Residency · Residency · Allergy Immunology

Oral Immunotherapy for Food Allergy

Overview and Rationale

Oral immunotherapy (OIT) involves the daily ingestion of gradually increasing amounts of allergenic food protein with the goal of raising the threshold for allergic reactions. The primary objectives are desensitization (raising the reaction threshold while on active treatment) and, ideally, sustained unresponsiveness (durable tolerance that persists after therapy is discontinued). OIT addresses a significant unmet need, as allergen avoidance alone imposes considerable psychosocial burden, the risk of accidental exposure remains ever-present, and the constant vigilance required profoundly affects quality of life for patients and their families. OIT is the most extensively studied form of food immunotherapy, supported by the most robust body of clinical trial evidence.

Immunologic Mechanisms of OIT

Desensitization

Desensitization is achieved in the majority of patients during active OIT and reflects functional changes in effector cells rather than a fundamental rewiring of the immune response. The key immunologic changes include mast cell and basophil hyporesponsiveness, with reduced mediator release upon allergen re-exposure, and decreased FcepsilonRI expression on mast cell surfaces. Allergen-specific IgE levels undergo a characteristic trajectory: a transient increase during the updosing phase, followed by a gradual decline during maintenance. Concurrently, allergen-specific IgG4 increases significantly, functioning as a "blocking antibody" that competes with IgE for allergen binding and inhibits IgE-facilitated allergen presentation to T cells via FcepsilonRII (CD23). A critical limitation is that the tolerance achieved through desensitization is maintained only with continued daily dosing and is lost within weeks to months of discontinuation.

Sustained Unresponsiveness

Sustained unresponsiveness, representing a more fundamental reprogramming of the immune system, is achieved in only a minority of patients. The immunologic hallmarks include induction of regulatory T cells (CD4+CD25+FoxP3+) producing interleukin-10 and TGF-beta, a shift from Th2 to Th1/Treg balance at the allergen-specific level, epigenetic modifications at the FoxP3 locus (specifically demethylation of the Treg-specific demethylated region, or TSDR), and generation of IL-10-producing regulatory B cells. A lower specific IgE-to-IgG4 ratio predicts the likelihood of sustained unresponsiveness, and longer duration of maintenance therapy increases the probability of achieving this outcome.

Peanut OIT

Palforzia (AR101) - FDA-Approved Peanut OIT

Palforzia became the first FDA-approved oral immunotherapy product in January 2020. It consists of standardized peanut protein powder packaged in pull-apart capsules for lower doses and sachets for higher doses. The approved indication is for patients aged 4 to 17 years with confirmed peanut allergy, with age indications subsequently expanded. The treatment protocol comprises three phases: an initial dose escalation day, during which five doses from 0.5 mg to 6 mg of peanut protein are administered over approximately 4 to 5 hours under medical supervision; an updosing phase spanning approximately 6 months, during which 11 dose levels are sequentially achieved with each dose increase administered in the clinic and daily home dosing between clinic visits; and a maintenance phase of indefinite duration at 300 mg of peanut protein daily.

The pivotal PALISADE trial, a phase 3 study reported by Vickery and colleagues in the New England Journal of Medicine in 2018, enrolled 496 participants aged 4 to 17 years and demonstrated that 67.2 percent tolerated 600 mg of peanut protein at the exit food challenge, compared with 4.0 percent in the placebo group. This desensitization threshold is equivalent to approximately 1 to 2 peanuts worth of protein, sufficient to provide protection against most accidental exposures but not intentional peanut consumption. Notably, 14.2 percent of participants discontinued treatment due to adverse events. The ARC trials confirmed tolerability across a broader age range.

Safety of Peanut OIT

Allergic reactions during OIT are expected and common, with approximately 90 percent of patients experiencing adverse events during treatment. Oral and pharyngeal symptoms (pruritus, tingling) are the most frequently reported. Gastrointestinal symptoms including abdominal pain, nausea, and vomiting occur in 30 to 40 percent of patients. Systemic allergic reactions requiring epinephrine occur in approximately 10 to 15 percent of patients during the build-up phase, with anaphylaxis occurring at a rate of approximately 0.2 percent per dose during build-up and lower rates during maintenance.

Eosinophilic esophagitis develops in approximately 2.7 to 8 percent of OIT-treated patients, representing a significant concern that requires ongoing monitoring. Patients should be monitored for dysphagia, food impaction, and persistent gastrointestinal symptoms. If EoE is confirmed on biopsy, treatment options include discontinuation of OIT or continuation of OIT with concomitant proton pump inhibitor therapy or swallowed topical corticosteroids.

