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

Peptide–MHC complexes: dressing up to manipulate T cells against autoimmunity and cancer

Antigen-specificity of T cells provides important clues to the pathogenesis of T cell-mediated autoimmune diseases and immune-evasion strategies of tumors. Identification of T cell clones involved in autoimmunity or cancer is achieved with soluble peptide–MHC (pMHC) complex multimers. Importantly, these complexes can also be used to manipulate disease-relevant T cells to restore homeostasis of T cell-mediated immune response. While auto-antigen-specific T cells can be deleted or anergized by T cell receptor engagement with cognate pMHC complexes in the absence of costimulation, integration of these complexes in artificial antigen-presenting systems can activate tumor antigen-specific T cells. Here the authors discuss the advancements in pMHC-complex-mediated immunotherapeutic strategies in autoimmunity and cancer and identify the lacunae in these strategies that need to be addressed to facilitate clinical implementation.

Bioconjugate Strategies for the Induction of Antigen-Specific Tolerance in Autoimmune Diseases

Antigen-specific immunotherapy (ASI) holds great promise for the treatment of autoimmune diseases. In mice, administration of major histocompatibility complex (MHC) binding synthetic peptides which modulate T cell receptor (TCR) signaling under subimmunogenic conditions induces selective tolerance without suppressing the global immune responses. However, clinical translation has yielded limited success. It has become apparent that the TCR signaling pathway via synthetic peptide antigen alone is inadequate to induce an effective tolerogenic immunity in autoimmune diseases. Bioconjugate strategies combining additional immunomodulatory functions with TCR signaling can amplify the antigen-specific immune tolerance and possibly lead to the development of new treatments in autoimmune diseases. In this review, we provide a summary of recent advances in the development of bioconjugates to achieve antigen-specific immune tolerance in vivo, with the discussion focused on the underlying design principles and challenges that must be overcome to target these therapies to patients suffering from autoimmune diseases.

Taming the TCR: antigen-specific immunotherapeutic agents for autoimmune diseases

Current treatments for autoimmune diseases are typically non-specific anti-inflammatory agents that affect not only the autoreactive cells but also the parts of the immune system that are required to maintain health. There is a need for the development of antigen-specific therapeutic agents that can effectively prevent the autoimmune attack while leaving the rest of the immune system functioning as normal. The simplest way to achieve this is using the autoantigen itself as a tolerizing agent; however, there is some risk involved with administering a potentially pathogenic antigen. In this review, we focus instead on the development and use of modified T cell receptor (TCR) ligands, in which the peptide ligand is modified to change the response by the T cell from a disease inducing to a protective response, and still retain the antigen-specificity necessary to target the autoreactive T cells. We review the use of modified TCR ligands as therapeutic agents in animal models of autoimmunity and in human autoimmune disease, and finally consider how they need to be improved in order to use them effectively in patients with autoimmune disease.

Long-term silencing of autoimmune diabetes and improved life expectancy by a soluble pHLA-DR4 chimera in a newly-humanized NOD/DR4/B7 mouse

Several human MHC class II (HLA) molecules are strongly associated with high incidence of autoimmune diseases including type 1 diabetes (T1D). The HLA-humanized mice may thus represent valuable tools to test HLA-based vaccines and therapeutics for human autoimmune diseases. Herein, we have tested the therapeutic potential of a soluble HLA-DR4-GAD65 271-280 (hu DEF-GAD65) chimera of human use in a newly-generated NOD/DR4/B7 double transgenic (dTg) mouse that develops spontaneously an accelerated T1D regardless the gender. The NOD/DR4/B7 dTg mice generated by a two-step crossing protocol express the HLA-DR*0401 molecules on 20% of antigen presenting cells, the human B7 molecules in pancreas, and HLA-DR4/GAD65-specific T-cells in the blood. Some 75% of pre-diabetic NOD/DR4/B7 dTg mice treated with hu DEF-GAD65 chimera remained euglycemic and showed a stabilized pancreatic insulitis 6 months after treatment. The 25% non responders developing hyperglycemia survived 3-4 months longer than their untreated littermates. T1D prevention by this reagent occurred by a Th2/TR-1 polarization in the pancreas. This study strongly suggests that the use of soluble pHLA reagents to suppress/stabilize the T1D progression and to extend the life expectancy in the absence of side effects is an efficient and safe therapeutic approach.

