Background
Phase 2/3 open-label single-arm (NI-0501-04). N=34 pediatric primary (familial) HLH, refractory/relapsed after or intolerant to conventional therapy (dexamethasone + etoposide ± cyclosporine). Median age 1.0 yr (range 0.1-13); genetically confirmed in ~80%; all had prior HLH-directed therapy. Emapalumab is an anti-IFN-γ monoclonal antibody.
Interventions and follow up
Treatment: Emapalumab 1 mg/kg IV every 3 days (escalated to ≤10 mg/kg by PK/clinical response) + background dexamethasone for up to 8 wk; allo-HCT in eligible patients
Primary endpoint: Overall response rate (CR + PR + HLH improvement) at end of treatment
mFollow up: Through HSCT and 1-yr post-HSCT
Primary endpoint: Overall response rate (CR + PR + HLH improvement) at end of treatment
mFollow up: Through HSCT and 1-yr post-HSCT
Results
ORR: 63% (21/34; 95% CI 45-79%) — CR 26%, PR 21%, HLH improvement 15%
Bridge to HSCT: 70% (24/34) proceeded to allo-HCT
1-yr OS post-HSCT: 73% among transplanted patients
Overall 1-yr OS (all enrolled): 38% (heavily pretreated, high-risk population)
Bridge to HSCT: 70% (24/34) proceeded to allo-HCT
1-yr OS post-HSCT: 73% among transplanted patients
Overall 1-yr OS (all enrolled): 38% (heavily pretreated, high-risk population)
Adverse events
Grade ≥3 infections: 35% — CMV reactivation 29%, disseminated histoplasmosis 6%, other opportunistic infections
Infusion-related reactions: 9%
Attribution: no grade ≥3 events clearly attributed to emapalumab in the majority; antiviral/antifungal prophylaxis required per protocol
Infusion-related reactions: 9%
Attribution: no grade ≥3 events clearly attributed to emapalumab in the majority; antiviral/antifungal prophylaxis required per protocol
Conclusions
Emapalumab achieved meaningful responses (ORR 63%) in children with primary HLH refractory to conventional therapy, enabling most to proceed to HSCT — the first IFN-γ-blocking agent approved for this indication.
Key Limitations
Small single-arm study (N=34), no comparator; concomitant dexamethasone confounds attribution. Surrogate ORR endpoint; low overall 1-yr OS (38%) reflects high-risk refractory population. Opportunistic-infection risk from IFN-γ blockade requires intensive prophylaxis.
Clinical Context
FDA-approved (2018) for primary HLH refractory/recurrent/intolerant to conventional therapy; bridges to allo-HCT. Positioned as second-line salvage after HLH-94/2004 backbone; competes with ruxolitinib and salvage chemoimmunotherapy in refractory disease.