Phase I/II Study on Safety and Efficacy of Gene Therapy for FHL3 Using Autologous CD34+ Cells and MUNC-T3 Transduced with UNC13D LV Vector

The primary objective of this study is to assess the initial **safety** of treatment with MUNC-CD34 and MUNC-T3 in patients with Familial Hemophagocytic Lymphohistiocytosis (FHL) caused by mutations in the human UNC13D gene. This includes evaluating the safety of the mobilisation procedure, conditioning regimen, and transplantation with the LV-EF1a-UNC13D lentiviral vector gene-modified autologous hematopoietic stem cells combined with transduced autologous T-cells. The clinical relevance of this objective lies in ensuring that the gene therapy approach is safe for patients, which is crucial for its potential use as a therapeutic option for FHL.

The secondary objectives are: - Characterize the engraftment of donor products through hematopoietic reconstitution after intravenous infusion of MUNC-CD34. - Assess the initial efficacy of the treatment. - Evaluate the long-term safety and efficacy of the therapy. - Estimate the cost of the complete procedure, from mobilisation to transplant, and the total cost over 24 months. These objectives aim to provide a comprehensive understanding of the treatment's effectiveness, safety over time, and economic implications, which are essential for its potential implementation in clinical practice.

The clinical trial involves participants diagnosed with **Familial Hemophagocytic Lymphohistiocytosis (FHL)**, specifically those with a mutation in the UNC13D gene. The study population includes both male and female subjects, ranging in age from 3 months to 17 years. Participants are selected based on their eligibility for an allogeneic hematopoietic stem cell transplantation (HSCT) in the absence of an HLA geno-identical donor, either at diagnosis or following the failure of a previous HSCT. The trial includes a vulnerable population, as it involves minors. The sponsor has not provided information regarding the total number of participants. Key lifestyle considerations, such as diet and physical activity, are not specified. The trial requires informed consent from parents or guardians and mandates the use of effective contraception for patients of childbearing age during the trial and for at least 12 months post-infusion. Participants must also be affiliated with Social Security. The sponsor has not disclosed additional details about the general health status or specific lifestyle habits of the participants.

The clinical trial is a **Phase I/II** open-label, non-randomized, monocentric, single-arm study designed to evaluate the safety and efficacy of gene therapy in patients with **Familial Hemophagocytic Lymphohistiocytosis (FHL)** caused by mutations in the **UNC13D** gene. The trial involves the transplantation of a single dose of autologous CD34+ cells transduced ex vivo with the UNC13D lentiviral vector. The investigational products, MUNC13.4-CD34 and MUNC13.4-T3 suspensions, are administered via **intravenous infusion**. The trial is expected to commence recruitment on September 9, 2024, and conclude by September 9, 2029.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to assess eligibility based on criteria such as age (3 months to 17 years), diagnosis of FHL due to UNC13D mutation, and absence of an HLA geno-identical donor. Following successful screening, participants will receive the investigational treatment and be monitored through follow-up visits. These visits will evaluate primary endpoints, including the incidence of transplantation-related mortality and adverse events, as well as secondary endpoints like hematopoietic reconstitution and long-term safety and efficacy. The end-of-study visit will mark the completion of the participant's involvement, which is anticipated to last up to 24 months post-infusion.

Participants may be withdrawn from the study early if they experience severe adverse events, fail to comply with study procedures, or if the investigator deems it in their best interest. The trial aims to provide comprehensive data on the initial safety and efficacy of the gene therapy, with primary endpoints assessed up to 12 months post-treatment and secondary endpoints evaluated at 6 and 24 months. The study will also estimate the cost of the complete procedure, from mobilization to transplant, over a 24-month period.

The clinical trial involves the administration of two experimental medications: **MUNC13.4-CD34 suspension** and **MUNC13.4-T3 suspension**. Both medications are formulated as a **suspension for injection** and are administered via **intravenous infusion**. The **MUNC13.4-CD34 suspension** contains the active substance **MUNC-CD34**, which is a structurally diverse substance used in cell therapy. This product is designed to be administered as a single dose of autologous CD34+ cells that have been transduced ex vivo with the UNC13D lentiviral vector expressing the UNC13D cDNA. The administration is intended for patients with Munc 13.4 deficiency, and the primary objective is to evaluate the safety and efficacy of this gene therapy approach.

The second experimental medication, **MUNC13.4-T3 suspension**, also formulated as a **suspension for injection**, contains the active substance **MUNC-T3**. Similar to the MUNC13.4-CD34 suspension, this product is a structurally diverse substance used in cell therapy. It involves the use of transduced autologous T-cells, which are modified using the same lentiviral vector technology. The administration of this medication is also via **intravenous infusion**. The trial aims to assess the initial safety of the treatment, including the mobilization procedure, conditioning regimen, and transplantation of the gene-modified cells.

Both experimental medications are not pediatric formulations and are not classified as orphan drugs. The trial does not include any non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatment. Participant compliance with the dosing schedule will be monitored throughout the study to ensure adherence to the protocol. The trial is conducted under the sponsorship of Assistance Publique - Hôpitaux de Paris, and the medications are authorized for use in this clinical setting.

The efficacy of the gene therapy treatment for **Familial Hemophagocytic Lymphohistiocytosis (FHL) type 3** caused by mutations in the UNC13D gene will be assessed through a series of primary and secondary endpoints. Primary endpoints include the incidence of Transplantation Related Mortality (TRM) up to three months post-treatment, the frequency and severity of clinical adverse events (AEs) and laboratory parameters throughout the research period, and the incidence of clinically detectable malignancy or abnormal clonal dominance related to the study treatment at 12 months, as determined by bone marrow analysis and VISA. Detection of Replication-Competent Lentivirus (RCL) will also be assessed at 12 months.

Secondary endpoints focus on characterizing the engraftment of donor products through hematopoietic reconstitution after intravenous infusion of MUNC-CD34, with specific attention to neutrophil and platelet recovery. The initial efficacy of the treatment will be evaluated by the persistent remission of Hemophagocytic Lymphohistiocytosis (HLH), assessed by Disease-free Survival (DFS) at six months, and Vector Copy Number (VCN) in Peripheral Blood Mononuclear Cells (PBMC) greater than 0.2 at six months. Long-term safety and efficacy will be assessed by persistent HLH remission evaluated by DFS at 24 months, VCN in PBMC greater than 0.2 at 24 months, and correction of degranulation function in T-CD3 at 24 months. Additionally, an estimate of the cost of the complete procedure, from mobilization to transplant, and the total cost over 24 months will be considered.