Phase I/II/III Study of rAAV8-hMD1 Gene Therapy in Ambulatory Boys with Duchenne Muscular Dystrophy, Including Dose Determination and Long-term Safety Evaluation

The primary objective of this clinical trial is to evaluate the **clinical efficacy** and safety of the investigational medicinal product (IMP) in boys with Duchenne Muscular Dystrophy. This study is structured in three phases: Part 1 aims to determine a safe and tolerable dose of the IMP with acceptable gene expression for subsequent evaluation. Part 2 focuses on demonstrating the clinical efficacy of the IMP compared to placebo at one year post-inclusion, as well as assessing its safety and tolerability. Part 3 involves a long-term follow-up to further assess the safety and tolerability of the IMP. The clinical relevance of this study lies in its potential to provide a new therapeutic option for Duchenne Muscular Dystrophy, a severe genetic disorder characterized by progressive muscle degeneration.

Secondary objectives include: - Assessing the **biodistribution** of the IMP. - Demonstrating the **pharmacodynamic activity** of the IMP. - Evaluating the **immunogenicity** of the IMP. - Comparing the efficacy on the disease course two years after inclusion between patients treated with the active IMP initially and those treated after a one-year delay.

The clinical trial involves a total of **50 participants** diagnosed with **Duchenne Muscular Dystrophy**. The study population consists exclusively of **ambulant male** subjects, aged between **6 to 10 years**. Participants were selected based on specific criteria, including a positive gene test confirming DMD mutations that abolish dystrophin production. The trial population is characterized by a **vulnerable population** status, given the young age and specific health condition of the participants. Lifestyle considerations such as body mass index (BMI) are taken into account, with specific percentile requirements for different parts of the study. The selection process ensures that participants are within the 75th percentile for BMI in Part 1 and the 95th percentile for body weight in Part 2, according to validated charts applicable in the country site. The trial does not include female subjects, focusing solely on the male demographic to assess the safety, tolerability, and efficacy of the investigational medicinal product (IMP) over the course of the study.

The clinical trial is designed to evaluate the efficacy and safety of a gene therapy product, **rAAV8-hMD1**, in boys with **Duchenne Muscular Dystrophy**. This study is structured as a **randomized, quadruple-blind, placebo-controlled** trial, encompassing three distinct phases: dose determination, efficacy and safety evaluation, and long-term safety follow-up. The trial is expected to span from October 2020 to October 2028, with participant involvement lasting approximately one year for the primary evaluation, followed by extended monitoring.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on criteria such as age, ambulatory status, and genetic confirmation of Duchenne Muscular Dystrophy. The trial will include regular follow-up visits to monitor safety and efficacy endpoints, such as changes in the North Star Ambulatory Assessment (NSAA) score at week 52, and secondary endpoints including adverse event incidence and pharmacokinetic/pharmacodynamic measures. The end-of-study visit will conclude the participant's active involvement, with continued safety assessments as needed.

Inclusion criteria require participants to be ambulant males aged 6 to 10 years, with a body mass index or weight within specified percentiles. Exclusion criteria are not explicitly detailed. Conditions for early termination from the study may include significant adverse events or non-compliance with study protocols. The investigational product, **rAAV8-hMD1**, is administered via parenteral use, with auxiliary treatments including **METHYLPREDNISOLONE** and **PREDNISOLONE** provided as supportive care. The trial aims to establish a safe and effective dose of the gene therapy, assess its clinical benefits compared to placebo, and ensure long-term safety for participants.

The clinical trial involves the administration of several treatments, including both experimental and non-experimental medications. The **experimental medication** in this study is rAAV8-hMD1, a genetically modified recombinant viral vector. This vector is composed of an adeno-associated viral vector serotype 8 containing the human MD1 gene, designed to express a sequence-optimized gene for human microdystrophin (hMD1) in appropriate tissues. The pharmaceutical form of rAAV8-hMD1 is a solution for infusion, and it is administered via parenteral use. The dosing schedule and frequency are determined based on the phase of the trial, with a focus on establishing a safe and tolerable dose with acceptable gene expression.

In addition to the experimental treatment, the trial includes the administration of **Methylprednisolone**, a corticosteroid used as an auxiliary treatment. Methylprednisolone is provided in the form of a powder for solution for injection and is administered through intravenous infusion. The frequency and dosage are aligned with standard clinical practices for corticosteroid use in similar therapeutic contexts.

Another auxiliary treatment used in the trial is **Prednisolone**, also a corticosteroid. Prednisolone is available in the form of effervescent tablets and is administered orally. The dosage and administration frequency are consistent with established guidelines for corticosteroid therapy.

The trial also utilizes **Soliris (Eculizumab)**, a protein-based medication, as an auxiliary treatment. Soliris is provided as a 300 mg concentrate for solution for infusion and is administered via intravenous infusion. The dosing schedule is determined by the trial protocol, ensuring compliance with safety and efficacy standards.

**Rapamune (Sirolimus)**, an oral solution, is included as an auxiliary treatment. Sirolimus is administered orally, with the dosage and frequency tailored to the specific needs of the trial participants, following established therapeutic guidelines.

As a comparator treatment, the trial employs **Ringer Lactate Fresenius Kabi France**, a solution for injection/infusion. This solution contains sodium lactate, potassium chloride, sodium chloride, and calcium chloride dihydrate. It is administered parenterally and serves as a placebo in the trial, providing a sterile solution intended for infusion after dilution. The administration of this solution is conducted in accordance with the trial's placebo-controlled design.

Participant compliance with the dosing schedules is monitored throughout the trial to ensure adherence to the protocol and to assess the safety and efficacy of the treatments. The trial is conducted under strict regulatory standards, with all medications and procedures adhering to the highest levels of clinical and ethical guidelines.

The clinical trial aims to assess the efficacy of a gene therapy for **Duchenne Muscular Dystrophy** (DMD) through a structured evaluation of primary and secondary endpoints. The primary efficacy endpoint is the change from baseline in the North Star Ambulatory Assessment (NSAA) score at week 52. This endpoint is designed to measure improvements in motor function, which is critical for evaluating the therapeutic impact of the investigational medicinal product (IMP) compared to placebo.

Secondary endpoints include safety and tolerability assessments, which will be measured by the incidence of adverse events (AEs) or serious adverse events (SAEs), and evaluated through changes in laboratory parameters, vital signs, and physical examinations. Additional clinical efficacy endpoints include the Time to 10 Meters Walk/Run Test (10MWRT), Time to Rise From Floor (RFF), and the 6-Minutes Walk Test (6MWT). Pharmacokinetic and pharmacodynamic (PK/PD) endpoints will also be assessed, including vector shedding quantification in blood, urine, saliva, and feces.

The efficacy parameters will be collected and analyzed at specified timepoints, with the primary endpoint being assessed at week 52. The use of validated scales and tests ensures the reliability and accuracy of the efficacy assessments. The trial is structured to include a dose determination part, followed by an efficacy and safety evaluation, and a long-term safety follow-up, providing a comprehensive assessment of the IMP's clinical benefits and risks.