determine the effective utilization of this structure-based approach in the development of a promising new therapeutic.

Important Role of Cathepsin S in Generating Peptides for TAP-Independent MHC Class I Crosspresentation In Vivo

The immune system detects viral infections and mutations in parenchymal cells when antigens from these cells are crosspresented on MHC class I molecules of professional antigen-presenting cells (APC). Exogenous antigens are crosspresented through TAP-dependent (cytosolic) or poorly understood TAP-independent (vacuolar) pathways. The TAP-independent pathway is blocked by the cysteine protease inhibitor, leupeptin, but not by proteasome inhibitors, which is opposite to the effects of these agents on the TAP-dependent pathway. Dendritic cells lacking the cysteine protease cathepsin S lack the TAP-independent pathway. Mice whose APC lack cathepsin S have reduced crosspriming to particulate and cell-associated antigens, as well as to influenza virus. Cathepsin S-deficient phagosomes generate a class I-presented peptide poorly. In contrast, cathepsin S-sufficient phagosomes and recombinant cathepsin S produce the mature epitope. Therefore, cathepsin S plays a major role in generating presented peptides for the vacuolar pathway of crosspresentation, and this mechanism is active in vivo.

Interaction between the antigen and antibody is controlled by the constant domains: normal mode dynamics of the HEL-HyHEL-10 complex

The antigen binding fragment (Fab) of a monoclonal antibody (HyHEL-10) consists of variable domains (Fv) and constant domains (CL-CH1). Normal modes have been calculated from the three-dimensional structures of hen egg lysozyme (HEL) with Fab, those of HEL with Fv, and so on. Only a small structural change was found between HEL-Fab and HEL-Fv complexes. However, HEL-Fv had a one order of magnitude lower dissociation constant than HEL-Fab. The Calpha fluctuations of HEL-Fab differed from those of HEL-Fv with normal mode calculation, and the dynamics can be thought to be related to the protein-protein interactions. CL-CH1 may have influence not only around local interfaces between CL-CH1 and Fv, but also around the interacting regions between HEL and Fv, which are longitudinally distant. Eighteen water molecules were found in HEL-Fv around the interface between HEL and Fv compared with one water molecule in HEL-Fab. These solvent molecules may occupy the holes and channels, which may occur due to imperfect complementarity of the complex. Therefore, the suppression of atomic vibration around the interface between Fv and HEL can be thought to be related to favorable and compact interface formation by complete desolvation. It is suggested that the ability to control the antigen-antibody affinity is obtained from modifying the CL-CH1. The second upper loop in the constant domain of the light chain (UL2-CL), which is a conserved gene in several light chains, showed the most remarkable fluctuation changes. UL2-CL could play an important role and could be attractive for modification in protein engineering.

The production and characterisation of a chimaeric human IgE antibody, recognising the major mite allergen Der p 1, and its chimaeric human IgG1 anti-idiotype

BACKGROUND

Two mouse monoclonal antibodies have been described, namely: mAb 2C7 (IgG2bkappa), which is directed against the major house dust mite allergen Der p 1, and mAb 2G10 (IgG1kappa), which is an anti-idiotypic antibody raised against mAb 2C7. Given its broad IgE specificity, anti-idiotype mAb 2G10 could potentially have immunomodulatory applications. For example, a chimaeric human IgG version of mAb 2G10 could prove to be a useful molecule for binding to mast cell and basophil FcepsilonRI bound IgE, and in doing so co-ligating FcepsilonRI with FcgammaRIIB, which has been reported to have downregulatory effects.

AIMS

To produce a chimaeric human IgE version of mAb 2C7 (mAb 2C7huE) and a chimaeric human IgG1 version of its anti-idiotype mAb 2G10 (mAb 2G10huG1).

METHODS

The Vkappa and VH regions of mAb 2C7 and its anti-idiotype mAb 2G10 were engineered into human constant regions of the IgE and IgG1 isotypes, respectively.

RESULTS

The production of chimaeric mAb 2C7huE and its anti-idiotype mAb 2G10huG1 confirmed that the respective mouse antibody V regions were successfully engineered into human constant regions and still retained the specificity of the original murine V regions.

