Replacement of renal function in uremic animals with a tissue-engineered kidney

Tube formation in Drosophila egg chambers

The reorganization of epithelial sheets into tubes is a fundamental process in the formation of many organs, such as the lungs, kidneys, gut, and neural tube. This process involves the patterning of distinct cell types and the coordination of those cells during the shape changes and rearrangements that produce the tube. A better understanding of the cellular and genetic mechanisms that regulate tube formation is necessary for tissue engineers to develop functional organs in vitro. The Drosophila egg chamber has emerged as an outstanding model for studying tubulogenesis. Synthesis of the dorsal respiratory appendages by the follicular epithelium resembles primary neurulation in vertebrates. This review summarizes work on the patterning and morphogenesis of the dorsal-appendage tubes and highlights key areas where mathematical modeling could contribute to our understanding of these processes.

Stem cells in urology

The shortage of donors for organ transplantation has stimulated research on stem cells as a potential resource for cell-based therapy in all human tissues. Stem cells have been used for regenerative medicine applications in many organ systems, including the genitourinary system. The potential applications for stem cell therapy have, however, been restricted by the ethical issues associated with embryonic stem cell research. Instead, scientists have explored other cell sources, including progenitor and stem cells derived from adult tissues and stem cells derived from the amniotic fluid and placenta. In addition, novel techniques for generating stem cells in the laboratory are being developed. These techniques include somatic cell nuclear transfer, in which the nucleus of an adult somatic cell is placed into an oocyte, and reprogramming of adult cells to induce stem-cell-like behavior. Such techniques are now being used in tissue engineering applications, and some of the most successful experiments have been in the field of urology. Techniques to regenerate bladder tissue have reached the clinic, and exciting progress is being made in other areas, such as regeneration of the kidney and urethra. Cell therapy as a treatment for incontinence and infertility might soon become a reality. Physicians should be optimistic that regenerative medicine and tissue engineering will one day provide mainstream treatment options for urologic disorders.

Stem cell and regenerative science applications in the development of bioengineering of renal tissue

A rising number of patients with acute and chronic renal failure worldwide have created urgency for clinicians and investigators to search out alternative therapies other than chronic renal dialysis and/or organ transplantation. This review focuses on the recent achievements in this area, and discusses the various approaches in the development of bioengineering of renal tissue including recent discoveries in the field of regenerative medicine research and stem cells. A variety of stem cells, ranging from embryonic, bone marrow, endogenous, and amniotic fluid, have been investigated and may prove useful as novel alternatives for organ regeneration both in vitro and in vivo. Tissue engineering, developmental biology, and therapeutic cloning techniques have significantly contributed to our understanding of some of the molecular mechanisms involved in renal regeneration and have demonstrated that renal tissue can be generated de novo with similar physiologic functions as native tissue. Ultimately all of these emerging technologies may provide viable therapeutic options for regenerative medicine applications focused on the bioengineering of renal tissue for the future.

Bioengineered tissues for urogenital repair in children

The most common congenital abnormalities involve the genitourinary system. These include hypospadias, in which the urethral opening develops in an improper position, and bladder exstrophy, in which the bladder develops on the outer surface of the abdomen. Children with these conditions will require immediate and multiple reconstructive surgeries. Currently, reconstruction may be performed with native nonurologic tissues (skin, gastrointestinal segments, or mucosa), homologous tissues from a donor (cadaver or living donor kidney), heterologous tissues or substances (bovine collagen), or artificial materials (silicone, polyurethane, teflon). However, these materials often lead to complications after reconstruction, either because the implanted tissue is rejected, or because inherently different functional parameters cause a mismatch in the system. For example, replacement of bladder tissue with gastrointestinal segments can be problematic due to the opposite ways in which these two tissues handle solutes-urologic tissue normally excretes material, and gastrointestinal tissue generally absorbs the same materials. This mismatched state can lead to metabolic complications as well as infection and other issues. The replacement of lost or deficient urologic tissues with functionally equivalent ones would improve the outcome of reconstructive surgery in the genitourinary system. This goal may soon be attainable with the use of tissue engineering techniques.

Engineering tissues, organs and cells

Patients suffering from diseased and injured organs may be treated with transplanted organs; however, there is a severe shortage of donor organs that is worsening yearly, given the ageing population. In the field of regenerative medicine and tissue engineering, scientists apply the principles of cell transplantation, materials science and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for tissue engineering applications. The stem cell field is also advancing rapidly, opening new options for therapy, including the use of amniotic and placental fetal stem cells. This review covers recent advances that have occurred in regenerative medicine and describes applications of these technologies using chemical compounds that may offer novel therapies for patients with end-stage organ failure.

Efficacy and safety of renal tubule cell therapy for acute renal failure

The mortality rate for patients with acute renal failure (ARF) remains unacceptably high. Although dialysis removes waste products and corrects fluid imbalance, it does not perform the absorptive, metabolic, endocrine, and immunologic functions of normal renal tubule cells. The renal tubule assist device (RAD) is composed of a conventional hemofilter lined by monolayers of renal cells. For testing whether short-term (up to 72 h) treatment with the RAD would improve survival in patients with ARF compared with conventional continuous renal replacement therapy (CRRT), a Phase II, multicenter, randomized, controlled, open-label trial involving 58 patients who had ARF and required CRRT was performed. Forty patients received continuous venovenous hemofiltration + RAD, and 18 received CRRT alone. The primary efficacy end point was all-cause mortality at 28 d; additional end points included all-cause mortality at 90 and 180 d, time to recovery of renal function, time to intensive care unit and hospital discharge, and safety. At day 28, the mortality rate was 33% in the RAD group and 61% in the CRRT group. Kaplan-Meier analysis revealed that survival through day 180 was significantly improved in the RAD group, and Cox proportional hazards models suggested that the risk for death was approximately 50% of that observed in the CRRT-alone group. RAD therapy was also associated with more rapid recovery of kidney function, was well tolerated, and had the expected adverse event profile for critically ill patients with ARF.

Renal differentiation of amniotic fluid stem cells

OBJECTIVES

The role of stem cells in regenerative medicine is evolving rapidly. Here, we describe the application, for kidney regeneration, of a novel non-genetically modified stem cell, derived from human amniotic fluid. We show that these pluripotent cells can develop and differentiate into de novo kidney structures during organogenesis in vitro.

