Stem Cell Therapy

Cell therapy involves the direct administration of cells into the body for healing purposes. The units of therapy in this approach are single cells. For regenerative medicine, the ultimate objective of cell therapy is to establish a long-term graft with the capacity to perform organ functions. A practical example is bone marrow transplantation, in which HSC are the units of therapy, engraft in the bone marrow, and repopulate the entire blood lineage.105

Intravenous administration describes the direct injection of dissociated cells into the bloodstream using a syringe. It is the simplest delivery route for cell therapies and is used for HSC therapy in the clinic. Kidney cells, however, are different from blood cells and do not typically circulate throughout the body. The kidney is furthermore a densely-packed organ with no obvious route for stem cells to traverse from the bloodstream into the nephrons. Whether kidney stem cells have the ability to engraft and regenerate the kidney after intravenous administration therefore needs to be tested in preclinical animal models. In these experiments, the kidneys are typically subjected to acute injury. This damages the glomerular filtration barrier, which can enhance penetration of cells into the kidney and subsequent engraftment.

In one example, human iPS cell-derived cells expressing a variety of NPC and adult kidney cell markers were injected into the mouse tail vein 24 hours after administration of the nephrotoxic drug cisplatin.106 Extensive engraftment was reported in proximal tubules, which coincided with a 55% reduction in urea levels in treated mice, compared with control animals administered with saline or undifferentiated iPS cells.106 These experiments suggest a possible benefit of iPS-derived kidney cells on kidney injury. However, the isolated cells were not shown to demonstrate the ability to form kidney organoids with segmented nephrons. It is therefore unclear whether the implanted cells contained bona fide NPC or whether new nephrons were actually formed.

Intravenous administration has also been applied to adult kidney cell populations. Human glomerular epithelial transitional cells (see earlier), administered intravenously into a mouse model of chemically-induced podocytopathy, were found in glomeruli, and were associated with a decrease in proteinuria.107 These cells also contributed to tubules after acute injury.80 As these cells cannot form new nephrons, this approach seeks to repair and replace, rather than to completely regenerate.

MSC can be readily obtained, for instance from a patient's adipose tissue. Intravenous administration of MSC in experimental models can have a beneficial effect on ischemia-reperfusion injury.99,102,108 This benefit can be obtained even in the absence of MSC engraftment, likely via a paracrine effect. However, MSC administered to injured kidneys do not contribute tangibly to new nephron formation and can differentiate ectopically into undesirable fat cells or fibroblasts within glomeruli.108,109 Collectively, these findings suggest that intravenous administration of cell therapeutics may provide some benefit in cases where the glomerular filtration barrier has been compromised but may also have unwanted side effects.

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Cell Therapy - an overview | ScienceDirect Topics