ACE2 and COVID-19: To determine whether this novel A3B-mediated proviral mechanism for CoV-2 infection was present in a second cell line, we infected A549-ACE2 and performed RT-qPCR to measure intracellular viral RNA at 3 days post-infection (MOI = 0.1 in Figure 4A, MOI = 1 in Supplementary Figure S4).