Increased membrane cholesterol in lymphocytes diverts T-cells toward an inflammatory response

Cell signaling for T-cell growth, differentiation, and apoptosis is initiated in the cholesterol-rich microdomains of the plasma membrane known as lipid rafts. Herein, we investigated whether enrichment of membrane cholesterol in lipid rafts affects antigen-specific CD4 T-helper cell functions. Enrichment of membrane cholesterol by 40–50% following squalene administration in mice was paralleled by an increased number of resting CD4 T helper cells in periphery. We also observed sensitization of the Th1 differentiation machinery through co-localization of IL-2Rα, IL-4Rα, and IL-12Rβ2 subunits with GM1 positive lipid rafts, and increased STAT-4 and STAT-5 phosphorylation following membrane cholesterol enrichment. Antigen stimulation or CD3/CD28 polyclonal stimulation of membrane cholesterol-enriched, resting CD4 T-cells followed a path of Th1 differentiation, which was more vigorous in the presence of increased IL-12 secretion by APCs enriched in membrane cholesterol. Enrichment of membrane cholesterol in antigen-specific, autoimmune Th1 cells fostered their organ-specific reactivity, as confirmed in an autoimmune mouse model for diabetes. However, membrane cholesterol enrichment in CD4⁺Foxp3⁺ T-reg cells did not alter their suppressogenic function. These findings revealed a differential regulatory effect of membrane cholesterol on the function of CD4 T-cell subsets. This first suggests that membrane cholesterol could be a new therapeutic target to modulate the immune functions, and second that increased membrane cholesterol in various physiopathological conditions may bias the immune system toward an inflammatory Th1 type response.

Dimeric MHC-peptides inserted into an immunoglobulin scaffold as new immunotherapeutic agents

The interactions of the T cell receptor (TCR) with cognate MHC-peptide and co-stimulatory molecules expressed at surface of antigen presenting cells (APC) leads to activation or tolerance of T cells. The development of molecular biological tools allowed for the preparation of soluble MHC-peptide molecules as surrogate for the APC. A decade ago a monomeric class II MHC molecule in which the peptide was covalently linked to β-chain of class II molecule was generated. This type of molecule had a low-binding affinity and did not cause the multimerization of TCR. The requirement of multimerization of TCR led to development of a new class of reagents, chimeric peptides covalently linked to MHC that was dimerized via Fc fragment of an immunoglobulin and linked to 3' end of the β-chain of MHC class II molecule. These soluble dimerized MHC-peptide chimeric molecules display high affinity for the TCR and caused multimerization of TCR without processing by an APC. Because dimeric molecules are devoid of co-stimulatory molecules interacting with CD28, a second signal, they induce anergy rather the activation of T cells. In this review, we compare the human and murine dimerized MHC class II-peptides and their effect on CD4(+) T cells, particularly the generation of T regulatory cells, which make these chimeric molecules an appealing approach for the treatment of autoimmune diseases.

Suppression of ongoing T cell-mediated autoimmunity by peptide-MHC class II dimer vaccination

Tissue-specific autoimmune diseases such as type 1 diabetes (T1D) are characterized by T cell-driven pathology. Administration of autoantigenic peptides provides a strategy to selectively target the pathogenic T cell response. Indeed, treatment with beta cell peptides effectively prevents T1D in NOD mice. However, the efficacy of peptide immunotherapy generally wanes as beta cell autoimmunity progresses and islet inflammation increases. With the goal of enhancing the efficacy of peptide immunotherapy, soluble (s)IA(g7)-Ig dimers covalently linked to beta cell autoantigen-derived peptides were tested for the capacity to suppress late preclinical T1D. NOD female mice with established beta cell autoimmunity were vaccinated i.v. with a short course of sIA(g7)-Ig dimers tethered to peptides derived from glutamic acid decarboxylase (GAD)65 (sIA(g7)-pGAD65). Treatment with sIA(g7)-pGAD65 dimers and the equivalent of only approximately 7 microg of native peptide effectively blocked the progression of insulitis and the development of diabetes. Furthermore, suppression of T1D was dependent on beta cell-specific IL-10-secreting CD4+ T cells, although the frequency of GAD65-specific FoxP3-expressing CD4+ T cells was also increased in sIA(g7)-pGAD65 dimer vaccinated NOD mice. These results demonstrate that MHC class II-Ig dimer vaccination is a robust approach to suppress ongoing T cell-mediated autoimmunity, and may provide a superior strategy of adjuvant-free peptide-based immunotherapy to induce immunoregulatory T cells.

