The IMPACT-CABG trial: A multicenter, randomized clinical trial of CD133⁺ stem cell therapy during coronary artery bypass grafting for ischemic cardiomyopathy

Objectives: The IMPACT-CABG trial is the first North American multicenter phase II randomized study of intramyocardial delivery of autologous CD133⁺ stem cells in patients with chronic ischemic cardiomyopathy undergoing coronary artery bypass grafting. The primary objective was to demonstrate safety, including freedom from major adverse cardiac events. The secondary objective was to evaluate feasibility of same-day autologous cell preparation. Although the trial was not powered to evaluate LV function, exploratory data were collected.

Methods: After 7 open-label patients who received cells, patients randomly received stem cells or placebo (N = 40 total, 20 per center). After completion of coronary anastomoses, up to 10 million CD133⁺, CD34⁺, CD45⁺ triple-positive cells or placebo were injected into the infarct and border zones. Patients were followed up clinically and underwent magnetic resonance imaging preoperatively and after 6 months.

Results: There were no procedural complications from bone marrow isolation and cell injection, no in-hospital mortality, and no protocol-related complications. Four patients had transient renal insufficiency, with 1 death during 6-month follow-up. Magnetic resonance imaging revealed that left ventricular volumes and ejection fractions improved in all patients (no difference between groups).

Conclusions: The trial successfully met both primary and secondary objectives, demonstrating that same-day isolation and autologous CD133⁺ cell delivery with coronary artery bypass grafting is safe and feasible. The positive findings support a larger randomized, multicenter trial, with higher numbers of transplanted cells to demonstrate beneficial effects. The upcoming IMPACT-CABG II trial will evaluate higher cell doses and pharmacologic enhancement to determine whether these cells improve perfusion and myocardial function.