A soluble ACE2 microbody protein fused to a single immunoglobulin Fc domain is a potent inhibitor of SARS-CoV-2

Tada, Takuya; Fan, Chen; Chen, Jennifer S.; Kaur, Ramanjit; Stapleford, Kenneth A.; Gristick, Harry; Dcosta, Belinda M.; Wilen, Craig B.; Nimigean, Crina M.; Landau, Nathaniel R.

Soluble forms of ACE2 have recently been shown to inhibit SARS-CoV-2 infection. We report on an improved soluble ACE2, termed a “microbody” in which the ACE2 ectodomain is fused to Fc domain 3 of the immunoglobulin heavy chain. The protein is smaller than previously described ACE2-Ig Fc fusion proteins and contains an H345A mutation in the ACE2 catalytic active site that inactivates the enzyme without reducing its affinity for the SARS-CoV-2 spike. The disulfide-bonded ACE2 microbody protein inhibits entry of SARS-CoV-2 spike protein pseudotyped virus and replication of live SARS-CoV-2 in vitro and in a mouse model. Its potency is 10-fold higher than soluble ACE2 and it can act after virus bound to the cell. The microbody inhibits the entry of β coronaviruses and virus with the variant D614G spike. The ACE2 microbody may be a valuable therapeutic for COVID-19 that is active against viral variants and future coronaviruses.