Emapalumab in children with primary hemophagocytic lymphohistiocytosis

Introduction. Primary hemophagocytic lymphohistiocytosis (pHLH) is a group of genetically determined diseases characterized by severe and lightning-fast systemic inflammation, cytopenia, and multi-organ damage with high mortality. The HLH-2004 protocol using high doses of dexamethasone and etoposide is widely used for the treatment of pHLH but it does not always lead to remission of the disease necessary for the next stage of treatment: hematopoietic stem cell transplantation. Aim: to retrospectively analyze the experience of emapalumab treatment in patients with pHLH. Materials and methods. A retrospective study was conducted to evaluate the effectiveness and safety of emapalumab in children with pHLH (n = 7) who had been treated at the Center from November 2019 to September 2024. The criterion for inclusion in the study was the diagnosis of pHLH established based on the criteria of the International Society for the Treatment of Histiocytic Disorders (The Histiocyte Society). The severity of the disease was assessed using an adapted H-score with the exclusion of signs of bone marrow hemophagocytosis. Results. We report the use of the interferon gamma inhibitor emapalumab in seven patients aged 6 to 39 months who had previously been treated according to the HLH-2004 protocol in combination with other immunosuppressants. Three patients received emapalumab at an average initial dose of 1.7 mg/kg and achieved remission at a median of 28 days. The other four patients received emapalumab at an average initial dose of 7.2 mg/kg, with the median time to remission of 14 days (p = 0.0015). A faster and longer-term remission was observed in the patients treated with higher doses of emapalumab. Conclusion. In this study, we demonstrated the safety and effectiveness of emapalumab treatment in children with refractory pHLH.