Open-label Study of ELA026 in Participants With Secondary Hemophagocytic Lymphohistiocytosis (sHLH)

Key Inclusion Criteria for Part 1: 1. ≥12 years at the time of HLH diagnosis (Cohort 1). 2. ≥6 years at the time of HLH diagnosis (Cohort 2-3). 3. Treatment naïve or relapsed/refractory (Cohorts 1 and 2). 4. Treatment naïve or early refractory (Cohort 3). 5. Participant with sHLH confirmed criteria based on fulfilling 5 out of 8 HLH-2004 diagnostic criteria. Key Inclusion Criteria for Part 2: 1. Cohort A: Adults with newly diagnosed, treatment-naïve, malignancy-associated sHLH. 2. Cohort B: Adults with newly diagnosed, treatment-naïve, non-malignancy-associated sHLH. 3. Cohort B: Adults with newly diagnosed, treatment-naïve, malignancy-associated sHLH, diagnosed by OHI index. 4. Cohort B: 13 to 17 years olds with newly diagnosed, treatment-naïve sHLH. 5. Cohort B: 6 to 12 year olds, with refractory sHLH (safety lead-in cohort). 6. Cohort B: 6 to 12 year olds, with newly diagnosed, treatment-naïve sHLH (after completion of safety lead-in cohort). Key Exclusion Criteria for Part 1: 1. Known or previous treatment for primary HLH 2. Any other significant concurrent, uncontrolled medical condition that in the opinion of the Investigator contraindicates participation in this study 3. Unknown trigger for sHLH 4. Active, relapsed/refractory malignancy for which no suitable therapies are available to treat the malignancy triggering the HLH 5. Allogeneic hemopoietic stem cell transplant (HSCT) within 100 days of the first dose of ELA026. 6. Ongoing administration of any therapies used to treat HLH (excluding dexamethasone) 7. Live or attenuated vaccine received within 6 weeks or bacille Calmette-Guerin (BCG) vaccine within 12 weeks prior to Screening Key Exclusion Criteria for Part 2: 1. Refractory sHLH (except for the safety lead-in cohort for 6-12 year olds in Cohort B). 2. Known or suspected primary or hereditary HLH. 3. Severe organ dysfunction. 4. Any other significant concurrent, uncontrolled medical condition that contraindicates participation in this study or prohibits completion of study procedures. 5. End-stage malignancy for which no suitable therapies are available to treat the malignancy triggering the HLH. 6. Allogeneic hemopoietic stem cell transplant within 100 days prior to the first dose of ELA026.