Clinical experience with emapalumab treatment in a group of children with primary hemophagocytic lymphohistiocytosis.

Primary hemophagocytic lymphohistiocytosis (pHLH) is a group of genetically determined disorders characterized by severe and fulminant systemic inflammation, cytopenia, and multiple organ involvement. A dexamethasone-and-etoposide-based HLH-2004 protocol is widely used to treat pHLH, yet often fails to produce the disease control required for the next treatment step: hematopoietic stem cell transplantation (HSCT). We report on the use of the interferon gamma inhibitor emapalumab in seven children aged 6-39 months with pHLH. Three patients received emapalumab at an average starting dose of 1.7 mg/kg and had no active HLH by median day 28. Four patients received emapalumab at an average starting dose of 7.2 mg/kg and had no active HLH by median day 14 (P = 0,0015). We suggest that the higher starting dose of emapalumab, as well as its combination with Janus kinase inhibitors, might increase the remission rate in pHLH and the success of subsequent HSCT.