This Phase 1 study will investigate the safety and tolerability of EDP1867 in healthy volunteers, participants with atopic dermatitis, and, optionally, in participants with psoriasis and/or asthma.

This is a phase 1a/1b, first in human, participant and investigator-blind sponsor-unblinded randomized placebo-controlled multiple dose study of EDP1867 in healthy volunteers and participants with moderate atopic dermatitis and, optionally, moderate psoriasis, and/or mild asthma. This study has been designed to investigate the clinical safety and tolerability of EDP1867 in healthy volunteers, participants with atopic dermatitis, and, optionally, in participants with psoriasis and/or asthma.

Key Inclusion Criteria:

1. Age ≥ 18 years to 65 years.

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

3. Participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and ECG monitoring at Screening and at Baseline.

   Additional Inclusion Criteria for Participants with Moderate Atopic Dermatitis

4. Participant has moderate atopic dermatitis with a minimum of 5% and a maximum of 40% BSA involvement, and an IGA score of 2 or 3.

5. Participant has had a confirmed diagnosis of atopic dermatitis for at least 6 months.

6. All participants must be using an emollient and should continue to use this once daily (or more, as needed) for at least 14 days prior to randomisation, and must continue this treatment once daily (or more, as needed) throughout the study.

   Additional Inclusion Criteria for Participants with Moderate Psoriasis

7. Participant has moderate plaque psoriasis with plaque covering BSA of ≥3% and ≤10% and meets both of the following additional criteria:

   1. PASI score of ≥6 and ≤15, and
   2. PGA score of 2 or 3.

8. Participant has a confirmed diagnosis of plaque psoriasis for at least 6 months.

   Additional Inclusion Criteria for Participants with Mild Asthma

9. Participant has a diagnosis of stable asthma for at least six months

10. FeNO of ≥40ppb.

11. FEV1 ≥70% of predicted normal.

Key Exclusion Criteria:

1. 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 (non-live vaccines are permitted).

2. Participant requires treatment with an anti-inflammatory drug during the study period.

3. Participant has an active infection (e.g. sepsis, pneumonia, abscess) or has had an infection requiring antibiotic treatment within 6 weeks prior to study intervention administration.

4. Participant has renal or liver impairment

5. Participant has active neoplastic disease or history of neoplastic disease within 5 years of Screening

6. Participant has undergone major surgery within 4 weeks prior to Screening.

7. Any known cardiac abnormality

8. Participant has a known history of human immunodeficiency virus (HIV)

9. Known, active hepatitis A, hepatitis B (HBV), or hepatitis C (HCV) infection

10. Participant with any type of GI tract disease

11. Participants with a history of any serious psychiatric condition; or on therapy for any psychiatric condition

12. The participant has taken any over-the-counter (OTC) or prescription medication, within 14 days prior to baseline (Day -1); or anticipates an inability to abstain from these products for the duration of the study period

13. The participant has a significant history of drug abuse or regular use of illicit drugs or a history of alcohol abuse within 1 year prior to Screening or has tested positive for drugs of abuse or alcohol at Screening or at baseline.

14. The participant has had an acute, clinically significant illness within 30 days prior to the first dose of study intervention.

    Additional Exclusion Criteria for Participants with Atopic Dermatitis

15. Participant is receiving systemic immunosuppressive or non-biologic atopic dermatitis therapy or has received such therapy within 4 weeks prior to Screening.

16. Participant has received treatment with biologic agents within 12 months prior to first dose.

17. Participant continues to use topical medications, other than emollients, that could affect atopic dermatitis 2 weeks prior to the start of dosing.

18. Participant intends to continue to use sunbeds and/or increase their sun exposure significantly from their normal lifestyle

    Additional Exclusion Criteria for Participants with Psoriasis

19. Psoriasis restricted to scalp, palm, and/or soles only.

20. Non-plaque type of psoriasis

21. Participant is receiving systemic immunosuppressive or nonbiologic psoriasis therapy or has received such therapy within 4 weeks prior to Screening

22. Participant has received treatment with biologic agents within 12 months prior to first dose.

23. Participant continues to use topical medications that could affect psoriasis within 2 weeks prior to the start of dosing

24. Participant intends to continue to use sunbeds and/or increase their sun exposure significantly from their normal lifestyle

    Additional Exclusion Criteria for Participants with Asthma

25. History of life-threatening asthma, or a visit to the emergency department for asthma in the 6 months prior to screening, or exacerbation requiring oral corticosteroids within the previous 3 months.

26. Smoker or nicotine user within the 3 months prior to screening; or a previous smoker with a greater than 10 pack year history.

27. Other significant non-reversible pulmonary disease

28. Use of the following medicines within the specified time-frame prior to screening:

    1. Long-acting inhaled β2-agonists: 8 weeks. Note: short-acting inhaled β2-agonists are permitted as required.
    2. Anti-IgE therapy: 6 months
    3. Inhaled corticosteroids: 8 weeks
    4. Oral or Injected corticosteroids: 8 weeks
    5. Intranasal or topical steroids: 4 weeks
    6. Leukotriene antagonists: 2 weeks
    7. Long-acting muscarinic antagonist: 8 weeks
    8. Xanthines (excluding caffeine), anticholinergics, cromoglycates: 1 week.