A Study to Evaluate the Efficacy, Safety, and Immunogenicity of mRNA-1647 Cytomegalovirus (CMV) Vaccine in Allogenic Hematopoietic Cell Transplantation (HCT) Participants.

May 15, 2026 updated by: ModernaTX, Inc.

A Phase 2, Observer-Blind, Placebo-Controlled Proof-of-Concept Trial to Evaluate Efficacy, Safety, and Immunogenicity of mRNA-1647 Cytomegalovirus Vaccine in Patients Who Have Undergone Allogeneic Hematopoietic Cell Transplantation (HCT)

The main purpose of the study is to evaluate the efficacy and safety of mRNA-1647 compared to placebo to prevent first clinically significant cytomegalovirus infection (CS-CMVi) in the period following cessation of CMV prophylactic treatment (for example, letermovir) on Day 100 post-HCT through Month 9 post-HCT.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Actual)

84

Phase

  • Phase 2

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Massachusetts
      • Boston, Massachusetts, United States, 02215
        • Dana-Farber Cancer Institute
    • Missouri
      • St Louis, Missouri, United States, 63110
        • Washington University School of Medicine
    • Washington
      • Seattle, Washington, United States, 98109
        • Fred Hutchinson Cancer Center

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Receipt of an allogeneic HCT.
  • CMV-seropositive, defined as a documented positive test for anti-CMV IgG.
  • High-risk for CMV: HCT from related, unrelated, or haploidentical donor with post-transplant cyclophosphamide for graft-versus-host-disease (GVHD) prophylaxis; or HCT from related or unrelated donor with at least one mismatch at any of the following human leukocyte antigen (HLA) gene loci (HLA-A, B, C, and DRB1); or HCT from related or unrelated donor with myeloablative conditioning.
  • Persons of nonchildbearing potential or of childbearing potential with negative urine or serum pregnancy test on the day of first study injection.
  • Persons of childbearing potential who have practiced adequate contraception or have abstained from all activities that could result in pregnancy for at least 28 days prior to the first dose.
  • Persons of childbearing potential who have agreed to continue adequate contraception or abstain from all activities that could result in pregnancy through 3 months after last study injection.
  • Persons who are not currently breast/chestfeeding.
  • Willingness to comply with study procedures and provide written informed consent.

Exclusion Criteria:

  • History of a diagnosis or condition that, in the judgment of the Investigator, may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures.
  • A documented positive human immunodeficiency virus (HIV) test.
  • Treatment with alemtuzumab (Campath®), antithymocyte globulin (ATG), or any equivalent in-vivo T cell depleting agent within 12 months.
  • HCT with ex-vivo T cell depletion.
  • Low risk for CMV: HCT from related or unrelated donor with reduced intensity conditioning (RIC) and no other high-risk features.
  • History of prior hematopoietic cell transplantation within 12 months.
  • Receipt of prior investigational CMV vaccines or participation in another CMV therapeutic study that may interfere with study outcome measures as determined by the Investigator.
  • Suspected or known allergic reaction to any component of any mRNA vaccine or its excipients.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: mRNA-1647
Participants will receive mRNA-1647 by intramuscular (IM) injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
Biological: mRNA-1647
Lyophilized product that is reconstituted with 0.9% sodium chloride (normal saline).
Placebo Comparator: Placebo
Participants will receive mRNA-1647 matching placebo by IM injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
Biological: Placebo
0.9% sodium chloride (normal saline) injection

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Time Frame
Time to the First Occurrence of an CS-CMVi Event as Measured by initiation of anti-CMV Antiviral Therapy
Time Frame: Day 100 to Month 9
Day 100 to Month 9
Number of Participants with Solicited Local and Systemic Reactogenicity Adverse Reactions (ARs)
Time Frame: Up to Day 187 (7 days after last study injection)
Up to Day 187 (7 days after last study injection)
Number of Unsolicited Adverse Events (AEs)
Time Frame: Up to Day 205 (25 days after last study injection)
Up to Day 205 (25 days after last study injection)
Number of Participants with Serious Adverse Events (SAEs)
Time Frame: Up to Day 365
Up to Day 365
Number of Participants with Severe AEs
Time Frame: Up to Day 365
Up to Day 365
Number of Participants with Grade ≥3 Acute Graft-Versus-Host Disease (GVHD)
Time Frame: Up to Day 365
Up to Day 365

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Number of Participants with First Occurrence of All CS-CMVi Events as Measured by Initiation of Anti-CMV Antiviral and/or End-Organ Disease
Time Frame: Day 100 to Month 9
Day 100 to Month 9
Number of Participants with an Occurrence of CMV Viremia
Time Frame: Day 100 to Month 9
CMV Viremia is defined as ≥300 international units/milliliters (IU/mL).
Day 100 to Month 9
Number of Participants with CMV End-Organ Disease
Time Frame: Day 100 to Month 9
Day 100 to Month 9
Duration of CMV Viremia
Time Frame: Day 100 to Month 9
Day 100 to Month 9
Duration of CMV Treatment
Time Frame: Day 100 to Month 9
Day 100 to Month 9
Titer of CMV-Specific Neutralizing Antibody (nAb)
Time Frame: Days 42, 67, 92, 117, 180, 205 and 270
Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Titer (GMT) of Anti-gB-Specific Immunoglobulin G (IgG) and Anti-Pentamer-Specific IgG as Measured by Enzyme-Linked Immunosorbent Assay (ELISA)
Time Frame: Days 42, 67, 92, 117, 180, 205 and 270
Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Concentration (GMC) of Anti-gB-Specific Immunoglobulin G (IgG) and Anti-Pentamer-Specific IgG as Measured by Enzyme-Linked Immunosorbent Assay (ELISA)
Time Frame: Days 42, 67, 92, 117, 180, 205 and 270
Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline GMTs or GMCs
Time Frame: Days 42, 67, 92, 117, 180, 205 and 270
Days 42, 67, 92, 117, 180, 205 and 270
Number of Participants with Non-Relapse Mortality at 9 Months Post-HCT.
Time Frame: Month 9
Month 9

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

ModernaTX, Inc.

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

April 5, 2023

Primary Completion (Estimated)

August 1, 2026

Study Completion (Estimated)

August 1, 2026

Study Registration Dates

First Submitted

January 4, 2023

First Submitted That Met QC Criteria

January 4, 2023

First Posted (Actual)

January 13, 2023

Study Record Updates

Last Update Posted (Actual)

May 18, 2026

Last Update Submitted That Met QC Criteria

May 15, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • mRNA-1647-P205

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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