Phase 2 Evaluation of rAAV9-LAMP2B Gene Therapy in Male Danon Disease Patients: Efficacy and Safety Assessment of Intravenous Administration

The primary objective of this study is to evaluate whether **RP-A501** (an AAV9 capsid containing the LAMP2B transgene; AAV9.LAMP2B) will result in significant improvement as assessed via the co-primary endpoint comprised of LAMP2 myocardial tissue expression and left ventricular mass index (LVMI). This is clinically relevant as it aims to address the underlying pathophysiology of **Danon Disease**, potentially improving cardiac function and patient outcomes.

Secondary objectives include:

• Assessing the impact of RP-A501 on the components of the co-primary endpoint.
• Evaluating the impact of RP-A501 on biomarker evidence of myocardial injury.
• Assessing the impact of RP-A501 on quality of life and heart failure symptoms.
• Evaluating the impact of RP-A501 on event-free survival.
• Assessing the impact of RP-A501 on safety.

The clinical trial involves a total of **10 male participants** diagnosed with **Danon Disease**, a rare genetic disorder. The study population is composed of individuals aged **8 years and older**, with a specific focus on those exhibiting left ventricular hypertrophy while maintaining preserved systolic function. Participants were selected based on the presence of a pathogenic or likely pathogenic variant of the LAMP2 gene. The trial exclusively includes male subjects, as indicated by the eligibility criteria. Participants are required to have a New York Heart Association (NYHA) Class II to III classification and an hsTnI level at least 20% above the upper limit of normal. All participants must have received vaccinations against Neisseria meningitidis, Streptococcus pneumoniae, and Hemophilus influenzae at least six weeks prior to the administration of the investigational therapy. The trial population is considered vulnerable, and participants must demonstrate the ability to comply with study procedures, including investigational therapy and follow-up evaluations. Lifestyle considerations such as diet and physical activity are not specified in the available data.

The clinical trial is designed to evaluate the efficacy and safety of **AAV9.LAMP2B**, a gene therapy for Danon Disease, in male patients. This is a Phase II, multi-center, open-label study. The trial employs a randomized, controlled design to ensure robust data collection and analysis. The estimated duration of the trial is from April 2024 to October 2029, with participant involvement expected to last up to 12 months, depending on individual response and adherence to the protocol.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on criteria such as documentation of a pathogenic variant of the LAMP2 gene, male gender, age of at least 8 years, and evidence of left ventricular hypertrophy. Following the screening, eligible participants will receive the investigational therapy and attend regular follow-up visits to monitor safety and efficacy outcomes. These visits will include assessments of myocardial tissue expression of LAMP2 protein, left ventricular mass index (LVMI), and other secondary endpoints such as hsTnI, NT-proBNP, and NYHA class. The end-of-study visit will conclude the participant's involvement, with a comprehensive evaluation of the treatment's impact.

Participants may be withdrawn from the study early if they experience significant adverse events, fail to comply with study procedures, or if the investigator deems it necessary for their safety. The trial's primary objective is to assess the improvement in LAMP2 myocardial tissue expression and LVMI, while secondary objectives include evaluating event-free survival and the incidence of treatment-emergent safety events. The study aims to provide valuable insights into the potential benefits of gene therapy for patients with Danon Disease.

The clinical trial involves the administration of **AAV9.LAMP2B**, a **solution for infusion** containing the active substance **adeno-associated virus serotype 9 vector containing the human LAMP2 isoform B transgene**. This investigational gene therapy is administered via **intravenous infusion**. The maximum daily and total dose is 67 trillion vector genomes, with a treatment period of one day. This product is designated as an orphan drug and is not formulated for pediatric use.

**Epysqli 300 mg concentrate for solution for infusion** and **BEKEMV 300 mg concentrate for solution for infusion** both contain the active substance **eculizumab**, a humanized monoclonal antibody. These are administered as a **solution for infusion** through **intravenous administration**. The maximum daily and total dose for each is 1200 mg, with a treatment period of up to three weeks. These products are not pediatric formulations and are not designated as orphan drugs.

**RITUXIMAB** is provided as a **concentrate for solution for infusion** and is administered via **intravenous infusion**. The active substance is **rituximab**, a humanized monoclonal antibody. The maximum daily and total dose is 750 mg/m², with a treatment period of two weeks. This product is designated as an orphan drug and is not formulated for pediatric use.

**SIROLIMUS** is available in two forms: **coated tablet** and **oral solution**. The active substance is **sirolimus**, a chemical compound. The maximum daily and total dose is 2 mg, with a treatment period of up to three weeks. This product is designated as an orphan drug and is not formulated for pediatric use.

**PARACETAMOL** is administered as a **tablet** for **oral use**. The active substance is **paracetamol**, a chemical compound. The maximum daily and total dose is 1 g, with a treatment period of two weeks. This product is not designated as an orphan drug and is not formulated for pediatric use.

**METHYLPREDNISOLONE SODIUM SUCCINATE** is provided as a **powder for solution for infusion** and is administered via **intravenous use**. The active substance is **methylprednisolone sodium succinate**, a corticosteroid. The maximum daily and total dose is 0.8 mg/kg, with a treatment period of up to four days. This product is not designated as an orphan drug and is not formulated for pediatric use.

**PREDNISONE** is administered as a **tablet** for **oral use**. The active substance is **prednisone**, a corticosteroid. The maximum daily and total dose is 60 mg, with a treatment period of up to three weeks. This product is not designated as an orphan drug and is not formulated for pediatric use.

**DIPHENHYDRAMINE HYDROCHLORIDE** is provided as a **tablet** for **oral use**. The active substance is **diphenhydramine hydrochloride**, a chemical compound. The maximum daily and total dose is 50 mg, with a treatment period of two weeks. This product is not designated as an orphan drug and is not formulated for pediatric use.

**PEGCETACOPLAN** is administered as a **solution for injection** via **subcutaneous injection**. The active substance is **pegcetacoplan**, a protein of other origin. The maximum daily dose is 54 mg, with a total dose of 324 mg over a treatment period of three weeks. This product is not designated as an orphan drug and is not formulated for pediatric use.

Participant compliance with the dosing schedule is monitored throughout the trial to ensure adherence to the prescribed treatment regimens. The trial includes both experimental and non-experimental treatments, with the latter serving as standard-of-care therapy or comparator treatments as applicable.

The efficacy of the clinical trial will be assessed through a co-primary endpoint, which includes the evaluation of myocardial tissue expression of the **LAMP2** protein and a decrease in the left ventricular mass index (LVMI). These parameters are critical in determining the effectiveness of the investigational therapy, RP-A501, in male patients with Danon Disease. Secondary endpoints will further evaluate efficacy by measuring additional parameters such as LAMP2 protein expression, LVMI, high-sensitivity troponin I (hsTnI), N-terminal pro b-type natriuretic peptide (NT-proBNP), Kansas City Cardiomyopathy Questionnaire (KCCQ) scores, and New York Heart Association (NYHA) class. Event-free survival, defined by the absence of death, heart transplant, mechanical circulatory support, or heart failure hospitalization, will also be monitored.

The collection and analysis of these efficacy parameters will be conducted at specified timepoints throughout the trial. The trial is designed to ensure comprehensive assessment of the investigational therapy's impact on the disease, with a focus on both clinical and patient-reported outcomes. The use of validated scales and laboratory tests will facilitate accurate measurement of the endpoints, ensuring the reliability of the efficacy data collected during the study.