A Study to Evaluate Safety and Efficacy of Empasiprubart in Adults With Dermatomyositis

Inclusion Criteria:

• Is at least 18 years of age and the local legal age of consent for clinical studieswhen signing the Informed Consent Form

• Is capable of providing signed informed consent and complying with protocolrequirements

• Agrees to use contraceptive measures consistent with local regulations and women ofchild-bearing potential must have a negative serum pregnancy test at screening and anegative urine pregnancy test before receiving the study drug

• Has a clinical diagnosis of dermatomyositis or juvenile dermatomyositis. Thediagnosis date for juvenile dermatomyositis should be ≤5 years before screening

• Has active muscle disease associated with classic dermatomyositis or juveniledermatomyositis at screening and before the first study drug adminisitration and atleast 1 of the following: elevated levels of creatine kinase, aldolase, lactatedehydrogenase, aspartate aminotransaminase or alanine aminotransferase at screening;or electromyography ≤18 weeks before the first study drug administration; or an MRIdepicting active muscle inflammation ≤18 weeks before the first study drugadministration; or muscle biopsy demonstrating signs of active inflammation ≤18weeks before the first study drug administration

• Has at least mild skin disease at screening

• Complies with the permitted background dermatomyositis treatment requirements atscreening

• Has had immunization with the first meningococcal, pneumococcal, and the singleHaemophilus influenza type B vaccine ≥14 days before the first study drugadministration

Exclusion Criteria:

• Known autoimmune disease or any medical condition that would interfere with anaccurate assessment of clinical symptoms of dermatomyositis or puts the participantat undue risk

• Naïve to standard dermatomyositis treatment according to local recommendations

• History of malignancy unless considered cured by adequate treatment with no evidenceof recurrence for ≥3 years before the first study drug administration. Adequatelytreated participants with the following cancers can be included at any time: Basalcell or squamous cell skin cancer; Carcinoma in situ of the cervix; Carcinoma insitu of the breast; Incidental histological findings of prostate cancer

• Clinically significant active infection that is not sufficiently resolved before thefirst study drug administration in the investigator's opinion

• Positive serum test at screening for active infection with any of the following:Hepatitis B virus, Hepatitis C virus, HIV

• Clinically significant disease, recent major surgery, or intention to have majorsurgery during the study; or any other medical condition that, in the investigator'sopinion, would confound the results of the study or put the participant at unduerisk

• Current participation in another interventional clinical study

• Known hypersensitivity to the study drug or any of its excipients

• History (within 12 months before screening) of or current alcohol, drug, ormedication abuse, as assessed by the investigator

• Pregnant or lactating state or intending to become pregnant during the study

• Previous participation in an empasiprubart clinical study with at least 1 dose ofstudy drug received

• Known complement component deficiency as assessed by the investigator

• Change in dermatomyositis physical therapy or exercise program from ≤4 weeks beforescreening

• Inflammatory or non-inflammatory myopathies other than dermatomyositis, such asdrug-induced or endocrine-induced myositis, infective myositis, polymyositis,immune-mediated necrotizing myopathy, inclusion body myositis, overlap myositis,metabolic myopathies, or muscle dystrophies

• Paraneoplastic dermatomyositis secondary to malignancy

• Glucocorticoid-induced myopathy

• Severe muscle damage

• Extensive or severe calcinosis

• Interstitial lung disease with at least 1 of the following: forced vital capacity (FVC) ≤60%; supplemental oxygen therapy; rapidly progressing uncontrolledinterstitial lung disease; moderate or severe interstitial lung disease