Extracellular vesicles (EVs) have emerged as critical mediators in cancer biology, playing sophisticated roles in both promoting immunotherapeutic resistance and offering innovative treatment opportunities. These membranous particles, released by various cell types including cancer cells, serve as vehicles for intercellular communication that can either undermine or enhance cancer treatment efficacy.
EVs Drive Immunotherapy Resistance Through Multiple Mechanisms
Cancer cells strategically exploit EVs to disseminate resistance mechanisms within the tumor microenvironment. These vesicles transport drug-resistant proteins and genetic material, facilitating the spread of therapeutic resistance to neighboring cells and ultimately leading to treatment failure. The immunosuppressive cargo carried by cancer-derived EVs includes molecules like TGF-β and PD-L1, which actively suppress immune cell activity and establish an environment that enables tumor evasion from immune surveillance.
The impact on specific immunotherapies is particularly concerning. Tumor-derived EVs carry functional PD-L1 that binds to PD-1 on T cells, effectively mimicking immune checkpoint interactions and reducing the efficacy of immune checkpoint inhibitors. These vesicles also scavenge tumor-associated antigens, reducing antigen availability for dendritic cell priming and compromising adaptive immune activation.
In CAR-T cell therapy, EVs from cancer-associated fibroblasts deliver immunosuppressive cytokines including TGF-β and IL-10, creating a tumor microenvironment enriched with regulatory T cells and myeloid-derived suppressor cells that suppress CAR-T cell activity. Exosomal miR-21 from adipocytes has been shown to downregulate apoptotic pathways in ovarian cancer cells, conferring resistance to paclitaxel treatment.
Engineered EVs Offer Therapeutic Innovation
Despite their role in resistance, EVs present significant opportunities for improving immunotherapy outcomes through strategic engineering. CAR-T cell-derived EVs have demonstrated particular promise, displaying CARs on their surface that enable bystander killing of antigen-negative tumor cells while overcoming tumor heterogeneity. These engineered vesicles lack PD-1 expression, making their antitumor activity resistant to suppression by PD-L1 treatment.
Dendritic cell-derived EVs serve as powerful vaccine platforms, carrying MHC molecules and costimulatory signals that can prime cytotoxic T cells and enhance antigen presentation. Research has shown that tumor neoantigen-loaded EV nanovaccines demonstrate efficient cargo loading and sustained delivery to lymph nodes, leading to robust antigen-specific immune responses with excellent biosafety profiles.
Natural killer cell-derived EVs exhibit potent antitumor capabilities, with studies showing strong anti-hepatocellular carcinoma effects through inhibition of serine/threonine protein kinase phosphorylation and activation of apoptosis markers. These vesicles demonstrate superior tumor penetration compared to traditional cell-based therapies while maintaining excellent targeting capacity.
Clinical Translation Challenges Require Strategic Solutions
The transition from laboratory research to clinical application faces several critical challenges that must be addressed for widespread therapeutic implementation. Large-scale synthesis represents a primary obstacle, as current production methods cannot meet clinical demand requirements.
Scale-out strategies using systems like the Integra CELLine Culture System have increased EV yield to 10.06 ± 0.97 mg/mL compared to 0.78 ± 0.14 mg/mL with traditional culture methods. Hollow fiber bioreactors enable automatic EV release and collection, though cell differentiation and density changes after extended culture periods can reduce single-cell EV yield.
Purification strategies require standardization to ensure clinical efficacy and safety. Current methods face challenges with co-isolated lipoproteins sharing similar characteristics with EVs, including density, size, and composition. The presence of LDL and HDL contamination remains problematic even with advanced purification techniques combining size exclusion chromatography and differential ultracentrifugation.
Long-term storage stability presents another significant hurdle. Cryoprotective agents like trehalose have shown promise, with 25 mM trehalose narrowing particle size distribution and maintaining biological activity in immune assays. Lyophilization techniques preserve both proteins and RNA within EVs when trehalose is present, with minimal impact on pharmacokinetics following intravenous injection.
Future Directions and Research Priorities
The field requires focused attention on three understudied dimensions to advance EV-based therapeutics. Spatiotemporal heterogeneity of EV cargo needs investigation, as current studies predominantly focus on bulk EV analysis while neglecting subpopulation-specific functions. Single-vesicle profiling technologies could help unravel the complexity of different EV subtypes and their distinct roles in treatment resistance.
EV-driven metabolic reprogramming represents another critical area, with emerging evidence suggesting that cancer-associated fibroblast EVs transfer metabolic enzymes like lactate dehydrogenase A to tumor cells, creating an acidic, nutrient-depleted microenvironment that impairs T-cell function.
The host-microbiota-EV axis remains largely unexplored despite clinical correlations between gut dysbiosis and immunotherapy failure. Gut microbiota-derived EVs modulate systemic immunity by regulating PD-L1 expression on dendritic cells, yet their impact on immune checkpoint blockade resistance requires further investigation.
Conclusion
Extracellular vesicles represent both a significant challenge and an unprecedented opportunity in cancer immunotherapy. While these vesicles facilitate immune evasion and therapy resistance through sophisticated cargo delivery systems, their engineering potential offers innovative strategies to enhance treatment efficacy. Success in clinical translation will depend on addressing production scalability, standardizing purification methods, and developing stable storage solutions. The dual nature of EVs as both resistance mediators and therapeutic tools positions them at the forefront of next-generation cancer treatment strategies, with the potential to transform how we approach immunotherapy in clinical practice.
