This study is about a serious condition called secondary hemophagocytic lymphohistiocytosis (sHLH), which happens when our immune system becomes overly active. Secondary means it happens due to other issues, like infections or certain diseases. The study looks at a drug named ELA026, which helps calm down the immune system by targeting specific cells. It will check if the drug is safe and works well in people with sHLH.

There are two parts to this study. Part 1 has already ended, and Part 2 is for new patients. The study involves people of different ages, including both kids and adults. During the study, everyone will get the medicine and there will be no placebo (dummy treatment).

• Part 2 is currently recruiting participants, including children 6-12 years old.
• Participants will receive the drug ELA026 through an IV (into the vein) or under the skin.
• The main goal is to ensure the drug is safe and effective for people with sHLH.