MATERIALS AND METHODS

Human amniotic fluid-derived stem cells (hAFSCs) were isolated from human male amniotic fluid obtained between 12 and 18 weeks gestation. Green fluorescent protein and Lac-Z-transfected hAFSCs were microinjected into murine embryonic kidneys (12.5-18 days gestation) and were maintained in a special co-culture system in vitro for 10 days. Techniques of live microscopy, histology, chromogenic in situ hybridization and reverse transcriptase polymerase chain reaction were used to characterize the hAFSCs during their integration and differentiation in concert with the growing organ.

RESULTS

Green fluorescent protein and Lac-Z-transfected hAFSCs demonstrated long-term viability in organ culture. Histological analysis of injected kidneys revealed that hAFSCs were capable of contributing to the development of primordial kidney structures including renal vesicle, C- and S-shaped bodies. Reverse transcriptase polymerase chain reaction confirmed expression of early kidney markers for: zona occludens-1, glial-derived neurotrophic factor and claudin.

CONCLUSIONS

Human amniotic fluid-derived stem cells may represent a potentially limitless source of ethically neutral, unmodified pluripotential cells for kidney regeneration.

Development of continuous implantable renal replacement: past and future

Most of the 400,000+ patients in the United States with kidney failure depend on dialysis treatments in dedicated dialysis centers for 3 h to 5 h, usually 3 times a week, but they still suffer from accelerated cardiovascular disease and infections. Extended daily dialysis, for 6 to 8 hours every day, seems to be associated with better outcomes but would overwhelm the dialysis networks and severely limit patient activity. Technology to miniaturize and automate home dialysis will be necessary to offer extended daily dialysis to most dialysis patients. Miniaturization of existing hollow-fiber polymer membranes is constrained by requirements for high driving pressures for circulation and convective clearance. Recent advances in membrane technology based on microelectromechanical systems (MEMS) promise to enable the development of continuous implantable renal replacement therapy. Silicon nanoporous membranes with a highly monodisperse pore size distribution have been produced using protocols amenable to low-cost batch fabrication similar to those used to produce microelectronics. Hydraulic permeability of the flat-sheet membranes with critical pore sizes in the range of 8-100 nm has been measured to confirm that conventional fluid transport models are sufficiently accurate for predictive design for bulk liquid flow in an implantable hemofilter. Membrane biocompatibility was tested in vitro with human proximal tubule cells and revealed that silicon does not exhibit cytotoxicity, as evidenced by the formation of confluent cell layers with tight junctions and central cilia. Filtration characterization demonstrated that the nanoporous membranes exhibit size-dependent solute rejection in agreement with steric hindrance models. These advances in membrane technology are fundamentally enabling for a paradigm shift from an in-center to implantable dialysis system.

Regenerative Medicine: Applications and Development in Urology

Purpose

Congenital abnormalities and acquired disorders can lead to organ damage and loss. Nowadays, transplantation represents the only effective treatment option. However, there is a marked decrease in the number of organ donors, which is even yearly worsening due to the population aging. The regenerative medicine represents a realistic option that allows to restore and maintain the normal functions of tissues and organs. This article reviews the principles of regenerative medicine and the recent advances with regard to its application to the genitourinary tract.

Recent findings

The field of regenerative medicine involves different areas of technology, such as tissue engineering, stem cells and cloning. Tissue engineering involves the field of cell transplantation, materials science and engineering in order to create functional replacement tissues. Stem cells and cloning permit the extraction of pluripotent, embryonic stem cells offering a potentially limitless source of cells for tissue engineering applications. Most current strategies for tissue engineering depend upon a sample of autologous cells from the patient's diseased organ. Biopsies from patients with extensive end-stage organ failure, however, may not yield enough normal cells. In these situations, stem cells are envisaged as being an alternative source. Stem cells can be derived from discarded human embryos (human embryonic stem cells), from fetal tissue or from adult sources (bone marrow, fat, skin). Therapeutic cloning offers a potentially limitless source of cells for tissue engineering applications. Regenerative medicine and tissue engineering scientists have increasingly applied the principles of cell transplantation, materials science and bioengineering to construct biological substitutes that will restore and maintain normal function in urological diseased and injured tissues such as kidney, ureter, bladder, urethra and penis.

Conclusions

Regenerative medicine offers several applications in acquired and congenital genitourinary diseases. Tissue engineering, stem cells and, mostly, cloning have been applied in experimental studies with excellent results. Few preliminary human applications have been developed with promising results.

Improvement of kidney failure with fetal kidney precursor cell transplantation

BACKGROUND

Current therapies for end-stage renal disease have severe limitations. Dialysis is only a temporary treatment and does not restore kidney function. Transplantation is limited by donor organ shortage and immune-related problems. Here, we show that the transplantation of fetal kidney precursor cells reconstitutes kidney tissues, reduces uremic symptoms, and provides life-saving metabolic support in kidney failure animal models.

METHODS

Kidney failure was surgically induced by resecting kidneys, leaving approximately 1/6 of the total kidney mass (5/6 nephrectomy). Fetal kidney precursor cells were isolated from metanephroi of E17.5 rat fetuses using collagenase/dispase digestion. Five weeks after the nephrectomy procedure, isolated fetal kidney precursor cells were transplanted under the kidney capsule of rats using fibrin gel matrix. Six and ten weeks after transplantation, animals were analyzed biochemically and the grafts were retrieved for histological analyses.

RESULTS

Five weeks after the nephrectomy, glomerular hypertrophy, and increased blood urea nitrogen and serum creatinine levels were observed. The cell transplantation into the kidneys of kidney failure-induced rats resulted in kidney tissue reconstitution and the transplanted cells were observed in the reconstitution region of the kidneys as evidenced by the presence of fluorescently labeled cells. In addition, biochemical parameters from serum and urine samples showed improved kidney functions compared with non-treated group without severe immune response after ten weeks.

CONCLUSION

Transplanting fetal kidney precursor cells showed the potential for the partial augmentation of kidney structure and function in the treatment of kidney failure.

