Surface Display of an Anti-CD3 scFv by Saccharomyces boulardii and Its Effect on DSS-Induced Colitis in Mice

Saccharomyces boulardii (Sb) is a probiotic yeast amenable to genetic manipulation, making it a promising platform for delivery of recombinant biotherapeutics to the intestinal lumen. In this study, we engineered a recombinant Sb strain to display an anti-CD3 single-chain variable fragment (scFv) on its surface and evaluated its potential as an oral antibody delivery system. To improve antibody accessibility, we tested different stalk lengths between the scFv and the SED1 anchoring domain. The strain with the longer stalk domain (Sb649) showed more stable surface display over time and was subsequently evaluated in a dextran sulfate sodium (DSS)-induced colitis model. Sb649-treated mice showed body weight values and disease activity profiles closer to those of healthy controls. Sb649 administration was also associated with transcriptional changes, including increased Foxp3 expression and no increase in Il6 in mesenteric lymph nodes, unlike DSS and DSS+SbWT-treated mice, along with increased Muc3 expression in the colon compared to DSS-treated mice. Together, these findings show that engineered Sb can stably display antibody fragments and support its potential as a platform for oral delivery of antibody-based immunotherapies to the gastrointestinal tract.