summary - A 2018 funding proposal (~$14.2M requested over 3.5 years) submitted by EcoHealth Alliance to DARPA’s PREEMPT program (which funds efforts to contain viral spillover risk in animal reservoirs), in collaboration with WIV, Duke-NUS, UNC-Chapel Hill, East China Normal University, the USGS National Wildlife Health Center, and Palo Alto Research Center. Proposed synthesizing full-length infectious clones of SARS-related bat coronaviruses and inserting novel or human-adapted proteolytic (furin) cleavage sites into their spike proteins, then testing resulting growth/infectivity in humanized mice and human airway-tissue cultures, among other gain-of-function-adjacent experiments. DARPA rejected the proposal in 2018, reportedly citing gain-of-function biosafety concerns. Leaked in September 2021 - roughly 3.5 years after SARS-CoV-2 emerged with a furin cleavage site absent from all then-known close relatives.
relevance_note - The single most concrete documentary link between the specific experimental idea “insert a furin cleavage site into a SARS-related bat coronavirus” and the institutions (WIV, EcoHealth) implicated in the lab-leak hypothesis. Important limits: the proposal was rejected by DARPA, and there is no direct evidence in the leaked documents themselves that the described furin-site-insertion experiments were subsequently performed via another funding route - this is a proposed-experiment match to the hypothesis, not proof the experiment happened.