Long-term Safety and Efficacy Study and Dose-Escalation Substudy of PF 06838435 in Individuals With Hemophilia B

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