Synthetic Biology and Engineered Live Biotherapeutics: Toward Increasing System Complexity.

Recent advances in synthetic biology and biological system engineering have allowed the design and construction of engineered live biotherapeutics targeting a range of human clinical applications. In this review, we outline how systems approaches have been used to move from simple constitutive systems, where a single therapeutic molecule is expressed, to systems that incorporate sensing of the in vivo environment, feedback, computation, and biocontainment. We outline examples where each of these capabilities are achieved in different human disorders, including cancer, inflammation, and metabolic disease, in a number of environments, including the gastrointestinal tract, the liver, and the oral cavity. Throughout, we highlight the challenges of developing microbial therapeutics that are both sensitive and specific. Finally, we discuss how these systems are leading to the realization of engineered live biotherapeutics in the clinic.