Xenobiotic kidney organogenesis from human mesenchymal stem cells using a growing rodent embryo

Evaluation of the ability of human induced nephron progenitor cells to form chimeric renal organoids using mouse embryonic renal progenitor cells

The number of patients with end-stage renal failure is increasing annually worldwide and the problem is compounded by a shortage of renal transplantation donors. In our previous research, we have shown that transplantation of renal progenitor cells into the nephrogenic region of heterologous fetuses can induce the development of nephrons. We have also developed transgenic mice in which specific renal progenitor cells can be removed by drugs. By combining these two technologies, we have succeeded in generating human-mouse chimeric kidneys in fetal mice. We hope to apply these technologies to regenerative medicine. The quality of nephron progenitor cells (NPCs) derived from human pluripotent stem cells is important for the generation of chimeric kidneys, but there is currently no simple evaluation system for the chimerogenic potential of human NPCs. In this study, we focused on the fact that the re-aggregation of mouse renal progenitor cells can be used for nephron formation, even when merged into single cells. First, we examined the conditions under which nephron formation is likely to occur in mice during re-aggregation. Next, to improve the differentiation potential of human NPCs derived from pluripotent stem cells, NPCs were sorted using Integrin subunit alpha 8 (ITGA8). Finally, we demonstrated chimera formation between different species by mixing mouse cells with purified, selectively-induced human NPCs under optimum conditions. We observed these chimeric organoids at different time points to learn about these human-mouse chimeric structures at various stages of renal development. We found that the rate of chimera formation was affected by the purity of the human NPCs and the cell ratios used. We demonstrated that chimeric nephrons can be generated using a simple model, even between distant species. We believe that this admixture of human and mouse renal progenitor cells is a promising technology with potential application for the evaluation of the chimera formation abilities of NPCs.

Mesenchymal stem cells therapy for acute kidney injury: A systematic review with meta-analysis based on rat model

Objective: To systematically evaluate the efficacy of mesenchymal stem cells (MSCs) for acute kidney injury (AKI) in preclinical studies and to explore the optimal transplantation strategy of MSCs by network meta-analysis with the aim of improving the efficacy of stem cell therapy. Methods: Computer searches of PubMed, Web of Science, Cochrane, Embase, CNKI, Wanfang, VIP, and CBM databases were conducted until 17 August 2022. Literature screening, data extraction and quality evaluation were performed independently by two researchers. Results and Discussion: A total of 50 randomized controlled animal studies were included. The results of traditional meta-analysis showed that MSCs could significantly improve the renal function and injured renal tissue of AKI rats in different subgroups. The results of network meta-analysis showed that although there was no significant difference in the therapeutic effect between different transplant routes and doses of MSCs, the results of surface under the cumulative ranking probability curve (SUCRA) showed that the therapeutic effect of intravenous transplantation of MSCs was better than that of arterial and intrarenal transplantation, and the therapeutic effect of high dose (>1×10⁶) was better than that of low dose (≤1×10⁶). However, the current preclinical studies have limitations in experimental design, measurement and reporting of results, and more high-quality studies, especially direct comparative evidence, are needed in the future to further confirm the best transplantation strategy of MSCs in AKI. Systematic Review Registration: identifier https://CRD42022361199, https://www.crd.york.ac.uk/prospero.

Tubular epithelial progenitors are excreted in urine during recovery from severe acute kidney injury and are able to expand and differentiate in vitro

Background

Acute kidney injury (AKI) is a serious condition associated with chronic kidney disease, dialysis requirement and a high risk of death. However, there are specialized repair mechanisms for the nephron, and migrated committed progenitor cells are the key players. Previous work has described a positive association between renal recovery and the excretion of tubular progenitor cells in the urine of kidney transplant recipients. The aim of this work was to describe such structures in non-transplanted AKI patients and to focus on their differentiation.

Methods

Morning urine was obtained from four patients with AKI stage 3 and need for RRT on a consecutive basis. Urine sediment gene expression was performed to assess which part of the tubular or glomerular segment was affected by injury, along with measurement of neprilysin. Urine output and sediment morphology were monitored, viable hyperplastic tubular epithelial clusters were isolated and characterized by antibody or cultured in vitro. These cells were monitored by phase contrast microscopy, gene, and protein expression over 9 days by qPCR and confocal immunofluorescence. Furthermore, UMOD secretion into the supernatant was quantitatively measured.

Results

Urinary neprilysin decreased rapidly with increasing urinary volume in ischemic, toxic, nephritic, and infection-associated AKI, whereas the decrease in sCr required at least 2 weeks. While urine output increased, dead cells were present in the sediment along with debris followed by hyperplastic agglomerates. Monitoring of urine sediment for tubular cell-specific gene transcript levels NPHS2 (podocyte), AQP1 and AQP6 (proximal tubule), and SLC12A1 (distal tubule) by qPCR revealed different components depending on the cause of AKI. Confocal immunofluorescence staining confirmed the presence of intact nephron-specific epithelial cells, some of which appeared in clusters expressing AQP1 and PAX8 and were 53% positive for the stem cell marker PROM1. Isolated tubule epithelial progenitor cells were grown in vitro, expanded, and reached confluence within 5-7 days, while the expression of AQP1 and UMOD increased, whereas PROM1 and Ki67 decreased. This was accompanied by a change in cell morphology from a disproportionately high nuclear/cytoplasmic ratio at day 2-7 with mitotic figures. In contrast, an apoptotic morphology of approximately 30% was found at day 9 with the appearance of multinucleated cells that were associable with different regions of the nephron tubule by marker proteins. At the same time, UMOD was detected in the culture supernatant.

Conclusion

During renal recovery, a high replicatory potential of tubular epithelial progenitor cells is found in urine. In vitro expansion and gene expression show differentiation into tubular cells with marker proteins specific for different nephron regions.

Generation of functional chimeric kidney containing exogenous progenitor-derived stroma and nephron via a conditional empty niche

Generation of new kidneys can be useful in various research fields, including organ transplantation. However, generating renal stroma, an important component tissue for structural support, endocrine function, and kidney development, remains difficult. Organ generation using an animal developmental niche can provide an appropriate in vivo environment for renal stroma differentiation. Here, we generate rat renal stroma with endocrine capacity by removing mouse stromal progenitor cells (SPCs) from the host developmental niche and transplanting rat SPCs. Furthermore, we develop a method to replace both nephron progenitor cells (NPCs) and SPCs, called the interspecies dual replacement of the progenitor (i-DROP) system, and successfully generate functional chimeric kidneys containing rat nephrons and stroma. This method can generate renal tissue from progenitors and reduce xenotransplant rejection. Moreover, it is a safe method, as donor cells do not stray into nontarget organs, thus accelerating research on stem cells, chimeras, and xenotransplantation.

