A Phase 3 interventional study of CSL222 (Adeno-associated viral vector serotype 5 [AAV5]-hFIXco-Padua) in Hemophilia B, sponsored by CSL Behring. Recruiting at 17 sites in 8 countries. Open to male participants aged 138 Months to 206 Months. Per ClinicalTrials.gov, last updated 2026-10-20.
Sponsored by CSL Behring (part of CSL Limited) · Phase 3, Interventional, and Treatment
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.
292 studies on the registry are indexed under Hemophilia B; 51 are open to participants now.
This study's planned enrollment of 20 is below the median of 26 across 171 interventional studies indexed under Hemophilia B.
Browse Hemophilia B studies →CSL Behring is the lead sponsor of 145 studies on the registry; 17 are open to participants now.
Of its 24 completed or terminated interventional studies of FDA-regulated products, 17 (71%) have results posted.
First submitted after CSL Behring became part of CSL Limited.
Counted across the registry records on this site, refreshed daily.
The criteria were revised on the registry on Oct 20, 2026. See what changed
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Completed the Lead-in Period: minimum of 6 months (26 weeks) of lead-in data collected and eligibility has been confirmed.
Exclusion Criteria:
Screening laboratory values (based on central laboratory results):
Visit L-Final laboratory values (based on central laboratory results) of:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
A yellow substance made when red blood cells are broken down, which the liver clears. A high level can mean a problem with the liver or the bile ducts.
Criteria often allow more for people with Gilbert’s syndrome, a harmless inherited condition that raises bilirubin.
The top of the normal range for a blood test, as set by the laboratory that runs it. Each lab prints its own range next to your result.
“≤ 2.5 × ULN” means the result can be up to two and a half times that top value.
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Blood cells that help blood clot. Too few raises the risk of bleeding and bruising. A usual adult range is about 150–400 × 10⁹/L (150,000–400,000 per µL); each lab has its own reference range.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Bilirubin
A yellow substance made when red blood cells are broken down, which the liver clears. A high level can mean a problem with the liver or the bile ducts.
Criteria often allow more for people with Gilbert’s syndrome, a harmless inherited condition that raises bilirubin.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ULN (upper limit of normal)
The top of the normal range for a blood test, as set by the laboratory that runs it. Each lab prints its own range next to your result.
“≤ 2.5 × ULN” means the result can be up to two and a half times that top value.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ALT and AST (liver enzymes)
Two enzymes measured in a routine blood test of the liver. Higher levels can mean the liver is under strain or damaged. SGPT and SGOT are older names for ALT and AST.
Criteria usually give a limit as a multiple of the upper limit of normal (ULN), often higher when cancer has spread to the liver.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hemoglobin (Hb)
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Platelets
Blood cells that help blood clot. Too few raises the risk of bleeding and bruising. A usual adult range is about 150–400 × 10⁹/L (150,000–400,000 per µL); each lab has its own reference range.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis C tests
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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)
Administered as a single IV infusion.
Also known as: Etranacogene Dezaparvovec
Annualized Bleeding Rate (ABR)
Time frame: 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)
Canadian Hemophilia Outcomes-Kids Life Assessment Tool (CHO-KLAT) total score and change from baseline
The CHO-KLAT is designed to measure aspects of quality of life for boys with hemophilia. CHO-KLAT is a 40-item questionnaire, available in both child self-report (for ages 7 to 18) and parent-proxy versions (for ages 4 to 18). Items are categorized into 7 key domains (Activities, Autonomy, Bleeding, Emotional Health, Hemophilia Knowledge, Social Functioning, and Treatment). The measure is scored on a scale of 0 to 100, with 100 indicating best health-related quality of life.
Time frame: At baseline and Month 18 post treatment
Endogenous FIX activity
Time frame: At baseline, and at months 6, 12, and 18 after treatment with CSL222
Change from baseline in endogenous FIX activity
Time frame: At baseline, and at months 6, 12, and 18 after treatment with CSL222
Annualized consumption of FIX replacement therapy
Mean annualized consumption (IU/year) of FIX replacement therapy (excluding FIX replacement for invasive procedures).
Time frame: 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
Mean annualized infusion rate (infusions/year) of FIX replacement therapy (excluding FIX replacement for invasive procedures).
Time frame: 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)
Number of participants remaining free of continuous FIX prophylaxis
Time frame: During the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222), and during months 7 to: 24, 36, 48, and 60 after treatment with CSL222
Percentage of participants remaining free of continuous FIX prophylaxis
Time frame: During the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222), and during months 7 to: 24, 36, 48, and 60 after treatment with CSL222
ABR for spontaneous, joint, and FIX-treated bleeding episodes
Time frame: For the Lead-In Period (at least 6 months) and during the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222)
Correlation of FIX activity levels and pre-CSL222 AAV5 NAb titer
Time frame: At the end of the Lead-in Period and during 6 to 18 months after treatment with CSL222
Number of new target joints and resolution of preexisting target joints
Time frame: During the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222), and then annually during the Posttreatment Follow-up Period (up to 5 years)
Number of participants with zero bleeds and zero FIX-treated bleeds
Time frame: During the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222), and during months 7 to: 24, 36, 48, and 60 after treatment with CSL222
Percentage of participants with zero bleeds and zero FIX-treated bleeds
Time frame: During the 52 weeks after stable FIX expression (months 7 to 18 after treatment with CSL222), and during months 7 to: 24, 36, 48, and 60 after treatment with CSL222
Change in the EuroQol-5 Dimensions-5 Levels (EQ-5D-5L) Visual Analogue Scale (VAS) Overall Score
The EQ-5D-5L questionnaire visual analogue scale (VAS) measures overall health status on a vertical VAS ranging from 0 to 100. A higher score indicates better quality of life. The change from baseline in the EQ-5D-5L VAS score will be determined.
