CTSB and infection: Infections by the Ebola virus, SARS-CoV, SARS-CoV-2, and murine leukemia virus require the cleavage of their capsid by cathepsin B or L protease to activate their membrane fusion capability [34], Akache et al. also suggested that cathepsin-mediated cleavage could prime AAV capsids for subsequent nuclear uncoating [21].