Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis

Modulating co-stimulation: a rational strategy in the treatment of rheumatoid arthritis?

Rheumatoid arthritis (RA) is a common destructive inflammatory disease that affects 0.5-1% of the population in many countries. Even though several new treatments have been introduced for patients with RA, a considerable proportion of patients do not benefit from these, and the need for alternative treatment strategies is clear. This review explores the potential for a therapy targeting the adaptive immune system by modulating co-stimulation of T cells with a CTLA4-Ig fusion protein (abatacept).

A HEV-restricted sulfotransferase is expressed in rheumatoid arthritis synovium and is induced by lymphotoxin-alpha/beta and TNF-alpha in cultured endothelial cells

BACKGROUND

The recruitment of lymphocytes to secondary lymphoid organs relies on interactions of circulating cells with high endothelial venules (HEV). HEV are exclusive to these organs under physiological conditions, but they can develop in chronically-inflamed tissues. The interaction of L-selectin on lymphocytes with sulfated glycoprotein ligands on HEV results in lymphocyte rolling, which represents the initial step in lymphocyte homing. HEV expression of GlcNAc6ST-2 (also known as HEC-GlcNAc6ST, GST-3, LSST or CHST4), an HEV-restricted sulfotransferase, is essential for the elaboration of L-selectin functional ligands as well as a critical epitope recognized by MECA-79 mAb.

RESULTS

We examined the expression of GlcNAc6ST-2 in relationship to the MECA-79 epitope in rheumatoid arthritis (RA) synovial vessels. Expression of GlcNAc6ST-2 was specific to RA synovial tissues as compared to osteoarthritis synovial tissues and localized to endothelial cells of HEV-like vessels and small flat-walled vessels. Double MECA-79 and GlcNAc6ST-2 staining showed colocalization of the MECA-79 epitope and GlcNAc6ST-2. We further found that both TNF-alpha and lymphotoxin-alphabeta induced GlcNAc6ST-2 mRNA and protein in cultured human umbilical vein endothelial cells.

CONCLUSION

These observations demonstrate that GlcNAc6ST-2 is induced in RA vessels and provide potential cytokine pathways for its induction. GlcNAc6ST-2 is a novel marker of activated vessels within RA ectopic lymphoid aggregates. This enzyme represents a potential therapeutic target for RA.

Management of therapy-resistant systemic lupus erythematosus with rituximab: report of a case and review of the literature

Therapy of systemic lupus erythematosus (SLE) with major organ involvement consists of aggressive immunosuppression with glucocorticoids and cytotoxic agents. When remission is achieved, maintenance therapy is begun to reduce the risk of relapse while minimizing toxicity. Remission with standard therapy is, however, not always achieved. We discribe a women with SLE and microangiopathic haemolytic anaemia and thrombocytopenia, pneumonitis and nephritis refractory to high-dose steroids, pulse cyclophosphamide, plasmapheresis and intravenous immunoglobulins. The anti-CD20 monoclonal antibody rituximab was administered, resulting in major clinical and biochemical improvement. Therapy-resistant SLE generally has an ominous prognosis. A few anecdotal reports and small open studies describe beneficial effects of rituximab in these cases. Rituximab may be a promising new approach to improve the dismal outcome of therapy-resistant SLE.

Rheumatoid arthritis: developing pharmacological therapies

Rheumatoid arthritis (RA) is a chronic inflammatory disease that often results in significant morbidity, mortality and disability. Over the past 20 years a better understanding of the pathogenesis of RA has led to the development of new approaches to disease treatment. The recent introduction of biological agents has changed the treatment paradigm for RA. The success of early biological therapies including TNF-alpha and IL-1 antagonists has spurred interest in the development of additional novel targets in the treatment of RA. Biological therapies approved for other indications, such as rituximab, are now being evaluated for the treatment of rheumatic diseases such as RA. A co-stimulatory blocker, abatacept, is also in pivotal Phase III trials. This article reviews evolving pharmacological therapies in RA with an emphasis on the newer approaches to treatment including inhibition of cognate signalling and T- and B-cell targets.

