Study Background
Wheat (Triticum aestivum) is one of the foods with wide global consumption and one of the Big
8 foods causing allergy. IgE-mediated wheat allergy tends to be associated with severe
anaphylactic reactions when compared with cow's milk, egg and soy. Wheat proteins can be
classified into four fractions, namely albumin, globulin, gliadin and glutenin, according to
their solubility. Among these proteins, Nilsson reported that omega-5 gliadin had the highest
specificity to diagnose IgE-mediated wheat allergy. Wheat allergic children also showed IgE
response to glutenins, alpha-, beta-, gamma-gliadins, and alpha amylase inhibitors. Depending
on ethnicity and cooking practices, the major wheat allergens causing clinical allergy vary
among populations. The diagnostic accuracy of conventional allergy tests such as skin prick
test (SPT) and blood sIgE assays for wheat allergy is suboptimal, while the roles of newer
diagnostic methods such as basophil activation test (BAT; based on functional
IgE-crosslinking) remains poorly defined for this food allergy.
For wheat-dependent exercise-induced anaphylaxis (WDEIA), omega-5 gliadins and
high-molecular-weight glutenin subunits were most often reported as major allergens. SPT and
sIgE to wheat might be negative, and even sIgE to omega-5 gliadins were only positive in
about 80% of these patients. BAT combined with florescence-activated cell sorting is a new
approach to complement wheat-dependent exercise-induced anaphylaxis diagnosis. BAT-derived
parameters such as the percentage of CD63+ or CD203c+ basophils have been shown to be
sensitive biomarkers for wheat allergy. Expression of CD203c induced by purified native
omega-5 gliadin provided the best power for discriminating between wheat allergic and
tolerant subjects. On the other hand, there has not been any head-to-head comparison between
BAT and conventional allergy tests for wheat allergy or evidence on the optimal stepwise
algorithms with these allergy tests for diagnosing wheat allergy. Such unmet clinical need
prompts our team to look for precision diagnostic approach to wheat allergy in children.
Unlike cow's milk and egg, many children with wheat allergy have persistent allergy into
school-age. A large retrospective study from the United States found that about one-third of
wheat allergic patients had persistent disease into adolescence. The standard of care for
wheat allergy is strict avoidance and prompt treatment of allergic reactions upon accidental
ingestion. However, complete wheat avoidance is difficult in real life as it is widely
present in common foods such as cakes, noodles, pasta, bread and even seasoning soya sauce.
Food oral immunotherapy (OIT) is conventionally achieved in a long-enough duration that
ultimately induces immunological tolerance of patients to oral intake of the allergenic food.
The immunological changes resulted from OIT involved both innate and adaptive mechanisms that
included reduced mediator release from mast cells and basophils, initial rise followed by
decrease in food-specific IgE and increased food-specific IgG4, expansion and affinity
maturation of specific memory B cells, and stimulation of regulatory T cells with release of
IL-10 and IFN-gamma. Standard OIT protocols consist of three phases. Typically, patients
start the first rush phase by eating a very small dose (equal to the eliciting dose from
double-blind, placebo-controlled food challenge [DBPCFC]) of the testing food then
incrementally for 6-8 doses per day. This phase carries a high risk of systemic reaction. At
the end of this phase, patient will be advised about the safe starting dose for home
administration. In the next build-up phase, patients will ingest increasing amount of food
every 1-2 weeks until they reach the maintenance dose (usually one serving dose). They will
maintain this dose for at least 1-2 years, after which be evaluated for outcomes of
desensitization and tolerance (or otherwise called sustained unresponsiveness [SU]).
Desensitization denotes a condition in which patients can tolerate maintenance dose while
consuming food regularly whereas SU denotes ability to tolerate doses even when patients
discontinue the regular dosing. There is limited evidence on the safest and most effective
OIT protocol for wheat.
Published clinical trials for wheat OIT adopted varying dosing regimens of different wheat
products such as macaroni, pasta, udon and bread. The largest cohort of wheat OIT involved 18
Japanese patients with wheat anaphylaxis. Nearly 90% of patients were successfully
desensitized after 2 years, but wheat tolerance decreased to 61% after two weeks of
discontinuation of maintenance dose. A 'very low dose' protocol was adopted in which patients
ingested 2 grams of udon noodles (equivalent to 53 mg of wheat protein [WP]) once a week as a
maintenance dose. After one year, only 56% of subjects achieved desensitization rate to 15
grams of udon noodles. These observations suggested that the degree of desensitization and
perhaps SU depends on the maintenance dose of wheat.
Most published studies reported the maintenance dose of 5-6 grams WP (equivalent to 2-3
pieces of bread), while some studies adopted the low-dose approach (e.g. 400 mg WP). Higher
desensitization rate was generally achieved with the former dosing (85% vs 55%), but there
was inconsistent result for SU. Comparison between wheat OIT at 2 times/week and 6 times/week
could not find any difference in the final target dose after 6 months. The current literature
is limited by the lack of head-to-head comparison with different dosing regimens. Thus, there
is another unmet need to develop effective OIT strategy for wheat allergy.
Aims of this Study
To investigate the diagnostic performance of SPT, sIgE and BAT for wheat allergy;
To compare the accuracy of allergy testing with crude wheat extract and wheat allergens
for diagnosing wheat allergy; and
To compare the efficacy and safety of low-dose and standard-dose OIT for treating wheat
allergy.
Study Design
This is a two-stage study, with the first stage (diagnosis) being to recruit 90 participants
for testing the diagnostic performance of different allergy tests (SPT, sIgE and BAT) with
crude wheat extract and wheat allergens for immediate-onset wheat allergy that is ascertained
by DBPCFC. Subjects will be recruited from both the territory-wide referral centre at
Paediatric Allergy Clinic of our Hospital and open recruitment via our team website
(https://www.allergycuhk.org/), social media and by mass emails to University staff.
