Immunotherapy for food allergy is an active area of research. Thorough follow-up of study participants is important for determining whether long-term desensitization and maintenance dosing is feasible. Findings from a number of clinical trials exploring the efficacy of oral, sublingual, and epicutaneous administration of various food allergens have been published [8, 9]. However, LTFU studies have been carried out by only a few groups [13, 14, 15, 16, 17, 18, 19]. To our knowledge, this study represents one of the longest (up to 72 months past reaching the maintenance dose in OIT) follow-up studies in OIT.
The participants chose to maintain (2 g and over; i.e. ‘high’) or reduce (300 mg to less than 2 g; i.e. ‘low’) their daily maintenance dose of allergens during the LTFU study. The choice to ingest high vs. low dose was not due to safety or allergy symptoms for any participant but rather based upon convenience and taste preference, and was made via a team approach by the participant/caregiver of the participant and clinicians. The main finding of this observational study was that all the participants were able to pass OFCs to 2 g to all their offending foods at the end of our follow-up phase, independent of their low or high long-term maintenance dose. Our results suggest that long-term OIT was possible at a broad age range (specifically, 6.4–46.9 years), and for multiple foods (specifically, almond, cashew, egg, hazelnut, milk, peanut, pecan, sesame, walnut). We also observed that compliance with regular ingestion of food allergens, strong, positive relationships with clinician-parent/participant, and frequent connections between families to support each other favored long-term OIT.
Participant safety is paramount in any allergen immunotherapy study; thus, the participants were counseled frequently on emergency measures. Adverse events were recorded through documented on call services, self-reports, and clinician reports at each visit. Virkud et al.  analyzed pooled data from 3 pediatric OIT studies (n = 87) for up to a median of approximately 1.6 years (0.9–3.1 years) and found that 40% of patients had at least one severe event and 12% needed injectable epinephrine. Our data demonstrate a trend in decreased allergic adverse events during the course of the longitudinal study. However, it is important to note that severe allergic reactions (nasal and skin specifically), albeit rare, still occurred randomly during the LTFU, emphasizing the need for constant vigilance and emergency preparedness.
We observed a general trend of decrease in SPT wheal size, and increase in IgE/IgG4 ratio in our LTFU cohort.
There were certain limitations to our LTFU study, such as inadequate power to study differences between participants ingesting n = 2 vs. 3 vs. 4 vs. 5 food allergens due to low sample sizes in each group. Also, we did not randomize for low vs. high dosing and left this as a decision for the clinical team with patient-based participation. Future studies using larger, randomized controlled studies are warranted. Despite these limitations, our study underscores the importance of longitudinal, follow-up studies to document whether or not desensitization can be sustained with adequate maintenance dosing over the long term.