While this manuscript was under review, Hoffmann et al.53 reported that human ACE2 is the entry receptor of SARS-CoV-2, and that serine protease TMPRSS2 is important for SARS-CoV-2 S activation, consistent with our findings. In agreement with our work, sera from convalescent SARS patients neutralized SARS-CoV-2 S pseudovirion entry with lower efficiency than SARS-CoV S pseudovirion entry, showing moderate cross-neutralization.