Direct enumeration of Borrelia-reactive CD4 T cells ex vivo by using MHC class II tetramers

Differential Optical Imaging of Antigen Presentation Machinery Using Molecular Optical Reporters

Detection of antigen presentation is central to understanding immunological processes and developing therapeutics for cancer, infectious diseases, and allergies. However, methods with the ability to dynamically and noninvasively distinguish between major histocompatibility complex class I (MHC-I) and MHC-II antigen presentations remain lacking. Herein, we develop activatable molecular optical reporters (MORs) for real-time differential imaging of antigen presentations in lymph nodes (LNs). These MORs are engineered to passively target LNs and activated through proteolytic cleavage by key enzymes in the MHC-I and MHC-II pathways, the immunoproteasome (iP) and cathepsin S (CTSS), respectively, triggering their chemiluminescent or fluorescent signals. Coupled with minimized signal crosstalk and high sensitivity, MORs delineate the subtle differences in the antigen presentation machinery across various disease models, including cancer and bacterial or viral infection, a feat unattainable for existing imaging methods. After systemic administration, MORs also allow real-time visualization of antigen presentation in the tumor microenvironment. Besides, MORs are validated to have potential for preclinical application in immunotherapeutics screening and clinical application in tissue biopsy. Thus, our study not only presents the first example of real-time, in vivo differential imaging of antigen presentation pathways but also opens new avenues for optical probes in immune contexture analysis.

Antigen-Specific CD4 T Cell and B Cell Responses to Borrelia burgdorferi

Long-lived T-dependent B cell responses fail to develop during persistent infection of mice with Borrelia burgdorferi, the causative agent of Lyme disease, raising questions about the induction and/or functionality of anti-B. burgdorferi adaptive immune responses. Yet, a lack of reagents has limited investigations into B. burgdorferi-specific T and B cells. We attempted two approaches to track B. burgdorferi-induced CD4 T cells. First, a B. burgdorferi mutant was generated with an influenza hemagglutinin (HA) peptide, HA111-119, inserted into the B. burgdorferi arthritis-related protein (Arp) locus. Although this B. burgdorferi arp::HA strain remained infectious, peptide-specific TCR transgenic CD4 T cells in vitro, or adoptively transferred into B. burgdorferi arp::HA-infected BALB/c mice, did not clonally expand above those of recipients infected with the parental B. burgdorferi strain or a B. burgdorferi mutant containing an irrelevant peptide. Some expansion, however, occurred in B. burgdorferi arp::HA-infected BALB/c SCID mice. Second, a (to our knowledge) newly identified I-Ab-restricted CD4 T cell epitope, Arp152-166, was used to generate Arp MHC class II tetramers. Flow cytometry showed small numbers of Arp-specific CD4 T cells emerging in mice infected with B. burgdorferi but not with Arp-deficient Borrelia afzelii. Although up to 30% of Arp-specific CD4 T cells were ICOS+PD-1+CXCR5+BCL6+ T follicular helper cells, their numbers declined after day 12, before germinal centers (GCs) are prominent. Although some Arp-specific B cells, identified using fluorochrome-labeled rArp proteins, had the phenotype of GC B cells, their frequencies did not correlate with anti-Arp serum IgG. The data suggest a failure not in the induction, but in the maintenance of GC T follicular helper and/or B cells to B. burgdorferi.

CD4 T cell responses in persistent Borrelia burgdorferi infection

Infection of mice with Borrelia burgdorferi (Bb), a tick-transmitted spirochete and the pathogen that causes Lyme disease in humans, triggers CD4 T cell activation in secondary lymphoid tissues, from which they disseminate into various infected tissues. Despite their activation and the appearance of CD4 T cell-dependent antibody responses, Bb establishes persistent infection in natural Bb reservoir hosts in the absence of overt disease, raising the question of the effectiveness of the anti-Bb T cell responses. Reviewing the existing literature, we propose that CD4 T cells might constitute a host cell target of Bb-mediated immune evasion, rendering these cells ineffective in orchestrating effective inflammatory responses and in supporting highly functional Bb-specific antibody induction. Supporting the induction of more effective CD4 T cell responses may help overcome Bb persistence.

Affinity-matured HLA class II dimers for robust staining of antigen-specific CD4+ T cells

Peptide-major histocompatibility complex (pMHC) multimers enable the detection of antigen-specific T cells in studies ranging from vaccine efficacy to cancer immunotherapy. However, this technology is unreliable when applied to pMHC class II for the detection of CD4⁺ T cells. Here, using a combination of molecular biological and immunological techniques, we cloned sequences encoding human leukocyte antigen (HLA)-DP, HLA-DQ and HLA-DR molecules with enhanced CD4 binding affinity (with a K_d of 8.9 ± 1.1 µM between CD4 and affinity-matured HLA-DP4) and produced affinity-matured class II dimers that stain antigen-specific T cells better than conventional multimers in both in vitro and ex vivo analyses. Using a comprehensive library of dimers for HLA-DP4, which is the most frequent HLA allele in many ancestry groups, we mapped 103 HLA-DP4-restricted epitopes derived from diverse tumor-associated antigens and cloned the cognate T-cell antigen receptor (TCR) genes from in vitro-stimulated CD4⁺ T cells. The availability of affinity-matured class II dimers across HLA-DP, HLA-DQ and HLA-DR alleles will aid in the investigation of human CD4⁺ T-cell responses.

Optimized Protocol for the Detection of Multifunctional Epitope-Specific CD4+ T Cells Combining MHC-II Tetramer and Intracellular Cytokine Staining Technologies

Analysis of multifunctional CD4+ T cells is fundamental for characterizing the immune responses to vaccination or infection. Major histocompatibility complex (MHC)/peptide tetramers represent a powerful technology for the detection of antigen-specific T cells by specific binding to their T-cell receptor, and their combination with functional assays is fundamental for characterizing the antigen-specific immune response. Here we optimized a protocol for the detection of multiple intracellular cytokines within epitope-specific CD4+ T cells identified by the MHC class II tetramer technology. The optimal procedure for assessing the functional activity of tetramer-binding CD4+ T cells was based on the simultaneous intracellular staining with both MHC tetramers and cytokine-specific antibodies upon in vitro restimulation of cells with the vaccine antigen. The protocol was selected among procedures that differently combine the steps of cellular restimulation and tetramer staining with intracellular cytokine labeling. This method can be applied to better understand the complex functional profile of CD4+ T-cell responses upon vaccination or infection.

The Mutation-Associated Neoantigen Functional Expansion of Specific T Cells (MANAFEST) Assay: A Sensitive Platform for Monitoring Antitumor Immunity

Mutation-associated neoantigens (MANA) are a target of antitumor T-cell immunity. Sensitive, simple, and standardized assays are needed to assess the repertoire of functional MANA-specific T cells in oncology. Assays analyzing in vitro cytokine production such as ELISpot and intracellular cytokine staining have been useful but have limited sensitivity in assessing tumor-specific T-cell responses and do not analyze antigen-specific T-cell repertoires. The FEST (Functional Expansion of Specific T cells) assay described herein integrates T-cell receptor sequencing of short-term, peptide-stimulated cultures with a bioinformatic platform to identify antigen-specific clonotypic amplifications. This assay can be adapted for all types of antigens, including MANAs via tumor exome-guided prediction of MANAs. Following in vitro identification by the MANAFEST assay, the MANA-specific CDR3 sequence can be used as a molecular barcode to detect and monitor the dynamics of these clonotypes in blood, tumor, and normal tissue of patients receiving immunotherapy. MANAFEST is compatible with high-throughput routine clinical and lab practices. Cancer Immunol Res; 6(8); 888-99. ©2018 AACR.

