CD34 and acute coronary syndrome: A meta-analysis by Rigato et al. showed that the numerical reduction of circulating CPCs, in particular CD34+/CD133+ hematopoietic cells, was associated with a 2-fold increased risk of future cardiovascular events and cardiovascular death in patients with suspected coronary artery disease, acute coronary syndrome, previous stroke, or in patients without acute events but with cardiovascular risk factors (32).