CS1 Added to Standard of Care Therapy for Pulmonary Arterial Hypertension

This Phase 2 study (EPIMODE) will evaluate the efficacy and safety of CS1 compared with placebo when added to standard-of-care therapy in participants with pulmonary arterial hypertension. Participants completing Treatment Period 1 (Week 36) will be re-randomized to continue or switch study treatment for Treatment Period 2 through Week 52.

Inclusion Criteria: * Age 18 to 80 years * WHO Group 1 pulmonary arterial hypertension * WHO Functional Class II or III * REVEAL Lite 2 score ≥6 * Receiving stable standard-of-care PAH therapy for at least 90 days prior to screening * Hemodynamic confirmation of PAH by right heart catheterization * 6-minute walk distance ≥150 m and \