CONCLUSION

The newly constructed chimaeric antibodies will be useful to investigate the downregulation of IgE mediated hypersensitivity by the crosslinking of FcepsilonRI with FcgammaRIIB.

Immunoglobulin heavy chain constant regions regulate immunity and tolerance to idiotypes of antibody variable regions

Particular syngeneic adjuvant-free monoclonal antibodies are immunogenic and elicit antibody responses against the variable region idiotypes (Ids). We here study how heavy-chain constant regions (C(H)) regulate immune responses to Ids of free, uncomplexed monoclonal antibodies. To this end, we selected two hybridomas, called Id(3) and Id(A.01), that produce immunogenic IgM(lambda)2 directed toward 2,4,6-trinitrophenyl, and subcloned rare IgG1, IgG3, IgE, or IgA class switch variants. The purified switch variants, which possessed the Ids of their IgM progenitors, were injected repeatedly without added adjuvant into BALB/c mice, and anti-Id IgG responses were determined. These repeated injections revealed that the immunogenicity of Ids was lost by switching to IgG1 and IgG3, restored when the Fc piece of IgG1 was removed, maintained by switching to IgE and monomeric IgA, and lost in polymeric IgA. Loss of immunogenicity was associated with acquisition of Id-specific tolerogenicity, as determined by immunization challenge with Id borne by IgM. An Id borne by IgG induced tolerance when injected at least 90 days before or 3-21 days after immunization with IgM Id was begun. Ids of IgG were also tolerogenic in mice deficient in Fc(gamma)RIIB or Fc(gamma)RI + III. The results suggest that Ids that have switched to IgG and pIgA negatively control immune responses to shared Ids, including the Ids of their IgM progenitors.

Antibody-mediated neutralization of cytomegalovirus: modulation of efficacy induced through the IgG constant region

Antibodies can neutralize the infectious properties of human cytomegalovirus (CMV). In vivo, the major neutralization determinants are located on glycoprotein B (gB). Recombinant human antibodies, that carry different constant regions (IgG1, IgG3 and the synthetic variant IgG3mA) against two of these epitopes were investigated for their ability to recruit the complement cascade for destruction of the virus. It was shown that all variants of an antibody against the antigenic domain (AD)-2 epitope displayed a similar neutralization activity despite the fact that improved C1q binding was observed for IgG3 and IgG3mA over the IgG1 variant. In contrast, an antibody against the AD-1 epitope carrying the normal IgG3 constant region, was less efficient than its IgG1 counterpart in neutralizing the virus in the absence of complement. However, it restored its activity in the presence of complement to the level of the naturally occurring IgG1 version. The same antibody was substantially more potent in neutralizing the virus in the presence of complement if it carried the IgG3mA constant region. This demonstrates the importance of the constant domain for the biological activity of AD-1 specific antibodies, a factor that should be taken into account when using antibody-based therapeutics or when inducing antibodies by vaccination.

B cells with the guts to switch

Expression of mIgM was thought to be esential for the differentiation of B cells expressing antibodies of other classes. New evidence suggests isotype class switching to IgA can occur in the absence of mIgM.

The structure of the IgE Cepsilon2 domain and its role in stabilizing the complex with its high-affinity receptor FcepsilonRIalpha

The stability of the complex between IgE and its high-affinity receptor, FcepsilonRI, on mast cells is a critical factor in the allergic response. The long half-life of the complex of IgE bound to this receptor in situ ( approximately 2 weeks, compared with only hours for the comparable IgG complex) contributes to the permanent sensitization of these cells and, hence, to the immediate response to allergens. Here we show that the second constant domain of IgE, Cepsilon2, which takes the place of the flexible hinge in IgG, contributes to this long half-life. When the Cepsilon2 domain is deleted from the IgE Fc fragment, leaving only the Cepsilon3 and Cepsilon4 domains (Cepsilon3-4 fragment), the rate of dissociation from the receptor is increased by greater than 1 order of magnitude. We report the structure of the Cepsilon2 domain by heteronuclear NMR spectroscopy and show by chemical shift perturbation that it interacts with FcepsilonRIalpha. By sedimentation equilibrium we show that the Cepsilon2 domain binds to the Cepsilon3-4 fragment of IgE. These interactions of Cepsilon2 with both FcepsilonRIalpha and Cepsilon3-4 provide a structural explanation for the exceptionally slow dissociation of the IgE-FcepsilonRIalpha complex.