Beneficial Impact of Interspecies Chimeric Renal Organoids Against a Xenogeneic Immune Response

Background

Animal fetal kidneys have the potential to be used as scaffolds for organ regeneration. We generated interspecies chimeric renal organoids by adding heterologous rat renal progenitor cells to single cells from mouse fetal kidneys and applying the renal development mechanism of mouse fetuses to rat renal progenitor cells to examine whether rat renal progenitor cells can differentiate into renal tissues of the three progenitor cell lineages of kidneys between different species. Furthermore, we investigated whether chimeric renal organoids with an increased proportion of recipient cells reduce xenogeneic rejection.

Methods

C57BL/6JJmsSlc mice (B6 mice) and Sprague-Dawley-Tg (CAG-EGFP) rat (GFP rats) fetuses were used as donors, and mature male NOD/Shi-scid, IL-2RγKO Jic mice (NOG mice) and Sprague-Dawley rats (SD rats) were used as recipients. First, fetal kidneys were removed from E13.5 B6 mice or E15.5 GFP rats and enzymatically dissociated into single cells. These cells were then mixed in equal proportions to produce chimeric renal organoids in vitro. The chimeric organoids were transplanted under the renal capsule of NOG mice, and maturation of the renal tissues in the organoids was observed histologically. Furthermore, chimeric organoids were prepared by changing the ratio of cells derived from mouse and rat fetal kidneys and transplanted under the renal capsule of SD rats subjected to mild immunosuppression to pathologically analyze the strength of the xenogeneic immune response.

Results

The cap mesenchyme was reconstructed in vitro, and nephron progenitor cells and ureteric buds were mosaically comprised GFP-negative mouse and GFP-positive rat cells. In the in vivo environment of immunodeficient mice, chimeric renal organoids mosaically differentiated and matured into renal tissues of three lineages. Chimeric renal organoids with high rates of recipient rat cells showed milder rejection than complete xenograft organoids. The vessels of recipient rats entered from the periphery of the transplanted chimeric renal organoids, which might reduce their immunogenicity.

Conclusion

Interspecies chimeric renal organoids may differentiate into mature renal tissues of each renal progenitor cell lineage. Furthermore, they may reduce transplant rejection compared with xenograft organoids.

Administration of retinoic acid to pregnant mice increases the number of fetal mouse glomeruli

The prevalence of chronic kidney disease (CKD) is increasing worldwide, and CKD is a serious global health problem. Low glomerular number is one of the risk factors for CKD; therefore, the glomerular number is associated with the risk of CKD. Increasing the glomerular number above normal levels may reduce the risk of CKD. It has been reported that, in vitro, the addition of retinoic acid (RA) to the culture medium increases the glomerular number. However, there is no report of an increase in glomerular number above normal levels with the addition of RA in vivo. In this study, RA (20 mg/kg) was administered intraperitoneally to pregnant mice once at embryonic day (E) 10.5, E12.5, E14.5, or E16.5. The fetuses were harvested at E18.5 and fetal mouse kidneys were evaluated. Fetal kidney volume and weight were significantly increased in the E16.5 group compared to the control group. The total glomerular number in the E16.5 group was also approximately 1.46 times higher than that in the control group. In summary, we established a method to increase the glomerular number in the fetal kidney by administration of RA to pregnant mice at E16.5. These results will facilitate the investigation of whether CKD risk is reduced when the glomerular number increases above normal.

Timing urinary tract reconstruction in rats to avoid hydronephrosis and fibrosis in the transplanted fetal metanephros as assessed using imaging

Chronic kidney disease leads to high morbidity rates among humans. Kidney transplantation is often necessary for severe symptoms; however, options for new curative treatments are desired because of donor shortage. For example, it has been established that the kidneys can efficiently generate urine after transplantation of the metanephros, ureter, and bladder as a group. After transplantation, the urine can indirectly flow into the recipient's bladder using a stepwise peristaltic ureter system method where the anastomosis is created via the recipient's ureter for urinary tract reconstruction. However, the growth of the regenerated metanephros varies significantly, whereas the time window for successful completion of the stepwise peristaltic ureter system that does not cause hydronephrosis of the metanephros with bladder (ureter) is quite narrow. Therefore, this study was conducted to periodically and noninvasively evaluate the growth of the transplanted metanephros, ureter, and bladder in rats through computed tomography and ultrasonography. The ultrasonographic findings highly correlated to the computed tomography findings and clearly showed the metanephros and bladder. We found that the degree of growth of the metanephros and the bladder after transplantation differed in each case. Most of the rats were ready for urinary tract reconstruction within 21 days after transplantation. Optimizing the urinary tract reconstruction using ultrasonography allowed for interventions to reduce long-term tubular dilation of the metanephros due to inhibited overdilation of the fetal bladder, thereby decreasing the fibrosis caused possibly by transforming growth factor-β1. These results may be significantly related to the long-term maturation of the fetal metanephros and can provide new insights into the physiology of transplant regeneration of the metanephros in higher animals. Thus, this study contributes to the evidence base for the possibility of kidney regeneration in human clinical trials.

Regenerated nephrons in kidney cortices ameliorate exacerbated serum creatinine levels in rats with adriamycin nephropathy

Kidney regeneration could be classified into 2 groups: kidney generation and kidney repair. We have attempted in vivo nephron generation for kidney repair, as a therapy for chronic renal failure (CRF), by exploiting cellular interactions via conditioned media. In the previous report, we demonstrated the generation of rich nephrons in rat intact kidney cortices through percapsular injection of mesenchymal stem cell (MSC)-differentiated tubular epithelial cells (TECs) after pretreatment of 3-dimensional culture using a small amount of gel complex and condensed medium. In this study, to verify the amelioration of serum creatinine (sCr) levels by regenerated nephrons in rats with CRF, we first created damaged kidneys through systemic administration of adriamycin, and implanted the pretreated MSC-differentiated TECs into unilateral kidney cortices 2 weeks after adriamycin administration (A-2W, that is I-0W). After recovery of acute kidney injury, the control rats without cell implantation showed re-exacerbation of sCr levels, resulting in death within A-12W. Alternatively, the cell-implanted rats had a formation of mature nephrons in I-3W, and showed significant amelioration of sCr levels in I-7W. As a result, these rats could live until euthanization in I-12W or I-16W, indicating the utility of cell injection therapy into a kidney (K-CIT) for CRF. We expect that our K-CIT or the refined methods will be applied to patients with CRF.