Memory T cells specific to citrullinated α-enolase are enriched in the rheumatic joint

ACPA-positive rheumatoid arthritis (RA) is associated with distinct HLA-DR alleles and immune responses to many citrullinated self-antigens. Herein we investigated the T cell epitope confined within α-enolase_326-340 in the context of HLA-DRB1*04:01 and assessed the corresponding CD4⁺ T cells in both the circulation and in the rheumatic joint. Comparative crystallographic analyses were performed for the native and citrullinated α-enolase_326-340 peptides in complex with HLA-DRB1*04:01. HLA-tetramers assembled with either the native or citrullinated peptide were used for ex vivo and in vitro assessment of α-enolase-specific T cells in peripheral blood, synovial fluid and synovial tissue by flow cytometry. The native and modified peptides take a completely conserved structural conformation within the peptide-binding cleft of HLA-DRB1*04:01. The citrulline residue-327 was located N-terminally, protruding towards TCRs. The frequencies of T cells recognizing native eno_326-340 were similar in synovial fluid and peripheral blood, while in contrast, the frequency of T cells recognizing cit-eno_326-340 was significantly elevated in synovial fluid compared to peripheral blood (3.6-fold, p = 0.0150). Additionally, citrulline-specific T cells with a memory phenotype were also significantly increased (1.6-fold, p = 0.0052) in synovial fluid compared to peripheral blood. The native T cell epitope confined within α-enolase_326-340 does not appear to lead to complete negative selection of cognate CD4⁺ T cells. In RA patient samples, only T cells recognizing the citrullinated version of α-enolase_326-340 were found at elevated frequencies implicating that neo-antigen formation is critical for breach of tolerance.

Immunogenetic Markers Definition in Latvian Patients with Lyme Borreliosis and Lyme Neuroborreliosis

The aim of this study was to determine the human leukocyte antigen (HLA)-DRB1 alleles in two groups of patients in Latvia: patients with Lyme borreliosis and patients with Lyme neuroborreliosis. The study included 216 patients with Lyme borreliosis, 29 patients with Lyme neuroborreliosis and 282 control persons. All surveyed persons were residents of Latvia. The HLA-DR genotyping was performed by polymerase chain reaction- sequence specific primer (PCR-SSP). The predisposition to the Lyme borreliosis is associated with the HLA-DRB1*07, -DRB1*17(03), -DRB1*04, -DRB1*15(02) alleles. The allele -DRB1*11(05), -DRB1*14(06) and -DRB1*13(06) were significantly more frequent in controls. In-group with Lyme neuroborreliosis differences were found for the -DRB1*07 and -DRB1*04 alleles, but only HLA-DRB1*07 allele was statistically significant after Bonferroni correction and associated with Lyme neuroborreliosis in Latvian patients.

Enhanced Detection of Antigen-Specific CD4+ T Cells Using Altered Peptide Flanking Residue Peptide-MHC Class II Multimers

Fluorochrome-conjugated peptide-MHC (pMHC) class I multimers are staple components of the immunologist's toolbox, enabling reliable quantification and analysis of Ag-specific CD8(+) T cells irrespective of functional outputs. In contrast, widespread use of the equivalent pMHC class II (pMHC-II) reagents has been hindered by intrinsically weaker TCR affinities for pMHC-II, a lack of cooperative binding between the TCR and CD4 coreceptor, and a low frequency of Ag-specific CD4(+) T cell populations in the peripheral blood. In this study, we show that peptide flanking regions, extending beyond the central nonamer core of MHC-II-bound peptides, can enhance TCR-pMHC-II binding and T cell activation without loss of specificity. Consistent with these findings, pMHC-II multimers incorporating peptide flanking residue modifications proved superior for the ex vivo detection, characterization, and manipulation of Ag-specific CD4(+) T cells, highlighting an unappreciated feature of TCR-pMHC-II interactions.

Major Histocompatibility Complex Class II Dextramers: New Tools for the Detection of antigen-Specific, CD4 T Cells in Basic and Clinical Research

The advent of major histocompatibility complex (MHC) tetramer technology has been a major contribution to T cell immunology, because tetramer reagents permit detection of antigen-specific T cells at the single-cell level in heterogeneous populations by flow cytometry. However, unlike MHC class I tetramers, the utility of MHC class II tetramers has been less frequently reported. MHC class II tetramers can be used successfully to enumerate the frequencies of antigen-specific CD4 T cells in cells activated in vitro, but their use for ex vivo analyses continues to be a problem, due in part to their activation dependency for binding with T cells. To circumvent this problem, we recently reported the creation of a new generation of reagents called MHC class II dextramers, which were found to be superior to their counterparts. In this review, we discuss the utility of class II dextramers vis-a-vis tetramers, with respect to their specificity and sensitivity, including potential applications and limitations.

Ex vivo peptide-MHC II tetramer analysis reveals distinct end-differentiation patterns of human pertussis-specific CD4(+) T cells following clinical infection

Pertussis is occurring in highly vaccinated populations, suggesting insufficient protective memory CD4(+) T cells to Bordetella (B.) pertussis. P.69 Pertactin (P.69 Prn) is an important virulence factor of B. pertussis, and P.69 Prn7-24 is an immunodominant CD4(+) T cell epitope in mice and broadly recognized in humans. P.69 Prn7-24 peptide-MHC II tetramers (DRB4*0101/IVKT) were designed to ex vivo interrogate the presence and differentiation state of P.69 Prn7-24 specific CD4(+) T cells in six symptomatic pertussis cases. Cases with relatively more CD45RA(-)CCR7(+) central memory CD4(+)DRB4*0101/IVKT(+) T cells secreted Th1 cytokines, while cases with more CD45RA(-)CCR7(-) effector memory CD4(+)DRB4*0101/IVKT(+) T cells secreted both Th1 and Th2 cytokines upon peptide stimulation. CD45RA(+)CCR7(-) terminal differentiation pattern was associated with low or non-functionality based on cytokine secretion. This study provides proof of principle for further peptide-MHC II tetramer guided approaches in the elucidation of limited immunological memory to B. pertussis and the resurgence of pertussis.

Characterization of T cell phenotype and function in a double transgenic (collagen-specific TCR/HLA-DR1) humanized model of arthritis

Introduction

T cells orchestrate joint inflammation in rheumatoid arthritis (RA), yet they are difficult to study due to the small numbers of antigen-specific cells. The goal of this study was to characterize a new humanized model of autoimmune arthritis and to describe the phenotypic and functional changes that occur in autoimmune T cells following the induction of pathological events.

Methods

We developed a double transgenic mouse containing both the HLA-DR1 transgene and an HLA-DR1-restricted collagen-specific TCR in order to obtain large numbers of antigen-specific T cells that can be used for immunologic studies.

Results

In vitro, CII-specific T cells from this mouse proliferated vigorously in response to the CII immunodominant peptide A2 and the cells altered their phenotype to become predominately CD62L^low and CD44^high “activated” T cells. The response was accompanied by the production of Th1, Th2, and Th17-type cytokines. Following immunization with bovine CII/CFA, these mice develop an accelerated arthritis compared to single transgenic HLA-DR1 mice. On the other hand, when the mice were treated orally with the analog peptide A12, (a suppressive analog of collagen we have previously described), arthritis was significantly suppressed, despite the fact that >90% of the CD4+ T cells express the TCR Tg. In GALT tissues taken from the A12-treated mice, IL-2, IFN-γ, and IL-17 production to the autoimmune collagen determinant dropped while high levels of IL-10 and IL-4 were produced.

