Antigen presentation by dendritic cells after immunization with DNA encoding a major histocompatibility complex class II-restricted viral epitope

Intramuscular and intracutaneous immunization with naked DNA can vaccinate animals to the encoded proteins, but the underlying mechanisms of antigen presentation are unclear. We used DNA that encodes an A/PR/8/34 influenza peptide for CD4 T cells and that elicits protective antiviral immunity. DNA-transfected, cultured muscle cells released the influenza polypeptide, which then could be presented on the major histocompatibility complex class II molecules of dendritic cells. When DNA was injected into muscles or skin, and antigen-presenting cells were isolated from either the draining lymph nodes or the skin, dendritic, but not B, cells presented antigen to T cells and carried plasmid DNA. We suggest that the uptake of DNA and/or the protein expressed by dendritic cells triggers immune responses to DNA vaccines.

Expression of HLA class II molecules in humanized NOD.Rag1KO.IL2RgcKO mice is critical for development and function of human T and B cells

BACKGROUND

Humanized mice able to reconstitute a surrogate human immune system (HIS) can be used for studies on human immunology and may provide a predictive preclinical model for human vaccines prior to clinical trials. However, current humanized mouse models show sub-optimal human T cell reconstitution and limited ability to support immunoglobulin class switching by human B cells. This limitation has been attributed to the lack of expression of Human Leukocyte Antigens (HLA) molecules in mouse lymphoid organs. Recently, humanized mice expressing HLA class I molecules have been generated but showed little improvement in human T cell reconstitution and function of T and B cells.

METHODS

We have generated NOD.Rag1KO.IL2RγcKO mice expressing HLA class II (HLA-DR4) molecules under the I-E(d) promoter that were infused as adults with HLA-DR-matched human hematopoietic stem cells (HSC). Littermates lacking expression of HLA-DR4 molecules were used as control.

RESULTS

HSC-infused HLA-DR4.NOD.Rag1KO.IL-2RγcKO mice developed a very high reconstitution rate (>90%) with long-lived and functional human T and B cells. Unlike previous humanized mouse models reported in the literature and our control mice, the HLA-DR4 expressing mice reconstituted serum levels (natural antibodies) of human IgM, IgG (all four subclasses), IgA, and IgE comparable to humans, and elicited high titers of specific human IgG antibodies upon tetanus toxoid vaccination.

CONCLUSIONS

Our study demonstrates the critical role of HLA class II molecules for development of functional human T cells able to support immunoglobulin class switching and efficiently respond to vaccination.

The RTS,S malaria vaccine

RTS,S is the most advanced candidate vaccine against human malaria. During its remarkable journey from conception and design in the early 1980s to the multicenter Phase 3 trial currently underway across sub-Saharan Africa, RTS,S has overcome tremendous challenges and disproved established vaccine paradigms. In the last several years, Phase 2 studies conducted in infants and children in endemic areas have established the efficacy of RTS,S for reducing morbidity due to clinical malaria. If the results are realized in the Phase 3 trial, the chances for licensure in the near future appear high. Such progress is all the more remarkable given our lack of clear understanding regarding how the vaccine activates the human immune system, the immune correlates of protection or the mechanism whereby a vaccine targeting sporozoites and liver stage parasites can reduce the clinical disease associated with parasitemia. These unanswered questions pose important challenges to be addressed in the quest to understand the protection afforded by RTS,S and to build a more efficacious second generation vaccine against malaria. This review will focus on current knowledge about the protective efficacy of RTS,S and what we have learned regarding its impact on the human immune system.

Down-regulation of diabetogenic CD4+ T cells by a soluble dimeric peptide-MHC class II chimera

Type 1 diabetes is an organ-specific autoimmune disease that is mediated by autoreactive T cells. We show here that administration of a soluble dimeric peptide-major histocompatibility complex (pMHC) class II chimera (DEF) to prediabetic double-transgenic mice prevents the onset of disease or, in animals that are already diabetic, restores normoglycemia. The antidiabetogenic effects of DEF rely on the induction of anergy in splenic autoreactive CD4+ T cells via alteration of early T cell receptor signaling and stimulation of interleukin 10-secreting T regulatory type 1 cells in the pancreas. Soluble dimeric pMHC class II may be useful in the development of immunospecific therapies for type 1 diabetes.

