Editing COVID-19 — Origins: The Laboratory Leak Hypothesis (section)

==== The Furin Cleavage Site ====
As described in the virology article, the furin cleavage site at the S1/S2 junction of the spike protein has no counterpart in closely related bat coronaviruses. Project DEFUSE — a 2018 DARPA grant proposal from EcoHealth Alliance that was rejected — specifically proposed inserting furin cleavage sites into bat coronaviruses to study human cell entry. The proposal was rejected by DARPA, which noted that it involved gain-of-function research. Whether the proposed research was conducted elsewhere with other funding is not known.