Microenvironment derived from metanephros transplantation inhibits the progression of acute kidney injury in glycerol-induced rat models

Background

Embryonic metanephros is the mammalian renal anlagen, which is considered as a potential source for the regeneration of functional whole kidneys. Some studies reported that metanephros implanted into unilateral nephrectomized animals can develop into kidney tissue. However, kidneys are nephrotoxic in renal failure patients, and whether metanephros can grow in nephrotoxic has not been reported. This study aims to investigate the growth of metanephros in acute nephrotoxic environment and analyze the therapeutic effect of metanephros microenvironment on acute kidney injury (AKI).

Methods

AKI was induced in 200 g Wistar rats by giving intramuscular injections of 50% glycerol (10 mL/kg) in their hind limbs. 45 rats were divided randomly into three groups (control, glycerin, and metanephros). Metanephros group was transplanted two metanephroi (embryonic day 15) into the renal capsule of AKI rats. Glycerin group was AKI rats without transplantation. Control group was untreated.

Results

Mature glomeruli and tubules were detected in the grafts in metanephros group, which means that metanephroi can grow into tissues with mature kidney structure under acute nephrotoxic. Then, we assessed the renal function of host rats and found that there were fewer tubular necrosis in metanephros group than glycerin group, and the serum creatinine and urea nitrogen were significantly lower in metanephros group than glycerin group.

Conclusion

These results suggested that embryonic metanephroi can grow into tissues with mature kidney structure under acute nephrotoxic, and the graft microenvironment was effective in inhibiting the progression of AKI, which provides a new approach for the treatment of acute renal injury.

Mesangial cell regeneration from exogenous stromal progenitor by utilizing embryonic kidney

Kidney regenerative medicine is expected to be the solution to the shortage of organs for transplantation. In a previous report, we transplanted exogenous renal progenitor cells (RPCs) including nephron progenitor cells (NPCs), stromal progenitor cells (SPCs), and the ureteric bud (UB) into the nephrogenic zone of animal embryos and succeeded in regenerating new nephrons from exogenous NPCs through a fetal developmental program. However, it was unknown whether the renal stromal lineage cells were regenerated from SPCs. The present study aimed to verify the differentiation of SPCs into mesangial cells and renal stromal lineage cells. Here, we found that simply transplanting RPCs, including SPCs, into the nephrogenic zone of wild-type fetal mice was insufficient for differentiation of SPCs. Therefore, to enrich the purity of SPCs, we sorted cells from RPCs by targeting platelet-derived growth factor receptor alpha (PDGFRa) which is a cell surface marker for immature stromal cells and transplanted the PDGFRa-positive sorted cells. As a result, we succeeded in regenerating a large number of mesangial cells and other renal stromal lineage cells including interstitial fibroblasts, vascular pericytes, and juxtaglomerular cells. We have established the method for regeneration of stromal cells from exogenous SPCs that may contribute to various fields, such as regenerative medicine and kidney embryology, and the creation of disease models for renal stromal disorders.

Kidney Regeneration in Later-Stage Mouse Embryos via Transplanted Renal Progenitor Cells

BACKGROUND

The limited availability of donor kidneys for transplantation has spurred interest in investigating alternative strategies, such as regenerating organs from stem cells transplanted into animal embryos. However, there is no known method for transplanting cells into later-stage embryos, which may be the most suitable host stages for organogenesis, particularly into regions useful for kidney regeneration.

METHODS

We demonstrated accurate transplantation of renal progenitor cells expressing green fluorescent protein to the fetal kidney development area by incising the opaque uterine muscle layer but not the transparent amniotic membrane. We allowed renal progenitor cell-transplanted fetuses to develop for 6 days postoperatively before removal for analysis. We also transplanted renal progenitor cells into conditional kidney-deficient mouse embryos. We determined growth and differentiation of transplanted cells in all cases.

RESULTS

Renal progenitor cell transplantation into the retroperitoneal cavity of fetuses at E13-E14 produced transplant-derived, vascularized glomeruli with filtration function and did not affect fetal growth or survival. Cells transplanted to the nephrogenic zone produced a chimera in the cap mesenchyme of donor and host nephron progenitor cells. Renal progenitor cells transplanted to conditional kidney-deficient fetuses induced the formation of a new nephron in the fetus that is connected to the host ureteric bud.

CONCLUSIONS

We developed a cell transplantation method for midstage to late-stage fetuses. In vivo kidney regeneration from renal progenitor cells using the renal developmental environment of the fetus shows promise. Our findings suggest that fetal transplantation methods may contribute to organ regeneration and developmental research.

In vivo regeneration of interspecies chimeric kidneys using a nephron progenitor cell replacement system

Kidney regeneration is expected to be a new alternative treatment to the currently limited treatments for chronic kidney disease. By transplanting exogeneous nephron progenitor cells (NPCs) into the metanephric mesenchyme of a xenogeneic foetus, we aimed to regenerate neo-kidneys that originate from transplanted NPCs. Previously, we generated a transgenic mouse model enabling drug-induced ablation of NPCs (the Six2-iDTR mouse). We demonstrated that eliminating existing native host NPCs allowed their 100% replacement with donor mouse or rat NPCs, which could generate neo-nephrons on a culture dish. To apply this method to humans in the future, we examined the possibility of the in vivo regeneration of nephrons between different species via NPC replacement. We injected NPCs-containing rat renal progenitor cells and diphtheria toxin below the renal capsule of E13.5 metanephroi (MNs) of Six2-iDTR mice; the injected MNs were then transplanted into recipient rats treated with immunosuppressants. Consequently, we successfully regenerated rat/mouse chimeric kidneys in recipient rats receiving the optimal immunosuppressive therapy. We revealed a functional connection between the neo-glomeruli and host vessels and proper neo-glomeruli filtration. In conclusion, we successfully regenerated interspecies kidneys in vivo that acquired a vascular system. This novel strategy may represent an effective method for human kidney regeneration.

