Wilms' tumor: starting off the kidney all over again?

Current Cell-Based Strategies for Whole Kidney Regeneration

Chronic kidney diseases affect thousands of people worldwide. Although hemodialysis alleviates the situation by filtering the patient's blood, it does not replace other kidney functions such as hormone release or homeostasis regulation. Consequently, orthotopic transplantation of donor organs is the ultimate treatment for patients suffering from end-stage renal failure. Unfortunately, the number of patients on the waiting list far exceeds the number of donors. In addition, recipients must remain on immunosuppressive medications for the remainder of their lives, which increases the risk of morbidity due to their weakened immune system. Despite recent advancements in whole organ transplantation, 40% of recipients will face rejection of implanted organs with a life expectancy of only 10 years. Bioengineered patient-specific kidneys could be an inexhaustible source of healthy kidneys without the risk of immune rejection. The purpose of this article is to review the pros and cons of several bioengineering strategies used in recent years and their unresolved issues. These strategies include repopulation of natural scaffolds with a patient's cells, de-novo generation of kidneys using patient-induced pluripotent stem cells combined with stepwise differentiation, and the creation of a patient's kidney in the embryos of other mammalian species.

Direct transcriptional reprogramming to nephron progenitors

The direct reprogramming of one cell fate to another represents an attractive option for the generation of specific endpoints for cellular therapy. This appears to require both the reactivation of critical transcription factor regulatory networks and chromatin remodelling. The direct reprogramming of mature renal epithelial cell lines to a nephron progenitor state has been reported. However, our limited knowledge of the optimal growth conditions to maintain this state remains a challenge for their therapeutic application. Here we examine whether nephron progenitors as an endpoint of direct reprogramming have been suitably defined and whether alternative options for reprogramming to kidney exist.

Wilms' tumor blastemal stem cells dedifferentiate to propagate the tumor bulk

An open question remains in cancer stem cell (CSC) biology whether CSCs are by definition at the top of the differentiation hierarchy of the tumor. Wilms’ tumor (WT), composed of blastema and differentiated renal elements resembling the nephrogenic zone of the developing kidney, is a valuable model for studying this question because early kidney differentiation is well characterized. WT neural cell adhesion molecule 1-positive (NCAM1⁺) aldehyde dehydrogenase 1-positive (ALDH1⁺) CSCs have been recently isolated and shown to harbor early renal progenitor traits. Herein, by generating pure blastema WT xenografts, composed solely of cells expressing the renal developmental markers SIX2 and NCAM1, we surprisingly show that sorted ALDH1⁺ WT CSCs do not correspond to earliest renal stem cells. Rather, gene expression and proteomic comparative analyses disclose a cell type skewed more toward epithelial differentiation than the bulk of the blastema. Thus, WT CSCs are likely to dedifferentiate to propagate WT blastema.

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The Wilms’ tumor (WT) blastema can be exclusively propagated in mice

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Gene and protein analyses place the WT CSC at a specific developmental stage

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WT CSCs do not correspond to the earliest renal stem cells

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WT CSCs are likely to dedifferentiate to propagate WT blastema

Human renal cancer stem cells

Cancer stem cells (CSCs), isolated in renal carcinomas, exhibit tumor-initiating capabilities and pluripotency. No specific CSC markers have been identified so far; therefore, their characterization is mainly based on functional studies. As they are resistant to chemo and radio therapy, renal CSCs may have a relevant role in tumor establishment, progression, and recurrence. CSCs were also shown to contribute to intra-tumor vasculogenesis through an endothelial differentiation and to favor the generation of the pre-metastatic niche through the release of exosomes/microvesicles.

Wilms tumor--a renal stem cell malignancy?

Wilms' tumor (WT; nephroblastoma) is the most common pediatric renal malignancy and rated fourth in overall incidence among childhood cancers. It is viewed as a prototype of differentiation failure in human neoplasia as it recapitulates the histology of the nephrogenic zone of the growing fetal kidney. The cellular origin of WT is unclear. However, recent genomic, genetic and epigenetic studies point to an early renal stem/progenitor cell that undergoes malignant transformation as the source for WT. In this context, classical WT shares genes and pathways activated in progenitors committed to the renal lineage. However, direct proof and characterization of the WT initiating cell have remained elusive. Novel methodologies recently adopted from the cancer stem cell scientific field, including the analysis of sorted single human tumor cells, have been applied to WT. These have enabled the identification of cell sub-populations that show similarities-in terms of molecular marker expression-to human fetal kidney progenitors and are, therefore, likely to be derivatives of the same lineage. Further elucidation of the WT cancer stem cell or the cell of origin in human tumors and in transgenic mouse models that generate murine tumors may not only provide novel therapeutic targets but also shed light on the normal kidney stem cell.