This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group, flexible-adaptive, group-sequential study (Part A), followed by an open-label LTE period (Part B) to investigate the efficacy, and safety of rilzabrutinib in participants with sickle-cell disease (SCD).

Study details include:

• Study duration: a 52-week double-blind period (Part A), followed by an open-label LTE period (Part B). Double-blind period has two parts, 50% (adult only) until the interim analysis (a proof-concept part analogous to a phase 2b study), and 50% (adult and children) after the interim analysis. Only the participants who complete double-blind treatment period (Part A) are eligible to continue to the LTE period. The duration of the LTE period (Part B) will be from the first-participant-in (FPI)-LTE (Part B) until the last participant who enters the LTE has completed 52 weeks.
• Treatment duration: 52-week double-blind period (Part A); LTE period (Part B) from the (FPI until the last participant who enters the LTE has completed 52 weeks.
• Visit frequency: Week visits based on the Schedule of Assessments.

Inclusion Criteria:

• Participants who have been diagnosed with SCD.
• Participants who have had between ≥2 and ≤10 episodes of documented clinical VOC within 12 months of the screening events.
• Participants who are either not on hydroxyurea and/or L-glutamine at the Screening Visit and does not plan to receive them during the course of the study or has received HU and/or L-glutamine for a minimum of 6 months. Participants on hydroxyurea and/or L-glutamine must have been on a stable weight-based dose level (mg/kg) for at least 3 months prior to the Screening Visit, with the intent to continue at the same weight-based dose level for the duration of the study, except for safety reasons.
• Participants with Eastern Cooperative Oncology Group (ECOG) performance status grade 2 or lower.
• Contraceptive use by men and women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
• For participants ≥10 to <18 years of age: the parent(s)/legal guardian(s) must provide written informed consent prior to any study-related procedures being performed.

Exclusion Criteria:

• Participants are excluded from the study if any of the following criteria apply: Participants with medical history of lymphoma, leukemia, or any malignancy within the past 5 years except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for the past 3 years.
• Clinically relevant cardiac abnormality, in the opinion of the Investigator or electrocardiogram (ECG) findings.
• Participants with history of stroke, or history of abnormal transcranial doppler.
• Participants with uncontrolled or active HBV infection and/or HCV infection including those receiving antiviral therapy at the time of screening.
• HIV infection.
• A history of active or latent tuberculosis (TB)
• Positive COVID-19 molecular test.
• Participant is taking or has received crizanlizumab (ADAKVEO®) within 90 days and/or voxelotor (OXBRYTA®) within 30 days prior to the Screening visit.

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org