Cofactor-enhanced reactions during OIT represent an important practical consideration. Exercise within 2 hours of dosing increases reaction risk, and similar potentiation occurs with hot baths, NSAIDs, alcohol, concurrent illness, sleep deprivation, and menstruation. The "2-2-2 rule" provides a practical framework: avoid exercise, hot baths, and alcohol for 2 hours before and 2 hours after each dose.

<image>A timeline infographic of the Palforzia (peanut OIT) treatment protocol. Horizontal timeline divided into three phases: (1) Initial dose escalation day (Day 1): shown in a clinic setting with 5 escalating doses from 0.5mg to 6mg over 4-5 hours, medical supervision required, observation period. (2) Updosing phase (~6 months): 11 dose levels shown as ascending steps from 3mg to 300mg, each step-up in clinic with 30-60 min observation, daily home dosing between visits. (3) Maintenance (indefinite): daily 300mg peanut protein at home. Below the timeline, a bar graph showing PALISADE trial results: 67.2% of treatment group vs 4.0% placebo tolerated 600mg challenge. Safety panel: pie chart of adverse events (oral symptoms 50%, GI symptoms 30%, systemic reactions requiring epinephrine 12%, EoE development 3-8%). Cofactor warning box listing exercise, heat, NSAIDs, illness restrictions.</image>

OIT for Other Foods

Milk OIT

Multiple clinical trials have demonstrated effective desensitization to milk protein through OIT, with typical maintenance doses of 150 to 300 mL of milk (2 to 4 grams of protein). Adverse event rates are comparable to peanut OIT. Sustained unresponsiveness rates of 30 to 40 percent have been observed after 1 to 2 years of maintenance, with higher rates achieved with longer treatment duration. For patients who already tolerate baked milk, this may serve as a first step in a graduated approach, potentially obviating the need for full OIT.

Egg OIT

Effective desensitization has been demonstrated in multiple randomized controlled trials, with maintenance doses of 2 to 4 grams of egg protein (equivalent to approximately one-third to two-thirds of an egg). Sustained unresponsiveness rates range from 28 to 50 percent at 2 to 4 years. The IMPACT study demonstrated that egg OIT initiated between ages 1 and 3 years achieved greater rates of sustained unresponsiveness compared with initiation in older children.

Multi-Food OIT

Simultaneous OIT targeting multiple food allergens (up to five or more) has been demonstrated to be feasible, as shown by Begin and colleagues and through the OUtMATCH approach. Combining OIT with omalizumab pretreatment significantly improves safety during multi-allergen build-up, reducing the reaction rate by approximately 70 to 90 percent. This approach offers the practical advantage of treating multiple allergies simultaneously rather than sequentially, substantially reducing the overall treatment timeline.

Omalizumab-Facilitated OIT

Omalizumab (anti-IgE) has been extensively studied as an adjunctive therapy to OIT. By reducing free IgE, downregulating FcepsilonRI, and raising the threshold for mast cell activation, omalizumab pretreatment allows faster updosing schedules with fewer adverse reactions. Omalizumab is typically initiated 8 to 16 weeks before OIT begins and continued through the build-up phase, with discontinuation once the maintenance dose is achieved. The OUtMATCH trial demonstrated that omalizumab monotherapy (without daily food dosing) increased food tolerance thresholds for multiple foods simultaneously, leading to FDA approval of omalizumab for food allergy independent of OIT.

Epicutaneous Immunotherapy (EPIT)

Viaskin Peanut

The Viaskin Peanut patch contains microgram quantities of peanut protein (250 micrograms) and is applied daily to the upper back with site rotation. The mechanism involves delivery of allergen to the epidermis, targeting Langerhans cells and inducing regulatory T cell responses. The PEPITES phase 3 trial in children aged 4 to 11 years demonstrated a response rate of 35.3 percent in the treatment group versus 13.6 percent with placebo. While desensitization is modest compared with OIT, the safety profile is markedly superior, with minimal systemic reactions and local skin reactions (erythema, pruritus) as the primary adverse events. Advantages include the absence of daily oral dosing, no exercise restrictions, no gastrointestinal side effects, and no reported risk of eosinophilic esophagitis. Disadvantages include lower efficacy compared with OIT, application site reactions, and challenges with patch adherence. The FDA regulatory pathway is ongoing with resubmission in progress.

Sublingual Immunotherapy (SLIT) for Food Allergy

Sublingual immunotherapy for food allergy involves holding a liquid allergen extract under the tongue for 2 minutes before swallowing. It has been studied for peanut, milk, hazelnut, and peach. Desensitization thresholds achieved with SLIT are lower than with OIT (typically 300 to 1000 mg of protein). The safety profile is superior to OIT, with fewer systemic reactions, though local oropharyngeal symptoms are common but mild. SLIT for food allergy remains primarily in the research stage with no FDA-approved products.

