Study of Etranacogene Dezaparvovec (CSL222) in Adolescent Males with Severe or Moderately Severe Hemophilia B

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What is this study about?

Hemophilia B is a rare bleeding disorder in which the blood does not clot properly due to a deficiency in a protein called Factor IX. This study aims to investigate the effectiveness, safety, and tolerability of CSL222 (also known as etranacogene dezaparvovec) in adolescent males between 12 and 18 years of age who have severe or moderately severe hemophilia B. Hemophilia B is characterized by prolonged bleeding after injuries, surgeries, or even spontaneous bleeding into joints and muscles.

The treatment being studied, CSL222, is a gene therapy designed to help the body produce its own Factor IX protein, which is essential for normal blood clotting. This therapy is administered as a single dose, potentially reducing the need for regular Factor IX replacement treatments that patients typically need. Before receiving the study treatment, participants will complete a lead-in period of at least 6 months where their current treatment and bleeding episodes are monitored.

During the study, researchers will track several outcomes including how often participants experience bleeding episodes, the amount of Factor IX protein in their blood, whether they still need regular Factor IX treatments, and any side effects that might occur. The study will also measure how the treatment affects participants’ quality of life using various assessment tools.

1 Study Entry and Lead-in Period

The study begins with a Lead-in Period lasting at least 6 months (26 weeks). During this time, your current factor IX (FIX) prophylaxis treatment will continue while baseline data is collected.

You will need to maintain your stable FIX prophylaxis regimen throughout this initial period to establish your baseline bleeding pattern and factor usage.

2 Eligibility Confirmation

After completing the Lead-in Period, your eligibility for the treatment phase will be confirmed. This includes verifying that you are between 12 and 18 years old and meet all other study criteria.

Various assessments will be conducted, including measuring your baseline factor IX activity levels and checking for antibodies against AAV5 (the viral vector used in the gene therapy).

3 Treatment Administration

You will receive a single dose of CSL222 (etranacogene dezaparvovec, also known as Hemgenix).

The medication will be administered as an intravenous infusion at a dose of 1×10¹³ genome copies/mL.

This is a gene therapy treatment designed to help your body produce factor IX, the clotting protein that is deficient in hemophilia B.

4 Post-treatment Monitoring

After receiving the gene therapy, you will be closely monitored for safety and effectiveness.

Regular blood tests will be performed to measure your factor IX activity levels and to check liver function through tests like ALT/AST (liver enzymes).

If significant changes in liver enzymes occur, you may receive corticosteroid treatment to manage this side effect.

5 Follow-up Assessments

Throughout the study, your bleeding episodes will be tracked, including spontaneous bleeds, joint bleeds, and bleeds requiring factor IX treatment.

Your factor IX consumption will be recorded to see if the gene therapy reduces your need for factor replacement therapy.

You will complete quality of life questionnaires (CHO-KLAT, EQ-5D-5L, and PROMIS) to assess how the treatment affects your daily life and well-being.

Liver ultrasounds will be performed to monitor your liver health.

6 Long-term Follow-up

The study includes long-term monitoring that will continue until the study end date (July 31, 2025, with overall study completion by October 24, 2033).

During this time, you will be assessed for the durability of treatment effect, including whether you can remain free of continuous factor IX prophylaxis.

You will be monitored for any delayed side effects or immune responses, including development of antibodies against factor IX (inhibitors) or the viral vector (AAV5).

Who Can Join the Study?

Must be born male
Must be between 11.5 years and 17 years old when giving consent to participate
Must have hemophilia B (a bleeding disorder) that is severe or moderately severe, with 2% or less of normal Factor IX (the blood clotting protein that is missing in hemophilia B)
Must currently be on regular preventive treatment (called prophylaxis) with Factor IX medication
Must have been on a stable, continuous Factor IX prophylaxis schedule for at least 2 months before screening
Must have received Factor IX treatment on at least 75 separate days before screening
Must complete the Lead-in Period (initial observation phase) of at least 6 months (26 weeks) before receiving the study treatment
Must be between 12 and 18 years old (but not yet 18) at the time of receiving the study treatment (CSL222)

Who Cannot Join the Study?

You cannot join if you are under 12 years old or 18 years or older.
You cannot join if you have mild hemophilia B (a bleeding disorder caused by low levels of clotting factor IX).
You cannot join if you have previously received any gene therapy product.
You cannot join if you have active hepatitis C virus infection (liver inflammation caused by a virus).
You cannot join if you have active hepatitis B virus infection.
You cannot join if you have a history of human immunodeficiency virus (HIV) infection with a detectable viral load.
You cannot join if you have a history of inhibitors (antibodies that block factor IX treatment) to factor IX.
You cannot join if you have a known allergy or hypersensitivity (severe allergic reaction) to any of the components of the study drug.
You cannot join if you have significant liver disease or abnormal liver function.
You cannot join if you have significant kidney disease or abnormal kidney function.
You cannot join if you have any condition that would make it unsafe for you to participate in the study.
You cannot join if you have participated in another clinical trial within 30 days before this study starts.

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country
Medical University Of Vienna	Vienna	Austria
Centre Hospitalier Universitaire De Lille	Lille	France
Katholieke Universiteit te Leuven	Leuven	Belgium

Other Sites

Site Name	City	Country
Hospital Sant Joan De Deu Barcelona	Esplugues De Llobregat	Spain
Ahxmobyewm Pykwqkjv Htpjvhjp Dx Mvkkpzonb	Marseille	France
Fzegzdize Pjlu Lp Iunawdyhdmfdm Bmfwjqlxd Dly Hpcolwfo Ufuvhcafcljta Lx Ptm	Madrid	Spain

Trial status

Country	Status	Recruitment Start
Austria	Not yet recruiting	31.07.2025
Belgium	Recruiting	31.07.2025
France	Not yet recruiting	31.07.2025
Spain	Not yet recruiting	31.07.2025

Trial locations

Investigated drugs:

Etranacogene Dezaparvovec

Etranacogene dezaparvovec (CSL222) is a gene therapy medication being studied to treat adolescent males with severe or moderately severe hemophilia B. Gene therapy works by introducing a functional copy of the gene that is missing or not working properly in people with hemophilia B. This may help the body produce the clotting factor that is lacking in hemophilia B patients, potentially reducing bleeding episodes and the need for regular factor replacement treatments.

Hemophilia B is a rare genetic bleeding disorder caused by a deficiency in clotting factor IX. This condition primarily affects males and is inherited in an X-linked recessive pattern. Patients with hemophilia B experience prolonged bleeding after injuries, surgeries, or even minor traumas due to their blood’s inability to clot properly. In severe or moderately severe forms, spontaneous bleeding episodes can occur in joints and muscles without apparent injury, potentially leading to joint damage over time. The severity of hemophilia B is classified based on the level of functional factor IX in the bloodstream, with lower levels corresponding to more severe disease manifestations.

Trial ID:

2023-505805-18-00

Protocol code:

CSL222_3004

NCT ID:

NCT07080905

Trial Phase:

Therapeutic confirmatory (Phase III)

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Study of Etranacogene Dezaparvovec (CSL222) in Adolescent Males with Severe or Moderately Severe Hemophilia B

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?