At the same time, developing technologies to deliver miRNAs to specific cells in vivo is highly essential for their therapeutic application. Despite having many strategies reported, the successful delivery approach in vivo is still limited. Clinical translation has been hampered by dose-dependent toxicity upon systemic administration [133, 134]. Intriguingly, Kalluri’s recent study showed that exosomes derived from normal fibroblast-like mesenchymal cells exhibited a superior ability to deliver RNAi to suppress pancreatic cancer growth, and showed minimum cytotoxic effects in vivo compared to synthetic nanoparticles. The engineered exosomes (known as iExosomes) target oncogenic KRAS with enhanced efficacy probably due to that CD47 on exosomes surface contributed to the evasion from immune clearance in the circulation, and KRAS-stimulated macropinocytosis increased pancreatic cancer cells uptake of iExosomes . This study offers insight into the therapeutic potential of exosomes in the delivery of nucleic acid-based drugs. However, in terms of using exosomes for specific targeting of angiogenesis-related miRNAs in tumor cells or ECs, there are several aspects to consider. New targeting moieties should be tested for selective homing of exosomes to certain tumor cells and tumor-associated ECs. New targeting moieties, such as peptides and antibody fragments, could be cloned into exosomal surface proteins, or directly attached to the surface of exosomes through chemical conjugation, therefore bypassing time-consuming cloning procedures. Furthermore, the use of miRNA sponge would allow for persistent suppression of miRNA in target tissues following exosome delivery. Additionally, it is critical to find a robust cell source that produces high quantities of exosomes for use in miRNA delivery. For instance, Myc-immortalized human ES-derived mesenchymal stem cells (MSCs) have been demonstrated as a scalable source for production of therapeutic exosomes for regenerative medicine .