Useful polyclonal antibodies against synthetic peptides corresponding to immunoglobulin light chain constant region for immunohistochemical detection of immunoglobulin light chain amyloidosis

For the immunohistochemical detection of immunoglobulin (Ig) light chain amyloidosis on formalin-fixed, paraffin-embedded tissue sections, we prepared polyclonal antibodies against synthetic peptides corresponding to positions 118-134 of Ig lambda light chain and positions 116-133 of Ig kappa light chain. Nineteen cases of systemic Ig lambda light chain amyloidosis (Alambda amyloidosis), 10 cases of systemic Ig kappa light chain amyloidosis (Akappa amyloidosis), one case of immunohistochemically unclassified systemic amyloidosis and five cases of localized Alambda amyloidosis were tested with these antibodies. Anti-lambda (118-134) antiserum and the affinity-purified antibody both reacted with 18 of the 19 cases of systemic Alambda amyloidosis and all cases of localized Alambda amyloidosis, although the immunoexpression was somewhat variable in intensity in different areas within the same specimen in both systemic and localized amyloidosis. The signal intensities in plasma cells and serum reacted for anti-lambda (118-134) antiserum were weaker than signals obtained with commercially available anti-Ig lambda light chain antibodies. Anti-kappa (116-133) antiserum and the affinity-purified antibody reacted with nine of the 10 cases of systemic Akappa amyloidosis. We conclude that these antibodies against synthetic peptides corresponding to the Ig light chain constant region are useful for the classification of amyloidosis on formalin-fixed, paraffin-embedded tissue sections.

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.

Characterization of CD4+ T cell responses during natural infection with Salmonella typhimurium

CD4+ T cells are important for resistance to infection with Salmonella typhimurium. However, the Ag specificity of this T cell response is unknown. Here, we demonstrate that a significant fraction of Salmonella-specific CD4+ T cells respond to the flagellar filament protein, FliC, and that this Ag has the capacity to protect naive mice from lethal Salmonella infection. To characterize this Ag-specific response further, we generated FliC-specific CD4+ T cell clones from mice that had resolved infection with an attenuated strain of Salmonella. These clones were found to respond to an epitope from a constant region of FliC, enabling them to cross-react with flagellar proteins expressed by a number of distinct Salmonella serovars.

A chimeric antibody with the human gamma1 constant region as a putative standard for assays to detect IgG beta2-glycoprotein I-dependent anticardiolipin and anti-beta2-glycoprotein I antibodies

OBJECTIVE

Thromboembolic manifestations or thrombocytopenia in association with anticardiolipin antibodies (aCL) or lupus anticoagulant are known as the antiphospholipid syndrome (APS). Efforts have been made to elucidate precise clinical features and adequate therapeutic options for treating patients with APS. However, the lack of a proper international standard for measurement of aCL makes it difficult to compare data derived from different laboratories. We attempted to design a chimeric antibody with human gamma constant regions and variable regions of WBCAL-1, a monoclonal antibody established from an APS-prone mouse which has a specificity similar to that of aCL in sera from humans with APS.

METHODS

Variable-region genes of WBCAL-1, which were cloned using reverse transcription-polymerase chain reaction, were inserted into plasmids containing human gamma1 and kappa constant-region genes. The construct was transfected to a mouse myeloma cell line. Stable transfectants that secreted a chimeric antibody, HCAL, into the culture supernatant were obtained. The reactivity of HCAL to cardiolipin and to beta2-glycoprotein I (beta2GPI) was studied using a solid-phase enzyme immunoassay. The binding of HCAL was compared with the binding of standards for IgG aCL and anti-beta2GPI antibody assays done in 18 independent laboratories.

