Pulmonary fibrosis is a chronic and progressive lung disease marked by abnormal scarring of the tissue surrounding the air sacs. This process thickens and stiffens the lungs, leading to shortness of breath, fatigue, and reduced oxygen exchange.
Current medications, such as pirfenidone and nintedanib, can slow disease progression but do not reverse tissue damage. As a result, researchers are pursuing regenerative strategies that can modulate inflammation, suppress fibrosis, and promote repair.
One of the most promising emerging therapies involves extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs). These nanosized, membrane-bound particles carry bioactive molecules—such as proteins, microRNAs (miRNAs), and metabolites—that influence immune responses and tissue repair. Importantly, MSC-EVs appear to replicate many benefits of stem cell therapy while avoiding the challenges of administering live cells, such as immune rejection or variable differentiation in vivo.
As part of this study, Li et al. examined the safety and efficacy of mesenchymal stromal cell–derived extracellular vesicles (MSC-EVs) from human umbilical cord (hUCMSC-EVs) in preclinical mouse models and in patients with pulmonary fibrosis.
Targeted Delivery Through Nebulization
Li’s research team developed a method for delivering hUCMSC-EVs via nebulization, producing a fine aerosol that can be inhaled directly into the lungs. This delivery route targets the site of disease, enhances local concentration, and minimizes systemic exposure.
In mouse models, fluorescently labeled hUCMSC-EVs rapidly accumulated in the lungs within hours of inhalation and persisted for several days, confirming targeted distribution. This lung-specific retention supports nebulization as a practical and efficient method for respiratory delivery.
Manufacturing and Quality Assurance
To ensure safety and consistency, the hUCMSC-EVs were produced under Good Manufacturing Practice (GMP) conditions using a standardized cell bank. Multiple critical quality control points were implemented throughout production, verifying vesicle size (50–400 nm), morphology, surface markers (CD9, CD63, CD81), and sterility.
Tests confirmed the absence of bacterial, viral, and mycoplasma contamination and validated biological activity through immune-modulating assays. Analysis of the vesicles’ RNA, protein, and metabolite content demonstrated high batch-to-batch reproducibility, underscoring their stability and reliability as a biologic product.
Molecular Composition and Mechanisms of Action
Comprehensive profiling revealed that microRNAs made up nearly 60% of the total RNA cargo within the hUCMSC-EVs, with over 1,400 unique miRNAs identified. Many are involved in regulating inflammation, cell differentiation, angiogenesis, and extracellular matrix remodeling—key pathways disrupted in fibrosis.
Proteomic analysis identified more than 1,000 proteins enriched in processes such as wound healing, cytoskeletal organization, and cell adhesion, while metabolomic profiling revealed over 100 metabolites related to amino acid and energy metabolism. According to the authors, these findings suggest that hUCMSC-EVs deliver a coordinated set of molecular signals that can reduce inflammation, inhibit fibroblast activation, and support tissue regeneration.
Preclinical Results in Pulmonary Fibrosis Models
Using the bleomycin-induced pulmonary fibrosis mouse model, the researchers assessed both safety and efficacy. Mice received various doses of nebulized hUCMSC-EVs, followed by imaging, physiological measurements, and histological evaluation.
The treatment significantly improved survival, restored lung volume, and reduced fibrotic lesions compared to control groups. Micro-CT scans showed reduced tissue density and less bronchial distortion, while histology confirmed preservation of alveolar architecture and decreased collagen accumulation.
Even when therapy began after fibrosis was established, hUCMSC-EVs slowed or partially reversed disease progression. Interestingly, moderate doses produced the most favorable outcomes, suggesting that efficacy may depend on optimizing dosage rather than simply increasing the quantity delivered.
Immune Modulation and Antifibrotic Mechanisms
Further analysis revealed that nebulized hUCMSC-EVs increased expression of miR-486-5p, a microRNA known to suppress inflammatory signaling and regulate macrophage behavior. Macrophages are central to the progression of pulmonary fibrosis: when activated into a pro-inflammatory (M1) state, they promote injury, while their alternative (M2) phenotype supports repair.
After EV treatment, Li et al. found that macrophages in the lung shifted toward an M2-dominant profile. This was accompanied by increased expression of antifibrotic and regenerative genes (IL-10, MMP13, HGF) and reduced levels of SPP1, a fibrosis-associated gene. These results indicate that hUCMSC-EVs exert their effects largely by reprogramming the immune environment, mitigating inflammation, and promoting resolution of tissue injury.
