The functional mechanisms of mesenchymal stem cells (MSCs) have become a research focus in recent years. Accumulating evidence supports the notion that MSCs act in a paracrine manner. Therefore, the biological factors in conditioned medium, including exosomes and soluble factors, derived from MSC cultures are being explored extensively. The results from most investigations show that MSC-conditioned medium or its components mediate some biological functions of MSCs. Several studies have reported that MSC-derived exosomes have functions similar to those of MSCs, such as repairing tissue damage, suppressing inflammatory responses, and modulating the immune system. However, the mechanisms are still not fully understood and the results remain controversial. Compared with cells, exosomes are more stable and reservable, have no risk of aneuploidy, a lower possibility of immune rejection following in vivo allogeneic administration, and may provide an alternative therapy for various diseases. In this review, we summarize the properties and biological functions of MSC-derived exosomes and discuss the related mechanisms.

We previously demonstrated that mesenchymal stem cells (MSCs) ameliorated experimental autoimmune uveoretinitis (EAU) in rats. Recently, MSC-derived exosomes (MSC-Exo) were thought to carry functions of MSCs. In this study, we tested the effect of local administration of human MSC-Exo on established EAU in the same species. Rats with EAU induced by immunization with interphotoreceptor retinol-binding protein 1177–1191 peptide were treated by periocular injections of increasing doses of MSC-Exo starting at the disease onset for 7 consecutive days. The in vitro effects of MSC-Exo on immune cell migration and responder T cell proliferation were examined by chemotactic assays and lymphocyte proliferation assays, respectively. We found that MSC-Exo greatly reduced the intensity of ongoing EAU as their parent cells by reducing the infiltration of T cell subsets, and other inflammatory cells, in the eyes. Furthermore, the chemoattractive effects of CCL2 and CCL21 on inflammatory cells were inhibited by MSC-Exo. However, no inhibitory effect of MSC-Exo on IRBP-specific T cell proliferation was observed. These results suggest that MSC-Exo effectively ameliorate EAU by inhibiting the migration of inflammatory cells, indicating a potential novel therapy of MSC-Exo for uveitis.

Although accumulated evidence supports the notion that mesenchymal stem cells (MSCs) act in a paracrine manner, the mechanisms are still not fully understood. Recently, MSC-derived exosomes (MSC-Exos), a type of microvesicle released from MSCs, were thought to carry functional proteins and RNAs to recipient cells and play therapeutic roles. In the present study, we intravitreally injected MSCs derived from either mouse adipose tissue or human umbilical cord and their exosomes to observe and compare their functions in a mouse model of laser-induced retinal injury. We found that both MSCs and their exosomes reduced damage, inhibited apoptosis and suppressed inflammatory responses to obtain better visual function to nearly the same extent in vivo. Obvious down-regulation of monocyte chemotactic protein (MCP)-1 in the retina was found after MSC-Exos injection. In vitro, MSC-Exos also down-regulated MCP-1 mRNA expression in primarily cultured retinal cells after thermal injury. It was further demonstrated that intravitreal injection of an MCP-1-neutralizing antibody promoted the recovery of retinal laser injury, whereas the therapeutic effect of exosomes was abolished when MSC-Exos and MCP-1 were administrated simultaneously. Collectively, these results suggest that MSC-Exos ameliorate laser-induced retinal injury partially through down-regulation of MCP-1.

Importance To our knowledge, a set of well-defined diagnostic criteria is not yet developed for the diagnosis of Vogt-Koyanagi-Harada (VKH) disease. Objective To develop and evaluate a set of diagnostic criteria for VKH disease using data from Chinese patients. Design, Setting, and Participants This case-control study reviewed medical records of patients from a tertiary referral center between October 2011 and October 2016. Data from 634 patients with VKH disease and 623 patients with non-VKH uveitis from southern China were used to develop the Diagnostic Criteria for VKH Disease (DCV). Data from an additional group of 537 patients with a definite VKH disease diagnosis and 525 patients with non-VKH uveitis from northern China were used to evaluate the diagnostic criteria. Main Outcomes and Measures Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver operating characteristic. Results Of the 1257 patients used to construct the DCV, 665 (52.9%) were male, and the mean (SD) age at disease onset was 38.6 (13.6) years. The 3-class model and 21 clinical findings were selected by latent class analysis. Variables with a high positive rate in the early-phase or late-phase VKH group or high specificity constituted essential parameters. Constellations of these essential parameters constructed the DCV. The sensitivity and NPV of the DCV were higher than those of the Revised Diagnostic Criteria for VKH Disease (RDC) (sensitivity: 94.6% vs 71.9%; difference, 22.7%; 95% CI, 18.5-27.0; NPV: 94.3% vs 76.6%; difference, 17.7%; 95% CI, 13.9-21.5). The specificity and PPV of the DCV were not different from that of the RDC (specificity: 92.2% vs 93.9%; difference, 1.7%; 95% CI, −1.4 to 4.8; PPV: 89.3% vs 92.3%; difference, 3.0%; 95% CI, −1.4 to 4.8). The area under the receiver operating characteristic curve of the DCV and the RDC were 0.934 (95% CI, 0.917-0.951) and 0.829 (95% CI, 0.803-0.855), respectively. Conclusions and Relevance The DCV were developed and evaluated using data from Chinese patients with VKH disease and showed a high sensitivity, NPV, and area under the receiver operating characteristic curve in comparison with the RDC. However, they were developed using a retrospective analysis and should be evaluated in prospective studies in other racial/ethnic populations.

Mesenchymal stem cells (MSCs) possess potent immunomodulatory activity and have been extensively investigated for their therapeutic potential in treating inflammatory disorders. However, the mechanisms underlying the immunosuppressive function of MSCs are not fully understood, hindering the development of standardized MSC-based therapies for clinical use. In this study, we profile the single-cell transcriptomes of MSCs isolated from adipose tissue (AD), bone marrow (BM), placental chorionic membrane (PM), and umbilical cord (UC). Our results demonstrate that MSCs undergo a progressive aging process and that the cellular senescence state influences their immunosuppressive activity by downregulating PD-L1 expression. Through integrated analysis of single-cell transcriptomic and proteomic data, we identify GATA2 as a regulator of MSC senescence and PD-L1 expression. Overall, our findings highlight the roles of cell aging and PD-L1 expression in modulating the immunosuppressive efficacy of MSCs and implicating perinatal MSC therapy for clinical applications in inflammatory disorders.