Effect of continuous bioartificial kidney therapy on porcine multiple organ dysfunction syndrome with acute renal failure

The bioartificial kidney (BK) was fabricated with primary culture of human proximal tubular cells growing in a hemofilter. A porcine model with multiple organ dysfunction syndrome, including acute renal failure, was induced by cecal ligation and puncture and bilateral ureteral ligation. The models were treated with BK (group A) or sham BK (group B) or without treatment (group C). Mean arterial pressure (mm Hg) was higher in group A (88.13 +/- 7.62) than in groups B and C (63.50 +/- 11.82, 53.50 +/- 2.52) at 24 hours (p < 0.01). Serum blood urea nitrogen, Cr, K, Pao2, and HCO3 were similar during the treatment periods between groups A and B, which were better than those in group C. In group A, tumor necrosis factor (TNF)-alpha (pg/mL) was 394.42 +/- 35.62 at 24 hours, lower than that of groups B and C (531.76 +/- 30.23, 552.89 +/- 27.81) (p < 0.05). Peak level of interleukin (IL)-10 (pg/mL) was higher in group A (272.36 +/- 48.89) than in groups B and C (106.30 +/- 29.69, 102.59 +/- 10.21) (p < 0.01). There was no difference of serum IL-6 between pretreatment and post-treatment in groups A and B, but serum IL-6 gradually increased in group C. The survival time (hours) was longer in group A than in other groups, which was prolonged by 46.20% and 58.39%. Results indicate that BK can ameliorate mean arterial pressure, decrease serum TNF-alpha, increase serum IL-10, and prolong survival time of pigs with multiple organ dysfunction syndrome and acute renal failure.

Cell Therapy in Kidney Disease: Cautious Optimism … But Optimism Nonetheless

The recently discovered therapeutic potential of stem or progenitor cells has initiated development of novel treatments in a number of diseases—treatments that could not only improve patients’ quality of life, but also halt or even prevent disease progression. Hypertension; fluctuations in glycemia, electrolytes, nutrient levels, and circulating volume; and frequent infections and the associated inflammation all greatly impair the endothelium in patients undergoing peritoneal dialysis. As our understanding of the regulatory function of the endothelium advances, focus is increasingly being placed on endothelial repair in acute and chronic renal failure and after renal transplantation. The potential of progenitor cells to repair damaged endothelium and to reduce inflammation in patients with renal failure remains unexamined; however, a successful cell therapy could reduce morbidity and mortality in kidney disease.

Important contributions have been made in identifying progenitor cell populations in the kidney, and further investigations into the relationships of these cells with the pathophysiology of the disease are underway. As the kidney disease field prepares for the first human trials of progenitor cell therapies, we deemed it important to review representative original research, and to share our perspectives and lessons learned from clinical trials of progenitor cell–based therapies that have commenced in patients with cardiovascular disease.

Bioartificial kidney in the treatment of acute renal failure associated with sepsis

Acute renal failure (ARF) associated with sepsis has a high rate of mortality. It is not merely a surrogate marker for severity of disease but also an independent predictor of mortality and a separate pathogenic entity, even when nearly physiological doses of fluid and small-molecule clearance are maintained with currently available renal replacement therapies (RRT). The techniques to remove cytokines, including high-volume haemofiltration, haemodialysis using high-cut-off haemofilters, and absorptive techniques, lead to some improvement in outcome but are still insufficient to reverse the complicated biological dysregulation resulting from ARF associated with sepsis. The novel and exciting technique of cell therapy, which is based on the principle of using functional cells to replace a greater range of renal functions, may add significant benefit to current RRT in dealing with this disease process. Because renal tubule cells appear to play critical roles in immunoregulation, renal tubule cell therapy during ARF associated with sepsis should alter the detrimental multiple-organ consequences of sepsis. The development of a bioartificial kidney consisting of a conventional haemofiltration cartridge in series with a renal tubule assist device containing renal proximal tubule cells represents a new therapeutic approach to this clinical disorder. The results to date of large animal studies and recent Phase I/II and Phase II clinical trials show that such a device replaces multiple kidney functions and modifies the sepsis condition to improve survival in ARF.

Stem cells for regeneration of urological structures

OBJECTIVES

This review focuses on advances in regenerative therapies using stem cells in urology.

METHODS

A detailed literature search was performed using the PubMed database of the National Center of Biotechnology Information. Publications of experimental investigations and clinical trials using stem cells in reconstructive urology have been summarized and critically reviewed.

RESULTS

Tissue engineering and autologous cell therapy techniques have been developed to generate prostheses for different urological tissues and organ systems. During the last decade, increasing numbers of studies have described stem cells in the context of therapeutic tools. The ability of adult and embryonic stem cells as well as progenitors to improve bladder wall architecture, improve renal tubule formation, or promote restoration of spermatogenesis or recovery of continence has been investigated in several animal models. Although results have been encouraging, only a myoblast-based therapy of incontinence has reached clinical trials.

CONCLUSIONS

Several populations of adult stem cells and progenitor cells have been studied as useful cellular sources in the treatment and reconstruction of urological organs. However, considerable basic research still needs to be performed to ensure the controlled differentiation and long-term fate of stem cells following transplantation.

Recent applications of regenerative medicine to urologic structures and related tissues

PURPOSE OF REVIEW

A severe shortage of donor tissues and organs exists, which is worsening yearly given the aging population. Currently, patients suffering from diseased and injured organs are treated with transplanted organs or cells. This paper reviews recent advances that have occurred in regenerative medicine and describes application of new technologies to treat diseased or damaged organs and tissues.

RECENT FINDINGS

Although most current strategies for tissue engineering depend upon a sample of autologous cells from the diseased organ of the patient, biopsies from patients with extensive end-stage organ failure may not yield enough normal cells. In these situations, stem cells are envisioned as being an alternative source. Stem cells can be derived from discarded human embryos (human embryonic stem cells), from fetal tissue, or from adult sources (bone marrow, fat, skin). Therapeutic cloning offers a potentially limitless source of cells for tissue engineering applications.

SUMMARY

Recently, scientists in the fields of regenerative medicine and tissue engineering have applied the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues.

Present status and perspectives of bioartificial kidneys

Currently, hemodialysis is not adequate as a renal replacement therapy because it provides intermittent treatment and does not provide the metabolic function of renal tubules. The next generation of artificial kidney should replace intermittent hemodialysis with continuous hemofiltration and provide the full metabolic function of renal tubules. The current decade has witnessed the development of bioartificial kidneys using artificial membranes and renal tubular epithelial cells. Active transport and metabolic functions were confirmed in the confluent monolayers of tubular cells on artificial membranes. Bioartificial kidneys have succeeded in improving the prognosis of patients with multiple organ dysfunction, presumably by lowering plasma cytokine levels in patients. For successful treatment of chronic renal failure using bioartificial kidneys, it is necessary to overcome some technical hurdles such as improving the antithrombogenic properties of the surface of artificial membranes and prolonging the function of renal tubule cells on an artificial membrane. Transfection of functional protein genes into renal tubule cells enables bioartificial tubule devices to increase their transport capacity and metabolic functions such as digoxin secretion and water transport. The development of wearable roller pumps is also essential for the clinical application of a continuous treatment system.

