Background: To study the effect of allogeneic umbilical cord mesenchymal stem cell transplantation on the structure and function of the thymus in aged C57 mice and provide a new method for the treatment of senile thymic atrophy.

Results: The changes in the thymus cortex and medulla volume and the lymphocyte ratio were analyzed by immunofluorescence. For thymus tissue sections, immunohistochemical staining was performed to detect p16, p53, SOD, becline1, LC3b, p62, sirt1, and sirt3. Changes in CK5, CK8, CD4 and CD8 expression were observed. Treatment with mUCMSCs could promote hair regeneration in aging mice and regenerate the thymus structure.

Conclusions: mUCMSCs inhibited senescence of the thymus and promoted structural and functional thymus regeneration by downregulating the senescence genes p53 and p16 and upregulating the SOD, Sirt1 and Sirt3 genes, but the mechanism requires further research.

Methods: C57 mice were obtained and met the requirements of thymic aging. mUCMSCs were infused via the tail vein at a dose of 1×107 cells/kg twice per week for 3 weeks. Six weeks after the last transplantation, the thymus was weighed, and the thymus-to-body weight ratio was calculated. The thymus tissue was stained with HE.