Oral Challenge Studies: Purpose, Design and Evaluation

1. Oral Challenge Studies: Purpose, Design and Evaluation Stefano Luccioli, MD

2. Goals Overview of oral challenge studies • Purpose • Design and conduct • Selection of subjects & materials • Blinding and dosing protocol • Statistics • Evaluation and interpretation of data • General issues • Sensitivity of subjects • Clinical response and severity

3. Purpose of challenge studies • Confirm diagnosis of food allergy • Gold standard: Double-blind, placebo-controlled food challenge (DBPCFC) • Evaluate tolerance • Evaluate allergenic foods/ingredients for certain subpopulations

4. Purpose of challenge studies • Determine minimal eliciting doses • Information on individual sensitivity • Therapeutic comparisons • LOEL/NOEL data for establishing thresholds • Insufficient animal model and epidemiological (market experience, case reports) data • Evaluate reaction severity- uncommon • Current biomarkers not predictive

5. Traditional Tox models Genetic Homogeneity One ingredient in food Defined endpoints for severity NOEL defined Reproducible Dose response Allergen food challenges Genetic Heterogeneity Multiple allergens in food Multiple endpoints; severity not well defined LOEL mainly; rare NOEL May not be reproducible Dose distribution Assessment of food ingredients

6. Design and Conduct of Oral Challenge Studies

7. Subjects • Subpopulations: Adults vs children vs infants • Men and women, multiethnic • Particular concerns/issues: • Diagnosis for equivocal IgE or clinical history • Evidence of tolerance • Coexistant allergies (i.e. milk/soy) • Specific ingredients (i.e. hypoallergenic infant formulas) • Exclusion of individuals: • Elevated food-specific IgE levels • Previous H/O anaphylaxis or unstable asthma • Self exclusion

8. Test materials • Type of food material • Various preparations per food • Ex: Peanut flour vs ground peanut vs peanut butter • Increased shelf-life for ease of administration • Liquid vs solid (dried) food • Fresh vs processed • Raw vs cooked • Dose units (mg food vs mg protein vs mg/kg)

9. Blinding • Foods – mask taste, smell, and texture • Vehicles (i.e. Milk shakes, oatmeal, tapioca) • GI effects; may not mask taste • Capsules • Delayed absorption; bypass oral cavity • Protocol – mask subject and/or researcher • Open • Singled-blinded (SB) • Double-blinded (DB) • Placebos –false positive “nocebo” responses

10. NOEL LOEL 2X 4X 8X 16X 64X 108X 32X Subj. symptom Obj. symptom Negative Open Challenge Dose protocol 10g solid 60g wet 4X X • Starting dose (X) varies (usually mg doses) • Time interval varies • Dose escalation of divided doses (usually 6 to 10) w/ placebos • Two to 10-fold dose increments • Stop after objective symptom; some also record subjective symptoms • Report eliciting discrete and/or cumulative dose 15-60min 7X 1-2 hrs

11. Other issues • Clinic/office –experimental setting • Medications • Fasting • Clinical history of reactivity • i.e. exercise, oral allergy syndrome

12. Statistical endpoints • Sampled population • Percentage that will react to challenge (i.e. food allergy diagnosis) • Percentage to have a mild vs severe initial reaction • General allergic population • Percentage that will or will not react to specific food concentration (s) during challenge • Confidence levels for incidence of allergic reactions

13. Sample size and confidence levels Incidence Confidence level 95% 99% 99.9% 1/10 = .1 *29 44 66 1/20 = .05 59 90 135 1/50 = .02 149 228 342 1/100 = .01 299 459 688 1/200 = .005 598 919 1380 1/500 = .002 1497 2301 3451 1/1000 = .001 2995 4604 6905 1/2000 = .0005 5992 9210 13814 1/5000 = .0002 14978 23030 34540 1/10000 = .0001 29957 46060 69080 } Number of individuals to be tested *Basis for hypoallergenicity determination for infant formulas

14. Evaluation/Interpretation of Challenge Study Data

15. General interpretation • Grouping of data for population statistics • Most studies not standardized* • Dose, blinding/testing materials, or interpretation of clinical symptoms • All sensitive populations included? • Statistical power for confidence levels • Should this include data from individuals nonreactive to oral challenge? • What about foreign challenge study data? *Standardization of protocols has been proposed; however, the bulk of currently available data is from non-standardized studies

16. General interpretation • Experimental exposure – non real-life • False positives/ negatives • Difficult to predict reactions to future exposures

17. Subject sensitivity • Genetic heterogeneity of individuals • Sensitization to different allergens within food • High variability in dose (million-fold) from least sensitive to most sensitive • Potential link with severity • Some studies suggest that the individuals most sensitive to low doses also appear to have the most severe reactions • Sensitivity/severity may vary with food type • Individual sensitivities may vary over time • Influenced by H/O asthma • Eating behaviors and other factors (exercise, alcohol, medications)

18. Severe 2 4 Moderate 1 3 Mild Dose of Allergenic protein Hypothetical Dose Response Curve**Model adapted from J. Hourihane 1- “Normal” 2- ?Unstable asthma, alcohol, exercise 3- ?Food matrix, antihistamines 4- ?Unidentified factors

19. Evaluation of Clinical Responses • Interpretation of eliciting dose • Subjective vs objective symptoms • Reaction severity • Dose-response endpoints

20. Allergic Response Endpoints ?Interpretation of:Fussiness/ behavior change (infants); Abdominal pain (infants); Skin flushing; Shortness of breath

21. Subjective vs objective symptoms • Objective symptoms • Measurable indicator of allergic response • Many different endpoints possible, including anaphylaxis • Interpretation may vary among investigators • Subjective symptoms • May result from nonallergic causes; often not recorded • Often occur prior to objective signs • Early adverse events/ LOELs? • Need to review challenge and placebo data

22. Other eliciting dose considerations • Starting dose • If response at this dose, cannot derive NOEL • Common finding with many diagnostic challenges • Is this the lowest eliciting dose? • Dose increments – 2 vs 10-fold • Time interval between doses • Some adverse reactions may be delayed > 60 min (i.e. eczema) • Discrete vs cumulative dose • How does this mimic true exposure?

23. Food /Protein ALLERGY • Unique toxicological response Sensitization B cell T cell IgE Antibody Elicitation • Release of mediators, cytokines (Amplification mechanism) • Rapidly progresses in severity Mast cell/ Basophil

24. Severity of allergic response is on a continuum SubjectiveObjectiveAnaphylaxisDeath • Not a fixed response - early observed objective symptom may rapidly progress to something worse • Degree of amplification varies - symptoms may not be reproducible on subsequent rechallenge

25. Reaction Severity • Most studies only report actual symptom • Few document severity of challenge response • Mild vs moderate vs severe • Should severe responses be interpreted differently? • Anxiety/stress; medications; asthma • Potentiating/ mitigating factors for severity • Challenge stops after initial positive response • Not a true dose-response study for severity • What is dose interval from mild to severe reaction?

26. Conclusions • Oral food challenges provide data on: • Clinical sensitivity to minimal eliciting doses • Reaction severity to initial dose • Challenge data currently available for interpretation is not standardized among studies • Current data pool may not include extremely sensitive population (with regards to severity) • Challenges have proven value as a diagnostic tool but not as a tool for predicting reaction severity to future exposures