For therapeutic kidney regeneration, individual resident renal cells should be integrated into an organized renal structure, since the kidney is anatomically complicated and resident cells communicate with each other to fulfill their functions. We have used a procedure based on the developmental process to regenerate an organized kidney tissue from human mesenchymal stem cells (hMSCs). Adult bone marrow hMSCs maintain plasticity and differentiate into several different cell types depending on their microenvironment. hMSCs were transduced with a retroviral expression vector carrying the gene for β-galactosidase and with an adenoviral expression vector carrying the gene for glial cell line-derived neurotrophic factor, and injected into a rat embryo immediately before ureteric bud sprouting [embryonic (E) day 11.5]. The whole embryo was cultured for 48 hours, and the kidneys were dissected out and placed into organ culture for 6 days. Abstract5-bromo-4chloro-3-indolyl-β-D-galactopyranoside (X-gal) assay and in situ hybridization for the human-specific alu sequence showed that the donor cells had integrated into the renal structure; they displayed morphologic characteristics of glomerular podocytes, tubular epithelial cells, and interstitial cells. Histologic analysis of serial sections showed that the glomerular epithelial cells were linked to tubular epithelial cells, and some of these extended toward the medulla. Reverse transcription-polymerase chain reaction (RT-PCR) analysis also revealed that lacZ-positive cells sorted from digested metanephros expressed genes specific for podocytes (nephrin, podocin, and GLEPP1) and for tubular epithelial cells [aquaporin-1, parathyroid hormone receptor1, and Na+-HCO3- cotransporter-1 (NBC-1)]. Furthermore, when hMSCs were injected into cultured metanephroi (E13), cell dispersal was not observed and the hMSCs remained aggregated. After 6 days of organ culture, the hMSCs had not contributed to kidney structures and did not express kidney-specific genes. These data suggest that during whole embryo culture hMSCs are involved in an initial step essential for commitment to a renal fate and further undergo a mesenchyme-to-epithelium transition or stromogenic differentiation during organ culture. To examine whether the hMSC-positive nephrons are viable, the procedure was carried out in the Fabry mouse, which does not express the gene encoding α-galactosidase A. α-galactosidase A activity was detected in the regenerated kidney and the accumulation of globotriaosylceramide (Gb3) was significantly suppressed. These findings, which show that mesenchymal cells can differentiate into each type of resident cell and organize into a renal structure, suggest a potential for therapeutic renal regeneration.