Bioengineered functional humanized livers: An emerging supportive modality to bridge the gap of organ transplantation for management of end-stage liver diseases

End stage liver diseases (ESLD) represent a major, neglected global public health crisis which requires an urgent action towards finding a proper cure. Orthotropic liver transplantation has been the only definitive treatment modality for ESLD. However, shortage of donor organs, timely unavailability, post-surgery related complications and financial burden on the patients limits the number of patients receiving the transplants. Since last two decades cell-based therapies have revolutionized the field of organ/tissue regeneration. However providing an alternative organ source to address the donor liver shortage still poses potential challenges. The developments made in this direction provide useful futuristic approaches, which could be translated into pre-clinical and clinical settings targeting appropriate applications in specific disease conditions. Earlier studies have demonstrated the applicability of this particular approach to generate functional organ in rodent system by connecting them with portal and hepatic circulatory networks. However, such strategy requires very high level of surgical expertise and also poses the technical and financial questions towards its future applicability. Hence, alternative sites for generating secondary organs are being tested in several types of disease conditions. Among different sites, omentum has been proved to be more appropriate site for implanting several kinds of functional tissue constructs without eliciting much immunological response. Hence, omentum may be considered as better site for transplanting humanized bioengineered ex vivo generated livers, thereby creating a secondary organ at intra-omental site. However, the expertise for generating such bioengineered organs are limited and only very few centres are involved for investigating the potential use of such implants in clinical practice due to gap between the clinical transplant surgeons and basic scientists working on the concept evolution. Herein we discuss the recent advances and challenges to create functional secondary organs through intra-omental transplantation of ex vivo generated bioengineered humanized livers and their further application in the management of ESLD as a supportive bridge for organ transplantation.

Regenerative potential of induced pluripotent stem cells derived from patients undergoing haemodialysis in kidney regeneration

Kidney regeneration from pluripotent stem cells is receiving a lot of attention because limited treatments are currently available for chronic kidney disease (CKD). It has been shown that uremic state in CKD is toxic to somatic stem/progenitor cells, such as endothelial progenitor and mesenchymal stem cells, affecting their differentiation and angiogenic potential. Recent studies reported that specific abnormalities caused by the non-inherited disease are often retained in induced pluripotent stem cell (iPSC)-derived products obtained from patients. Thus, it is indispensable to first assess whether iPSCs derived from patients with CKD due to non-inherited disease (CKD-iPSCs) have the ability to generate kidneys. In this study, we generated iPSCs from patients undergoing haemodialysis due to diabetes nephropathy and glomerulonephritis (HD-iPSCs) as representatives of CKD-iPSCs or from healthy controls (HC-iPSCs). HD-iPSCs differentiated into nephron progenitor cells (NPCs) with similar efficiency to HC-iPSCs. Additionally, HD-iPSC-derived NPCs expressed comparable levels of NPC markers and differentiated into vascularised glomeruli upon transplantation into mice, as HC-iPSC-derived NPCs. Our results indicate the potential of HD-iPSCs as a feasible cell source for kidney regeneration. This is the first study paving the way for CKD patient-stem cell-derived kidney regeneration, emphasising the potential of CKD-iPSCs.

Optimal route of diphtheria toxin administration to eliminate native nephron progenitor cells in vivo for kidney regeneration

To address the lack of organs for transplantation, we previously developed a method for organ regeneration in which nephron progenitor cell (NPC) replacement is performed via the diphtheria toxin receptor (DTR) system. In transgenic mice with NPC-specific expression of DTR, NPCs were eliminated by DT and replaced with NPCs lacking the DTR with the ability to differentiate into nephrons. However, this method has only been verified in vitro. For applications to natural models, such as animal fetuses, it is necessary to determine the optimal administration route and dose of DT. In this study, two DT administration routes (intra-peritoneal and intra-amniotic injection) were evaluated in fetal mice. The fetus was delivered by caesarean section at E18.5, and the fetal mouse kidney and RNA expression were evaluated. Additionally, the effect of the DT dose (25, 5, 0.5, and 0.05 ng/fetus-body) was studied. Intra-amniotic injection of DT led to a reduction in kidney volume, loss of glomeruli, and decreased differentiation marker expression. The intra-peritoneal route was not sufficient for NPC elimination. By establishing that intra-amniotic injection is the optimal administration route for DT, these results will facilitate studies of kidney regeneration in vivo. In addition, this method might be useful for analysis of kidney development at various time points by deleting NPCs during development.

The use of Peritoneal Mesothelium as a Potential Source of Adult Stem Cells

At the dawn of the 21st century, classical curative medicine is being challenged by the fact that efforts to fight and prevent not a few diseases, are in many circumstances, beyond the power of the pharmacological armamentarium of the medical profession. On the other hand, replacement of lost function by mechanical or biophysical devices, or even by organ transplantation, prolongs life but generally derives in new and, at times, unsolvable problems.

Regenerative therapy using stem cells began a revolutionary trend that may well change both the therapeutic approach to not a few of the diseases resulting from failing organs, as well as the fate and quality of life of millions of patients.

The presence of pluripotent mesenchymal cells in the mesothelial monolayer as well as in the submesothelial connective tissue raises the possibility of using the peritoneal mesothelium in regenerative therapies. This perception of the problem is also based on observations made in humans as well as in laboratory animals showing bone, bone marrow, cartilaginous tissue, glomerular-like structures and creation of blood conducts, pathological situations (mesothelioma, sclerosing peritonitis), or after in vivo or ex vivo experimental interventions. The main concept emerging from this information is that peritoneal mesothelial cells are endowed with such a degree of plasticity that, if placed in the appropriate micro-environment, they have a remarkable potential to generate other mesenchymal-derived cell lines.

Intensive research is required to define the best environmental conditions to take advantage of this plasticity and make the peritoneal mesothelium an actual option to be applied in regenerative medicine.

Autogenous hepatic tissue transplantation into the omentum in a novel ectopic liver regeneration murine model

BACKGROUND

Liver regeneration involves hyperplasia and hypertrophy of hepatic cells. The capacity of macroscopic liver tissue to regenerate in ectopic sites is unknown. We aim to develop a novel in vivo model of ectopic liver survivability and regeneration and assess its functionality.

METHODS

Adult male Sprague-Dawley rats (n = 23) were divided into four groups: (1) single-stage (SS) group, wedge liver resection was performed, and the parenchyma was directly implanted into the omentum; (2) double-stage (DS) group, omentum pedicle was transposed over the left hepatic lobe followed by wedge liver resection along with omental flap; (3) Biogel + DS group, rats received intraperitoneal injection of inert polymer particles prior to DS; (4) Biogel + DS + portal vein ligation (PVL) group, Biogel + DS rats underwent subsequent PVL. Hepatobiliary iminodiacetic acid scintigraphy assessed bile excretion from ectopic hepatic implants.

RESULTS

Histologically, the scores of necrosis (P < 0.001) and fibrosis (P = 0.004) were significantly improved in rats undergoing DS procedure (groups 2, 3, and 4) compared with the SS group. Biogel rats (Biogel + DS and Biogel + DS + PVL) demonstrated statistically increased scores of bile duct neoformation (P = 0.002) compared to those without the particles (SS and DS). Scintigraphy demonstrated similar uptake of radiotracer by ectopic hepatic implants in groups 2, 3, and 4.

