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Gene therapy offers hope for hemophilia b patients

NCT ID NCT03307980

Disease control Sponsor: Pfizer Source: ClinicalTrials.gov ↗

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 25, 2026 · Last updated Aug 12, 2026 · Updated 3 times

Summary

This study tests a gene therapy (PF-06838435) for people with severe hemophilia B, a bleeding disorder. The therapy uses a harmless virus to deliver a working gene for clotting factor IX. Researchers are following 21 participants long-term to see if it is safe and reduces bleeding. Some participants receive a higher dose in a substudy.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
PF-06838435 (a gene therapy using a modified virus to deliver a working factor IX gene)
What this could lead to
If successful, this gene therapy could allow people with hemophilia B to produce their own clotting factor, reducing or eliminating the need for regular infusions.
What could go wrong
This is a small, early-phase study (21 participants) focused on safety. Gene therapy carries risks like immune reactions or the treatment not lasting long-term. It may not work for everyone.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 2

Tests whether the treatment actually works, and watches for side effects, in a larger group.

Participants

21 people

The number who actually took part.

Started

Jun 2017

Finished

Jul 2026

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

18 to 65 years

Sex

Male participants only

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

This study is currently only enrolling into the dose-escalation substudy with subsequent long-term follow-up. The Eligibility Criteria for entry into the dose-escalation substudy is presented below: Inclusion Criteria: 1. Able to provide informed consent and comply with requirements of the study 2. Males age 18 to 65 years with confirmed diagnosis of hemophilia B (≤2 IU/dL or ≤2% endogenous factor IX) 3. Received ≥50 exposure days to factor IX products 4. No measurable factor IX inhibitor as assessed by the central laboratory and have no prior history of inhibitors to factor IX protein 5. Agree to refrain from donating sperm and either abstain from intercourse or use reliable barrier contraception until 3 consecutive semen samples are negative for vector sequences Exclusion Criteria: 1. Evidence of active hepatitis B or C 2. Currently on antiviral therapy for hepatitis B or C 3. Have significant underlying liver disease 4. Serological evidence\* of HIV-1 or HIV-2 with CD4 counts ≤200/mm3 (\* participants who are HIV+ and stable with CD4 count \>200/mm3 and undetectable viral load are eligible to enroll) 5. Neutralizing antibody titers to the capsid portion of PF-06838435 above the established threshold 6. Sensitivity to heparin or heparin induced thrombocytopenia; sensitivity to any of the study interventions, or components thereof, or drug or other allergy 7. Previously dosed in a gene therapy research trial at any time or in an interventional clinical study within 3 months of screening visit 8. Any concurrent clinically significant major disease or condition 9. Unable or unwilling to comply with the study procedures

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Conditions

The condition(s) this trial relates to.

hemophilia A hemophilia B

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Hemophilia B

Contacts and locations

Locations

  • Ege Universitesi Tip Fakultesi Cocuk Sagligi ve Hastaliklari Anabilim Dali

    Izmir, 35100, Turkey (Türkiye)

  • Istanbul Universitesi Onkoloji Enstitusu Çocuk Hematoloji Onkoloji Bilim Dali

    Istanbul, 34093, Turkey (Türkiye)

  • Istanbul University Clinical Trials Excellence Center

    Istanbul, 34452, Turkey (Türkiye)

  • LA Center for Bleeding and Clotting Disorders

    New Orleans, Louisiana, 70112, United States

  • LA Center for Bleeding and Clotting Disorders - Metairie

    Metairie, Louisiana, 70001, United States

  • Louisiana Center for Advanced Medicine

    Slidell, Louisiana, 70461, United States

  • McGill University Health Center - Research Institute

    Montreal, Quebec, H4A 3J1, Canada

  • McMaster University

    Hamilton, Ontario, L8S 3L8, Canada

  • McMaster University Medical Centre - Hamilton Health Sciences

    Hamilton, Ontario, L8N 3Z5, Canada

  • Mississippi Center for Advanced Medicine

    Madison, Mississippi, 39110, United States

  • Royal Prince Alfred Hospital

    Camperdown, New South Wales, 2050, Australia

  • The Children's Hospital of Philadelphia

    Philadelphia, Pennsylvania, 19104, United States

  • The Research Institute of the McGill University Health Centre

    Montreal, Quebec, H3H 2R9, Canada

  • Tulane Lakeside Hospital

    Metairie, Louisiana, 70001, United States

  • Tulane University Clinical Translational Unit

    New Orleans, Louisiana, 70112, United States

  • Tulane University Hospitals and Clinic

    New Orleans, Louisiana, 70112, United States

  • Tulane University School of Medicine

    New Orleans, Louisiana, 70112, United States

  • UC Davis Comprehensive Cancer Center

    Sacramento, California, 95817, United States

  • UC Davis Ellison Ambulatory Care Clinic

    Sacramento, California, 95817, United States

  • UC Davis Medical Center

    Sacramento, California, 95817, United States

  • UC Davis Medical Center department of Radiology

    Sacramento, California, 95817, United States

  • UC Davis Midtown Cancer Center

    Sacramento, California, 95817, United States

  • UC DavisHealth Main Hospital

    Sacramento, California, 95817, United States

  • University Medical Center New Orleans

    New Orleans, Louisiana, 70112, United States

  • Weill Cornell Medicine - New York Presbyterian Hospital

    New York, New York, 10065, United States

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