A peptide-major histocompatibility complex II chimera favors survival of pancreatic beta-islets grafted in type 1 diabetic mice

BACKGROUND

Transplantation of pancreatic islets showed a tremendous progress over the years as a promising, new therapeutic strategy in patients with type 1 diabetes. However, additional immunosuppressive drug therapy is required to prevent rejection of engrafted islets. The current immunosuppressive therapies showed limited success in maintaining long-term islet survival as required to achieve insulin independence in type 1 diabetes, and they induce severe adverse effects. Herein, we analyzed the effects of a soluble peptide-major histocompatibility complex (MHC) class II chimera aimed at devising an antigen-specific therapy for suppression of anti-islet T cell responses and to improve the survival of pancreatic islets transplants.

METHODS

Pancreatic islets from transgenic mice expressing the hemagglutinin antigen in the beta islets under the rat insulin promoter (RIP-HA) were grafted under the kidney capsule of diabetic, double transgenic mice expressing hemagglutinin in the pancreas and T cells specific for hemagglutinin (RIP-HA, TCR-HA). The recipient double transgenic mice were treated or not with the soluble peptide-MHC II chimera, and the progression of diabetes, graft survival, and T cell responses to the grafted islets were analyzed.

RESULTS

The peptide-MHC II chimera protected syngeneic pancreatic islet transplants against the islet-reactive CD4 T cells, and prolonged the survival of transplanted islets. Protection of transplanted islets occurred by polarization of antigen-specific memory CD4 T cells toward a Th2 anti-inflammatory response.

CONCLUSIONS

The peptide-MHC II chimera approach is an efficient and specific therapeutic approach to suppress anti-islet T cell responses and provides a long survival of pancreatic grafted islets.

Monitoring antigen-specific T cells using MHC-Ig dimers

The lack of high affinity reagents has made distinguishing T cells on the basis of antigen specificity difficult to accomplish. This unit provides protocols that utilize innovations in molecular design to permit construction of soluble multivalent MHC complexes (MHC-Ig dimers) with high avidity for cognate T cell receptors. MHC-Ig dimers display stable binding properties when they interact with antigen-specific T cells thus allowing their use in the staining of antigen-specific T cells by flow cytometry. Methods for constructing and detecting these MHC-Ig dimers are included along with protocols for applying their use for the quantitation of antigen-specific T cells.

Recombinant expression of the beta-subunit of HLA-DR10 for the selection of novel lymphoma targeting molecules

Selective high-affinity ligands (SHALs) were selected as substitutes for monoclonal antibodies (mAbs) to deliver radioisotopes to malignant tumors. Because a SHAL (5 KD) is considerably smaller in comparison to an antibody (150 KD), a significant therapeutic index (TI) enhancement for radioimmunotherapy (RIT) is anticipated. The antibody-antigen (Ab-Ag) model system chosen for the development of SHALs consists of Lym-1, a MAb with proven selectivity in non-Hodgkin's lymphoma (NHL) patients and its well-characterized Ag, the beta subunit of HLA DR10. Whereas Lym-1 is readily available, the subunit of HLA-DR10 is not. Native, heterodimeric (alpha and beta subunits) HLA-DR10 can be purified from Raji cells, which are known to overexpress this Ag. Inconsistent homogeneity between preparations of HLA-DR10 solubilized in the presence of detergents prompted us to express a recombinant form of the beta subunit of HLA-DR10 in Escherichia coli. Negligible production yields (<or=50 microg/L) were achieved by the expression of the full-length protein in a soluble form. By contrast, yields of 240 mg/L were obtained by expressing only the extracellular domain (ED) of the beta subunit of HLA-DR10 in an insoluble form (inclusion bodies). The recovery yield of refolded protein was 75%. Circular dichroism (CD) and Lym-1 binding studies indicated that the recombinant ED of the beta subunit of HLA-DR10 was properly folded. Therefore, this recombinant protein can be used as a surrogate for native heterodimeric HLA DR10 for the in vitro selection of SHALs and related targeting molecules.

