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

3. Goals 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 Overview of oral challenge studies

4. 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

5. 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

6. Assessment of food ingredients 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

7. Design and Conduct of Oral Challenge Studies

8. 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

9. 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)

10. 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

11. Dose protocol 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 X2X4X8X16X 32X 64X 108X 15-60min LOEL NOEL 4X 7X Negative Obj. symptom Subj. symptom Open Challenge 1-2 hrs 10g solid 60g wet

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

13. 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

14. 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 921013814 1/5000 =.0002 149782303034540 1/10000 =.0001 299574606069080 Sample size and confidence levels *Basis for hypoallergenicity determination for infant formulas } Number of individuals to be tested

15. Evaluation/Interpretation of Challenge Study Data

16. 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

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

18. 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)

19. Hypothetical Dose Response Curve* * Model adapted from J. Hourihane 1 - “Normal” 2- ?Unstable asthma, alcohol, exercise 3- ?Food matrix, antihistamines 4- ?Unidentified factors

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

21. Allergic Response Endpoints Subjective SymptomsObjective Symptoms Skin pruritus (Itching)Urticaria (hives), Eczema, Angioedema (swelling) NauseaVomiting, diarrhea Throat dryness/tightnessLaryngeal swelling, Voice hoarseness, stridor (inspiratory wheeze), Cough Shortness of breath, chest pain Respiratory distress (i.e.,  breathing rate), Wheezing Feeling of faintness, dizzinessSyncope (fainting), Hypotension (low blood pressure) “Sense of impending doom”Shock (very low blood pressure), dysrhythmia (abnormal heart rhythm) ?Interpretation of: Fussiness/ behavior change (infants); Abdominal pain (infants); Skin flushing; Shortness of breath

22. 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

23. 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 ?

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

25.  Severity of allergic response is on a continuum Subjective Objective Anaphylaxis Death 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

26. 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?

27. 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