A Phase 2 interventional study of PF-06838435 (formerly SPK-9001) in Hemophilia B, sponsored by Pfizer. Completed at 25 sites in 4 countries. Open to male participants aged 18 Years to 65 Years. Per ClinicalTrials.gov, last updated 2026-08-11.
Sponsored by Pfizer · Phase 2, Interventional, and Treatment
Long-term safety and efficacy follow-up for participants with Hemophilia B who were previously treated in the C0371005 (formerly SPK-9001-101) study, and a dose-escalation sub-study evaluating safety, tolerability, and kinetics of a higher dose with long-term safety and efficacy follow-up. Participants in the substudy do not need to have participated in C0371005.
Evaluation of the long-term level of persistence and potential late or delayed adverse events associated with PF-06838435 (formerly SPK-9001), assessment of the durability of the transgene expression, and determination of the effects of PF-06838435 on clinical outcomes in individuals who have previously received a single administration of PF-06838435 in the C0371005 study. Amendment 2 of this study incorporates a dose-escalation substudy to evaluate the safety, tolerability, and kinetics of a single IV infusion of PF-06838435 at a higher dose than that used in the C0371005 study. The dose-escalation participants will also be followed for long-term safety and efficacy.
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:
Exclusion Criteria:
Single intravaneous infusion of PF-06838435. After 2 participants receive initial dose, data will be evaluated and a decision will be made to escalate or reduce the dose being evaluated, increase the number of participants receiving the dose, or stop dosing. Multiple iterations may be undertaken.
Biological: PF-06838435 (formerly SPK-9001)
Gene Therapy: A novel, bioengineered adeno-associated viral vector carrying human factor IX variant
Incidence of PF-06838435 related adverse events
Time frame: Baseline up to Year 6
Incidence of clinically significant changes from baseline
Clinically significant changes in physical examination, vital signs, laboratory values. (to be reported as AEs, regardless of causality)
Time frame: Baseline up to 52 weeks
Incidence of protocol-defined medically important events
Clinical thrombotic events, FIX inhibitor development as assessed by Nijmegen Bethesda assay, Hypersensitivity reaction (eg, bronchospasm and anaphylaxis), Hepatic malignancy, Study intervention-related elevated hepatic transaminases that fail to improve or resolve, Malignancy assessed as having reasonable possibility of being related to study intervention (to be reported as SAEs).
Time frame: Baseline up to 52 weeks
Immune response against AAV capsid protein and hFIX transgene
Positive immune response based on peripheral blood mononuclear cell (PBMC) results by interferon gamma enzyme-linked immunospot assay (ELISPOT).
Time frame: Baseline up to 52 weeks
Coagulation Clotting Assay for FIX activity levels
Coagulation Clotting assays to assess FIX activity levels (percent of normal)
Time frame: Baseline up to Year 6
Mean and standard deviation of vector-derived FIX Activity levels
Mean and standard deviation of peak and steady-state FIX Activity
Time frame: Baseline up to 52 weeks
Mean and standard deviation of FIX Antigen levels
Mean and standard deviation of FIX Antigen levels
Time frame: Baseline up to 52 weeks
Annualized bleeding rate (ABR)
ABR (not including those for surgery)
Time frame: Baseline up to Year 6
Annualized (factor FIX) infusion rate
AIR (not including those for surgery)
Time frame: Baseline up to Year 6
Total factor consumption (IU)
total quantity of factor infused annually (not including those for surgery) as recorded on the infusion log
Time frame: Baseline up to Year 6
Total number of bleeding events
spontaneous and traumatic
Time frame: Baseline up to Year 6
Haem-A-QoL
Quality-of-life (QoL) assessment
Time frame: Baseline up to Year 6
EQ-5D-5L
Quality-of-life (QoL) assessment
Time frame: Baseline up to Year 6
Brief Pain Inventory
Quality-of-life (QoL) assessment
Time frame: Year 2 up to Year 6
McGill Pain Questionnaire
Quality-of-life (QoL) assessment
Time frame: Baseline up to 52 weeks
Plan to share: Yes — Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.
This study is completed, as verified in Aug 2026. You cannot join it, but the record below documents what was studied.
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