Long-Term Safety Follow-Up of Autologous CD34+ Cells Transduced with w1.6_hWASP_WPRE (VSVg) Lentiviral Vector in Wiskott-Aldrich Syndrome Patients

The primary objective of this study is the **long-term follow-up** of patients with Wiskott-Aldrich Syndrome (WAS) who have undergone autologous transplantation with CD34+ cells transduced with the w1.6_hWASP_WPRE (VSVg) lentiviral vector. This objective is clinically relevant as it aims to assess the sustained safety and potential long-term effects of this gene therapy approach, which is crucial for understanding its viability as a treatment option for WAS, a rare genetic disorder characterized by immunodeficiency and thrombocytopenia.

The clinical trial involves a total of **five male participants** who are part of a vulnerable population. The study focuses on the **treatment of Wiskott-Aldrich Syndrome** and includes patients who have previously been enrolled in phase I/II studies and treated with a single infusion of autologous CD34+ cells transduced with the w1.6_hWASP_WPRE (VSVg) lentiviral vector. The age range of the participants spans from **2 to 17 years**. Participants were selected based on their prior involvement in specific studies conducted in France and the United Kingdom, and the requirement for informed consent from parents, guardians, or the patients themselves. The trial does not include female subjects, and no specific lifestyle considerations such as diet or physical activity are mentioned. The sponsor has not provided additional information regarding the general health status of the participants.

The clinical trial is designed to evaluate the long-term safety and efficacy of **etuvetidigene autotemcel** in patients with **Wiskott-Aldrich syndrome** who have previously undergone autologous transplantation with CD34+ cells transduced with the w1.6_hWASP_WPRE (VSVg) lentiviral vector. This study is a phase IV, non-randomized, open-label, long-term follow-up trial. The trial aims to monitor the incidence and nature of serious adverse events (SAEs), including malignancies, hematologic, autoimmune events, and mortality over a 13-year period following gene therapy. The study will also assess the safety of the gene therapy procedure through annual evaluations of lentiviral integration sites, vector copy numbers, and replication-competent lentivirus (RCL) presence.

Participants will be involved in the study for up to 15 years, with the trial expected to conclude by January 2029. The study includes multiple follow-up visits at 3, 4, 5, 6, 7, 8, 9, and 10 years post-gene therapy, during which clinical status, hematological reconstitution, and immune system recovery will be evaluated. Additional assessments will be conducted at 11, 12, 13, 14, and 15 years post-gene therapy if adverse events of special interest (AESI) occur. The primary endpoints focus on the safety profile of the gene therapy, while secondary endpoints include the evaluation of associated treatment needs and bone marrow integrity.

Participants are required to have been enrolled in the initial phase I/II studies and must have received a single infusion of the investigational product. Informed consent must have been obtained from the patients or their guardians. The study allows for early termination if participants experience significant adverse events or if they withdraw consent. The investigational product is administered via intravenous infusion, and the maximum treatment period is limited to a single administration. The trial is not categorized as low intervention, reflecting the complexity and potential risks associated with the gene therapy procedure.

The clinical trial involves the administration of **etuvetidigene autotemcel**, an experimental medication designed for the treatment of Wiskott-Aldrich Syndrome. This investigational product is composed of **autologous CD34+ cells** that have been transduced ex vivo with the w1.6_hWASP_WPRE (VSVg) lentiviral vector, which encodes the human Wiskott-Aldrich syndrome protein (WASP) gene. The pharmaceutical form of this medication is a **solution for infusion**, and it is administered via **intravenous administration**. The maximum daily dose and total dose amount are both set at 500,000 cells, with a treatment period limited to a single day. The product is not formulated specifically for pediatric use, although it is designated as an orphan drug, indicating its use in rare conditions.

In this study, no non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatments are utilized. The focus is solely on the long-term safety follow-up of patients who have received the autologous transplantation of the transduced CD34+ cells. Participant compliance with the dosing schedule is monitored throughout the trial to ensure adherence to the protocol. The investigational product is developed by GENETHON, and it is classified as a structurally diverse substance under cell therapy, highlighting its advanced therapeutic nature.

Efficacy in this clinical trial will be assessed through a series of primary and secondary endpoints designed to evaluate the long-term safety and clinical outcomes of patients with **Wiskott-Aldrich Syndrome** (WAS) who have undergone gene therapy. The primary endpoints include the evaluation of the incidence and type of serious adverse events (SAEs), particularly focusing on delayed events such as malignancies, hematologic, autoimmune events, and mortality over a 13-year follow-up period. Additionally, the safety of the gene therapy procedure will be assessed through gene transfer analysis, including lentiviral integration sites and vector copy numbers (VCN) in different cell subpopulations, as well as the presence of replication-competent lentivirus (RCL) at yearly post-gene therapy visits. Clinical status evaluations will occur at 3, 4, 5, 6, 7, 8, 9, and 10 years post-therapy, focusing on weight, complete clinical exams, and the evolution of key medical events related to WAS, such as eczema status, infections, bleeding symptoms, and autoimmune manifestations. Hematological reconstitution will be assessed through complete blood count (CBC) including platelet count and size, while the reconstitution of cell-mediated and humoral immunity will be evaluated through immunophenotyping panels, restoration of antibody production, lymphocyte proliferation assays, and humoral response to antigens.

Secondary endpoints include the evaluation of the evolution of the need for associated treatments, such as immunoglobulins and antimicrobial drugs, at yearly post-gene therapy visits. The representation of TCR families will be assessed by PCR, TREC, and TCR V beta panel at 3, 4, and 5 years post-therapy. Bone marrow integrity will also be optionally evaluated through bone marrow aspiration at the same time points. These assessments will provide comprehensive data on the efficacy and safety of the gene therapy over an extended follow-up period, contributing to the understanding of its long-term impact on patients with WAS.