Antigen-specific signaling by a soluble, dimeric peptide/major histocompatibility complex class II/Fc chimera leading to T helper cell type 2 differentiation

Interaction between a T cell receptor (TCR) and various ligands, i.e. , anti-TCR antibodies, superantigens, peptides, or altered peptide ligands in the context of major histocompatibility complex (MHC) molecules can trigger different T helper cell (Th) effector functions. Herein, we studied the T cell response induced by a soluble, dimeric peptide/MHC class II chimera, namely hemagglutinin (HA)110-120/I-E(d)alphabeta/Fcgamma2a (DEF). We have previously demonstrated that the soluble DEF molecule binds stably and specifically to HA110-120-specific TCRs expressed by a T cell hybridoma. Administration of DEF in vivo induced differentiation of resting and activated peptide-specific T cells toward a Th2 response, as indicated by the increase of interleukin (IL)-4, IL-10, and specific immunoglobulin (Ig)G1 antibodies and decrease of IL-2, specific IgG2a antibodies, and cytotoxic T lymphocyte activity. In contrast to HA110-120 peptide presented by the DEF molecule to T cells, the nominal synthetic peptide induced a predominant Th1 response, and the PR8 virus-derived HA110-120 peptides induced a mixed Th1/Th2 response. Independent of antigen processing, soluble DEF was almost 2 logs more potent in stimulating cognate T cells than the nominal peptide. Polarization of cognate T cells toward the Th2 response occurred upon interaction of soluble DEF with TCR and CD4 molecules followed by early activation of p56(lck) and ZAP-70 tyrosine kinases, and negative signaling of the signal transducer and activator of transcription (STAT)4 pathway of Th1 differentiation. DEF-like molecules may provide a new tool to study the mechanisms of signaling toward Th2 differentiation and may also provide a potential immunotherapeutic approach to modulate autoreactive T cells toward protective Th2 immune responses.

Efficient loading of identical viral peptide onto class II molecules by antigenized immunoglobulin and influenza virus

Several prior reports have identified peptides that are naturally associated with major histocompatibility complex (MHC) class II molecules on presenting cells. We have examined the delivery of a peptide from exogenous sources to MHC class II molecules. The peptide derives from the influenza virus hemagglutinin (HA) and activates a CD4+ T cell hybridoma. In functional assays of antigen presentation, this epitope is delivered effectively to T cells either in the context of influenza virus or chimeric immunoglobulin (Ig) molecules (Ig-HA) in which the peptide has replaced the CDR3 loop of the heavy chain. We find that the identical 11-mer peptide can be isolated from mouse MHC class II antigens whether the exogenous source of peptide is free HA peptide, the Ig-HA chimera, or ultraviolet-inactivated PR8 influenza virus. The Ig-HA chimera proves to be the most efficient vehicle for charging class II molecules via the exogenous route. Given the fact that self Igs represent natural long-lived carriers, we suggest that antigenized Igs have considerable potential for peptide delivery to MHC molecules in situ.

Characterization of mutated protein encoded by partially duplicated fibrillin-1 gene in tight skin (TSK) mice

Fibrillin-1 (Fbn-1) is a ubiquitous protein present in the extracellular matrix of various organs and it is a major component of microfibrils embedded in the core of elastic fibers. In humans, mutations or deletions of the Fbn-1 gene are associated with several genetic diseases. In addition, several microsatellite alleles near Fbn-1 gene were found associated with diffuse scleroderma. In TSK/+ mice, which develop a scleroderma-like syndrome, the Fbn-1 gene exhibits an inframe duplication of exons 17-40. In this study, we report that the synthesis and secretion of wild-type Fbn-1 in TSK/+ is higher than that of the mutated Fbn-1 protein excluding the possibility that TSK genetic defect is due to a loss of the wild allele. We also demonstrate for the first time that TGF-beta, which plays a crucial role in skin fibrosis, binds to both wild-type and mutated Fbn-1. The amount of bound TGF-beta was higher in mutated than wild-type Fbn-1 and appears related to the number of TGF-beta binding motifs.