In the second stage (treatment) of this study, 72 subjects with challenge-confirmed wheat
allergy who fail DBPCFC from Stage I will undergo a randomized, double-blind and
parallel-group clinical trial with wheat OIT. Each subject had allergy tests done at baseline
(T0; see Stage I), who will be randomly assigned to one of the two intervention groups with
low-dose OIT and standard-dose OIT for 12 months.
WHEAT OIT: pasta of various types (e.g. macaroni/spaghetti/vermicelli/penne) containing
10-13% WP by content will be used, mainly decided by subject preference. A subject eats the
same type of pasta throughout OIT as far as possible, while subjects' families need to notify
our coordinating dietitian of any deviation in wheat product ingestion during the study
period. Study dietitian will package the exact OIT doses for dispensing to subjects.
Different Phases in Stage II
Randomization and Blinding: subjects will enter this Stage and randomized into Rush Induction
within two weeks of screening/baseline DBPCFC. Randomisation at 1:1 ratio to low-dose or
standard-dose OIT will be stratified by age (3-6 years; 7-11 years; 12-17 years) as younger
subjects more likely outgrow wheat allergy naturally. The coordinating dietitian prepares the
randomization sequence at the study start and put individual randomization numbers inside
sealed envelopes. This dietitian will notify the field staff of that number upon subject's
informed consent. Investigators, field staff and subjects/families will be blinded to the
nature of interventions (low-dose vs standard-dose) throughout the 12-month randomisation
period, and they will assess desensitization and SU by DBPCFC according to pre-defined
PRACTALL criteria. On the other hand, families will be aware of the nature of intervention
(i.e. observer-blinded) but asked not to disclose this to field staff.
Rush (T0): subjects will receive increasing doses of wheat every 20 minutes to reach a final
dose of 650 mg WP (or 5 grams wheat product; low-dose group) and 5 grams WP (or 38 grams
wheat product; standard-dose group) as pasta. In both groups, subjects will consume a total
of 38 grams pasta daily, with that of low-dose group made up of 5 grams wheat-based pasta and
33 grams gluten-free pasta. Study dietitian will offer nutritional counselling to families
and prepare the Rush doses. Subjects who complete Rush protocol without reaction will
commence the Build-up Phase at a daily dose of 650 mg WP (low-dose group) or 5 grams WP
(standard-dose group) (Dose 8 of Rush) on the day after the Rush Induction day. A subject
reacting to one of the 8 doses during Rush Induction will cease the Rush schedule and
commence the Build-up Phase at the dose immediately below the reaction-eliciting dose on the
day after the Rush Induction day.
Build-up: subjects will be given the group-appropriate daily incremental dose of wheat OIT
every 2 weeks until the maintenance dose of 38-gram wheat/gluten-free product is reached. In
unavoidable circumstances (e.g. examinations), there is +/- 7 days of window for build-up
visits to accommodate parent/subject availability. Each dose increase will be administered in
hospital under medical supervision. If a participant reacts to a build-up dose on the day of
the Up-dose visit and the reaction is consistent with the pre-defined stopping criteria for
Rush, then the participant will remain on the previous tolerated dose.
Maintenance: subjects will consume a daily wheat dose as appropriate to the assigned
treatment arm for 6 days per week at home until a total of 12 months of treatment. Subjects
will return every 12 +/- 2 weeks for review. They will undergo wheat DBPCFC at treatment
termination (T1) and 4 weeks later (T2). SPT and blood tests for sIgE levels against wheat
will be repeated at these two time points for assessing the immunomodulatory effects of OIT.
Evaluation of Compliance with Interventions: subjects will return unused doses and used
treatment packs as well as study diaries to our dietitian at each visit so that we can audit
their treatment compliance and study progress. Subjects will be considered as compliant to
intervention (i.e. per protocol) if they consume >=75% treatment doses over a 6-month period.
Data analysis will be performed by both intention-to-treat and per protocol principles.
Assessment and Documentation of Adverse Events: the incidence and severity of
treatment-emergent adverse events will be monitored and recorded during the Treatment Phase.
The severity of an adverse event will be categorised according to whether the event is
allergic or non-allergic. The severity of allergic adverse events will be categorised based
on NIH NIAID Consortium for Food Allergy Research specific grading system for allergic
reactions. For non-allergic adverse events, their severity will be classified according to
the ICH guidelines.
Data analysis
For Stage I, wheat allergic and tolerant groups will be defined by the gold standard DBPCFC
according to our published methods. Allergy test results (SPT, sIgE, BAT) and DBPCFC scores
will be analyzed by parametric or non-parametric tests, with significance set at P<0.05. To
evaluate the diagnostic performance of different allergy tests, Mann-Whitney U test will be
used to compare test results between allergic and tolerant subjects. The optimal cut-offs of
allergy tests for challenge-confirmed wheat allergy will be determined from area-under-curve
of receiver-operating-characteristic curves by SPSS for Windows version 25. The investigators
determine the best algorithm for wheat allergy by a stepwise approach.
For Stage II, clinical trial data will be analyzed both intention-to-treat and per protocol.
All available data from subjects who received any investigational product will be included in
safety data analysis. All demographic and baseline continuous outcomes will be presented as
mean and standard deviation (or medians and interquartile ranges for skewed data), whilst
categorical outcomes will be presented as number and percentage. Unless specified otherwise,
statistical significance will be set at 5%. Inter-group comparisons regarding categorical
outcomes will be analyzed by logistic regression with adjustment for age as the
stratification variable. Continuous outcomes will be analyzed by linear regression models
adjusted for the same stratification.