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A Study of Mezagitamab Compared to Placebo for Adults with Chronic Primary Immune Thrombocytopenia

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What is this trial about?

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

This study involves people with Chronic Primary Immune Thrombocytopenia, which is a long-lasting condition where the body's defense system mistakenly attacks and destroys blood cells called platelets. Platelets are important because they help blood to clot and stop bleeding. When there are too few platelets in the blood, people may bruise easily or have problems with bleeding. The study will test a medicine called Mezagitamab, which is also known by its code name TAK-079. This medicine will be given as an injection under the skin. Some people in the study will receive Mezagitamab while others will receive a placebo.

The purpose of the study is to find out if Mezagitamab can help increase the number of platelets in the blood and keep them at a safe level over time in adults with this condition. The study will also look at whether the medicine is safe and how well it works compared to placebo. People taking part may continue some of their current treatments for this condition during the study if their doctor thinks it is appropriate. These might include medicines that help the body make more platelets or certain steroid medicines.

During the study, participants will receive injections of either Mezagitamab or placebo for up to 24 months. Regular blood tests will be done to measure platelet levels, and doctors will check for any bleeding problems or side effects. The study will measure how many people achieve and maintain a platelet count that is considered safe, which is at least 50,000 platelets per microliter of blood. Participants will also be asked about their symptoms and quality of life throughout the study.

The research process

The trial runs in 9 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial treatment period

    Upon joining the study, you will be randomly assigned to receive either mezagitamab or placebo. The placebo is an inactive substance that looks like the actual medication but contains no active ingredient.

    The medication will be administered as a subcutaneous injection, which means it will be injected under the skin.

    This is a double-blind study, meaning neither you nor the medical staff will know whether you are receiving mezagitamab or placebo during the treatment period.

  2. Step 2

    Baseline assessment

    Before starting the treatment, your baseline platelet count will be measured. Platelets are small blood cells that help your blood to clot.

    Your symptoms will be assessed using a questionnaire called the ITP-PAQ, which evaluates how immune thrombocytopenia affects your daily life.

    Any bleeding events will be documented using the ITP-BAT assessment tool, which measures bleeding in different areas of your body including skin, mucous membranes, and internal organs.

  3. Step 3

    Weekly monitoring through week 24

    Your platelet count will be measured weekly throughout the 24-week treatment period.

    The medical team will monitor whether your platelet count reaches at least 50,000 per microliter, which is considered a therapeutic target.

    Special attention will be given to platelet measurements taken between week 19 and week 24, as these will determine if you have achieved a durable response to treatment.

  4. Step 4

    Assessment at week 16

    At week 16, your platelet count will be measured before receiving the scheduled injection.

    You will complete the ITP-PAQ questionnaire again to assess any changes in your symptoms compared to the beginning of the study.

    The medical team will evaluate whether your platelet count has reached at least 50,000 per microliter at this time point.

  5. Step 5

    Assessment at week 24

    At week 24, which marks the end of the main treatment period, comprehensive assessments will be performed.

    Your platelet count will be measured to determine if you have achieved a durable platelet response, defined as having a platelet count of at least 50,000 per microliter on at least 4 out of 6 weekly measurements between week 19 and week 24.

    You will complete the ITP-PAQ questionnaire again to evaluate changes in your symptoms throughout the study period.

    The medical team will review all bleeding events that occurred during the study period.

  6. Step 6

    Ongoing monitoring throughout the study

    Throughout the entire study period, the medical team will monitor for any bleeding events. These are classified by severity and location, including bleeding in the skin, mucous membranes, or internal organs.

    The time it takes for your platelet count to first reach 50,000 per microliter will be recorded.

    The number of weeks during which your platelet count remains at least 30,000 per microliter and has at least doubled from your baseline level will be counted.

    The medical team will track whether you achieve a complete platelet response, which means reaching a platelet count of at least 100,000 per microliter on at least 2 visits during the study.

  7. Step 7

    Continuation of existing treatments

    If you are currently taking other medications for immune thrombocytopenia, you may continue taking them during the study, provided the dose has been stable for at least 4 weeks before starting the study medication.

    Permitted medications include one thrombopoietin receptor agonist (such as romiplostim, eltrombopag, avatrombopag, or hetrombopag), which helps stimulate platelet production.

    You may also continue taking one oral corticosteroid given daily or every other day, at a dose not exceeding 20 milligrams of prednisone daily or an equivalent dose.

    Additionally, you may continue taking fostamatinib if this was part of your treatment before joining the study.

    The doses and frequency of these medications are expected to remain stable throughout the study period.

  8. Step 8

    Rescue therapy monitoring

    If your platelet count drops to dangerously low levels or you experience significant bleeding, you may require rescue therapy. This refers to additional emergency treatment to quickly increase your platelet count.

