Cyclosporine A rescues the influenza virus fusion with IFITM3-expressing cells by relocating the restriction factor to intraluminal vesicles of multivesicular bodies

Interferon-induced transmembrane protein 3 (IFITM3) blocks fusion of many enveloped viruses with endosomes, likely by rigidifying the cell membrane. We and others have previously reported that cyclosporine A (CsA) treatment rescues the ability of the influenza A virus (IAV) to fuse with and infect IFITM3-expressing cells, but the mechanism of such rescue remained controversial. Here, we employed correlative light-electron microscopy (CLEM) and on-section electron tomography workflow to visualize