[Rituximab: a original biotherapy in auto-immune disorders]

SUBJECT

After several decades of hegemony of the T lymphocyte, recent work has suggested the importance of the B lymphocyte in auto-immune diseases. As a consequence, there has emerged over the last few years the idea of using anti-B lymphocyte therapy, in particular rituximab (a chimeric anti-CD20 monoclonal antibody).

CURRENT TOPICS AND IMPORTANT RESULTS

This review addresses various current topics: a) the role of B lymphocytes in auto-immune diseases, notably their capacity to be antigen presenting cells and to be activated by original systems like Blys/Baff; b) the mechanism of action of rituximab (apoptosis, complement-dependent cytotoxicity and antibody-dependent cell cytotoxicity) and the phenomena explaining failures and cases escaping treatment, in particular among lymphoproliferations; c) The results include efficacy and tolerance data for the principal auto-immune affections. Among these, the most promising indications would seem to be for rheumatoid polyarthritis and systemic lupus erythematosis, although some preliminary open studies point to an effect in Goujerot-Sjögren's syndrome, neuropathies, auto-immune cytopenia, idiopathic thrombocytopenic purpura, cryoagglutinins, blistering cutaneous affections...

PERSPECTIVES AND PROJECTS

Controlled studies will be required to determine the true efficacy and tolerance of this molecule, as it is imperative to validate these new immunotherapeutic strategies, above all when they concern innovative and expensive therapy. Nevertheless, these different observations arouse great hopes and at the same time exciting questions, notably as to the role of B lymphocytes in auto-immune diseases.

Graft-versus-tumor response in patients with multiple myeloma is associated with antibody response to BCMA, a plasma-cell membrane receptor

Donor lymphocyte infusions (DLIs) induce effective graft-versus-tumor responses in patients with multiple myeloma who relapse after allogeneic hematopoietic stem-cell transplantation. The graft-versus-myeloma response is presumably mediated primarily by donor T cells, but recent studies have also demonstrated the presence of antibodies specific for a variety of myeloma-associated antigens in patients who achieve complete remission after DLI. One of the B-cell antigens identified in these studies was B-cell maturation antigen (BCMA), a transmembrane receptor of the tumor necrosis factor (TNF) superfamily that is selectively expressed by mature B cells. The present studies were undertaken to characterize the functional significance of antibodies to BCMA in vivo. Using transfected cells expressing BCMA, antibodies in patient serum were found to react with the cell-surface domain of BCMA. Post-DLI patient serum was able to induce complement-mediated lysis and antibody-dependent cellular cytotoxicity (ADCC) of transfected cells and primary myeloma cells expressing BCMA. BCMA antibodies were only found in post-DLI responders and not in other allogeneic transplant patients or healthy donors. These results demonstrate that BCMA is a target of donor B-cell immunity in patients with myeloma who respond to DLI. Antibody responses to cell-surface BCMA may contribute directly to tumor rejection in vivo.

How do follicular dendritic cells interact intimately with B cells in the germinal centre?

The germinal centre is a dynamic microenvironment where antigen-activated B cells rapidly expand and differentiate, generating plasma cells and memory B cells. These cellular events are accompanied by dramatic changes in the antibody molecules that undergo somatic hypermutation and isotype switching. Follicular dendritic cells (FDCs) are the stromal cells located in the germinal centre. Although the capacity of FDCs to present antigen to B cells through antigen-antibody complexes has been recognized for many years, additional critical functions of FDCs have only recently been recognized. FDCs prevent apoptosis of germinal centre B cells and stimulate cellular interaction and proliferation. Here, we review the FDC signalling molecules that have recently been identified, some of which offer potential therapeutic targets for autoimmune diseases and B-cell lymphomas.

