Toxicity from a single injection of human umbilical cord mesenchymal stem cells into rat ovaries.

Intraovarian injection of human umbilical cord mesenchymal stem cells (hUC-MSCs) has been applied and with promising therapeutic effects, but its toxicity and safety remain uncertain. This study evaluated the toxic effects and the affected target organs after a single injection of hUC-MSCs into bilateral rat ovaries. Sixty Sprague-Dawley rats were randomly divided into four groups and intraovarian injected with three different doses of hUC-MSC suspension. Toxicity-related manifestations occurred over the following 14 days postinjection. On day (D)5 and D15, we assessed the clinical pathology; immunotoxicity, including the cytokine IFN-γ, TNF-α, IL-4, and IL-6 levels; the immune organs, and the organ weights. On D5, inflammatory cells mainly infiltrated the ovaries of the low- and medium-dose groups, whereas inflammatory cells infiltrated the oviduct in the medium- and high-dose groups. On D15, inflammatory cells infiltrated the corpus luteal cysts, ovarian sacs and oviducts in each group. Body weights; organ weights; immunotoxicity; clinical pathology and histopathological examinations of the immune organs did not significantly differ among the groups. No obvious hUC-MSC-related clinical symptoms were observed except in the rats that died. The high-dose group exhibited significantly higher mortality than did the control and low-dose groups. Deaths in the high-dose group, who received approximately 50 times the standard clinical dose, were related to the intraovarian hUC-MSC injection. The maximum tolerated dose was approximately ten times the standard clinical dose. The ovary and oviduct may be the target organs for this toxicity. This report provides dosage references and guidance for clinical applications of intraovarian hUC-MSC injections.