An understanding of endothelial progenitor cell (EPC) biology offers the tantalising reward of addressing some of the fundamental issues in biology relating to vascular repair as well as a potential solution to the holy grail of coronary intervention—the prevention of restenosis.

However, the paper by Mills et al in this month’s issue of Heart1 (see page 2003) raises further questions in this already complex area of research that is struggling to define a method for characterising EPCs and even the form in which they may exist.2 The work reported here uses two methods to characterise EPCs (one based on surface marker expression and the other on functional capacity) following angioplasty and, interestingly, shows that while the level of circulating “EPCs” with a functional phenotype increases, no increase is seen in the putative progenitor cells (CD34⁺KDR⁺) as characterised by surface marker expression. …