Conclusions

We have developed a humanized model of autoimmune arthritis that will be useful for the study of T cell directed therapies as well as T cell mediated mechanisms of autoimmune diseases.

Multimer monitoring of CMV-specific T cells in research and in clinical applications

Multimer monitoring has become a standard technique for detection of antigen-specific T cells. The term "multimer" refers to a group of reagents based on the multimerisation of molecules in order to raise avidity and thus stabilize binding to their ligand. Multimers for detection of antigen-specific T-cell responses are based on major histocompatibility complex class I peptide complexes. Multimer staining enables fast and direct visualization of antigen-specific T cells; thus, it is widely applied to assess antiviral immunity, e.g., monitor patients in vaccination trials or confirm purity of cell products for adoptive transfer. Assessment of T-cell immunity against persistent pathogens like cytomegalovirus (CMV) is of major importance in immunosuppressed patients. Recent advancements of multimers facilitate reversible labeling and allow isolation of epitope-specific T cells for adoptive transfer. Here, we give an overview on the different multimers and their applications, with an emphasis on CMV-specific T-cell responses.

Increased frequency of intestinal CD4+ T cells reactive with mycobacteria in patients with Crohn's disease

OBJECTIVE

The aim of this study was to assess the frequency of mycobacteria and Escherichia coli reactive T cells in intestinal biopsies from patients with Crohn's disease (CD) and ulcerative colitis (UC).

MATERIALS AND METHODS

The biopsies were obtained by colonoscopy from adult patients with active CD (n = 5) and active UC (n = 4). The number of CD4+ T cell clones expanded and screened from each patient varied from 383 to 3972 giving a total of 16639 individual clones. The T cell clones were tested for responses to Mycobacterium avium subspecies paratuberculosis (MAP) and E. coli. The cytokine profile of 42 individual T cell clones from four CD patients was assessed.

RESULTS

The frequency of mycobacteria reactive T cell clones in CD patients ranged from 0.17 to 1.63% and was higher (p = 0.038) than the frequency of E. coli reactive T cells ranging from 0 to 0.18%. No or very low numbers of mycobacteria reactive clones were detected in three UC patients while the fourth UC patient had a frequency similar to what was observed in CD patients. The frequencies of E. coli reactive T cell clones in UC patients ranged from 0 to 0.52%. T cell clones (n = 42) from CD patients all produced IL-17 and/or IFN-γ. Several clones were also able to produce IL-10.

CONCLUSIONS

The high frequency of intestinal tissue resident T cells reactive to mycobacteria suggests that an adaptive immune response have taken place and argues that these bacteria may contribute to the chronic inflammation in CD.

Relatively low level of antigen-specific monocytes detected in blood from untreated tuberculosis patients using CD4+ T-cell receptor tetramers

The in vivo kinetics of antigen-presenting cells (APCs) in patients with advanced and convalescent tuberculosis (TB) is not well characterized. In order to target Mycobacterium tuberculosis (MTB) peptides- and HLA-DR-holding monocytes and macrophages, 2 MTB peptide-specific CD4⁺ T-cell receptor (TCR) tetramers eu and hu were successfully constructed. Peripheral blood (PBL) samples from inpatients with advanced pulmonary TB (PTB) were analyzed using flow cytometry, and the percentages of tetramer-bound CD14⁺ monocytes ranged from 0.26–1.44% and 0.21–0.95%, respectively; significantly higher than those measured in PBL samples obtained from non-TB patients, healthy donors, and umbilical cords. These tetramers were also able to specifically detect macrophages in situ via immunofluorescent staining. The results of the continuous time-point tracking of the tetramer-positive rates in PBL samples from active PTB outpatients undergoing treatment show that the median percentages were at first low before treatment, increased to their highest levels during the first month, and then began to decrease during the second month until finally reaching and maintaining a relatively low level after 3–6 months. These results suggest that there is a relatively low level of MTB-specific monocytes in advanced and untreated patients. Further experiments show that MTB induces apoptosis in CD14⁺ cells, and the percentage of apoptotic monocytes dramatically decreases after treatment. Therefore, the relatively low level of MTB-specific monocytes is probably related to the apoptosis or necrosis of APCs due to live bacteria and their growth. The bactericidal effects of anti-TB drugs, as well as other unknown factors, would induce a peak value during the first month of treatment, and a relatively low level would be subsequently reached and maintained until all of the involved factors reached equilibrium. These tetramers have diagnostic potential and can provide valuable insights into the mechanisms of antigen presentation and its relationship with TB infection and latent TB infection.

Mycobacterium tuberculosis (MTB) is one of the most dangerous pathogens in the world. It is estimated that one-third of the world population contracts the bacteria during their lives. Approximately 5–10% of infected individuals will eventually develop an active form of the disease. Cellular immunity plays an important role in immunity against tuberculosis (TB); however, the host's defense mechanisms are not completely understood. Here, we developed a novel tool: MTB antigen-specific tetrameric CD4⁺ T-cell receptor (TCR) complexes that can detect MTB peptide-specific antigen presenting cells (APCs) in blood and local tissues. We found that a relatively low level of antigen-specific monocytes (i.e., APCs) was detected in peripheral blood (PBL) samples from untreated TB patients, and then increased to their peak levels during the first month after treatment, which probably had something to do with the decrease in APC apoptosis. Our research provides a new method for tracking dynamic changes in APCs that are associated with TB infection and latent TB infection, and an additional tool for the studies of TB immunity and its pathogenesis.

Associations of HLA DR and DQ molecules with Lyme borreliosis in Latvian patients

Background

Many autoimmune diseases are associated with variants of HLA genes such as those encoding the MHC complex. This correlation is not absolute, but may help in understanding of the molecular mechanism of disease. The purpose of this study was to determine HLA-DR,-DQ alleles in Latvian patients with Lyme borreliosis and control (healthy) persons. Case patients and control subjects were similar in age, gender and ethnic heritage and differed only as regards the presence of Borrelia burgdorferi infection. The study included 25 patients with clinical stage – erythema migrans and 30 control (healthy) persons. HLA genotyping was performed by PCR with sequence-specific primers.

Results

The results show difference in HLA-DRB1 alleles distribution between patients and control subjects. The frequencies of HLA-DRB1 *04 (OR 11.24; p < 0.007) and HLA-DRB1 *17 (03) (OR 8.05; p < 0.033) were increased in the Lyme disease patients. And the frequency of allele DRB1*13 (OR 0.12; p < 0.017) was lower in Borreliosis patients and higher in control group. But, significant differences in frequencies of HLA-DQ alleles we did not detect.

Conclusions

HLA predisposition to Lyme borreliosis appears not to be limited to HLA molecules, but some HLA-DR alleles also have a significant influence, and, may have implications in our understanding of pathogenesis of this disease. In particular, HLA-DRB1*04 and DRB1 *17 (03) may contribute to the Lyme borreliosis development in Latvian population

MHC class II tetramers

MHC class II tetramers have emerged as an important tool for characterization of the specificity and phenotype of CD4 T cell immune responses, useful in a large variety of disease and vaccine studies. Issues of specific T cell frequency, biodistribution, and avidity, coupled with the large genetic diversity of potential class II restriction elements, require targeted experimental design. Translational opportunities for immune disease monitoring are driving the rapid development of HLA class II tetramer use in clinical applications, together with innovations in tetramer production and epitope discovery.