RESULTS

In the presence of beta2GPI, HCAL bound to the wells of cardiolipin-coated microtiter plates in a dose-dependent manner and reacted with beta2GPI on oxygenated polystyrene plates. The aCL activity of HCAL can be converted into GPL units (IgG phospholipid units), which is widely used to quantify IgG aCL activity, using the following formula: 1 GPL unit = 32.9 x (concentration of HCAL [in microg/ml])(0.503). The reactivity of HCAL to cardiolipin or beta2GPI was similar to the reactivity of standards for IgG aCL or anti-beta2GPI antibody assays done in collaborative laboratories.

CONCLUSION

Because the reactivity of HCAL is similar to that of aCL in sera from humans with APS, HCAL will be useful as a standard for human IgG aCL and anti-beta2GPI antibody assays.

Novel tetravalent and bispecific IgG-like antibody molecules combining single-chain diabodies with the immunoglobulin gamma1 Fc or CH3 region

Although bispecific IgG molecules have been successfully applied for antibody-mediated immunotherapy of tumours, applicability is hampered by the difficulties associated with their generation. In the present study, we have used a bispecific single-chain diabody (scDb) directed against carcinoembryonic antigen and Escherichia coli beta-galactosidase as a model to generate bispecific IgG-like antibody molecules. We show that the fusion of this single-chain diabody to the Fc (scDb-Fc) or CH3 (scDb-CH3) region of the human immunoglobulin gamma1 chain results in the expression of dimeric fusion proteins exhibiting four functional antigen binding sites with increased functional affinity. This strategy represents a new and convenient way to generate IgG-like multivalent and bispecific molecules that are efficiently secreted from mammalian cells.

The structure of an entire noncovalent immunoglobulin kappa light-chain dimer (Bence-Jones protein) reveals a weak and unusual constant domains association

Monoclonal free light chains secreted in immunoproliferative disorders are frequently involved in renal complications, including a specific proximal tubule impairment, Fanconi's syndrome. The latter is characterized in most cases by intracellular crystallization including a light-chain variable-domain fragment which resists lysosomal proteases. Bence-Jones protein (BJP) DEL was isolated from a patient with myeloma-associated Fanconi's syndrome. The crystal structure of this human kappa immunoglobulin light-chain noncovalent dimer was determined using molecular replacement with the structure of molecule REI, as the variable domain, and that of BJP LOC as the constant domain. To our knowledge, DEL is the first complete kappa BJP structure described to date. The R-factor is 20.7% at 2.8 A resolution. The BJP DEL dimer was compared with other light-chain dimers and with Fab fragments with a kappa light chain. Although the domain-folding pattern was similar, the relative positions of the constant domains differed. BJP DEL showed a noncanonical quaternary structural arrangement which may be attributable to the poor CL-CL affinity and lack of an interchain disulfide bridge, combined with the conformational editing effect of the crystal-packing forces. Our results suggest that, in the absence of a disulfide bridge, most BJP CLs are probably mobile in solution. This may explain their high susceptibility to proteases and the absence of naturally occurring crystals for these dimers. Furthermore, these findings of an unusual quaternary structure of an immunoglobulin light-chain association extend our knowledge about the large and highly diverse structures of the immunoglobulin superfamily.

Antibodies of sharks: revolution and evolution

The combinatorial immune response is restricted to jawed vertebrates with cartilaginous fishes being the lowest extant species to have the mechanism for diversification and an extensive panoply of immunoglobulins, T-cell receptors and MHC products. Here, we review the molecular events of the "big bang" or rapid evolutionary appearance of the functionally complete combinatorial immune system coincident with the appearance of ancestral jawed vertebrates, suggesting that this event was catalyzed by horizontal transfer of DNA processing systems. We analyze the nature and extent of variable and constant domain diversity among the distinct immunoglobulin sets of carcharhine sharks focusing upon the lambda-like light chains and the mu and omega heavy chains. The detection and isolation of natural antibodies from the blood of unimmunized sharks illustrates a surprising range of recognition specificities and the existence of polyspecificity suggests that the antibody-forming system of sharks offers unique opportunities for studies of immunological regulation. Although the homologies between shark and mammalian immunoglobulins are unequivocal, major differences in segmental gene organization present challenges to our understanding of basic immunological phenomena such as clonal restriction.

