- Display proteins on exosome surfaces
- Coat exosomes with targeting ligands
- Target specific cellular destinations
- Create stable XStamp cell lines
XStamp™ Exosome Targeting Technology
Exosomes are extracellular nanoshuttles that facilitate communication between cells and can be engineered as therapeutic shuttles to deliver biological molecules or drugs to target disease cells. SBI has developed an exosome surface display system that enables desired protein sequences to be placed efficiently on the surfaces of engineered exosomes called the "XStamp" technology. The patented XStamp technology is based upon a C-terminal fusion of the C1C2 domain from MFG-E8. Protein sequences that are fused to the XStamp tag will efficiently display the protein ligand fusion on the surfaces of secreted exosomes. The technology can be used to place cellular "addresses" on exosomes that send them to specific destinations for cargo delivery.
MFG-E8 Localizes to Exosome Surfaces (C1C2 domain)
Fluorescently-labeled antibodies for MFG-E8, CD58 and CD81 were used in combination for FACs analysis. The CD58 marker is a known cell surface marker that is absent on exosomes. CD81 is known to be present both in cells and exosomes. The FACs data show that MFG-E8 is exclusively detected on exosomes and not present in the cells.
The XStamp System
To take advantage of the localization of MFG-E8 on exosomes, the C1C2 domain (XStamp domain) of the protein's gene was cloned into SBI's MSCV-MCS-EF1-Puro lentivector and a 5' secretion signal sequence (SS) was placed within the multiple cloning site. The protein ligand chosen to display on exosomes is cloned into the MCS and fused to the C1C2 domain. The XStamp lentivector also features a downstream EF1-Puromycin cassette for selection and stable cell line development. The lentivector constructs can be used in transient transfection expression studies as well as for packaging into lentivirus to stably transduce cells to create cellular factories producing engineered exosomes.