Dexosomes as a therapeutic cancer vaccine: from bench to bedside

Exosomes released from dendritic cells, now referred as dexosomes, have recently been extensively characterized. Preclinical studies in mice have shown that, when properly loaded with tumor antigens, dexosomes can elicit a strong antitumor activity. Before dexosomes could be used in humans as a therapeutic vaccine, extensive development work had to be performed to meet the present regulatory requirements. First a manufacturing process amenable to cGMP for isolating and purifying dexosomes was established. Methods for loading the Major Histocompatibility Complex (MHC) molecules class II and I in a quantitative and reproducible way were developed. The most challenging task was the establishment of a quality control method for accessing the biological activity of individual lots. Such a method must remain relatively simple and reflect the mechanism of action of dexosomes. This was accomplished by measuring the transfer of a MHC class II superantigen complex to an antigen presenting cell that was MHC class II negative. More than 100 separate dexosome lots were prepared from blood cells of healthy volunteers to evaluate the variability of the manufacturing process. The analysis of the data showed that the main source of variability was related to the heterogeneity of the human population and not to the manufacturing process. These studies allowed to perform two phase I clinical trials. A total of 24 cancer patients received Dex therapy. Dexosome production from cells of cancer patient was found equivalent to that of normal volunteer. No adverse events related to this therapy were reported. Evidence of dexosome bioactivity was observed.