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Purpose: Exosomes deliver signals to target cells and could thus be exploited as an innovative therapeutic tool. We investigated the ability of membrane TRAIL-armed exosomes to deliver proapoptotic signals to cancer cells and mediate growth inhibition in different tumor models. Experimental Methods and Results: K562 cells, transduced with lentiviral human membrane TRAIL, were used for the production of TRAIL+ exosomes, which were studied by nanoparticle tracking analysis, cytofluorimetry, immunoelectronmicroscopy, Western blot, and ELISA. In vitro, TRAIL+ exosomes induced more pronounced apoptosis (detected by Annexin V/ propidium iodide and activated caspase-3) in TRAIL-death receptor (DR)5+ cells (SUDHL4 lymphoma and INT12 melanoma), with respect to the DR5 - DR4+ KMS11 multiple myeloma. Intratumor injection of TRAIL+ exosomes, but not mock exosomes, induced growth inhibition of SUDHL4 (68%) and INT12 (51%), and necrosis in KMS11 tumors. After rapid blood clearance, systemically administered TRAIL+ exosomes accumulatedintheliver,lungs,andspleenandhomedtothetumor site, leading to a significant reduction of tumor growth (58%) in SUDHL4-bearing mice. The treatment of INT12-bearing animals promoted tumor necrosis and a not statistically significant tumor volume reduction. In KMS11-bearing mice, despite massive perivascular necrosis, no significant tumor growth inhibition was detected. Conclusions: TRAIL-armed exosomes can induce apoptosis in cancer cells and control tumor progression in vivo. Therapeutic efficacy was particularly evident in intratumor setting, while depended on tumor model upon systemic administration. Thanks to their ability to deliver multiple signals, exosomes thus represent a promising therapeutic tool in cancer.

Mesenchymal stromal cells (MSCs), seeded onto a scaffold and associated with platelet-gel, may represent an innovative treatment to improve bone repair. The preparation of MSCs for clinical use requires the fulfillment of Good Manufacturing Practice indications. The aim of this study was to validate a Good Manufacturing Practice–grade protocol of tissue engineering for bone regeneration, seeding platelet lysate (PL)–cultured MSCs onto an hydroxyapatite clinical-grade scaffold. Six large-scale experiments were performed. MSC expansions were performed comparing fetal bovine serum 10% and PL 5%. We demonstrated that PL lots contain high levels of growth factors possibly responsible of accelerated growth rate, since the number of colony-forming unit–fibroblast and population doublings were always significantly higher in PL cultures. MSCs were characterized for their phenotype and multilineage differentiation capacity, demonstrating appropriate features for both conditions. Gene expression analysis revealed higher expression of typical osteogenic genes of PL-cultured MSCs, when compared to fetal bovine serum MSCs. Cell transformation was excluded by analysis of karyotype, absence of growth without anchorage, and p53/c-myc gene expression. Scaffolds were precoated with retronectin before MSC seeding. MSC adhesion, distribution, and proliferation were demonstrated through the whole surface of the scaffold by scanning electron microscopy analysis or by immunofluorescence and MSC osteogenic differentiation through quantitative reverse transcriptase–polymerase chain reaction of typical osteogenic genes. The present report offers a model of an MSC-based bioengineered device, using an hydroxyapatite clinical-grade scaffold, and supports its potential use in tissue engineering to repair bone defects