March 13, 2026-
A single infusion of GS001, an investigational AAV gene therapy, has demonstrated sustained increases in factor VIII (FVIII) levels for up to nearly three years in patients with severe hemophilia A—while using significantly lower doses than currently approved therapies.
The findings come from a Phase 1 pilot study (NCT04728841) evaluating the safety, tolerability, and biological activity of GS001 in 12 adult men with severe hemophilia A.
AAV8-based approach to improve durability
GS001 utilizes an engineered AAV8 vector to deliver a functional, truncated version of the F8 gene to liver cells. This AAV-mediated gene transfer enables endogenous production of FVIII—the clotting protein deficient in hemophilia A.
Unlike some earlier approaches, GS001 is designed to:
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Enhance transgene stability and expression
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Overcome size limitations of the F8 gene
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Maintain durable FVIII production at lower vector doses
Promising efficacy at reduced doses
Patients received a single intravenous infusion at either:
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2×10¹² vg/kg (low dose)
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4×10¹² vg/kg (high dose)
Both doses are substantially lower than those used in approved AAV gene therapies, highlighting improved delivery efficiency.
Key outcomes include:
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Rapid FVIII expression, detectable within 1 week and peaking at 5–7 weeks
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Sustained FVIII levels:
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Low-dose group: maintained moderate hemophilia range up to ~3 years
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High-dose group: maintained mild hemophilia range beyond 2 years
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Significant reductions in:
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Annual bleeding rates
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FVIII replacement therapy usage
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No patients in the high-dose group required on-demand FVIII treatment
Managing immune responses to AAV
As with many AAV-based gene therapies, immune responses remain a key challenge. To address this, patients received prophylactic immunosuppression:
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Prednisone alone, or
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Prednisone + tacrolimus
The combination regimen showed enhanced control of immune responses, particularly by suppressing T-cell activity targeting transduced liver cells, leading to:
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Faster FVIII expression
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Higher and more sustained FVIII levels
Favorable safety profile
GS001 was well tolerated across both dose groups:
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Most common adverse events: transient liver enzyme elevations
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No serious treatment-related adverse events reported
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No increased infection risk associated with immunosuppression
Advancing next-generation AAV therapies
These results highlight the potential of next-generation AAV8 gene therapy platforms to achieve durable clinical benefit at lower doses, which could improve safety, reduce manufacturing burden, and expand patient access.
The study, published in Signal Transduction and Targeted Therapy, supports further development of GS001 as a promising AAV-based treatment option for hemophilia A.
