Two independent reports published in Nature Biotechnology and accompanying coverage describe engineered Escherichia coli strains capable of sustained intratumoral nitric oxide production via synthetic arginine–NO circuits. In mouse models the bacteria promoted vascular normalization, reprogrammed the tumor microenvironment, reinvigorated CD8+ T cells and potentiated anti‑PD‑L1 checkpoint therapy, producing durable regressions in some models. Authors and institutions highlighted the approach as a microbial synthetic biology strategy to remodel immunosuppressive tumors and expand combinations with checkpoint inhibitors; the papers detail strain engineering, safety controls and mechanistic biomarker changes tied to improved immune infiltration.