Production and characterization of a set of mouse-human chimeric immunoglobulin G (IgG) subclass and IgA monoclonal antibodies with identical variable regions specific for Pseudomonas aeruginosa serogroup O6 lipopolysaccharide

The heavy- and light-chain variable regions from a murine monoclonal antibody that recognize Pseudomonas aeruginosa serogroup O6 lipopolysaccharide (LPS) were used to generate a series of chimeric mouse-human monoclonal antibodies with identical variable regions. The murine variable-region gene segments were cloned into an immunoglobulin (Ig) cDNA expression vector that contained the human kappa light-chain and IgG1 constant regions. The IgG1 heavy-chain constant region was then replaced with the human IgG2, IgG3, IgG4, or IgA1 heavy-chain constant region. The five different expression vectors were transfected into Chinese hamster ovary cells for antibody production. The chimeric antibodies exhibited immunoreactivity and affinity similar to that of the parental murine IgG antibody toward whole cells of a serogroup O6 strain. In vitro complement deposition assays demonstrated that the chimeric IgG4 and IgA antibodies did not mediate the deposition of complement component C3 onto the surface of either purified LPS or whole bacteria. The chimeric IgG1 and IgG3 antibodies were similar in their ability to deposit C3 onto the surface of both bacteria and LPS, while IgG2 antibody was more effective at depositing C3 onto the surface of bacteria than onto purified LPS. The pattern of opsonophagocytic activity of the chimeric monoclonal antibodies was similar to that of complement deposition onto bacterial cells in that the chimeric IgG1 and IgG3 had the highest opsonic activity. Although IgG2 deposited more C3 onto the bacterial surface than did IgG4 or IgA, all three of these isotypes had low opsonic activity against the serogroup O6 target strain. This series of related antibodies will help reveal functional differences in efficacy among protective antibodies to P. aeruginosa and will be critical for defining the optimal formulation of either a vaccine for active immunization or a polyclonal intravenous IgG or monoclonal antibody cocktail for passive immunotherapy.

Expression and characterisation of single-chain antibody fragments produced in transgenic plants against the organic herbicides atrazine and paraquat

Single-chain antibody fragments (scAbs), which have a human C-kappa constant domain and a hexa-histidine tail attached to the carboxy terminus of the single-chain Fv (ScFv) fragments to facilitate purification, have been raised against the herbicides paraquat and atrazine and expressed in transgenic Nicotiana tabacum cv. Samsun NN. Prior to purification, the anti-atrazine scAb is expressed as up to 0.014% of soluble leaf protein and has a binding profile in ELISA, against an atrazine-bovine serum albumin (BSA) conjugate, similar to that of the scAb produced in Escherichia coli. Competition ELISA has shown that the plant-derived scAb also recognises free atrazine. Following antibody affinity purification to isolate dimers, the affinity for immobilised antigen approaches that of the parental monoclonal antibody. This was confirmed by surface plasmon resonance analysis. The purified scAb also recognises related triazine herbicides. When isolated from cell-suspension cultures, the anti-paraquat scAb binds to a paraquat conjugate in a concentration-dependent manner, with a profile similar to the parental monoclonal antibody. This is the first demonstration that functional scAbs against organic pollutants can be produced in transgenic plants and that the scAbs may be appropriate for the development of immunoassay-based detection systems.

Constant region of a kappa III immunoglobulin light chain as a major AL-amyloid protein

AL-amyloidoses are generally described as a group of disorders in which N-terminal fragments of monoclonal immunoglobulin light chains are transferred into amyloid fibrils. We have, by amino acid sequence analyses and immunological methods, characterized the Bence-Jones protein and the corresponding AL protein as a kappa III immunoglobulin light chain from material of a patient with systemic AL-amyloidosis presenting as a local inguinal tumour. The two proteins showed some unique features. The major part of the AL amyloid fibril protein consisted of C-terminal fragments of the Bence-Jones protein. Furthermore, both the Bence-Jones protein and the AL protein were glycosylated, with possibly a glycosylation in the constant part of the light chain.

