In a groundbreaking development that could revolutionize cancer therapy, researchers have unveiled a novel approach to combat lung metastasis and tumor recurrence by utilizing CAR macrophages generated in situ from mRNA delivered via small extracellular vesicles (sEVs). This innovative strategy taps into the immune system’s innate versatility, harnessing engineered macrophages to target and dismantle metastatic cancer cells with unprecedented precision and efficiency. The study, led by Xiao et al. and published in Nature Communications, offers a compelling glimpse into the future of cell-based immunotherapies, where therapeutic cells are created directly inside the patient’s body rather than administered externally.
Conventional approaches to treating lung metastasis face substantial hurdles, primarily due to the complexity of metastatic niches and the immune suppressive environments tumors often establish. Chimeric Antigen Receptor (CAR) T-cell therapies have shown promise against certain blood cancers but struggle against solid tumors, including lung metastases. Macrophages, as tissue-resident immune cells known for their plasticity and phagocytic capabilities, present a promising alternative platform for CAR engineering. Unlike T cells, macrophages can infiltrate tumor masses and modulate the immune microenvironment, making them potent effectors against solid tumor lesions.
Central to this breakthrough is the delivery of CAR-encoding messenger RNA (mRNA) directly to macrophages within the lung tissue, circumventing the complexities and costs associated with ex vivo cell manipulation and expansion. The researchers developed a delivery system based on small extracellular vesicles (sEVs), nanoscale lipid bilayer-enclosed particles naturally secreted by cells, which are well-known for their biocompatibility, stability, and inherent ability to cross biological barriers to facilitate intercellular communication. By loading sEVs with mRNA encoding the CAR construct, the team was able to efficiently transfect lung macrophages in situ, thereby generating CAR macrophages where they are needed most.
This approach addresses several critical limitations faced by current CAR therapies. First, it eliminates the need for personalized cell collection and manufacturing—a time-consuming and expensive process. Second, it enables repeated dosing, allowing the modulation of therapeutic intensity over time. Third, in situ generation minimizes systemic toxicities by concentrating the engineered immune effectors within the tumor-bearing organ, reducing off-target effects.
From a mechanistic perspective, the study meticulously characterized how sEV-delivered mRNA is taken up by tissue macrophages and translated into functional CAR proteins. Advanced imaging techniques confirmed that these CAR macrophages actively engaged and phagocytosed lung metastatic tumor cells expressing the target antigen. Furthermore, transcriptomic and proteomic analyses revealed upregulation of pro-inflammatory and anti-tumoral pathways, suggesting that the CAR macrophages not only eliminate cancer cells directly but also reshape the immunosuppressive tumor microenvironment to favor endogenous immune responses.
Preclinical murine models of metastatic lung cancer served as a vital platform to test the therapeutic efficacy of the mRNA-sEV system. Mice treated with sEV-CAR-mRNA exhibited significantly reduced tumor burden and prolonged survival compared with control groups. Notably, the recurrence rate after primary tumor resection was also markedly decreased, highlighting the potential of this strategy to diminish minimal residual disease and prevent relapse—a persistent challenge in oncology.
An intriguing aspect of the research lies in the modularity and versatility of the system. By altering the sequence of the CAR mRNA, sEVs can be programmed to target a broad spectrum of tumor antigens, potentially allowing rapid adaptation to different cancer types or the emergence of tumor antigen escape variants. This adaptability holds immense promise for personalized medicine, offering a platform technology that can be tailored to individual patients’ tumor profiles without the delays of bespoke cell engineering.
The safety profile of this approach was addressed through comprehensive toxicological assessments. Unlike viral vector-based gene therapies, mRNA-based delivery via sEVs exhibits transient expression, reducing the risks of insertional mutagenesis or long-term off-target effects. Additionally, the natural origin and biocompatibility of sEVs likely minimize immune reactions against the delivery vehicle itself, an often overlooked but significant hurdle in gene therapy.
The implications of this advancement extend beyond lung metastasis to a wider landscape of metastatic and recurrent cancers. The lung is a common site for secondary tumor seeding from various primary cancers such as breast, colon, and melanoma. Therefore, an effective, minimally invasive immunotherapeutic tool that can generate potent anti-tumor macrophages directly at these metastatic sites could transform clinical outcomes for countless patients worldwide.
Technically, the production and purification of therapeutic sEVs loaded with CAR mRNA were optimized through state-of-the-art engineering, including electroporation for mRNA loading and size exclusion chromatography for high-purity vesicle isolation. The research team also explored modifications to the vesicle surface to enhance tissue targeting and uptake efficiency, leveraging ligands and antibodies that recognize markers enriched on lung-resident macrophages.
This study fundamentally challenges the current paradigm of cell-based immunotherapies being exclusively ex vivo constructs. In situ generation of engineered immune effectors redefines the therapeutic landscape, shifting focus toward biomimetic delivery systems that integrate seamlessly within the patient’s immune ecosystem. Furthermore, the reduction in manufacturing bottlenecks and logistic complications associated with cell therapies may democratize access to these potent treatments globally.
Future directions will undoubtedly explore clinical translation pathways, including scaling sEV production under good manufacturing practice (GMP) conditions and conducting detailed pharmacokinetic and pharmacodynamic studies in larger animal models. Human trials will be essential to validate safety and efficacy, but the preclinical data are already compelling.
Moreover, it remains an open question how tumor heterogeneity and the evolving immunosuppressive milieu in patients might influence the effectiveness of in situ CAR macrophage generation. The interplay between engineered macrophages and other immune cells, including T cells and dendritic cells, will be critical to understand for harnessing synergistic anti-tumor responses.
In conclusion, the innovative approach delineated by Xiao and colleagues represents a significant leap forward in immuno-oncology. By delivering CAR-encoding mRNA via small extracellular vesicles directly to lung-resident macrophages, they have pioneered a platform for in situ immune reprogramming with robust anti-cancer efficacy against metastatic lesions and tumor recurrence. This strategy holds transformative potential not only for lung metastases but also for the broader challenge of treating solid tumors across multiple organs. As research progresses, this elegant fusion of synthetic biology, immunology, and nanotechnology could pave the way for next-generation cancer therapies marked by precision, safety, and accessibility.
Subject of Research:
Article Title:
Article References:
Xiao, Y., Zhu, T., Chen, Z. et al. Lung metastasis and recurrence is mitigated by CAR macrophages, in-situ-generated from mRNA delivered by small extracellular vesicles. Nat Commun 16, 7166 (2025). https://doi.org/10.1038/s41467-025-62506-2
Image Credits: AI Generated
