SB-525 gene therapy looks viable for hemophilia A


Interim data suggest SB-525, an investigational gene therapy, may be safe and effective for patients with severe hemophilia A.

In the phase 1/2 Alta trial, SB-525 produced dose-dependent increases in factor VIII activity, with two of eight patients achieving normal factor VIII levels.

In addition, SB-525 was considered well tolerated. One patient did experience treatment-related serious adverse events – hypotension and fever – but these resolved within 24 hours.

Sangamo Therapeutics and Pfizer recently released these data in a press release and conference call.

The data include eight patients with severe hemophilia A who received SB-525 at 9e11 vg/kg, 2e12 vg/kg, 1e13 vg/kg, and 3e13 vg/kg.

Patient 1 (9e11 vg/kg), Patient 2 (9e11 vg/kg), and Patient 3 (2e12 vg/kg) did not experience clinically relevant increases in factor VIII levels and still require prophylactic recombinant factor VIII therapy.

Patient 4 (2e12 vg/kg) and Patient 5 (1e13 vg/kg) discontinued factor VIII therapy but have experienced spontaneous bleeds. Patient 4 had three bleeds in 48 weeks of follow-up, and Patient 5 had two bleeds in 40 weeks of follow-up.

Patient 6 (1e13 vg/kg), Patient 7 (3e13 vg/kg), and Patient 8 (3e13 vg/kg) have stopped factor VIII therapy and remain free of spontaneous bleeds at 28 weeks, 12 weeks, and 6 weeks of follow-up, respectively.

Patients 7 and 8 have achieved normal factor VIII levels. At 6 weeks, their factor VIII levels reached 140% and 94% of normal, respectively, according to a one-stage clotting assay, and 93% and 65%, respectively, according to a chromogenic assay.

“It appears the patients achieve their peak factor level at week 5 to 7 and maintain that level,” Edward Conner, MD, chief medical officer of Sangamo, said during the conference call.

The adverse events observed in this trial include grade 1 tachycardia (n = 1), grade 1 fatigue (n = 1), grade 1 alanine aminotransferase increase (n = 3), grade 1 myalgia (n = 1), grade 2 pyrexia (n = 2), and grade 3 hypotension (n = 1).

“These interim results indicate that SB-525 has the potential to comprise a well-tolerated, reliable, and predictable treatment, features that we believe will be a hallmark of the future gene therapy treatment of hemophilia A,” Dr. Conner said during the call.

Sangamo and Pfizer are enrolling additional patients in this trial, with the goal of expanding the 3e13 vg/kg cohort by up to five patients. The companies plan to present longer-term follow-up data at an upcoming scientific meeting.

The Alta trial is sponsored by Sangamo Therapeutics in collaboration with Pfizer.

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