Phase 3 Evaluation of Exagamglogene Autotemcel Efficacy and Safety in Severe Sickle Cell Disease (βS/βC Genotype) with Plerixafor and Busulfan

The primary objective of this Phase 3 study is to evaluate the **efficacy** of a single dose of exagamglogene autotemcel (Exa-cel) in adolescent and adult subjects with severe sickle cell disease (SCD), specifically those with the βS/βC genotype (HbSC). This is clinically relevant as it aims to determine the potential of Exa-cel to improve clinical outcomes in a population with limited treatment options, addressing a significant unmet medical need in severe SCD management.

Secondary objectives include:

• Evaluating the **safety** of a single dose of Exa-cel in the same patient population, which is crucial for understanding the risk-benefit profile of the treatment.
• Assessing the effects of Exa-cel infusion on disease-specific events and clinical status, providing insights into the broader impact of the treatment on patient health and quality of life.
• Quantifying **gene editing efficiency**, which is essential for determining the precision and effectiveness of the CRISPR-Cas9 gene editing approach used in Exa-cel.

The clinical trial involves a total of **9 participants** diagnosed with **sickle cell anaemia**, specifically those with the **βS/βC genotype (HbSC)**. The study population includes both **male and female** subjects, encompassing an **age range** that includes adolescents and adults. Participants were selected based on their documented **βS/βC genotype** and the presence of severe sickle cell disease, characterized by specific clinical events such as acute pain episodes, acute chest syndrome, priapism, or splenic sequestration. All subjects are required to have a **Karnofsky performance status** of at least 80% for those aged 16 and older, or a **Lansky performance status** of at least 80% for those under 16. The trial does not involve a vulnerable population, and participants must be eligible for an autologous stem cell transplant as determined by the investigator. Additionally, participants must be willing to engage in long-term follow-up studies for a total of 15 years post-infusion. The trial does not specify any particular lifestyle considerations such as diet or physical activity.

The clinical trial is designed to evaluate the **efficacy** and safety of a single dose of exagamglogene autotemcel in subjects with severe **sickle cell anaemia**. This is a Phase 3, randomized, double-blind, controlled trial. The trial is expected to commence on November 1, 2023, and conclude by December 28, 2029. Participants will be involved in the study for a duration that includes the initial treatment and follow-up period, with a total follow-up of 15 years post-infusion. The trial will include several key visits: an inclusion (screening) visit, multiple follow-up visits, and an end-of-study visit. The inclusion visit will confirm eligibility based on criteria such as documented βS/βC genotype and severe sickle cell disease, defined by specific clinical events. Follow-up visits will monitor the primary endpoint, which is the proportion of subjects who have not experienced any severe vaso-occlusive crises for at least 12 consecutive months. Secondary endpoints include safety and tolerability assessments, as well as various hematological and clinical outcomes. The end-of-study visit will conclude the participant's active involvement in the trial. Participants may be terminated early from the study if they do not meet ongoing eligibility criteria, experience adverse events that contraindicate continued participation, or withdraw consent. The trial will utilize exagamglogene autotemcel, administered as a dispersion for infusion, with busulfan used as a conditioning agent. The study aims to provide comprehensive data on the long-term effects and potential benefits of this gene therapy approach in managing severe sickle cell disease.

The clinical trial involves the administration of **Mozobil** (plerixafor) 20 mg/ml, a **solution for injection**. This pharmaceutical form is administered via subcutaneous injection. The maximum daily dose is 20 mg, and the treatment period is limited to one day. Plerixafor is a chemical substance classified as a hematopoietic stem cell mobilizer. The product is manufactured by Genzyme Europe B.V. and is not a pediatric formulation. Participant compliance with the dosing schedule will be monitored throughout the trial.

Another treatment used in the trial is **Busulfan Fresenius Kabi** 6 mg/ml, a concentrate for **solution for infusion**. This cytotoxic agent is administered intravenously. The maximum daily dose is 6 mg, with a treatment period of one day. Busulfan, also known as busulphan, is a chemical substance produced by Fresenius Kabi Deutschland GmbH. It is not formulated for pediatric use. The administration and dosing schedule will be closely monitored to ensure participant compliance.

The experimental medication in this trial is **Exagamglogene Autotemcel**, also known as Exa-cel, which is a **dispersion for infusion**. This product is administered via intravenous infusion. The active substance, exagamglogene autotemcel, is a structurally diverse substance used in cell therapy. It employs CRISPR-Cas9 gene editing to disrupt the BCL11A erythroid enhancer genetic locus, thereby restoring the natural production of fetal hemoglobin (HbF). The maximum dose is 20 units, with a treatment period of one day. This product is manufactured by Vertex Pharmaceuticals, Incorporated, and is designated as an orphan drug. Compliance with the administration protocol will be monitored throughout the study.

The efficacy of the clinical trial will be assessed through a series of primary and secondary endpoints. The primary endpoint is the proportion of subjects who have not experienced any severe vaso-occlusive crises (VOCs) for at least 12 consecutive months, starting 60 days after the last red blood cell transfusion for post-transplant support or sickle cell disease management. Secondary endpoints include the safety and tolerability of **exa-cel** based on adverse events, clinical laboratory values, neutrophil and platelet engraftment, transplant-related mortality, and all-cause mortality. Additionally, the proportion of subjects with fetal hemoglobin (HbF) levels of at least 20% at Month 6 will be evaluated.

Further secondary endpoints involve the proportion of subjects free from inpatient hospitalization for severe VOCs sustained for at least 12 months after **exa-cel** infusion, starting 60 days post-transfusion. The trial will also measure the relative reduction from baseline in the annualized rate of severe VOCs and inpatient hospitalizations up to 24 months after infusion. Other assessments include the duration of severe VOC-free periods, changes in hemoglobin concentration, and the proportion of alleles with intended genetic modification present in peripheral blood and CD34+ cells of the bone marrow over time.

Patient-reported outcomes (PROs) will be evaluated using various scales, including the 11-point numerical rating scale for pain, the Functional Assessment of Cancer Therapy-Bone Marrow Transplant (FACT-BMT), and the Adult Sickle Cell Quality of Life Measurement System (ASCQ-Me). For adolescents, the Pediatric Quality of Life Inventory (PedsQL) and EQ-5D-Youth will be utilized. Changes in reticulocyte count and hemolysis biomarker concentrations, such as indirect bilirubin, haptoglobin, and lactate dehydrogenase (LDH), will also be monitored. The trial aims to provide comprehensive data on the efficacy of **exa-cel** in subjects with severe sickle cell disease, **βS/βC** genotype.