The pulmonary microvasculature entraps induced vascular progenitor cells (iVPCs) systemically delivered after cardiac ischemia-reperfusion injury: Indication for preservation of heart function via paracrine effects beyond engraftment

Objective: Stem cell-based regenerative therapies have been intensively studied with the aim to define an ideal cell type for the treatment of myocardial infarction. We tested systemically delivered, platelet-targeted induced vascular progenitor cells (iVPCs) to study their potential to salvage damaged myocardium after ischemia-reperfusion injury. Methods: Using a mouse model of ischemia-reperfusion injury, we tested the potential of platelet- targeted iVPCs (1x106 targ-iVPCs) compared to non-targ-iVPCs and a saline control. Bioluminescence imaging, echocardiography and histological analyses were performed. Results: 4 weeks after ischemia-reperfusion injury, systemic delivery of targ-iVPCs led to reduced fibrosis and infarct size (PBS: 25.7±3.9 vs targ-iVPC: 18.4±6.6 vs non-targ-iVPC: 25.1±3.7 %I/LV, p<0.05), increased neovascularization, and restored cardiac function (PBS: 44.0±4.2 vs targ-iVPC: 54.3±4.5 vs non-targ-iVPC: 46.4±3.8 %EF, p<0.01). Cell tracking experiments revealed entrapment of intravenously injected iVPCs in the pulmonary microvasculature in both cell-treated groups. Conclusions: Systemic delivery of iVPCs after cardiac ischemia-reperfusion injury is limited by pulmonary entrapment of the cells. Nevertheless, targ-iVPCs reduced infarct size, fibrosis, increased neovascularization, and most importantly retained cardiac function. These findings contribute to the mechanistic discussion of cell-based therapy and ultimately identify activated platelet-targeted iVPCs as candidates for cell therapy and also describe cell therapy benefits without the necessity of engrafting.