Study of ENP-501 in Peanut-Allergic and Non-Allergic Participants

Inclusion Criteria: Part 1: * 14-50 years of age (inclusive) * Otherwise medically healthy and able to participate in the study * Able to perform spirometry testing in accordance with the American Thoracic Society (ATS) guidelines (2019) * All women of child-bearing potential, agree to either abstain from sexual activity or agree to use an adequate method of contraception for the duration of the study and for 30 days after the last dose of investigational product * Signed and dated written informed consent from the participant and/or parent or guardian * Signed and dated assent from participant under 18 in accordance with local IRB regulations * Willing and able to avoid peanut and peanut contaminants for the duration of the trial Part 1 Cohort 1 only (NPA Participants) * No known clinical history of peanut allergy with regular exposure to peanuts in daily life, i.e ingests peanuts without symptoms * Negative Skin Prick Test (SPT) (wheal diameter of \<3 mm) to peanut Part 1 Cohort 2 only (PA Participants) * A documented clinical history of peanut allergy, which includes the development of symptoms (e.g., urticaria, flushing, rhinorrhea and sneezing, throat tightness or hoarseness, wheezing, vomiting) verified by a physician * At least two of the three following requirements: 1. Positive Skin Prick Test (SPT) (wheal diameter of ≥ 8 mm) to peanut 2. An elevated serum peanut specific IgE level ≥ 7 kUA/L (ImmunoCAP®) 3. An Ara-h2 IgE level of ≥ 2 kUA/L (ImmunoCAP®) Part 2: * 14 to 50 years of age (inclusive) * A documented clinical history of peanut allergy, which includes the development of symptoms (e.g., urticaria, flushing, rhinorrhea and sneezing, throat tightness or hoarseness, wheezing, vomiting) verified by a physician * At least two of the three following requirements at screening: 1. Positive SPT (wheal diameter of ≥ 3 mm) to peanut 2. Serum peanut-specific IgE level ≥ 0.7 kUA/L (ImmunoCAP®) 3. An Ara-h2 IgE level of ≥ 0.5 kUA/L (ImmunoCAP®) within 1 year of enrollment * Participant must be willing and able to complete a DBPCFC at screening and EOT (24-hours after last dose) and experience dose-limiting symptoms at or before the 300 mg challenge dose of peanut protein during a Double Blind, Placebo Controlled Food Challenge (DBPCFC) conducted in accordance with Practical Issues in Allergology, Joint United States/European Union Initiative (PRACTALL) guidelines * Otherwise medically healthy and able to participate in the study * Able to perform spirometry testing in accordance with the ATS guidelines (2019) * All women of child-bearing potential, agree to either abstain from sexual activity or agree to use an adequate method of contraception for the duration of the study and for 30 days after the last dose of investigational product * Signed and dated written informed consent from the participant and/or parent or guardian * Signed and dated assent from participant under 18 in accordance with local IRB regulations * Willing and able to avoid peanut and peanut contaminants for the duration of the trial Exclusion Criteria: * History of severe anaphylactic event requiring mechanical ventilation or use of intravenous (IV) vasopressor drugs * Clinically significant screening electrocardiogram (ECG) abnormality or corrected QTcF \>/= 450 msec at Screening * FEV1 value \< 80% predicted at Screening * Any hospitalization in the past year for asthma, \>1 course of oral steroids for asthma in the past 6 months, or any emergency room visit in the past 6 months for asthma * Poorly controlled atopic dermatitis * Eosinophilic gastrointestinal disease * Use of oral or IV corticosteroids within 30 days of Screening * Use of tricyclic antidepressants within 6 months of Screening * Inability to discontinue antihistamines for at least 5 half-lives before skin testing * Use of omalizumab or other immunomodulatory therapy (not including corticosteroids) or biologic therapy within one year of Screening * Use of any food allergen-specific or other non-traditional form of allergen immunotherapy within one year of Screening * Use of immunosuppressive drugs within 30 days of Screening * Use of ß-blockers (oral) * Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, or renal disease by history, physical examination, and/or laboratory studies including urinalysis * Pregnant or breast-feeding (if female) * Behavioral, cognitive, or psychiatric disease that in the opinion of the Investigator affects the ability of the participant to understand and cooperate with the study protocol * Known allergy to inactive ingredients of investigational product (active or placebo) * Participation in another interventional clinical trial within 30 days of Screening or within 5 half-lives of the other IP * Residing at the same address as another participant in this or any peanut immunotherapy study