Phase I Clinical Trial: Safety and Feasibility
Following preclinical success, a randomized, single-blind, placebo-controlled Phase I clinical trial was conducted in 24 adults with pulmonary fibrosis confirmed by high-resolution CT imaging. Participants continued standard therapy; half received nebulized hUCMSC-EVs twice daily for seven days, and half received saline.
Safety was the primary endpoint. Throughout treatment and one year of follow-up, no serious adverse events, allergic reactions, or clinically significant laboratory abnormalities were observed. Blood counts, liver and kidney function, and inflammatory markers remained stable, confirming a strong safety profile for inhaled hUCMSC-EVs.
Early Clinical Indicators of Efficacy
Although designed primarily to assess safety, the study also collected exploratory measures of lung function and patient-reported outcomes.
Patients who received nebulized hUCMSC-EVs demonstrated notable improvements in forced vital capacity (FVC) and maximal voluntary ventilation (MVV) compared to the control group. Questionnaire scores also improved: St. George’s Respiratory Questionnaire results decreased, indicating reduced symptom burden, while Leicester Cough Questionnaire scores increased, reflecting improved quality of life.
Radiographic evaluation revealed stable disease in most participants, consistent with the short treatment duration, but two patients with post-inflammatory pulmonary fibrosis showed partial regression of fibrotic lesions on CT imaging. According to the authors, these cases highlight the potential for genuine structural recovery with this therapy.
Advantages of Nebulized Delivery
Nebulized administration offers several advantages for chronic lung diseases. Delivering therapy directly to the lungs ensures higher local concentrations and reduces systemic exposure, minimizing potential side effects. It also allows for noninvasive, repeatable dosing, which is more patient-friendly than intravenous infusion.
The preclinical biodistribution data align with these advantages, showing sustained lung localization with gradual clearance—an ideal profile for localized therapy in fibrotic lung disease.
Comparison with Other EV-Based Therapies
The study adds to a growing body of evidence supporting nebulized EVs as a safe and feasible approach for pulmonary diseases. Previous preclinical studies have shown benefits of EVs derived from adipose MSCs or platelets in models of emphysema and acute lung injury. However, hUCMSC-EVs may be uniquely advantageous due to their scalable production, immune compatibility, and consistent molecular content.
Current Limitations and Research Needs
Despite encouraging findings, several limitations remain. The Phase I study involved a small cohort and short treatment period. Larger, longer-term trials are necessary to evaluate sustained clinical benefit, dose optimization, and durability of effect.
Because EVs are complex biologics, their content can vary based on donor source and culture conditions. Ongoing work in standardization and molecular characterization will be critical to ensure reproducibility at scale. Future studies should also identify biomarkers to predict which patient populations—such as those with post-inflammatory fibrosis—may respond best to this therapy.
Clinical Implications and Future Outlook
For clinicians and researchers, hUCMSC-EVs represent an innovative, cell-free approach to addressing the underlying inflammation and scarring of pulmonary fibrosis. The therapy combines the biological sophistication of stem cells with the precision and safety of a targeted inhalation route.
Early evidence suggests that nebulized hUCMSC-EVs are not only safe but may improve lung function and quality of life when added to standard therapy. If validated in larger studies, this strategy could complement existing medications, offering patients a regenerative option that directly addresses tissue repair rather than symptom control alone.
Conclusion
According to Li et al., nebulized hUCMSC-EVs demonstrate strong potential as a next-generation therapy for pulmonary fibrosis. Produced under GMP conditions and characterized with rigorous quality controls, these vesicles carry bioactive molecules capable of regulating immune activity, reducing fibrosis, and supporting lung repair.
Preclinical studies showed clear survival and structural benefits in animal models, while early human data confirmed safety and signaled meaningful clinical improvement.
Although further research is required to confirm long-term efficacy and optimize treatment protocols, this study marks a significant step forward in regenerative pulmonary medicine. Nebulized MSC-derived extracellular vesicles may ultimately provide a practical, effective, and safe tool to slow or even reverse the devastating effects of pulmonary fibrosis.
Source: Li M, Huang H, Wei X, Li H, Li J, Xie B, Yang Y, Fang X, Wang L, Zhang X, Wang H, Li M, Lin Y, Wang D, Wang Y, Zhao T, Sheng J, Hao X, Yan M, Xu L, Chang Z. Clinical investigation on nebulized human umbilical cord MSC-derived extracellular vesicles for pulmonary fibrosis treatment. Signal Transduct Target Ther. 2025 Jun 4;10(1):179. doi: 10.1038/s41392-025-02262-3. Erratum in: Signal Transduct Target Ther. 2025 Jul 17;10(1):235. doi: 10.1038/s41392-025-02293-w. PMID: 40461474; PMCID: PMC12134356.
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