Genetically Engineered Probiotics: Design, Therapeutics, and Clinical Translation.

Genetically engineered probiotics (GEPs) aim to address transient colonization and the intra- and inter-subject variability that limit conventional probiotics. These strains utilize Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas editing, programmable gene circuits, and biosensors in chassis such as E. coli Nissle 1917 and L. lactis. This narrative review summarizes the current engineering toolkits and standards (e.g., SEVA), chassis selection criteria, biocontainment strategies, and translational requirements under CMC/GMP frameworks and discusses regulatory considerations for clinical translation. Representative examples include IL-10-secreting Lactococcus lactis and phenylalanine-metabolizing strains for phenylketonuria (SYNB1618/SYNB1934), which illustrate pharmacodynamic target engagement and short-term preclinical safety. We outline clinical advancements in predefined pharmacodynamics, durability of function, monitoring shedding and horizontal gene transfer, and genomic-microbiome-informed patient stratification. Systems modeling approaches (Genome-Scale Metabolic Model/ Agent-Based Model) are discussed as tools to guide rational design. GEPs offer programmable “sense-and-respond” therapeutics, with successful clinical adoption depending on durable efficacy, long-term safety, and clearly defined regulatory pathways.