The finding of low white blood cell counts in patients with COVID-1923 suggests that the ability of GM-CSF to increase select leukocyte populations, particularly phagocytes, may be of therapeutic value in COVID-19, especially given GM-CSF’s ability to treat life-threatening infections, and as data from Wuhan, China have shown that half of all COVID-19 patients who died had evidence of secondary infections50. Here, CSF2 is linked to infection.