SARS-CoV-2 viral infection led to the devastating COVID-19 pandemic, where illness stemmed from interactions between virions and recipient host cells resulting in multi-layered pathological consequences. The role of the infection portal is now understood to be the cellular angiotensin converting enzyme-2 (ACE2) receptor, which binds to viral spike (S) protein initiating virion internalisation process. Since SARS-CoV-2 virions bear some resemblance to endogenously produced small extracellular vesicles (sEVs) McGill University researchers reasoned that EVs engineered to express S protein (viral mimics) may interfere with viral infection. Here, they report generation of HEK293T cells producing sEVs enriched for transmembrane S-protein tagged with green fluorescent protein (S/GFP). Strikingly, S protein drove the GFP tag to the membrane of sEVs, while GFP alone was not efficiently included in the sEV cargo. High-throughput quantitative proteomics revealed that S/GFP sEVs contained over 1000 proteins including canonical components of the exosomal pathway such as ALIX, syntenin-1, and tetraspanins (CD81, CD9), but depleted for calnexin and cytochrome c. The researchers found that 84 sEV proteins were significantly altered by the presence of S/GFP. S protein expressing EVs efficiently adhered to target cells in an ACE2-dependent manner, but they were poorly internalised. Importantly, prolonged administration of S/GFP EV to K18-hACE2 mice provided a significant protection against SARS-CoV-2 infection. Thus, the generation of sEV containing S protein can be considered as a novel therapeutic approach in reducing the transmission of SARS-CoV-2.
Quantitative profiles of EV proteins affected by S/GFP expression
(a) Relative abundances of EV proteins were calculated based on weighted spectral count by the Scaffold program. Volcano plot shows the significantly changed proteins with more than 2-fold upregulation in S/GFP EV proteomes comparing with other (control and GFP) EV proteomes. (b) 27 proteins with more than average three quantitative value of proteins from total 39 upregulated proteins in the S/GFP EV proteome are represented. Functionally related proteins are grouped into categories designated in bold. (c) Interaction partners of S protein in EV proteomes are visualised by Cytoscape (Shannon et al.,) using BioGRID database (Oughtred et al., ). Inferred interactions between proteins with more than 2-fold upregulation in S/GFP EV are indicated with red edge