Phase I/II Open-Label Study Evaluating Safety of Intravenous ATA-200 Gene Therapy in Pediatric Patients with Limb-Girdle Muscular Dystrophy Type R5

The primary objective of this study is to assess the **safety** and tolerability of intravenous administration of ATA-200 in pediatric ambulant patients with limb-girdle muscular dystrophy type R5 (LGMDR5) at two different dosage levels. This evaluation is crucial for determining the recommended dose for future studies, ensuring that the treatment is both safe and effective for this patient population.

Secondary objectives include:

• To collect preliminary efficacy data, which will provide initial insights into the potential therapeutic benefits of ATA-200 in treating LGMDR5.

The clinical trial involves a study population of **ambulant pediatric patients** diagnosed with **limb-girdle muscular dystrophy type R5**. The participants include both male and female subjects, aged between 6 and less than 12 years. The sponsor has not provided the total number of participants. The trial population was selected based on specific criteria, including a confirmed diagnosis of LGMDR5 before the age of 10, the ability to perform a 10-meter walk test within 15 seconds without assistance, and a stable medical status that allows adherence to the study protocol. Participants are required to be seronegative for neutralizing antibodies against AAV8. The study does not specify any particular lifestyle considerations such as diet or physical activity. The trial focuses on a vulnerable population, emphasizing the need for careful monitoring and adherence to ethical standards.

The clinical trial is designed as a **Phase I/II**, open-label, dose escalation study to evaluate the safety and tolerability of intravenous administration of ATA-200, a genetically modified recombinant viral vector, in pediatric patients diagnosed with **limb-girdle muscular dystrophy type R5**. The trial aims to assess two different dosage levels of ATA-200 and select the recommended dose for future studies. The study is expected to commence on January 1, 2024, and conclude by January 1, 2030, with the primary objective of evaluating the incidence of adverse events and clinically relevant abnormalities in vital signs, physical examination findings, and laboratory determinations.

Participants will be involved in the study for the duration of the trial, with specific visits scheduled to monitor their health and response to the treatment. The sequence of study visits includes an initial screening visit to confirm eligibility based on criteria such as age, confirmed diagnosis, and ability to perform specific physical tests. Following the screening, participants will undergo regular follow-up visits to assess safety and efficacy endpoints, including muscle function tests, respiratory assessments, and muscle biopsies. The end-of-study visit will conclude the participant's involvement, where final assessments will be conducted to gather comprehensive data on the treatment's impact.

Inclusion criteria require participants to be ambulant male or female patients aged between 6 and 12 years, with a confirmed diagnosis of LGMDR5 before the age of 10. Participants must be able to perform the 10-meter walk test within 15 seconds without assistance and have seronegative status for neutralizing antibodies against AAV8. The study will exclude individuals who do not meet these criteria or whose medical status is deemed insufficiently stable by the investigator. Conditions that may lead to early termination from the study include the development of significant adverse events or inability to adhere to the study protocol.

The clinical trial involves the administration of **rAAV8-hSGCG**, a genetically modified recombinant viral vector. This investigational product is a **solution for infusion** and is administered via **intravenous infusion**. The active substance is an **adeno-associated virus serotype 8** expressing the human gamma-sarcoglycan gene, designed to deliver the human gamma-sarcoglycan gene to patients with gamma-sarcoglycanopathy, also known as limb-girdle muscular dystrophy LGMDR5. The product is identified by the sponsor product code ATA-200 and is provided by ATAMYO THERAPEUTICS. The trial aims to evaluate the safety and tolerability of this gene therapy at two different dosage levels.

In addition to the experimental treatment, the trial includes the use of **PREDNISOLONE**, a glucocorticoid, as a non-experimental treatment. Prednisolone is administered orally in a pharmaceutical form identified as PHF00082MIG. The role of prednisolone in the trial is auxiliary, and it is not the primary focus of the study.

Another auxiliary treatment used in the trial is **METHYLPREDNISOLONE**, which is administered as an **intravenous bolus**. The pharmaceutical form is identified as PHF00243MIG, and it contains the active substances **lidocaine hydrochloride monohydrate** and **methylprednisolone acetate**. This treatment is categorized under glucocorticoids and serves as a supportive therapy within the trial.

Lastly, the trial includes the use of **Rapamune 1 mg/mL oral solution**, which contains the active substance **sirolimus**. This product is an **oral solution** and is administered orally. Sirolimus is an immunosuppressant and is used as an auxiliary treatment in the trial. The product is provided by PFIZER EUROPE MA EEIG and is identified by the marketing authorization number EU/1/01/171/001.

The efficacy of the clinical trial will be assessed using a comprehensive set of parameters designed to evaluate various aspects of muscle function, strength, respiratory capacity, and quality of life in patients with **gamma-sarcoglycanopathy**. The primary efficacy endpoints include muscle function tests such as the North Star Assessment for Neuromuscular Disorders (NSAD) and the Performance of the Upper Limb (PUL). Timed function tests will also be conducted, including the 10-meter walk test (10MWT), 100-Meter Walk Test (100MWT), Time to Rise From Floor (RFF), and the 4-Stair climb test.

Muscle strength will be measured using Myotools and Hand Held Dynamometry (HHD). Imaging assessments will involve Muscle Nuclear Magnetic Resonance Imaging (NMRI) and spectroscopy, focusing on quantitative NMRI, including fat-water separation. Respiratory assessments will include pulmonary function tests such as forced vital capacity (FVC), minimal inspiratory/expiratory pressure (MIP/MEP), and the sniff nasal inspiratory pressure (SNIP) test, along with a respiratory questionnaire.

Muscle biopsy will be performed to assess histological parameters, including the centronucleation index and fibrosis assessment. The quantification of vector copy number per diploid cell (VCN) and SGCG transgene expression at protein and mRNA levels will be evaluated. Immunohistochemistry will be used to quantify human sarcolemmal SGCG-positive fibers and human alpha-sarcoglycan positive fibers. Exploratory biomarkers such as TMEM8 for regeneration, FN1 for fibrosis, and CD11b for inflammation will also be analyzed.

Patient-reported outcomes and quality of life will be assessed using the Fatigue Visual Analog Scale (VAS), EQ-5D-Y and EQ-5D-Y proxy 1 questionnaires, and the ACTIVLIM neuromuscular scale. Changes in video outcomes capturing disease hallmarks will be documented. Biomarkers such as creatine kinase (CK), myomesin-3, and circulating microRNA will be measured, with blood and urine samples collected for biobanking. These assessments will be conducted at specified intervals throughout the trial to ensure a comprehensive evaluation of the treatment's efficacy.