AVV9-minidystrophin (Pfizer- PF-06939926) for Duchenne Muscular Dystrophy: Clinical Study Update

AVV9-minidystrophin (Pfizer- PF-06939926) for Duchenne Muscular Dystrophy 

Clinical Stage and Regulatory Timeline

PF-06939926 is an investigational gene transfer therapy intended to deliver its mini-dystrophin-encoding gene to muscle tissue for the targeted production of the micro-dystrophin protein.(AAV9.Muscle-promoter.micro-dystrophin). Pfizer is initiating phase 3 pivotal trial to determine safety, efficacy of the PF-06939926 with 3e14 vg/kg dose.

Viral Vector and Gene Construct

AAV9.MuscleProtomter.mini-dystrophin (3.9Kb), The propriety muscle promoter drives the expression of the minidystrophin gene in the muscle tissue. AAV9 have shown to have high tropism for skeletal and cardiac muscle. 

Clinical Phase

Pfizer is currently conducting a Phase 3 (NCT04281485) randomized, double-blind, placebo-controlled study to safety and efficacy of the exogenous gene transfer in DMD subjects. The Phase 1b study conducted to determine the safety and tolerability of the AAV9.Muscle-promoter.micro-dystrophin is completed and one year data is provided in the ASGCT Investor call. 

Number of Participants in Phase 3 Study- 99

Outcome Measures

Primary Outcome Measures

  • Change from Baseline in North Star Ambulatory Assessment (NSAA) at 52 weeks

Secondary Outcome Measures
  • Change from Baseline in mini-dystrophin expression level in muscle up to 52 weeks
  • Quantification of Mini-dystrophin expression level from a muscle biopsy using by liquid chromatography mass spectrometry (LC-MS).Change from Baseline in distribution of mini-dystrophin expression in the muscle
  • Mini-dystrophin distribution from a muscle biopsy will be assessed by immunofluorescence
  • Change from Baseline in serum creatine kinase (CK)

 Key Results from Phase 1b

A single dose of 1.0e14 vg/kg or 3.0 e14 vg/kg AAV9.MuscleProtomter.mini-dystrophin was infused through a peripheral limb vein. Dose-dependent increase in mini-dystrophin expression was observed, and high dose 3.0 e14 vg/kg showed the efficacy and tolerability.  

In the high-dose cohort (n=3) for whom 12-month data are available, the mean percent normal dystrophin at 12 months was 51.6% mean normal dystrophin level. Significant and Sustained Distribution of Dystrophin in muscle biopsy were observed by immunofluorescence

All clinical subject (both low does and high dose patient) showed a significant functional improvement from baseline NSAA scores after one year, compared with the scores in an independent, external control group. 

Durability (Up to 2 years):

Improved NSAA Total Score By Age at Time of Assessment 1 Years The increases in dystrophin levels observed at 2 months were generally sustained at 12 months, and 5 of the 6 boys showed an increase in mini-dystrophin concentration between the 2- and 12-month time points.


Serious Adverse Events: Three SAE were observed.

  • Persistent vomiting resulting in dehydration (required admission for IV anti-emetics and fluids)
  • Acute kidney injury with atypical hemolytic uremic syndrome (aHUS)-like complement activation (required hemodialysis and eculizumab)
  • Thrombocytopenia with aHUS-like complement activation (required platelet transfusion and eculizumab)


Antibody Response: Not Reported

T cell Response (ELISpot): Not Reported


Pfizer Slide Deck Phase 1b result

Pfizer Press Release