Cell surface display of functional human MHC class II proteins: yeast display versus insect cell display

Reliable and robust systems for engineering functional major histocompatibility complex class II (MHCII) proteins have proved elusive. Availability of such systems would enable the engineering of peptide-MHCII (pMHCII) complexes for therapeutic and diagnostic applications. In this paper, we have developed a system based on insect cell surface display that allows functional expression of heterodimeric DR2 molecules with or without a covalently bound human myelin basic protein (MBP) peptide, which is amenable to directed evolution of DR2-MBP variants with improved T cell receptor (TCR)-binding affinity. This study represents the first example of functional display of human pMHCII complexes on insect cell surface. In the process of developing this pMHCII engineering system, we have also explored the potential of using yeast surface display for the same application. Our data suggest that yeast display is a useful system for analysis and engineering of peptide binding of MHCII proteins, but not suitable for directed evolution of pMHC complexes that bind with low affinity to self-reactive TCRs.

Relationship between immunity to Borrelia burgdorferi outer-surface protein A (OspA) and Lyme arthritis

Antibiotic-refractory Lyme arthritis may result from Borrelia burgdorferi-induced autoimmunity in affected joints. Such patients usually have certain HLA-DRB1 molecules that bind an epitope of B. burgdorferi outer-surface protein A (OspA₁₆₃₋₁₇₅), and cellular and humoral immune responses to OspA are greater in patients with antibiotic-refractory arthritis than in those with antibiotic-responsive arthritis. Recent work in a mouse model suggests that, during B. burgdorferi infection, OspA in genetically susceptible individuals stimulates a particularly strong T(H)1 response, which may be one of several factors that can help set the stage for a putative autoimmune response in affected joints. However, vaccination with OspA did not induce arthritis in this mouse model, and case and control comparisons in human vaccine trials did not show an increased frequency of arthritis among OspA-vaccinated individuals. Thus, a vaccine-induced immune response to OspA does not replicate the sequence of events needed in the natural infection to induce antibiotic-refractory Lyme arthritis.

The potential of multimer technologies in type 1 diabetes prediction strategies

Type 1 diabetes is an autoimmune disease which occurs in (human leukocyte antigen) genetically predisposed individuals as a consequence of the organ-specific immune destruction of the insulin-producing β cells in the islets of Langherans within the pancreas. Type 1 diabetes is the result of a breakdown in immune regulation that leads to expansion of autoreactive CD4+ and CD8+ T cells, autoantibody-producing B lymphocytes and activation of the innate immune system. Islet-related autoantibodies revealed themselves to be good predictors of future onset of the disease, although they are not directly pathogenetic; T cells instead play a dominant role in disease initiation and progression. In this review, we first discuss the approaches that several laboratories attempted to measure human islet autoantigen-specific T-cell function in type 1 diabetes. T-cell assays could be used in combination with standardized autoantibody screenings to improve predictive strategies. They could also help to monitor in long-term follow-up the efficacy of tolerogenic immunotherapeutic strategies when established at the onset of the disease, and help to predict the recurrence of disease. Although some recent developments based on enzyme-linked immunosorbent spot and immunoblotting techniques have been able to distinguish with good sensitivity and specificity patients from controls, T-cell results, as revealed by international workshops, were indeed largely inconclusive. Nowadays, novel technologies have been exploited that could contribute to answering the tantalizing question of identifying autoreactive T cells. We particularly focus on and discuss MHC multimer tools and emphasize the advantages they can offer but also their weaknesses when used in combination with other T-cell assays. Copyright © 2011 John Wiley & Sons, Ltd.

Use of HLA-DR*08032/E7 and HLA-DR*0818/E7 tetramers in tracking of epitope-specific CD4+ T cells in active and convalescent tuberculosis patients compared with control donors

Comparative tracking of tetramer-positive and epitope-specific CD4(+) T cells in blood and other tissues from tuberculosis (TB) patients during TB development and treatment using control donor samples is not well characterized. In this study, a novel HLA-DR-restricted peptide E7 from the ESAT-6 protein of Mycobacterium tuberculosis (MTB) was used to prepare modified HLA-DR*08032/E7 tetramer (tetramer 1) and HLA-DR*0818/E7 tetramer (tetramer 2) to monitor a series of samples from TB patients and control donors. Tetramer staining showed that (1) by direct staining of single sample and flow cytometric analyses, detection of tetramer-positive CD4(+) T cells ranged from 0.1% to 8.8% (median 0.67% in tetramer 1 and 0.5% in tetramer 2), 0.1 to 10.7% (0.74% and 0.71%), 0.02 to 2.2% (0.25% and 0.25%), 0.02 to 0.48% (0.2% and 0.2%) and most at under 0-0.2% (0.2% and 0.16%) in the initial pulmonary TB (PTB) patients' blood, pleural fluid (PLF) of initial tuberculous pleuritis patients, non-TB patients' blood, healthy donors' blood and umbilical cord blood, respectively; significantly higher levels of CD4(+) T cells were detected in samples of TB patients than in three control donor groups; (2) by direct staining of time point TB samples and flow cytometric analyses, along with TB symptom amendment at day 60, tetramer-positive CD4(+) T cells began to decrease, until after 90-120 days, reached and kept at a relatively low even normal level about at 0.03-0.3%; (3) by enrichment approach, at least 10-fold increased memory tetramer-positive CD4(+) T cells were seen; (4) by in situ staining, tetramer-positive, IFN-γ-producing and/or TNF-α-producing CD4(+) T cells in the lymph node and lung granuloma and cavernous tissues of TB patients could be determined. Therefore, by further increasing the sample size tested to confirm the specificity and sensitivity of tetrameric molecules, it should be possible to develop them for use as research and diagnostic reagents.

On-chip activation and subsequent detection of individual antigen-specific T cells

The frequencies of antigen-specific CD4+ T cells in samples of human tissue have been difficult to determine accurately ex vivo, particularly for autoimmune diseases such as multiple sclerosis or type 1 diabetes. Conventional approaches involve the expansion of primary T cells in vitro to increase the numbers of cells, and a subsequent assessment of the frequencies of antigen-specific T cells in the expanded population by limiting dilution or by using fluorescently labeled tetramers of peptide-loaded major histocompatibility complex (MHC) receptors. Here we describe an alternative approach that uses arrays of subnanoliter wells coated with recombinant peptide-loaded MHC class II monomers to isolate and stimulate individual CD4+ T cells in an antigen-specific manner. In these experiments, activation was monitored using microengraving to capture two cytokines (IFNgamma and IL-17) released from single cells. This new method should enable direct enumeration of antigen-specific CD4+ T cells ex vivo from clinical samples.

HLA-DR alleles determine responsiveness to Borrelia burgdorferi antigens in a mouse model of self-perpetuating arthritis

OBJECTIVE

Arthritis is a prominent manifestation of Lyme disease, which is caused by infection with Borrelia burgdorferi (Bb). Chronic Lyme arthritis persisting even after antibiotic treatment is linked to HLA-DRB1*0401 (DR4) and related alleles. In contrast, patients whose Lyme arthritis resolves within 3 months postinfection show an increased frequency of HLA-DRB1*1101 (DR11). The aim of this study was to analyze the underlying mechanism by which HLA-DR alleles confer genetic susceptibility or resistance to antibiotic-refractory Lyme arthritis.

