Genetically bio-engineered PD-L1 targeted exosomes for immunotherapy of resistant triple negative breast cancer.

Immunotherapy has transformed cancer treatment by harnessing the immune system to target tumor cells, with PD-L1 inhibition emerging as a promising strategy. Exosomes, which naturally function as nanocarriers, offer significant potential for delivering therapeutic payloads, while genetic engineering allows for improved cargo specificity and efficacy. Here, for the first time, we genetically engineered exosomes to express anti-PD-L1 (PDL E) on their surface, enabling targeted drug delivery and immunotherapeutic activity. These engineered exosomes were then loaded with STAT3 siRNA (PDL ESi) and evaluated against doxorubicin-resistant MDA-MB-231 cells in combination with paclitaxel. Both in vitro and in vivo studies demonstrated a pronounced reduction in tumor burden (P < 0.001) and progression. Mechanistic investigations revealed that these exosomes activated apoptotic pathways, including the PI3K/AKT/mTOR axis, while inhibiting survival signals such as BCL-2, thereby enhancing tumor cell apoptosis. Notably, PD-L1 expression was downregulated in tandem with modulation of the STAT3/Nrf2 signaling axis, further augmenting the anti-tumor immune response. Toxicity studies in MCF-10 A cells showed that PDL ESi was well-tolerated, with no off-target effects. Imaging analyses in both 3D spheroids and tumor xenograft models confirmed the efficient tumor targeting of PDL E, demonstrating their time-dependent accumulation at the tumor site. Collectively, these findings highlight the promise of PD-L1-targeted, genetically engineered exosomes as a versatile platform for combination cancer therapy, providing a multifaceted strategy to overcome therapeutic resistance in TNBC.