Species-specific binding of CD4 to the beta 2 domain of major histocompatibility complex class II molecules

Preclinical Development of a Tolerogenic Peptide From Glutamate Decarboxylase as a Candidate for Antigen-Specific Immunotherapy in Type 1 Diabetes

Dysregulation and loss of immune tolerance toward pancreatic β-cell autoantigens are features of type 1 diabetes (T1D). Until recently, life-long insulin injection was the only approved treatment for T1D, but it does not address the underlying disease pathology. The aim for antigen-specific immunotherapy (ASI) is to restore tolerance. ASI holds potential as a new therapeutic strategy for treating autoimmune diseases with well-characterized antigens. Peptide ASI using processing-independent CD4+ T-cell epitopes (PIPs) shows promising results in several autoimmune diseases. Here, we successfully applied the principles of PIP design to the T1D autoantigen glutamate decarboxylase 65 (GAD65). Peptides spanning GAD65 predicted to be pan-HLA-DR binding were selected. Peptide 10 (P10) displayed enriched responses in peripheral blood mononuclear cells from people with T1D. The minimal epitope of the P10 peptide was fine mapped using T-cell hybridomas generated from HLA-DRB1*04:01 transgenic mice. This minimal epitope, P10Sol, was demonstrated, using a novel activation-induced marker assay, to induce tolerance to the parent peptide in the transgenic mice. Finally, we show that GAD65 P10Sol PIP is recognized by CD4+ T cells from people with T1D who possess a range of HLA-DR alleles and, therefore, can be defined as a pan-DR-binding peptide with therapeutic potential.

ARTICLE HIGHLIGHTS

There are currently no approved antigen-specific immunotherapies (ASIs) for people with type 1 diabetes (T1D). We aimed to develop a peptide for ASI for T1D based on the T1D-associated auto-antigen glutamate decarboxylase 65 (GAD65). A minimal and soluble peptide derived from GAD65 was demonstrated to induce tolerance in an HLA transgenic mouse. Our data suggest this peptide derived from the GAD65 islet protein should be tested for therapeutic potential in people with T1D who have residual β-cell function.

HLA-transgenic mouse models to study autoimmune central nervous system diseases

It is known that certain human leukocyte antigen (HLA) genes are associated with autoimmune central nervous system (CNS) diseases, such as multiple sclerosis (MS), but their exact role in disease susceptibility and etiopathogenesis remains unclear. The best studied HLA-associated autoimmune CNS disease is MS, and thus will be the primary focus of this review. Other HLA-associated autoimmune CNS diseases, such as autoimmune encephalitis and neuromyelitis optica will be discussed. The lack of animal models to accurately capture the complex human autoimmune response remains a major challenge. HLA transgenic (tg) mice provide researchers with powerful tools to investigate the underlying mechanisms promoting susceptibility and progression of HLA-associated autoimmune CNS diseases, as well as for elucidating the myelin epitopes potentially targeted by T cells in autoimmune disease patients. We will discuss the potential role(s) of autoimmune disease-associated HLA alleles in autoimmune CNS diseases and highlight information provided by studies using HLA tg mice to investigate the underlying pathological mechanisms and opportunities to use these models for development of novel therapies.

MHC class II-deficient mice allow functional human CD4+ T-cell development

Humanized mouse models have been developed to study cell-mediated immune responses to human pathogens in vivo. How immunocompetent human T cells are selected in a murine thymus in such humanized mice remains poorly explored. To gain insights into this mechanism, we investigated the differentiation of human immune compartments in mouse MHC class II-deficient immune-compromised mice (humanized Ab0 mice). We observed a strong reduction in human CD4+ T-cell development but despite this reduction Ab0 mice had no disadvantage during Epstein-Barr virus (EBV) infection. Viral loads were equally well controlled in humanized Ab0 mice compared to humanized NSG mice, and improved T-cell recognition of autologous EBV-transformed B cells was observed, especially with respect to cytotoxicity. MHC class II blocking experiments with CD4+ T cells from humanized Ab0 mice demonstrated MHC class II restriction of lymphoblastoid cell line recognition. These findings suggest that a small number of CD4+ T cells in humanized mice can be solely selected on human MHC class II molecules, presumably expressed by reconstituted human immune cells, leading to improved effector functions.

Latest models for the discovery and development of rheumatoid arthritis drugs

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic autoimmune disease that reduces the quality of life. The current speed of development of therapeutic agents against RA is not satisfactory. Models on which initial experiments are conducted do not fully reflect human pathogenesis. Overcoming this oversimplification might be a crucial step to accelerate studies on RA treatment.

AREAS COVERED

The current approaches to produce novel models or to improve currently available models for the development of RA drugs have been discussed. Advantages and drawbacks of two- and three-dimensional cell cultures and animal models have been described based on recently published results of the studies. Moreover, approaches such as tissue engineering or organ-on-a-chip have been reviewed.

EXPERT OPINION

The cell cultures and animal models used to date appear to be of limited value due to the complexity of the processes involved in RA. Current models in RA research should take into account the heterogeneity of patients in terms of disease subtypes, course, and activity. Several advanced models and tools using human cells and tissues have been developed, including three-dimensional tissues, liquid bioreactors, and more complex joint-on-a-chip devices. This may increase knowledge of the molecular mechanisms leading to disease development, to help identify new biomarkers for early detection, and to develop preventive strategies and more effective treatments.

Preclinical models of arthritis for studying immunotherapy and immune tolerance

Increasingly earlier identification of individuals at high risk of rheumatoid arthritis (RA) (eg, with autoantibodies and mild symptoms) improves the feasibility of preventing or curing disease. The use of antigen-specific immunotherapies to reinstate immunological self-tolerance represent a highly attractive strategy due to their potential to induce disease resolution, in contrast to existing approaches that require long-term treatment of underlying symptoms.Preclinical animal models have been used to understand disease mechanisms and to evaluate novel immunotherapeutic approaches. However, models are required to understand critical processes supporting disease development such as the breach of self-tolerance that triggers autoimmunity and the progression from asymptomatic autoimmunity to joint pain and bone loss. These models would also be useful in evaluating the response to treatment in the pre-RA period.This review proposes that focusing on immune processes contributing to initial disease induction rather than end-stage pathological consequences is essential to allow development and evaluation of novel immunotherapies for early intervention. We will describe and critique existing models in arthritis and the broader field of autoimmunity that may fulfil these criteria. We will also identify key gaps in our ability to study these processes in animal models, to highlight where further research should be targeted.

The novel HLA-DPB1*571:01 allele characterized by SMRT DNA sequencing in an African Caribbean individual

A single nucleotide substitution in exon 3 of HLA-DPB1*105:01 results in a new allele, HLA-DPB1*571:01.

