Exosomes are nano-sized vesicles that serve as mediators for cell-to-cell communication. With their unique nucleic acids, proteins, and lipids cargo compositions that reflect the characteristics of producer cells, exosomes can be utilized as cell-free therapeutics. Among exosomes derived from various cellular origins, mesenchymal stem cell-derived exosomes (MSC-exosomes) have gained great attention due to their immunomodulatory and regenerative functions. Indeed, many studies have shown anti-inflammatory, anti-aging and wound healing effects of MSC-exosomes in various in vitro and in vivo models. In addition, recent advances in the field of exosome biology have enabled development of specific guidelines and quality control methods, which will ultimately lead to clinical application of exosomes. This review highlights recent studies that investigate therapeutic potential of MSC-exosomes and relevant mode of actions for skin diseases, as well as quality control measures required for development of exosome-derived therapeutics.

Exosomes are nano-sized vesicles (30–200 nm) constantly released by almost all cells. The ability of exosomes to travel between cells and deliver their cargo, which includes lipids, proteins, and nucleic acids, makes them an appealing cell-free therapy option to treat multiple diseases. Here, we investigated for the first time whether human adipose tissue-derived mesenchymal stem cell-derived exosomes (ASC-exosomes) can ameliorate atopic dermatitis (AD) in an in vivo mouse model. When injected either intravenously (IV) or subcutaneously (SC) into NC/Nga mice treated with house dust mite antigens, ASC-exosomes were found to reduce pathological symptoms such as clinical score, the levels of serum IgE, the number of eosinophils in blood, and the infiltration of mast cells, CD86+, and CD206+ cells in skin lesions. ASC-exosomes also significantly reduced mRNA expression of various inflammatory cytokines such as interleukin (IL)-4, IL-23, IL-31, and tumor necrosis factor-α (TNF-α) in AD skin lesions of Nc/Nga mice. Taken together, these results suggest that ASC-exosomes can be a novel promising cell-free therapeutic modality for AD treatment.

Atopic dermatitis (AD) is a multifactorial, heterogeneous disease associated with epidermal barrier disruption and intense systemic inflammation. Previously, we showed that exosomes derived from human adipose tissue-derived mesenchymal stem cells (ASC-exosomes) attenuate AD-like symptoms by reducing multiple inflammatory cytokine levels. Here, we investigated ASC-exosomes’ effects on skin barrier restoration by analyzing protein and lipid contents. We found that subcutaneous injection of ASC-exosomes in an oxazolone-induced dermatitis model remarkably reduced trans-epidermal water loss, while enhancing stratum corneum (SC) hydration and markedly decreasing the levels of inflammatory cytokines such as IL-4, IL-5, IL-13, TNF-α, IFN-γ, IL-17, and TSLP, all in a dose-dependent manner. Interestingly, ASC-exosomes induced the production of ceramides and dihydroceramides. Electron microscopic analysis revealed enhanced epidermal lamellar bodies and formation of lamellar layer at the interface of the SC and stratum granulosum with ASC-exosomes treatment. Deep RNA sequencing analysis of skin lesions demonstrated that ASC-exosomes restores the expression of genes involved in skin barrier, lipid metabolism, cell cycle, and inflammatory response in the diseased area. Collectively, our results suggest that ASC-exosomes effectively restore epidermal barrier functions in AD by facilitating the de novo synthesis of ceramides, resulting in a promising cell-free therapeutic option for treating AD.

Exosomes are nano-sized membranous vesicles produced by nearly all types of cells. Since exosome-like vesicles are produced in an evolutionarily conserved manner for information and function transfer from the originating cells to recipient cells, an increasing number of studies have focused on their application as therapeutic agents, drug delivery vehicles, and diagnostic targets. Analysis of the in vivo distribution of exosomes is a prerequisite for the development of exosome-based therapeutics and drug delivery vehicles with accurate prediction of therapeutic dose and potential side effects. Various attempts to evaluate the biodistribution of exosomes obtained from different sources have been reported. In this review, we examined the current trends and the advantages and disadvantages of the methods used to determine the biodistribution of exosomes by molecular imaging. We also reviewed 29 publications to compare the methods employed to isolate, analyze, and label exosomes as well as to determine the biodistribution of labeled exosomes.

Acute kidney injury (AKI) is a fatal medical episode caused by sudden kidney damage or failure, leading to the death of patients within a few hours or days. Previous studies demonstrated that exosomes derived from various mesenchymal stem/stromal cells (MSC-exosomes) have positive effects on renal injuries in multiple experimental animal models of kidney diseases including AKI. However, the mass production of exosomes is a challenge not only in preclinical studies with large animals but also for successful clinical applications. In this respect, tangential flow filtration (TFF) is suitable for good manufacturing practice (GMP)-compliant large-scale production of high-quality exosomes. Until now, no studies have been reported on the use of TFF, but rather ultracentrifugation has been almost exclusively used, to isolate exosomes for AKI therapeutic application in preclinical studies. Here, we demonstrated the reproducible large-scale production of exosomes derived from adipose tissue-derived MSC (ASC-exosomes) using TFF and the lifesaving effect of the ASC-exosomes in a lethal model of cisplatin-induced rat AKI. Our results suggest the possibility of large-scale stable production of ASC-exosomes without loss of function and their successful application in life-threatening diseases.

Epidermal permeability barrier defects are associated with several skin diseases, including atopic dermatitis (AD). Using an AD mouse model, we previously demonstrated that topically administered small extracellular vesicles (sEVs) (prepared following the International Society of Extracellular Vesicles recommendations) from human adipose tissue‐derived mesenchymal stem cells (ASC) ameliorate skin inflammation and normalize barrier function in parallel with increased ceramide (a key barrier lipid) production. To elucidate how ASC‐sEVs alleviate these AD skin abnormalities, we characterized lipids and ceramide metabolic enzymes in ASC‐sEVs versus donor ASCs. Our study revealed that free fatty acid, ceramide, and sphingomyelin are enriched in ASC‐sEVs versus donor ASCs, while the synthetic enzymes of ceramide (and acidic sphingomyelinase), and sphingosine‐1‐phosphate (sphingosine kinase) are significantly higher in ASC‐sEVs versus donor ASCs. Conversely, ceramide (ceramidase), and sphingosine‐1‐phosphate hydrolytic enzymes (sphingosine‐1‐phosphate lyase and sphingosine‐1‐phosphate phosphatase) are lower in ASC‐sEVs, suggesting that ceramide and sphingosine‐1‐phosphate levels could elevate in cells that receive ASC‐sEVs. ASC‐sEV‐mediated increases in sphingosine‐1‐phosphate suppress pro‐inflammatory cytokine production in AD‐model human keratinocytes. Additionally, keratinocyte differentiation, which is required for a competent epidermal permeability barrier, was restored in AD‐model human keratinocytes treated with ASC‐sEVs. Taken together, cells that endocytose ASC‐sEVs can normalize epidermal permeability barrier function as well as alleviate inflammation by stimulating a sphingosine‐1‐phosphate signalling pathway.