RecruitingPhase 3NCT07080905

Phase 3, Open-label, Single-dose Study of CSL222 in Adolescent Male Subjects (≥ 12 to < 18 Years of Age) With Severe or Moderately Severe Hemophilia B

Phase 3, Open-label, Single-dose, Multicenter Study Investigating Efficacy, Safety, and Tolerability of CSL222 (Etranacogene Dezaparvovec) Administered to Adolescent Male Subjects (≥ 12 to < 18 Years of Age) With Severe or Moderately Severe Hemophilia B

Sponsor

CSL Behring

Enrollment

20 participants

Start Date

Jul 28, 2025

Study Type

INTERVENTIONAL

Conditions

Hemophilia B

Summary

This is a phase 3, prospective, open-label, single-arm, single-dose, multicenter study investigating the efficacy, safety, and tolerability of CSL222 (AAV5-hFIXco-Padua) in adolescent male participants with severe or moderately severe hemophilia B.

Eligibility

Sex: MALEMin Age: 138 MonthsMax Age: 206 Months

Inclusion Criteria7

Assigned male sex at birth
Aged ≥138 months (11 years and 6 months) to less than (\<) 206 months (17 years and 2 months) at the time of informed consent / assent.
Congenital hemophilia B with known severe or moderately severe FIX deficiency (less than or equal to \[≤\] 2% of normal circulating FIX) for which the participant has been on continuous FIX prophylaxis.
On stable continuous FIX prophylaxis for at least 2 months before Screening.
Minimum of 75 previous exposure days of treatment with FIX protein before Screening.
Completed the Lead-in Period: minimum of 6 months (26 weeks) of lead-in data collected and eligibility has been confirmed.
Aged ≥ 12 to \< 18 years at the time of CSL222 treatment.

Exclusion Criteria21

History of FIX inhibitors or positive FIX inhibitor test at Screening (based on central laboratory results).
Screening laboratory values (based on central laboratory results):
Total bilirubin \> 2 × the upper limit of normal (ULN).
Alanine aminotransferase (ALT) \> 2 × the ULN.
Aspartate aminotransferase (AST) \> 2 × the ULN.
Alkaline phosphatase (ALP) \> 2 × the ULN.
Serum creatinine \> 2 × the ULN.
Hemoglobin \< 8 g/dL.
Any condition other than hemophilia B resulting in an increased bleeding tendency.
Thrombocytopenia, defined as a platelet count below 50 × 10\^9/L, at screening (based on central laboratory results).
Any uncontrolled or untreated infection (human immunodeficiency virus, hepatitis C, etc) or any other significant concurrent, uncontrolled medical condition, as evaluated by the investigator, including, but not limited to renal, hepatic, cardiovascular, hematological, gastrointestinal, endocrine, pulmonary, neurological, cerebral, or psychiatric disease, alcoholism, drug dependency, or any other psychological disorder evaluated by the investigator to interfere with adherence to the Clinical Study Protocol procedures or with the degree of tolerance to CSL222.
Positive FIX inhibitor test at Visit L-Final (based on central laboratory results)
AAV5 NAb titer \> 1:900 as assessed at Visit LX (last visit before Visit L-Final).
Visit L-Final laboratory values (based on central laboratory results) of:
Total bilirubin \> 2 × the ULN
ALT \> 2 × the ULN.
AST \> 2 × the ULN.
ALP \> 2 × the ULN.
Serum creatinine \> 2 × the ULN.
Hemoglobin \< 8 g/dL.
Thrombocytopenia, defined as a platelet count below 50 × 10\^9/L, at Visit L-Final (based on central laboratory results).