Research Project: Charleston Bioengineered Kidney Project

The goal of Charleston Bioengineered Kidney Project is to engineer a functional living human kidney suitable for surgical implantation using principles of directed tissue self-assembly and tissue fusion. This is a multidisciplinary project which incorporates multiple innovative bioengineering technologies and expertise from a broad spectrum of disciplines. The conceptual framework, engineering principles, design, potential cell source as well as the first preliminary data demonstrating the feasibility of the proposed Charleston Bioengineered Kidney Project are outlined. The potential challenges are described. Finally, the experts' opinion about the proposed project is also presented.

Regulation of chondrocyte differentiation level via co-culture with osteoblasts

The close apposition of osteoblasts and chondrocytes in bone and their interaction during bone development and regeneration suggest that they may each regulate the other's growth and differentiation. In these studies, osteoblasts and chondrocytes were co-cultured in vitro, with both direct and indirect contact. Proliferation of the co-cultured chondrocytes was enhanced using soluble factors produced from the osteoblasts, and the differentiation level of the osteoblasts influenced the differentiation level of the chondrocytes. In addition, the chondrocytes regulated differentiation of the co-cultured osteoblasts using soluble factors and direct contact. These data support the possibility of direct, reciprocal instructive interactions between chondrocytes and osteoblasts in a variety of normal processes and further suggest that it may be necessary to account for this signaling in the regeneration of complex tissues comprising cartilage and mineralized tissue.

The future of hemodialysis membranes

Hemodialytic treatment of patients with either acute or chronic renal failure has had a dramatic impact on the mortality rates of these patients. Unfortunately, this membrane-based therapy is still incomplete renal replacement, as the mortality and morbidity of these patients remain unacceptably high. Much progress must be made to improve the biocompatibility of hemodialysis membranes as well as their hydraulic and permselective properties to remove small solutes and 'middle molecules' in compact cartridges. The next directions of development will leverage materials and mechanical engineering technology, including microfluidics and nanofabrication, to further improve the clearance functions of the kidney to replicate glomerular permselectivity while retaining high rates of hydraulic permeability. The extension of membrane technology to biohybrid devices utilizing progenitor/stem cells will be another substantive advance for renal replacement therapy. The ability to not only replace solute and water clearance but also active reabsorptive transport and metabolic activity will add additional benefit to the therapy of patients suffering from renal failure. This area of translational research is rich in creative opportunities to improve the unmet medical needs of patients with either chronic or acute renal failure.

Differentiated Growth of Human Renal Tubule Cells on Thin-Film and Nanostructured Materials

Over 300,000 Americans are dependent on hemodialysis as treatment for renal failure, and kidney transplantation is limited by scarcity of donor organs. This shortage has prompted research into tissue engineering of renal replacement therapy. Existing bioartificial kidneys are large and their use labor intensive, but they have shown improved survival compared to conventional therapy in preclinical studies and an US Food and Drug Administration-approved phase 2 clinical trial. This hybrid technology will require miniaturization of hemofilters, cell culture substrates, sensors, and integration of control electronics. Using the same harvesting and isolation techniques used in preparing bioartificial kidneys for clinical use, we characterized human renal tubule cell growth on a variety of silicon and related thin-film material substrates commonly used in the construction of microelectromechanical systems (MEMS), as well as novel silicon nanopore membranes (SNMs). Human cortical tubular epithelial cells (HCTC) were seeded onto samples of single-crystal silicon, polycrystalline silicon, silicon dioxide, silicon nitride, SU-8 photoresist, SNMs, and polyester tissue culture inserts, and grown to confluence. The cells formed confluent monolayers with tight junctions and central cilia. Transepithelial resistances were similar between SNMs and polyester membranes. The differentiated growth of human tubular epithelial cells on MEMS materials strongly suggests that miniaturization of the existing bioartificial kidney will be feasible, paving the way for widespread application of this novel technology.

Recent developments in tissue engineering and regenerative medicine

PURPOSE OF REVIEW

Currently, patients suffering from diseased and injured organs are treated with transplanted organs or cells. There is, however, a severe shortage of donor tissues and organs that is worsening yearly given the aging population. This paper reviews recent advances that have occurred in regenerative medicine and describes applications of new technologies to treat diseased or damaged organs and tissues.

RECENT FINDINGS

Most current strategies for tissue engineering depend upon a sample of autologous cells from the diseased organ of the patient. Biopsies from patients with extensive end-stage organ failure, however, may not yield enough normal cells. In these situations, stem cells are envisioned as being an alternative source. Stem cells can be derived from discarded human embryos (human embryonic stem cells), from fetal tissue or from adult sources (bone marrow, fat, skin). Therapeutic cloning offers a potentially limitless source of cells for tissue engineering applications.

SUMMARY

Increasingly, scientists in the fields of regenerative medicine and tissue engineering have applied the principles of cell transplantation, material science and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues.

Cellular to tissue informatics: approaches to optimizing cellular function of engineered tissue

Tissue engineering is a rapidly expanding, multi-disciplinary field in biomedicine. It provides the ability to manipulate living cells and biomaterials for the purpose of restoring, maintaining, and enhancing tissue and organ function. Scientists have engineered various tissues in the body, from skin substitutes to artificial nerves to heart tissues, with varying degrees of success. Although the field of tissue engineering has come a long way since its first successful demonstration by Bisceglie in the 1930s, methods of coaxing them into functional tissues have been predominantly empirical to date. To successfully develop tissue-engineered organs, it is important to understand how to maintain the cells under conditions that maximize their ability to perform their physiological roles, regardless of their environment. In that context, a methodology that combines empirical data with mathematical and statistical techniques, such as metabolic engineering and cellular informatics, to systematically determine the optimal (1) type of cell to use, (2) scaffold properties and the corresponding processing conditions to achieve those properties, and (3) the required types and levels of environmental factors and the operating conditions needed in the bioreactor, will enable the design of viable and functional tissues tailored to the specific requirements of individual situations.

