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Sickle Cell DiseasePhase 3NCT05951205

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

A Phase 3 study testing Exa-cel in people with Sickle Cell Disease, run by Vertex Pharmaceuticals Incorporated.

Withdrawn

Withdrawn. The study stopped before anyone enrolled.

Official record
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Trial summary

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). Read more about this study

Who is it for?
Ages 12 to 35 years
Conditions the study is for
Sickle Cell Disease
What is being tested?
Exa-cel
Type of treatment
Injection or infusion
Could I receive a placebo?
No, everyone receives an active treatment
How many people
0 participants
Where
No sites listed yet
Study dates
31 Jul 2027to 31 Dec 2033
Phase
Phase 3
Are there results?
None posted in the registry

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 12 to 35 years
  • All sexes
  • No healthy volunteers
  • Child, Adult

Who may be able to join

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

Who cannot join

  • 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.

About this study

Official title: 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).

Being tested
Exa-cel
Medical subject headings
Anemia, Sickle Cell

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • Exa-celBiological

    Also called Exagamglogene autotemcel, CTX001

    Administered by intravenous (IV) infusion following myeloablative conditioning with busulfan.

Study groups in NCT05951205
Study groupRoleWhat they receive
Exa-celExperimentalParticipants 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.
Receives: Biological: Exa-cel

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Proportion of Participants with an Average Fetal Hemoglobin (HbF) Greater Than or Equal To (>=) 20 percent (%) on or After 6 Months

    Measured: From 60 Days after Last Red Blood Cell (RBC) transfusion up to 24 Months after exa-cel infusion

Secondary outcomes (31)

  1. Number of Participants With Adverse Events (AEs) and Serious Adverse Events (SAEs)

    Measured: From Signing of Informed Consent up to 24 Months After exa-cel Infusion

  2. 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)

    Measured: Within 42 Days After exa-cel Infusion

  3. Time to Neutrophil Engraftment

    Measured: Up to 24 months After exa-cel Infusion

  4. Time to Platelet Engraftment

    Measured: Up to 24 months After exa-cel Infusion

  5. Incidence of Transplant-Related Mortality (TRM)

    Measured: Up to 100 Days After exa-cel Infusion

  6. Incidence of Transplant-Related Mortality (TRM)

    Measured: Within 12 Months After exa-cel Infusion

  7. Incidence of All-cause Mortality

    Measured: From Signing of Informed Consent up to 24 Months After exa-cel Infusion

  8. Proportion of Participants With No Severe Vaso-Occlusive Crises (VOCs) for At least 12 Months (VF12)

    Measured: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion

  9. Proportion of Participants Free from Inpatient Hospitalization For Severe VOCs Sustained for At least 12 Months (HF12)

    Measured: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion

  10. Relative Reduction in Annualized Rate of Severe VOCs

    Measured: From Baseline up to 24 Months After exa-cel Infusion

  11. Duration of Severe VOC Free in Participants who Have Achieved VF12

    Measured: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion

  12. Relative Reduction in Rate of Inpatient Hospitalizations for Severe VOCs

    Measured: From Baseline up to 24 Months After exa-cel Infusion

  13. Relative Reduction in Annualized Duration of Hospitalization for Severe VOCs

    Measured: From Baseline up to 24 Months After exa-cel Infusion

  14. Proportion of Participants With Sustained HbF >= 20 % for At least 3, 6, or 12 months

    Measured: From 60 Days after Last RBC transfusion up to 24 Months After exa-cel Infusion

  15. Relative Reduction in Annualized Volume of RBC Transfusions

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  16. HbF Concentration Over Time

    Measured: Up To 24 Months After exa-cel Infusion

  17. Total Hemoglobin (Hb) Concentration Over Time

    Measured: Up To 24 Months After exa-cel Infusion

  18. Change In Reticulocyte Count Over Time

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  19. Change in Indirect Bilirubin Over Time

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  20. Change in Haptoglobin Over Time

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  21. Change in Lactate dehydrogenase (LDH) Over Time

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  22. Time to First Detectable Haptoglobin

    Measured: Up to 24 Months After exa-cel Infusion

  23. Time to First Normalized LDH

    Measured: Up to 24 Months After exa-cel Infusion

  24. Proportion of Alleles With Intended Genetic Modification Present in Peripheral Blood Over Time

    Measured: Up To 24 Months After exa-cel Infusion

  25. Proportion of Alleles With Intended Genetic Modification Present in CD34+ Cells of the Bone Marrow Over Time

    Measured: Up To 24 Months After exa-cel Infusion

  26. Change in Pain Scale (11-point numerical rating scale (NRS)) Assessment Over Time In Adults (>=18 Years)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  27. Change in Functional Assessment of Cancer Therapy-Bone Marrow Transplant (FACT-BMT) Over Time In Adults (>=18 Years)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  28. Change in Adult Sickle Cell Quality of Life Measurement System (ASCQ-Me)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  29. Change in Pain Scale (11-point NRS) Assessment Over Time In Adolescents (12 to <18 years of age)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  30. Change in Pediatric Quality of Life Inventory (PedsQL; self-report and parent proxy versions) Generic Core In Adolescents (12 to <18 years of age)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

  31. Change in PedsQL SCD module (self-report and parent proxy versions) In Adolescents (12 to <18 years of age)

    Measured: From Baseline Up To 24 Months After exa-cel Infusion

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted18 Jul 2023
  2. Study start31 Jul 2027 (estimated)
  3. Primary completion31 Dec 2033 (estimated)
  4. Study completion31 Dec 2033 (estimated)

Why it stopped: Modification to the clinical development plan

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 3
Primary purpose
Treatment
Allocation
Not applicable
Intervention model
Single group
Masking
None (open label)
Enrolment
0 participants (actual)
IDs, dates and publications
ClinicalTrials.gov ID
NCT05951205
Sponsor's protocol ID
VX21-CTX001-171
Other IDs
2023-503247-34-00, 2021-006375-41, 2023
Status last verified
Mar 2026
First submitted
23 Jun 2023
Last updated
25 Mar 2026
Results posted
No
FDA-regulated drug
Yes
FDA-regulated device
No
Individual data sharing
No: 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/

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing Exa-cel in people with Sickle Cell Disease, run by Vertex Pharmaceuticals Incorporated.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 2 inclusion and 4 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: withdrawn, as of the sponsor's last update on 25 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

The study was withdrawn before enrolling participants, so there are no results.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

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). It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT05951205.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 25 Mar 2026.

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