CpG motifs of DNA vaccines induce the expression of chemokines and MHC class II molecules on myocytes

Determining how an immune response is initiated after in vivo transfection of myocytes with plasmids encoding foreign antigens is essential to understand the mechanisms of intramuscular (i. m.) genetic immunization. Since myocytes are facultative antigen-presenting cells lacking MHC class II and co-stimulatory molecules, it was assumed that their unique role upon DNA vaccination is to synthesize and secrete the protein encoded by the plasmid. Here we describe that i. m. injection of unmethylated CpG motifs induced the expression of chemokines (monocyte chemotactic protein-1) and MHC class II molecules on myocytes. Our results indicate that immunostimulatory DNA sequences (CpG motifs) of DNA vaccines augment synthesis of chemokine by myocytes with subsequent recruitment of inflammatory cells secreting IFN-gamma, a potent cytokine that up-regulates the expression of MHC class II molecules on myocytes. A myoblast cell line triple transfected with plasmids encoding MHC class II molecules and an immunodominant CD4 T cell epitope of influenza virus presented the endogenously synthesized peptide and activated specific T cells. These findings suggest that one mechanism for the immunogenicity of DNA vaccines consists in the presentation of peptides to CD4 T cells by in vivo plasmid-transfected myocytes.

Engineering and characterization of a murine MHC class II-immunoglobulin chimera expressing an immunodominant CD4 T viral epitope

T cells recognize peptides derived from the processing of proteins by antigen presenting cells (APCs) in association with the major histocompatibility complex (MHC) molecules. We have engineered a murine MHC class II antigen presenting molecule consisting of the extracellular domains of I-E(d)alpha and I-E(d)beta chains to which the CD4 T cell immunodominant epitope HA110-120 of the hemagglutinin (HA) of the A/PR/8/34 influenza virus was covalently linked at the N-terminus of the I-E(d)beta chain. The HA110-120-I-E(d)alphabeta complex was dimerized by the Fc portion of an IgG2a linked at the C-terminus of the I-E(d)beta chain. SF9 insect cells infected with baculovirus carrying both I-E(d)alpha and HA110-120-I-E(d)beta-Fcgamma2a genes, secreted a disulfide-stabilized dimer of the HA110-120-I-E(d)alphabeta-Fcgamma2a molecule, designated as DEF. The chimeric molecule preserved the structural integrity of both MHC-peptide complex and Fc portion of IgG2a, and was able to: (i) bind specifically to the cognate T cell receptors (TCRs) and to the immunoglobulin FcgammaRII receptor (FcR), (ii) induce complement-mediated cell cytotoxicity, and (iii) trigger early production of IL-2 in cognate T cells. Chimeric antigen presenting molecules with these characteristics may represent a novel platform for the development of immunomodulatory agents of therapeutic use.

Towards development of T-cell vaccines

Recent studies on the recognition of antigens by CD4+ and CD8+ T cells have revealed new ways of preparing efficient T-cell vaccines. Here, Constantin Bona and colleagues discuss several approaches for the development of T-cell vaccines, with applications ranging from the induction of protective immunity against intracellular parasites to the development of therapeutic agents against autoimmune disorders, allergic diseases and cancer.