Importance of Cellular Microenvironment and Circulatory Dynamics in B Cell Immunotherapy

B cell immunotherapy has emerged as a mainstay in the treatment of lymphomas and autoimmune diseases. Although the microenvironment has recently been demonstrated to play critical roles in B cell homeostasis, its contribution to immunotherapy is unknown. To analyze the in vivo factors that regulate mechanisms involved in B cell immunotherapy, we used a murine model for human CD20 (hCD20) expression in which treatment of hCD20(+) mice with anti-hCD20 mAbs mimics B cell depletion observed in humans. We demonstrate in this study that factors derived from the microenvironment, including signals from the B cell-activating factor belonging to the TNF family/BLyS survival factor, integrin-regulated homeostasis, and circulatory dynamics of B cells define distinct in vivo mechanism(s) and sensitivities of cells in anti-hCD20 mAb-directed therapies. These findings provide new insights into the mechanisms of immunotherapy and define new opportunities in the treatment of cancers and autoimmune diseases.

Fibroblast-Like Synoviocytes of Mesenchymal Origin Express Functional B Cell-Activating Factor of the TNF Family in Response to Proinflammatory Cytokines

Immunohistochemical analysis revealed that the intimal lining cells of synovial tissue of inflamed joints of patients with rheumatoid arthritis differed from that of normal joints or of diseased joints in osteoarthritis in that they stained with mAb specific for the B cell-activating factor of the TNF family (BAFF; also called BLyS). We generated fibroblast-like synoviocytes (FLS) cell lines that were bereft of myelomonocytic cells to examine whether mesenchymal-derived FLS could express this critical B cell survival factor. We found that FLS expressed low amounts of BAFF mRNA relative to that of myelomonocytic cells. However, when various cytokines/factors were added to such FLS cell lines, we found that IFN-gamma or TNF-alpha were unique in that they could induce significant increases in BAFF mRNA and protein. Even minute amounts of IFN-gamma primed FLS for TNF-alpha, allowing the latter to stimulate significantly higher levels of BAFF mRNA and protein than could TNF-alpha alone. Consistent with this, B cells cocultured with IFN-gamma and/or TNF-alpha-treated FLS had a significantly greater viability than B cells cocultured with nontreated FLS. The enhanced protection of B cells afforded by IFN-gamma/TNF-alpha-treated FLS was inhibited by the addition of BAFF-R:Fc fusion protein. We conclude that the proinflammatory cytokines IFN-gamma and TNF-alpha can induce mesenchymal-derived FLS to express functional BAFF in vitro. The induced expression of BAFF on FLS by proinflammatory cytokines may enhance the capacity of such cells to protect B cells from apoptosis in inflammatory microenvironments in vivo.

Rituximab in the treatment of dermatomyositis: An open-label pilot study

OBJECTIVE

To test the hypothesis that B cells play a role in the pathophysiology of dermatomyositis (DM) by examining the effect of B cell depletion in patients with symptomatic DM. Patients were treated with rituximab, a CD20+ B cell-depleting monoclonal antibody.

METHODS

This was an open-label uncontrolled pilot trial in 7 adult patients with DM, 6 of whom had longstanding illness that was responding inadequately to a number of currently available immunosuppressive agents. All patients received 4 intravenous infusions of rituximab given at weekly intervals. Patients were followed up for up to 1 year without further treatment with rituximab. One patient was lost to followup. The principal efficacy outcome was muscle strength, measured by quantitative dynomometry.

RESULTS

All 6 evaluable patients exhibited major clinical improvement, with muscle strength increasing over baseline by 36-113%. Maximal improvements in muscle strength occurred as early as 12 weeks after the initial infusion of rituximab. CD20+ B cells were effectively depleted in all patients by 12 weeks. Four patients experienced a return of symptoms that coincided with the return of B cells before the 52-week end point. Two patients maintained their increased muscle strength at 52 weeks, and 1 of these patients maintained this strength even after the return of B cells. Other symptoms of DM, including rash, alopecia, and reduced forced vital capacity, improved markedly in patients with these symptoms. Rituximab was well tolerated, with no treatment-related severe or serious adverse events during the observation period of this study.

CONCLUSION

This small open-label study of DM patients treated with rituximab provided sufficiently encouraging results to justify a more formal evaluation of the value of B cell depletion therapy in the treatment of DM.