Chimeric anti-TAG72 receptors with immunoglobulin constant Fc domains and gamma or zeta signalling chains

We recently described the generation and expression of a chimeric T cell receptor with specificity for the tumor antigen TAG72 consisting of the single chain antibody (scFv) B72.3-scFv and the gamma chain of the FcepsilonRI receptor. The corresponding chimeric receptor containing the zeta chain of the TCR as signalling unit is not functionally expressed reflecting that the requirements for functional expression of chimeric receptors containing the gamma signalling chain are apparently different compared to those containing the CD3zeta signalling chain of the TCR. We describe a novel set of chimeric anti-TAG72 receptors including in their extracellular moiety the constant immunoglobulin CH2/3 domains that allow stable expression of chimeric gamma as well as zeta receptors. We designed anti-TAG72 receptors that consist of a scFv fragment derived from an anti-TAG72 second generation antibody (CC49) and of the CH2/3 domains of the human IgG and intracellularily either of the zeta or gamma signalling chain. The recombinant CC49-CH2/3-zeta and CC49-CH2/3-gamma DNA, respectively, was transfected into MD45 T cells and expressed under control of the RSV LTR. Both receptors were found on the cell membrane of transfected cells as demonstrated by flow cytometry analysis using an anti-human IgG Fc antibody directed to the CH2/3 immunoglobulin domains of the chimeric receptor. Specific cross-linking of the chimeric zeta as well as the gamma receptor by antigen or anti-human Ig antibodies resulted in specific activation of transfected cells. Our results demonstrate that both the gamma chain and the zeta chain++ containing receptor are stably expressed and convert T cells to specificity for the TAG72 antigen. This receptor design will facilitate efficient generation of genetically modified peripheral T cells and may provide valuable tools for the cellular immunotherapy of TAG72+ tumors.

Amino acid differences in the N-terminus of C(H)2 influence the relative abilities of IgG2 and IgG3 to activate complement

The four human IgG isotypes are highly conserved in amino acid sequence, but show differential ability to activate complement (C'): IgG3 and IgG1 are very active, IgG2 is active under certain conditions, and IgG4 is inactive. Although the second constant domain [C(H)2] is critical for C' activation, the individual amino acids that confer isotype-specific activity have not been identified. We have generated a series of mutants between IgG2 and IgG3, resulting in the exchange of the four N-terminal and six C-terminal polymorphic residues within C(H)2. Mutants containing the N-terminus of the C(H)2 of IgG3 were as effective as wildtype IgG3 in C1q binding, C1 activation and terminal complex (MAC) formation, but had reduced ability to effect C'-mediated lysis. IgG2 and mutants containing the N-terminal portion of the C(H)2 of IgG2 were reduced compared to IgG3 in activating C1, binding C1q and inducing assembly of the MAC, and were inactive in mediating lysis of target cells. Thus, the amino acid sequence differences in the N-terminus of C(H)2 play a critical role in determining the relative abilities of IgG2 and IgG3 to bind C1q and activate the C' cascade although additional residues of C(H)2 must be involved in mediating optimal target cells lysis. The sequence of the N-terminus of C(H)2 was less critical in determining C4 and C3 binding. Characterization of domain exchange mutants suggests that intermediate steps may be partly dependent on domains other than C(H)2. IgGs that do not direct target cell lysis nevertheless activate intermediate steps in the pathway, which may contribute to immune complex-associated disorders.

Role of repetitive antigen patterns for induction of antibodies against antibodies

Antibody responses against antibodies, such as rheumatoid factors, are found in several immunopathological diseases and may play a role in disease pathogenesis. Experience shows that they are usually difficult to induce experimentally. Antibodies specific for immunoglobulin constant regions (anti-allotypic) or for variable regions (anti-idiotypic) have been investigated in animal models; the latter have even been postulated to regulate antibody and T cell responses via network-like interactions. Why and how such anti-antibodies are induced during autoimmune diseases, has remained largely unclear. Because repetitively arranged epitopes in a paracrystalline structure of a viral envelope cross-link B cell receptors efficiently to induce a prompt T-independent IgM response, this study used immune complexes containing viruses or bacteria to evaluate the role of antigen pattern for induction of anti-antibody responses. We present evidence that antibodies bound to strictly ordered, but not to irregularly arranged, antigens dramatically enhance induction of anti-antibodies, already after a single immunization and without using adjuvants. The results indicate a novel link between anti-antibody responses and infectious agents, and suggest a similar role for repetitive self-antigens such as DNA or collagen involved in chronic immunopathological diseases.

