This is a cross-over, Phase 1, 3-treatment period single sequence study. The purpose of this study is to characterize pharmacokinetics (PK), safety, and tolerability of single ascending oral doses of SAR441566 in healthy male Japanese participants, 18-55 years of age.

The duration of the study for a participant will be up to approximately 65 days.

Inclusion Criteria:

• Japanese participants whose Japanese ethnicity is defined according to the following criteria: born in Japan or born outside of Japan, and are descendent of 4 ethnic Japanese grandparents who were all born in Japan.
• Male participants between the ages of 18 and 55 years, inclusive
• Certified as healthy by a comprehensive clinical assessment (detailed medical history and complete physical examination including 12-lead ECG, and clinical laboratory tests)
• Body weight between 50.0 and 100.0 kg, inclusive, and body mass index (BMI) between 18.0 and 30.0 kg/m^2, inclusive.

Exclusion Criteria:

Participants are excluded from the study if any of the following criteria apply:

• Any history or presence of clinically relevant cardiovascular, pulmonary, gastrointestinal, hepatic, renal, metabolic, hematological, neurological, dermatological (including phototoxic dermatitis), osteomuscular, articular, psychiatric, systemic, ocular, immune disorders or infectious disease, or signs of acute illness.
• Receipt of live (attenuated) vaccines within 3 months and/or non live vaccines (eg, COVID-19 vaccination) within 4 weeks prior to first dose on Day 1, or planned to receive these vaccines at any time throughout the study.
• History of tuberculosis and/or a positive QuantiFERON-TB Gold (QFT) test.
• Positive result on any of the following tests: hepatitis B surface (HBs Ag) antigen, anti-hepatitis B core antibody (anti-HBc Ab), anti-hepatitis C virus antibody (anti-HCV Ab), anti-human immunodeficiency virus 1 and 2 antibodies (anti-HIV1 and anti HIV2 Ab), SARS-CoV-2
• Any medication within 14 days before inclusion (before first study treatment administration) or within 5 times the elimination half-life or pharmacodynamic half-life of the medication whichever the longest.

The above information is not intended to contain all considerations relevant to a 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.