    The medical team will record if rescue therapy is needed, when it is first required, and how often it is used during the study period.

  9. Step 9

    Safety monitoring

    Blood samples will be collected at specified times to measure the concentration of mezagitamab in your bloodstream.

    The medical team will monitor for the development of anti-drug antibodies, which are proteins your immune system might produce in response to the medication.

    If anti-drug antibodies are detected, the levels will be measured to determine if they affect how the medication works.

    The medical team will also check for neutralizing antibodies, which are a specific type of anti-drug antibody that can reduce the effectiveness of the medication.

Who can join the trial?

11 criteria

  • You must be 18 years of age or older to participate in this study.
  • You must have been diagnosed with primary immune thrombocytopenia, which is a condition where your immune system destroys your blood platelets (the cells that help your blood clot). This diagnosis must have lasted for at least 12 months.
  • Your diagnosis must follow recognized medical guidelines for immune thrombocytopenia.
  • You must have previously responded to at least one treatment for immune thrombocytopenia, meaning that treatment helped raise your platelet count (the number of clotting cells in your blood) to 50,000 per microliter or higher. This previous treatment should not have been a thrombopoietin receptor agonist, which is a type of medicine that stimulates your body to make more platelets.
  • You must have tried at least one first-line therapy (initial treatment such as corticosteroids, which are anti-inflammatory medicines) and at least one second-line therapy (additional treatment such as thrombopoietin receptor agonists, rituximab, fostamatinib, or mycophenolate) for immune thrombocytopenia, and either these treatments did not work well enough or you could not tolerate them due to side effects.
  • Not working well enough means the treatment did not keep your platelet count at 50,000 per microliter or higher on a regular basis, or did not at least double your starting platelet count.
  • Not tolerating a treatment means you experienced side effects that were serious enough that you had to stop taking that medicine.
  • Your current average platelet count must be less than 30,000 per microliter, with each individual measurement being 35,000 per microliter or lower. This must be confirmed by at least two separate blood tests taken at least 5 days apart during the screening period, with at least one test done within 14 days before starting the study medication.
  • If you are currently taking standard treatment for immune thrombocytopenia and plan to continue it during the study, your dose and how often you take it must have stayed the same for at least 4 weeks before starting the study medication, and should remain the same throughout the study.
  • You may continue taking one medication from each of the following groups: one thrombopoietin receptor agonist (such as romiplostim, eltrombopag, avatrombopag, or hetrombopag), one oral corticosteroid taken daily or every other day (not more than 20 milligrams of prednisone daily or an equivalent dose), and fostamatinib.
  • If you do not plan to continue taking these medications during the study, you must stop taking them before the study begins, following a proper washout period (a time period to allow the medication to leave your body).

Who cannot join the trial?

4 criteria

  • The source data does not provide specific exclusion criteria for this clinical trial
  • This study is for chronic primary immune thrombocytopenia, which is a long-lasting condition where the body's defense system mistakenly destroys blood cells called platelets that help stop bleeding
  • The trial accepts participants who are 18 years of age or older
  • Both men and women can participate in this study
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Investigated drugs

  • Mezagitamab

    is an investigational medication given as an injection under the skin. It is being studied as a treatment for people with chronic primary immune thrombocytopenia, a condition where the body's immune system destroys its own blood platelets, leading to low platelet counts and increased risk of bleeding.

  • Placebo

    is an inactive substance that looks like the real medication but contains no active medicine. It is used in this study to compare against mezagitamab to help determine if the actual medication is effective.

What is already known about the treatment

Mezagitamab – Mezagitamab is an investigational medication given as a subcutaneous injection, meaning it is administered under the skin. It is currently being studied in Phase 3 clinical trials to evaluate its effectiveness and safety for treating chronic primary immune thrombocytopenia, a blood disorder where the immune system destroys platelets, leading to low platelet counts and increased bleeding risk. The medication works at the molecular level by targeting specific immune system components to help restore normal platelet production and prevent their destruction. It belongs to a class of medications designed to modulate the immune system's response in autoimmune blood disorders.

Investigated diseases

Chronic Primary Immune Thrombocytopenia – Chronic Primary Immune Thrombocytopenia is a blood disorder where the immune system mistakenly destroys platelets, which are blood cells necessary for normal clotting. The condition is characterized by low platelet counts that persist for more than 12 months without an identifiable cause. People with this disease may experience easy bruising, bleeding from the gums or nose, and small purple spots on the skin called petechiae. The disorder occurs when antibodies attach to platelets and mark them for destruction by the spleen and other parts of the immune system. The platelet count typically falls below normal levels, which can lead to various bleeding symptoms ranging from mild to more significant. This is considered a rare disease that requires ongoing management to maintain safe platelet levels.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-514401-54-00Protocol codeTAK-079-3002Estimated enrolment201 patientsSponsorTakeda Development Center Americas Inc.

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