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Mesenchymal stem cells have made remarkable progress in recent years. Many studies have reported that human umbilical cord mesenchymal stem cells (hUC-MSCs) have no toxicity, but thromboembolism appeared in patients treated with hUC-MSCs. Therefore, people are still worried about the safety of clinical application. The study aims to determine the safety, potential toxic mechanism and biodistribution of hUC-MSCs. F344RG rats were given 5 or 50 million cells/kg of hUC-MSCs by single administration in compliance with Good Laboratory Practice standards. Standard toxicity was performed. RNA sequencing was then performed to explore the potential toxic mechanisms. In parallel, the biodistribution of hUC-MSCs was examined. The dose of 5 million cells/kg hUC-MSCs had no obvious toxicity on symptom, weight, food intake, hematology, serum biochemistry, urine biochemistry, cytokines, and histopathology. However, blood-tinged secretions in the urethral orifice and 20% mortality occurred at 50 million cells/kg. Disseminated intravascular coagulopathy (DIC) is the leading cause of death. hUC-MSCs significantly upregulated complement and coagulation cascade pathways gene expression, resulting in DIC. Besides, hUC-MSCs upregulated fibrinolytic system suppressor genes A2m, Serping1 and Serpinf2. hUC-MSCs survived in rats for less than 28 days, no hUC-MSC was detected in tissues outside the lungs. There was no toxicity in F344RG rats at 5 million cells/kg, but some toxicities were detected at 50 million cells/kg. hUC-MSCs significantly upregulated complement and coagulation cascade pathways, upregulated the expression of fibrinolytic system suppressor genes A2m, Serping1 and Serpinf2, to inhibit fibrinolytic system, caused DIC, which provided a new insight into the toxic mechanism of hUC-MSCs. [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) have demonstrated promising advantages in the therapies of many diseases, while its multi-directional differentiation potential and immunotoxicity are the major concerns hindered their clinical translation. In this study, human umbilical Mesenchymal stem cell (hUC-MSCs) were labeled with a near-infrared fluorescent dye DiR before infused into cynomolgus monkeys, and the amount of hUC-MSCs in the peripheral blood were dynamically estimated from 5 min to 28 days post a single administration at 3 × 106 cells/kg and 2 × 107 cells/kg intravenously. As results, some hUC-MSCs distributed to the whole body within 5 min, while most of the cells accumulate in the lungs along with the systemic blood circulation, and subsequently released into the blood. The toxicity potentials of hUC-MSCs were investigated in another 30 cynomolgus monkeys, and the cells were repeatedly administrated at doses of 3 × 106 cells/kg and 2 × 107 cells/kg for 5 times on a weekly basis, with a recovery period of 1 months. hUC-MSCs showed no obvious toxic effects in cynomolgus monkeys, except xenogeneic immune rejection to human stem cells. Low levels of the hUC-MSC gene were detected in the peripheral blood of a few animals administered 2 × 107 cells/kg at 30 min subsequent to the first and last administration, and there was no significant difference in the copy number of the hUC-MSC gene in the blood samples compared with the first and last administration, indicating that the hUC-MSC was not significantly amplified in vivo, and it its safe in non-human primates. Our study for the first time verified the safety of long-term use of hUC-MSCs in primates. We have pioneered a technology for the real-time detection of hUC-MSCs in peripheral blood and provide dynamicand rapid monitoring of the distribution characteristics of hUC-MSCs in vivo. Here, we provide data supporting the application of such products for clinical treatment and the application of stem cells in major refractory diseases and regenerative medicine. [ABSTRACT FROM AUTHOR]