Published Online: March 26, 2013
Currently, there is intense interest in the development of an interventional treatment for food allergies, and for peanut allergy specifically. One of the most promising and widely studied approaches is oral immunotherapy (OIT), in which an individual ingests a daily dose of peanut protein. OIT has now been studied in research centers around the world and, although there are some differences between studies, protocols typically begin with a dose of a few milligrams of protein per day (one peanut kernel equals approximately 250 milligrams of protein); these amounts are then gradually increased, often to several grams per day. Sublingual immunotherapy (SLIT) is a different treatment approach that has been less well studied and uses a daily liquid peanut extract placed under the tongue. SLIT doses commonly start at several micrograms per day and are similarly increased over time to several milligrams per day, substantially lower than that used for OIT, but similar to the doses found effective in treatment of nasal allergy. Although each approach may have certain advantages, they have not previously been directly compared in the treatment of peanut allergy.
In a recent Letter to the Editor in The Journal of Allergy & Clinical Immunology (JACI), Chin, Vickery and colleagues retrospectively compared the impact of two years of therapy on clinical and immunologic outcomes from 23 subjects receiving peanut OIT and 27 subjects receiving peanut SLIT. The OIT study was a multicenter study involving subjects at the University of North Carolina and the University of Arkansas for Medical Sciences; the SLIT study occurred only at UNC. Both studies were randomized, placebo-controlled trials in which subjects underwent a peanut challenge at one year of treatment to measure the amount of peanut required to elicit a reaction. At this point, the study was unblinded and all subjects that were initially randomized to placebo “crossed over” and began receiving active treatment. Only data from actively-treated subjects were used in this analysis.
The authors found that subjects receiving OIT were three times more likely to pass this 12 month peanut challenge than SLIT subjects, whose responses during the challenges were much more variable. Similarly, basophils, white blood cells that may become activated during an allergic reaction, were suppressed to a greater degree in subjects treated with OIT compared to SLIT. Despite similar levels of peanut-specific IgE and IgG4 at baseline, OIT induced significantly greater changes in these antibodies compared to SLIT after two years of therapy. There were no differences between the groups in skin prick test size, peanut-specific IgA antibodies, or the number of regulatory T cells.
This retrospective analysis was the first to compare these two experimental treatments, but post-hoc studies like this have notable limitations. These interim findings suggest, but do not prove, that OIT has greater clinical and immunologic effects than SLIT among subjects in immunotherapy clinical trials. It is too early to conclude that one treatment is “better” than the other. Studies with more rigorous designs will be necessary to address this. Furthermore, a detailed comparison of the safety of each approach was not part of this study, and there may be important differences between the two approaches in this respect that could influence the priority with which these modalities are pursued.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.