A Long-Term Extension Trial in Participants With Atopic Dermatitis Who Participated in Previous EDP1815 Trials

This is an Open-Label Extension (OLE) study to evaluate the long-term safety, tolerability, and efficacy of EDP1815 in participants with mild, moderate, and severe atopic dermatitis who have completed the treatment period of a prior clinical study ("parent study") with EDP1815.

The current parent study of this protocol is the EDP1815-207 study; A Phase 2, Multicenter, Double-Blind, Placebo-Controlled, Multiple-Cohort Study Investigating the Effect of EDP1815 in Participants for the Treatment of Mild, Moderate and Severe Atopic Dermatitis.

Atopic dermatitis (atopic eczema) is a very common type of skin disease. It typically causes red, dry, and itchy skin and may have a significant impact on quality of life. Rashes may appear on the arms and behind the knees, or anywhere else on the body. While there are existing therapies, there is currently no cure for atopic dermatitis.

This study is an Open Label Extension (OLE) study to the first parent study; i.e., the EDP1815-207 study (NCT05121480). The total number of participants will be dependent on the number of participants who elect and are eligible to participate in the Open Label Extension study following participation in EDP1815-207.

All participants in this study will be treated with EDP1815, regardless of the treatment assignment in the EDP1815-207 study. There will be no placebo drug administered in this study. To minimize bias, during dosing in EDP1815-208, investigators and participants will continue to be blinded to participants' treatment allocation in the parent study whilst it is ongoing. Participants in this study will be treated with EDP1815 for up to 36 weeks, followed by a follow-up visit at approximately 4 weeks after the end of treatment.

The maximum study duration is up to 40 weeks for all participants. The participants may move directly from the parent study into the open label treatment phase without a break in study treatment, or within 7 days of completing the treatment period of the parent study. If the participants move directly into this study without a break in treatment from the parent study, the Day -1 visit should be performed at the same time as the end of treatment visit of the parent study.

The primary endpoint of safety and tolerability will be measured using the incidence and rate per 100 patient-years of treatment-emergent adverse events during the 36-week treatment period and the 4-week follow-up period of this study; and during the treatment period of this study and the parent study. TEAEs will be defined as all events starting after first dose of study drug, and on or before 28 days after last dose for each participant. All TEAEs will be included in the assessments of incidences and rates, regardless of compliance with study medication, use of other medications or deviations from the study protocol.

The secondary endpoint of efficacy will be measured using the Eczema Area and Severity Index (EASI) Score. Additionally, the Investigator's Global Assessment (IGA), percentage of Body Surface Area (BSA), Product of the IGA and BSA (IGA\*BSA), the SCORing Atopic Dermatitis (SCORAD), the Dermatology Life Quality Index (DLQI), the Peak Pruritus Numerical Rating Scale (PP-NRS), the Sleep Disturbance Numerical Rating Scale (SD-NRS), the Patient Oriented Eczema Measure (POEM) and the Atopic Dermatitis Control Tool (ADCT) will also be measured throughout the study. The number of courses of treatment with rescue therapies; and with antibiotic treatment due to skin infection, per participant, will also be measured.

Eligibility Criteria:
Inclusion Criteria:

1. Must have provided informed consent.
2. Must have completed the treatment period in a parent study of EDP1815 in atopic dermatitis and complied with the parent protocol.
3. Must agree to use emollients.
4. Must continue to follow contraception criteria.

Exclusion Criteria:

1. Participants who are currently enrolled in another investigational drug study or plans to receive another investigational drug during this study.
2. Have any other conditions, which would make the participant unsuitable for inclusion or could interfere with the participant participating in or completing the study.
3. Use of phototherapy, a biologic agent, or a systemic immunosuppressive agent that could affect AD, including systemic corticosteroids, within 7 days prior to Day -1, unless used as a rescue treatment as part of the parent study protocol.
4. Use of topical atopic dermatitis therapies, including topical corticosteroids, topical calcineurin inhibitors, topical PDE-4 inhibitors, and topical JAK inhibitors, within 7 days prior to enrolling in the study, unless used as a rescue treatment as part of the EDP1815-207 protocol.
5. Has received live or live-attenuated vaccination prior to enrollment or intends to have such a vaccination during the study.
6. Hypersensitivity to P histicola or to any of the excipients.
7. Unwillingness to comply with study procedures, including follow-up, as specified by this protocol, or unwillingness to cooperate fully with the Investigator.