Evaluation of a fit-for-purpose assay to monitor antigen-specific functional CD4+ T-cell subpopulations in rheumatoid arthritis using flow cytometry-based peptide-MHC class-II tetramer staining

Antigen-specific T cells can serve as a response biomarker in non-clinical or clinical immunotherapy studies in autoimmune disease. There are protocols with optimized multimer staining methods to detect peptide (p)MHCII+ CD4+ T cells, and some qualified and validated protocols for pMHCI+ CD8+ T cells. However, no protocol is fully or partially qualified to enumerate and characterize antigen-specific pMHCII+ CD4+ T cells from patient samples. Implementing such an assay requires a desired level of specificity and precision, in terms of assay repeatability and reproducibility. In transgenic type II collagen (CII)-immunized HLA-DR1/DR4 humanized mouse models of collagen-induced arthritis (CIA), CII259-273-specific T cells dominantly expand. Therefore antigen-specific T cells recognizing this epitope presented by rheumatoid arthritis (RA)-associated risk HLA-DR allomorphs are of interest to understand disease progression and responses to immunotherapy in RA patients. Using HLA-DRB1∗04:01 or ∗01:01-collagen type II (CII)259-273 tetramers, we evaluated parameters influencing precision and reproducibility of an optimized flow cytometry-based method for antigen-specific CD4+ T cells and eight specific subpopulations with and without tetramer positivity. We evaluated specificity, precision, and reproducibility for research environments and non-regulated laboratories. The assay has excellent overall precision with %CV<25% for intra-assay repeatability, inter-analyst precision, and inter-assay reproducibility. The precision of the assay correlated negatively with the cell viability after thawing, indicating that post-thaw viability is a critical parameter for reproducibility. This assay is suitable for longitudinal analysis of treatment response and disease activity outcome in RA patients, and adaptable for translational or immunotherapy clinical trial settings.

CD8+ T Cells Expressing an HLA-DR1 Chimeric Antigen Receptor Target Autoimmune CD4+ T Cells in an Antigen-Specific Manner and Inhibit the Development of Autoimmune Arthritis

Ag-specific immunotherapy is a long-term goal for the treatment of autoimmune diseases; however developing a means of therapeutically targeting autoimmune T cells in an Ag-specific manner has been difficult. Through the engineering of an HLA-DR1 chimeric Ag receptor (CAR), we have produced CD8⁺ CAR T cells that target CD4⁺ T cells in an Ag-specific manner and tested their ability to inhibit the development of autoimmune arthritis in a mouse model. The DR1 CAR molecule was engineered to contain CD3ζ activation and CD28 signaling domains and a covalently linked autoantigenic peptide from type II collagen (CII; DR1-CII) to provide specificity for targeting the autoimmune T cells. Stimulation of the DR1-CII CAR T cells by an anti-DR Ab induced cytokine production, indicating that the DR1-CAR functions as a chimeric molecule. In vitro CTL assays using cloned CD4⁺ T cells as target cells demonstrated that the DR1-CII CAR T cells efficiently recognize and kill CD4⁺ T cells that are specific for the CII autoantigen. The CTL function was highly specific, as no killing was observed using DR1-restricted CD4⁺ T cells that recognize other Ags. When B6.DR1 mice, in which autoimmune arthritis had been induced, were treated with the DR1-CII CAR T cells, the CII-specific autoimmune CD4⁺ T cell response was significantly decreased, autoantibody production was suppressed, and the incidence and severity of the autoimmune arthritis was diminished. These data demonstrate that HLA-DR CAR T cells have the potential to provide a highly specific therapeutic approach for the treatment of autoimmune disease.

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 role of posttranslational modifications in generating neo-epitopes that bind to rheumatoid arthritis-associated HLA-DR alleles and promote autoimmune T cell responses

