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Study of GS-4321 for Healthy People and Patients With Chronic Hepatitis Delta Virus Infection

Verified siteInvestigationalNo placebo
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What is this trial about?

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

This study is looking at Chronic Hepatitis Delta, which is a liver infection caused by the hepatitis delta virus. The study will test a treatment called GS-4321, which is a type of monoclonal antibody, meaning it is a laboratory-made protein designed to target specific parts of the virus. Some participants will receive GS-4321 while others will receive placebo. The purpose of the study is to see how safe the treatment is, how well it is tolerated by the body, how the body processes the medication, and whether it can reduce the amount of virus in the blood.

The study has two parts. In Part A, healthy volunteers will receive a single dose of GS-4321 given either as an injection under the skin or into a vein. This part will help researchers understand how the medication moves through the body and whether it causes any unwanted effects. In Part B, people who have chronic hepatitis delta infection will receive multiple doses of GS-4321 over time. These participants must already be taking certain medications for hepatitis B, such as entecavir, tenofovir alafenamide, or tenofovir disoproxil fumarate. Researchers will check the virus levels in the blood and monitor liver function through blood tests and measurements of liver stiffness using a special imaging method called elastography.

Throughout the study, participants will have regular visits where blood samples will be taken to measure virus levels, check how the liver is working, and look for any side effects. The study will also check whether participants develop immune responses to the medication by looking for antidrug antibodies in the blood. For those in Part B, the treatment period will last up to 96 weeks, with regular monitoring to see how well the medication works in reducing virus levels and improving liver health markers such as alanine aminotransferase, which is a substance in the blood that can indicate liver inflammation.

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

    Initial screening and preparation

    Your eligibility for the study will be confirmed. You must be between 18 and 70 years of age.

    If you are participating in Part A, you will be confirmed as healthy based on medical history, physical examination, vital signs, and laboratory tests. Your body mass index (a measure of body fat based on height and weight) must be 30.0 or less.

    If you are participating in Part B, you must have chronic hepatitis delta for at least 6 months. You must already be taking one of the following medications: entecavir, tenofovir alafenamide, or tenofovir disoproxil fumarate.

    For Part B, your liver condition will be assessed. You must have either non-cirrhotic liver disease (liver stiffness less than 12.5 measured by a scan) or compensated cirrhotic liver disease (liver stiffness 12.5 or higher but with stable liver function).

    For Part B, your hepatitis delta virus levels must be greater than 500 international units per milliliter, and your alanine aminotransferase (a liver enzyme) levels must meet specific criteria.

    If you are of childbearing potential and engage in heterosexual intercourse, you must agree to use specific contraception methods during the study.

  2. Step 2

    Treatment administration in Part A

    If you are in Part A (healthy participants), you will receive a single dose of GS-4321 or placebo.

    The medication will be administered either as an injection under the skin (subcutaneous) or directly into a vein (intravenous).

    The dose will vary as part of the study design to evaluate increasing dose levels.

  3. Step 3

    Treatment administration in Part B

    If you are in Part B (participants with chronic hepatitis delta), you will receive multiple doses of GS-4321 or placebo.

    The medication will be given as an injection.

    The dose will vary as part of the study design to evaluate increasing dose levels.

    You will continue receiving doses over a period of 24 weeks.

  4. Step 4

    Monitoring during treatment in Part A

    If you are in Part A, blood samples will be collected at specific times to measure how the medication moves through your body.

    You will be monitored for any side effects or adverse events.

    Laboratory tests will be performed to check for any abnormalities.

    Your body will be checked for the development of antidrug antibodies (proteins your immune system might produce in response to the medication).

  5. Step 5

    Monitoring during treatment in Part B

    If you are in Part B, you will have regular visits at Weeks 4, 8, 12, 16, 20, and 24 during the treatment period.

    Blood samples will be collected to measure hepatitis delta virus levels in your blood.

    Your alanine aminotransferase levels (liver enzyme) will be checked regularly.

    Blood samples will be collected to measure how the medication moves through your body.

    You will be monitored for any side effects or adverse events.

    Laboratory tests will be performed to check for any abnormalities.

    Your body will be checked for the development of antidrug antibodies.

    Tests will be performed to check if the virus develops any changes that might affect how well the medication works.

  6. Step 6

    Follow-up period for Part B

    If you are in Part B, after completing the 24-week treatment period, you will continue to be monitored during a follow-up period.

    Follow-up visits will occur at Weeks 36, 48, 60, 72, 84, and 96.

    During these visits, your hepatitis delta virus levels and liver enzyme levels will continue to be measured.

    Your liver stiffness will be measured at Weeks 24, 48, and 96 using a scan to assess any changes in your liver condition.

    You will continue to be monitored for any side effects or adverse events.

    The total duration of your participation, including treatment and follow-up, will be 96 weeks (approximately 2 years).