CONCLUSIONS

Omental transposition provided adequate microcirculation for proliferation of ectopic hepatic cells after liver resection. Inert polymers enhanced the regeneration by promoting differentiation of new bile ducts. The ectopic hepatic implants showed preserved function on scintigraphy. This model provides insights into the capacity of liver parenchyma to regenerate in ectopic sites and the potential as therapeutic target for cell therapy in end-stage liver disease.

Generation of interspecies limited chimeric nephrons using a conditional nephron progenitor cell replacement system

Animal fetuses and embryos may have applications in the generation of human organs. Progenitor cells may be an appropriate cell source for regenerative organs because of their safety and availability. However, regenerative organs derived from exogenous lineage progenitors in developing animal fetuses have not yet been obtained. Here, we established a combination system through which donor cells could be precisely injected into the nephrogenic zone and native nephron progenitor cells (NPCs) could be eliminated in a time- and tissue-specific manner. We successfully achieved removal of Six2+ NPCs within the nephrogenic niche and complete replacement of transplanted NPCs with donor cells. These NPCs developed into mature glomeruli and renal tubules, and blood flow was observed following transplantation in vivo. Furthermore, this artificial nephron could be obtained using NPCs from different species. Thus, this technique enables in vivo differentiation from progenitor cells into nephrons, providing insights into nephrogenesis and organ regeneration.

The transplantation of tissue-specific progenitor cells may be an approach in organ regeneration. Here the authors show that the nephron progenitor population of a developing mouse kidney, when ablated, can be replaced by exogenously supplied rat nephron progenitors, generating interspecies nephrons.

Effect of adipose-derived mesenchymal stem cell transplantation on vascular calcification in rats with adenine-induced kidney disease

Previous studies have investigated the use of mesenchymal stem cells (MSCs) to treat damaged kidneys. However, the effect of adipose-derived MSCs (ASCs) on vascular calcification in chronic kidney disease (CKD) is still poorly understood. In the present study, we explored the potential of ASCs for the treatment of CKD and vascular calcification. CKD was induced in male Sprague-Dawley rats by feeding them a diet containing 0.75% adenine for 4 weeks. ASCs transplantation significantly reduced serum inorganic phosphorus (Pi) as compared to that in the control. The histopathology of the kidneys showed a greater dilation of tubular lumens and interstitial fibrosis in the control group. Calcium and Pi contents of the aorta in the ASCs transplantation group were lower than those in the control group. Von Kossa staining of the thoracic aorta media revealed that ASCs transplantation suppressed vascular calcification. Thus, this study revealed that autogenic ASCs transplantation inhibits kidney damage and suppresses the progression of vascular calcification in the CKD rat model, suggesting that autogenic ASCs transplantation is a novel approach for preventing the progression of CKD and vascular calcification.

Current Bioengineering and Regenerative Strategies for the Generation of Kidney Grafts on Demand

Currently in the USA, one name is added to the organ transplant waiting list every 15 min. As this list grows rapidly, fewer than one-third of waiting patients can receive matched organs from donors. Unfortunately, many patients who require a transplant have to wait for long periods of time, and many of them die before receiving the desired organ. In the USA alone, over 100,000 patients are waiting for a kidney transplant. However, it is a problem that affects around 6% of the word population. Therefore, seeking alternative solutions to this problem is an urgent work. Here, we review the current promising regenerative technologies for kidney function replacement. Despite many approaches being applied in the different ways outlined in this work, obtaining an organ capable of performing complex functions such as osmoregulation, excretion or hormone synthesis is still a long-term goal. However, in the future, the efforts in these areas may eliminate the long waiting list for kidney transplants, providing a definitive solution for patients with end-stage renal disease.

Embryonic kidney function in a chronic renal failure model in rodents

BACKGROUND

Rapid advancements have been made in alternative treatments for renal diseases. Our goal for renal regeneration is to establish a kidney graft derived from human embryonic tissues. In this study, we investigated the effects of host renal failure on the structure and activity of transplanted embryonic kidney and bladder, and found that diuretics effectively induced urine production in the transplanted kidney.

METHODS

Uremic conditions were reproduced using a 5/6 renal infarction rat model. An embryonic kidney plus bladder (embryonic day 15) was isolated from a pregnant Lewis rat and transplanted into the para-aortic area of a 5/6 renal-infarcted Lewis rat. Following growth, the embryonic bladder was successfully anastomosed to the host ureter.

RESULTS

We assessed graft function in terms of survival rates and found no differences between normal (n = 5) and renal failure (n = 8) groups (median survival: 70.5 vs 74.5 h; p = 0.331) in terms of survival, indicating that the grafts prolonged rat survival, even under renal failure conditions. Furosemide (n = 9) significantly increased urine volume compared with saline-treated controls (n = 7; p < 0.05), confirming that the grafts were functional. We also demonstrated the possibilities of an in vivo imaging system for determining the viability of transplanted embryonic kidney with bladder.

CONCLUSION

The results of this study demonstrate that transplanted embryonic kidney and bladder can grow and function effectively, even under uremic conditions.

Detection of initial angiogenesis from dorsal aorta into metanephroi and elucidation of its role in kidney development

Reconstruction of blood vessels is considered the most difficult part for the complicated organs, therefore, blood vessel construction is regarded as a key point for kidney regeneration in vitro. Vasculogenesis and angiogenesis are the two mechanisms to form blood vessels in embryonic organs, and most studies resided in vaculogenesis. Angiogenesis resided mostly in adult diseases such as wound healing, growth of tumors, and psoriasis diseases. However, renal angiogenesis is simply attributed to the sprouting of pre-existing blood vessel from dorsal aorta into metanephroi, and its occurrence is considered to be at a late stage of metanephric development. Since no techniques are available for delicate detection, the initial angiogenesis from dorsal aorta into metanephroi as well as its role in kidney development still remained unclear. In this study, we developed a method to detect the initial angiogenesis of dorsal aorta into metanephroi, and firstly clarified that dorsal aorta angiogenesis occurred at an early stage of metanephric development. We also elucidated the role of dorsal aorta angiogenesis in promoting the early blood vessel formation, tubule formation and glomeruli maturation. It is suggested that blood flow and dynamic circulation of various factors at the early developing stage may be prerequisite to a successful construction of blood vessels in the complicated organs either in vitro or in vivo. These findings contribute to a better understanding of dorsal aorta angiogenesis during kidney development and shed light on its significant value for the application of tissue engineering to complicated organs.