Immunogenicity of a contiguous T-B synthetic epitope of the A/PR/8/34 influenza virus

A contiguously linked T-B synthetic viral epitope (110HA120-150HA159,T-B) was investigated for its potency in inducing humoral and cellular immune responses in vivo. The T-cell epitope 110HA120 corresponds to the site 1 hemagglutinin (HA) of the A/PR/8/34 (PR8) influenza virus and is recognized by CD4 T cells in association with I-Ed class II major histocompatibility complex molecules. The 150HA159 represents a major B-cell epitope of the HA protein. T-B dipeptide emulsified in Freund's complete adjuvant was able to induce strong antiviral antibody titers and a high frequency of specific T-cell precursors after a single inoculation in BALB/c mice. In contrast, immunization under identical conditions with equimolar mixtures of T and B peptides did not elicit antibody titers or a cellular immune response. As indicated by the isotypes of antiviral antibodies, the T-B dipeptide preferentially induced a Th1-like immune response. Challenge with T-B dipeptide, but not with T or B peptide alone, stimulated peptide-specific T memory cells in mice previously primed with PR8 virus or with T-B dipeptide. As a consequence, 71 and 57% of these mice, respectively, survived infection with two 100% lethal doses of PR8 virus. Our results suggest that, inasmuch as contiguity between T- and B-cell epitopes provides enough signaling capacity to trigger the mechanisms of T-B-cell cooperation in vivo, a T-B contiguous epitope may well represent a minimal built-in subunit vaccine. Aside from their potential bioavailability, the T-B contiguous epitopes may also represent attractive tools for investigating the molecular mechanisms of T-B-cell cooperation responsible for antiviral protection.

Immunochemical and molecular characterization of anti-RNA polymerase I autoantibodies produced by tight skin mouse

Autoantibodies against nuclear proteins like RNA polymerase I (RNA pol I) are produced in a number of rheumatic autoimmune diseases. Production of antibodies specific for the 190-kD subunit of RNA pol I appears to be characteristic in the patients with systemic sclerosis. Previous investigations have shown that the tight skin (TSK) mouse is an experimental model for systemic sclerosis. In the present study we show that the TSK mice produce high titers of anti-RNA pol I antibodies, both of IgM and IgG classes. To characterize the immunochemical properties of these antibodies we obtained a large panel of hybridomas from these mice. Analysis of these hybridomas revealed that clonal frequency of autoreactive B cells specific for RNA pol I are higher in the TSK mice that in the controls. mAbs obtained from the TSK mice were specific for the 190-kD subunit and cross-reacted with Escherichia coli and phage T7 RNA polymerases (155-, 150-, and 107-kD polypeptides). We have also demonstrated that these antibodies bind better to the phosphorylated enzymes. The anti-RNA pol I mAbs were divided into three groups in terms of their functional property. The first group of antibodies increased the catalytic activity of the enzyme whereas the antibodies of the second group inhibited the enzymatic activity. Competitive inhibition RIAs showed that these two groups of antibodies bound to distinct epitopes. The third group of antibodies was neutral and had no activity on the enzyme function. These results suggest that TSK mouse anti-RNA pol I antibodies recognize three or more conserved epitopes. To understand the molecular basis of the generation of such autoreactive antibodies we analyzed their V gene repertoire. Northern analysis of RNAs of 14 TSK hybridomas showed that the VH genes encoding these antibodies were mainly from VH J558 family. It is possible that these genes were derived from a single germline gene or from a set of related genes of a single subgroup.

Towards development of T-cell vaccines

Recent studies on the recognition of antigens by CD4+ and CD8+ T cells have revealed new ways of preparing efficient T-cell vaccines. Here, Constantin Bona and colleagues discuss several approaches for the development of T-cell vaccines, with applications ranging from the induction of protective immunity against intracellular parasites to the development of therapeutic agents against autoimmune disorders, allergic diseases and cancer.

Engineering of doubly antigenized immunoglobulins expressing T and B viral epitopes

BACKGROUND

Concomitant with the advent of molecular biology techniques and the ability of immunoglobulins (Ig) to recognize proteins, carbohydrates, lipopeptides and nucleic acids, vaccinologists have taken advantage to develop a variety of prophylactic and therapeutic vaccine prototypes. Presentation of epitopes to the immune system by Ig molecules as a carrier platform offers several advantages: (i) long exposure of the antigen to antigen processing cells (APCs) by virtue of their long half life, (ii) lack of the immune response to self Ig, focusing the immune response to protective epitopes rather than irrelevant epitopes, (iii) it takes advantage of the properties of Fc fragment of various isotypes like crossing the placenta (IgG) or homing in epithelia (IgA), and (iv) targeting various antigens by virtue of their binding specificity.

