CD34 and myocardial infarction: In a study using a mouse model for myocardial infarction, Mackie et al. (74) confirmed that injecting CD34 + HSCs pretreated by Sonic Hedgehog (Shh) and the exosomes secreted from such stem cells into the peripheral area of myocardial infarction could not only enhance the vitality of CD34 + cells and induced angiogenesis in the infarct area but could also stimulate the activation of Shh signal pathway of other cell types through exosomes, significantly promoting angiogenesis and reduced myocardial infarction area.