Treatment with abatacept was associated with lower rates of disease activity in almost half of adult patients with dermatomyositis (DM) and polymyositis (PM) in a phase 2b, randomized, treatment delayed-start trial ( identifier: NCT01315938) published in the Annals of the Rheumatic Diseases.

The investigators sought to examine the efficacy and safety of abatacept in patients with DM or PM who were refractory to conventional therapies. A total of 20 patients between 18 and 80 years of age with either DM (n=9) or PM (n=11) were enrolled in this pilot study. Half of the patients were randomly assigned to immediate active treatment with abatacept at week 0 (arm A) and half were assigned to 3-month treatment delayed-start (arm B).

The primary end point was the number of responders based on the International Myositis Assessment and Clinical Studies Group definition of improvement after 6 months of abatacept therapy. Analysis of the primary outcome was based on the intention-to-treat principle. Among the secondary end points was the number of responders in the early treatment arm vs the delayed treatment arm at 3 months. Repeat muscle biopsies were examined for the presence of cellular markers and cytokines.

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Participants were all treated with abatacept for 6 months, receiving a total of 7 intravenous infusions at either weeks 0, 2, 4, 8, 12, and 20 (arm A) or at weeks 12, 14, 16, 20, 24, 28, and 32 (arm B).

Following 6 months of active treatment with abatacept, 42% (8 of 19) of intention-to-treat patients were responders, with lower disease activity, achieving the International Myositis Assessment and Clinical Studies Group definition of improvement; 58% (11 of 19) of patients were considered nonresponders. A significant improvement in muscle performance was observed for the entire patient population after 6 months of active treatment, as demonstrated by an increase in the Manual Muscle Test-8 (P =.0471) and decrease in muscle disease activity (P =.0435).

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Overall, 8 adverse events were deemed to be related to the study drug — 4 mild and 4 moderate; 3 serious adverse events, none related to the treatment, were reported. A significant increase in regulatory T cells (Foxp3+ Tregs) was observed following abatacept treatment (P <.05), but other biomarkers remained unchanged in repeat muscle biopsies.

The investigators concluded that abatacept therapy is clinically efficacious in a subgroup of individuals with DM or PM and has an acceptable safety profile among refractory patients. The increased frequency of Foxp3+ Tregs in those undergoing repeat muscle biopsies suggests a positive treatment effect on muscle tissue.

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Tjärnlund A, Tang Q, Wick C, et al. Abatacept in the treatment of adult dermatomyositis and polymyositis: a randomised, phase IIb treatment delayed-start trial [published online October 9, 2017]. Ann Rheum Dis. doi:10.1136/annrheumdis-2017-211751