Humanized Mouse Models of Rheumatoid Arthritis for Studies on Immunopathogenesis and Preclinical Testing of Cell-Based Therapies

Rodent models of rheumatoid arthritis (RA) have been used over decades to study the immunopathogenesis of the disease and to explore intervention strategies. Nevertheless, mouse models of RA reach their limit when it comes to testing of new therapeutic approaches such as cell-based therapies. Differences between the human and the murine immune system make it difficult to draw reliable conclusions about the success of immunotherapies. To overcome this issue, humanized mouse models have been established that mimic components of the human immune system in mice. Two main strategies have been pursued for humanization: the introduction of human transgenes such as human leukocyte antigen molecules or specific T cell receptors, and the generation of mouse/human chimera by transferring human cells or tissues into immunodeficient mice. Recently, both approaches have been combined to achieve more sophisticated humanized models of autoimmune diseases. This review discusses limitations of conventional mouse models of RA-like disease and provides a closer look into studies in humanized mice exploring their usefulness and necessity as preclinical models for testing of cell-based therapies in autoimmune diseases such as RA.

Immunobiology of Cellular Transplantation

The goal of cellular transplantation is to allow long-term function of the grafted cells using minimal host immunosuppression. To this end, the major strategies to implant cells and tissues are through: (i) the pretreatment of the graft to reduce tissue immunogenicity; (ii) the application of immunoisolation technologies to prevent host sensitization to implanted cells; and (iii) the induction of immunological tolerance to the donor tissues. Further, a major dilemma facing clinical tissue grafting is the shortage of donor tissue for transplantation. This problem requires the consideration of tissues from other species (xenografts) as a potential source of donor material. In light of these issues, the focus of this discussion is on the T cell-dependent response to allogeneic and xenogeneic transplants and the implications of this reactivity on the field of cellular replacement therapy.

HLA-DR*0401 expression in the NOD mice prevents the development of autoimmune diabetes by multiple alterations in the T-cell compartment

Several human HLA alleles have been found associated with type 1 diabetes (T1D), but their precise role is not clearly defined. Herein, we report that a human MHC class II (HLA-DR*0401) allele transgene that has been expressed into NOD (H-2(g7)I-E(null)) mice prone to T1D rendered the mice resistant to the disease. T1D resistance occurred in the context of multi-point T-cell alterations such as: (i) skewed CD4/CD8 T-cell ratio, (ii) decreased size of CD4(+)CD44(high) T memory pool, (iii) aberrant TCR Vβ repertoire, (iv) increased neonatal number of Foxp3(+) and TR-1(+) regulatory cells, and (v) reduced IFN-γ inflammatory response vs. enhanced IL-10 suppressogenic response of T-cells upon polyclonal and antigen-specific stimulation. The T-cells from NOD/DR4 Tg mice were unable to induce or suppress diabetes in NOD/RAG deficient mice. This study describes a multifaceted regulatory function of the HLA-DR*0401 allele strongly associated with the lack of T1D development in NOD mice.

Association of the porcine cluster of differentiation 4 gene with T lymphocyte subpopulations and its expression in immune tissues

Cluster of differentiation 4 (CD4) is mainly expressed on CD4⁺ T cells, which plays an important role in immune response. The aim of this study was to detect the association between polymorphisms of the CD4 gene and T lymphocyte subpopulations in pigs, and to investigate the effects of genetic variation on the CD4 gene expression level in immune tissues. Five missense mutations in the CD4 gene were identified using DNA pooling sequencing assays, and two main haplotypes (CCTCC and AGCTG) in strong linkage disequilibrium (with frequencies of 50.26% and 46.34%, respectively) were detected in the population of Large White pigs. Our results indicated that the five SNPs and the two haplotypes were significantly associated with the proportions of CD4⁻CD8⁻, CD4⁺CD8⁺, CD4⁺CD8⁻, CD4⁺ and CD4⁺/CD8⁺ in peripheral blood (p<0.05). Gene expression analysis showed the mRNA level of the CD4 gene in thymus was significantly higher than that in lymph node and spleen (p<0.05). However, no significant difference was observed between animals with CCTCC/CCTCC genotype and animals with AGCTG/AGCTG genotype in the three immune tissues (p>0.05). These results indicate that the CD4 gene may influence T lymphocyte subpopulations and can be considered as a candidate gene affecting immunity in pigs.

Affinity maturation of human CD4 by yeast surface display and crystal structure of a CD4-HLA-DR1 complex

Helper T-cell activation generally requires the coreceptor CD4, which binds MHC class II molecules. A remarkable feature of the CD4-MHC class II interaction is its exceptionally low affinity, which ranges from K(D) = ∼200 μM to >2 mM. Investigating the biological role of the much lower affinity of this interaction than those of other cell-cell recognition molecules will require CD4 mutants with enhanced binding to MHC class II for testing in models of T-cell development. To this end, we used in vitro-directed evolution to increase the affinity of human CD4 for HLA-DR1. A mutant CD4 library was displayed on the surface of yeast and selected using HLA-DR1 tetramers or monomers, resulting in isolation of a CD4 clone containing 11 mutations. Reversion mutagenesis showed that most of the affinity increase derived from just two substitutions, Gln40Tyr and Thr45Trp. A CD4 variant bearing these mutations bound HLA-DR1 with K(D) = 8.8 μM, compared with >400 μM for wild-type CD4. To understand the basis for improved affinity, we determined the structure of this CD4 variant in complex with HLA-DR1 to 2.4 Å resolution. The structure provides an atomic-level description of the CD4-binding site on MHC class II and reveals how CD4 recognizes highly polymorphic HLA-DR, -DP, and -DQ molecules by targeting invariant residues in their α2 and β2 domains. In addition, the CD4 mutants reported here constitute unique tools for probing the influence of CD4 affinity on T-cell activation and development.

Human intrathymic development: a selective approach

Human T lymphocytes can be generated from CD34 progenitor cells from different sources. This can be obtained in an in vivo model wherein human thymic tissue and fetal liver is transplanted in an immunodeficient mouse. However, human T cells are also generated in immunodeficient mice without co-transplantation of human thymus or in in vitro hybrid human-mouse fetal thymus organ culture. This shows that xenogeneic mouse thymus tissue supports human T cell differentiation. Finally, human T cells are generated on co-culture with murine stromal cells that express the Delta-like1 ligand for the Notch receptor. How these different environments influence the human T cell repertoire is reviewed and discussed.

