PROS1 and COVID-19: Our crystal structural analysis on the R3P1-E4 scFv and RBD protein complex showed that both the heavy and light chain of R3P1-E4 directly interacted with the RBM of SARS-CoV-2 S protein through the residues extensively overlapped with the binding sites for hACE2, suggesting R3P1-E4 neutralizes SARS-CoV-2 infection through competition with hACE2 binding to RBM of the SARS-CoV-2 S protein.