OBJECTIVES

This study was aimed to genetically and enzymatically engineer immunoglobulins (Igs) able to express and to deliver concomitantly immunodominant T and B viral epitopes.

STUDY DESIGN

Using a genetic engineering approach we replaced the complementary determining region 3 (CDR3) and complementary determining region 2 (CDR2) of an anti-arsonate 91A3 mAb with the immunodominant HA110-120 T cell epitope and HA150-159 B cell epitope of hemagglutinin (HA) of influenza A/PR8 virus, respectively. The second doubly antigenized Ig (Ig-HA-Gal-B) was constructed on an Ig in which CDR3 was replaced with HA110-120 T cell epitope while the HA150-159 B cell epitope was enzymatically assembled through an imidic bond on the galactose (Gal) residues of the carbohydrate moiety.

RESULTS AND CONCLUSIONS

Both genetically and genetically/enzymatically doubly antigenized Ig constructs (dAIg) were properly folded and they were able to activate peptide-specific T cells and to elicit anti-viral antibody response in mice. This demonstrates that the CDR loops as well as carbohydrate moieties of immunoglobulins represent permissive sites for grafting foreign epitopes without altering the structural integrity of immunoglobulins and the immunogenicity of the viral peptides.

Antigen-specific downregulation of T cells by doxorubicin delivered through a recombinant MHC II--peptide chimera

As the number of drugs with potential therapeutic use for T-cell-mediated diseases increases, there is a need to find methods of delivering such drugs to T cells. The major histocompatibility complex (MHC)--peptide complexes are the only antigen-specific ligands for the T-cell receptor (TCR) expressed on T cells, and they may be an appropriate drug delivery system. We engineered a soluble bivalent MHC class II-peptide chimera on the immunoglobulin scaffold (I-E(d)alpha beta/Fc gamma 2a/HA110-120, DEF) that binds stably and specifically to CD4 T cells recognizing the HA110-120 peptide. Doxorubicin, a powerful antimitogenic anthracycline, was enzymatically assembled on the galactose residues of a DEF chimera. The DEF-gal-Dox construct preserved both the binding capacity to hemagglutinin (HA)-specific T cells, and the drug toxicity. Brief exposure of HA-specific T cells to DEF-gal-Dox construct in vitro was followed by drug internalization in the lysosomes, translocation to the nucleus, and apoptosis. Administration of DEF-gal-Dox to mice expressing the TCR-HA transgene reduced the frequency of TCR-HA T cells in the spleen and thymus by 27% and 42%, and inhibited HA proliferative capacity by 40% and 60%, respectively. It has not been demonstrated previously that pharmacologically active drugs able to modulate T-cell functions can be delivered to T cells in an antigen-specific manner by soluble, bivalent MHC II-peptide chimeras.

Insights into the pathogenesis of type 1 diabetes: a hint for novel immunospecific therapies

Type 1 diabetes is an organ-specific autoimmune disease whose incidence is increasing worldwide. At present, there is no effective therapy to prevent or cure this disease. The genetic background (MHC and non-MHC genes) and environmental factors (pathogens, drugs, and diet) are critical for the initiation of the autoimmune response against the pancreatic beta-cells. Recognition of the pancreatic autoantigens by T cells in a predetermined environment of antigen-presenting cells, costimulation, and cytokines is crucial for the selective activation of diabetogenic or protective/regulatory T cells. Once the autoimmune process is triggered, epitope spreading and sustaining the autoimmune responses by continuous antigen stimulation leads to expansion of effector cells, which launch the attack on the beta-cells. Despite of some controversy, most of the studies in humans and animal models suggest that CD4 (Th1) T cells are directly involved in the autoimmune attack by secretion of pro-inflammatory cytokines and recruitment of cytotoxic CD8 T cells. Secretion of anti-inflammatory cytokines by Th2 cells is protective against the disease. Therapy with peptides derived from major target antigens, such as glutamic acid decarboxylase 65 or proinsulin, can prevent the disease in animal models by rising protective Th2 cells. Herein, we review the recent progress in the immunopathogenesis of Type 1 diabetes and insights into the development of new diagnostic tools and antigen-specific immunomodulators, such as MHC-peptide chimeras.