An MHC class II restriction bias in CD4 T cell responses toward I-A is altered to I-E in DM-deficient mice

The MHC-encoded cofactor DM catalyzes endosomal loading of peptides onto MHC class II molecules. Despite evidence from in vitro experiments that DM acts to selectively edit the repertoire of class II:peptide complexes, the consequence of DM expression in vivo, or a predictive pattern of DM activity in the specificity of CD4 T cell responses has remained unresolved. Therefore, to characterize DM function in vivo we used wild-type (WT) or DM-deficient (DM(-/-)) mice of the H-2(d) MHC haplotype and tested the hypothesis that DM promotes narrowing of the repertoire of class II:peptide complexes displayed by APC, leading to a correspondingly selective CD4 T cell response. Surprisingly, our results indicated that DM(-/-) mice do not exhibit a broadened CD4 T cell response relative to WT mice, but rather shift their immunodominance pattern to new peptides, a pattern associated with a change in class II isotype-restriction. Specifically, we found that CD4 T cell responses in WT mice were primarily restricted to the I-A class II molecule, whereas DM(-/-) mice recognize peptides in the context of I-E. The observed shift in isotype-restriction appeared to be due in part to a modification in the peripheral CD4 T cell repertoire available for peptide recognition.

Collagen-Induced Arthritis Mediated by HLA-DR1 (*0101) and HLA-DR4 (*0401)

Although associations between the expression of particular HLA genes and susceptibility to specific autoimmune diseases has been known for some time, the role HLA molecules play in the autoimmune response is unclear. Through the establishment of chimeric HLA-DR/I-E transgenes, the authors examined the function of the rheumatoid arthritis (RA) susceptibility alleles HLA-DR1 (DRB1*0101) and DR4 (DRB1*0401) in presenting antigenic peptides derived from the model antigen, type II collagen (CII), and in mediating an autoimmune response. As a transgene, these chimeric DR molecules confer susceptibility to an autoimmune arthritis induced by immunization with human CII. Both the DR1 and DR4-restricted T cell responses to CII are focused on an immunodominant determinant CII(263-270). Peptide binding studies revealed that the majority of the CII-peptide binding affinity for DR1 and DR4 is controlled by the Phe at 263 and, unexpectedly, the adjacent Lys. Only these 2 CII amino acids were found to provide binding anchors. Amino acid substitutions at the remaining positions had either no effect or significantly increased the affinity of the hCII peptide. These data indicate that DR1 and DR4 bind this CII peptide in a nearly identical manner and that the primary structure of CII may dictate a different binding motif for DR1 and DR4 than has been described for other peptides. In all, these studies demonstrate that DR1 and DR4 are capable of binding peptides derived from human type II collagen (hCII) and support the hypothesis that autoimmune responses to hCII play a role in the pathogenesis of RA.

The systemic immune response is more prominent than the mucosal immune response in the pathogenesis of periodontal disease

BACKGROUND/AIM

The diseased periodontium appears to express features of a systemic and a mucosal immune response. Our aims were to determine differences in immunoglobulin expression between gingivitis and periodontitis lesions and to ascertain whether immune and inflammatory cells were recruited into the diseased periodontium by the mucosal addressin adhesion molecule (MAdCAM-1).

METHODS

In situ hybridization and immunohistochemistry were used to detect the expression of chemokines, adhesion molecules and immunoglobulins in tissue sections of gingival and granulation tissues excised from periodontitis-affected sites and of healthy tissue and gingivitis-affected tissue excised during crown-lengthening procedures.

RESULTS

Greater numbers of plasma cells were observed in periodontitis gingival/granulation tissue lesions compared with gingivitis lesions. While IgA1 were predominant in all lesions, IgA2 and J-chain expressing plasma cells were present in increased proportions in gingival tissues compared with granulation tissue. Intracellular adhesion molecule-1 (ICAM-1) was higher in periodontitis than in gingivitis and interleukin-8 mRNA was higher in lesions with a pronounced neutrophil infiltrate. Vascular cell adhesion molecule-1 (VCAM-1) localized to the deep connective tissue and indicated the presence of a systemic type of immune response in this region. Periodontal tissues (n=71 biopsies) did not appear to express MAdCAM-1, in positive control sections of small intestine where it was detected.

CONCLUSION

Overall, the systemic-type immune response is predominant, and although the mucosal immune response is minor and limited to the superficial tissues it may have an important role in the host defense to periodontal pathogens.

Specific stimulation of MHC-transgenic mouse T-cell hybridomas with xenogeneic APC

From the recombinant human leukocyte antigen (HLA)-DR1/H2-E(k) major histocompatibility complex (MHC) class II-transgenic mice, we have generated two CD4(+) T-cell hybridomas specific for peptides which were derived from human prostatic acid phosphatase (PAP) complexed to the human class II molecule HLA-DR1. Both hybridomas strongly react to PAP-pulsed antigen-presenting cells (APC) from transgenic mice. Interestingly, these hybridomas also responded to PAP antigen presented by HLA-DR1-positive human APC. The species-mismatched T-cell stimulation occurs despite the biologic discordance in participating accessory molecules, which are required for the optimal T-cell-APC interaction. Our results demonstrate various degrees of functional interaction between coreceptors, costimulatory molecules, and integrins, which are expressed on the surface of T-cell hybridomas and heterologous APC.

A therapeutic CD4 monoclonal antibody inhibits TCR-zeta chain phosphorylation, zeta-associated protein of 70-kDa Tyr319 phosphorylation, and TCR internalization in primary human T cells

The molecular mechanisms mediating the inhibitory effects of a humanized CD4 mAb YHB.46 on primary human CD4(+) T cells were investigated. Preincubation of T cells with soluble YHB.46 caused a general inhibition of TCR-stimulated protein tyrosine phosphorylation events, including a reduction in phosphorylation of p95(vav), linker for activation of T cells, and Src homology 2 domain-containing leukocyte protein of 76-kDa signaling molecules. A marked reduction in activation of the Ras/mitogen-activated protein kinase pathway was also observed. Examination of the earliest initiation events of TCR signal transduction showed that YHB.46 inhibited TCR-zeta chain phosphorylation together with recruitment and tyrosine phosphorylation of the zeta-associated protein of 70-kDa tyrosine kinase, particularly at Tyr(319), as well as reduced recruitment of p56(lck) to the TCR-zeta and zeta-associated protein of 70-kDa complex. These inhibitory events were associated with inhibition of TCR endocytosis. Our results show that the YHB.46 mAb is a powerful inhibitor of the early initiating events of TCR signal transduction.

