Harnessing Platelet-Endothelial Interactions for Exosome Delivery

PROJECT SUMMARY
Studies have demonstrated that adult stem cells such as mesenchymal stem cells (MSCs) repair
myocardial infarction (MI) or ischemia/reperfusion (I/R) injury by indirect paracrine mechanisms rather than by
differentiation and tissue replacement. In the past decade, exosomes have emerged as promising cell-free
agents for treating ischemic injury. Several exosome-based therapeutic companies have launched early phase
clinical trials. Like most therapeutics, there is an urgent need for effective delivery strategy to ensure a
sufficient number of exosomes to reach the injured tissue. Since they are nanosized natural lipid bilayer
particles, one option is vascular delivery. However, high and repeated dosing is needed due to a large degree
of off-target distribution to the mononuclear phagocyte system and other organs, such as the liver, spleen and
lungs. Moreover, MSC-derived exosomes (MSC-XOs) need to compete with naturally existing exosomes in
body fluids. Cellular binding and uptake of MSC-XOs also hinder the therapeutic effects. Novel approaches are
required to deliver therapeutic exosomes to cells in injured tissues. Ideally, modified exosomes should 1)
reduce the clearance by the mononuclear phagocyte system, 2) bind to injured blood vessels, and 3) be
efficiently uptake by target cell types in injured tissues. It has been established that acute MI can induce
vascular damage and expose components of the subendothelial matrix including collagen, fibronectin and von
Willebrand factor (vWF) to recruit platelets. Platelets can bind to and accumulate on injured vasculature
following MI. Instead of generically modifying the parental cells or chemically engineering exosomes, we used
platelet membranes to envelope exosomes (to make P-XOs) and increase their macropinocytosis-mediated
cellular internalization, and their ability to target the injured tissue. In this proposed study, we plan to
investigate the fabrication, characterization and toxicity of P-XOs (AIM 1). After that, we will test the therapeutic
effect of P-XOs on a mouse model (AIM 2) and a porcine model (AIM 3) with cardiac injury. Our study will
provide new insights on cellular internalization mechanism of exosomes, targeting properties and mechanism
of the P-XOs treatment. Together, the proposed mechanistic and translational experiments will provide a
scientific premise to understand system administrated exosomes while suggesting new approaches for
promoting targeting and therapeutic effect of therapeutic exosomes.