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A Randomized, Double‑Blind, Placebo‑Controlled Study of Momelotinib Dihydrochloride Monohydrate in Patients with VEXAS Syndrome

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What is this trial about?

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

VEXAS Syndrome is a rare condition that can cause severe inflammation, anemia, and problems with the bone marrow. The study tests an oral tablet called momelotinib, which is taken by mouth, and compares it with a matching placebo that looks the same but does not contain active medicine.

The purpose of the study is to evaluate the overall response rate at week 26. Participants are randomly assigned to receive either the study drug or placebo, and neither the participants nor the study staff know which one is given. Over several months, participants take the medication daily and attend regular visits where doctors check for improvements, record any disease flare‑ups, and monitor safety. The study looks at how many people achieve a partial or complete improvement, how long they stay free of flares, and any side effects that may occur.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline Visit and Randomization

    After joining the study, you will attend a baseline visit where a complete medical history, physical examination, and laboratory tests are performed.

    During this visit you will be randomly assigned to receive either momelotinib tablets or matching placebo tablets, and you will remain unaware of which treatment you receive because the study is double‑blind.

  2. Step 2

    Start of Study Medication

    You will begin taking the study tablets by mouth.

    Each tablet contains momelotinib dihydrochloride monohydrate (or a matching placebo); the exact dose is defined in the study protocol and is taken once daily.

    You will continue the daily tablets for at least 26 weeks, and you may remain on the medication for a longer period if you stay in the study.

  3. Step 3

    Regular Safety and Efficacy Visits

    You will attend scheduled clinic visits, typically every four weeks, during which study staff will check for side effects and record any disease flare.

    Blood samples will be collected to measure drug levels, known as PK (pharmacokinetic) concentrations, and you will complete questionnaires about your symptoms and quality of life.

  4. Step 4

    Week 26 Evaluation

    At week 26 the study will assess your response to the medication.

    The primary outcome is whether you achieve a partial response (PR) or a complete response (CR).

    Additional measurements include the number of flare‑free days, steroid dose requirements, and selected safety parameters.

  5. Step 5

    Continued Treatment Through Week 52

    If you remain in the study, you will keep taking the daily tablets through week 52.

    Further efficacy assessments will be performed, such as response rates, health‑related quality‑of‑life questionnaires, and continued safety monitoring.

  6. Step 6

    Long‑Term Follow‑Up

    After the 52‑week period, you may be followed for up to 36 months to monitor long‑term safety and survival.

    Periodic visits will collect information on any new health events, ongoing disease activity, and overall well‑being.

Who can join the trial?

6 criteria

  • Be at least 18 years old or the legal age of consent in the country where the study is done.
  • Have a confirmed diagnosis of VEXAS syndrome, which means two things: a lab test shows a specific change called a UBA1 mutation, and you have had inflammation affecting at least one organ system within the past six months.
  • Be taking a glucocorticoid medication such as prednisone or prednisolone for at least four weeks in a row, and have taken it for at least ten days before the randomization visit.
  • If you are a female, you must not be pregnant or breastfeeding, and you must either be unable to have children (non‑childbearing potential) or, if you could have children, be using a highly effective method of birth control.
  • Be able to sign the study’s informed consent form and agree to follow the study’s rules and requirements.
  • Have an Eastern Cooperative Oncology Group Performance Status (ECOG PS) score of 0, 1, or 2 at the screening visit. This score measures how well you can do daily activities, where 0 means fully active and 2 means you are up and about more than half of the day but cannot work.

Who cannot join the trial?

