Nanobody-displayed outer membrane vesicles modulate PD-L1+ MDSCs to improve radio-immunotherapy

Myeloid-derived suppressor cells (MDSCs) represent one of the major obstacles to cancer immunotherapy by inducing T cell exhaustion and dampening immune activation. Here, we demonstrate that radiotherapy-induced inflammation promotes the enrichment of PD-L1 + MDSCs, in which inflammation-triggered JAK-STAT3 signaling drives PD-L1 upregulation, while the PI3K/AKT/mTOR axis sustains their immunosuppressive program. To counter this, we engineered bacterial outer membrane vesicles (P-O nb /B) that combine intrinsic myeloid-preferential uptake with PD-L1 nanobody display and co-loaded the PI3K/mTOR inhibitor BEZ235 to preferentially modulate PD-L1 + MDSCs. In vitro and in vivo analyses showed that P-O nb /B preferentially accumulates within suppressive myeloid compartments and inhibits PI3K/mTOR signaling, thereby reducing intratumoral MDSCs burden and immunosuppressive mediators, alleviating PD-1 + LAG-3 + T cell exhaustion, and enhancing Granzyme B + T cell and NK cell activity. In combination with radiotherapy, P-O nb /B significantly suppressed tumor growth and metastasis. Collectively, our work supports a model in which radiotherapy-evoked inflammatory cues promote the emergence of PD-L1 + MDSCs, while sustained PI3K/mTOR signaling preserves their suppressive state. By enabling myeloid-directed, PD-L1-guided delivery of a pathway inhibitor, P-O nb /B provides a translatable framework to reprogram suppressive myeloid niches and improve the therapeutic window of radio-immunotherapy.