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A Phase 2a Study of Empasiprubart IV Monotherapy in Adults with AChR‑Ab Seropositive Generalized Myasthenia Gravis

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What is this trial about?

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

Myasthenia Gravis is a rare autoimmune disorder in which the immune system mistakenly attacks the connection between nerves and muscles, leading to varying degrees of muscle weakness. A specific form called AChR-Ab seropositive Generalized Myasthenia Gravis is identified by the presence of antibodies that target the acetylcholine receptor. The study evaluates two investigational medicines: Vyvgart, a solution that contains the active substance efgartigimod alfa and is administered by subcutaneous injection (a shot given under the skin), and Empasiprubart, which is given through an IV infusion (the medicine is slowly delivered into a vein). A matching placebo that looks the same but contains no active drug is also included.

The purpose of the study is to determine the safety and tolerability of these regimens in people with this condition. Participants are randomly assigned to receive either the active medication or the placebo, and neither the participants nor the study staff know which treatment is given. Over a period of several weeks, participants attend regular visits where vital signs, laboratory tests, and symptom questionnaires such as the MG-ADL (a simple survey that asks about daily activities affected by muscle weakness) are collected to monitor any side effects and changes in disease symptoms.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment confirmation

    After joining the study, confirmation of participation is recorded in the trial database.

  2. Step 2

    Baseline assessments

    A complete medical history is taken and a physical examination is performed.

    Measurements of vital signs (blood pressure, heart rate, temperature), an electrocardiogram (ecg), and laboratory tests are collected.

    Disease‑specific questionnaires, including the myasthenia gravis activities of daily living (mg‑adl) score and the quantitative myasthenia gravis (qmg) score, are completed to establish baseline severity.

  3. Step 3

    Randomization

    The participant is assigned, in a blinded manner, to receive either empasiprubart or a matching placebo.

    The assignment is concealed from both the participant and the study staff.

  4. Step 4

    First iv infusion

    The assigned product is administered by iv infusion (intravenous infusion).

    The dose of empasiprubart is 0 mg/kg (milligrams per kilogram of body weight) or the equivalent volume of placebo.

    The infusion is performed in a clinical setting by qualified personnel.

  5. Step 5

    Scheduled follow‑up visits

    The participant returns for regular visits according to the study schedule.

    At each visit, vital signs, ecg, and laboratory parameters are checked for safety.

    The study team records any adverse events or serious adverse events that occur.

    Additional infusions of the assigned product are given as specified by the protocol.

  6. Step 6

    Efficacy assessments at week 12

    At the end of the 12‑week treatment period, the participant completes the mg‑adl and qmg questionnaires again.

    The same safety measurements (vital signs, ecg, laboratory tests) are repeated.

    The data are used to evaluate changes in disease severity and to compare the active product with placebo.

  7. Step 7

    Final study visit

    After the week‑12 assessments, a final visit is conducted to collect all remaining safety information.

    The participant receives a summary of study procedures and any required post‑study instructions.

Who can join the trial?

7 criteria

  • Must be at least 18 years old and legally able to give consent for a clinical study.
  • Must have a doctor‑confirmed diagnosis of myasthenia gravis (a condition that causes muscle weakness) that meets the study’s severity requirements.
  • If you are already taking medicines for myasthenia gravis—such as nonsteroidal immunosuppressive drugs (medicines that lower immune activity without using steroids), corticosteroids (steroid medicines that reduce inflammation), or acetylcholinesterase inhibitors (drugs that improve nerve‑muscle communication)—your dose must have been stable (unchanged) for a set period before screening.
  • Must test positive for anti‑acetylcholine receptor antibodies (AChR‑Ab), meaning these specific antibodies are present in your blood.
  • Must have a confirmed case of generalized myasthenia gravis and be classified as Myasthenia Gravis Foundation of America (MGFA) Class II, III, IVa, or IVb (these classes describe the level of muscle weakness).
  • Must have received vaccination against the bacteria Neisseria meningitidis (which can cause meningitis) and Streptococcus pneumoniae (which can cause pneumonia) within the past five years, or be willing to receive these vaccines at least 14 days before the first dose of the study drug.
  • Both men and women are eligible to participate.

Who cannot join the trial?

6 criteria

  • You have another autoimmune disease or any other health problem that could interfere with measuring the study’s symptoms or make participation unsafe.
  • Your myasthenia gravis is classified as MGFA Class V, which means the disease is very severe and affects breathing.
  • You have been diagnosed with systemic lupus erythematosus (SLE), an autoimmune condition that can involve the skin, joints, kidneys and other organs.
  • You are currently taking complement inhibitors such as eculizumab, zilucoplan, ravulizumab, or similar drugs that block part of the immune system.
  • You have received an FcRn antagonist (a medicine that blocks the neonatal Fc receptor), for example efgartigimod, within the last 4 weeks.
  • You have previously been treated with the study drug empasiprubart.
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Investigated drugs

  • Vyvgart

    is a medication given as a subcutaneous (under‑the‑skin) injection. It contains a protein that targets a part of the immune system that is thought to be involved in myasthenia gravis. In this study the drug is being tested to see if it is safe, how well patients can tolerate it, and whether it helps improve the muscle weakness that people with myasthenia gravis experience.

  • ARGX-117

    (also called empasiprubart) is given as an intravenous (IV) infusion, meaning it is delivered directly into a vein. It is designed to block a specific immune pathway that contributes to the development of myasthenia gravis. In the trial this drug is being used alone (monotherapy) to evaluate its safety, tolerability, and effectiveness in reducing the symptoms of generalized myasthenia gravis that is positive for acetylcholine‑receptor antibodies.

What is already known about the treatment

  • Vyvgart

    This medication is given as a 1000 mg solution for subcutaneous injection using a pre‑filled syringe. It is an approved orphan drug that is already used in clinical practice for treating generalized myasthenia gravis, a rare autoimmune disease. The drug works by attaching to a protein called the neonatal Fc receptor, which lowers the amount of harmful antibodies in the bloodstream. It belongs to the class of FcRn antagonists that reduce IgG antibodies.

  • Empasiprubart

    This drug is administered by intravenous infusion as a concentrate that is mixed with fluid before being given. It is still an investigational product being tested in a Phase 2a study for patients with AChR‑positive generalized myasthenia gravis. Empasiprubart is a monoclonal antibody that blocks a part of the complement system, helping to stop the immune attack on muscle receptors. It is classified as a complement‑inhibiting monoclonal antibody.

Investigated diseases

Acetylcholine Receptor Antibody‑Positive Generalized Myasthenia Gravis - It is an autoimmune disorder where the immune system creates antibodies that block or destroy acetylcholine receptors at the nerve‑muscle junction. This interference reduces the ability of nerves to activate muscles, causing weakness that worsens with activity and improves with rest. The weakness often begins with the eyes, leading to drooping eyelids or double vision, and later spreads to the face, throat, and limbs. As it progresses, individuals may have difficulty chewing, swallowing, or holding up their arms for extended periods. Fatigue and fluctuating strength are characteristic features throughout the disease course.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-522939-33-00Protocol codeARGX-999-2-MG-20002Estimated enrolment40 patientsSponsorArgenx

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