# Balancing Promise and Peril: Hemophilia Gene Therapy Insights

## TL;DR

This paper reviews progress in gene therapy for hemophilia, highlighting recent approvals and ongoing challenges in achieving long-term cures.

## Contribution

The paper provides a comprehensive synthesis of clinical trial findings and challenges in hemophilia gene therapy.

## Key findings

- Valoctocogene roxaparvovec and Etranacogene dezaparvovec have been approved for severe hemophilia A and B.
- Non-factor replacement therapies offer improved efficacy for patients with inhibitors.
- Viral vector-based approaches face biological constraints and long-term safety concerns.

## Abstract

Hemophilia is an inherited disorder characterized by impaired blood clotting caused by mutations in the genes responsible for producing coagulation factor (F) VIII (hemophilia A, HA) or FIX (hemophilia B, HB). Current treatment primarily relies on replacement therapy, involving frequent and costly infusions of FVIII or FIX concentrates. While effective, these treatments come with the risk of developing neutralizing antibodies (inhibitors) against the infused factor. In recent years, non‐factor replacement therapies have emerged as innovative treatment options, offering enhanced efficacy especially for patients with inhibitors. Despite their advantages, these approaches still fall short of providing a definitive, long‐term cure. Since hemophilia is a monogenic disease, it presents an excellent opportunity for cell and gene therapy approaches aimed at achieving durable treatment and potentially a cure. Over the past three decades, remarkable advancements have been made in hemophilia gene therapy, culminating in the approval of Valoctocogene roxaparvovec (ROCTAVIAN, AAV‐FVIII) and Etranacogene dezaparvovec (HEMGENIX, AAV‐FIX) for patients with severe HA and HB, respectively. Nevertheless, gene therapy poses questions regarding its long‐term efficacy and safety. This review synthesizes findings from clinical trials, addresses persistent challenges in hemophilia gene therapy, and underscores the biological constraints and limitations inherent to viral vector‐based approaches.