Purification of antigenized immunoglobulins derivatized with monomethoxypolyethylene glycol

Genetically engineered immunoglobulins (Igs) carrying viral B or T cell peptides in the CDR3 loop, function as efficient delivery system of the defined viral epitopes. Two of these antigenized Igs (AIgs) were derivatized with 2-O-monomethoxypolyethylene glycol-4,6-dichloro-s-triazine (mPEG). Herein, we describe a two-step strategy to purify mPEG-derivatized AIgs (AIgs-mPEG). Unreacted mPEG polymers were removed by size-exclusion chromatography using ammonium hydrogencarbonate as a buffer system. Mildly PEGylated AIgs were isolated from free and highly derivatized AIgs by anion-exchange chromatography. Electrophoretic analysis indicated that the AIgs-mPEG preparation contained less than 4 x 10(-4) M unreacted mPEG. This strategy may be applied to other mPEG-derivatized monoclonal antibodies.

Kinetics of anti-fibrillin-1 autoantibodies in MCTD and CREST syndrome

Using a highly sensitive Radioimmunoassay (RIA), the kinetics of synthesis of anti-fibrillin (Fbn-1) autoantibodies were studied in 17 patients with mixed connective tissue disease (MCTD) and two with CREST syndrome calcinosis, Raynaud's oesophageal dismotility, sclerodectyly and teleangiectasis who were found to be positive for this autoimmune response. IgG autoantibodies specific for recombinant Fbn-1 (rFbn-1) (aa 369-425) were found in all patients excepting one with MCTD, multiple sclerosis, and dermatomyositis. IgM were found in fewer cases. Several kinetics patterns of anti-Fbn-1 autoantibodies were observed: a) long lasting persistence of IgG and IgM autoantibodies up to 14 years; b) fluctuation of antibodies during various periods up to 16 years; c) disappearance of antibody response after several years, and d) patients producing IgG but not IgM autoantibodies. No differences in the synthesis of autoantibodies were observed between MCTD patients with a stable disease, and those developing during the course features of systemic sclerosis (SSc), Sjogren's syndrome, or rheumatoid-like arthritis. In one patient displaying a lupus-like syndrome for 3 years, the appearance of anti-Fbn-1 autoantibodies coincided with the occurrence of MCTD and scleroderma. While the detection of anti-Fbn-1 autoantibodies may be clinically useful in differential diagnosis or eventual prognosis of patients with connective tissue diseases, their role in the pathogenesis of scleroderma syndromes requires further investigation.

Contrasting efficacy of presentation by major histocompatibility complex class I and class II products when peptides are administered within a common protein carrier, self immunoglobulin

Major histocompatibility complex (MHC) class I and II products are specialized to present antigens via different intracellular processing routes. Peptides originating from proteins in the cytoplasm can gain access to class I peptide-binding grooves, most likely in the rough endoplasmic reticulum. Peptides from proteins in acidic endocytic vacuoles gain access to class II. It has been proposed that MHC class I products also can capture peptides from "exogenous" or noninfectious sources, and this assumption underlies the use of intact proteins as vaccines for CD8+ cytotoxic T lymphocytes. Here we describe quantitative information comparing the efficacy of peptide presentation from exogenous proteins by administering a class I- and II-restricted peptide within the same context, the CDR3 loop of the VH domain of a self immunoglobulin. Antigen-presenting cells (APC), including primary dendritic cells, efficiently present an influenza hemagglutinin peptide from the immunoglobulin (Ig) carrier (50% maximal response at 10 nM Ig-HA) to an MHC class II-restricted T cell. In contrast, these same APC are unable to present an influenza nucleoprotein (NP) peptide from the same context (1 microM Ig-NP) to an MHC class I-restricted T cell. Ig-NP DNA transfectants do present the nucleoprotein viral peptide on class I. Thus, peptides within the complementarity-determining region loops of Ig carriers can be presented on class I or II MHC products, but the endocytic compartment, when offered MHC class I- and II-restricted peptides within the same carrier protein context, favors presentation by class II by at least 1000-fold.

