Engineered live biotherapeutic products: design decisions, failure modes, and clinical translation

Engineered live biotherapeutic products (LBPs) are viable microorganisms deliberately modified to perform a therapeutic function in a patient. Recombinant therapeutic strains are considered separately from conventional probiotics, donor-derived microbiota products, vaccines, living diagnostics, environmental systems, and systemically administered oncolytic bacteria. Selected oncology platforms share engineering constraints with LBPs, although their classification as LBPs depends on the specific therapy. The target product profile sets the niche, route, and exposure requirements against which chassis, genetic control, and payload release are assessed. Fitness costs, genetic stability, basal leakage, and clearance constrain circuit complexity. Formulation and manufacturing must preserve viability and mechanism-linked potency, with process control and independent containment layers evaluated quantitatively during development. Human studies of engineered metabolic strains support feasibility, short-term tolerability, clearance, and pharmacodynamic activity, although broad or durable clinical benefit has not yet been shown. Microbiota products approved by the U.S. Food and Drug Administration (FDA) provide regulatory precedents for live microbial medicines, with approval specific to each unengineered product. Clinical trials require separate assessment of target engagement and patient benefit.