Haemophagocytic lymphohistiocytosis (HLH) is a severe immune system disorder characterized by over‐stimulation of some cells of the immune system. Primary HLH, more common in children, results from genetic abnormalities that leads to malfunction of certain white blood cells, causing the immune system to generate an excessive amount of a chemical substance called interferon gamma (IFNγ). Increased activity of IFNγ leads to severe tissue damage and multi‐organ failure. HLH is a very rare disease with a high mortality rate with a median survival time that ranges from less than 2 months to 6 months after diagnosis if untreated. Even with treatment, only 55‐65% of the patients are expected to survive upto 5 years.
Emapalumab is a type of drug called a monoclonal antibody, under development for the treatment of primary HLH in children. It acts by neutralising IFNγ activity produced by over‐stimulated cells of the immune system. It is administered as an intravenous infusion and may be used in addition to current treatment. If licensed, emapalumab will be a targeted therapy for patients with primary HLH and has the potential to increase the length of survival.