Management of Sight-Threatening Uveitis

Over the past 2 decades therapy for the treatment of intraocular inflammation (uveitis) has developed into a highly differentiated approach with an increasing number of drug options. This paper primarily summarises literature from the past 5 years (2000 to May 2004), gives an update on systemic immunosuppressive therapy for non-infectious uveitis and speculates about new developments that could become relevant in the near future for the treatment of uveitis patients. The spectrum of immunosuppressive drugs has been notably expanded by tumor necrosis factor inhibitors, but with some limitations to uveitis. Behcet's disease is an example of uveitis where a multisystem disorder can affect the eye very severely. This clinical example has been used to investigate the utility of many different types of immunosuppressive therapies and the clinical approach is extensively discussed in this review. An accompanying table summarises the proposed mode of action, standard dosage, common adverse effects, as well as estimated cost of current treatment options.

Rituximab treatment in patients with primary Sjögren's syndrome: An open-label phase II study

OBJECTIVE

To investigate the safety and efficacy of B cell depletion treatment of patients with active primary Sjögren's syndrome of short duration (early primary SS) and patients with primary SS and mucosa-associated lymphoid tissue (MALT)-type lymphoma (MALT/primary SS).

METHODS

Fifteen patients with primary SS were included in this phase II trial. Inclusion criteria for the early primary SS group were B cell hyperactivity (IgG >15 gm/liter), presence of autoantibodies (IgM rheumatoid factor, anti-SSA/SSB), and short disease duration (<4 years). Inclusion criteria for the MALT/primary SS group were primary SS and an associated MALT-type lymphoma (Ann Arbor stage IE) localized in the parotid gland. Patients were treated with 4 infusions of rituximab (375 mg/m2) given weekly after pretreatment with prednisone (25 mg) and clemastine. Patients were evaluated, using immunologic, salivary/lacrimal function, and subjective parameters, at baseline and at 5 and 12 weeks after the first infusion.

RESULTS

Significant improvement of subjective symptoms and an increase in salivary gland function was observed in patients with residual salivary gland function. Immunologic analysis showed a rapid decrease of peripheral B cells and stable levels of IgG. Human anti-chimeric antibodies (HACAs) developed in 4 of 15 patients (27%), all with early primary SS. Three of these patients developed a serum sickness-like disorder. Of the 7 patients with MALT/primary SS, complete remission was achieved in 3, and disease was stable in 3 and progressive in 1.

CONCLUSION

Findings of this phase II study suggest that rituximab is effective in the treatment of primary SS. The high incidence of HACAs and associated side effects observed in this study needs further evaluation.

B lymphocyte

Recent studies have revealed that B cells play a critical role in autoimmunity and disease expression through various functions, including autoantibody production, cytokine secretion, antigen presentation, and co-stimulatory effect. Selective targeting of B cells has been recently achieved using a chimeric monoclonal antibody against CD20 (Rituximab). Significant clinical efficacy has been demonstrated in several autoimmune diseases including rheumatoid arthritis and systemic lupus erythematosus by the infusion of this antibody. Rituxumab significantly improves the symptoms during the long period of complete B cell depletion. Understanding the dynamics of B cell involvement in autoimmune diseases will be crucial to the development of B cell-targeted strategies. Conversely, the findings derived from studies of anti-B cell therapy provide us a lot of important clues to clarify the pathogenesis of autoimmune diseases. This review focuses on recent data demonstrating the roles of B cells in autoimmune diseases as well as the current studies concerning the treatment of autoimmune diseases by Rituximab.

Immunological therapies for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory arthritis of the synovial joints that causes loss of function and a shortened life expectancy. In the last 10 years there have been major advances in the treatment of RA, including more aggressive use of disease-modifying anti-rheumatic drugs and the development of immune therapies targeted to molecules and cells important in the immunopathogenesis of RA. Molecular messengers that travel between cells (cytokines) have been found to be of major importance. Blocking the cytokine tumour necrosis factor alpha (TNF-alpha) produces significant improvement in RA, ankylosing spondylitis, psoriatic arthritis, psoriasis and Crohn's disease. The use of cytokine blockers has shown the extent to which immune and inflammatory pathways are shared in a number of inflammatory diseases. There has also been an important proof of principle that blocking single cytokines can produce profound effects in inflammatory diseases.