Collagen vitrigel: a novel scaffold that can facilitate a three-dimensional culture for reconstructing organoids

Three-dimensional reconstructed organoids in vitro are valuable for not only regenerative medicine but also drug development. However, the manipulation of conventional three-dimensional cultures is not simple. We describe a nylon membrane ring-embedded or a pressed silk sheet-embedded scaffold made of collagen "vitrigel" that can facilitate three-dimensional cultures for reconstructing an epithelial-mesenchymal model or a hard connective tissue model, respectively. Here we define vitrigel as a gel in a stable state produced by rehydration after the vitrification of a traditional hydrogel. The collagen vitrigel was successfully prepared in three steps involving a gelation process in which a cold and clear neutral salt solution containing type I collagen formed an opaque and soft gel by incubation at 37 degrees C, a vitrification process in which the gel becomes a rigid material like glass after sufficient drying out, and finally a rehydration process to convert the vitrified material into a thin and transparent gel membrane with enhanced gel strength. The framework-embedded collagen vitrigel scaffold that can be easily reversed by forceps was prepared by inserting a nylon ring or a silk sheet in the collagen solution prior to the gelation. The scaffold enabled culturing anchorage-dependent cells on both surfaces of the collagen vitrigel by the manipulation of two-dimensional cultures and consequently resulted in reconstructing a three-dimensional organoid. An intestinal epithelial-mesenchymal model was reconstructed by coculturing fibroblasts on the opposite side of monolayered Caco-2 cells on the nylon ring-embedded collagen vitrigel. Also, fibroblasts seeded on both surfaces of the silk sheet-embedded collagen vitrigel proliferated well and formed multilayers and some cells invaded into the vitrigel framed by the network of numerous strong silk filaments, suggesting a reconstruction of a hard connective tissue model. These data demonstrate that the collagen vitrigel is a valuable scaffold for tissue engineering.

Tissue engineering, stem cells and cloning: current concepts and changing trends

Organ damage or loss can occur from congenital disorders, cancer, trauma, infection, inflammation, iatrogenic injuries or other conditions and often necessitates reconstruction or replacement. Replacement may take the form of organ transplant. At present, there is a severe shortage of donor organs that is worsening with the aging of the population. Tissue engineering follows the principles of cell transplantation, materials science and engineering towards the development of biological substitutes that can restore and maintain normal tissue function. Therapeutic cloning involves the introduction of a nucleus from a donor cell into an enucleated oocyte to generate embryonic stem cell lines whose genetic material is identical to that of its source. These autologous stem cells have the potential to become almost any type of cell in the adult body, and thus would be useful in tissue and organ replacement applications. This paper reviews recent advances in stem cell research and regenerative medicine, and describes the clinical applications of these technologies as novel therapies for tissue or organ loss.

Stem cell approaches for the treatment of renal failure

The inadequacy of current treatment modalities and insufficiency of donor organs for cadaveric transplantation have driven a search for improved methods of dealing with renal failure. The rising concept of cell-based therapeutics has provided a framework around which new approaches are being generated, and its combination with advances in stem cell research stands to bring both fields to clinical fruition. This budding partnership is presently in its very early stages, but an examination of the cell-based therapies currently under development clearly shows the magnitude of the role that stem cells will ultimately play. The issue over reports of unexpected plasticity in adult stem cell differentiation remains a focus of debate, and evidence for bone marrow-derived stem cell contributions to renal repair has been challenged. The search for adult renal stem cells, which could have a considerable impact on much of the work discussed here, appears to be narrowing. The use of embryonic tissue in research continues to provide valuable insights but will be the subject of intense societal scrutiny and debate before it reaches the stage of clinical application. Embryonic stem (ES) cells, with their ability to generate all, or nearly all, of the cell types in the adult body and a possible source of cells genetically identical to the donor, hold great promise but face ethical and political hurdles for human use. Immunoisolation of heterologous cells by encapsulation creates opportunities for their safe use as a component of implanted or ex vivo devices.

Reconstruction of renal glomerular tissue using collagen vitrigel scaffold

The construction of renal glomerular tissue has provided an important tool not only for the understanding of renal physiology and pathology in blood ultrafiltration and cell dysfunction, but also in the application of tissue engineering to glomeruli regeneration and nephritic therapy. In this study, a novel method to reconstruct glomerular tissue combining cultured cells on a collagen vitrigel scaffold is described. The method consists of two newly developed techniques, one to isolate glomerular epithelial and mesangial cells rapidly from kidney, which facilitates the prolongation of cell population doublings and allows a long-term cell culture without losing cellular features, and another to prepare a stable and thin transparent collagen gel membrane termed collagen vitrigel that can facilitate three-dimensional cultures for reconstructing an epithelial-mesenchymal model. By combining the two methods, we cocultured glomerular epithelial and mesangial cells on both surfaces of the collagen vitrigel by the manipulation of two-dimensional cultures, resulting in the successful reconstruction of a three-dimensional glomerular organoid. The coculture results showed that the collagen vitrigel maintains cell growth and cell viability for more than 1 month, and surprisingly, the epithelial layer demonstrated polarity formation, which usually appears in in vivo normal epithelial cells existing at the glomerular basement membrane, but seldom appears in epithelial cells cultured in vitro. Moreover, the coculture results showed that fibronectin, an extracellular matrix component, and integrin beta1, a receptor of fibronectin, were detected in high amounts on both cells, suggesting our collagen vitrigel can provide a suitable environment for cell-cell interactions that stabilize the cell structure and may contribute to the polarity formation of epithelial cells.

The Future of Renal Support: High-Flux Dialysis to Bioartificial Kidneys

Renal failure continues to cause a major burden of morbidity and mortality in both its acute and chronic forms, regardless of advances in current renal replacement therapies. A bioartificial kidney that includes a conventional dialysis filter and a renal tubule assist device containing approximately 10(8) renal proximal tubule cells was recently successfully engineered. This therapeutic modality may decrease the survival gap between current renal replacement therapies and healthy kidney functions and may lessen the heavy burden of morbidity and mortality associated with renal failure, both acute and chronic, in the near future.

