The efficacy of GAMIFANT was evaluated in a multicenter, open-label, single-arm trial NI-0501-04 (NCT01818492) in 27 pediatric patients with suspected or confirmed primary HLH with either refractory, recurrent, or progressive disease during conventional HLH therapy or who were intolerant of conventional HLH therapy.
Patients were required to fulfill the following criteria for enrollment: primary HLH based on a molecular diagnosis or family history consistent with primary HLH or five out of the 8 criteria fulfilled: fever, splenomegaly, cytopenias affecting 2 of 3 lineages in the peripheral blood (hemoglobin < 9 , platelets < 100 x 109/L, neutrophils < 1 x 109/L), hypertriglyceridemia (fasting triglycerides > 3 mmol/L or ≥ 265 mg/dL) and/or hypofibrinogenemia (≤ 1.5 g/L), hemophagocytosis in bone marrow, spleen, or lymph nodes with no evidence of malignancy, low or absent NK-cell activity, ferritin ≥ 500 mcg/L, soluble CD25 ≥ 2400 U/mL. Patients had to have evidence of active disease as assessed by treating physician. Patients had to fulfill one of the following criteria as assessed by the treating physician: having not responded or not achieved a satisfactory response or not maintained a satisfactory response to conventional HLH therapy, or intolerance to conventional HLH treatments. Patients with active infections caused by specific pathogens favored by IFNγ neutralization were excluded from the trial (e.g., mycobacteria and Histoplasma Capsulatum). Patients received prophylaxis for Herpes Zoster, Pneumocystis jirovecii, and fungal infections.
Twenty-seven patients enrolled and received treatment in the study and twenty patients (74%) completed the study. Seven patients (26%) were prematurely withdrawn. Twenty-two patients (81%) enrolled onto the open-label extension study which monitored patients for up to 1 year after HSCT or after the last GAMIFANT infusion (NI-0501-05; NCT02069899).
The study treatment duration was up to 8 weeks after which patients could continue treatment on the extension study. All patients received an initial starting dose of GAMIFANT of 1 mg/kg every 3 days. Subsequent doses could be increased to a maximum of 10 mg/kg based on clinical and laboratory parameters interpreted as unsatisfactory response. Forty-four percent of patients remained at a dose of 1 mg/kg, 30% of patients increased to 3-4 mg/kg and 26% of patients increased to 6-10 mg/kg. The median time to dose increase was 27 days (range: 3-31 days) with 22% of patients requiring a dose increase in the first week of treatment.
All patients received dexamethasone as background HLH treatment with doses between 5 to 10 mg/m2/day. Cyclosporine A was continued if administered prior to screening. Patients receiving methotrexate and glucocorticoids administered intrathecally at baseline could continue these treatments.
In Study NI-0501-04, the median patient age was 1 year (0.2 to 13). Fifty-nine percent of the patients were female, 63% were Caucasian, 11% were Asian, and 11% were Black.
A genetic mutation known to cause HLH was present in 82% of patients. The most frequent causative mutations were FHL3-UNC13D (MUNC 13-4) (26%), FHL2-PRF1 (19%), and Griscelli Syndrome type 2 (19%).
The HLH mutations in the population enrolled are described in Table 3.
Table 3: HLH Mutations in Patients with Primary HLH with Prior Therapy | GAMIFANT (N=27) |
|---|
| HLH Genetic Confirmation | 22 (82) |
|---|
| FHL3 – UNC13D | 7 (26) |
| FHL2 – PRF1 | 5 (19) |
| Griscelli Syndrome type 2 (RAB27A) | 5 (19) |
| FHL5 – STXBP2 (UNC18B) | 2 (7.4) |
| FHL4 – STX11 | 1 (3.7) |
| X-linked Lymphoproliferative Disorder 1 | 1 (3.7) |
| X-linked Lymphoproliferative Disorder 2 | 1 (3.7) |
All patients received previous HLH treatments. Patients received a median of 3 prior agents before enrollment into the trial. Prior regimens included combinations of the following agents: dexamethasone, etoposide, cyclosporine A, and anti-thymocyte globulin.
At baseline entry into the study, 78% of patients had elevated ferritin levels, thrombocytopenia (70% with platelet count of < 100 x 109cells/L), hypertriglyceridemia (67%) with triglyceride level > 3 mmol/L. Central nervous system findings were present in 37% of patients. Forty-one percent of patients had active infections not due to specific pathogens favored by IFNγ neutralization at the time of GAMIFANT initiation.
The efficacy of GAMIFANT was based upon overall response rate (ORR) at the end of treatment, defined as achievement of either a complete or partial response or HLH improvement. ORR was evaluated using an algorithm that included the following objective clinical and laboratory parameters: fever, splenomegaly, central nervous system symptoms, complete blood count, fibrinogen and/or D-dimer, ferritin, and soluble CD25 (also referred to as soluble interleukin-2 receptor) levels. Complete response was defined as normalization of all HLH abnormalities (i.e., no fever, no splenomegaly, neutrophils > 1x109/L, platelets > 100x109/L, ferritin < 2,000 μg/L, fibrinogen > 1.50 g/L, D-dimer < 500 μg/L, normal CNS symptoms, no worsening of sCD25 > 2-fold baseline). Partial response was defined as normalization of ≥ 3 HLH abnormalities. HLH improvement was defined as ≥ 3 HLH abnormalities improved by at least 50% from baseline.
Table 4: Overall Response Rate at End of Treatment | GAMIFANT (N=27) |
|---|
| Overall Response Rate |
|---|
| N (%) | 17 (63) |
| (95% CI) | (0.42, 0.81) |
| p-value | 0.013 |
| Overall Response by Category |
|---|
| Complete response, n (%) | 7 (26) |
| Partial response | 8 (30) |
| HLH improvement | 2 (7.4) |
| CI = confidence interval |
The median duration of first response, defined as time from achievement of first response to loss of first response, is not reached (range: 4-56+ days). Seventy percent (19/27) of patients proceeded to HSCT.