The primary objective of this study is to assess the safety and tolerability of STMC-103H compared to placebo in allergic subjects who are otherwise healthy.

This is a first-in-human trial of this live biotherapeutic product. The primary objective is to assess safety and tolerability in allergic subjects who are otherwise healthy, with twice daily dosing in descending age groups.

Inclusion Criteria:

• Voluntary informed consent from subject or legally acceptable representative and/or child assent from the subject (as applicable).
• For part 1, subjects of 18 years to 40 years of age at the timing of the signature on the informed consent.
• For part 2, subjects of 12 years to 17 years of age at the timing of the signature on the informed consent.
• For part 3, subjects of 2 years to 11 years of age at the timing of the signature on the informed consent.
• Good health and free of significant diseases or clinically significant abnormal findings on physical exam and laboratory evaluations.
• No history or presence of gastrointestinal, hepatic, or renal disease/disorder.
• History of allergic disease confirmed by 2 or more episodes in past 5 years.
• Positive skin prick test to two or more common allergens.
• Subjects who are of childbearing potential must agree to remain abstinent from heterosexual activity or agree to use (or have their partner use) acceptable contraception to prevent pregnancy within projected duration of the trial.

Exclusion Criteria:

• Presence or history of any significant acute or chronic medical illness, except for allergic disease.

• BMI > 32 kg/m2 at the time of signing consent.

• Current or persistent moderate to sever asthma that requires use of control medication (Step 3 or above, according to Asthma Step Program).

• Presence of rhinitis secondary to causes other than allergy.

• History of anaphylaxis.

• Any known allergies to two or more of the following three antibiotics: Augmentin, tetracycline, or bacitracin.

• Inability to be venipunctured and/or tolerate venous access (Parts 1 and 2 only).

• Consistent consumption of probiotics ≥ 2 days / week over multiple weeks within the 3 months prior to the study Baseline Visit.

• Regular use of any of the following medications:

  • Intranasal or systemic corticosteroids (in 1 month prior to screening or during study)
  • Leukotriene modifiers (in 1 month prior to screening or during study)
  • Intranasal cromolyn (in 2 weeks prior to screening or during study)
  • Intranasal or systemic decongestants (in 3 days prior to screening or during study)
  • Cetirizine, fexofenadine, loratadine, desloratadine, hydroxyzine (in 10 days prior to screening or during study)
  • Intranasal antihistamines (in 3 days prior to screening or during study)
  • Other systemic antihistamines (in 3 days prior to screening or during study)

• Allergies to excipients in the Investigational Product formulation.

• Allergy to soy in any form.

• Presently consuming alcohol more than 2 glasses per day or has history of alcohol dependence or alcohol abuse during the past one year prior to screening.

• Presently a smoker or ex-smoker with history of smoking (subject must abstain from smoking throughout the study).

• History or presence of significant recreational or illicit drug abuse in past 1 year.

• Participation in another clinical study within 30 days prior to screening.

• Use of any probiotic or prebiotic in the past 3 months prior to screening.

Double-blind