ABSTRACT

In 1997, Asahara and colleagues [1] reported that some circulating blood cells possessed the potential to differentiate in vitro into adherent cells displaying cell surface antigens typical for endothelial cells and simultaneous loss of many typical hematopoietic markers. The injection of these adherent endothelial-like cells promoted vascular repair and restoration of blood ow in animals with induced hindlimb ischemia. The cells displaying these properties were called circulating endothelial progenitor cells (EPCs). EPC was proposed to be derived from circulating bone marrow-derived cells expressing the cell surface proteins CD34 and/or the kinase insert domain receptor (KDR; the human vascular endothelial growth factor 2 receptor). The authors further proposed that circulating EPC could integrate into the areas of ischemic tissue in the experimentally injured animals and directly assist in new blood vessel formation, thus, displaying postnatal vasculogenic activity. Thousands of papers have been published under the term EPC since that rst publication in 1997. EPC has been evaluated as a biomarker for a variety of cardiovascular diseases [2-4], stroke [5,6], autoimmune disease [7], cancer [8-11], diabetes [12-14], pulmonary diseases [15,16], and infections [17,18]. EPC plays roles in vascular repair and regeneration in a host of preclinical animal models [19-21] and in numerous clinical trials of cardiovascular disorders in human subjects (see www.clinicaltrials.gov). One would expect that this vast number of papers would provide a clear indication of the unique EPC-identifying markers; however, no unique identier for this cell has been reported for human subjects. This has led to great confusion, controversy, and debate regarding the best methods for dening human EPC [22-24]. Nonetheless, investigators have pushed forward to test the safety and benet of these potentially useful cells in human subjects in an attempt to treat serious systemic illnesses that lack highly effective current therapies [23,25]. Given modest improvements in patient outcomes, a trend in recent clinical trials is to isolate more

CONTENTS

1.1 Introduction ............................................................................................................................3 1.2 Methods to Dene Human EPCs ........................................................................................4 1.3 mRNA Expression Pattern Analysis of EPC Subsets .......................................................7 1.4 MicroRNA Expression Pattern Analysis of EPC Subsets.................................................8 1.5 Proteomic Approaches to Comparison of EPC Subsets ...................................................9 1.6 Summary ............................................................................................................................... 10 References ....................................................................................................................................... 10

specic subsets of bone marrow cells to enrich the autologous cell product in hopes of providing more benet to the patients [25,26].