This is a Phase 2, multicenter, randomized, double-blind placebo controlled, 2-arm study to evaluate the effect of amlitelimab on vaccine antibody responses, and the safety of amlitelimab concurrently administered with non-live vaccines in adult participants with moderate-to-severe atopic dermatitis (AD).

The purpose of this study is to compare the immune responses to concomitantly administered Boostrix (tetanus, diphtheria, and acellular pertussis [Tdap]) and Pneumovax 23 (PPSV) vaccines in adult participants with moderate-to-severe AD treated with amlitelimab versus placebo. The study will evaluate the percentage of participants achieving a positive anti-tetanus response at Week 16 (primary endpoint) and a positive anti-pneumococcal response at Week 16 (key secondary endpoint).

Study details include:

The study duration will be up to 36 weeks (for participants not entering the LTS17367 [RIVER-AD]).

The screening period will be 9 days to 4 weeks. The treatment duration will be up to 16 weeks. The post-treatment safety follow-up period will be16 weeks. The number of visits will be up to 7 (or 6 for those entering LTS17367 [RIVER-AD]).

The study duration will be up to 36 weeks

Inclusion Criteria:

• Participants must be 18 years of age (when signing informed consent form)
• Diagnosis of AD for at least 1 year (defined by the American Academy of Dermatology Consensus Criteria)
• Documented history (within 6 months before screening) of either inadequate response or inadvisability to topical treatments
• Validated Investigator Global Assessment scale for atopic dermatitis (vIGA-AD) of 3 or 4 at baseline visit
• Eczema area and severity index (EASI) score of 12 or higher at baseline
• AD involvement of 10% or more of body surface area (BSA) at baseline
• Able and willing to comply with requested study visits and procedures
• Body weight ≥40 kg and ≤150 kg

Exclusion Criteria:

• Skin co-morbidity that would adversely affect the ability to undertake AD assessments
• Receipt of any vaccine (expect influenza and COVID-19 vaccines) within 3 months prior to screening
• Receipt of any pneumococcal vaccine within approximate timeframe of 5 years prior to screening
• Prior receipt of two or more doses of Pneumovax 23 at any time
• Receipt of any tetanus-, diphtheria-, or pertussis-containing vaccine within approximate timeframe of 5 years prior to screening
• Participants for whom administration of the pneumococcal vaccine provided in this study is contraindicated or medically inadvisable, according to local label of the vaccine
• Participants for whom administration of the tetanus, diphtheria, and pertussis vaccine provided in this study is contraindicated or medically inadvisable, according to local label of the vaccine
• Having received any of the specified therapy within the specified timeframe(s) prior to the baseline visit
• Known history of or suspected significant current immunosuppression
• Any malignancies or history of malignancies prior to baseline (excluding non-melanoma skin cancer excised and cured >5 years prior to baseline)
• History of solid organ or stem cell transplant
• Any active or chronic infection including helminthic infection requiring systemic treatment within 2 weeks prior baseline
• Positive for human immunodeficiency virus (HIV), Hepatitis B or hepatitis C at screening visit
• Participants with active tuberculosis (TB), latent TB, a history of incompletely treated TB, suspected extrapulmonary TB infection, or who are at high risk of contracting TB

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