Abstract

Isolation and Purification of Extracellular Vesicles: Current Directions

William Whitford, Strategic Solutions Leader, GE Healthcare Life Sciences

When isolating vesicles for therapeutic applications, it’s advantageous to have a very good understanding of diverse individual characteristics of the target subpopulation. There are many reasons for this, including that the three major groups of EVs have been described (and even defined) according to their mechanism of generation: macrovesicles, apoptotic bodies and exosomes. While the latter are often assumed to represent a homogenous population, significant work on exosomes has revealed distinct subpopulations of differing properties.  These properties include physical behaviors in manipulation, and such molecular composition as proteomic and nucleic acid repertoires.  Significantly, these subpopulations have also been reported to mediate differential effects upon recipient cells and tissues. All-in-all, it has been reported that different populations of exosome types may be generated from differing cell and tissue types, culture techniques, isolation strategies, and even the scale of an identified isolation technology.  
 
Furthermore, it has been reported that no individual isolation technique will exquisitely separate any subpopulation from all others.  This is because each characteristic is presented by more than one sub-type. For example, separation based on size solely cannot isolate any of the three major EV groups, since they significantly overlap in size.  For similar reasons no single technology can even isolate any particular sub-type of exosomes.
 
Finally, the impurities to be removed in the production of EV-based pharmaceutical ingredients are primarily free proteins and host cell DNA– but virus and endotoxin must also be considered.  Many isolation and purification process have been described, and the study points to the value of including some sort of specific capture step.  Approaches to this type of purification will be reviewed.