Association between thePTPN22 gene and rheumatoid arthritis and juvenile idiopathic arthritis in a UK population: Further support thatPTPN22 is an autoimmunity gene

OBJECTIVE

The protein tyrosine phosphatase N22 (PTPN22) gene exhibits regulatory activities for both T cells and B cells. A missense single-nucleotide polymorphism (SNP) within this gene (rs2476601) has recently been associated with 4 autoimmune diseases: rheumatoid arthritis (RA), systemic lupus erythematosus, autoimmune thyroid disease, and type 1 diabetes mellitus, all of which are T cell-mediated and associated with the elaboration of autoantibody. The aim of this study was to investigate associations of the missense SNP of PTPN22 in a number of autoimmune diseases in the UK population, including RA, juvenile idiopathic arthritis (JIA), psoriasis, psoriatic arthritis (PsA), and multiple sclerosis (MS), some of which have not been examined previously.

METHODS

The PTPN22 missense SNP was genotyped in 886 RA, 661 JIA, 279 psoriasis, 455 PsA, and 379 MS patients and in 595 healthy controls. Association with the PTPN22 SNP was analyzed by chi-square test as implemented in Stata software.

RESULTS

There was a significant association between the PTPN22 SNP and RA (P = 1.8 x 10(-8)) and JIA (P = 0.0005). In contrast, no association with psoriasis, PsA, or MS was detected.

CONCLUSION

We replicated the findings of a previous association with RA and identified a novel association with JIA. Together with previous data showing associations with other autoimmune diseases, our findings provide further evidence that the PTPN22 gene plays a role in the pathogenesis of a subgroup of autoimmune diseases.

Antibody responses to H-Y minor histocompatibility antigens correlate with chronic graft-versus-host disease and disease remission

Minor histocompatibility antigens (mHAs) are known targets of donor T cells after allogeneic hematopoietic stem cell transplantation (HSCT). In contrast, B-cell responses to mHAs have not been extensively characterized and the clinical significance of antibodies to mHAs is unknown. We tested 121 patients who underwent HSCT and 134 healthy donors for immunoglobulin G (IgG) antibodies against 5 mHAs encoded by genes on the Y chromosome (DBY, UTY, ZFY, RPS4Y, and EIF1AY). Antibodies to at least one H-Y protein developed in 52% of male patients with female donors compared with 8.7% of male patients with male donors (P < .0001), and in 41.4% of healthy females compared with 7.8% of healthy males (P < .0001). H-Y antibodies develop 4 to 12 months after transplantation and persist for long periods. The clinical significance of H-Y antibodies was characterized in 75 male patients with hematologic malignancies who received stem cells from female donors (F --> M HSCT). The presence of H-Y antibodies correlated with chronic graft-versus-host disease (GVHD) by univariate (odds ratio [OR] = 15.5; P < .0001) and multivariable logistic regression analysis (OR = 56.5; P < .0001). Antibody response to Y-chromosome encoded histocompatibility antigens (H-Y antigens) was also associated with maintenance of disease remission (P < .0001). B cells may provide a new target for immune intervention in chronic GVHD.

Emerging approaches for the therapy of autoimmune and chronic inflammatory disease

Progress in defining protein and gene signatures that characterize autoimmune-mediated inflammatory diseases has uncovered a large number of potential therapeutic targets. Preclinical data from rodent models can be generated rapidly, as can data from the genetic crosses of gene-deficient mice on autoimmune-susceptible backgrounds. But humans are not the same as mice, and however robust preclinical data might appear, therapeutic intervention in patients with autoimmune disease remains the definitive experiment. Several studies published in the past year have tested paradigms of autoimmune disease in clinical trials. Recent therapeutic approaches for targeting B-cell subsets and co-stimulatory pathways are described here in detail. It is our belief that the future of immunotherapy in the clinic will depend to some extent upon the availability of biomarkers for defining biological signatures of immune function in vivo.

