Real-world treatment patterns and outcomes in patients with primary hemophagocytic lymphohistiocytosis treated with emapalumab

Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening, hyperinflammatory syndrome. Emapalumab, a fully human monoclonal antibody that neutralizes the proinflammatory cytokine interferon-gamma, is approved in the United States to treat primary HLH (pHLH) in patients with refractory, recurrent, progressive disease or intolerance with conventional HLH. REAL-HLH, a retrospective study, conducted across 33 US hospitals, evaluated real-world treatment patterns and outcomes in patients treated with ≥1 dose of emapalumab between November 20, 2018, and October 31, 2021. Forty-six patients met the pHLH classification criteria. Median (range) age at diagnosis was 1.0 (0.3-21.0) year. Emapalumab was initiated for treating refractory (19/46), recurrent (14/46), or progressive (7/46) pHLH. At initiation, 15/46 patients were in the intensive care unit and 35/46 had received prior HLH-related therapies. Emapalumab treatment resulted in normalization of key laboratory parameters, including chemokine ligand 9 (CXCL9) (24/33; 72.7%), ferritin (20/45; 44.4%), fibrinogen (37/38; 97.4%), platelets (39/46; 84.8%), and absolute neutrophil count (40/45; 88.9%). Forty-two (91.3%) patients were considered eligible for transplant. Pre-transplant survival was 38/42 (90.5%). Thirty-one (73.8%) transplant-eligible patients proceeded to transplant and 23/31 (74.2%) of those transplanted were alive at the end of the follow-up period. Twelve-month survival probability from emapalumab initiation for the entire cohort (n=46) was 73.1%. There were no discontinuations due to adverse events. In conclusion, results from the REAL-HLH study, which describes treatment patterns, effectiveness, and outcomes in patients with pHLH treated with emapalumab in real-world settings, are consistent with the emapalumab pivotal phase 2/3 pHLH trial.