METHODS

We generated DR11-transgenic (DR11-Tg) mice on a murine MHCII-/- background and compared their immune response to Bb antigens with the response of DR4-Tg mice after immunization with Bb outer surface protein A (OspA) or infection with live Bb.

RESULTS

T cells from OspA-immunized and Bb-infected DR11-Tg mice had defective production of interferon-gamma as compared with those from DR4-Tg mice. In contrast, DR11-Tg mice developed higher titers of anti-OspA and anti-Bb antibodies, respectively, than did DR4-Tg mice. Consistent with this observation, we found that the Bb-infected DR11-Tg mice had a decreased spirochetal burden as compared with the DR4-Tg mice, as measured by quantitative polymerase chain reaction.

CONCLUSION

This study provides direct evidence that in the presence of HLA-DR11, the immune response against Bb antigens is directed toward a protective antibody response. In contrast, an inflammatory Th1 response is induced in the presence of DR4. These observations offer an explanation for the differential genetic susceptibility of DR4+ and DR11+ individuals to the development of chronic Lyme arthritis and, eventually, the progression to antibiotic-refractory Lyme arthritis.

DR*W201/P65 tetramer visualization of epitope-specific CD4 T-cell during M. tuberculosis infection and its resting memory pool after BCG vaccination

BACKGROUND

In vivo kinetics and frequencies of epitope-specific CD4 T cells in lymphoid compartments during M. tuberculosis infection and their resting memory pool after BCG vaccination remain unknown.

METHODOLOGY/FINDINGS

Macaque DR*W201 tetramer loaded with Ag85B peptide 65 was developed to directly measure epitope-specific CD4 T cells in blood and tissues form macaques after M. tuberculosis infection or BCG vaccination via direct staining and tetramer-enriched approach. The tetramer-based enrichment approach showed that P65 epitope-specific CD4 T cells emerged at mean frequencies of approximately 500 and approximately 4500 per 10(7) PBL at days 28 and 42, respectively, and at day 63 increased further to approximately 22,000/10(7) PBL after M. tuberculosis infection. Direct tetramer staining showed that the tetramer-bound P65-specific T cells constituted about 0.2-0.3% of CD4 T cells in PBL, lymph nodes, spleens, and lungs at day 63 post-infection. 10-fold expansion of these tetramer-bound epitope-specific CD4 T cells was seen after the P65 peptide stimulation of PBL and tissue lymphocytes. The tetramer-based enrichment approach detected BCG-elicited resting memory P65-specific CD4 T cells at a mean frequency of 2,700 per 10(7) PBL.

SIGNIFICANCE

Our work represents the first elucidation of in vivo kinetics and frequencies for tetramer-bound epitope-specific CD4 T cells in the blood, lymphoid tissues and lungs over times after M. tuberculosis infection, and BCG immunization.

Molecular Mimicry toBorrelia burgdorferi: Pathway to Autoimmunity?

Lyme borreliosis is due to infection with the tick-borne spirochete Borrelia burgdorferi, and is associated with persistent infection unless treated with antibiotics. The persistent nature of infection by B. burgdorferi can lead to development of chronic disease, as found in patients infected before recognition of the effectiveness of antibiotic therapy. Much speculation has surrounded the possibility that autoimmune mechanisms are involved in chronic symptoms. In most cases, involvement of autoimmunity in Lyme disease has not received experimental support. The exception is in a small group of patients with chronic arthritis whose abnormal joint symptoms persist after apparent elimination of the bacteria. In this review, the evidence supporting autoimmune mechanisms in Lyme disease will be discussed.

Human naive and memory CD4+ T cell repertoires specific for naturally processed antigens analyzed using libraries of amplified T cells

The enormous diversity of the naive T cell repertoire is instrumental in generating an immune response to virtually any foreign antigen that can be processed into peptides that bind to MHC molecules. The low frequency of antigen-specific naive T cells, their high activation threshold, and the constrains of antigen-processing and presentation have hampered analysis of naive repertoires to complex protein antigens. In this study, libraries of polyclonally expanded naive T cells were used to determine frequency and antigen dose-response of human naive CD4(+) T cells specific for a variety of antigens and to isolate antigen-specific T cell clones. In the naive repertoire, T cells specific for primary antigens, such as KLH and Bacillus anthracis protective antigen, and for recall antigens, such as tetanus toxoid, cytomegalovirus, and Mycobacterium tuberculosis purified protein derivative, were detected at frequencies ranging from 5 to 170 cells per 10(6) naive T cells. Antigen concentrations required for half-maximal response (EC50) varied over several orders of magnitude for different naive T cells. In contrast, in the memory repertoire, T cells specific for primary antigens were not detected, whereas T cells specific for recall antigens were detected at high frequencies and displayed EC50 values in the low range of antigen concentrations. The method described may find applications for evaluation of vaccine candidates, for testing antigenicity of therapeutic proteins, drugs, and chemicals, and for generation of antigen-specific T cell clones for adoptive cellular immunotherapy.

HLA type and immune response to Borrelia burgdorferi outer surface protein a in people in whom arthritis developed after Lyme disease vaccination

OBJECTIVE

To investigate whether persons with treatment-resistant Lyme arthritis-associated HLA alleles might develop arthritis as a result of an autoimmune reaction triggered by Borrelia burgdorferi outer surface protein A (OspA), the Lyme disease vaccine antigen.

METHODS

Persons in whom inflammatory arthritis had developed after Lyme disease vaccine (cases) were compared with 3 control groups: 1) inflammatory arthritis but not Lyme disease vaccine (arthritis controls), 2) Lyme disease vaccine but not inflammatory arthritis (vaccine controls), and 3) neither Lyme disease vaccine nor inflammatory arthritis (normal controls). HLA-DRB1 allele typing, Western blotting for Lyme antigen, and T cell reactivity testing were performed.

RESULTS

Twenty-seven cases were matched with 162 controls (54 in each control group). Odds ratios (ORs) for the presence of 1 or 2 treatment-resistant Lyme arthritis alleles were 0.8 (95% confidence interval [95% CI] 0.3-2.1), 1.6 (95% CI 0.5-4.4), and 1.75 (95% CI 0.6-5.3) in cases versus arthritis controls, vaccine controls, and normal controls, respectively. There were no significant differences in the frequency of DRB1 alleles. T cell response to OspA was similar between cases and vaccine controls, as measured using the stimulation index (OR 1.6 [95% CI 0.5-5.1]) or change in uptake of tritiated thymidine (counts per minute) (OR 0.7 [95% CI 0.2-2.3]), but cases were less likely to have IgG antibodies to OspA (OR 0.3 [95% CI 0.1-0.8]). Cases were sampled closer to the time of vaccination (median 3.59 years versus 5.48 years), and fewer cases had received 3 doses of vaccine (37% versus 93%).

CONCLUSION

Treatment-resistant Lyme arthritis alleles were not found more commonly in persons who developed arthritis after Lyme disease vaccination, and immune responses to OspA were not significantly more common in arthritis cases. These results suggest that Lyme disease vaccine is not a major factor in the development of arthritis in these cases.

CD4 memory T cells: what are they and what can they do?

Immunological memory provides the basis for successful vaccines. It is important to understand the properties of memory cells. There is much known about the phenotype and functions of memory CD8 T cells, less about memory B cells, while CD4 memory T cells have proved difficult to study. Differences in the types of memory CD4 cells studied and the difficulties of tracking the small number of cells have led to conflicting and unclear results. Here we discuss the different systems used to study CD4 memory cells and ask whether, and in what circumstances, memory CD4 cells could provide protection against infections.

