In light of the emerging notion that GM-CSF might be a key biomarker of SARS-CoV-2-induced cytokine storm in a subset of COVID-19 patients with more severe outcome (Hue et al. 2020; Gibellini et al. 2020; Blot et al. 2020; Thwaites et al. 2021; Zhao et al. 2021), future GM-CSF-targeting clinical trials should be conducted in a subset of COVID-19 patients with particularly elevated blood GM-CSF levels. The gene discussed is CSF2; the disease is COVID-19.