The role of immune tolerance in preventing and treating arthritis

It has become increasingly clear that the innate and adaptive arms of the immune response cooperate in generating autoimmune damage in the pathogenesis of rheumatoid arthritis and juvenile idiopathic arthritis. Treatment targets the immunologic pathophysiology of the disease and is based on regaining immune tolerance. Recently introduced biological agents neutralize or simply block cytokines and their proinflammatory pathways, with favorable clinical outcome. However, major downsides are their lack of specificity and the need of continuous administration to be effective. Possibly, more can be gained from a specific approach. Indeed, recent findings suggest that targeting antigen-specific T cells can reinstate regulatory mechanisms and thus induce immune tolerization. This improved understanding has paved the way to novel immunotherapeutic approaches, some of which will be discussed here.

Pharmacogenetics/pharmacogenomics and antirheumatic drugs in rheumatology

Genomic medicine has raised many expectations with regard to individualized therapies. Drug response is a complex function of many genes interacting with environmental and behavioral factors. In addition, poor prescribing, interactions between drugs and an incomplete understanding of the metabolism of many drugs, which are administered simultaneously to treat concomitant morbidities, are leading causes of the occurrence of adverse drug reactions in chronic non-inflammatory and autoimmune rheumatic diseases. Symptomatic non-steroidal anti-inflammatory drugs, as well as disease-modifying drugs, are complicated by drop-outs (poor patient compliance) in a large percentage of patients. Even though intensive and careful monitoring is always clearly advisable, preliminary data suggest that typing of genes controlling the effects, metabolism and response of drugs might be of clinical utility to define the ‘at-risk’ genotype.

The role and clinical implications of G6PI in experimental models of rheumatoid arthritis

The antigens that trigger the pathogenic immune response in rheumatoid arthritis (RA) remain unknown. Until recently it was assumed that either viral or microbial antigens, or joint-specific antigens were the target of arthritogenic T and B lymphocytes in RA. Consequently, murine models of arthritis are induced by immunization with either joint-specific antigens such as type II collagen or microbial products such as streptococcal cell wall. In the K/B×N T-cell receptor transgenic mouse model arthritis is caused by a systemic autoimmune response to the ubiquitously expressed glycolytic enzyme glucose-6-phosphate isomerase (G6PI). The autoreactive transgenic T cells recognize G6PI and provide help for the production of arthritogenic IgG antibodies against G6PI. More recently it was shown that G6PI immunization induces severe symmetrical peripheral polyarthritis in genetically unaltered DBA/I mice. In that model CD4⁺ T cells are necessary not only for the induction but also for the effector phase of arthritis. Here we review the pathomechanisms that lead from systemic autoreactivity to arthritis in these models, consider the relevance of anti-G6PI immune reactivity for RA, and discuss the insights into the pathogenesis of RA and possibly other autoimmune conditions that can be gained from these models.

Tolerance and short term efficacy of rituximab in 43 patients with systemic autoimmune diseases

OBJECTIVE

To assess the tolerance and efficacy of rituximab in patients with various autoimmune diseases seen in daily rheumatological practice.

METHODS

866 rheumatology and internal medicine practitioners were contacted by e-mail to obtain the files of patients treated with rituximab for systemic autoimmune diseases. Patients with lymphoma were analysed if the evolution of the autoimmune disease could be evaluated.

RESULTS

In all, 43 of 49 cases could be analysed, including 14 with rheumatoid arthritis (RA), 13 with systemic lupus erythematosus (SLE), six with primary Sjogren's syndrome (pSS), five with systemic vasculitis, and five with other autoimmune diseases. Rituximab was prescribed for lymphoma in two patients with RA and two with pSS. In the 39 other cases, rituximab was given because of the refractory character of the autoimmune disease. The mean follow up period was 8.3 months (range 2 to 26). There were 11 adverse events in 10 patients and treatment had to be discontinued in six. Efficacy was observed in 30 patients (70%): RA 11, SLE 9, pSS 5, vasculitis 2, antisynthetase syndromes 2, sarcoidosis 1. The mean decrease in corticosteroid intake was 9.5 mg/d (range 0 to 50) in responders. Seven patients experienced relapse after mean 8.1 months (5 to 15). Three patients died because of refractory autoimmune disease.

