Adult Stem Cell Therapy for Injured Solid-Organ Tissue (with Emphasis on Cardiac Tissue Repair)

Adult hematopoietic tissue-derived stem cells are primarily used for hematopoietic reconstitution in patients with malignant lympho-hematopoietic disorders undergoing stem cell transplantation. Their therapeutic use for solidorgan tissue repair such as cardiac tissue is a novel treatment strategy. Besides hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs) and even solid-organ tissue resident stem cells (e.g. cardiac stem cells [CSC]) are known to contribute to solid-organ tissue repair. Stem cell delivery for cardiac tissue repair is by transvascular or intramyocardial injection. Myocardial tissue engineering takes advantage of biocompatible materials as stem cell carriers (scaffolds). Stem cell concentration at the site of tissue injury and engineering the stem cell microenvironment are additional components that determine treatment outcome. Mechanisms that explain how stem cells generate solid-organ specific cells include nuclear re-programming (transdifferentiation), cell fusion, and paracrine secretion of transplanted cells (e.g., MSCs). One preferred therapeutic concept is the stepwise induction of neovascularization followed by activation of the solid-organ resident stem cell pool. Cardiac tissue repair in patients with acute myocardial infarction is currently at the forefront of clinical stem cell treatment research. The outcome of major clinical trials will be discussed.