Evaluation of Autologous Thymic Treg Cell Infusion for Acute Rejection Prevention in Pediatric Heart Transplant Recipients

The primary objective of this clinical trial is to evaluate the **feasibility**, safety, and efficacy of the infusion of autologous thyTreg cells in the prevention of acute rejection in children who have undergone heart transplantation. This is clinically relevant as acute rejection is a significant complication post-transplantation, and effective prevention strategies are crucial for improving patient outcomes and graft survival.

Secondary objectives include:

• Evaluating the recovery of the population of circulating Treg and its phenotype throughout the follow-up, assessing the immunological state of the patient, and the reduction of immunological markers associated with rejection.
• Determining the incidence of episodes of acute rejection in the two years following transplantation and assessing the efficacy of treatment in preventing these episodes.
• Assessing the tolerability of the product under investigation.

The clinical trial involves a **pediatric** population under two years of age, comprising both male and female subjects. The study focuses on children who are candidates for heart transplantation, specifically evaluating the efficacy of autologous thyTreg cells in preventing acute rejection. Participants are required to have no contraindications to immunosuppressive drugs, and their parents or guardians must provide informed consent, demonstrating an understanding of the study's purpose and risks. The trial includes a vulnerable population, given the young age of the participants. The sponsor has not provided information regarding the total number of participants in the study.

The clinical trial is a **randomized**, exploratory, and prospective study designed to evaluate the safety and efficacy of the transfusion of autologous TREG cells obtained from thymic tissue in preventing rejection in heart-transplanted children. The trial is structured as a **Phase I/II** study, focusing on the feasibility, safety, and efficacy of the infusion of autologous **thyTreg** cells. The primary endpoint is the repopulation of Treg cells in the patient, assessed by the increase in their blood values and the recovery of the Treg/T-effector cell ratio compared to pre-transplantation values. Secondary endpoints include the incidence of acute myocardial rejection episodes, restoration of immunological homeostasis, patient survival, and safety according to NCI-CTCAE V4.03 criteria.

The trial is expected to commence recruitment on December 9, 2024, and conclude by December 20, 2025. Participants will be involved in the study for a duration of up to two years post-transplant, with follow-up visits scheduled at multiple intervals: +7, +14, +21, +30, +60, +90, +120, +150, +180, +270, +365, +545, and +730 days. The inclusion criteria specify that participants must be under two years of age, meet all requirements for a heart transplant, and have no contraindications to immunosuppressive drugs. Parents or guardians must provide informed consent. There are no specified exclusion criteria.

Study visits will begin with a screening visit to confirm eligibility, followed by regular follow-up visits to monitor the primary and secondary endpoints. The end-of-study visit will occur at the two-year mark post-transplant. Participants may be terminated early from the study if they experience significant adverse events, fail to comply with study procedures, or withdraw consent. The investigational product, **thyTreg**, is administered as a **solution for infusion** via the **intravenous** route. The study is not classified as a low-intervention trial, and the product is categorized as an advanced therapy product.

The clinical trial involves the administration of **thyTreg**, an advanced therapy product consisting of autologous T-lymphocytes. These cells are differentiated, expanded, and stimulated with IL-2, originating from thymic tissue. The pharmaceutical form of **thyTreg** is a **solution for infusion**, and it is administered via the **intravenous** route. The primary objective of the trial is to evaluate the feasibility, safety, and efficacy of this treatment in preventing acute rejection in children who have undergone heart transplantation. The **thyTreg** cells are structurally diverse substances used in cell therapy, specifically designed for this purpose.

In this study, no non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatments are mentioned. The focus is solely on the experimental administration of **thyTreg**. The trial does not specify a maximum daily dose, total dose, or treatment period, indicating that these parameters may be determined based on individual patient response and clinical judgment. Participant compliance with the dosing schedule will be monitored throughout the trial to ensure adherence to the protocol and to assess the treatment's impact on preventing rejection in the pediatric heart transplant population.

The efficacy of the clinical trial will be assessed through both primary and secondary endpoints. The primary endpoint focuses on the **repopulation of Treg cells** in the patient, which will be determined by the increase in their blood values and the recovery of the Treg/T-effector cell ratio compared to pre-transplantation values. This will provide a direct measure of the treatment's impact on the immune system's regulatory components.

Secondary endpoints include several parameters: the incidence of acute myocardial rejection episodes, diagnosed via echocardiography and/or biopsy, requiring treatment within two years post-transplant; restoration of immunological homeostasis, assessed by measuring the percentages and absolute values of various immune cell populations, including T, B, NK, and Treg lymphocytes, as well as monocytes, dendritic cells, and granulocytes, at specified timepoints post-transplant (+7, +14, +21, +30, +60, +90, +120, +150, +180, +270, +365, +545, +730 days); patient survival; and safety, evaluated according to NCI-CTCAE V4.03 criteria.