Background Although peanut oral immunotherapy (OIT) has been conclusively shown to cause desensitization, it is currently unknown whether clinical protection persists after stopping therapy. Objective Our primary objective was to determine whether peanut OIT can induce sustained unresponsiveness following withdrawal of OIT. Methods We conducted a pilot clinical trial of peanut OIT at two U.S. centers. Subjects aged 1–16 were recruited and treated for up to five years with peanut OIT. The protocol was modified over time to permit dose increases to a maximum of 4000 mg peanut protein/day. Blood was collected at multiple time points. Clinical endpoints were measured with 5000 mg double-blinded, placebo-controlled food challenges once specific criteria were met. Results Of the 39 subjects originally enrolled, 24 completed the protocol and had evaluable outcomes. 12/24 (50%) successfully passed a challenge one month after stopping OIT and achieved sustained unresponsiveness. Peanut was added to the diet. At baseline and the time of challenge, such subjects had smaller skin tests as well as lower IgE levels specific for peanut, Ara h 1, and Ara h 2, and lower ratios of peanut-specific:total IgE, compared to subjects not passing. There were no differences in peanut IgG4 levels or functional activity at end-of-study. Conclusions This is the first demonstration of sustained unresponsiveness after peanut OIT, occurring in half of subjects treated up to five years. OIT favorably modified the peanut-specific immune response in all subjects completing the protocol. Smaller skin tests and lower allergen-specific IgE levels were predictive of successful outcome.

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