This is an open-label, Phase 2/Phase 3, long-term extension study for treatment of participants of previous amlitelimab clinical trials in moderate to severe atopic dermatitis.

The purpose of this study is to characterize the safety and efficacy of amlitelimab in treated participants with moderate to severe atopic dermatitis (AD) who have previously been enrolled in an amlitelimab clinical trial. All participants will have visits during the treatment period every 4 weeks. Responder participants rolling over from EFC17599 and EFC17600, and responder participants enrolling through screening from DRI17366 will be initiated into drug withdrawal (with no drug administration) at LTS17367 baseline visit to monitor durability of treatment response. If these responder participants relapse during LTS17367, they will have treatment restored. Non-responder participants rolling over from EFC17599 or EFC17600, and non-responder participants enrolling through screening from DRI17366 will have treatment administration from LTS17367 baseline. Participants rolling over from DRI17366, SFY17915 and INT18404 will also have treatment administration from LTS17367 baseline.

Remote visits with home dosing are allowed for the purpose of study drug administration, when applicable. In the case of remote visit with home dosing, the participant or a caregiver may administer study drug after appropriate training. Alternatively, if needed, and based on the investigator's judgement, home visits with healthcare professional assistance or on-site study drug administration visits can be performed. Where participants discontinue amlitelimab permanently during LTS17367, safety follow up will be performed for a minimum of 140 days from the last amlitelimab administration.

Inclusion Criteria:

• Participant must be at least 12 years of age inclusive at the time of signing the informed consent.

• Participated in an amlitelimab clinical trial for moderate to severe AD and received study treatment, adequately completed the assessments required for the treatment period.

  • Have reached the rollover timepoint to LTS17367 at the last visit of the treatment period of their feeder study SFY17915, INT18404, EFC17599, or EFC17600

  • Participants in DRI17366 must only be enrolled from 1 of the following 3 groups:

    • The first group: participants at Week 24 in the DRI17336 study who have not achieved an ≥ Eczema Area and Skin Severity Index (EASI)-75 and are Investigator Global Assessment (IGA) ≥ 2.
    • The second group: participants entering LTS17367 between Week 28 and Week 52 of the feeder study, due to loss of clinical response in the part 2 of the feeder study. Timepoints for entering LTS17367 are Weeks 28, 32, 36, 40, 44, 48 or 52.
    • The third group: participants at Week 24 in DRI17366 who have been re-randomized and who subsequently complete the study to Week 52, enter safety follow-up and experience worsening of their AD during safety follow-up.

  • Participated in DRI17366 completing the previous study safety follow up (Week 68) and wish to re-initiate treatment with amlitelimab up to one year after the last visit

• Complied with the previous clinical trial protocol to the satisfaction of the investigator

• Body weight must be ≥25 kg

• Provided signed informed assent/or consent and able to comply with the requirements of the protocol Exclusion Criteria:

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

• Developed a medical condition that would preclude participation as described in the section for permanent discontinuation of the feeder study or LTS17367 protocol

• Known history of or suspected current significant immunosuppression, including history of invasive opportunistic infections or helminthic infections despite infection resolution or otherwise recurrent infections of abnormal frequency or prolonged duration

• History of solid organ or stem cell transplant

• Any malignancies or history of malignancies prior to baseline (except for non-melanoma skin cancer that has been excised and completely cured for more than 5 years prior to baseline)

• Participants positive for human immunodeficiency virus (HIV); participants with any of the following results at Screening (Visit 1) or at any point during the feeder study: presence of HBsAg with or without HBV DNA PCR test, or presence of anti-HBc Ab or presence of anti-HBs Ab with positive HBV DNA PCR test; positive HCVAb confirmed by positive HCV RNA PCR test

• History (within last 2 years prior to baseline) of prescription drug or substance abuse, including alcohol, considered significant by the Investigator

• Participants with active TB, latent TB, a history of incompletely treated TB, suspected extrapulmonary TB infection, non-TB mycobacterial infection, or who are at high risk of contracting TB (such as close contact with individuals with active or latent TB) or received Bacillus Calmette-Guérin (BCG)-vaccination within 12 weeks prior to screening

• Participants with an indeterminate or a confirmed positive IGRA test are excluded from the study unless all of the following conditions are met:

  1. Have a history of prior documented completed chemoprophylaxis for latent TB infection (with a treatment regimen as per local guidelines), OR treated for active TB infection
  2. Have been in written form approved for participation in the present trial by a TB specialist who ruled out latent or active TB infection or other mycobacterial infection in the participant
  3. For whom review and approval from Sponsor have been granted are eligible

• Severe concomitant illness that would in the Investigator's opinion inhibit the participant's participation in the study, including for example, but not limited to, hypertension, renal disease, neurological conditions, heart failure and pulmonary disease

• Skin co-morbidity that would adversely affect the ability to undertake AD assessments (e.g., psoriasis, tinea corporis, lupus erythematosus) as per Investigator's judgment

• Any medical condition which, in the opinion of the Investigator may present an unreasonable risk to the study participant as a result of his/her participation in this clinical study, may make participant's participation unreliable, or may interfere with study assessments

• In the Investigator's opinion, medical conditions related to prior AD medications that have not healed/fully recovered for more than 2 weeks before screening visit, including, but not limited to, conjunctivitis, keratitis, eosinophilic conditions, arthralgia, herpes zoster, thrombosis

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