PD-L1-targeted OMV priming licenses myeloid co-stimulation and chemokine circuits to potentiate CAR-T therapy in advanced-stage solid tumors

Abstract Background Chimeric antigen receptor T (CAR-T) cell therapy has achieved remarkable success in hematologic malignancies, yet its efficacy in solid tumors is frequently limited by an immunosuppressive tumor microenvironment (TME) that restrains trafficking, persistence, and effector function. Targeted priming strategies that remodel myeloid compartments and reinforce intratumoral co-stimulation may help overcome these barriers. Methods We engineered bacterial outer membrane vesicles displaying PD-L1-targeting single-chain variable fragment (OMV PD−L1 scFv ). Their tumor-targeting and immunomodulatory functions, including DC maturation, co-stimulatory capacity, macrophage polarization, and phagocytosis, were evaluated in vitro. The potent antitumor efficacy and TME remodeling were examined in syngeneic models, specifically highlighting its synergy with dose-de-escalated CAR-T therapy. Single-cell RNA sequencing (scRNA-seq) further elucidated the mechanisms of early immune rewiring and intercellular communication programs associated with OMV priming. Results OMV PD−L1 scFv demonstrated enhanced tumor accumulation following systemic administration and promoted myeloid licensing by increasing DC maturation and co-stimulatory competence while repolarizing macrophages toward pro-inflammatory, tumor-phagocytic program. In vivo, OMV PD−L1 scFv remodeled the TME and improved CAR-T activation, tumor trafficking, and antitumor efficacy, achieving robust tumor control even at reduced CAR-T dosages in advanced solid tumors. scRNA-seq analyses highlighted transcriptomic signatures consistent with coordinated lymphoid and myeloid remodeling, characterized by enriched profiles of improved T-cell functional states, a potential transcriptomic basis for Xcl1 -mediated DC recruitment, strengthened DC-to-T co-stimulatory CD28 axis, and predicted enrichment of chemokine-driven myeloid–lymphoid communication involving Ccl3/4/5–Ccr5 . Conclusions PD-L1-directed OMV priming provides a modular, systemic strategy to reprogram the solid-tumor immune ecosystem by licensing myeloid compartments and reinforcing intratumoral co-stimulation, thereby supporting improved CAR-T recruitment and function. These findings establish engineered OMVs as a mechanistically grounded priming platform to complement CAR design for solid tumor immunotherapy.