The role of infections in autoimmune disease

Autoimmunity occurs when the immune system recognizes and attacks host tissue. In addition to genetic factors, environmental triggers (in particular viruses, bacteria and other infectious pathogens) are thought to play a major role in the development of autoimmune diseases. In this review, we (i) describe the ways in which an infectious agent can initiate or exacerbate autoimmunity; (ii) discuss the evidence linking certain infectious agents to autoimmune diseases in humans; and (iii) describe the animal models used to study the link between infection and autoimmunity.

Identification of CD4 T-cell epitopes in soluble liver antigen/liver pancreas autoantigen in autoimmune hepatitis

BACKGROUND & AIMS

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease associated with autoantibodies and liver-infiltrating lymphocytes. Although autoantibodies are tested routinely to diagnose and classify AIH, liver-infiltrating lymphocytes are regarded as the primary factor for disease pathogenesis. The purpose of this study was to identify and characterize autoantigenic peptides within human AIH-specific soluble liver antigen/liver pancreas antigen (SLA/LP) that are targeted by CD4(+) T cells and restricted by the disease susceptibility gene HLA-DRB1*0301.

METHODS

HLA-DRB1*0301 transgenic mice were immunized with SLA/LP. Antibody and T-cell responses were analyzed with SLA/LP-overlapping peptides in enzyme immunoassay, proliferation, and enzyme-linked immunospot (ELISpot) assays. Minimal optimal T-cell epitopes were identified, characterized with cloned T-cell hybridomas, and confirmed in tetramer and ELISpot assays with AIH patients' peripheral blood mononuclear cells.

RESULTS

All mice developed SLA/LP-specific IgG1/IgG2a antibodies against the same SLA/LP peptides as human beings. T cells targeted several peptides within SLA/LP, 2 of which were DR3-restricted and one overlapped the sequence recognized by human autoantibodies. Minimal optimal epitopes were mapped, DRB1*0301/epitope-tetramers were generated, and the frequency and function of HLA-DRB1*0301-restricted autoantigen-specific T cells in AIH patients were analyzed with tetramer and interferon-gamma ELISpot assays.

CONCLUSIONS

This study identified T-cell epitopes within SLA/LP, restricted by the disease susceptibility gene DRB1*0301 and in close proximity to the human autoantibody epitope. These results and the generated reagents now provide the opportunity to directly monitor autoreactive T cells in AIH patients in clinical studies.

Different development of myelin basic protein agonist- and antagonist-specific human TCR transgenic T cells in the thymus and periphery

Myelin basic protein (MBP)-specific T cells are thought to play a role in the development of multiple sclerosis. MBP residues 111-129 compose an immunodominant epitope cluster restricted by HLA-DRB1*0401. The sequence of residues 111-129 of MBP (MBP(111-129)) differs in humans (MBP122:Arg) and mice (MBP122:Lys) at aa 122. We previously found that approximately 50% of human MBP(111-129) (MBP122:Arg)-specific T cell clones, including MS2-3C8 can proliferate in response to mouse MBP(111-129) (MBP122:Lys). However, the other half of T cell clones, including HD4-1C2, cannot proliferate in response to MBP(111-129) (MBP122:Lys). We found that MBP(111-129) (MBP122:Lys) is an antagonist for HD4-1C2 TCR, therefore, MS2-3C8 and HD4-1C2 TCRs are agonist- and antagonist-specific TCRs in mice, respectively. Therefore, we examined the development of HD4-1C2 TCR and MS2-3C8 TCR transgenic (Tg) T cells in the thymus and periphery. We found that dual TCR expression exclusively facilitates the development of MBP(111-129) TCR Tg T cells in the periphery of HD4-1C2 TCR/HLA-DRB1*0401 Tg mice although it is not required for their development in the thymus. We also found that MS2-3C8 TCR Tg CD8(+) T cells develop along with MS2-3C8 TCR Tg CD4(+) T cells, and that dual TCR expression was crucial for the development of MS2-3C8 TCR Tg CD4(+) and CD8(+) T cells in the thymus and periphery, respectively. These results suggest that thymic and peripheral development of MBP-specific T cells are different; however, dual TCR expression can facilitate their development.

Varicella zoster virus glycoprotein E-specific CD4+ T cells show evidence of recent activation and effector differentiation, consistent with frequent exposure to replicative cycle antigens in healthy immune donors

Varicella zoster viru (VZV)-specific T cell responses are believed to be vital in recovery from primary VZV infection and also in the prevention of viral reactivation. While glycoprotein E (gE) is the most abundant and one of the most immunogenic proteins of the virus, there are no data addressing potential T cell epitopes within gE, nor the phenotype of specific T cells. Using interferon gamma enzyme-linked immunospot assays and intracellular cytokine assays, we identified gE-specific immune responses in 20 adult healthy immune donors which were found to be dominated by the CD4+ subset of T cells. We characterized three immune dominant epitopes within gE restricted through DRB1*1501, DRB1*07 and DRB4*01, and used DRB1*1501 class II tetrameric complexes to determine the ex vivo frequency and phenotype of specific T cells. In healthy immune donors, the cells were largely positive for CCR7, CD28 and CD27, but expressed variable CD62L and low levels of cutaneous lymphocyte associated antigen with evidence of recent activation. In summary, we show that circulating gE-specific CD4+ T cells are detected at a relatively high frequency in healthy immune donors and show evidence of recent activation and mixed central and effector memory phenotype. These data would be compatible with frequent exposure to replicative cycle antigens in healthy donors and are consistent with a role for gE-specific CD4+ T cells in the control of viral replication.

Conserved mycobacterial lipoglycoproteins activate TLR2 but also require glycosylation for MHC class II-restricted T cell activation

CD4(+) T cell clones derived from a leprosy lesion and patient blood were used to monitor the isolation and identification of an Ag associated with the self-limited form of the disease. Biochemical purification and genetic analysis identified the T cell Ag as a conserved mycobacterial lipoglycoprotein LprG. LprG-mediated activation of CD4(+) T cells required specific MHC class II restriction molecules and intracellular processing. Although LprG activated TLR2, this alone was not sufficient to stimulate or inhibit T cell activation. A striking finding was that the carbohydrate moieties of LprG were required for optimal T cell activation, because recombinant LprG produced in Escherichia coli, or recombinant LprG produced in Mycobacterium smegmatis and digested by alpha-mannosidase, did not activate T cells. This study demonstrates that the universe of bacterial T cell Ags includes lipoglycoproteins, which act as TLR2 ligands but also require glycosylation for MHC class II-restricted T cell activation in vivo.

Class II major histocompatibility complex tetramer staining: progress, problems, and prospects

The use of major histocompatibility complex (MHC) tetramers in the detection and analysis of antigen-specific T cells has become more widespread since its introduction 11 years ago. Early challenges in the application of tetramer staining to CD4+ T cells centred around difficulties in the expression of various class II MHC allelic variants and the detection of low-frequency T cells in mixed populations. As many of the technical obstacles to class II MHC tetramer staining have been overcome, the focus has returned to uncertainties concerning how oligomer valency and T-cell receptor/MHC affinity affect tetramer binding. Such issues have become more important with an increase in the number of studies relying on direct ex vivo analysis of antigen-specific CD4+ T cells. In this review we discuss which problems in class II MHC tetramer staining have been solved to date, and which matters remain to be considered.

