Although there are several studies supporting the efficacy of tocilizumab (TCZ) in Rheumatoid Arthritis (RA) and systemic onset juvenile idiopathic arthritis, it's use in other autoimmune disorders has also been propose. A consensus statement on blocking the effects of IL-6 in RA and other autoimmune conditions has been recently published. IL-6 is involved in the growth and differentiation of many inflammatory cells. In addition to its initial role in triggering B-cell stimulating factor, it also induces T cell growth and differentiation and plays a critical role in both adaptive and innate immune responses. IL-6, produced by many cells including T cells, B cells, monocytes and endothelial cells, binds to its receptor (IL-6R) and subsequently triggers several intracellular pathways leading to the release of inflammatory mediators and stimulation of the immune system. Inhibition of IL-6 has been studied in phase II and III clinical trials of RA. It has led to a decrease in acute phase reactants and other indicators of chronic inflammation. IL-6 is also a potential therapeutic target in systemic sclerosis, and since IL-6 induces differentiation of B cells into antibody forming cells and contributes to T cells transforming into effector cells, its use in Systemic Lupus erythematosus (SLE) has also been suggested.
The use of TCZ in myositis proposed in this protocol is supported by the aforementioned rationale and its efficacy in other rheumatologic disorders. Patients with refractory polymyositis (PM) were treated with tocilizumab and responded favorably. In dermatomyositis, tissue inflammation implicates soluble cytokine networks contributing to disease pathogenesis. Work on a mouse model of myositis noted IL-6 as a mediator of muscle inflammation. Other investigators studying peripheral blood samples and clinical data on both adult and juvenile dermatomyositis (DM) noted that serum levels of IL-6 were significantly correlated with disease activity. In this same study, correlations between serum IL-6 levels and both the type I interferon gene and chemokine signatures were also identified in DM. These authors suggest that the coordinated dysregulation of IL-6 production and Type I interferon signaling implicates these pathways as contributing to disease pathogenesis in DM.
In a mouse model of PM, C protein-induced myositis (CIM), the pathology reportedly mimics that seen in human PM. Mice were treated with anti-IL-6 receptor monoclonal antibodies or control antibodies and muscle tissue was histologically and immunohistochemically analyzed. CIM was ameliorated in this mouse model implicating IL-6 in the development of myositis. These results not only identified this model as useful to understanding PM but they suggest that IL-6 blockade be considered as a new therapeutic approach in the treatment of myositis.
Thus, the collective findings described above provide evidence for the involvement of IL-6 in the pathogenesis of both adult PM and DM as well as supporting its role from animal models and human studies.
Patients will be included in the trial based on the following criteria:
Criteria for core set measures for study entry:
If on prednisone, the dose must be stable for 4 weeks prior to the screening visit. Tapering of the prednisone dose will only be allowed after the subject meets the DOI or if safety/toxicity issues supervene.
If an IS agent was discontinued prior to the screening visit there may be a washout as stipulated below or individualized according to the patients treating physician:
A patient will be excluded if any of the following criteria are met:
Abnormal laboratory values noted below: