Pfizer and genomic medicines company Sangamo Therapeutics have started dosing in the Phase III AFFINE trial of giroctocogene fitelparvovec (SB-525) for the treatment of haemophilia A patients.

Giroctocogene fitelparvovec is made up of a recombinant adeno-associated virus serotype 6 vector (AAV6) that encodes the complementary deoxyribonucleic acid for B domain deleted human clotting factor VIII (FVIII).

Haemophilia, a genetic haematological rare condition, leads to deficiency of a blood clotting protein. Patients with haemophilia A are deficient in FVIII.

The global, open-label, multi-centre, single-arm AFFINE trial will assess the efficacy and safety of giroctocogene fitelparvovec in more than 60 adults with moderately severe to severe haemophilia A.

Annual bleed rate (ABR) over 12 months after receiving the investigational gene therapy will be the trial’s primary endpoint. This will be compared to ABR on FVIII replacement therapy obtained in the Phase III lead-in trial period.

After a single dosing, participants will be assessed for a period of five years to analyse the drug candidate’s durability and efficacy.

Results from the Phase III lead-in trial will be taken as a baseline for the AFFINE trial.

Recent data from the Phase I/II Alta trial showed clinically meaningful factor levels and decreased bleeds, with giroctocogene fitelparvovec generally well tolerated.

Pfizer global product development rare disease chief development officer Brenda Cooperstone said: “Enrolment in the lead-in study is progressing well and recruitment is on track for Phase III.

“Given the Phase I/II study findings to date, we believe that giroctocogene fitelparvovec has the potential to sustain factor levels and reduce annual bleed rates, suggesting this one-time gene therapy could potentially transform the standard of care for eligible patients worldwide.”

Pfizer and Sangamo entered into giroctocogene fitelparvovec partnership in May 2017. As part of the collaboration, Sangamo has now received $30m in milestone payment.