"We do know that the insertion of such FCS sequences into SARS-like viruses was a specific goal of work proposed by the EHA-WIV-UNC partnership within a 2018 gr

"We do know that the insertion of such FCS sequences into SARS-like viruses was a specific goal of work proposed by the EHA-WIV-UNC partnership within a 2018 grant proposal (“DEFUSE”) that was submitted to the US Defense Advanced Research Projects Agency (DARPA) (25). The 2018 proposal to DARPA was not funded, but we do not know whether some of the proposed work was subsequently carried out in 2018 or 2019, perhaps using another source of funding. "We also know that that this research team would be familiar with several previous experiments involving the successful insertion of an FCS sequence into SARS-CoV-1 (26) and other coronaviruses, and they had a lot of experience in construction of chimeric SARS-like viruses (27–29). In addition, the research team would also have some familiarity with the FCS sequence and the FCS-dependent activation mechanism of human ENaC α (19), which was extensively characterized at UNC (17, 18). For a research team assessing the pandemic potential of SARS-related coronaviruses, the FCS of human ENaC—an FCS known to be efficiently cleaved by host furin present in the target location (epithelial cells) of an important target organ (lung), of the target organism (human)—might be a rational, if not obvious, choice of FCS to introduce into a virus to alter its infectivity, in line with other work performed previously." https://www.pnas.org/doi/10.1073/pnas.2202769119 https://www.pnas.org/doi/10.1073/pnas.2202769119