Growing human organs in pigs-A dream or reality?

Organ transplantation has been the last line of therapy for saving patients experiencing end-stage organ failure. However, the success of organ transplantation is critically dependent on the availability of donor organs. There are high expectations for research on organ regeneration as a solution to the donor shortage issue faced by transplantation medicine. Thus, generation of human organs from pluripotent stem cells is now one of the ultimate goals of regenerative medicine. In recent years, several approaches to using pluripotent stem cells to generate organs of complex structure and function have been developed. Reproductive biology plays an indispensable role in the development of innovative organ regeneration researches. In this review, we discuss the potential of the animal biotechnology aiming at making human organs using pigs as a platform.

Selected renal cells modulate disease progression in rodent models of chronic kidney disease via NF-κB and TGF-β1 pathways

AIM

Identification of mechanistic pathways for selected renal cell (SRC) therapeutic bioactivity in rodent models of chronic kidney disease.

MATERIALS & METHODS

In vivo and in vitro functional bioassays applied to investigate regenerative outcomes associated with delivery of SRC to diseased rodent kidney.

RESULTS

In vivo, SRC reduces chronic infiltration by monocytes/macrophages. SRC attenuates NF-κB and PAI-1 responses while simultaneously promoting host tubular cell expansion through trophic cues. In vitro, SRC-derived conditioned media attenuates TNF-α-induced NF-κB response, TGF-β-mediated PAI-1 response and increases expression of transcripts associated with cell cycle regulation. Observed bioactive responses were from vesicle and nonvesicle-associated factors, including specific miRNAs.

CONCLUSION

We identify a paracrine mechanism for SRC immunomodulatory and trophic cues on host renal tissues, catalyzing long-term functional benefits in vivo.

Urine excretion strategy for stem cell-generated embryonic kidneys

There have been several recent attempts to generate, de novo, a functional whole kidney from stem cells using the organogenic niche or blastocyst complementation methods. However, none of these attempts succeeded in constructing a urinary excretion pathway for the stem cell-generated embryonic kidney. First, we transplanted metanephroi from cloned pig fetuses into gilts; the metanephroi grew to about 3 cm and produced urine, although hydronephrosis eventually was observed because of the lack of an excretion pathway. Second, we demonstrated the construction of urine excretion pathways in rats. Rat metanephroi or metanephroi with bladders (developed from cloacas) were transplanted into host rats. Histopathologic analysis showed that tubular lumina dilation and interstitial fibrosis were reduced in kidneys developed from cloacal transplants compared with metanephroi transplantation. Then we connected the host animal's ureter to the cloacal-developed bladder, a technique we called the "stepwise peristaltic ureter" (SWPU) system. The application of the SWPU system avoided hydronephrosis and permitted the cloacas to differentiate well, with cloacal urine being excreted persistently through the recipient ureter. Finally, we demonstrated a viable preclinical application of the SWPU system in cloned pigs. The SWPU system also inhibited hydronephrosis in the pig study. To our knowledge, this is the first report showing that the SWPU system may resolve two important problems in the generation of kidneys from stem cells: construction of a urine excretion pathway and continued growth of the newly generated kidney.

Autologous transplantation of mesenchymal stromal cells tends to prevent progress of interstitial fibrosis in a rhesus Macaca mulatta monkey model of chronic kidney disease

BACKGROUND AIMS

Chronic kidney disease (CKD) attributed to cisplatin is well documented. Mesenchymal stromal cells (MSCs) are proven to be renotropic. Although they have been shown to improve function in CKD and reduce fibrosis in different experimental rodent models, their efficiency in primates is unknown. The present study aimed to evaluate the prevention of CKD and reduction of fibrosis in monkeys treated with MSCs after cisplatin nephrotoxicity.

METHODS

We induced CKD in adult rhesus Macaca mulatta monkeys by means of intravenous administration of cisplatin. Autologous MSCs were transplanted by means of intrarenal arterial injections to assess the adverse effects of cisplatin in two CKD models: preventative and stable. Preventative CKD monkeys (n = 3) underwent cell transplantation 4 days after the cisplatin injection. The stable CKD monkeys (n = 2) underwent cell transplantation 6 months after the cisplatin injection. Non-treated (n = 4) and normal saline-injected animals (n = 3) comprised the control and vehicle groups, respectively. We followed the animals for survival rate, serum biochemistry, urine analysis and histopathological indices.

RESULTS

In the preventive CKD model, MSC transplantation tended to improve some renal functions but significantly reduced the histopathologic score compared with the vehicle and control groups. In the stable CKD model, MSCs did not ameliorate renal function or pathological score.

CONCLUSIONS

These results suggest that MSCs tend to delay progression of CKD and fibrosis but do not reduce established interstitial fibrosis in this unique primate model of cisplatin-induced nephrotoxicity.

Stem cell therapy for kidney disease

INTRODUCTION

Kidney diseases are a global public health problem whose incidence is rapidly growing due to a global rise in the aged population and the increasing prevalence of cardiovascular disease, hypertension and diabetes. With the emergence of stem cells as potential therapeutic agents, attempts in using them to significantly reduce the burden of these diseases have increased.

AREAS COVERED

Several types of stem cells have been proven to be likely candidates for treating kidney diseases. We discuss in detail the potential use of mesenchymal stem cells in preclinical and clinical works, with additional populations that have been studied briefly described. Moreover, we discuss current knowledge on endogenous kidney regeneration ability and on the possibility to modulate it using chemical and biological agents.

EXPERT OPINION

Stem cell therapy is a promising new treatment for kidney disease documented in many animal studies. Mesenchymal stem cells have emerged as a promising cell type, but their efficacy in clinical trials is still controversial. Identification of progenitor cells in the adult kidney is another step forward in regenerative medicine, suggesting the repair potential of the adult kidney and the possible modulation of renal progenitors in situ using pharmacological approaches.

Current Bioengineering Methods for Whole Kidney Regeneration

Kidney regeneration is likely to provide an inexhaustible source of tissues and organs for immunosuppression-free transplantation. It is currently garnering considerable attention and might replace kidney dialysis as the ultimate therapeutic strategy for renal failure. However, anatomical complications make kidney regeneration difficult. Here, we review recent advances in the field of kidney regeneration, including (i) the directed differentiation of induced pluripotent stem cells/embryonic stem cells into kidney cells; (ii) blastocyst decomplementation; (iii) use of a decellularized cadaveric scaffold; (iv) embryonic organ transplantation; and (v) use of a nephrogenic niche for growing xenoembryos for de novo kidney regeneration from stem cells. All these approaches represent potentially promising therapeutic strategies for the treatment of patients with chronic kidney disease. Although many obstacles to kidney regeneration remain, we hope that innovative strategies and reliable research will ultimately allow the restoration of renal function in patients with end-stage kidney disease.

