Development of targeted exosomes for delivery of biotherapeutics

Abstract

Cells release nanosized membrane-enclosed vesicles termed extracellular vesicles. These naturally occurring vesicles have been established as important players in communication between cells, mainly through transfer of their content. This inherent ability makes extracellular vesicles outstanding candidates for development into drug delivery vehicles. Cells are considered to release a number of extracellular vesicle types with unique size, biogenesis, and cargo: exosomes, microvesicles, and apoptotic bodies. Exosomes are the most well studied vesicle type and are considered to have homogenous characteristics. However, fractionation of isolated exosomes with sucrose density gradient flotation allowed for identification of two distinct exosome subpopulations with unique size and composition. Subpopulations derived from melanoma cells were found to have differential effects on gene expression of recipient cells. Secondly, development of a size exclusion chromatography based approach allowed for more in-depth study on exosome heterogeneity. Four exosome subpopulations with different size and composition were derived from ovarian cancer cells. Preliminary findings point to a potential pathophysiological role of ovarian-cancer derived exosomes, with unique roles of subpopulations in ovarian cancer metastasis. In addition, differential properties of exosome subpopulations were explored in development of B cell targeted exosomes. Single chain variable fragments targeting B cell surface antigens CD19 and CD22 were successfully expressed on exosomes. Targeting of CD22 resulted in increased and rapid uptake as compared to targeting of CD19. Moreover, data suggested that specific exosome subpopulations are responsible for the latter observation. Findings demonstrate a promising approach for the delivery of biotherapeutics into malignant B cells. In conclusion, this works shows the heterogeneous nature of exosomes and the release of subpopulations with potential unique biological roles. Addressing heterogeneity is one of the key topics of research on extracellular vesicles and will allow for in depth study on their underlying biogenesis and in turn benefit development of extracellular vesicle based therapeutics. </p