VLP assays

HEK293T cells were seeded to 9 cm dishes. The plasmid constructs were co‐transfected with TransIT‐293 (Mirus Bio) and 5 μg of each plasmid (pcDNA3.1 N‐FLAG, pcDNA3.1 M‐FLAG, pcDNA3.1 E‐FLAG, pQCXIH Bst2‐HA, pQCXIH Bst2‐C3A‐HA, pcDNA3.1 Spike [codon optimised], pLVX ORF3a‐Strep). SARS‐CoV‐2 VLPs were harvested 48 h post transfection. VLPs were purified from culture supernatants by centrifugation at 500 g, 10 min, followed by a second centrifugation at 2,000 g for 20 min. Collected supernatants were filtered through 0.45 μm filters before filtrates were layered on top of 20% sucrose cushions, and then centrifuged at 100,000 g for 3 h. The final pellets were resuspended in pre‐chilled lysis buffer.