Transplantation of metanephroi to sites within the abdominal cavity

A novel approach to circumventing the shortage in transplantable donor organs is the use of embryonic primordia that develop inside the host. Previously published work has shown that transplantation of rat fetal kidney primordia (metanephroi) onto the omentum of adult rat hosts results in growth and development of the metanephroi into functioning kidney units capable of providing a measurable renal function. However, for anatomical and physiological reasons the omentum may not provide the ideal site for transplantation and may limit the maximum renal function that the transplants can achieve. We postulate that it may be possible to increase the renal function of the transplants by transplantation to sites with increased blood flow. To test this we transplanted rat embryonic day 15 metanephroi into the retroperitoneal fat adjacent to major blood vessels in the peritoneum of unilaterally nephrectomized rats; 21 days later the transplants were examined and suitable transplants connected to the host urinary system. Approximately 130 days later the glomerular filtration rate of the connected transplants was analyzed. Our results show that transplantation of metanephroi to the regions highlighted in this study results in an increased presence of urinary cysts, suggesting increased early renal function in the transplants compared to metanephroi transplanted onto the omentum, but most importantly we show that we can increase the renal function of the transplants to a level comparable with other renal therapies such as dialysis. This work suggests life-sustaining renal function could be achieved through transplantation of renal primordia.

Tissue engineering, stem cells, cloning, and parthenogenesis: new paradigms for therapy

Patients suffering from diseased and injured organs may be treated with transplanted organs. However, there is a severe shortage of donor organs which is worsening yearly due to the aging population. Scientists in the field of tissue engineering apply the principles of cell transplantation, materials science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Both therapeutic cloning (nucleus from a donor cell is transferred into an enucleated oocyte), and parthenogenesis (oocyte is activated and stimulated to divide), permit extraction of pluripotent embryonic stem cells, and offer a potentially limitless source of cells for tissue engineering applications. The stem cell field is also advancing rapidly, opening new options for therapy. The present article reviews recent progress in tissue engineering and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Tissue engineering applications of therapeutic cloning

Few treatment options are available for patients suffering from diseased and injured organs because of a severe shortage of donor organs available for transplantation. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for replacement therapy. Scientists in the field of tissue engineering apply the principles of cell transplantation, material science, and engineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. The present chapter reviews recent advances that have occurred in therapeutic cloning and tissue engineering and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Initial clinical results of the bioartificial kidney containing human cells in ICU patients with acute renal failure

BACKGROUND

Acute renal failure (ARF) in intensive care unit patients continues to have mortality rates exceeding 70%, despite hemodialysis or continuous renal replacement therapy (CRRT). The delivery of cellular metabolic function to CRRT may provide more complete renal replacement therapy, thereby changing the natural history of this disease process. An FDA-approved Phase I/II clinical trial on 10 patients has been completed, and demonstrated that this experimental treatment can be delivered safely for up to 24 hours.

METHODS

The bioartificial kidney is a synthetic hemofilter connected in series with a bioreactor cartridge containing approximately 10(9) human proximal tubule cells, as a renal tubule assist device (RAD), within an extracorporeal perfusion circuit utilizing standard hemofiltration pump systems. All 10 patients had ARF and multiorgan failure (MOF), with predicted hospital mortality rates averaging above 85%.

RESULTS

Data indicate that the RAD maintains viability, durability, and functionality in this ex vivo clinical setting. The device also demonstrated differentiated metabolic and endocrinologic activity, with glutathione degradation and endocrinologic conversion of 25-OH-D(3) to 1,25-(OH)(2)-D(3). All but one treated patient with more than a 3-day follow-up in the intensive care unit showed improvement as assessed by acute physiologic scores 1 to 7 days following therapy. Six of the 10 treated patients survived past 30 days. One patient expired within 12 hours after RAD treatment due to his family's request to withdraw ventilatory life support. Three other patients died due to complications from acute or chronic comorbidities unrelated to ARF or RAD therapy. Plasma cytokine levels suggest that RAD therapy produced dynamic and individualized responses in patients. For the subset of patients who had excessive proinflammatory levels, RAD treatment resulted in significant declines in granulocyte colony stimulating factor (G-CSF), interleukin (IL)-6, IL-10, and IL-6/IL-10 ratios.

CONCLUSION

The addition of human renal tubule cell therapy to CRRT has been accomplished and demonstrates metabolic activity with systemic effects in patients with ARF and MOF. These initial clinical results are encouraging, so that a randomized, controlled Phase II clinical trial is underway to further assess the clinical safety and efficacy of this new therapeutic approach.

Renal cell therapy in the treatment of patients with acute and chronic renal failure

Hemodialysis and hemofiltration have been important technologies in saving the lives of patients with acute (ARF) and chronic renal failure by clearing small solutes from plasma and thereby preventing death from acidemia, hyperkalemia, volume overload, and uremia. These therapeutic approaches, however, are still suboptimal, as patients with ARF have mortality rates exceeding 50%, and patients with end-stage renal disease (ESRD) have, on average, a life expectancy of 4-5 years. The preeminent cause of death in patients with ARF is the development of sepsis or the systemic inflammatory response syndrome with resulting systemic vasodilation, hypotension, ischemic injury to solid organs, multi-organ failure, and death. This vasodilation is due to persistent and excessive pro-inflammation. Similarly, the reduced survival times of patients with ESRD on chronic dialysis have been associated with a persistent and chronic systemic pro-inflammatory state. We have hypothesized that the loss of renal tubule cell mass acutely in acute tubule necrosis and chronically in ESRD results in an immunologically dysregulated state leading to excessive pro-inflammation. The replacement of renal tubule cell function may thus change the current dismal prognosis of patients with these disorders. In this regard, this report presents the first patient ever treated with a bioartificial kidney consisting of a synthetic hemofilter in series with a renal tubule assist device (RAD) containing approximately 10(9) human renal tubule cells. This treatment in a critically ill patient with multi-organ failure and ARF in the intensive care unit was associated temporally with improved cardiovascular parameters and enhanced native kidney function. Multiple systemic plasma cytokine levels and gene expression profiles of peripheral white blood cells were also temporally changed with cell therapy. Clinical trials in patients suffering from either ARF or ESRD are currently ongoing to evaluate the influence of the RAD on the inflammatory response in these groups of patients.

