TMPRSS2 and infection: In agreement with antiviral mechanisms and with previous observations [19], we found the following: NH4Cl, which can elevate endosomal pH, prevented infection with either pseudovirus; E-64d, which targets cathepsin B/L, was only active against spike protein-pseudotyped virus; and camostat, an inhibitor of TMPRSS2, did not alter the entry of either pseudovirus in 293T-hACE2 cells in which TMPRSS2 protein was marginally expressed.