Objective To analyze the composition and function of residual cells in pre-transplantation human thymic slices by single-cell transcriptomics sequencing(scRNA-seq),and established a quality assessment method for thymic slices based on the expression levels of molecular markers in the culture supernatant.Methods The discarded thymus from 18 patients with congenital heart disease undergoing surgical treatment in Department of Cardiothoracic Surgery of Children's Hospital Affiliated to Chongqing Medical University from May 2023 to January 2024 were collected and prepared into thymic slices.After the slices were cultured in vitro for 14 d,scRNA-seq was employed to identify the residual cell types,and gene ontology(GO)and Kyoto encyclopedia of genes and genomes(KEGG)enrichment analysis was performed to analyze the biological function of the residual cells.Then based on the literature concerning thymic slice culture,the molecular markers indicating thymocyte function were screened out.ELISA was applied to detect the changes in protein levels of molecular markers in the supernatant.Receiver operating characteristic(ROC)curve was plotted and assess the value of the molecular markers in the supernatant in evaluating the quality of thymic slices with area under the curve(AUC).Then,the qualified and unqualified thymic slices determined by our obtained molecular markers were transplanted subcutaneously into male nude mice(6～8 weeks old,weighing 14～17 g),respectively,and the male nude mice without transplantation of the thymic slices served as control group.Flow cytometry and histologic analysis were utilized to observe the immune reconstitution after transplantation.Results ① scRNA-seq identified 11 cell types in thymic slices,dominated with epithelial cells,fibroblasts,and T cells.GO and KEGG enrichment analysis showed that epithelial cells were involved in enrichment entries related to chemotaxis,epithelial cell development,cell matrix adhesion and tight junction;fibroblasts were involved in enrichment entries related to extracellular matrix,epithelial cell proliferation,negative regulation of cell migration,and regulation of actin cytoskeleton;T cells were mainly related to T cell differentiation,regulation of T cell activation,T cell apoptosis,and T cell receptor signaling.② Molecular markers,CCL19,CCL21,CXCL12,CXCL16,IL16 and SELL were identified to indicate thymocyte function.Compared with the levels of the first day,the protein secretions of CCL19,CCL21,CXCL12 and CXCL16 were significantly increased during in vitro culture(P<0.05),while the protein secretions of IL16 and L-selectin(protein form of SELL)were significantly decreased(P<0.05).The combined predictor Pre1 from subset of cytokines(IL16 and L-selectin)had the highest value in the quality assessment of thymic slices after 1 d of culture(AUC=0.883),and the combined predictor Pre2 from subset of cytokines(CCL19,CCL21,CXCL12 and CXCL16)had the highest value in the quality assessment after 14 d of culture(AUC=0.948).③ Transplantation in nude mice indicated that the qualified thymic slices could develop to thymus structure in vivo,and effectively increase the proportion of T cells in peripheral blood(P<0.01),while the unqualified thymic slices could not obtain the reconstitution of T cell development.Conclusion The main residual component cells in thymic slices are epithelial cells,fibroblasts and T cells.IL16 and L-selectin can be used as potential indicators to determine the quality of donor thymic samples.CCL19,CCL21,CXCL12 and CXCL16 can effectively evaluate the quality of thymic slices before transplantation.

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.