A combinatorial construct library enables an expanded expression range of secreted therapeutic proteins by probiotic yeast.

Orally administered engineered probiotics, including Saccharomyces cerevisiae var. boulardii (Sb), are of emerging interest as protein therapeutic delivery platforms to treat gastrointestinal diseases. Tools to readily optimize protein output are required to optimize the therapeutic index of Sb-produced therapies. In this study, a 125-plex Sb secretion construct library was developed consisting of all possible combinations of five promoters, five secretion signals, and five terminators, which enabled a greater than 1800-fold range in Sb expression of a Gaussia luciferase (GLuc) reporter. Secretion signal and promoter identities had significant effects on secretion output. This library further enabled a 28-fold improvement of binding activity of Sb-secreted haPD-1, an established anti-tumor immunotherapeutic, and improved haPD-1 detection in mouse stool samples following oral gavage of Sb_haPD-1. Sb secretion trends of both GLuc and haPD-1 in vitro mirrored payload expression in vivo. This protein secretion library toolkit will serve as a valuable resource to rapidly optimize protein therapeutic output from engineered Sb.