Home › Trials › NCT06003387

Gene therapy for adults with Hemophilia B and specific antibodies

Phase 3b, Open-label, Multicenter, Single-dose Study Investigating Efficacy and Safety of CSL222 (Etranacogene Dezaparvovec) Gene Therapy Administered to Adult Subjects With Severe or Moderately Severe Hemophilia B With Detectable Pretreatment AAV5 Neutralizing Antibodies

Phase 3 Interventional CSL Behring · NCT06003387

This study is testing a new gene therapy called CSL222 to see if it can help adults with Hemophilia B who have certain antibodies reduce their bleeding risks.

Quick facts

PhasePhase 3
Study typeInterventional
Enrollment35 (estimated)
Ages18 Years and up
SexAll
SponsorCSL Behring Industry-sponsored
Locations26 sites (San Diego, California and 25 other locations)
Trial IDNCT06003387 on ClinicalTrials.gov

What this trial studies

This clinical trial evaluates the efficacy and safety of CSL222, a gene therapy designed for adults with severe or moderately severe Hemophilia B who have detectable neutralizing antibodies against adeno-associated virus serotype 5 (AAV5). Participants will receive CSL222 to assess its ability to reduce bleeding risks associated with their condition. The study focuses on individuals who have been on routine factor IX prophylaxis and have a history of exposure to factor replacement therapy. The trial aims to determine if this gene therapy can effectively manage their hemophilia symptoms.

Who should consider this trial

Good fit: Ideal candidates are adults aged 18 and older with severe or moderately severe Hemophilia B and detectable AAV5 neutralizing antibodies.

Not a fit: Patients without detectable AAV5 neutralizing antibodies or those with mild Hemophilia B may not benefit from this therapy.

Why it matters

Potential benefit: If successful, this therapy could significantly reduce bleeding episodes and improve the quality of life for patients with Hemophilia B.

How similar studies have performed: Previous studies involving gene therapies for hemophilia have shown promising results, indicating potential for success in this approach.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

* Considered legally an adult, as defined by country regulations.
* Has 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 is on continuous routine FIX prophylaxis.
* Has 2 consecutive detectable AAV5 NAb titer results between Screening and Visit L-Final using a validated AAV5 NAb assay (based on central laboratory results).
* Has greater than (\>) 150 previous exposure days to FIX replacement therapy.
* Has been on stable FIX prophylaxis for at least 2 months before Screening.
* Has demonstrated capability to independently, accurately, and in a timely manner complete the eDiary during the Lead-in Period, as judged by the investigator.
* Acceptance to adhere to contraception guidelines.
* Able to provide informed consent after receipt of verbal and written information about the study.
* Investigator believes that the participant (or the participant's legally acceptable representative\[s\]) understands the nature, scope, and possible consequences of the study and is able to adhere to the study procedures.

Exclusion Criteria:

* History of FIX inhibitors or positive FIX inhibitor test at Prescreening, Screening or Visit L-Final (based on central laboratory results).
* Screening or Visit L-Final laboratory values (based on central laboratory results) of total bilirubin \> 2 × the upper limit of normal (ULN) (except if caused by Gilbert's syndrome).
* Screening or Visit L-Final laboratory values (based on central laboratory results) of any of the following laboratory abnormalities:
* a) ALT \> 2 × the ULN
* b) AST \> 2 × the ULN
* c) Alkaline phosphatase \> 2 × the ULN
* d) Serum creatinine \> 2 × the ULN
* e) Hemoglobin less than (\<) 8 g/dL
* Any condition other than hemophilia B resulting in an increased bleeding tendency.
* Thrombocytopenia, defined as a platelet count \<50 × 10\^9/L, at Screening or Visit L Final (based on central laboratory results).
* Any uncontrolled or untreated infection (human immunodeficiency virus \[HIV\], hepatitis B virus \[HBV\] and hepatitis C virus \[HCV\], or any other significant concurrent, uncontrolled medical condition 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.
* Known history of allergy to corticosteroids or known medical condition that would require chronic administration of oral corticosteroids.
* Known uncontrolled allergic conditions or allergy / hypersensitivity to any component of the CSL222 excipients (ie, sucrose, potassium chloride, potassium dihydrogen phosphate, sodium chloride, and disodium hydrogen phosphate).
* Previous AAV5 gene therapy treatment.
* Receipt of an experimental agent or device within 60 days before Screening until the end of the study.

Where this trial is running

San Diego, California and 25 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Hemophilia B
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.