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Safety and Efficacy Study of FOXP3‑T4 and Aldesleukin in Patients with IPEX Syndrome

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What is this trial about?

A plain-language summary of the goals, design and what participants do

IPEX syndrome is a rare inherited disorder in which a change (mutation) in the FOXP3 gene prevents the body’s immune system from keeping itself in check, leading to harmful auto‑immune attacks. The study investigates a new therapy that uses a specially prepared cell product called FOXP3-T4, which contains the normal FOXP3 gene delivered by a harmless virus called a lentiviral vector. This product is given through an intravenous infusion to create more functional regulatory T cells, a type of immune cell that helps stop unwanted immune reactions. Some participants also receive a low dose of the medicine aldesleukin, which is a form of the natural protein IL‑2 that supports the growth of these regulatory cells.

The purpose of the study is to see whether the combined approach is safe and can improve immune balance in people with IPEX syndrome. Participants receive the cell infusion once, and those assigned to the additional medication get small injections under the skin at regular intervals. After treatment, patients are followed for up to two years with routine check‑ups to monitor health, any side effects, and signs of improvement in their condition.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Study enrollment

    After providing consent, the patient joins the trial and baseline assessments are performed, including collection of medical history and laboratory tests.

  2. Step 2

    Intravenous infusion of <b>fo xp3-t4</b>

    The patient receives a single infusion of the investigational product fo xp3-t4 through a vein. the product is a dispersion for infusion that contains the gene‑modified cells designed to express the foxp3 protein.

    The infusion is administered in a clinical setting by trained staff and the patient is observed for immediate reactions.

  3. Step 3

    Subcutaneous low‑dose <b>il‑2</b> injections (if applicable)

    If the treatment plan includes combined therapy, the patient begins low‑dose injections of il‑2 (aldesleukin) under the skin.

    The injections are given according to the study protocol; specific dose, frequency and duration are defined by the investigators and are not disclosed in this summary.

  4. Step 4

    Clinical monitoring visits

    The patient attends regular follow‑up visits to evaluate safety and efficacy. during each visit, blood samples and clinical examinations are performed.

    Monitoring continues for up to 24 months after the infusion of fo xp3-t4.

  5. Step 5

    Final assessment at 24 months

    At the end of the 24‑month follow‑up period, a comprehensive evaluation is performed to determine the long‑term safety and efficacy of the treatment.

Who can join the trial?

10 criteria

  • Must be a male patient.
  • Must be between 1 and 45 years old (the first three participants must be aged 10‑45 years).
  • Must have IPEX syndrome, a rare immune disorder confirmed by a genetic test showing a mutation in the FOXP3 gene (this gene helps regulate immune cells).
  • Must have already tried at least one other treatment and can be enrolled even if the disease is currently under control (second‑line treatment or later).
  • Must have ongoing IPEX symptoms and be taking immunosuppressive medications (drugs that lower the activity of the immune system).
  • Must not be able to receive a hematopoietic stem cell transplantation (HSCT) or have no suitable donor available (HSCT is a transplant of blood‑forming stem cells).
  • If the patient previously had an allogeneic HSCT (stem cells from another person) that resulted in engraftment failure (the donor cells did not take hold), they are still eligible.
  • A parent or legal guardian must sign the informed consent form (a document that explains the study and its risks).
  • If the patient is of child‑bearing age, they must agree to use an effective method of contraception during the trial and for at least 12 months after the infusion.
  • Must be covered by a French or European social security scheme (health insurance).

Who cannot join the trial?

9 criteria

  • Unwilling to return for follow‑up visits during the 2‑year study and the 15‑year long‑term follow‑up period.
  • Receiving state medical aid (AME) unless an exemption is granted.
  • Having a serious psychiatric disorder (a mental health condition that could make it difficult to follow study procedures).
  • Being eligible for a HLA‑matched sibling or unrelated donor blood stem cell transplant and willing to undergo that transplant (a type of bone‑marrow transplant that matches the immune system markers).
  • Having an infection with HIV‑1, HIV‑2, or HTLV‑1 (viruses that affect the immune system).
  • Having a severe IPEX presentation that requires a rapid allogeneic HSCT (a transplant of stem cells from another person) within 3 months.
  • Having an allergy (hypersensitivity) to IL‑2 (interleukin‑2, a medication used in the study) or any ingredient in its formulation.
  • Having uncontrolled or ongoing active infections.
  • Having a short life expectancy.
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Investigated drugs

  • FOXP3-T4

    is a gene‑therapy product that uses a harmless virus to deliver the FoxP3 gene into a patient’s own CD4+ T cells. These modified cells become regulatory T cells, which can help calm the immune system. In the trial the cells are grown in the laboratory, then given back to the patient through an intravenous (IV) infusion. The goal is to see if adding these engineered cells can improve safety and reduce the disease symptoms in people with IPEX syndrome.

  • ILT-101 liquide

    contains a low dose of the immune‑system protein IL‑2, known as aldesleukin. It is given as a subcutaneous injection (under the skin). The purpose of this medication is to support the survival and function of the regulatory T cells that are introduced with FOXP3‑T4, helping them work better in the body. The trial will evaluate how this low‑dose IL‑2 contributes to safety and effectiveness when used together with the gene‑modified cells.

What is already known about the treatment

  • FOXP3-T4

    FOXP3‑T4 is given by intravenous infusion using a sterile dispersion for infusion. It is an experimental gene‑therapy product that is still under clinical study and not yet approved for general medical use. The treatment is aimed at patients with IPEX syndrome, a rare disorder where the immune system attacks the body. It works by delivering a copy of the FOXP3 gene into the patient’s T cells, turning them into regulatory cells that help calm the immune response; it is classified as a cell‑based gene‑therapy immunomodulator.

  • ALDESLEUKIN

    Aldesleukin is supplied as a solution for injection and is administered by subcutaneous injection. It is an approved recombinant interleukin‑2 drug that is also being studied for low‑dose use in autoimmune conditions. In this trial it is used together with FOXP3‑T4 to support regulatory T cells in people with IPEX syndrome. The drug mimics natural IL‑2, binds to the IL‑2 receptor, and encourages the growth of immune‑regulating cells; it belongs to the cytokine immunomodulator class.

Investigated diseases

IPEX syndrome - IPEX syndrome is a rare primary immunodeficiency caused by changes in the FOXP3 gene, which is needed for special immune cells that keep the body’s defenses in balance. Without functional FOXP3, these regulatory cells are reduced or absent, so the immune system can mistakenly attack the body’s own tissues. The condition usually appears in early childhood and may involve skin rashes, diarrhea, and problems with hormone-producing glands. As the disease progresses, more organs can become affected, leading to a wider range of autoimmune symptoms. The severity and number of affected organs can increase over time if the underlying immune imbalance continues.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase ITrial ID2025-523305-15-00Protocol codeAPHP251137Estimated enrolment5 patientsSponsorAssistance Publique Hopitaux De Paris

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