Safety Study of DIAG723 and Sodium Chloride in Adults with Hereditary Hemorrhagic Telangiectasia

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What is this study about?

Hereditary Hemorrhagic Telangiectasia is a rare genetic condition that causes abnormal blood vessel connections, leading to frequent nosebleeds, anemia, and other bleeding problems. The study investigates a new treatment called DIAG723, which is a human bispecific monoclonal antibody targeting ALK1 and BMPRII and is given by subcutaneous injection. Some participants will receive a harmless placebo (saline solution) for comparison.

The purpose of the study is to evaluate the safety and tolerability of the investigational drug in adults with the condition. Participants will first receive single doses that increase in amount (Part A) and later receive several doses over a longer period (Parts B and C). Throughout the trial, volunteers will attend regular clinic visits where doctors will check vital signs, perform simple physical exams, and draw blood to look for any side effects.

During the study, participants will also answer brief questionnaires about the frequency and severity of nosebleeds and overall quality of life. Standard medical care for the disease will continue as needed, and any changes in health will be closely monitored to ensure safety.

1 initial enrollment and baseline assessments

after signing the consent form, you will undergo a series of baseline tests that include blood work, vital signs, physical exam, and an electrocardiogram to record your health status before receiving any study medication.

your medical history of hereditary hemorrhagic telangiectasia will be confirmed and documented.

2 first dose administration (part a – single ascending dose)

you will receive a subcutaneous injection of diag723 at a dose determined by the study protocol. the exact amount is not disclosed here, but it will be given once during this visit.

if you are assigned to the placebo group, you will receive a subcutaneous injection of sodium chloride instead of the active drug.

3 post‑dose monitoring

after the injection, you will stay at the clinic for several hours so that staff can observe you for any immediate reactions or side effects.

vital signs and a short physical exam will be repeated during this observation period.

4 follow‑up visits after single dose

you will return to the clinic on scheduled days (for example, days 1, 3, 7, 14, and 28) for blood tests, vital‑sign checks, and questionnaires about nosebleeds and overall well‑being.

these visits allow the study team to assess safety and how your body handles the drug.

5 transition to multiple‑dose phase (parts b and c)

if you continue in the study, you will begin a series of repeated subcutaneous injections of diag723 or placebo according to the assigned multiple‑dose schedule.

the injections are typically given once a week for a predetermined number of weeks (the exact number is defined by the protocol).

6 ongoing safety assessments during multiple‑dose phase

at each weekly visit, you will receive the injection, have vital signs taken, and provide blood samples for laboratory tests.

the study team will also record any adverse events, changes in nosebleed frequency, hemoglobin levels, and need for transfusions.

7 end‑of‑treatment visit

after the final scheduled injection, you will have a comprehensive assessment that includes blood work, physical exam, electrocardiogram, and questionnaires about quality of life.

the purpose is to capture the overall safety profile after completing the dosing period.

8 post‑treatment follow‑up

you will be asked to return for one or more follow‑up visits several weeks after the last dose to ensure that any late‑appearing side effects are identified.

these visits involve the same safety checks as earlier visits but no further study medication is given.

Who Can Join the Study?

Be 18 years of age or older at the time you sign the consent form.
Have a confirmed diagnosis of Hereditary Hemorrhagic Telangiectasia (HHT) based on either the Curacao criteria (a set of clinical signs) or a genetic test.
Have adequate hepatic (liver) and renal (kidney) function as defined by the study.
For Parts B and C: Have moderate‑to‑severe HHT, which may include frequent nosebleeds (recurrent epistaxis) and/or anemia (low red blood cell count) that requires medical management.
For Part C only: Also have confirmed pulmonary arterial hypertension (PAH) (high blood pressure in the arteries of the lungs) as defined by the study.
Be able and willing to follow all study procedures and requirements.
Provide written informed consent before any study‑specific procedures are performed.

Who Cannot Join the Study?

Having a serious health problem that is not under control and could affect the study results.
Any medical condition that the doctor feels makes you unsuitable for the study.
Recent blood clots (thromboembolic events) or serious heart and blood‑vessel problems (cardiovascular disease).
Active or recent infections that are important to health, such as hepatitis B, hepatitis C, HIV, or tuberculosis.
Using drugs that stop new blood‑vessel growth (anti‑angiogenic therapies) or other medicines that the study rules out.
Having had recent nose procedures that destroy tissue (nasal ablative procedures) or other nose treatments that could affect the measurement of nosebleeds (epistaxis).
Known allergic reaction (hypersensitivity) to lab‑made proteins that target specific body parts (monoclonal antibodies) or any ingredient in the study drug.
Being pregnant or breastfeeding.
Being enrolled in another experimental study or having taken another experimental medicine recently.
Having taken the study drug DIAG723 before (relevant for the multiple‑dose part of the trial).

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country	Status
Saarland University Hospital	Homburg	Germany
Universitaetsklinikum Essen AöR	Essen	Germany

Other Sites

No sites found in this category

Trial status

Country	Status	Recruitment Start
Germany	Not yet recruiting	02.11.2026

Trial locations

Investigated Drugs:

Sodium Chloride

DIAG723 is an experimental medicine that is a special type of antibody designed to attach to two proteins in the body called ALK‑1 and BMPRII. These proteins help control how blood vessels grow and repair themselves. By binding to both proteins, DIAG723 aims to activate them and improve the abnormal blood vessel formation that occurs in people with hereditary hemorrhagic telangiectasia (HHT). In the trial, participants receive DIAG723 as a small injection under the skin. The study is testing how safe the medicine is and how well patients can tolerate it when given in gradually increasing single doses and when given repeatedly over several weeks.

Investigated Diseases:

Hereditary haemorrhagic telangiectasia

Hereditary Hemorrhagic Telangiectasia – Hereditary Hemorrhagic Telangiectasia is a genetic disorder that causes abnormal development of blood vessels. Small, fragile vessels called telangiectasias appear on the skin and mucous membranes, often leading to frequent nosebleeds. Larger abnormal connections between arteries and veins, known as arteriovenous malformations, can form in organs such as the lungs, liver, and brain. These vascular lesions tend to increase in number and size over time. As the disease progresses, bleeding episodes may become more common and organ involvement can expand.

Trial ID:

2026-526271-29-00

Protocol code:

DIAG723-PT-CL-001

NCT ID:

NCT07623525

Trial Phase:

Phase I and Phase II (Integrated) – First administration to humans

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Safety Study of DIAG723 and Sodium Chloride in Adults with Hereditary Hemorrhagic Telangiectasia

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?