Decline in the frequencies of Borrelia burgdorferi OspA161 175-specific T cells after antibiotic therapy in HLA-DRB1*0401-positive patients with antibiotic-responsive or antibiotic-refractory lyme arthritis

Synovitis in patients with antibiotic-refractory Lyme arthritis persists for months to several years after antibiotic therapy. This course, which may result from infection-induced autoimmunity, is associated with T cell recognition of Borrelia burgdorferi outer surface protein A (OspA(161-175)) and with HLA-DR molecules that bind this epitope, including the DRB1*0401 molecule. In this study, we used tetramer reagents to determine the frequencies of OspA(161-175)-specific T cells in samples of PBMC and synovial fluid mononuclear cells (SFMC) from 13 DRB1*0401-positive patients with antibiotic-responsive or antibiotic-refractory arthritis. Initially, three of the six patients (50%) with antibiotic-responsive arthritis and four of the seven patients (57%) with antibiotic-refractory arthritis had frequencies of OspA(161-175)-specific CD4(+) T cells in peripheral blood above the cutoff value of 4 per 10(5) cells. Among the five patients with concomitant PBMC and SFMC, four (80%) had OspA tetramer-positive cells at both sites, but the mean frequency of such cells was 16 times higher in SFMC, reaching levels as high as 1,177 per 10(5) cells. In the two patients in each patient group in whom serial samples were available, the frequencies of OspA(161-175)-specific T cells declined to low or undetectable levels during or soon after antibiotic therapy, months before the resolution of synovitis in the two patients with antibiotic-refractory arthritis. Thus, the majority of patients with Lyme arthritis initially have increased frequencies of OspA(161-175)-specific T cells. However, the marked decline in the frequency of such cells with antibiotic therapy suggests that persistent synovitis in the refractory group is not perpetuated by these cells.

MHC class II tetramer guided detection of Mycobacterium tuberculosis-specific CD4+ T cells in peripheral blood from patients with pulmonary tuberculosis

Novel diagnostic tools are needed to diagnose latent infection and to provide biologically meaningful surrogate markers to define cellular immune responses against Mycobacterium tuberculosis (MTB). Interferon gamma-based assays have recently been developed in addition to the more than 100-year-old tuberculin skin test (TST) for the immune diagnosis of MTB in blood. The advent of soluble MHC/peptide tetramer molecules allows to objectively enumerate antigen-specific T cells. We identified novel MHC class II-restricted MTB epitopes and used HLA-DR4 tetrameric complexes to visualize ex vivo CD4(+) T cells directed against the antigens Ag85B and the 19-kDa lipoprotein, shared between MTB and other Mycobacterium species, and CD4(+) T cells which recognize the MTB-associated ESAT-6 antigen. MTB-reactive CD4(+) T cells reside predominantly in the CD45RA(+) CD28(+) and CD45(-) CD28(+) T-cell subset and recognize naturally processed and presented MTB epitopes. HLA-DR4-restricted, Ag85B or ESAT-6-specific CD4(+) T cells show similar dynamics over time in peripheral blood mononuclear cells (PBMC) when compared with CD8(+) T cells directed against the corresponding HLA-A2-presented MTB epitopes in patients with pulmonary MTB infection and subsequent successful therapy. This was not found to be true for T-cell responses directed against the 19-kDa lipoprotein. The dissection of the cellular immune response in M. tuberculosis infection will enable novel strategies for monitoring MTB vaccine candidates and to gauge CD4(+) T cells directed against MTB.

Tetramer visualization of gut-homing gluten-specific T cells in the peripheral blood of celiac disease patients

Tetramers of MHC-peptide complexes are used for detection and characterization of antigen-specific T cell responses, but they require knowledge about both antigenic peptide and the MHC restriction element. The successful application of these reagents in human diseases involving CD4+ T cells is limited. Celiac disease, an intestinal inflammation driven by mucosal CD4+ T cells recognizing wheat gluten peptides in the context of disease-associated HLA-DQ molecules, is an ideal model to test the potential clinical use of these reagents. We investigated whether gluten-specific T cells can be detected in the peripheral blood of celiac disease patients using DQ2 tetramers. Nine DQ2+ patients and six control individuals on a gluten-free diet were recruited to the study. Participants consumed 160 g of gluten-containing bread daily for 3 days. After bread-challenge, gluten-specific T cells were detectable in the peripheral blood of celiac patients but not controls both directly by tetramer staining and indirectly by enzyme-linked immunospot. These T cells expressed the beta(7) integrin indicative of gut-homing properties. Most of the cells had a memory phenotype, but many other phenotypic markers showed a heterogeneous pattern. Tetramer staining of gluten-specific T cells has the potential to be used for diagnosis of celiac disease.

Clonal diversification in OspA-specific antibodies from peripheral circulation of a chronic Lyme arthritis patient

Chronic, antibiotic treatment-resistant Lyme arthritis develops in a subset of patients following infection with the tick-borne spirochete Borrelia burgdorferi and persists after apparent microbial clearance. IgG responses to Outer Surface Protein (Osp) A, an abundant spirochetal lipoprotein, correlate with both severity and duration of joint inflammation. Characterization of this OspA-directed antibody response is, therefore, important for understanding some of the mechanisms that sustain persistent pathology. Such analyses in Lyme arthritis patients have been previously hampered by relatively small amounts of clinical blood samples, as well as the general intractability and low success rates of B-cell immortalization procedures. Here we describe a robust method for generation of OspA-specific monoclonal antibody fragments from archival cell samples employing a three-step procedure -- isolation of single OspA-specific B-cells, their ex vivo clonal expansion and production of expressed immunoglobulins as single chain variable region fragments (scFvs). Interestingly, two of three scFvs generated from a single patient were of a common clonal origin, additional somatic mutations in the downstream member resulting in a concomitant modulation of antigen binding affinity. Computational docking of OspA into corresponding Fv domains, generated by molecular modeling, reveals subtle binding site differences which could account for the observed alteration in ligand binding. Besides their utility as standards in routine diagnostic assays, being the first described OspA-specific human monoclonal reagents, these scFvs are useful tools for analysis of the anti-OspA repertoire in patients and for identification of putative human mimics of the bacterial protein.

Detection of low avidity desmoglein 3-reactive T cells in pemphigus vulgaris using HLA-DR beta 1*0402 tetramers

In the present study, we developed a HLA class II tetramer-based detection system utilizing DRB1*0402 tetramers loaded with recently identified immunodominant peptides of desmoglein 3 (Dsg3), the major autoantigen of pemphigus vulgaris (PV). Initial experiments demonstrated staining of a Dsg3-reactive T cell hybridoma which was derived from HLA-DR0402-transgenic mice with loaded PE-labeled DRbeta1*0402 tetramers. However, staining of autoreactive T cell clones (TCC) derived from PV patients resulted only in positive staining by addition of exogenous peptides to the staining reactions. There was a dose-dependent specific binding of TCC to the tetramers with the agonistic Dsg3 peptide which was not altered by exogenous unrelated Dsg3 peptide. Noteworthy, the TCC did not stain with HLA-DR4 tetramers complexed with unrelated Dsg3 peptides. The findings of this study suggest that HLA class II tetramers may provide a highly specific approach to monitor ex vivo the T cellular autoimmune response against Dsg3 in patients with PV.

