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

NCT07080905 | Recruiting Phase 3 DMC FDA Drug FDA Device

• 2 other identifiers: CSL222_30042023-505805-18-00
• Study Type: interventional
• Target: 20
• Locations: 5 countries
• Sites: 10

Brief 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.

Conditions

Hemophilia B

Outcome Measures

Primary Outcomes (1)

• Annualized Bleeding Rate (ABR)

  For the Lead-In Period (at least 6 months) and for the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222)

Secondary Outcomes (31)

• Canadian Hemophilia Outcomes-Kids Life Assessment Tool (CHO-KLAT) total score and change from baseline

  At baseline and Month 18 post treatment

• Endogenous FIX activity

  At baseline, and at months 6, 12, and 18 after treatment with CSL222

• Change from baseline in endogenous FIX activity

  At baseline, and at months 6, 12, and 18 after treatment with CSL222

• Annualized consumption of FIX replacement therapy

  For the Lead-In Period (at least 6 months), for the 52 weeks following stable FIX expression (months 7 to 18 after treatment with CSL222), and annually in the Posttreatment Follow-up Period (up to 5 years)

• Annualized infusion rate of FIX replacement therapy

  For the Lead-In Period (at least 6 months), for the 52 weeks following stable FIX expression (months 7 to 18 after treatment with CSL222), and annually in the Posttreatment Follow-up Period (up to 5 years)

Study Arms (1)

CSL222

EXPERIMENTAL

Participants will receive CSL222 as a single intravenous (IV) infusion of 2 × 10\^13 genome copies per kilogram of body weight (gc/kg).

Genetic: CSL222 (Adeno-associated viral vector serotype 5 [AAV5]-hFIXco-Padua)

Interventions

CSL222 (Adeno-associated viral vector serotype 5 [AAV5]-hFIXco-Padua) GENETIC

Administered as a single IV infusion.

Also known as: Etranacogene Dezaparvovec

CSL222

Eligibility Criteria

• Age: 138 Months - 206 Months
• Gender Eligibility Details: Assigned male at birth.
• Healthy Volunteers: No
• Age Groups: Child (0-17)

You may qualify if:

• 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.

You may not qualify if:

• 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

Sponsors & Collaborators

• CSL Behring: lead

Study Sites (10)

Center for Inherited Blood Disorders

Orange, California, 92868, United States

RECRUITING

University of Florida

Gainesville, Florida, 32611, United States

RECRUITING

Arthur M. Blank Hospital - Children's Healthcare of Atlanta

Atlanta, Georgia, 30329, United States

RECRUITING

University of Michigan Medical Center

Ann Arbor, Michigan, 48109, United States

RECRUITING

St. Jude Children's Research Hospital

Memphis, Tennessee, 38105, United States

RECRUITING

Medical University Vienna

Vienna, 1090, Austria

RECRUITING

UZ Leuven - Centrum voor Moleculaire en Vasculaire Biologie

Leuven, 3000, Belgium

RECRUITING

Chaim Sheba Medical Center

Ramat Gan, 5262000, Israel

RECRUITING

St Thomas Hospital

London, SE1 7EH, United Kingdom

RECRUITING

John Radcliffe Hospital - Oxford University Hospitals NHS

Oxford, OX3 9DU, United Kingdom

RECRUITING

MeSH Terms

Conditions

Hemophilia B

Condition Hierarchy (Ancestors)

Blood Coagulation Disorders, Inherited; Blood Coagulation Disorders; Hematologic Diseases; Hemic and Lymphatic Diseases; Coagulation Protein Disorders; Hemorrhagic Disorders; Genetic Diseases, Inborn; Congenital, Hereditary, and Neonatal Diseases and Abnormalities; Genetic Diseases, X-Linked

Study Officials

• Study Director

  CSL Behring

  STUDY DIRECTOR

Central Study Contacts

Trial Registration Coordinator

CONTACT

1-610-878-4697; clinicaltrials@cslbehring.com

Study Design

• Study Type: interventional
• Phase: phase 3
• Allocation: NA
• Masking: NONE
• Purpose: TREATMENT
• Intervention Model: SINGLE GROUP
• Sponsor Type: INDUSTRY
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 7, 2025
• First Posted: July 23, 2025
• Study Start: July 28, 2025
• Primary Completion (Estimated): October 24, 2033
• Study Completion (Estimated): October 24, 2033
• Last Updated: April 16, 2026

Record last verified: 2026-04

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP
• Time Frame: Requests for IPD will generally be considered once review by major regulatory authorities (ie FDA, EMA) is complete and the primary publication is available.
• Access Criteria: Proposed research should seek to answer a previously unanswered important medical or scientific question. Applicable country specific privacy and other laws and regulations will be considered and may prevent sharing of IPD. If the request is approved and the researcher has executed an appropriate data sharing agreement, IPD that has been appropriately anonymized will be available.

Locations

BE (1); IL (1); US (5); GB (2); AU (1)