Cell therapy for refractory angina: time for more ACTion.

Chronic ischemic heart disease is a major cause of patient morbidity and healthcare expenditure. The development of therapies aimed to enhance angiogenesis is targeted for patients with severe ischemic symptoms that persist despite optimized medical therapy and in whom coronary revascularization procedures are no longer feasible or helpful. Several different stem, progenitor and mature cell types have so far shown potential to improve myocardial perfusion and vascularity after transplantation in preclinical models of ischemia. However, human studies of cell-based transfer have heavily focused on preventing cardiac remodeling and dysfunction in the setting of myocardial infarction, while relatively few have addressed the use of cells to treat patients suffering from chronic debilitating angina. To this end, the recent ACT34-CMI trial represents a seminal milestone in the clinical evolution of cell therapy for chronic ischemic heart disease. In this phase II placebo-controlled study, myocardial injection of autologous peripheral blood-derived CD34+ progenitor cells was shown to confer considerable benefit for symptom frequency and exercise tolerance in patients with refractory, class III and IV angina. The present commentary reviews the key lessons from this unique trial and considers its contributions in moving the field of cell-based cardiovascular research forward.