Oral Immunotherapy (OIT)
A food allergy patient taking oral immunotherapy (OIT) ingests increasing doses of their allergen to desensitize their immune system, training their immune system to not react to the problem food. OIT has a long history – one early account of using OIT to treat egg allergy was published in 1908.
OIT typically starts with very small doses of food allergen consumed under medical supervision. These doses are increased, then increased again, and so on, until a small, tolerated dose is reached that can be taken at home each day. Every one to several weeks, the daily dose is increased, until a maintenance dose is reached that is consumed each day for months or years. Typical OIT doses of food protein are measured in milligrams or grams.
Food allergy patients have accessed OIT through clinical trials or from allergists/immunologists in practice. The food allergies treated with OIT in clinical trials include allergies to milk, egg, peanut, tree nut, wheat, soy and sesame, as well as baked milk and baked egg. OIT has been used in private practice with the goal of treating these food allergies and others. Many OIT studies have been small, and the design of these experiments has varied. OIT protocols also vary among practices.
In January 2020, an OIT treatment for peanut allergy received approval from the U.S. Food and Drug Administration (FDA). Palforzia® – developed by Aimmune Therapeutics and previously known as AR101 – is an OIT peanut flour product with known protein content. Palforzia dosing is standardized, starting at the same small amount and increasing on the same schedule to a final daily maintenance dose of 300 mg peanut protein, roughly equal to one peanut kernel, which is lower than most peanut OIT maintenance doses.
How Effective Is OIT?
Published desensitization rates in OIT studies range from 30 percent to more than 90 percent. In studies that retest patients after maintenance dosing stops, only some of the patients who are desensitized achieve sustained unresponsiveness, the ability to eat the problem food after stopping daily maintenance dosing for some time.
Palforzia, the peanut OIT product approved by the FDA for the U.S. market in January 2020, has been shown to increase peanut tolerance significantly compared to an inactive treatment (placebo) that does not contain peanut. PALISADE was a Phase 3 clinical trial for Palforzia, a large study with nearly 500 peanut-allergic children aged 4-17 that tested the drug's safety and effectiveness. After one year of treatment, half of the Palforzia-treated children were able to eat one gram of peanut protein without symptoms. In contrast, only 2 percent of children who received a peanut-free placebo could tolerate this dose. Two-thirds of the children who started treatment with Palforzia – and 85 percent of those who completed the active treatment – could tolerate eating at least 600 mg of peanut protein (approximately two peanut kernels), a dose that was tolerated by only 4 percent of children who received placebo. This level of peanut tolerance is clinically significant: a recent study reports that raising a patient's tolerance from 100 mg of peanut protein or less to 300 mg of peanut protein lowers the risk of an allergic reaction to cross-contact peanut residue in snack foods by 95 percent, and reaction risk declines even further if a patient's tolerance increases from 300 mg of peanut protein to one gram.
A follow-up study found that continued daily dosing with 300 mg of Palforzia resulted in increased peanut tolerance above the levels achieved during the one-year PALISADE trial.
How Safe Is OIT?
Reactions are common during OIT. Most of these reactions involve localized symptoms, such as itchy mouth or upset stomach, but severe reactions that affect multiple organ systems (anaphylaxis) can happen. Factors that can increase the likelihood of a systemic reaction include infection, exercise, hot showers and nonsteroidal anti-inflammatory drugs like ibuprofen. Individuals who undertake OIT typically schedule their daily doses at a time when they won’t be very active afterword, and the dose may be decreased temporarily to accommodate illness.
A significant fraction of patients, 10-30 percent, decide to leave OIT treatment because they don’t tolerate OIT reaction symptoms, especially symptoms that affect the gut. During or after OIT, a minority of patients (3-15 percent) develop eosinophilic esophagitis (EoE). This allergic condition damages the tube-shaped organ that carries food from the mouth to the stomach. EoE can also develop in children who outgrow a food allergy on their own, without OIT. We don’t know whether OIT directly causes EoE to develop, or whether OIT treatment uncovers EoE that had previously been controlled by avoiding trigger food(s).
Reports from the PALISADE trial of Palforzia fit these broader findings. One in five AR101-treated patients left the trial. Thirteen percent dropped out due to adverse reactions, including one child who experienced severe anaphylaxis requiring epinephrine and one child with eosinophilic esophagitis.