Evaluation of Efficacy and Safety of a Single Dose of Exa-cel in Participants With Severe Sickle Cell Disease, βS/ βC Genotype

March 20, 2026 updated by: Vertex Pharmaceuticals Incorporated

A Phase 3 Study to Evaluate Efficacy and Safety of a Single Dose of Exa-cel in Subjects With Severe Sickle Cell Disease, βS/βC Genotype

The purpose of the study is to evaluate the efficacy and safety of CTX001 (exa-cel) in adolescent and adult participants with severe sickle cell disease (SCD), βS/βC genotype (HbSC).

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Withdrawn

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Phase 3

Contacts and Locations

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

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

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

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

No

Description

Key Inclusion Criteria:

  • Participants with documented βS/βC (HbSC) genotype
  • Participants must be eligible for autologous stem cell transplant as per investigator's judgment

Key Exclusion Criteria:

  • A willing and healthy 10/10 human leukocyte antigen (HLA)-matched related donor is available per investigator's judgement
  • Participants with prior hematopoietic stem cell transplant (HSCT)
  • Treatment with regular RBC transfusions that, in the opinion of the investigator, cannot be interrupted after engraftment.

Other protocol defined Inclusion/Exclusion criteria may apply.

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: Treatment
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: Exa-cel
Participants will receive a single infusion of exa-cel (autologous CD34+ hHSPCs modified with CRISPR-Cas9 at the erythroid lineage-specific enhancer of the BCL11A gene) through a central venous catheter.
Biological: Exa-cel
Administered by intravenous (IV) infusion following myeloablative conditioning with busulfan.
Other Names:
  • Exagamglogene autotemcel
  • CTX001

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Time Frame
Proportion of Participants with an Average Fetal Hemoglobin (HbF) Greater Than or Equal To (>=) 20 percent (%) on or After 6 Months
Time Frame: From 60 Days after Last Red Blood Cell (RBC) transfusion up to 24 Months after exa-cel infusion
From 60 Days after Last Red Blood Cell (RBC) transfusion up to 24 Months after exa-cel infusion

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Time Frame
Number of Participants With Adverse Events (AEs) and Serious Adverse Events (SAEs)
Time Frame: From Signing of Informed Consent up to 24 Months After exa-cel Infusion
From Signing of Informed Consent up to 24 Months After exa-cel Infusion
Proportion of Participants With Neutrophil Engraftment (First day of 3 Consecutive Measurements of Absolute Neutrophil Count (ANC) >=500 per Microliter [mcgL] on 3 Different Days)
Time Frame: Within 42 Days After exa-cel Infusion
Within 42 Days After exa-cel Infusion
Time to Neutrophil Engraftment
Time Frame: Up to 24 months After exa-cel Infusion
Up to 24 months After exa-cel Infusion
Time to Platelet Engraftment
Time Frame: Up to 24 months After exa-cel Infusion
Up to 24 months After exa-cel Infusion
Incidence of Transplant-Related Mortality (TRM)
Time Frame: Up to 100 Days After exa-cel Infusion
Up to 100 Days After exa-cel Infusion
Incidence of Transplant-Related Mortality (TRM)
Time Frame: Within 12 Months After exa-cel Infusion
Within 12 Months After exa-cel Infusion
Incidence of All-cause Mortality
Time Frame: From Signing of Informed Consent up to 24 Months After exa-cel Infusion
From Signing of Informed Consent up to 24 Months After exa-cel Infusion
Proportion of Participants With No Severe Vaso-Occlusive Crises (VOCs) for At least 12 Months (VF12)
Time Frame: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
Proportion of Participants Free from Inpatient Hospitalization For Severe VOCs Sustained for At least 12 Months (HF12)
Time Frame: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
Relative Reduction in Annualized Rate of Severe VOCs
Time Frame: From Baseline up to 24 Months After exa-cel Infusion
From Baseline up to 24 Months After exa-cel Infusion
Duration of Severe VOC Free in Participants who Have Achieved VF12
Time Frame: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
Relative Reduction in Rate of Inpatient Hospitalizations for Severe VOCs
Time Frame: From Baseline up to 24 Months After exa-cel Infusion
From Baseline up to 24 Months After exa-cel Infusion
Relative Reduction in Annualized Duration of Hospitalization for Severe VOCs
Time Frame: From Baseline up to 24 Months After exa-cel Infusion
From Baseline up to 24 Months After exa-cel Infusion
Proportion of Participants With Sustained HbF >= 20 % for At least 3, 6, or 12 months
Time Frame: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion
Relative Reduction in Annualized Volume of RBC Transfusions
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
HbF Concentration Over Time
Time Frame: Up To 24 Months After exa-cel Infusion
Up To 24 Months After exa-cel Infusion
Total Hemoglobin (Hb) Concentration Over Time
Time Frame: Up To 24 Months After exa-cel Infusion
Up To 24 Months After exa-cel Infusion
Change In Reticulocyte Count Over Time
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Indirect Bilirubin Over Time
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Haptoglobin Over Time
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Lactate dehydrogenase (LDH) Over Time
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Time to First Detectable Haptoglobin
Time Frame: Up to 24 Months After exa-cel Infusion
Up to 24 Months After exa-cel Infusion
Time to First Normalized LDH
Time Frame: Up to 24 Months After exa-cel Infusion
Up to 24 Months After exa-cel Infusion
Proportion of Alleles With Intended Genetic Modification Present in Peripheral Blood Over Time
Time Frame: Up To 24 Months After exa-cel Infusion
Up To 24 Months After exa-cel Infusion
Proportion of Alleles With Intended Genetic Modification Present in CD34+ Cells of the Bone Marrow Over Time
Time Frame: Up To 24 Months After exa-cel Infusion
Up To 24 Months After exa-cel Infusion
Change in Pain Scale (11-point numerical rating scale (NRS)) Assessment Over Time In Adults (>=18 Years)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Functional Assessment of Cancer Therapy-Bone Marrow Transplant (FACT-BMT) Over Time In Adults (>=18 Years)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Adult Sickle Cell Quality of Life Measurement System (ASCQ-Me)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Pain Scale (11-point NRS) Assessment Over Time In Adolescents (12 to <18 years of age)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in Pediatric Quality of Life Inventory (PedsQL; self-report and parent proxy versions) Generic Core In Adolescents (12 to <18 years of age)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion
Change in PedsQL SCD module (self-report and parent proxy versions) In Adolescents (12 to <18 years of age)
Time Frame: From Baseline Up To 24 Months After exa-cel Infusion
From Baseline Up To 24 Months After exa-cel Infusion

Collaborators and Investigators

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

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Vertex Pharmaceuticals Incorporated

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 (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
July 31, 2027

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
December 31, 2033

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
December 31, 2033

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
June 23, 2023

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
July 14, 2023

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
July 18, 2023

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
March 25, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 20, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
March 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • VX21-CTX001-171
  • 2023-503247-34-00 (Other Identifier: EU CT number)
  • 2021-006375-41 (EudraCT Number)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Details on Vertex data sharing criteria and process for requesting access can be found at: https://www.vrtx.com/our-science/clinical-trials-data-sharing/

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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