Over the past few decades, allergies have been on the rise worldwide, particularly in the United States. Immunotherapy (or allergy shots), in which incremental exposure to allergens sensitizes the immune system to the allergen, have been effective for some allergies, such as dust mites. For food allergies, the effectiveness of oral exposure in infancy to sensitize patients to the allergen was under debate for many years.1 Last year, the LEAP study performed a much-needed randomized controlled trial for the effect of peanut exposure in early childhood on formation of peanut allergy. Their results were striking and conclusive – the prevalence of peanut allergy in the avoidance group was 17.2%, whereas the prevalence in the consumption group was 3.2%.
At the end of 60 months of exposure or avoidance of peanuts, the LEAP-study ended. However, the long-term effects of this early exposure on peanut tolerance remained unclear. To address this, the LEAP-On study group instructed all LEAP study members (those in both the avoidance and consumption groups) to avoid peanut exposure for 12 months after the end of the LEAP trial. The primary endpoint, peanut allergy at 72 months, was significantly more frequent in the patients that had avoided peanuts in the LEAP trial (18.6%) compared to the consumption group (4.8%, p<0.001). These results indicate that four years of consumption of peanuts in early childhood is sufficient to produce tolerance to peanuts that is maintained over the subsequent year, even with peanut avoidance for that year.
In addition, the authors report that there were three cases of new peanut allergy in both groups during the 12 months after the LEAP study. However, there was no statistical difference in peanut allergy over the year of avoidance in the LEAP consumption group (3.7% at 60 months, 4.8% at 72 months, p=0.250), indicating that avoidance after consumption did not increase de novo peanut allergy formation.
While it is clear that peanut tolerance is stable for 12 months after oral exposure, a variety of questions remain. First, how long will this tolerance be stable? Is it necessary to have exposure this early in life in order to acquire such tolerance? And importantly, do these results apply to other food allergens, beyond peanuts? Hopefully, with follow up studies and more randomized controlled trials, we can begin to tackle the ever-rising rates of allergies.
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Rachel is a fifth-year MD/PhD student at Harvard Medical School. She is originally from Okemos, MI, and graduated from Stanford University in 2011. For her PhD research, she is studying the regulation of cell growth in response to nutrients.