Programmable bacterial vaccine vectors: A Design-Build-Control framework for precision immune engineering.

Live bacterial vectors combine intrinsic adjuvanticity, mucosal targeting, and programmable antigen delivery within a single engineerable chassis, yet their development has historically relied on empirical attenuation rather than systematic design. We present a Design-Build-Control framework, adapted from synthetic biology paradigms, that reframes bacterial vector engineering as a unified biotechnological problem. Design principles govern trade-offs among safety, immunogenicity, tissue tropism, and route of administration. Build-stage strategies translate these principles into genetically stable vector platforms through attenuation, balanced-lethal systems, and antibiotic-free plasmid maintenance. Control-stage tools, including inducible promoters, quorum-sensing circuits, and kill switches, enable dynamic regulation of vector behavior within the host. We apply this framework across major platform classes, including live attenuated Gram-negative and Gram-positive bacteria, probiotic chassis, and non-replicating systems such as outer membrane vesicles, bacterial ghosts, and spores, and examine how biomaterial-based formulation, including encapsulation and mucoadhesive coatings, extends engineering control into manufacturing and delivery. We evaluate translational determinants, including genetic stability, environmental containment, and regulatory compliance, alongside applications spanning infectious disease, oncology, and veterinary medicine. We further assess the emerging role of artificial intelligence in bacterial-vector design, distinguishing established computational applications, experimentally validated approaches, and prospective uses that still require experimental validation. By integrating advances in synthetic biology, biomaterials, and computational design, this review presents programmable bacterial vectors as an emerging biotechnology platform and proposes a Design-Build-Control (DBC) framework for systematically evaluating biosafety, manufacturability, and clinical translation.