CONCLUSIONS

Despite absence of marketing authorisation, rituximab is used to treat various refractory autoimmune diseases in daily rheumatological practice. This study showed good tolerance and short term clinical efficacy, with marked corticosteroid reduction in patients with SLE, pSS, vasculitis, and polymyositis.

[Therapy of inflammatory kidney diseases. More than steroids?]

The term "inflammatory kidney diseases" characterizes primarily immunopathogenetically driven diseases, affecting both kidneys. Bacterial infections, or primarily interstitial nephritis, shall not be considered in this overview. Classification and terminology of inflammatory kidney diseases follow morphological criteria, acuteness of the clinical course, and concomitant organ affection. The clinical course and pathology of inflammatory kidney diseases have been reviewed extensively in this journal in 1997 and 2002.

Clinical and pathophysiological significance of the autoimmune response to citrullinated proteins in rheumatoid arthritis

Rheumatoid arthritis (RA) is the most frequent human autoimmune disease, affecting about 1% of the adult population worldwide. A better knowledge of the autoimmune mechanisms involved is essential. We identified the epithelial targets of various autoantibodies specifically associated to RA, as variants of (pro)filaggrin. We also showed that these targets correspond to deiminated ("citrullinated") proteins, of which arginyl residues have been posttranslationally transformed into citrullyl residues by a peptidylarginine deiminase (PAD). Moreover, we and others established that citrullyl residues are indispensable elements of the epitopes recognized by these autoantibodies but only in the context of specific aminoacid sequences. We also demonstrated that these autoantibodies to citrullinated proteins (ACPA) are secreted by plasma cells of the synovial tissue and that their major targets correspond to citrullinated forms of the alpha- and beta-chains of fibrin, abundant in the tissue. These results have allowed the development of new efficient immunochemical methods for the detection of ACPA. Some of them are already commercially available. These new methods have permitted the high diagnostic value of ACPA which are present very early in the course of the disease, and also their prognostic value, to be confirmed. ACPA detection should therefore prove to be also a very valuable tool to guide the choice of therapeutic strategies, from the earliest stages of the disease. The synthesis of ACPA in the rheumatoid synovial tissue and the existence therein of a specific antigenic target constitute a strong argument for the involvement of this specific immunological conflict in the pathophysiology of RA. Indeed, it could lead to activation of effector mechanisms with pro-inflammatory effects, thus to formation in the tissue of new fibrin deposits, secondarily citrullinated. We therefore, propose a new pathophysiological model accounting for the self-maintenance and chronicity of rheumatoid inflammation. Numerous questions about the pathophysiological significance of the autoimmune response to deiminated proteins in RA remain to be answered to confirm this model.

Emerging biological therapies in rheumatoid arthritis

The introduction of TNFalpha inhibitors has radically changed the management of patients with refractory rheumatoid arthritis (RA) or spondyloarthropathy. However, among patients with RA unresponsive to methotrexate, only two-thirds respond to TNFalpha inhibitors. Fortunately, more than 5 years after infliximab was introduced on the market, preliminary evidence that emerging biological agents are effective is beginning to accumulate, generating new hope for patients who fail to respond to TNFalpha inhibitors. These novel biological therapies grew out of original pathophysiological hypotheses, a fact that vividly illustrates the importance of basic pathophysiological research for developing new medications. This review provides detailed information on three biological therapies whose efficacy in RA was demonstrated in recently published randomized placebo-controlled trials: a monoclonal antibody to the IL-6 receptor (MRA), CTLA4-Ig (abatacept), and a monoclonal B-cell-specific antibody to CD20 (rituximab). Good risk/benefit ratios seem to be achieved with MRA alone or with abatacept or rituximab combined with methotrexate. However, as yet, no radiographic data are available for these treatments. One of the challenges for the future is to identify ingenious combinations of biological therapies capable of improving the quality and duration of responses without exacerbating side effects.