While antibodies to citrullinated proteins have become a diagnostic hallmark in rheumatoid arthritis (RA), we still do not understand how the autoimmune T cell response is influenced by these citrullinated proteins. To investigate the role of citrullinated antigens in HLA-DR1- and DR4-restricted T cell responses, we utilized mouse models that express these MHC-II alleles to determine the relationship between citrullinated peptide affinity for these DR molecules and the ability of these peptides to induce a T cell response. Using a set of peptides from proteins thought to be targeted by the autoimmune T cell responses in RA, aggrecan, vimentin, fibrinogen, and type II collagen, we found that while citrullination can enhance the binding affinity for these DR alleles, it does not always do so, even when in the critical P4 position. Moreover, if peptide citrullination does enhance HLA-DR binding affinity, it does not necessarily predict the generation of a T cell response. Conversely, citrullinated peptides can stimulate T cells without changing the peptide binding affinity for HLA-DR1 or DR4. Furthermore, citrullination of an autoantigen, type II collagen, which enhances binding affinity to HLA-DR1 did not enhance the severity of autoimmune arthritis in HLA-DR1 transgenic mice. Additional analysis of clonal T cell populations stimulated by these peptides indicated cross recognition of citrullinated and wild type peptides can occur in some instances, while in others cases the citrullination generates a novel T cell epitope. Finally, cytokine profiles of the wild type and citrullinated peptide stimulated T cells unveiled a significant disconnect between proliferation and cytokine production. Altogether, these data demonstrate the lack of support for a simplified model with universal correlation between affinity for HLA-DR alleles, immunogenicity and arthritogenicity of citrullinated peptides. Additionally they highlight the complexity of both T cell receptor recognition of citrulline as well as its potential conformational effects on the peptide:HLA-DR complex as recognized by a self-reactive cell receptor.

Autoantigens in rheumatoid arthritis and the potential for antigen-specific tolerising immunotherapy

Autoimmune diseases, including rheumatoid arthritis, develop and persist due to impaired immune self-tolerance, which has evolved to regulate inflammatory responses to injury or infection. After diagnosis, patients rarely achieve drug-free remission, and although at-risk individuals can be identified with genotyping, antibody tests, and symptoms, rheumatoid arthritis cannot yet be successfully prevented. Precision medicine is increasingly offering solutions to diseases that were previously considered to be incurable, and immunotherapy has begun to achieve this aim in cancer. Comparatively, modulating autoantigen-specific immune responses with immunotherapy for the cure of autoimmune diseases is at a relatively immature stage. Current treatments using non-specific immune or inflammatory suppression increase susceptibility to infection, and are rarely curative. However, early stage clinical trials suggesting that immunotherapy might allow extended duration of remission and even prevention of progression to disease suggest modulating tolerance in rheumatoid arthritis could be a promising opportunity for therapy.

Dendritic cells, T cells and their interaction in rheumatoid arthritis

Dendritic cells (DCs) are the key professional antigen-presenting cells which bridge innate and adaptive immune responses, inducing the priming and differentiation of naive to effector CD4+ T cells, the cross-priming of CD8+ T cells and the promotion of B cell antibody responses. DCs also play a critical role in the maintenance of immune homeostasis and tolerance. DC-T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). Here we describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self-peptide by DCs that triggers differentiation and activation of autoreactive T cells. Finally, we discuss the emerging field of targeting the DC-T cell interaction for antigen-specific immunotherapy of RA.

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.

Rapid identification and expression of human TCRs in retrogenic mice

Single-cell paired TCR identification is a powerful tool, but has been limited in its previous incompatibility with further functional analysis. The current protocol describes a method to clone and functionally evaluate in vivo TCRs derived from single antigen-responsive human T cells and monoclonal T cell lines. We have improved upon current PCR-based TCR sequencing protocols by developing primers that allow amplification of human TCRα and TCRβ variable regions, while incorporating specific restriction cut sites for direct subcloning into the template retroviral vector. This streamlined approach for generating human:mouse chimeric TCR vectors allows for rapid TCR expression in humanized-retrogenic (hu-Rg) mice through retroviral mediated stem cell gene transfer. Using widely available techniques and equipment, this method is easily adaptable by most laboratories. This is the first TCR identification protocol that is efficiently combined with subsequent in vivo TCR expression.

Engineered regulatory T cells coexpressing MHC class II:peptide complexes are efficient inhibitors of autoimmune T cell function and prevent the development of autoimmune arthritis