Protective immunity elicited by vaccination with DNA encoding for a B cell and a T cell epitope of the A/PR/8/34 influenza virus

Numerous reports have demonstrated that immunization with plasmids bearing influenza virus hemagglutinin (HA) or nucleoprotein (NP) genes elicits humoral and cellular protective responses. Herein we describe the generation of a plasmid (pVH-TB) encoding for a VH region of a self-Ig in which both the major B cell epitope HA150-159 and the immunodominant CD4 T cell epitope HA110-120 of HA of the A/PR/8/34 influenza virus were genetically inserted in the CDR2 and CDR3 loops, respectively. Our results demonstrate unequivocally that i.m. injection of pVH-TB plasmid in BALB/c mice elicited specific cellular and humoral immune responses able to protect against infection with lethal doses of A/PR/8/34 influenza virus.

Antibody response elicited by T-dependent and T-independent antigens in gene targeted kappa-deficient mice

Animal models substantially contribute to the understanding of the pathogenesis of various human diseases, including those associated with genetic defects. Our study investigated the characteristics of antibody responses elicited by T-dependent and T-independent antigens in mice rendered kappa-deficient by targeted deletion of the J kappa C kappa gene segments. It is known that in normal murine species the kappa repertoire dominates the antibody repertoire (kappa/lambda ratio = 95:5). Our results indicate that the kappa gene deletion causes the alternative usage of lambda 1 (93%) and lambda 2 (7%) light chains, confirming previous studies demonstrating that in kappa-deficient mice all B cells express Ig lambda receptors. The anti-trinitrophenylbenzene (TNP) response in K-/- mice was compensated for by lambda 1 and lambda 2 bearing Igs. However, isoelectric focusing analysis of anti-TNP antibodies showed a considerably more restricted pattern of lambda anti-TNP antibodies in K-/- as compared with kappa antibodies in normal mice. No major differences were observed in the affinity for the hapten of kappa or lambda 1 or lambda 2 mAbs obtained from 129/Sv and K-/- mice. Furthermore, lambda 1 and lambda 2 chains can reconstitute the expression of an idiotype (460Id) borne on kappa anti-TNP antibodies. The 460Id was detected both in polyclonal and monoclonal anti-TNP antibodies obtained from K-/- mice. Our results clearly showed that the kappa anti-TNP repertoire is compensated by the lambda repertoire even though the latter is clonally restricted in K-/- mice.

Enzymatically mediated engineering of multivalent MHC class II-peptide chimeras

We previously reported the genetic engineering of the first soluble, bivalent major histocompatibility complex (MHC) class II-peptide ligand for T-cell receptor (TCR). This ligand binds stably and specifically to cognate T-cells and exhibits immunomodulatory effects in vitro and in vivo. The increase in valence of MHC class II-peptide ligands was shown to parallel their avidity for cognate TCRs and potency in stimulating cognate T-cells. We describe a new enzymatic method to increase the valence of MHC-peptide ligands by cross-linking the N-glycan moieties of dimeric MHC II-peptide units through a flexible, bifunctional polyethylene glycol linker. Using this method, we generated covalently stabilized tetravalent and octavalent MHC II-peptide ligands which bound stably and specifically to cognate TCR and preserved their structural integrity in blood and lymphoid organs for 72 h. Depending on the TCR/CD4 occupancy and degree of TCR/CD4 co-clustering, the multivalent MHC II-peptide ligands polarized efficiently the antigen-specific CD4(+) T-cells toward type 2 cell differentiation or induced T-cell anergy and apoptosis. The enzymatically mediated engineering of multivalent MHC-peptide ligands for cognate TCRs may provide rational grounds for the development of new therapeutic agents endowed with strong modulatory effects on antigen-specific T-cells.

