This thesis describes results of translation research (bedside to bench and back) in JDM. It focuses both on the state of literature and the research of biomarkers in JDM with the view to improving the care and outcome of patients.
Chapter 2, through the SHARE initiative, gives an overview of the current literature with the goal of providing recommendations for clinicians in both diagnosis and treatment of JDM patients in order to unify the management in Europe. Recommendations were developed by an evidence-informed consensus process resulting in total, in seven overarching principles, 33 recommendations on diagnosis and 19 recommendations on therapy. Topics include assessment of skin, muscle and major organ involvement and treatment suggestion at disease onset and in refractory disease. Disease activity and damage scores have been developed, principally for clinical trials, but may be challenging and time consuming to use in daily clinical practice.
Up to now, disease activity and damage score relay mainly on clinical evaluation, so, one of the major setbacks in the care of JDM patients is the lack of an objective marker to define response to treatment and disease remission.
Having stated this, we describe in Chapter 3, 4 and 5 the detection of new biomarkers, Galectin-9 and CXCL10 and TNFRII, which have been detected by a multiplex immunoassay. This assay allows the measurement of a large panel of proteins in a single sample and a very small volume and is therefore a technique especially suitable for pediatric patients. We discovered these markers in a study cohort of Dutch patients; they had a remarkably high discriminative power between patients with active disease and those in disease remission, even in a very small cohort (chapter 3). The three proteins have also been shown to normalize in patients, which gained remission after autologous stem cell transplantation (aSCT) and are still high in those in which disease remained active (chapter 4). Of note, the markers did not decline directly after conditioning. Instead, the levels showed a slow and steady reduction after successful transplantation, correlating with improving clinical scores of the patients. This underscores the utility of these markers even in patients with a high immunosuppression. Furthermore, as CXCL10 and Galectin-9 are produced by immune and non-immune cells, these data suggests, that after aSCT non immune cells continue to produce these cytokines and sustain a low inflammation after aSCT.
Thanks to an international collaboration with the Juvenile Dermatomyositis Research Group (JDRG) in the UK and with the help of the Dutch JDM patient’s organization (Bas Stichting), we were able to validate these markers in a larger cohort. The study showed that Galectin-9 is the strongest biomarker in terms of discriminative power between active and remitting disease (chapter 5). We also measured Galectin-9 in other autoimmune diseases and could show that levels of Galectin-9 was higher in patients with JDM compared to patients with systemic erythematodes lupus or morphea and could discriminate between active disease and disease remission only in JDM.
To ease access for patients, we tested these markers also on dried blood spots (DBS). For the DBS, several blood drops are collected on a card, but the tested marker must be stable at room temperature and for a longer time period, as the cards are supposed to be sent from home by mail (chapter 5). Only one of the markers showed enough stability: CXCL10. In conclusion, we validated two biomarkers measured in serum or plasma to discriminate active and remitting disease: Galectin-9 and CXCL-10. Further studies with interventional and prospective design are needed to prove their utility in clinics regarding tapering and stopping medication.
In the last chapter (chapter 6), the role of regulatory T cells (Treg) in muscle and peripheral blood of JDM patients was established. We showed that patients with JDM had normal Treg percentages in peripheral blood compared to age matched controls, independent of disease activity, while in patients with high dose steroid treatment increased Treg percentages were observed. Furthermore, Treg from JDM patients in disease remission did exert suppressive function in vitro, while those from patients with active disease were not consistently suppressive. Thus, Tregs are able to migrate towards the inflamed tissue, but somehow are unable to suppress inflammation. In conclusion, Tregs are probably involved in JDM pathogenesis, but are not controlling the disease. Promotion of Treg function and frequency may improve disease outcome.