A Study for Long-term Follow-up of Hemophagocytic Lymphohistiocytosis (HLH) Participants Who Received Treatment With Emapalumab (NI-0501), an Anti-interferon Gamma Monoclonal Antibody

Adverse events were defined as any undesirable experience occurring in a participant during the study, whether or not considered related to emapalumab.

Time frame: From the date of enrollment in this study up to 1 year either after HSCT or after the last administration of emapalumab (maximum duration: 639 days)

Population: Participants who previously received treatment in a parent study (NI-0501-04 or NI-0501-06) or under compassionate use and who provided informed consent for participation in Study NI-0501-05.

Circulating Emapalumab level in Enrolled-04 Cohort who continued to receive treatment with emapalumab in the current study (NI-0501-05).

Time frame: First infusion day (infusion duration: 1-2 hours) in Study NI-0501-05, last infusion day (infusion Day 188), 12 months post-transplant

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who had data available for specified timepoints. Circulating emapalumab level post-transplant included participants who had HSCT and data available at 12 months post-HSCT (Samples were not to be taken once it had been determined that emapalumab was below measurable level of 62.5 µg/L).

Time frame: Baseline (first NI-0501-05 visit), Day 100, Month 6

Population: Enrolled-06 population included participants previously enrolled and treated in Study NI-0501-06 (participants with MAS in Still's disease) who provided informed consent for participation in Study NI-0501-05 and had available data at specified timepoints (Samples were not to be taken once it had been determined that emapalumab was below measurable level of 62.5 µg/L).

Cumulative duration of response: total number of days in response from 1st achievement of overall response until HSCT or last treatment date if the participant did not undergo HSCT. Overall response: achievement of either Complete (CR) or Partial Response (PR), or HLH Improvement (HI). CR: no fever, normal spleen size, no cytopenia (absolute neutrophil count \[ANC\] ≥1.0 x 10\^9/L and platelet count ≥ 100 x 10\^9/L), no hyperferritinemia (serum ferritin \<2000 μg/L), no coagulopathy (normal D-dimer and/or fibrinogen \>150 mg/dL), no neurological and cerebrospinal fluid \[CSF\] abnormalities attributed to HLH, no sustained worsening of soluble cluster of differentiation (CD) 25. PR: at least 3 HLH clinical and laboratory criteria (including central nervous system \[CNS\] abnormalities) met the CR criteria, no progression of other aspects of HLH disease pathology. HI: improvement (\>50% change from baseline) of at least 3 HLH clinical and laboratory abnormalities (including CNS involvement).

Time frame: From 1st achievement of overall response until HSCT or last treatment date if participant did not undergo HSCT (maximum 250 days)

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who had at least 1 response.

Duration of first response was defined as the number of days between first date of response and first date of loss of response or death. Response was defined as macrophage activation syndrome (MAS) remission, which was resolution of clinical signs and symptoms according to the Investigator (MAS clinical signs and symptoms score ≤ 1) and normalization of laboratory parameters relevant to MAS as follows: white blood cells (WBC) and platelet count above the upper limit of normal (LLN), Lactate dehydrogenase \< 1.5 × lower limit of normal (ULN), aspartate aminotransferase/alanine aminotransferase \<1.5 × ULN, fibrinogen \> 100 mg/dL, ferritin level decreased by at least 80% from values at screening or baseline (whichever was higher) or \< 2000 ng/mL, whichever was lower.

Time frame: From first date of response and first date of loss of response or death (maximum 416 days)

Population: Enrolled-06 population included participants previously enrolled and treated in Study NI-0501-06 (participants with MAS in Still's disease) who provided informed consent for participation in Study NI-0501-05 and who had at least 1 response.

MAS activity was monitored using a visual analogue scale ranging from 0 to 10 with a higher score indicted higher disease activity.

Time frame: Baseline (first NI-0501-05 visit), Day 100, Month 12/End of Study

Population: Enrolled-06 population included participants previously enrolled and treated in Study NI-0501-06 (participants with MAS in Still's disease) who provided informed consent for participation in Study NI-0501-05 and had available data for MAS activity.

Time frame: From enrolment up to 12 months post-transplant or last emapalumab infusion (maximum 639 days)

Population: Participants who previously received treatment in a parent study (NI-0501-04 or NI-0501-06) or under CU and who provided informed consent for participation in Study NI-0501-05. Number of participants analysed included participants who had available data for anti-drug antibody.

Overall survival was defined as time from the date of the last emapalumab dose to the date of death. Participants without an event were censored at the time of last contact or 12 months after last dose (whichever came first). As some participants had their last emapalumab dose in the parent study (NI-0501-04), data from both NI-0501-05 and NI-0501-04 studies were considered for the assessment of overall survival. Kaplan-Meier methodology was used for estimation.

Time frame: From the date of last of emapalumab dose to the date of death or last contact or 12 months after last dose, whichever came first (maximum 366 days)

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05.

Overall survival was defined as time from the date of last emapalumab dose to the date of death. Participants without an event were censored at the time of last contact or 12 months after last dose (whichever came first). As participants in the Enrolled-06 Cohort did not receive emapalumab in the current study, data from both NI-0501-05 and NI-0501-06 studies were considered for the assessment of overall survival. Kaplan-Meier methodology was used for estimation.

Time frame: From the date of last of emapalumab dose to the date of death or last contact or 12 months after last dose, whichever came first (maximum 366 days)

Population: Enrolled-06 population included participants previously enrolled and treated in Study NI-0501-06 (participants with MAS in Still's disease) who provided informed consent for participation in Study NI-0501-05.

For participants who underwent HSCT, achievement of donor chimerism was considered based on donor chimerism in peripheral blood completed, that is, donor cells \>95%.

Time frame: From HSCT to 12 months

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who underwent HSCT.

For participants who underwent HSCT either in parent study (NI-0501-04) or current study (NI-0501-05), engraftment rate was based on the number of participants experiencing primary or secondary graft failure (blood stem cell transplant failure, engraft failure, or transplant dysfunction), as reported as an adverse event.

Time frame: From HSCT up to 12 months

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who underwent HSCT.

Occurrence of graft-versus-host-disease, reported in Study NI-0501-05 as an AE.

Time frame: From HSCT to 12 months

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who underwent HSCT.

Time frame: First infusion day (infusion duration: 1-2 hours) in Study NI-0501-05, Day 100 post-transplant, 12 months post-transplant

Population: Enrolled-04 population included participants previously enrolled and treated in Study NI-0501-04 (participants with primary HLH) who provided informed consent for participation in Study NI-0501-05 and who had data available for specified timepoints. Total human interferon gamma levels post-transplant included participants who underwent HSCT and data available at Day 100 and 12 months post-HSCT.

Time frame: Baseline (first NI-0501-05 visit), Day 100, Month 12/End of Study

Population: Enrolled-06 population included participants previously enrolled and treated in Study NI-0501-06 (participants with MAS in Still's disease) who provided informed consent for participation in Study NI-0501-05 and had available data at specified timepoints.