(MED-TH-07.3) Gene therapy

Gene therapy has emerged as a transformative hemophilia A (HA) treatment. Unlike conventional replacement therapy, which requires frequent factor VIII (FVIII) infusions, or even the recent non-replacement options, gene therapy offers the potential for long-term therapeutic benefits. By addressing the underlying genetic deficiency in FVIII, gene therapy enables sustained endogenous FVIII expression, reducing reliance on external supplementation and significantly lowering the frequency of bleeding episodes.

Clinical trials using adeno-associated viral (AAV) vectors to deliver the FVIII transgene to hepatocytes have shown promising results. Many patients have achieved durable FVIII activity levels sufficient to prevent spontaneous bleeding, leading to an improved quality of life. These advancements culminated in the approval of the first licensed gene therapy product, Roctavian (valoctocogene roxaparvovec), an AAV5 vector-based therapy designed for adults with HA.

Regardless of these advantages, several challenges and limitations remain. The durability of FVIII expression varies among patients, with some experiencing a decline in transgene expression over time. Immune responses to the viral vector can lead to adverse effects or reduce therapeutic efficacy. Additionally, gene therapy is not yet suitable for all HA patients, particularly those with pre-existing immunity to AAV or severe liver disease. Long-term safety concerns, including potential hepatotoxicity and risks associated with vector integration, require further investigation. Moreover, the high cost and limited accessibility have restricted gene therapy’s widespread adoption, with only a few patients receiving treatment in the initial years following its market approval.

Beyond AAV-based gene therapy, emerging strategies such as cell therapy and advanced gene-editing technologies offer new possibilities for HA treatment. Stem cell-based therapy (CD68-driven expression) and platelet-targeted FVIII delivery have demonstrated promising clinical data. These cutting-edge approaches aim to overcome current gene therapy limitations, including immune responses and transgene silencing.

Despite the emergence of promising new treatment alternatives for HA, gene therapy continues to be a transformative option. Over 75% of patients in clinical trials remain off prophylaxis for several years post-gene therapy. Reducing costs to make gene therapy more accessible in emerging markets could significantly broaden its availability, helping to address the needs of a large patient population that still lacks effective prophylactic treatment worldwide.