A Pilot Study of KPL-914 in Recurrent Pericarditis

Inclusion Criteria for All Participants: * Has given consent (or assent, if applicable) and signed an Informed Consent Form (ICF) (or informed assent form, if applicable). * Male or female, of any ethnic origin. * 6 to 75 years of age, inclusive. * If used, has received non-steroidal anti-inflammatory drugs (NSAIDs), and/or colchicine and/or corticosteroids (in any combination) at stable dose levels for at least 7 days prior to study drug dosing (although stable doses for a shorter period will be acceptable if in the opinion of the Investigator, in consultation with the Sponsor, a shorter period of stability is not anticipated to alter the baseline CRP values) and is anticipated to continue these concomitant medications at these dose levels for the duration of the active Treatment Period. * If female of child-bearing potential, must be nonpregnant and nonlactating and must agree to use an effective method of contraception, e.g., hormonal contraception or double-barrier birth control. * Is able to adequately maintain a medication diary. * Agrees to refrain from making any new, major life-style changes that may affect pericarditis symptoms (e.g., starting a new diet or changing exercise pattern) from the time of signature of the ICF (or informed assent form, if applicable) to the End-of-Trial Visit. Parts 1, 2 and 4: Subjects eligible for Parts 1, 2 and 4 have to present during a symptomatic episode of recurrent idiopathic pericarditis (RIP; Parts 1 and 2) and post pericardiotomy syndrome (PPS; Part 4) and a history of at least one pericarditis recurrence. They can be enrolled into Part 1 or 4 if the CRP value at screening is \>1 mg/dL, and into Part 2 if a CRP ≤1 mg/dL (attributed to concomitant medications e.g., corticosteroids), and there is an evidence of pericardial inflammation on cardiac MRI confirmed by the imaging core lab. Enrollment into Part 3 and 5: Subjects eligible for Part 3 of this study have to present with corticosteroid-dependent RIP or PPS and history of at least 2 pericarditis recurrences. Exclusion Criteria for All Participants: * Has a diagnosis of pericarditis that was secondary to specific excluded etiologies, including tuberculous, neoplastic, or purulent etiologies, post-myocardial infarction (early or late), thoracic trauma, myocarditis, or systemic diseases including autoinflammatory diseases, autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus, etc.). * Has a history of immunodepression, including a positive human immunodeficiency virus test result. * Has received treatment within the 6-month period before dosing with any systemic immunosuppressants (other than, for example, corticosteroids or mycophenolate) which, in the opinion of the Investigator (in consultation with the Sponsor), may interfere with the study endpoints. * Currently receiving other interleukin (IL)-1 or IL-6 blockers, Janus-activating kinase (JAK) or tumor necrosis factor (TNF) inhibitors.