Trial of IMO-8400 in Adult Patients With Dermatomyositis

Inclusion Criteria: * Has definite or probable DM based on the criteria of Bohan and Peter * Has a Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI)-Activity score ≥15 * Patients with muscle weakness are eligible; however having muscle weakness is not mandatory. * Study participants must have a diagnostic evaluation for cancer if the diagnosis of DM was within 2 years prior to the Screening Visit Exclusion Criteria: * Has ongoing severe dysphagia (e.g., requires a feeding tube) for the 3 months prior to Screening * Has known hypersensitivity to any oligodeoxynucleotide * Has a history of drug or alcohol abuse within one year of screening, or evidence of drug abuse by urine drug screening * Has body weight \>140 kg * Has a diagnosis of Juvenile DM, IBM, drug-induced toxic myopathy, metabolic myopathy, dystrophy, cancer-associated DM, or connective tissue disease-associated DM (e.g., overlap syndrome) * Has received one or more of following prohibited treatments within the interval noted prior to Screening (Visit 1): 1. Rituximab within 24 weeks (Note: patients who received rituximab are only eligible for inclusion if B-cell counts are confirmed to be within normal limits) 2. Intravenous corticosteroids within 12 weeks 3. Antimalarials (e.g., hydroxychloroquine) within 36 weeks 4. Topical corticosteroids (excluding scalp) within 2 weeks * Has evidence of or has required treatment for cancer (except for treated, non-invasive carcinoma of the skin or cured cervical carcinoma-in-situ) within 5 years * Has interstitial lung disease requiring the use of supplemental oxygen