Tissue engineering and regenerative medicine: concepts for clinical application

Patients suffering from diseased and injured organs may be treated with transplanted organs. However, there is a severe shortage of donor organs that is worsening yearly given the aging population. Scientists in the field of regenerative medicine and tissue engineering apply the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for tissue engineering applications. The stem cell field is also advancing rapidly, opening new options for therapy. This paper reviews recent advances that have occurred in regenerative medicine and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Embryonic committed stem cells as a solution to kidney donor shortage

The number of human kidney transplants has increased rapidly in recent years, but the need greatly exceeds organ availability. Induction of appropriate kidney differentiation and growth from stem or progenitor cell populations represents an attractive option to combat chronic kidney donor shortage. In an analogy to haematopoietic stem cells, which are much more efficient in giving rise to blood than to other cell types, if any at all, renal stem cells could afford an unlimited source for regenerating nephrons. While a single nephrogenic stem cell has not been characterised, indirect evidence suggests that a renal stem cell population is contained within the metanephric mesenchyme, which along with a branch of the Wolffian duct represents the direct precursor of the mature kidney. Human tissue fragments derived from these developing precursors can regenerate renal structures when grafted into mice. Moreover, recent data pinpoints a window of time in human and pig kidney development that may be optimal for transplantation into mature recipients. 'Window' transplants are defined by their remarkable ability to grow, differentiate and undergo vascularisation, achieving successful organogenesis of urine-producing miniature kidneys with no evidence of transdifferentiation into non-renal cell types, lack of tumourigenicity and reduced immunogenicity compared with adult counterparts. In contrast, 'non-window' transplants (earlier or later in gestation) can form teratomas or are more prone to immune rejection and are less suitable for organogenesis. Hopefully, the use of stage-specific early human and porcine kidney precursors to cultivate mature kidney cells in vivo, possibly in conjunction with other modalities of stem cell technology and tissue engineering, will prove valuable to sustain life in patients with failing kidneys.

Research into the development of a wearable bioartificial kidney with a continuous hemofilter and a bioartificial tubule device using tubular epithelial cells

Current hemodialysis treatment is insufficient because of intermittent treatment and loss of tubular function. In order to overcome the loss of tubular function, a bioartificial kidney has been developed consisting of continuous hemofiltration (CHF) with 10 L/day of filtrate and a bioartificial tubule device using proximal tubular epithelial cells and hollow fiber membranes. Ten L/day of CHF enabled plasma levels of urea, creatinine, uric acid and, beta2-microglobulin in eight renal failure patients to be maintained at remarkably low levels. The concept was tested with 6 L (4 mL/min) of 10 L/day (7 mL/min) filtrate regenerated by a bioartificial tubule device and 4 L/day (3 mL/min) replaced by food and drinks. Lewis lung cancer-porcine kidney 1 (LLC-PK1) cells with a cell density of 107 cells/mL were seeded inside polysulfone hollow fiber modules four times at 1 h intervals while rotating the module 90 degrees each time, and were cultured for 48 h to form confluent monolayers. The leak rates of urea and creatinine across LLC-PK1 cell-attached polysulfone membrane modules (membrane areas: 56 cm2 and 4000 cm2) were investigated. Via conversion from 56 m2 to 1 m2 hollow fiber modules with LLC-PK1 cells for 24 h, the transport rates of H2O, glucose and Na+ were, respectively, 40, 65 and 35% of the target transported amounts from 6 L/day of filtrate. The rates are expected to approach 100% when 4-5 g/dL of albumin is added to the basal portion of the medium since the results were obtained without the addition of albumin for colloidal osmotic pressure.

Advances in cell therapy for renal failure

Cell therapy is one of the most exciting fields in translational medicine. It stands at the intersection of a variety of rapidly developing scientific disciplines: stem cell biology, immunology, tissue engineering, molecular biology, biomaterials, transplantation biology, regenerative medicine and clinical research. Cell-based therapy may develop into a new therapeutic platform to treat a vast array of clinical disorders. Blood transfusions and bone marrow transplantation are prime examples of the successful application of cell-based therapeutics; but recent advances in cellular and molecular biology have expanded the potential applications of this approach. Although recombinant genetic engineering to produce a variety of therapeutics, such as human erythropoietin and insulin has proven successful, these treatments are unable to completely correct or reverse disease states, because most common disease processes are not due to the deficiency of a single protein but develop due to alterations in the complex interactions of a variety of cell components. In these complex situations, cell-based therapy may be a more successful strategy by providing a dynamic, interactive and individualized therapeutic approach that responds to the pathophysiological condition of the patient. In this regard, cells may provide innovative methods for drug delivery of biologics, immunotherapy, and tissue regenerative or replacement engineering [Nature 392 (1998) 518-524, Nat Biotechnol 20 (2002) 339-343]. The translation of this discipline to medicinal practice has tremendous potential, but in many applications technological issues need to be overcome. Since many cell-based indications are already being evaluated in the clinic, the field appears to be on the threshold of a number of successes. This review will focus on our group's use of human stem/progenitor cells in the treatment of acute and chronic renal failure as extensions to current successful renal substitution processes of hemodialysis and hemofiltration.

Therapeutic cloning applications for organ transplantation

A severe shortage of donor organs available for transplantation in the United States leaves patients suffering from diseased and injured organs with few treatment options. Scientists in the field of tissue engineering apply the principles of cell transplantation, material science, and engineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for tissue engineering applications. The present chapter reviews recent advances that have occurred in therapeutic cloning and tissue engineering and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Tissue engineering for the replacement of organ function in the genitourinary system

Acquired and congenital abnormalities may lead to genitourinary organ damage or loss, requiring eventual reconstruction. Tissue engineering follows the principles of cell transplantation, materials science, and engineering toward the development of biological substitutes that would restore and maintain normal function. Tissue engineering may involve matrices alone, wherein the body's natural ability to regenerate is used to orient or direct new tissue growth, or the use of matrices with cells. Both synthetic and natural biodegradable materials have been used, either alone or as cell delivery vehicles. Tissue engineering has been applied experimentally for the reconstitution of several urologic tissues and organs, including bladder, ureter, urethra, kidney, testis, and genitalia. Fetal applications have also been explored. Recently, several tissue engineering technologies have been used clinically including the use of cells as bulking agents for the treatment of vesicoureteral reflux and incontinence and urethral replacement. Recent progress suggests that engineered genitourinary tissues may have clinical applicability in the future.

Therapeutic Cloning and Tissue Engineering

A severe shortage of donor organs available for transplantation in the United States leaves patients suffering from diseased and injured organs with few treatment options. Scientists in the field of tissue engineering apply the principles of cell transplantation, material science, and engineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for tissue engineering applications. The present chapter reviews recent advances that have occurred in therapeutic cloning and tissue engineering and describes applications of these new technologies that may offer novel therapies for patients with end-stage organ failure.