Soluble, dimeric HLA DR4-peptide chimeras: an approach for detection and immunoregulation of human type-1 diabetes

Still there are no effective methods to predict or cure type 1 diabetes (T1D) in humans. Soluble, dimeric MHC class II-peptide (DEF) chimeras have potential for both early diagnosis and immunospecific therapy. DEF chimeras prevent and reverse diabetes in mice by stimulating antigen-specific type 1 T regulatory cell (Tr1)-like cells. We also showed that diabetes could be predicted by changes in the phenotype of autoreactive CD4 T cells in peripheral blood. Herein, we demonstrated that human DEF (HLA-DR*0401/Fcgamma1) chimeras expressing peptides of beta-cell antigens stimulate Tr1-like cells in blood of patients with T1D, non-diabetic relatives, and controls. Furthermore, the specific and stable binding of DEF chimeras to cognate TCR and CD4 coreceptor allowed quantification and phenotyping of autoreactive CD4 T cells in non-stimulated blood by FACS. Our results indicate that (1) autoreactive CD4 T cells to GAD65 autoantigen are commonly present in humans expressing diabetes-susceptible HLA-DR*0401 molecules; (2) these autoreactive T cells undergo avidity maturation upon encountering the self antigen early in life; (3) the disease is associated with an imbalance between autoreactive CD4+CD25+ and CD4+CD69+ T cells specific for GAD65. Based on this, we propose a model to explain the kinetics of autoreactive CD4 T cells in blood during the natural history of T1D.

Efficacy of clonal deletion vs. anergy of self-reactive CD4 T-cells for the prevention and reversal of autoimmune diabetes

The self-reactive CD4 T-cells play an essential role in triggering and sustaining organ-specific autoimmune diseases. Silencing or elimination of these cells can prevent and reverse an autoimmune process. We have previously showed that a single dose-administration of a soluble dimeric MHC II-peptide chimera (DEF) in double-transgenic mice delayed the onset autoimmune diabetes, and restored the euglycemia in already diabetic mice for a period of 1 week. DEF dimer protection relied on induction of anergy of diabetogenic CD4 T-cells in spleen, and stimulation of IL-10-secreting T regulatory type 1 cells in pancreas. Herein, we show that an octameric form of DEF has doubled the period of protection and reversal of disease by clonal deletion of diabetogenic CD4 T-cells in both the thymic and peripheral compartments. Deletion occurred by activation-induced cell death subsequent to repartitioning and signaling of FAS-FADD apoptotic module in the plasma membrane lipid rafts. Our previous and present data indicated first, that DEF valence translates into various effects on the antigen-specific CD4 T-cells, i.e., Th2 immune deviation, anergy, and apoptosis. Second, the present findings argue for a better efficacy of clonal deletion than anergy of diabetogenic CD4 T-cells for the protection and reversal of autoimmune diabetes.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.

HLA-Ig-based artificial antigen-presenting cells: setting the terms of engagement

Recent advances in molecular medicine have shown that soluble MHC-multimers can be valuable tools for both the stimulation of as well as the analysis of antigen-specific T cells in vitro. In this review, we describe the use of dimeric major histocompatibility complexes, HLA-Ig, to visualize antigen-specific T cells as well as their potential to stimulate immune responses as part of an artificial antigen-presenting cell (aAPC). The use of HLA-Ig-based aAPC represents an exciting new approach to generate antigen-specific CTL for adoptive immunotherapy that helps to overcome many of the obstacles associated with limitations in current approaches to adoptive immunotherapy.

A model for antigen-specific T-cell anergy: displacement of CD4-p56(lck) signalosome from the lipid rafts by a soluble, dimeric peptide-MHC class II chimera