Comparing Food Immunotherapy Modalities

OIT vs. EPIT vs. SLIT

The three modalities differ substantially in their efficacy-safety balance. In terms of efficacy (threshold increase), OIT is markedly superior to SLIT, which in turn is superior to EPIT. In terms of safety, the gradient is reversed: EPIT has the fewest adverse events, followed by SLIT, then OIT. The risk of eosinophilic esophagitis is highest with OIT (2.7 to 8 percent), rare with SLIT, and unreported with EPIT. The proportion achieving sustained unresponsiveness may be highest with OIT, though data for EPIT and SLIT remain limited. Each modality has distinct practical considerations: OIT requires daily food dosing with exercise and other restrictions, EPIT involves daily patch application, and SLIT involves daily sublingual drops or tablets.

<image>A three-column comparison illustration of food immunotherapy modalities (OIT, SLIT, EPIT). Each column shows: (1) Administration method diagram - OIT: measured dose of food protein ingested orally; SLIT: drops held under tongue; EPIT: patch on upper back with allergen in contact with skin. (2) Dose range (OIT: milligrams to grams; SLIT: micrograms to milligrams; EPIT: micrograms). (3) Efficacy bar graph showing approximate desensitization rates. (4) Safety profile with adverse event rates (systemic reactions, GI symptoms, EoE risk). (5) Immunologic mechanism boxes: OIT primarily gut-associated lymphoid tissue; SLIT sublingual DC activation; EPIT epidermal Langerhans cell Treg induction. (6) Practical considerations icons: daily dosing requirements, exercise restrictions, clinic visit frequency. Bottom row: development status (OIT: FDA-approved Palforzia; SLIT: investigational; EPIT: Phase 3/regulatory submission).</image>

Monitoring and Long-Term Management

During OIT

Clinic visits are required for each dose increase, with 30 to 60 minutes of observation following each escalation. Monitoring includes symptom diaries and growth parameters in children. Reassessment at 12 months should include repeat skin prick testing, serum-specific IgE, and component testing. Expected immunologic changes include a transient rise followed by decline in specific IgE, a significant rise in IgG4, and a decrease in skin prick test wheal size. Any new dysphagia, food impaction, or persistent gastrointestinal symptoms should prompt upper endoscopy with biopsy to evaluate for eosinophilic esophagitis.

After Achieving Maintenance

Daily dosing must continue indefinitely to maintain desensitization. Assessment of sustained unresponsiveness requires discontinuing OIT for 4 to 12 weeks followed by a supervised oral food challenge. If the challenge is passed, cautious diet liberalization may be undertaken with periodic re-challenges recommended. If the challenge is failed, maintenance dosing should be resumed. Predictors of sustained unresponsiveness include lower specific IgE, higher IgG4, longer maintenance duration, and lower basophil reactivity.

Key Clinical Pearls

• OIT achieves desensitization (not cure) in most patients; sustained unresponsiveness requires prolonged treatment and occurs in a minority
• Palforzia (peanut OIT) desensitizes to ~600 mg peanut protein (1-2 peanuts); sufficient to protect from most accidental exposures but not intentional consumption
• EoE is a significant concern with OIT (~2.7-8% incidence); screen with symptom monitoring and EGD if dysphagia develops
• Exercise, hot baths, NSAIDs, illness, and alcohol within 2 hours of OIT dosing increase reaction risk ("cofactor-enhanced reactions")
• Omalizumab co-treatment reduces OIT adverse events by 70-90% and enables safer multi-food OIT protocols
• EPIT (Viaskin Peanut) offers a safer but less efficacious alternative to OIT; no EoE risk reported
• Patients must continue carrying epinephrine auto-injectors even while on OIT; accidental high-dose exposure or cofactor-enhanced reactions can still cause anaphylaxis

References

1. Vickery BP, et al. AR101 oral immunotherapy for peanut allergy (PALISADE). N Engl J Med. 2018;379(21):1991-2001.
2. Sampson HA, et al. Effect of varying doses of epicutaneous immunotherapy vs placebo on reaction to peanut protein exposure (PEPITES). JAMA. 2017;318(18):1798-1809.
3. Wood RA, et al. Omalizumab for the treatment of multiple food allergies (OUtMATCH). N Engl J Med. 2024;390(10):889-899.
4. Chu DK, et al. Oral immunotherapy for peanut allergy (PACE): a systematic review and meta-analysis of efficacy and safety. Lancet. 2019;393(10187):2222-2232.
5. Bird JA, et al. Efficacy and safety of AR101 in oral immunotherapy for peanut allergy (ARC001). J Allergy Clin Immunol Pract. 2018;6(2):476-485.

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