Lacticaseibacillus rhamnosus GG in a chewable colonizes the nose and facilitates local immune benefits in allergic rhinoconjunctivitis patients

ABSTRACT Current treatments fall short in managing allergic rhinitis (AR), emphasizing the need for additional strategies. Beneficial bacteria application shows promise in AR; however, most studies focus on oral probiotic administration without monitoring the applied strains in the upper respiratory tract (URT) and their local effects. In this randomized, double-blind, placebo-controlled trial, the probiotic Lacticaseibacillus rhamnosus GG was administered via chewable tablets in seasonal AR patients, randomized to probiotic ( n = 33) or placebo ( n = 31) groups. Per-protocol analysis of the URT microbiome, immune markers, and AR symptoms was performed. L. rhamnosus GG trafficked from chewables to the oropharynx (77%, P = 0.02) and nasopharynx (41%, P < 0.0001). Control of self-reported AR symptoms via validated questionnaires under grass pollen exposure was observed after 2 weeks of probiotic administration and not upon placebo. A local decrease in salivary interleukin-4 ( P < 0.05) and nasal IL-13 ( P < 0.0001) was observed in the probiotic group. These data indicate that L. rhamnosus GG chewables can target the URT and exert local effects on key allergy cytokines after temporal probiotic engraftment. IMPORTANCE Allergic rhinitis (AR) or hay fever is a highly prevalent condition, impacting nearly half the population in some countries. Supplementation of beneficial bacteria or probiotics has gained increasing attention in AR, and a key innovative way to do this is direct administration to the upper airways. Our study shows for the first time that the model probiotic strain Lacticaseibacillus rhamnosus GG can traffic to the nose in AR patients when administered via a slow-releasing chewable tablet. This trafficking is associated with local benefits in the airways, including on grass pollen-induced nasal symptoms and allergy-related cytokines.