Enzymatically mediated, glycosidic conjugation of immunoglobulins with viral epitopes

We developed a novel enzymatic procedure to couple a peptide to the sugar moieties of immunoglobulins (Igs). The synthesis of the conjugates consists in galactose (Gal) oxidation of desialylated Igs followed by covalent attachment of the peptides with concurrent stabilization of the Schiff bases upon mild reduction. The peptide used in this study, corresponds to the amino acid residues 110-120 of hemagglutinin (HA) of PR8 A virus and is recognized by CD4 T helper cells in association with I-Ed class II major histocompatibility complex (MHC). The degree of coupling as determined by competitive inhibition of radioimmunoassay (IRIA) using FPLC purified conjugates was estimated at 11.4 peptides per IgG molecule. Coupling of HA110-120 peptide to the sugar moiety of various mouse and human Igs was confirmed by Western blot analysis developed with anti-HA110-120 antibodies. Complete detachment of the peptide from the conjugates by N-deglycosylation with PGNase F indicated a defined specificity of coupling HA peptide to the N-linked oligosaccharides of Igs. To facilitate quick release of the peptides from the conjugates into the lysosomal compartment of the antigen processing cells (APC) we introduced at the alpha amino terminus of the peptide (HAc110-120), a cleavage site for cathepsins (AAAL). The immunoglobulin-galactose-HAc110-120 conjugates (IGP) were able to activate HA110-120 specific T hybridoma cells as efficient as influenza PR8 A virus and 40-100-fold higher than the synthetic peptide itself.

A sensitive method to detect defined peptide among those eluted from murine MHC class II molecules

We developed a sensitive competitive inhibition radioimmunoassay able to trace pmoles of a defined peptide eluted from major histocompatibility complex (MHC) class II molecules that were subsequently fractionated by RP-HPLC. In this assay we used a model synthetic peptide corresponding to amino acid residues 110-120 from the hemagglutinin (HA) of PR8 influenza virus, and affinity purified rabbit antibodies specific for this peptide. The HA110-120 peptide binds to I-Ed class II molecules on the surface of APCs and is recognized by specific CD4+ T helper cells. 2PK3 B lymphoma cells (H-2d) were pulsed with HA110-120 peptide or PR8 virus, lysed, the MHC class II molecules extracted, and bound peptides eluted. After separation by RP-HPLC, the fractions were tested for inhibition of the binding of rabbit anti-HA110-120 antibodies to peptide coated microtiter plates. A significant inhibitory activity was observed with one peak when the cells were pulsed with HA110-120 peptide and two peaks when pulsed with PR8 virus. The inhibitory activity was correlated with the presence of HA110-120 peptide as demonstrated by peptide sequencing. The assay is reproducible and sensitive to 1 pmol of antigenic peptide. This assay can be useful to identify microbial peptides with defined structure and antigenicity among the multiple peptides bound to class II molecules.

Escape from self-tolerance leads to neonatal insulin-dependent diabetes mellitus

Double transgenic (dTg) mice expressing the hemagglutinin (HA) of influenza virus under the insulin promoter and the TCR specific for the immunodominant CD4 T cell epitope of HA (HA110-120) develop insulin-dependent diabetes mellitus (IDDM). In order to gain information on the breaking down of neonatal self-tolerance we studied the occurrence of IDDM after birth. Our results showed that newborn mice develop fulminant IDDM characterized by occurrence of insulitis as early as 3 days after birth, followed by hyperglycemia by 7 days, and significant hypoinsulinemia by 28 days. The neonatal breakdown of self-tolerance of T cells positively selected in the thymus is supported by the facts that: (i) peripheral HA110-120 specific T cells from neonates are fully functional and proliferated upon stimulation with the nominal peptide, and (ii) peptide-specific T cells were accumulated in the pancreas of dTg mice as early as 3 days after birth. Our results demonstrate that diabetes occurring in young dTg mice is due to early activation of self-reactive T cells immediately after birth. Accumulation of specific T cells in the target organ leads to destruction of pancreatic beta-cells and IDDM. These mice may provide a useful model to evaluate new strategies for the prevention of diabetes.