$SRNE STI-1499 and STI-2020 were tested for binding to full length Spike proteins derived from naturally emerging viruses including the USA/WA-1/2020 (WA-1) isolate as well as an emerging SARS-CoV-2 isolate that bears a D →G mutation at amino acid residue 614 in the Spike protein (D614G). Binding studies demonstrated equivalent binding affinity for both nAbs against cell surface-expressed Spike protein with the D614G mutation as well as that of the WA-1 isolate. To determine the neutralizing activity of STI-1499 and STI-2020 against the aforementioned SARS-CoV-2 clinical isolates (vide supra), nAbs were evaluated in the virus neutralization assay. Both nAbs exhibited equipotent neutralization of the virus isolates. In keeping with observed improved binding properties, STI-2020 neutralized both isolates with an IC50 of 0.055 μg/ml and an IC99 of 0.078 μg/ml, a greater than 50-fold enhancement of neutralizing potency over the parental STI-1499 nAb."
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