T helper subset differentiation in the absence of invariant chain

The outcome of murine infection with Leishmania major is regulated by major histocompatibility complex class II-restricted T helper cells. Invariant chain-deficient (Ii -/-) mice have impaired ability to present major histocompatibility complex class II-restricted antigens, and reduced numbers of CD4+ T cells. Despite these deficits, C57BL/6 Ii -/- mice controlled L. major infection comparably to wild-type mice. As assessed by mRNA analysis and in vitro antigen restimulation for IFN-gamma, Ii -/- mice had normal induction of Th1 subset differentiation even though antigen-dependent proliferation of their lymph node cells was substantially compromised. In addition, BALB/c Ii -/- mice exhibited a progressive course of infection and Th2 effector cell development that were comparable to that seen in wild-type BALB/c mice. We wished to determine whether this unexpected efficiency of T helper subset induction despite inefficient T cell stimulation could be modeled in vitro. In the presence of rIL-12 or rIL-4 naive parasite-specific transgenic T cells could mature into IFN-gamma-or IL-4-secreting T helper cells, respectively, even when antigen presentation was suboptimal or antigen dose was submitogenic. These experiments demonstrate that activation of T helper cells to a threshold required for IL-2 production or proliferation is not required to achieve induction of disease-regulating T helper cell effector functions, and that pathogen-associated secondary activation signals may facilitate the full differentiation of T helper subsets during limiting presentation of antigenic peptides.

Ig N-glycan orientation can influence interactions with the complement system

This study was prompted by the paradoxical observation that a pair of dinitrophenyl-specific murine monoclonal IgG2a Abs had similar monosaccharide content and yet differed in their binding to lectins. The differential lectin-binding properties were lost when the Abs were denatured, suggesting that variations in lectin binding reflected the conformational accessibility of the N-glycans rather than intrinsic differences in the lectin binding capacity of the glycans themselves. This hypothesis was supported by experiments indicating that the degree to which the N-glycans on the Abs were reactive with beta-1,4-galactosyltransferase or susceptible to peptide N-glycosidase F corresponded directly to their relative accessibility to lectins. Moreover, the relative susceptibility to these enzymes and accessibility to lectins was inversely related to the capacity of the Abs to activate the classical pathway, suggesting that the orientation of the more accessible N-glycan might inhibit C1q binding. This hypothesis was supported by evidence that enzymatic cleavage of the more accessible N-glycan resulted in enhanced Clq, C4b, and C3b deposition. Conversely, removal of the less accessible N-glycan expressed by the other Ab inhibited C1q, C4b, and C3b deposition. The respective increase or decrease in C3b deposition on the two deglycosylated Abs was magnified when complement activation was performed in factor B-depleted serum, suggesting that N-glycan conformation primarily affects the classical pathway. Collectively, these data suggest that the orientation of the N-glycan expressed on Igs can profoundly influence interaction with the complement system.

Can immunoglobulin C(H)1 constant region domain modulate antigen binding affinity of antibodies?

Although the switch process is frequently associated with affinity maturation, the constant region is not assumed to play a role in Ag-Ab binding. In the present work, we demonstrate that two clonally related human monoclonal Igs sharing identical V(H) and V(L) sequences, but expressing different isotypes (IgA1kappa(PER) and IgG1kappa(PER)), bind tubulin with significantly different affinities. This difference was mainly accounted for by a disparity in the association rate constants. These results suggest that affinity maturation of this clone could be achieved through class switching in the absence of further somatic mutations. Since the differences observed were found at the Fab level, they also suggest a role for the C(H)1 domain in structuring the Ag-binding site into a more kinetically competent form.

