Evelo will investigate the safety and tolerability of EDP1815 and its potential to be a medicinal product in healthy volunteers and individuals with mild to moderate psoriasis and atopic dermatitis.

This will be a randomized, double-blind, placebo-controlled clinical study with dose escalations to assess safety, tolerability, and pharmacodynamic effect of EDP1815. Since this clinical study is the first study in humans, the participants will be healthy volunteers or subjects with mild to moderate psoriasis or atopic dermatitis who are otherwise well. Investigation of EDP1815 in this patient population provides an opportunity to gain pharmacodynamic information using a range of tissue biopsies and composite clinical endpoints.

Inclusion Criteria:

General:

Participant has a body mass index of ≥ 18 kg/m2 to ≤ 35 kg/m2 at Screening.

Healthy Volunteers:

Participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and cardiac monitoring.

Mild to moderate psoriasis:

1. Participant has had a confirmed diagnosis of mild to moderate plaque-type psoriasis for at least 6 months involving ≤ 10% of body surface area (BSA) (excluding the scalp).
2. Participant has a minimum of 2 psoriatic lesions with at least 1 plaque in a site suitable for biopsy.

Mild to moderate atopic dermatitis:

1. Mild to moderate atopic dermatitis with a minimum of 3% to a maximum of 15% BSA involvement.
2. Participant has had a confirmed diagnosis of mild to moderate atopic dermatitis for at least 6 months (IGA score of 2 or 3).
3. Participant has a minimum of 2 atopic dermatitis lesions with at least 1 in a site suitable for biopsy.

Exclusion Criteria:

1. Female participant who is pregnant, or plans to become pregnant during the study, or breastfeeding, or sexually active with childbearing potential who is not using a medically accepted birth control method.

2. Participant has received live attenuated vaccination within 6 weeks prior to Screening or intends to have such a vaccination during the course of the study.

3. Participant has received any investigational drug or experimental procedure within 90 days or 5 half-lives, whichever is longer, prior to study intervention administration.

4. Participant requires treatment with an anti-inflammatory drug during the study period. Paracetamol will be permitted for use as an antipyretic and/or analgesic (maximum of 4 grams/day in any 24 hour period).

5. Participant has an active infection (e.g. sepsis, pneumonia, abscess) or has had an infection requiring antibiotic treatment within 6 weeks prior to Investigational Medicinal Product (IMP) administration. When in doubt, the investigator should confer with the Sponsor study physician.

6. Participant has renal or liver impairment, defined as:

   1. For healthy volunteers: i. For women, serum creatinine level ≥ 125 μmol/L; for men, ≥ 135 μmol/L, or ii. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≥ 1.5 x upper limit of normal (ULN), or iii. Alkaline phosphatase (ALP) and/or bilirubin > 1.5 x ULN
   2. For participants with mild to moderate atopic dermatitis or psoriasis: i. For women, serum creatinine level ≥ 125 μmol/L; for men, ≥ 135 μmol/L, or ii. ALT or AST > 2 x ULN and/or bilirubin > 1.5 x ULN