Cell therapy of renal failure

The kidney is unique in that it is the first organ for which long-term ex vivo substitutive therapy has been available. The first hemodialyzer was successfully applied to a human patient with acute renal failure in 1948, and the first successful allograft transplantation was performed with a kidney in 1951. Both treatments are used today. There is ample evidence that the small solute clearance function provided by hemodialysis does not confer the same survival advantage as a functional kidney, both in acute and in chronic renal failure. To mimic the metabolic, endocrine, and immunologic functions of the kidney, our group has successfully engineered a bioartificial device that includes a conventional dialysis filter and a bioreactor containing 10(9) renal proximal tubule cells. We have demonstrated differentiated activity of these cells both in vitro and ex vivo in a large animal model. The bioreactor has been shown to confer a survival advantage in two large animal models of gram-negative sepsis, seemingly due to modulation of inflammatory mediators. This bioartificial kidney has now completed a Phase I clinical trial in acute renal failure.

Renal cell therapy is associated with dynamic and individualized responses in patients with acute renal failure

BACKGROUND

Renal cell therapy in conjunction with continuous hemofiltration techniques may provide important cellular metabolic activities to patients with acute renal failure (ARF) and may thereby change the natural history of this disorder. The development of a tissue-engineered bioartificial kidney consisting of a conventional hemofiltration cartridge in series with a renal tubule assist device (RAD) containing 10(9) human renal proximal tubule cells provides an opportunity to evaluate this form of therapy in patients with ARF in the intensive care unit.

METHODS

Nine patients with ARF and multi-organ systems failure (MOSF) have been treated so far with a tissue-engineered kidney in an FDA-approved Phase I/II clinical study currently underway. Acute physiologic parameters and serum cytokine levels were assessed before, during and after treatment with a bioartificial kidney.

RESULTS

Use of the RAD in this clinical setting demonstrates maintenance of cell viability and functionality. Cardiovascular stability appears to be maintained during RAD treatment. Human tubule cells in the RAD demonstrated differentiated metabolic and endocrinologic activity. Acute physiologic and plasma cytokine data demonstrate that renal cell therapy is associated with rapid and variable responses in patients with ARF and MOSF.

CONCLUSION

The initial clinical experience with the bioartificial kidney and the RAD suggests that renal tubule cell therapy may provide a dynamic and individualized treatment program as assessed by acute physiologic and biochemical indices.

Cell therapy with a tissue-engineered kidney reduces the multiple-organ consequences of septic shock

OBJECTIVE

Gram-negative septic shock has a clinical mortality rate approaching 50%. The cause of death is secondary to a systemic inflammatory response syndrome with resulting cardiovascular collapse, ischemic damage to vital organs, and multiple-organ systems failure. Renal tubule cell injury occurs early in septic shock but is not clinically appreciated. Since renal tubule cells appear to play a critical role in the immunoregulation of stress states, renal cell therapy during septic shock may alter the detrimental multiple-organ consequences of systemic Gram-negative infection. The development of a tissue-engineered bioartificial kidney consisting of a conventional hemofiltration cartridge in series with a renal tubule assist device (RAD) containing 109 renal proximal tubule cells may be a new therapeutic approach to this clinical disorder.

DESIGN

Laboratory study.

SETTING

University medical school.

SUBJECTS

Pigs weighing 30-35 kg.

INTERVENTIONS

To assess the effect of the bioartificial kidney and the RAD in septic shock, pigs were administered 30 x 10(10) bacteria/kg body weight of Escherichia coli into the peritoneal cavity and within 1 hr were immediately placed in a continuous venovenous hemofiltration extracorporeal circuit with either a sham RAD without cells or a RAD with cells.

MEASUREMENTS AND MAIN RESULTS

In this animal model, septic shock resulted within hours in acute tubule necrosis in the kidneys of all animals. Renal cell therapy resulted in significantly higher cardiac outputs and renal blood flow rates in treated animals compared with sham controls. RAD treatment also was associated with significantly lower plasma circulating concentrations of interleukin-6 and interferon-gamma compared with sham-treated animals. IL-6 release rates from peripheral blood mononuclear cells isolated from RAD-treated animals were significantly higher after endotoxin stimulation than those isolated from control animals. These physiologic and molecular alterations were associated with nearly a doubling of the average survival time in the RAD-treated group compared with the sham control group.

CONCLUSION

These results demonstrate that renal cell therapy ameliorates cardiac and vascular dysfunction, alters systemic cytokine abnormalities, and improves survival time in a large animal model of Gram-negative septic shock. A cell therapeutic approach with a tissue-engineered bioartificial kidney may be a new treatment modality for this current unmet medical need.

Development of bioartificial kidneys

Bioartificial kidneys, which consist of continuous haemofiltration and bioartificial tubules using tubular epithelial cells, have been studied since 1987. The bioartificial tubules consist of hollow fibre modules and tubular epithelial cells grown on the hollow fibre membranes after coating with extracellular matrices. The kinds of tubular epithelial cells, extracellular matrices and artificial membranes therefore have been investigated and then the most appropriate cell and materials have been selected on the basis of the development of bioartificial kidneys. Successful seeding to form confluent monolayers on the surfaces of hollow fibers is not easy, but this method has already been established. Renal assist devices using human renal proximal tubular epithelial cells have been used in the treatment of acute renal failure patients with endotoxemia by Humes et al., and successful treatment of acute renal failure patients with these devices was reported in 2001 and 2002, in which the improved mortality rate of those patients was shown. A bioartificial kidney, in which cDNA of multidrug resistance protein-1 was transfected into tubular epithelial cells that were then grown on the outer surfaces of hollow fibers, was used in the experimental treatment of digoxin-intoxicated dogs. Rapidly reduced digoxin levels were noted in the plasma of the dogs after treatment. Bioartificial kidneys, however, have never been used in the long-term treatment of a maintenance dialysis patient, although patients need those kidneys. In order to establish long-term treatment with a bioartificial kidney, each haemofilter has to function for more than one week without systemic anticoagulation and a bioartificial tubule must function for 3-4 weeks.

Tissue engineering, stem cells, and cloning for the regeneration of urologic organs

Tissue engineering efforts are currently being undertaken for every type of tissue and organ within the urinary system. Most of the effort expended to engineer genitourinary tissues has occurred within the last decade. Tissue engineering techniques require a cell culture facility designed for human application. Personnel who have mastered the techniques of cell harvest, culture, and expansion as well as polymer design are essential for the successful application of this technology. Various engineered genitourinary tissues are at different stages of development, with some already being used clinically, a few in preclinical trials, and some in the discovery stage. Recent progress suggests that engineered urologic tissues may have an expanded clinical applicability in the future.