Functional human T lymphocyte development from cord blood CD34+ cells in nonobese diabetic/Shi-scid, IL-2 receptor gamma null mice

An experimental model for human T lymphocyte development from hemopoietic stem cells is necessary to study the complex processes of T cell differentiation in vivo. In this study, we report a newly developed nonobese diabetic (NOD)/Shi-scid, IL-2Rgamma null (NOD/SCID/gamma(c)(null)) mouse model for human T lymphopoiesis. When these mice were transplanted with human cord blood CD34(+) cells, the mice reproductively developed human T cells in their thymus and migrated into peripheral lymphoid organs. Furthermore, these T cells bear polyclonal TCR-alphabeta, and respond not only to mitogenic stimuli, such as PHA and IL-2, but to allogenic human cells. These results indicate that functional human T lymphocytes can be reconstituted from CD34(+) cells in NOD/SCID/gamma(c)(null) mice. This newly developed mouse model is expected to become a useful tool for the analysis of human T lymphopoiesis and immune response, and an animal model for studying T lymphotropic viral infections, such as HIV.

Crystal structure of the human CD4 N-terminal two-domain fragment complexed to a class II MHC molecule

The structural basis of the interaction between the CD4 coreceptor and a class II major histocompatibility complex (MHC) is described. The crystal structure of a complex containing the human CD4 N-terminal two-domain fragment and the murine I-A(k) class II MHC molecule with associated peptide (pMHCII) shows that only the "top corner" of the CD4 molecule directly contacts pMHCII. The CD4 Phe-43 side chain extends into a hydrophobic concavity formed by MHC residues from both alpha 2 and beta 2 domains. A ternary model of the CD4-pMHCII-T-cell receptor (TCR) reveals that the complex appears V-shaped with the membrane-proximal pMHCII at the apex. This configuration excludes a direct TCR-CD4 interaction and suggests how TCR and CD4 signaling is coordinated around the antigenic pMHCII complex. Human CD4 binds to HIV gp120 in a manner strikingly similar to the way in which CD4 interacts with pMHCII. Additional contacts between gp120 and CD4 give the CD4-gp120 complex a greater affinity. Thus, ligation of the viral envelope glycoprotein to CD4 occludes the pMHCII-binding site on CD4, contributing to immunodeficiency.

A multiple transgenic mouse model with a partially humanized activation pathway for helper T cell responses

Mice expressing human CD4 and human MHC II molecules provide a valuable model both for the investigation of the immunopathogenetic role of human autoantigens and for the development of therapeutic strategies based on modulating helper T cell activation in vivo. Here we present a novel mouse model expressing HLA-DR17 (a split antigen of HLA-DR3) together with human CD4 in the absence of murine cd4 (CD4/DR3 mice). Human CD4 accurately replaces murine cd4 within T cells. In particular, the preservation of cd8(+) and CD4(+) T cell subsets distinguishes CD4/DR3 mice from other multiple transgenic models in which the alternative T cell subsets are fundamentally disturbed. Moreover, human CD4 is also faithfully expressed on antigen presenting cells such as dendritic cells and monocyte/macrophages, so that the overall transgenic CD4 expression pattern resembles very closely that of humans. HLA-DR3 expression in the thymus correlates very closely to that of mouse MHC II. In contrast, only 70% of mouse MHC II positive cells in spleen, lymph node, and peripheral blood coexpress HLA-DR3. No significant bias was found with regard to particular leucocytes in this respect. The stimulation of helper T cells clearly depends on the interaction between the human transgene products, since mAbs to HLA-DR and/or CD4 completely blocked in vitro recall responses to tetanus toxoid. CD4/DR3 mice represent a partially humanized animal model which will facilitate studies of DR3-associated autoimmune responses and the in vivo determination of the therapeutic potential of mAbs to human CD4.

Induction of CTL response by a minimal epitope vaccine in HLA A*0201/DR1 transgenic mice: dependence on HLA class II restricted T(H) response

CTL play a pivotal role in the immune response during viral infections. In this study, the HLA class II restricted T(H) requirement for optimal in vivo induction of HLA class I restricted CTL responses has been investigated. Towards this goal, transgenic mice expressing both HLA class I (A*0201 or A2.1) and class II (DRB1*0101 or DR1) molecules have been derived. Immunization of these mice with an HLA A*0201-restricted and CMV-specific CTL epitope (pp65(495-503)), and either of three different tetanus toxin-derived MHC class II-binding T(H) epitopes, resulted in a vigorous CTL response. CTL specific for the pp65(495-503) epitope were dramatically enhanced in mice expressing both the HLA-DR1 and HLA-A*0201 transgenes. Notably, preinjection of three TT peptides (TT(639-652), TT(830-843), and TT(947-967)) increased the capability of HLA A*0201/DR1 Tg mice to respond to subsequent immunization with the T(H) + CTL peptide mixture. These results indicate that the use of HLA A*0201/DR1 Tg mice constitute a versatile model system (in lieu of immunizing humans) for the study of both HLA class I and class II restricted T-cell responses. These studies provide a rational model for the design and assessment of new minimal-epitope vaccines based on their in vivo induction of a pathogen-specific CTL response.

HLA class II transgenic mice: models of the human CD4+ T-cell immune response

This review examines the field of current HLA class II transgenic mouse models and the individual approaches applied in production of these mice. The majority of these mice have been created with the objective of obtaining a disease model with clinical features mimicking human autoimmune disease. The development process of a different type of HLA class II transgenic mice, which are designed to function as a substitute for a normal human immune system in studies of human autoantigens, is described. Several HLA-DR4 transgenic lines with normally expressed HLA-DR4 molecules have been produced. To obtain adequate positive selection of the HLA-DR4-restricted CD4+ T-cell repertoire in these mice it is essential both to introduce a human CD4 transgene, and to delete the murine major histocompatibility complex (MHC) class II molecules. These HLA-DR4 transgenic mice have been used to determine the immunogenic CD4+ T-cell epitopes of several human autoantigenic proteins.

Differential Requirements for CD4 in TCR-Ligand Interactions

The coreceptor molecule, CD4, plays an integral part in T cell activation; it is involved in both extracellular Ag recognition and intracellular signaling. We wanted to examine the functional role of CD4 in the recognition of agonist and altered peptide ligands (APLs). We generated two CD4-deficient T cell lines expressing well-characterized TCRs specific for Hb(64–76)/I-Ek. Although the responsiveness of the T cell lines to the agonist peptide was differently affected by the loss of CD4 expression, the recognition of APLs was in both cases dramatically reduced. Nearly full responsiveness to the agonist peptide was achieved by expression of a CD4 variant that did not associate with p56lck; however, the stimulation by APLs was only partially restored. Importantly, the expression of a CD4 variant in which domains interacting with MHC class II molecules have been mutated failed to restore the reactivity to all ligands. CD4-deficient T cells were able to be antagonized by APLs, indicating that CD4 was not required for antagonism. Overall, these findings support the concepts that CD4 is an integral part of the initial formation of the immunological synapse, and that the requirement for different CD4 functions in T cell activation varies depending upon the potency of the ligand.