Soluble, dimeric peptide-MHC chimeras were shown to induce Ag-specific T cell anergy in vitro and in vivo. In this study, we describe a mechanism by which a soluble, dimeric peptide MHC class II chimera (DEF) induces Ag-specific T cell anergy. The anergic cells showed a displacement of the CD4-p56(lck) signaling module from the GM1-rich plasma membrane microdomains (lipid rafts), and subsequently an increase in p59(fyn) kinase activity, a dominant expression of p21 inhibitory TCR zeta-chain, and a poor phosphorylation and recruitment of zeta-associated protein of 70 kDa kinase to the TCR's immunoreceptor tyrosine-based activation motifs. The Th1 and Th2 transcription was suppressed and the cells were arrested in the Th0 stage of differentiation. Recovery from DEF anergy occurred late and spontaneously at the expense of low thresholds for activation-induced cell death. In contrast to DEF, a combination of TCR and CD4 mAbs did not induce such alterations or anergy, indicating that the ligand-mediated topology of TCR and CD4 coengagement can differentially affect the T cell function. Our results argue for a model of anergy in which the defective partitioning of signaling molecules in lipid rafts is an early, negative signaling event in T cells. Physiological ligands like DEF chimeras may provide new tools for silencing the autoimmune processes, and may also help in deciphering new mechanisms of negative regulation in T cells.

Generation and use of alternative multimers of peptide/MHC complexes

For many years, the detection of antigen-specific T cells has relied on indirect in vitro assays such as cytokine secretion, proliferation or chromium release assays. Things have dramatically changed during the past few years, thanks to the imagination of several investigators who have developed very elegant strategies to produce multivalent peptide/MHC complexes. One of these strategies has been to produce peptide-loaded monomeric biotinylated MHC molecules, which could be obtained as tetramers upon incubation with tetravalent streptavidin. Although this latter approach has been by far the most popular, this review focuses on other strategies which have also been successful.

T-cell tolerance and autoimmune diabetes

Herein we describe the major signaling events that occur in T-cells upon T-cell receptor (TCR) engagement, and the mechanisms responsible for the induction of T-cell anergy that may ultimately lead to the development of immunospecific therapies in T-cell mediated autoimmune diseases. A new type of antigen presenting molecule (dimeric MHC class-II/peptide, DEF) endowed with antigen-specific immunomodulatory effects such as induction of Th2 polarization and T-cell anergy is also described as a potential antidiabetogenic agent. According to our preliminary results, the MHC II/peptide-based approach may provide rational grounds for further development of antigen-specific immunotherapeutic agents such as human-like MHC lI/peptide chimeras endowed with efficient down-regulatory effects in CD4 T-cell-mediated autoimmune diseases such as Type 1 diabetes, multiple sclerosis, primary biliary cirrhosis, and rheumatoid arthritis.

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.

Modulation of CD4 T cell function by soluble MHC II-peptide chimeras

Peptides antigens of 8 to 24 amino acid residues in length that are derived from processing of foreign proteins by antigen presenting cells (APC), and then presented to T cells in the context of major histocompatibility complex molecules (MHC) expressed by APC, are the only physiological ligands for T cell receptor (TCR). Co-ligation of TCR and CD4 co-receptor on T cells by MHC II-peptide complexes (signal 1) leads to various T cell functions depending on the nature of TCR and CD4 co-ligation, and whether costimulatory receptors (signal 2) such as CD28, CTLA-4, CD40L are involved in this interaction. Recently, the advance of genetic engineering led to the generation of a new class of antigen-specific ligands for TCR, i.e., soluble MHC class I-, and MHC class II-peptide chimeras. In principle, these chimeric molecules consist of an antigenic peptide which is covalently linked to the amino terminus of alpha-chain in the case of MHC I, or beta-chains in the case of MHC II molecules. Conceptually, such TCR/CD4 ligands shall provide the signal 1 to T cells. Since soluble MHC-peptide chimeras showed remarkable regulatory effects on peptide-specific T cells in vitro and in vivo, they may represent a new generation of immunospecific T cell modulators with potential therapeutic applicability in autoimmune and infectious diseases. This review is focused on the immunomodulatory effects of soluble, MHC class II-peptide chimeras, and discuss these effects in the context of the most accepted theories on T cell regulation.

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.

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.

Present difficulties and future promise of MHC multimers in autoimmune exploration

Class I tetramers have been used to track cytotoxic T cells during bacterial and viral infections. During the past year, the use of such molecules has revealed important information about the role of CD8(+) T cells in autoimmune diabetes. Furthermore, class II multimers have been produced and successfully used to stain autoreactive CD4(+) T cells from patients with rheumatoid arthritis or Borrelia-burgdorferi-induced Lyme arthritis.

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.