Regulatory T cells (Tregs) are critical homeostatic components in preventing the development of autoimmunity, and are a major focus for their therapeutic potential for autoimmune diseases. To enhance the efficacy of Tregs in adoptive therapy, we developed a strategy for generating engineered Tregs that have the capacity to target autoimmune T cells in an Ag-specific manner. Using a retroviral expression system encoding Foxp3 and HLA-DR1 covalently linked to the immunodominant peptide of the autoantigen type II collagen (DR1-CII), naive T cells were engineered to become Tregs that express DR1-CII complexes on their surface. When these cells were tested for their ability to prevent the development of collagen induced arthritis, both the engineered DR1-CII-Foxp3 and Foxp3 only Tregs significantly reduced the severity and incidence of disease. However, the mechanism by which these two populations of Tregs inhibited disease differed significantly. Disease inhibition by the DR1-CII-Foxp3 Tregs was accompanied by significantly lower numbers of autoimmune CII-specific T cells in vivo and lower levels of autoantibodies in comparison with engineered Tregs expressing Foxp3 alone. In addition, the numbers of IFN-γ- and IL-17-expressing T cells in mice treated with DR1-CII-Foxp3 Tregs were also significantly reduced in comparison with mice treated with Foxp3 engineered Tregs or vector control cells. These data indicate that the coexpression of class II autoantigen-peptide complexes on Tregs provides these cells with a distinct capacity to regulate autoimmune T cell responses that differs from that used by conventional Tregs.

Wnt signaling pathway in rheumatoid arthritis, with special emphasis on the different roles in synovial inflammation and bone remodeling

Rheumatoid arthritis (RA) is a chronic symmetrical autoimmune disease of unknown etiology that affects primarily the diarthrodial joints. Characteristic features of RA pathogenesis are synovial inflammation and proliferation accompanied by cartilage erosion and bone loss. Fibroblast-like synoviocytes (FLS) display an important role in the pathogenesis of RA. Several lines of evidence show that the Wnt signaling pathway significantly participates in the RA pathogenesis. The Wnt proteins are glycoproteins that bind to the Fz receptors on the cell surface, which leads to several important biological functions, such as cell differentiation, embryonic development, limb development and joint formation. Accumulated evidence has suggested that this signaling pathway plays a key role in the FLS activation, bone resorption and joint destruction during RA development. Greater knowledge of the role of the Wnt signaling pathway in RA could improve understanding of the RA pathogenesis and the differences in RA clinical presentation and prognosis. In this review, new advances of the Wnt signaling pathway in RA pathogenesis are discussed, with special emphasis on its different roles in synovial inflammation and bone remodeling. Further studies are needed to reveal the important role of the members of the Wnt signaling pathway in the RA pathogenesis and treatment.

Characterization of inhibitory T cells induced by an analog of type II collagen in an HLA-DR1 humanized mouse model of autoimmune arthritis

Introduction

We used DR1 transgenic mice and covalently linked DR1 multimers to characterize analog-specific inhibitory T cells in collagen-induced arthritis (CIA). Because of the low numbers of antigen-specific T cells in wild-type mice, functional T-cell studies in autoimmune arthritis have been challenging. The use of T-cell receptor (TCR) transgenic mice has provided useful information, but such T cells may not represent the heterogeneous T-cell response that occurs in natural settings. Our focus was to develop tools to identify and characterize the population of immunoregulatory T cells induced in wild-type mice by an analog peptide of CII_259-273, which contains amino acid substitutions at positions 263 (N) and 266 (D) (analog peptide A12).

Methods

DR1 multimers, developed by loading empty class II molecules with exogenous peptide, provide a method for visualizing antigen-specific T cells with flow cytometry. However, the low binding avidity of A12 for the major histocompatibility complex (MHC) made this strategy untenable. To overcome this problem, we generated DR1 multimers in which the analog peptide A12 was covalently linked, hoping that the low-avidity analog would occupy enough binding clefts to allow detection of the responsive T cells.

Results

Staining with the tetramer revealed that A12-specific T cells were readily detectable at 10 days after immunization. These CD4(+) T cells are a highly selective subset of the TCR repertoire and have a limited clonality. Analysis of cytokine expression showed that cells detected by tetramer (A12) expressed primarily suppressive cytokines (interleukin-4 (IL-4) and IL-10) in response to collagen, compared with control cells. Although they did not express Fox-p3, they were extremely effective in preventing and suppressing inflammatory arthritis.

Conclusions

In summary, our studies showed that the use of covalently linked multimers allows characterization of analog-specific T cells that are otherwise difficult to detect. The suppressive character of the analog-specific T-cell response suggests that these cells attenuate autoimmunity and differ significantly in phenotype from the inflammatory T cells predominantly found in arthritic joints. Such reagents will become powerful tools to study T-cell responses in RA patients in upcoming clinical trials.