  7. Step 7

    Study completion

    After completing all scheduled visits and assessments, your participation in the study will be complete.

    All collected data will be used to evaluate the safety, tolerability, and effectiveness of GS-4321.

Who can join the trial?

15 criteria

  • You must be between 18 and 69 years old
  • You must be able to understand and sign a consent form agreeing to participate in the study
  • You must be willing to follow the treatment plan and attend all follow-up visits
  • If you are able to become pregnant or father a child and are sexually active with partners of the opposite sex, you must agree to use specific birth control methods as required by the study
  • You must be healthy enough to participate in the study, as determined by your medical history, physical examination, vital signs (measurements like blood pressure, heart rate, and temperature), and laboratory test results from screening
  • Your body mass index or BMI (a measure of body fat based on your height and weight) must be 30.0 or less at the time of screening and when you are admitted to the study
  • You must be between 18 and 69 years old
  • You must be able to understand and sign a consent form agreeing to participate in the study
  • You must be willing to follow the treatment plan and attend all follow-up visits
  • If you are able to become pregnant or father a child and are sexually active with partners of the opposite sex, you must agree to use specific birth control methods as required by the study
  • You must have had chronic hepatitis delta (a long-term liver infection caused by the hepatitis delta virus) for at least 6 months before screening, confirmed by your previous medical records
  • You must be taking one of the following medications: entecavir, tenofovir alafenamide, or tenofovir disoproxil fumarate (medicines used to treat hepatitis B virus infection) at or before joining the study; these medications can be part of a combination pill used to treat HIV
  • Your liver must be either without cirrhosis (scarring of the liver) or have compensated cirrhosis, which means: For no cirrhosis, your liver stiffness (measured by a special test called elastography) must be less than 12.5 within 6 months before or at screening; For compensated cirrhosis, your liver stiffness must be 12.5 or higher within 6 months before or at screening, and your Child-Turcotte-Pugh score (a scoring system that measures how well your liver is functioning) must be less than 7 at screening
  • Your HDV RNA (the amount of hepatitis delta virus genetic material in your blood) must be greater than 500 units per milliliter at screening
  • Your ALT level (a liver enzyme that shows liver health) must be greater than the upper limit of normal or ULN (the highest normal value) but less than 10 times the upper limit of normal at screening for some groups, or less than 10 times the upper limit of normal for another group

Who cannot join the trial?

8 criteria

  • The study does not list specific reasons that would prevent you from participating. Your doctor will review your individual health situation to determine if this study is right for you.
  • General factors that typically affect study participation include other medical conditions you may have, medications you are currently taking, and results from your laboratory tests.
  • Women who are pregnant or breastfeeding (feeding a baby with breast milk) may not be able to participate.
  • If you have severe liver damage or other serious health problems, you may not be eligible.
  • Certain infections or diseases affecting your immune system (the body's defense against illness) may prevent participation.
  • If you are taking medications that could interfere with the study drug, you may not be able to join.
  • People with known allergies to similar medications may be excluded.
  • Your doctor will discuss with you whether you meet all the requirements to participate safely in this study.
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Investigated drugs

GS-4321 is an investigational medication being studied for the treatment of chronic hepatitis delta, which is a liver infection. This medication is being tested to see if it can help fight the virus that causes this infection. In this study, the medication will be given in two different ways: as an injection under the skin or directly into a vein. Researchers want to learn how safe the medication is, how well the body processes it, and whether it can effectively reduce the virus in people with chronic hepatitis delta.

What is already known about the treatment

GS-4321 – GS-4321 is an investigational medication currently being studied in Phase 1/2 clinical trials for the treatment of chronic hepatitis delta, a serious liver infection caused by the hepatitis delta virus. The drug is administered either as a subcutaneous injection (under the skin) or through intravenous infusion (directly into a vein), and researchers are evaluating different dose levels to determine the safest and most effective amount. The study aims to assess how well the medication works against the virus, how the body processes it, and whether it is safe and well-tolerated in both healthy volunteers and patients with chronic hepatitis delta infection. While the specific mechanism of action at the molecular level is not detailed in the available trial information, the medication is being developed as an antiviral agent targeting the hepatitis delta virus.

Investigated diseases

Chronic Hepatitis Delta – Chronic Hepatitis Delta is a liver infection caused by the hepatitis delta virus, which can only occur in people who are already infected with hepatitis B virus. The virus attacks liver cells and causes inflammation that persists over time. This ongoing inflammation can lead to progressive damage to the liver tissue. Over months and years, the continued liver damage may result in scarring of the liver. As the disease advances, the liver's ability to function properly becomes increasingly impaired. The condition represents one of the more serious forms of viral hepatitis affecting the liver.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase I/IITrial ID2025-522729-36-00Protocol codeGS-US-567-6968Estimated enrolment107 patientsSponsorGilead Sciences Inc.

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).