Editor’s Pick


Pfizer is nearly ready to resume dosing in its phase 3 hemophilia A gene therapy trial.

Pfizer Inc. is finally almost ready to resume dosing in its Phase 3 hemophilia A gene therapy trial. Six months after the FDA ended the clinical holding of the test, the research institutions will begin re-registration to resume dosing in October. 

In early November, the FDA stopped a study of the gyrotocogen fitelparvovec in collaboration with Sangamo Therapeutics, confirming a voluntary pause in testing and dosing already implemented by Pfizer.

Pfizer ended the break after seeing more than 150% factor VIII activity in the blood of some patients. 

In March, the FDA suspended the clinical hold, but Pfizer maintained a voluntary pause while it worked to meet “all necessary conditions,” including updated study protocols from regulators. Pfizer now has everything to support continued enrollment and dosing. 

The situation took longer than expected. In February, Sangamo told investors that Pfizer planned to reopen trials in the first half of 2022. By May, the goal had changed to restarting the trial in the third quarter of 2022 and reporting key data in the second half of 2023.

The target for data declines was lowered again in August and is now in the first half of 2019 after a further delay. 

Pfizer was quite deep into the clinical trial when it stopped recruiting, and more than 50% of the 63 intended participants had participated.

At the time of the cancelled registration, BioMarin was working to get its competitor’s hemophilia A gene therapy under way. The goal is to resubmit  for FDA approval by the end of the month. 

Whether or not gene therapy can significantly affect the hemophilia A market remains an open question. Durability is a major concern, as studies of both candidates observe a decline in factor VIII activity over time.


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