Allele-specific and peptide-dependent recognition of swine leukocyte antigen class I by human cytotoxic T-cell clones

BACKGROUND

The T-cell mediated immune responses play a major role in xenograft rejection. However, the mechanisms behind human T-cell recognition of porcine xenoantigens remain to be elucidated.

METHODS

Human CD8+ T-cell lines were generated against porcine aortic endothelial cells (PAECs) from y/y and z/z haplotypes of Yucatan inbred swine. T-cell clones were obtained by limiting dilution. The human T-cell receptor (TCR)-swine leukocyte antigen (SLA) class I interaction was characterized.

RESULTS

The human CD8+ T-cell mediated direct recognition of PAECs was SLA haplotype-specific. The haplotype specificity was restricted by the SLA class I allelic polymorphism. To characterize the role of SLA-bound peptides in the human TCR-SLA class I interaction, we stripped peptides from SLA molecules by a brief acid treatment. Using z/z-specific CD8+ T cells as effectors, we demonstrated that the acid-treatment, which stripped SLA molecules of bound peptides, decreased the lysis of PAECs by 72%. Addition of peptides eluted from affinity purified z/z SLA class I molecules, but not from the irrelevant y/y SLA class I, restored the lysis of acid-treated z/z PAECs. In addition, the lysis of a human HLA class I negative cell line, 721.221, transfected with a relevant SLA class I allele derived from the z/z haplotype, was significantly increased with the addition of relevant z/z peptides. These experiments indicated that both SLA class I and bound peptides were required for recognition by human CD8+ T cells. Cloning studies identified two groups of xenoreactive T-cell clones. Group I clones recognized distinct porcine peptides in the context of SLA class I molecules, whereas group II clones recognized human endogenous cross-reactive peptides presented by SLA class I.

CONCLUSIONS

Our results demonstrated that, despite the differences in MHC molecules between species, human T-cell recognition of porcine MHC is similar to direct allo-recognition, that is, human TCR recognizes xenogeneic SLA-peptide complexes.

A novel HLA-DR12 allele (DRB1*1206) found in a Korean B-cell line

At least 6 HLA-DRB1*12 alleles have been identified to date with nucleotide polymorphism occurring at codons 37, 57-58, 60, 67, 85 and 87. In this report, we describe the identification of another new HLA-DRB1*12 allele: DRB1*1206. This novel allele was found in an Epstein-Barr virus (EBV)-transformed Korean B-cell line "K-KT" having the HLA-phenotype A3, 24; B44, 61; Cw3; Bw4, 6; DR12, 13 during full-length cDNA isolation for cell line characterization and for production of HLA-DR recombinant proteins. The allele was identified initially by cycle sequencing of subcloned HLA-DRB full-length cDNA.

HLA-DR4 (DRB1*0401) Transgenic Mice Expressing an Altered CD4-Binding Site: Specificity and Magnitude of DR4-Restricted T Cell Response

Optimum function of HLA-DR molecules in transgenic mice requires efficient interaction between the class II molecules on APCs and CD4 on T cells. Residues 110 and 139 of the second domain of class II molecules are considered to be critical for recognition of CD4. We generated an HLA-DR4β(NT) transgene construct in which positions 110 and 139 were altered to resemble endogenous mouse H2 Aβ molecules. This construct was introduced into (B10 × SWR) embryos, and DR4β(NT) transgenic mice were produced. The transgene was transferred into B10.RFB3 (Eβ0 Eαp) mice. The transgene-encoded DR4β molecules paired with endogenous Eα chains to form stable DR4β/Eα dimers expressed on the cell surface. The hybrid dimers showed similar Ag-binding specificity to HLA-DR4 molecules and positively selected CD4+ T cells in vivo. Immunization of HLA-DR4β(NT) transgenic mice with DR4-restricted peptides induced T cell proliferation in vitro. While the purified T cells from DR4β(NT) transgenic mice responded strongly to the HA(307–319) presented by M12C3 transfectants expressing altered DR4β/Eα heterodimers, the response to the same peptides presented by transfectants expressing wild-type DR4β/Eα molecules was substantially reduced. Taken together, these data confirmed in vitro studies on the importance of these residues in CD4-MHC class II interaction. The altered HLA-DR4β transgenic mice were able to overcome the species barrier and generate efficient HLA-DR4-restricted CD4-specific immune responses. Thus, residues 110 and 139 were critical for the interaction of class II with CD4 T cells during thymic selection as well as peripheral immune responses.

HLA-DQ6 and HLA-DQ8 Transgenic Mice Respond to Ragweed Allergens and Recognize a Distinct Set of Epitopes on Short and Giant Ragweed Group 5 Antigens

We have investigated the genetic and molecular basis of immune responsiveness to short ragweed (SRW) (Ambrosia artemisiifolia) extract, and group 5 allergens from short and giant (Ambrosia trifida) ragweed using transgenic mice expressing DQ6 (HLA-DQA1*0103, HLA-DQB1*0601) and DQ8 (HLA-DQA1*0301, HLA-DQB1*0302) genes in class II knockout (Aβ0) mice. Panels of overlapping peptides spanning the Amb a 5 and Amb t 5 Ags were synthesized. Mice were immunized with whole SRW extract or individual peptides s.c. and lymph node cells (LNC) were challenged in vitro. Strong T cell responses to SRW extract were measured in both HLA-DQ transgenic mice, while control, HLA-DQ6−/DQ8−/H-2Aβ0, mice were unresponsive. IL-5 and IL-10 were the primary cytokines produced by in vitro challenged LNC of SRW-primed transgenic mice. HLA-DQ6-restricted T cell responses were detected to all three peptides of Amb t 5 and two determinants (residues 1–20 and 11–30) on Amb a 5. In contrast, LNC of HLA-DQ8 mice did not recognize peptide 11–30 of Amb t 5 Ag, but recognized several Amb a 5 determinants. The immune response in transgenic mice was dependent upon CD4+ T cells and was HLA-DQ restricted. Primed with purified Amb t 5, both transgenics recognized peptide 21–40, and an additional DQ6-restricted epitope was found within residue 1–20. SRW-immunized HLA-DQ6 mice respond to peptide 11–30 of Amb a 5, while HLA-DQ8 mice strongly recognize peptide 1–20. These results demonstrate the specificity of HLA class II polymorphism in allergen sensitivity and pave the way for developing antagonistic peptides for desensitization.