Autoantibodies from synovial lesions in chronic, antibiotic treatment-resistant Lyme arthritis bind cytokeratin-10

Although the causative agent of Lyme disease is definitively known to be the tick-borne spirochete, Borrelia burgdorferi, the etiology of chronic joint inflammation that ensues in a subset of patients remains less well understood. Persistence of arthritis after apparent eradication of the spirochete suggests an autoimmune reaction downstream of the original bacterial infection. We have generated recombinant Ab probes from synovial lesions within affected arthritic joints in an attempt to recapitulate disease-relevant Ag-binding specificities at the site of injury. Using this panel of intra-articular probes, as well as Ab fragments derived from patient peripheral blood, we have identified cytokeratin 10, present in synovial microvascular endothelium, as a target ligand and a putative autoantigen in chronic, antibiotic treatment-resistant Lyme arthritis. Furthermore, there is cross-reactivity between cytokeratin 10 and a prominent B. burgdorferi Ag, outer surface protein A. Release of the self protein in the context of inflammation-induced tissue injury and the resulting in situ response to it could set in motion a feed-forward loop, which amplifies the inflammatory process, thereby rendering it chronic and self-perpetuating, even in the absence of the inciting pathogen.

Efficient Immunization and Cross-Priming by Vaccine Adjuvants Containing TLR3 or TLR9 Agonists Complexed to Cationic Liposomes

Complexing TLR9 agonists such as plasmid DNA to cationic liposomes markedly potentiates their ability to activate innate immunity. We therefore reasoned that liposomes complexed with DNA or other TLR agonists could be used as effective vaccine adjuvants. To test this hypothesis, the vaccine adjuvant effects of liposomes complexed to TLR agonists were assessed in mice. We found that liposomes complexed to nucleic acids (liposome-Ag-nucleic acid complexes; LANAC) were particularly effective adjuvants for eliciting CD4(+) and CD8(+) T cell responses against peptide and protein Ags. Notably, LANAC containing TLR3 or TLR9 agonists effectively cross-primed CD8(+) T cell responses against even low doses of protein Ags, and this effect was independent of CD4(+) T cell help. Ag-specific CD8(+) T cells elicited by LANAC adjuvants were functionally active and persisted for long periods of time in tissues. In a therapeutic tumor vaccine model, immunization with the melanoma peptide trp2 and LANAC adjuvant controlled the growth of established B16 melanoma tumors. In a prophylactic vaccine model, immunization with the Mycobacterium tuberculosis protein ESAT-6 with LANAC adjuvant elicited significant protective immunity against aerosol challenge with virulent M. tuberculosis. These results suggest that certain TLR agonists can be combined with cationic liposomes to produce uniquely effective vaccine adjuvants capable of eliciting strong T cell responses against protein and peptide Ags.

Antibiotic-refractory Lyme arthritis is associated with HLA-DR molecules that bind a Borrelia burgdorferi peptide

An association has previously been shown between antibiotic-refractory Lyme arthritis, the human histocompatibility leukocyte antigen (HLA)–DR4 molecule, and T cell recognition of an epitope of Borrelia burgdorferi outer-surface protein A (OspA_163–175). We studied the frequencies of HLA-DRB1-DQA1-DQB1 haplotypes in 121 patients with antibiotic-refractory or antibiotic-responsive Lyme arthritis and correlated these frequencies with in vitro binding of the OspA_163–175 peptide to 14 DRB molecules. Among the 121 patients, the frequencies of HLA-DRB1-DQA1-DQB1 haplotypes were similar to those in control subjects. However, when stratified by antibiotic response, the frequencies of DRB1 alleles in the 71 patients with antibiotic-refractory arthritis differed significantly from those in the 50 antibiotic-responsive patients (log likelihood test, P = 0.006; exact test, P = 0.008; effect size, Wn = 0.38). 7 of the 14 DRB molecules (DRB1*0401, 0101, 0404, 0405, DRB5*0101, DRB1*0402, and 0102) showed strong to weak binding of OspA_163–175, whereas the other seven showed negligible or no binding of the peptide. Altogether, 79% of the antibiotic-refractory patients had at least one of the seven known OspA peptide–binding DR molecules compared with 46% of the antibiotic-responsive patients (odds ratio = 4.4; P < 0.001). We conclude that binding of a single spirochetal peptide to certain DRB molecules is a marker for antibiotic-refractory Lyme arthritis and might play a role in the pathogenesis of the disease.

Major histocompatibility complex and T cell interactions of a universal T cell epitope from Plasmodium falciparum circumsporozoite protein

A 20-residue sequence from the C-terminal region of the circumsporozoite protein of the malaria parasite Plasmodium falciparum is considered a universal helper T cell epitope because it is immunogenic in individuals of many major histocompatibility complex (MHC) haplotypes. Subunit vaccines containing T* and the major B cell epitope of the circumsporozoite protein induce high antibody titers to the malaria parasite and significant T cell responses in humans. In this study we have evaluated the specificity of the T* sequence with regard to its binding to the human class II MHC protein DR4 (HLA-DRB1*0401), its interactions with antigen receptors on T cells, and the effect of natural variants of this sequence on its immunogenicity. Computational approaches identified multiple potential DR4-binding epitopes within T*, and experimental binding studies confirmed the following two tight binding epitopes: one located toward the N terminus (the T*-1 epitope) and one at the C terminus (the T*-5 epitope). Immunization of a human DR4 volunteer with a peptide-based vaccine containing the T* sequence elicited CD4+ T cells that recognize each of these epitopes. Here we present an analysis of the immunodominant N-terminal epitope T*-1. T*-1 residues important for interaction with DR4 and with antigen receptors on T*-specific T cells were mapped. MHC tetramers carrying DR4/T*-1 MHC-peptide complexes stained and efficiently stimulated these cells in vitro. T*-1 overlaps a region of the protein that has been described as highly polymorphic; however, the particular T*-1 residues required for anchoring to DR4 were highly conserved in Plasmodium sequences described to date.

Immune control of Babesia bovis infection

Babesia bovis causes an acute and often fatal infection in adult cattle, which if resolved, leads to a state of persistent infection in otherwise clinically healthy cattle. Persistently infected cattle are generally resistant to reinfection with related parasite strains, and this resistance in the face of infection is termed concomitant immunity. Young animals are generally more resistant than adults to B. bovis infection, which is dependent on the spleen. Despite the discovery of B. bovis over a century ago, there are still no safe and effective vaccines that protect cattle against this most virulent of babesial pathogens. Immunodominant antigens identified by serological reactivity and dominant T-cell antigens have failed to protect cattle against challenge. This review describes the innate and acquired immune mechanisms that define resistance in young calves and correlate with the development of concomitant immunity in older cattle following recovery from clinical disease. The first sections will discuss the innate immune responses by peripheral blood- and spleen-derived macrophages in cattle induced by B. bovis merozoites and their products that limit parasite replication, and comparison of natural killer cell responses in the spleens of young (resistant) and adult (susceptible) cattle. Later sections will describe a proteomic approach to discover novel antigens, especially those recognized by immune CD4+ T lymphocytes. Because immunodominant antigens have failed to stimulate protective immunity, identification of subdominant antigens may prove to be important for effective vaccines. Identification of CD4+ T-cell immunogenic proteins and their epitopes, together with the MHC class II restricting elements, now makes possible the development of MHC class II tetramers and application of this technology to both quantify antigen-specific lymphocytes during infection and discover novel antigenic epitopes. Finally, with the imminent completion of the B. bovis genome-sequencing project, strategies using combined genomic and proteomic approaches to identify novel vaccine candidates will be reviewed. The availability of an annotated B. bovis genome will, for the first time, enable identification of non-immunodominant proteins that may stimulate protective immunity.