Binding specificities of a polyreactive and a monoreactive human monoclonal IgG rheumatoid factor: role of oligosaccharides

The immunological specificites of two human rheumatoid factor-reactive IgG monoclonal antibodies derived from unstimulated rheumatoid synovial lymphocytes have been analysed. A malaria antigen-reactive IgG monoclonal antibody from an immune donor served as a control. Purified IgG monoclonal antibody from one IgG-RF hybridoma (L1), but not from the other IgG-RF hybridoma (D1) or the anti-malaria monoclonal antibody, exhibited dose-dependent binding to multiple self and non-self antigens such as ds-DNA, cytochrome-c, bovine thyroglobulin, transferrin, cellulose and lipopolysaccharide and therefore was considered polyreactive. The immunological specificity was confirmed by inhibition experiments using the same soluble antigens as inhibitors. The polyreactivity of the IgG-RF MoAb was markedly inhibited by absorption with glycoproteins such as thyroglobulin, a commonly used target for xenoreactive natural antibodies, and cytochrome-c, indicating that the monoclonal antibody is reactive with epitopes expressed on these ligands. Since some naturally occurring antibodies are carbohydrate specific, the authors tested the IgG-RF MoAb for possible carbohydrate specificity. Absorption with certain polysaccharides containing only one or two different sugar moieties did not inhibit the binding reactivities to any of the tested antigens. Polyreactivity of the monoclonal antibody, unlike most xenoreactive natural antibodies, was not caused by reactivity with (gal alpha 1-3gal) as indicated by the remaining binding reactivity after alpha-galactosidase treatment of the antigen. Removal of the N-linked glycosylation sites within the Fc portion of target IgG markedly reduced the antibody binding. The findings suggest that the carbohydrate content of the antigen is necessary for binding of the polyreactive IgG-RF MoAb. Reactivity to carbohydrate antigens may readily explain the so-called multispecificity of certain antibodies.

IL4 and IL13 receptors share the gamma c chain and activate STAT6, STAT3 and STAT5 proteins in normal human B cells

IL13 induces the same biological effects as IL4 in normal human B cells. We show that as in the IL4R complex, both IL4R alpha and IL2R gamma c are components of the IL13R and that both cytokines induced STAT6, STAT3 and STAT5 activation in B cells. In spite of this similar downstream signalling, IL4 and IL13 used a different set of Janus kinases: IL13 is unable to activate JAK1 and JAK3.

Structural mutations in the constant region of the T-cell antigen receptor (TCR)beta chain and their effect on TCR alpha and beta chain interaction

The region responsible for T-cell receptor (TCR)alpha and beta chain assembly has previously been shown to reside in their extracellular domains. In an attempt to delineate further the structural requirements for TCR alpha and beta chain assembly, chimeric TCR beta chains with increasing length of constant (C) region and mutant TCR beta chains with C-domain point mutations were constructed. Their ability to assemble with wild-type TCR alpha chain was evaluated in non-T (COS cells) or T cells. The results reveal that the C beta domain is the binding region to TCR alpha chain, whereas the intact variable (V), diversity (D) and joining (J) regions with a short C-domain of beta chain are not sufficient for the TCR alpha and beta chain assembly. The unique interchain disulphide bond between TCR alpha and beta chains is not required for the TCR alpha beta heterodimer formation.

Human constant regions influence the antibody binding characteristics of mouse-human chimeric IgG subclasses

Although antibody affinity is primarily determined by immunoglobulin variable region structure human IgG antibodies of the four subclasses specific for the same antigen have been shown to differ in their affinity. To explore the influence of the immunoglobulin constant region on functional antibody affinity, a set of V region identical mouse-human chimeric IgG subclasses specific for TAG72 (tumour-associated glycoprotein) were studied. Biomolecular interaction analysis (BIA) was used to determine the binding kinetics of whole IgG subclasses and F(ab')2 fragments. Despite identical V regions, binding kinetics differed for the four subclasses. The apparent dissociation rate constants of the intact immunoglobulins ranked IgG4 < IgG3 < IgG2 < IgG1. In contrast, analysis of the binding characteriztics of the F(ab')2 fragments derived from IgG1, IgG2 and IgG4 revealed identical binding kinetics. The structure of the constant regions of the humanized IgG subclass antibodies clearly influenced functional antibody affinity, as has been described for the murine IgG subclasses. The exact mechanism for this phenomenon remains obscure but such differences should be taken into account when designing or choosing antibodies for therapeutic use.