Exosomes As Therapeutics
Exosomes are a rising star in the world of therapeutics. These nanosized (50 – 200 nm) extracellular vesicles expelled by cells came to the gained prominence following the paper from Lotvall et al. 2007 (1). This seminal paper described how cells can use exosomes to carry mRNAs between cells and thereby regulating gene expression in neighbouring cells.
With unique surface markers, exosomes have the potential to seek and deliver their payload to specific tissue types or disease states. Crucially, they have the capacity to shield the payload from degradation, to evade recognition and subsequent removal by the immune system (2).
In the quest for novel therapeutics, exosomes are now being implicated in the development of diseases including Alzheimer’s, cancers, diabetes and obesity are particularly attractive for CNS disease treatments as they can cross the blood-brain barrier. A growing number of technology companies are actively exploring the manipulation of this system to carry a range of therapeutic types including RNA, proteins, gene therapy vectors and even CRISPR packages.
1:DOI: 10.1038/ncb1596 2: DOI: s41423-020-0391-1
Different Approaches to Exosome Production:
- Intrinsic – where the exosome is the product. For example, natural exosomes from certain types of MSCs have been found to be better than using the cells themselves.
- Engineered – exosomes made by the producer cells which are then loaded up with a therapeutic molecule (RNA, DNA, protein or CRISPR tools). This is the basis for candidate COVID-19 vaccines which are loaded with mRNA to make the patient cells manufacture identifiable viral proteins. Exosomes can be engineered with direct tropism so they reach specific target cells.
- Cell engineered – where the DNA of the donor cell is genetically modified to directly express the therapeutic molecule within the exosome.
It is hoped that engineered exosomes, with their tailor made surface markers, will enable customized delivery of precision-targeted medicines with resulting improved efficacy and safety profiles.
Making Master Cell Banks for Stable Producer Cell Lines
Stable producer cells can be established for the production of engineered and cell-engineered exosomes. The most common cell types for producing these exosomes are typically HEK 293, 293F, MSCs, iPSCs and cardiosphere-derived cells.
As in other areas, the establishment of master cell banks, using single cell cloning, can be seen as the basis of a reliable factory for cells bringing:
- Consistency in production process
- Process control as part of a GMP methodology
- Provide required assurance for the regulator