Induction of Autoimmune Arthritis in HLA-DR4 (DRB1*0401) Transgenic Mice by Immunization with Human and Bovine Type II Collagen

Although associations between the expression of particular HLA genes and the susceptibility to specific autoimmune diseases has been known for some time, the role that these HLA molecules play in the autoimmune response is unclear. Through the establishment of a chimeric HLA-DR/I-E transgene, we have examined the function of the rheumatoid arthritis (RA) susceptibility allele HLA-DR4 (DRB1*0401) in presenting antigenic peptides derived from the model Ag, type II collagen (CII), and in mediating an autoimmune response. As a transgene, the chimeric DR4 molecule conferred susceptibility to an autoimmune arthritis induced by immunization with human CII or bovine CII. These mice developed an inflammatory, autoimmune arthritis that was similar both histologically and in severity to that previously described for the collagen-induced arthritis model. The DR4-mediated autoimmune arthritis was accompanied by T cell and B cell responses to both the immunogen and the autoantigen, murine CII. The DR4-restricted T cell response to human CII was focused on an immunodominant determinant within CII263–270 and a minor determinant within CII286–300, the same CII determinants recently identified for yet another RA susceptibility allele, HLA-DR1 (DRB1*0101). Thus these data demonstrate that, like HLA-DR1, HLA-DR4 is capable of binding peptides derived from human CII and therefore probably plays a role in the autoimmune response to human CII observed in RA patients.

T cell receptor recognition of MHC class II-bound peptide flanking residues enhances immunogenicity and results in altered TCR V region usage

Naturally processed MHC class II-bound peptides possess ragged NH2 and COOH termini. It is not known whether these peptide flanking residues (PFRs), which lie outside the MHC anchor residues, are recognized by the TCR or influence immunogenicity. Here we analyzed T cell responses to the COOH-terminal PFR of the H-2A(k) immunodominant epitope of hen egg lysozyme (HEL) 52-61. Surprisingly, the majority of T cells were completely dependent on, and specific for, the COOH-terminal PFR of the immunogen. In addition, there were striking correlations between TCR V beta usage and PFR dependence. We hypothesize that the V alpha CDR1 region recognizes NH2-terminal PFRs, while the V beta CDR1 region recognizes COOH-terminal PFRs. Last, peptides containing PFRs were considerably more immunogenic and mediated a greater recall response to the HEL protein. These results demonstrate that PFRs, which are a unique characteristic of peptides bound to MHC class II molecules, can have a profound effect on TCR recognition and T cell function. These data may have important implications for peptide-based immunotherapy and vaccine development.

Quantitative but not qualitative variation in MHC class II alters CD4 interaction and influences T cell repertoire formation

The influence of the interaction between CD4 and MHC class II molecules on selection of the T cell repertoire was studied in transgenic mice expressing human or human/mouse hybrid MHC class II beta chains. Either wild-type DR beta chains (DR1 beta) or hybrid beta chains comprising the beta1 domain of DR and the beta2, transmembrane, and intracytoplasmic domains of I-E (DRbeta 1Ebeta2) were introduced into and expressed in transgenic mice as a heterodimer with endogenous I-E alpha. Mice expressing low levels of DR1beta:I-E alpha or those expressing low or higher levels of the hybrid DRbeta 1Ebeta2:I-E alpha were studied. Immunization with a suboptimal dose of influenza nucleoprotein peptide exposed a fivefold lower frequency of DR-restricted, peptide-specific, IL-2-secreting T cells in the mice with low-level expression of DRbeta1 Ebeta2:I-E alpha when compared to mice expressing the same molecule at higher levels. The frequency in DRbeta wild-type mice was only twofold lower than that measured in mice with comparable levels of expression of DRbeta 1Ebeta2. These results suggest that positive selection is sensitive to quantitative variation in MHC class II density, unmasked when antigen is limiting, but is relatively insensitive to qualitative variation in the MHC class II: CD4 interaction.

An HLA-DR1 transgene confers susceptibility to collagen-induced arthritis elicited with human type II collagen

Rheumatoid arthritis (RA) is an autoimmune disease that is strongly associated with the expression of several HLA-DR haplotypes, including DR1 (DRB1*0101). Although the antigen that initiates RA remains elusive, it has been shown that many patients have autoimmunity directed to type II collagen (CII). To test the hypothesis that HLA-DR1 is capable of mediating an immune response to CII, we have generated transgenic mice expressing chimeric (human/mouse) HLA-DR1. When the DR1 transgenic mice were immunized with human CII (hCII), they developed a severe autoimmune arthritis, evidenced by severe swelling and erythema of the limbs and marked inflammation and erosion of articular joints. The development of the autoimmune arthritis was accompanied by strong DR1-restricted T and B cell responses to hCII. The T cell response was focused on a dominant determinant contained within CII(259-273) from which an eight amino acid core was defined. The B cell response was characterized by high titers of antibody specific for hCII, and a high degree of cross-reactivity with murine type II collagen. These data demonstrate that HLA-DR1 is capable of presenting peptides derived from hCII, and suggest that this DR1 transgenic model will be useful in the development of DR1-specific therapies for RA.

Selective T cell receptor Vbeta gene usage by alloreactive T cells responding to defined HLA-DR alleles

Previous studies have provided strong evidence for restricted Vbeta gene usage in response to DR synthetic peptides presented in context by self MHC molecules, i.e., via the indirect pathway of allorecognition. Although numerous studies have suggested a role for the T cell receptor (TCR) beta chain in the direct pathway of allorecognition, it is not clear whether a particular HLA allele elicits a consistent pattern of restricted Vbeta gene usage by resting T cells from different individuals. To address this problem, HLA class II homozygous cell lines that do not express class I antigens were used to study the role of the TCR Vbeta elements in direct recognition of specific DR alleles. Analysis of TCR V gene usage revealed that each DR allele tested elicited the same pattern of preferential Vbeta gene usage in all individuals studied. For example, the DRB1*0101 allele was preferentially recognized by T cells expressing Vbeta2, Vbeta13.1, Vbeta18, and Vbeta20, and the DRB1*1301 caused expansion of Vbeta4-, Vbeta6-, Vbeta8-, and Vbeta18-bearing T cells. Similarly, analysis of TCR V gene usage in response to defined DR alleles expressed on homozygous cell lines that express class I was also made possible by using anti-class I antibodies to block class I recognition and focus the response on the DR molecule. The results showed that the DRB1*1501 allele expressed on two distinct homozygous lines elicited the preferential expansion of Vbeta2, Vbeta8, and Vbeta13.2 T cells. Similarly, the DRB1*0301 allele expressed on normal, Epstein-Barr virus-transformed, or transfected fibroblasts was found to elicit the same pattern of Vbeta expansion and to selectively stimulate T cells bearing Vbeta2, Vbeta16, and Vbeta17 elements. In contrast to this highly reproducible pattern of Vbeta gene usage elicited by specific DR alleles, extensive heterogeneity in the CDR3 region was found and no preferential Jbeta or Valpha gene usage was observed in response to any of the DR alleles tested. The data suggest that, similar to the situation with the indirect pathway, TCR Vbeta elements are involved in the direct pathway of allorecognition. Although some overlap may exist, different sets of Vbeta elements may be preferentially used for each of these pathways. Inasmuch as HLA-identical siblings, but not HLA-identical unrelated individuals, express a very similar TCR repertoire, our data suggest that additional factors are involved in shaping the repertoire. Preferential activation of T-cell subsets by specific DR alleles may play an important role in primary alloresponses, e.g., in mixed lymphocyte reactions, and organ transplantation. Elucidation of the Vbeta specificity of each DR allele may have an impact on therapeutic strategies aimed at blocking specific alloresponse and prolonging graft survival in transplant recipients while avoiding the hazardous sequelae of nonspecific immunosuppression.