Kidney regeneration using developing xenoembryo

PURPOSE OF REVIEW

We provide an overview of the recent progress in kidney regeneration with a particular focus on our previous study, which used developing xenoembryos for differentiating human mesenchymal stem cells (hMSCs). The principle of the methodology, recent advances, and limitations and challenges associated with kidney regeneration are outlined.

RECENT FINDINGS

Our primary study objective is to generate neokidney from dialysis patient-derived hMSCs. We previously showed that glial cell-derived neurotrophic factor-expressing hMSCs can differentiate into functional chimeric nephrons in developing mammalian embryos. Recently, we succeeded in eliminating xenotissues in transgenic oestrogen receptor-E2F transcription factor 1 (ER-E2F1) mice by introducing a suicide gene. We also showed MSCs derived from dialysis patients can be used for kidney regeneration. Blastocyst complementation strategy was used to generate chimeric nephrons by injecting mouse pluripotent stem cells into spalt-like transcription factor 1 (Sall1) knockout mouse blastocysts.

SUMMARY

Kidney tissue can be generated from human mouse pluripotent stem cells or MSCs by several methods. The size and function of regenerated kidney tissue do not meet the transplantation requirements for clinical applications. Although many outstanding problems remain for kidney regeneration, including ethical issues and the formation of chimeric structures, the neokidney generation exclusively from dialysis patient-derived cells is expected to be a reality in the future.

Generation of a felinized swine endothelial cell line by expression of feline decay-accelerating factor

Embryonic stem cell research has facilitated the generation of many cell types for the production of tissues and organs for both humans and companion animals. Because ≥30% of pet cats suffer from chronic kidney disease (CKD), xenotransplantation between pigs and cats has been studied. For a successful pig to cat xenotransplant, the immune reaction must be overcome, especially hyperacute rejection. In this study, we isolated the gene for feline decay-accelerating factor (fDAF), an inhibitor of complement proteins, and transfected a swine endothelial cell line with fDAF to "felinize" the pig cells. These fDAF-expressing cells were resistant to feline serum containing anti-pig antibodies, suggesting that felinized pig cells were resistant to hyperacute rejection. Our results suggest that a "felinized" pig kidney can be generated for the treatment of CKD in cats in the future.

Current strategies and challenges in engineering a bioartificial kidney

Renal replacement therapy was an early pioneer in both extra-corporeal organ replacement and whole organ transplantation. Today, the success of this pioneering work is directly demonstrated in the millions of patients worldwide successfully treated with dialysis and kidney transplantation. However, there remain significant shortcomings to current treatment modalities that limit clinical outcomes and quality of life. To address these problems, researchers have turned to using cell-based therapies for the development of a bioartificial kidney. These approaches aim to recapitulate the numerous functions of the healthy kidney including solute clearance, fluid homeostasis and metabolic and endocrine functions. This review will examine the state-of-the-art in kidney bioengineering by evaluating the various techniques currently being utilized to create a bioartificial kidney. These promising new technologies, however, still need to address key issues that may limit the widespread adoption of cell therapy including cell sourcing, organ scaffolding, and immune response. Additionally, while these new methods have shown success in animal models, it remains to be seen whether these techniques can be successfully adapted for clinical treatment in humans.

Adipose tissue-derived mesenchymal stem cells in long-term dialysis patients display downregulation of PCAF expression and poor angiogenesis activation

We previously demonstrated that mesenchymal stem cells (MSCs) differentiate into functional kidney cells capable of urine and erythropoietin production, indicating that they may be used for kidney regeneration. However, the viability of MSCs from dialysis patients may be affected under uremic conditions. In this study, we isolated MSCs from the adipose tissues of end-stage kidney disease (ESKD) patients undergoing long-term dialysis (KD-MSCs; mean: 72.3 months) and from healthy controls (HC-MSCs) to compare their viability. KD-MSCs and HC-MSCs were assessed for their proliferation potential, senescence, and differentiation capacities into adipocytes, osteoblasts, and chondrocytes. Gene expression of stem cell-specific transcription factors was analyzed by PCR array and confirmed by western blot analysis at the protein level. No significant differences of proliferation potential, senescence, or differentiation capacity were observed between KD-MSCs and HC-MSCs. However, gene and protein expression of p300/CBP-associated factor (PCAF) was significantly suppressed in KD-MSCs. Because PCAF is a histone acetyltransferase that mediates regulation of hypoxia-inducible factor-1α (HIF-1α), we examined the hypoxic response in MSCs. HC-MSCs but not KD-MSCs showed upregulation of PCAF protein expression under hypoxia. Similarly, HIF-1α and vascular endothelial growth factor (VEGF) expression did not increase under hypoxia in KD-MSCs but did so in HC-MSCs. Additionally, a directed in vivo angiogenesis assay revealed a decrease in angiogenesis activation of KD-MSCs. In conclusion, long-term uremia leads to persistent and systematic downregulation of PCAF gene and protein expression and poor angiogenesis activation of MSCs from patients with ESKD. Furthermore, PCAF, HIF-1α, and VEGF expression were not upregulated by hypoxic stimulation of KD-MSCs. These results suggest that the hypoxic response may be blunted in MSCs from ESKD patients.

Mesenchymal stem cell treatment for chronic renal failure

Chronic renal failure is an important clinical problem with significant socioeconomic impact worldwide. Despite advances in renal replacement therapies and organ transplantation, poor quality of life for dialysis patients and long transplant waiting lists remain major concerns for nephrologists treating this condition. There is therefore a pressing need for novel therapies to promote renal cellular repair and tissue remodeling. Over the past decade, advances in the field of regenerative medicine allowed development of cell therapies suitable for kidney repair. Mesenchymal stem cells (MSCs) are undifferentiated cells that possess immunomodulatory and tissue trophic properties and the ability to differentiate into multiple cell types. Studies in animal models of chronic renal failure have uncovered a unique potential of these cells for improving function and regenerating the damaged kidney. Nevertheless, several limitations pertaining to inadequate engraftment, difficulty to monitor, and untoward effects of MSCs remain to be addressed. Adverse effects observed following intravascular administration of MSCs include immune rejection, adipogenic differentiation, malignant transformation, and prothrombotic events. Nonetheless, most studies indicate a remarkable capability of MSCs to achieve kidney repair. This review summarizes the regenerative potential of MSCs to provide functional recovery from renal failure, focusing on their application and the current challenges facing clinical translation.

