[The kidney].

Whole-organ engineering of the kidney is particularly difficult because of its structural complexity and of the morphological and functional heterogeneity of renal cell types. As for other organs, research is currently focused on:--the matrix to support recellularization: synthetic, biodegradable or biological. Use of the extracellular matrix as a biological scaffold is the most promising approach. Rodent, porcine and rhesus monkey kidneys have been decellularized to obtain scaffolds with a preserved extracellular matrix and vasculature.--The source of cells for recellularization: embryonic stem cells, fetal cells, adult-derived stem cells, progenitor cells and adult-derived inducible, pluripotent stem cells have all been used. Nephron development results from mutual inducive interactions between the urethral bud and the metanephric mesenchyme, a process that can be reproduced in vitro. Ex-vivo "fabrication" of a kidney that could be implanted with no risk of rejection in patients with chronic renal failure appears ultimately feasible. Another area of research is the use of renal assistance devices--the bioartificial kidney--based on a bioreactor containing renal epithelial cells derived from tubules that maintain their reabsorptive, metabolic and endocrine functions. Phase II clinical trials have given encouraging results.