Associations between six classical HLA loci and rheumatoid arthritis: a comprehensive analysis

Although the HLA region contributes to one-third of the genetic factors affecting rheumatoid arthritis (RA), there are few reports on the association of the disease with any of the HLA loci other than the DRB1. In this study we examined the association between RA and the alleles of the six classical HLA loci including DRB1. Six HLA loci (HLA-A, -B, -C, -DRB1, -DQB1 and -DPB1) of 1659 Japanese subjects (622 cases; 488 anti-cyclic citrullinated peptides (CCP) antibody (Ab) positive (82.6%); 103 anti-CCP Ab negative (17.4%); 31 not known and 1037 controls) were genotyped. Disease types and positivity/negativity for CCP autoantibodies were used to stratify the cases. Statistical and genetic assessments were performed by Fisher's exact tests, odds ratio, trend tests and haplotype estimation. None of the HLA loci were significantly associated with CCP sero-negative cases after Bonferroni correction and we therefore limited further analyses to using only the anti CCP-positive RA cases and both anti-CCP positive and anti-CCP negative controls. Some alleles of the non-DRB1 HLA loci showed significant association with RA, which could be explained by linkage disequilibrium with DRB1 alleles. However, DPB1*02:01, DPB1*04:01 and DPB1*09:01 conferred RA risk/protection independently from DRB1. DPB1*02:01 was significantly associated with the highly erosive disease type. The odds ratio of the four HLA-loci haplotypes with DRB1*04:05 and DQB1*04:01, which were the high-risk HLA alleles in Japanese, varied from 1.01 to 5.58. C*07:04, and B*15:18 showed similar P-values and odds ratios to DRB1*04:01, which was located on the same haplotype. This haplotype analysis showed that the DRB1 gene as well as five other HLA loci is required for a more comprehensive understanding of the genetic association between HLA and RA than analyzing DRB1 alone.

Genetics of rheumatoid arthritis: time for a change!

PURPOSE OF REVIEW

To review recent progress in the genetics of rheumatoid arthritis (RA) and discuss the implications for understanding the pathogenesis of the disease as well as clinical application.

RECENT FINDINGS

Protection against anticitrullinated protein antibody (ACPA) positive RA was shown to be associated wit DRB1*1301. Genome-wide association studies (GWASs) added about 10 new loci to the list of already more than 20 loci associated with RA, so the list is now over 30. Typing for the known risk loci is not helpful for prediction of the risk for RA. It is remarkable how few functional studies have been published.

SUMMARY

Known genetic factors explain 50-60% of the genetic variance for susceptibility to ACPA-positive and 30-50% for ACPA-negative RA. Searching for the remaining missing or hidden heritability is in all probability not going to yield much for prediction and/or targeted intervention. Therefore, I conclude that if you want to find more genes you should have a lot of patience, time and money, stop with convential GWAS and invest in large-scale sequencing of selected patients and controls. I have a better suggestion, however: use the information that is already available to perform functional studies in order to understand the mechanism of the known associations!

Identification of small-molecule inhibitors against human leukocyte antigen-death receptor 4 (HLA-DR4) through a comprehensive strategy

Rheumatoid arthritis (RA) is an autoimmune disease mediated by T-lymphocytes and associated with the human leukocyte antigen-death receptor 4 (HLA-DR4). The HLA-DR4 protein selectively interacts with the antigenic peptides on the cell surface and presents them to the T cell receptor (TCR) on CD4+ T cells. The HLA-DR4-antigen-TCR complex initiates the autoimmune response and eventually causes the chronic inflammation within patients bodies. To inhibit HLA-DR4-restricted T cell activation, an ideal approach is to discover non-T cell stimulating substrates that specifically bind to HLA-DR4. In this paper, a comprehensive structure-based design strategy involved de novo design approach, pharmacophore search, and dock method was presented and applied to "simplify" the known binding peptide ligand of HLA-DR4 and identified specific small-molecule inhibitors for HLA-DR4. The designed three-step strategy successfully identified five nonpeptide ligands with novel scaffolds from a chemical library containing 4 × 10(6) commercially available compounds within a tolerable computing time. The identified five chemicals, BAS-0219606, T0506-2494, 6436645, 3S-71981, and KM 11073, are all non-T cell stimulators and are able to significantly inhibit HLA-DR4-restricted T cell activation induced by type II collagen (CII) 263-272 peptide. IC(50) for the best two potentials, BAS-0219606 and T0506-2494, was 31 and 17 μM, respectively, which is equivalent or better than the known peptide ligands. It is hopeful that they can be used as effective therapeutic means for further treatment of RA patients. In addition, the comprehensive strategy presented in this paper exhibited itself to be an effective flow line from peptide ligands to small-molecule inhibitors and will have applications to other targets.