33 criteria

  • More than one stay in an intensive care unit (ICU) because of a VEXAS flare in the past 6 months.
  • History of severe side effects from corticosteroids affecting the heart, nerves, lungs (including asthma or COPD), kidneys, liver, hormones (such as uncontrolled diabetes), mental health, weak bones, eye problems (glaucoma or corneal ulcers), severe nausea/vomiting, or stomach/intestine disease.
  • Known allergy or strong reaction to momelotinib, its breakdown products, or any of its inactive ingredients.
  • Presence of peripheral neuropathy (nerve damage in the hands or feet) that is grade 2 or worse (moderate to severe).
  • Past widespread infection caused by mycobacteria (such as tuberculosis) that spread throughout the body.
  • Positive test for human immunodeficiency virus (HIV).
  • Positive QuantiFERON test (a blood test that checks for tuberculosis infection) during screening.
  • Inability to take medication that prevents Pneumocystis jiroveci pneumonia (a type of lung infection).
  • Significant anemia caused by lack of iron, vitamin B12, or folate; by autoimmune or hereditary red‑cell destruction; by gastrointestinal bleeding; or by thalassemia (a genetic blood disorder).
  • More than one previous treatment specifically aimed at VEXAS before or after diagnosis, or for another medical condition.
  • Use of certain medicines too close to the start of the study:
    • VEXAS‑directed drugs: need a washout period of up to 5 drug half‑lives or 14 days if the drug’s half‑life is short.
    • Other non‑steroid anti‑inflammatory drugs: stop for 14 days or 5 half‑lives (whichever is longer); biologic drugs: stop for 28 days or 2 half‑lives (whichever is longer).
    • Hematologic support therapy (such as ESA, danazol, luspatercept, G‑CSF): stop for 4 weeks.
    • Cell‑depleting drugs such as rituximab (anti‑CD20): stop for 12 months.
    • Any experimental drug not listed: stop for 5 half‑lives or 60 days (whichever is longer).
    • Ongoing use of steroids for other conditions that would interfere with the required steroid taper schedule or study assessments.
    • High‑risk or very high‑risk myelodysplastic syndrome (MDS) according to the IPSS‑R scoring system with a score above 3.5.
    • Long‑term use of systemic steroids for more than 4 years or inability to stop steroid treatment.
    • Planned allogeneic stem cell transplant (donor transplant) for MDS or VEXAS within the next year.
    • Any major surgery performed within 28 days before starting the study.
    • Previous stem cell transplant (donor or self) or solid organ transplant (except cornea).
    • Active hepatitis B or hepatitis C infection, unless special protocol criteria are met.
    • Any of the following heart problems in the past 6 months:
      • Unstable chest pain (angina)
      • Symptomatic heart failure
      • Uncontrolled irregular heartbeat (arrhythmia)
      • Abnormal QT interval on ECG (QTc >450 ms, or >480 ms with bundle branch block)
      • Peripheral blood blast (immature blood cell) count of 10% or higher.
      • Multiple myeloma (any stage) or other active plasma‑cell disorders that need treatment.
      • Cancer (other than the disease being studied or low‑risk MDS) that has progressed or required active treatment within the past 24 months, except for skin cancers such as basal cell or squamous cell carcinoma, or carcinoma in place.
      • Uncontrolled other illnesses within 12 weeks before starting momelotinib.
      • Ongoing side effects from previous therapy that have not improved to mild (grade ≤1) or to the level before the previous treatment.
      • Psychiatric illness, social situation, or any other condition that would limit the ability to give informed consent, follow study rules, or affect interpretation of results.
      • Any significant gastrointestinal (stomach or intestine) problems that could affect drug absorption or swallowing.
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Investigated drugs

Momelotinib is an oral tablet taken by mouth that belongs to a class of medicines called Janus kinase (JAK) inhibitors. In this study, it is being tested to see if it can help improve the signs and symptoms of VEXAS syndrome, a rare inflammatory condition. Researchers are looking at how well the drug works and how safe it is for patients over a period of several weeks. The medication is designed to target specific pathways in the immune system that are thought to be over‑active in VEXAS, with the goal of reducing inflammation and improving overall health.

What is already known about the treatment

Momelotinib - Momelotinib is taken as an oral tablet that you swallow whole. It is an approved treatment for certain blood cancers and is currently being studied in clinical trials for VEXAS syndrome, a rare immune disorder. The drug works by blocking the JAK1 and JAK2 enzymes, which lowers abnormal signals that cause inflammation and excess blood cell growth. Momelotinib belongs to the class of JAK inhibitors and is designated as an orphan drug for rare diseases.

Investigated diseases

VEXAS syndrome - VEXAS syndrome is an adult‑onset inflammatory disorder caused by acquired mutations in the UBA1 gene. It typically begins with recurrent fevers, skin rashes, and joint pain, and it often includes low blood cell counts such as anemia or low platelets. Over time patients may develop vasculitis, lung inflammation, or cartilage damage, and symptoms can flare and then improve. The disease course is variable, with some individuals experiencing frequent flares that can affect multiple organ systems.
Trial detailsLast updated 21 Oct 2026
Age18+ yearsPhasePhase IVTrial ID2025-524416-11-00Protocol code223401Estimated enrolment84 patientsSponsorGlaxosmithkline Research & Development Limited

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