Kidney regeneration with stem cells: an overview

BACKGROUND

Kidney regeneration is currently gaining considerable attention in place of kidney dialysis as the ultimate therapeutic strategy for renal failure. However, because of anatomical complications, the kidney is believed to be the hardest organ to regenerate. Such a complicated organ is virtually impossible to imagine being completely rebuilt de novo from stem cells. Nevertheless, several research groups are attempting this large challenge.

SUMMARY

There are 4 major strategies for de novo kidney regeneration from stem cells. These strategies include the use of: (i) a decellularized cadaveric scaffold, (ii) blastocyst decomplementation, (iii) a nephrogenic niche for growing a xeno-embyro, and (iv) self-assembly potential. All of these strategies may be applicable in the clinical setting, but a substantial preparation period appears to be required.

KEY MESSAGES

Although many outstanding problems remain for kidney regeneration, including ethical issues and the formation of chimeric structures, trials provide hope for dialysis patients and kidney regeneration is expected to be a reality in the future.

Organogenesis for kidney regeneration

PURPOSE OF REVIEW

The kidney has an elaborate and complicated structure comprising several cell types. Damage or destruction of the kidney thus necessitates reconstruction of all the component cell types to regenerate a functional three-dimensional renal structure. Therefore, despite all the recent advances in our understanding and technical approaches to stem cell and developmental biology, the anatomical complexity of the renal system makes de-novo kidney regeneration the most difficult challenge for organ regenerative therapy.

RECENT FINDINGS

To build a transplantable neo-kidney, some investigators propose using organogenesis. We suggest the metanephros of the developing kidney and blastocyst complementation can potentially generate a whole kidney with the required three-dimensional structure and renal function to produce urine and erythropoietin. In addition, some researchers are investigating the in-vitro differentiation of pluripotent stem cells into mature renal cells for in-vivo use.

SUMMARY

We review the current challenges to making a transplantable neo-kidney using stem cells.

Cellular interactions via conditioned media induce in vivo nephron generation from tubular epithelial cells or mesenchymal stem cells

There are some successful reports of kidney generation by utilizing the natural course of kidney development, namely, the use of an artificially treated metanephros, blastocyst or ureteric bud. Under a novel concept of cellular interactions via conditioned media (CMs), we have attempted in vivo nephron generation from tubular epithelial cells (TECs) or mesenchymal stem cells (MSCs). Here we used 10× CMs of vascular endothelial cells (VECs) and TECs, which is the first to introduce a CM into the field of organ regeneration. We first present stimulative cross-talks induced by these CMs between VECs and TECs on cell proliferation and morphological changes. In MSCs, TEC-CM suppressed these changes, however, induced cytokeratin expression, indicating the differentiation of MSCs into TECs. As a result, glomerular and tubular structures were created following the implantation of TECs or MSCs with both CMs. Our findings suggest that the cellular interactions via CMs might induce in vivo nephron generation from TECs or MSCs. As a promoting factor, CMs could also be applied to the regeneration of other organs and tissues.

Human embryonic stem cells differentiate into functional renal proximal tubular-like cells

Renal cells are used in basic research, disease models, tissue engineering, drug screening, and in vitro toxicology. In order to provide a reliable source of human renal cells, we developed a protocol for the differentiation of human embryonic stem cells into renal epithelial cells. The differentiated stem cells expressed markers characteristic of renal proximal tubular cells and their precursors, whereas markers of other renal cell types were not expressed or expressed at low levels. Marker expression patterns of these differentiated stem cells and in vitro cultivated primary human renal proximal tubular cells were comparable. The differentiated stem cells showed morphological and functional characteristics of renal proximal tubular cells, and generated tubular structures in vitro and in vivo. In addition, the differentiated stem cells contributed in organ cultures for the formation of simple epithelia in the kidney cortex. Bioreactor experiments showed that these cells retained their functional characteristics under conditions as applied in bioartificial kidneys. Thus, our results show that human embryonic stem cells can differentiate into renal proximal tubular-like cells. Our approach would provide a source for human renal proximal tubular cells that are not affected by problems associated with immortalized cell lines or primary cells.

Donor chimera model for tolerance induction in transplantation

Tolerance induction is the basis of a successful transplantation with the goal being the re-establishment of homeostasis after transplantation. Non-autograft transplantation disrupts this maintenance drastically which would be avoided by administration of a novel procedure. At present, the blood group antigens and the genotypes of the donor and recipient are cross-matched before transplantation combined with a drug regimen that confers general immunosuppression. But the 'specific' unresponsiveness of the recipient to the donor organ, implied by 'tolerance', is not achieved in this process. This article introduces the 'donor chimera model' via the concept of the 'closed transplantation loop' approach for tolerance induction which seeks to limit the use of immunosuppressive therapy after transplantation.

Xenotransplanted embryonic kidney provides a niche for endogenous mesenchymal stem cell differentiation into erythropoietin-producing tissue

Recent findings have demonstrated that stem cells can differentiate into mature tissue when supplied with a niche containing factors identical to those in the normal developmental program. A niche for the development of an organ can be provided by xenotransplantation of a similar developing organ. However, this process has many technical, safety, and ethical concerns. Here, we established xenotransplantation models that control endogenous mesenchymal stem cell (MSC) differentiation into mature erythropoietin (EPO)-producing tissue in a niche provided by a developing xenometanephros. Transplantation of rat metanephroi into mouse omentum, and similarly pig metanephroi into cat omentum, led to the recruitment of host cells and EPO production. EPO-expressing cells were not differentiated from integrating vessels because they did not coexpress endothelial markers (Tie-2 and VE-cadherin). Instead, EPO-expressing cells were shown to be derived from circulating host cells, as shown by enhanced green fluorescent protein (EGFP) expression in the grown transplants of chimeric mice bearing bone marrow from a transgenic mouse expressing EGFP under the control of the EPO promoter. These results suggest that donor cell recruitment and differentiation in a xenotransplanted developing organ may be consistent between species. The cells responsible for EPO expression were identified as MSCs by injecting human bone marrow-derived MSCs and endothelial progenitor cells into NOD/SCID mice. Furthermore, using metanephroi from transgenic ER-E2F1 suicide-inducible mice, the xenotissue component could be eliminated, leaving autologous EPO-producing tissue. Our findings may alleviate adverse effects due to long-lasting immunosuppression and help mitigate ethical concerns.