Time frame: At baseline, during the Lead-In Period (at least 6 months), and in the Posttreatment Follow-up Period (up to 5 years)
Change in the EQ-5D-5L Index Scores
The EQ-5D-5L questionnaire descriptive system of health-related quality of life consists of 5 dimensions (mobility, self-care, usual activities, pain/discomfort, anxiety/depression) for which responses will be recorded on 5 levels of severity (no problems, slight problems, moderate problems, severe problems, and extreme problems). The responses will be converted into a single index utility score (typically between -0.6 and 1). A higher score indicates better quality of life. The change from baseline in the EQ-5D-5L index score will be determined.
Time frame: At baseline, during the Lead-In Period (at least 6 months), and in the Posttreatment Follow-up Period (up to 5 years)
Change in the Patient-Reported Outcomes Measurement Information System (PROMIS)-25 total score
For participants of age 12-16 years. PROMIS-25 is a collection of short forms measuring quality of life in children. It includes domains of physical function mobility, anxiety, depression, fatigue, peer relationships, and pain interference. Each domain consists of 4 questions and are scored from 1 to 5. PROMIS-25 also includes one question on pain intensity that is available as a numeric rating scale and is scored from 0 (no pain) to 10 (worst imaginable pain).
Time frame: At baseline, during the Lead-In Period (at least 6 months), and in the Posttreatment Follow-up Period (up to 5 years)
Change from baseline in PROMIS-29 total score
For participants of age ≥ 17 years. PROMIS-29 is a collection of short forms consisting of 7 PROMIS domains in depression, anxiety, physical function, pain interference, fatigue, sleep disturbance, and ability to participate in social roles and activities. Each domain consists of 4 questions and are scored from 1 to 5. PROMIS-29 also includes 1 question on pain intensity that is available as a numeric rating scale and is scored from 0 (no pain) to 10 (worst imaginable pain).
Time frame: At baseline, during the Lead-In Period (at least 6 months), and in the Posttreatment Follow-up Period (up to 5 years)
Number of participants with endogenous FIX activity of ≥ 5%
Time frame: Up to 5 years after treatment with CSL222
Percentage of participants with endogenous FIX activity of ≥ 5%
Time frame: Up to 5 years after treatment with CSL222
Adverse events - number of participants
Time frame: During the Lead-in Period (at least 6 months) and during the Posttreatment Follow-up Period (up to 5 years).
Adverse events - percentage of participants
Time frame: During the Lead-in Period (at least 6 months) and during the Posttreatment Follow-up Period (up to 5 years).
Adverse events - number of events
Time frame: During the Lead-in Period (at least 6 months) and during the Posttreatment Follow-up Period (up to 5 years).
Change in liver ultrasound
Time frame: At baseline, month 12 and every 6 months thereafter up to 5 years after CSL222 treatment
Number of participants with antibodies against AAV5
Time frame: From treatment with CSL222 through end of study (up to 5 years after treatment with CSL222)
Number of participants who develop FIX inhibitors
Time frame: From treatment with CSL222 through end of study (up to 5 years after treatment with CSL222)
Number of clinically significant clinical laboratory tests (Hematology and Biochemistry) reported as an AE
Time frame: At baseline and up to 5 years after treatment with CSL222
Number of participants with clinically significant ALT/AST levels
Time frame: At baseline and up to 5 years after treatment with CSL222
Percentage of participants with clinically significant ALT/AST levels
Time frame: At baseline and up to 5 years after treatment with CSL222
Number of participants using corticosteroid for change in AST/ALT levels
Time frame: Up to 5 years after treatment with CSL222
Duration of corticosteroid use for change in AST/ALT levels
Time frame: Up to 5 years after treatment with CSL222
Mean inflammatory markers values
Inflammatory markers include interleukin (IL) -1-beta, IL-2, IL-6, interferon-gamma, and monocyte chemoattractant protein-1 (MCP-1) will be measured and reported as picograms per milliliter (pg/mL).
Time frame: Up to 5 years after treatment with CSL222
Change from baseline in Inflammatory markers
Inflammatory markers include IL -1-beta, IL-2, IL-6, interferon-gamma, and MCP-1
Time frame: At baseline and up to 5 years after treatment with CSL222
Plan to share: Yes — CSL will consider on a case-by-case basis requests to share Individual Patient Data (IPD) with external bona-fide, qualified scientific and medical researchers. For information on the process and requirements for submitting a voluntary data sharing request for IPD, please contact CSL at clinicaltrials@cslbehring.com.
Supporting information: Study protocol, Statistical analysis plan
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.
No publications or documents are linked to this record.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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