The two membrane proximal domains of CD4 interact with the T cell receptor

During T cell activation, CD4 is intimately involved in colocalizing the T cell receptor (TCR) with its specific peptide ligand bound to class II molecules of the major histocompatibility complex (MHC). Previously, the COOH-terminal residues, Trp62/63, which flank the immunodominant epitope of hen egg lysozyme (HEL 52-61), were shown to have a profound effect on TCR recognition. CD4 maintains the fidelity of this interaction when short peptides are used. To determine which portion of CD4 was responsible for this effect, a series of CD4 mutants were made and transfected into CD4 loss variants of two HEL 52-61-specific T cell hybridomas. Surprisingly, some CD4 mutants that failed to interact with MHC class II molecules (D2 domain mutant) or with p56kk (cytoplasmic-tailless mutant) restored responsiveness. Nevertheless, a significant reduction in association between cytoplasmic-tailless CD4 and the TCR, as determined by fluorescence resonance energy transfer, was observed. Thus, neither colocalization of CD4 and the TCR nor signal transduction via CD4 was solely responsible for the functional restoration of these T cell hybridomas by wild-type CD4. However, substitution of the two membrane proximal domains of murine CD4 (D3 and D4) with domains from human CD4 or intercellular adhesion molecule 1 not only abrogated its ability to restore function, but also substantially reduced its ability to associate with the TCR. Furthermore, the mouse/human CD4 chimera had a potent dominant negative effect on T cell function in the presence of equimolar concentrations of wild-type CD4. These data suggest that the D3/D4 domains of CD4 may interact directly or indirectly with the TCR-CD3 complex and influence the signal transduction processes. Given the striking structural differences between CD4 and CD8 in this region, these data define a novel and unique function for CD4.

The myelin basic protein-specific T cell repertoire in (transgenic) Lewis rat/SCID mouse chimeras: preferential V beta 8.2 T cell receptor usage depends on an intact Lewis thymic microenvironment

In the Lewis rat, myelin basic protein (MBP)-specific, encephalitogenic T cells preferentially recognize sequence 68-88, and use the V beta 8.2 gene to encode their T cell receptors. To analyze the structural prerequisites for the development of the MBP-specific T cell repertoire, we reconstituted severe-combined immunodeficient (SCID) mice with fetal (embryonic day 15-16) Lewis rat lymphoid tissue, and then isolated MBP-specific T cell lines from the adult chimeras after immunization. Two types of chimera were constructed: SCID mice reconstituted with rat fetal liver cells only, allowing T cell maturation within a chimeric SCID thymus consisting of mouse thymic epithelium and rat interdigitating dendritic cells, and SCID mice reconstituted with rat fetal liver cells and rat fetal thymus grafts, allowing T cell maturation within the chimeric SCID and the intact Lewis rat thymic microenvironment. Without exception, the T cell lines isolated from MBP-immunized SCID chimeras were restricted by MHC class II of the Lewis rat (RT1.B1), and none by I-Ad of the SCID mouse. Most of the T cell lines recognized the immunodominant MBP epitope 68-88. In striking contrast to intact Lewis rats, in SCID mice reconstituted by rat fetal liver only, MBP-specific T cell clones used a seemingly random repertoire of V beta genes without a bias for V beta 8.2. In chimeras containing fetal Lewis liver plus fetal thymus grafted under the kidney capsule, however, dominant utilization of V beta 8.2 was restored. The migration of liver-derived stem cells through rat thymus grafts was documented by combining fetal tissues from wild-type and transgenic Lewis rats. The results confirm that the recognition of the immunodominant epitope 68-88 by MBP-specific encephalitogenic T cells is a genetically determined feature of the Lewis rat T cell repertoire. They further suggest that the formation of the repertoire requires T cell differentiation in a syngeneic thymic microenvironment.

Indefinite survival of neural xenografts induced with anti-CD4 monoclonal antibodies

Xenografts of neural tissue are usually rapidly rejected when transplanted into the central nervous system of adult recipient animals. This study has examined the cell mediated immune response to both concordant (between closely related species) and discordant (between distantly related species) neural xenografts in the mouse, and has investigated the role of the CD4+ and CD8+ T lymphocyte subsets in this process using monoclonal antibodies specific for the CD4 and CD8 cell surface glycoproteins. We have established that: (1) in this model system concordant neural xenograft rejection occurs within 15-30 days; however, xenograft survival can be dramatically prolonged with CD4+, but not CD8+, T lymphocyte depletion; (2) the administration of two successive courses of a high dose of anti-CD4 monoclonal antibody treatment results in indefinite concordant neural xenograft survival; (3) the mechanism by which the high dose anti-CD4 monoclonal antibody therapy appears to function involves the depletion of intrathymic CD4+ cells; (4) anti-CD4 monoclonal antibody treatment enhances discordant neural xenograft survival, to beyond 60 days in many cases. These results demonstrate that CD4+ T lymphocytes are of central importance in the immune response to both concordant and discordant neural xenoantigens. Thus the use of anti-CD4 monoclonal antibody therapy is an effective strategy to prolong significantly the survival of xenogeneic neural transplants. Furthermore this treatment caused no obvious deleterious side-effects. These findings have implications for future cross-species studies in experimental neurobiology and, possibly, in clinical neural transplantation.

