Multiple teams reported engineered Escherichia coli Nissle 1917 strains that sustain intratumoral nitric oxide (NO) production through synthetic circuits, promoting vascular normalization, myeloid reprogramming and enhanced CD8+ T‑cell responses. In preclinical models, NO‑producing bacteria synergized with anti‑PD‑L1 checkpoint blockade to drive durable tumor regressions in both hematologic and solid tumor models. Papers published in Nature Biotechnology detailed circuit design, arginine‑NO metabolic routing, and safety controls enabling persistent yet controlled NO production. The work demonstrates a modular bacterial approach to reshape the tumor microenvironment and enhance responsiveness to existing immunotherapies, while flagging translational challenges such as containment, dosing, and human microbiome interactions.