This study was designed to explore the immune reconstitution efficacy of human thymic slices transplanted into renal capsule,subcutaneous or muscle of nude mice,and further explore the optimal location of heterotopic transplantation.The thymus tissue discarded from congenital heart disease patients was made into 0.5-1 mm thick tissue sections and cultured in vitro to remove immune cells.H&E staining and immunohistochemical staining were used to assess the residual tissue structure and cell types in thymic slices,while quantitative PCR methods were used to assess the function of residual cells in thymic slices.Then thymic slices were transplanted into the renal capsule,subcutaneous or muscle of nude mice,and the immune reconstitution efficacy was compared by flow cytometry and histology.Data showed that after 14 days of culture in vitro,the clearance rate of T lymphocytes in the thymic slices was more than 90%,and the epithelial cell network structure of the tissue was intact,while a large number of macrophages,dendritic cells and endothelial cells remained.Quantitative PCR results showed that the gene expression levels of epithelial cell markers and secreted cytokines in cultured thymic slices could be effectively maintained.Flow cytometry showed that at 16 weeks after transplantation,the proportion of T cells in peripheral blood of mice in different transplantation groups were significantly increased,whereas the proportion of T cells in muscle group was the highest.In situ histological examination showed that the regeneration of thymus tissue was detected at all three transplant sites.In addition,the graft detection rate was 40%in the renal capsule group,60%in the subcutaneous group and 100%in the musclegroup.In conclusion,the human thymic slices cultured in vitro for 14 days retain a complete thymic matrix microenvironment.Transplantation of human thymic slices can effectively reconstruct the ratio of T cells in nude mice,and the muscle is the most effective transplantation site.