HLA-DQ8 transgenic mice are highly susceptible to collagen-induced arthritis: a novel model for human polyarthritis

Genetic studies have indicated that susceptibility to rheumatoid arthritis (RA) maps to the HLA-DR locus of the major histocompatibility complex. Strong linkage disequilibrium between certain HLA-DQ genes and HLA-DR genes associated with RA, however, suggests that HLA-DQ molecules may also play a role in RA susceptibility. To examine the role of HLA-DQ molecules in arthritis, we generated transgenic mice expressing the DQA1*0301 and DQB1*0302 genes from an RA predisposing haplotype (DQ8/DR4Dw4). The transgenes were introduced into mouse class II-deficient H-2Ab0 mice, and their susceptibility to experimental collagen-induced arthritis was evaluated. The HLA-DQ8+,H-2Ab0 mice displayed good expression of the DQ8 molecule, while no surface expression of endogenous murine class II molecules could be detected. The DQ8 molecule also induced the selection of CD4+ T cells expressing a normal repertoire of V beta T cell receptors. Immunization of HLA-DQ8+,H-2Ab0 mice with bovine type II collagen (CII) induced a strong antibody response that was cross-reactive to homologous mouse CII. Also, in vitro proliferative responses against bovine CII, which were blocked in the presence of an antibody specific for HLA-DQ and mouse CD4, were detected. Finally, a severe polyarthritis developed in a majority of HLA-DQ8+,H-2Ab0 mice, which was indistinguishable from the disease observed in arthritis susceptible B10.T(6R) (H-2Aq) controls. In contrast, HLA-DQ8-,H-2Ab0 fullsibs did not generate CII antibody and were completely resistant to arthritis. Therefore, these results strongly suggest that HLA-DQ8 molecules contribute to genetic susceptibility to arthritis and also establish a novel animal model for the study of human arthritis.

The T cell response of HLA-DR transgenic mice to human myelin basic protein and other antigens in the presence and absence of human CD4

Analysis of HLA class II transgenic mice has progressed in recent years from analysis of single chain HLA class II transgenes with expression of mixed mouse/human heterodimers to double transgenic mice expressing normal human heterodimers. Previous studies have used either HLA transgenic mice in which there is a species-matched interaction with CD4 or mice which lack this interaction. Since both systems are reported to generate HLA-restricted responses, the matter of the requirement for species-matched CD4 remains unclear. We have generated triple transgenic mice expressing three human transgenes, DRA, DRB, and CD4, and compared HLA-restricted responses to peptide between human-CD4+ (Hu-CD4+) and Hu-CD4- littermates. We saw no difference between Hu-CD4+ and Hu-CD4- groups, supporting the notion that for some responses at least the requirement for species-matched CD4 may not be absolute. Evidence for positive selection of mouse T cell receptors in HLA-DR transgenic mice came both from the acquisition of new, HLA-restricted responses to various peptides and from an increased frequency of T cells using the TCR V beta 4 gene segment. An important goal with respect to the analysis of function in HLA transgenic mice is the clarification of mechanisms which underpin the recognition of self-antigens in human autoimmune disease. As a first step towards 'humanized' disease models in HLA transgenic mice, we analyzed the responses of HLA-DR transgenic mice to the human MPB 139-154 peptide which has been implicated as an epitope recognized by T cells of multiple sclerosis patients. We obtained T cell responses to this epitope in transgenic mice but not in nontransgenic controls. This study suggests that HLA transgenic mice will be valuable in the analysis of HLA-restricted T cell epitopes implicated in human disease and possibly in the design of new disease models.

Human CD4-major histocompatibility complex class II (DQw6) transgenic mice in an endogenous CD4/CD8-deficient background: reconstitution of phenotype and human-restricted function

To reconstitute the human immune system in mice, transgenic mice expressing human CD4 and human major histocompatibility complex (MHC) class II (DQw6) molecules in an endogenous CD4- and CD8-deficient background (mCD4/8-/-), after homologous recombination, have been generated. We report that expression of human CD4 molecule in mCD4/8-/- mice rescues thymocyte development and completely restores the T cell compartment in peripheral lymphoid organs. Upon vesicular stomatitis virus (VSV) challenge, the reconstituted mature T cell population effectively provide T help to B cells in immunoglobulin class switching from IgM to specific IgG-neutralizing antibodies. Human CD4+DQw6+ double transgenic mice are tolerant to DQw6 and the DQw6 molecule functions in antigen presentation, effectively generating a human MHC class II-restricted T cell response to streptococcal M6C2 peptide. These data show that both the hCD4 and DQw6 molecules are functional in mCD4/8-/- mice, fully and stably reconstituting this limb of the human immune system in mice. This animal model provides a powerful in vivo tool to dissect the human CD4-human class II MHC interaction, especially its role in human autoimmune diseases, superantigen-mediated diseases, and acquired immunodeficiency syndrome (AIDS).

Functional interaction between human histocompatibility leukocyte antigen (HLA) class II and mouse CD4 molecule in antigen recognition by T cells in HLA-DR and DQ transgenic mice

Studies in vitro have suggested that a species barrier exists in functional interaction between human histocompatibility leukocyte antigen (HLA) class II and mouse CD4 molecules. However, whether mouse CD4+ T cells restricted by HLA class II molecules are generated in HLA class II transgenic mice and respond to peptide antigens across this barrier has remained unclear. In an analysis of T cell responses to synthetic peptides in mice transgenic for HLA-DR51 and -DQ6, we found that DR51 and DQ6 transgenic mice acquired significant T cell response to influenza hemagglutinin-derived peptide 307-319 (HA 307) and Streptococcus pyogenes M12 protein-derived peptide 347-397 (M6C2), respectively. Inhibition studies with several monoclonal antibodies showed that transgenic HLA class II molecules presented these peptides to mouse CD4+ T cells. Furthermore, T cell lines specific for HA 307 or M6C2 obtained from the transgenic mice could respond to the peptide in the context of relevant HLA class II molecules expressed on mouse L cell transfectants that lack the expression of mouse MHC class II. These findings indicate that interaction between HLA class II and mouse CD4 molecules is sufficient for provoking peptide-specific HLA class II-restricted T cell responses in HLA class II transgenic mice.

Human major histocompatibility complex class II-restricted T cell responses in transgenic mice

Transgenic mice expressing human major histocompatibility complex (MHC) class II molecules would provide a valuable model system for studying human immunology. However, attempts to obtain human class II-restricted T cell responses in such transgenic mice have had only limited success, possibly due to an inability of mouse CD4 to interact efficiently with human MHC class II molecules. To circumvent this problem, we constructed recombinant MHC class II genes in which the peptide-binding domain was derived from human DR sequences whereas the CD4-binding domain was derived from mouse I-E sequences. Purified chimeric human/mouse MHC class II molecules were capable of specifically binding DR-restricted peptides. Human B cell transformants that expressed these chimeric MHC class II molecules could present peptide antigens to human T cell clones. Expression of these chimeric class II molecules in transgenic mice led to the intrathymic deletion of T cells expressing superantigen-reactive V beta gene segments, indicating that the chimeric class II molecules could influence the selection of the mouse T cell repertoire. These transgenic mice were fully capable of mounting human DR-restricted immune responses after challenge with peptide or whole protein antigens. Thus, the chimeric class II molecules can serve as functional antigen presentation molecules in vivo. In addition, transgenic mice expressing chimeric class II molecules could be used to generate antigen-specific mouse T cell hybridomas that were capable of interacting with human antigen-presenting cells.