ACE2 and osteosarcoma: We generated pooled populations of human osteosarcoma (U2OS) cells, chosen for their flat morphology and lack of critical fusion machinery (Beck et al., 2011), which stably express fluorescently tagged ACE2 or spike (full-length, ‘FL’ vs. receptor-binding domain, ‘RBD’; see Figure 1A for domain organization), using the B7 transmembrane (‘TM’) domain (Liao et al., 2001; Lin et al., 2013) as a control.