This is a single center randomized parallel-group partially-blinded, 4-arm Phase 1 study to evaluate the phototoxic potential of two dose levels of SAR441566 treatment compared to placebo and the active comparator, ciprofloxacin, in healthy adults, 18 to 55 years of age.

There will be two parts:

• Part I is a randomized placebo-controlled trial comparing sensitivity to ultraviolet (UV) light in participants treated with SAR441566 to those treated with placebo.
• Part II is an open label arm consisting of participants treated with ciprofloxacin which induces mild phototoxicity and serves as a positive control.

The overall duration of the study for each participant will be up to approximately 48 days

Inclusion Criteria:

• Male or female participants who are between 18 and 55 years of age, (inclusive), at the time of signing the informed consent
• Participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and ECG.
• Participants with Fitzpatrick skin type classification of I, II, or III (I always burns easily, never tans, II always burns easily, tans minimally, III Burns moderately, tans gradually)
• Body weight within 50.0 and 100.0 kg (inclusive), and body mass index (BMI) within the range 18.0 and 32.0 kg/m2 (inclusive)

Exclusion Criteria:

• A positive hepatitis B (HBsAg, anti-HBc), hepatitis C or HIV test at screening, indicative of a current or past infection
• A history of active tuberculosis (TB) or positive serological test for TB (Quantiferon TB Gold or T-SPOT)
• History of invasive opportunistic infections
• Participants with a history of Clostridium difficile-associated diarrhea
• Participants with a history of malignancy occurring within 5 years before inclusion (except adequately treated carcinoma in situ of the cervix, or adequately treated non-metastatic squamous cell or basal cell carcinoma of the skin)
• Active skin disorders or alterations such as tattoos on the back where photosensitivity testing will be performed or unprotected ultraviolet exposure of the test areas within 4 weeks prior to baseline photo testing that the Investigator considers will interfere with study assessments
• Abnormal skin response during preliminary or baseline phototoxicity evaluations
• Any medication within 14 days before inclusion or within 5 times the elimination half-life or pharmacodynamic half-life of the medication (whichever is longer); any acetaminophen intake within 2 days prior the inclusion and any biologics (antibody or its derivatives) given within 4 months before screening
• Any participant enrolled or having participated, in this or any other clinical study involving an IMP or in any other type of medical research within the past 14 days (last day of IMP dosing in the previous clinical trial) or 5 half-lives whichever is longer, before screening
• Clinical signs and symptoms consistent with COVID-19 or laboratory-confirmed SARS-CoV-2 infection; SARS-CoV-2 infection within 4 weeks prior to screening; and/or history of severe course of COVID-19
• If female, pregnancy (defined as positive beta-HCG blood test and/or positive urine pregnancy test), breast-feeding

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

Applicable for Part I