Intravenous iRGD‐Guided, RBC‐Membrane Camouflaged <i>Lactococcus Lactis</i> Remodels Cold NSCLC and Enhances PD‐1 Blockade

Resistance to programmed-death-1/programmed-death-ligand-1 (PD-1/PD-L1) blockade in non-small-cell lung cancer (NSCLC) arises mainly from weak tumor immunogenicity and limited effector T-cell infiltration. Here, this work presents an intravenously deliverable "living medicine" that addresses these barriers through biomimetic cloaking, tumor-penetrating guidance, and synthetic-biology-driven cytokine release. Lactococcus lactis is engineered to co-secrete Flt3L and OX40L (FOLactis) and then camouflage with red-blood-cell membranes, producing long-circulating mRBC@FOLactis. Conjugation of the iRGD peptide (iRGD-mRBC@FOLactis) enables trans-endothelial migration and deep (≥200 µm) interstitial penetration, yielding a fourfold increase in intratumorally bacterial accumulation versus unmodified FOLactis. In the orthotopic Lewis lung carcinoma (LLC) model, a single intravenous dose of iRGD-mRBC@FOLactis combined with anti-PD-1 antibody achieves complete tumor regression in 60% of mice, doubles median survival (p < 0.001), and generates systemic tumor-specific immune memory. Mechanistically, local Flt3L and OX40L secretion expands cross-presenting dendritic cells (DCs), boosts CD8⁺ T-cell priming, and converts immunologically "cold" tumors into inflamed, T-cell-rich lesions, thereby overcoming primary resistance to checkpoint blockade. This multifunctional probiotic platform establishes a generalizable strategy for systemic delivery of living therapeutics and offers a powerful adjunct to PD-1/PD-L1 blockade for NSCLC and other treatment-resistant solid tumors.