Given the innate immune cells are linked to COVID-19 immunopathogenesis39, our analysis revealed monocyte-derived cfDNA showed the strongest correlation with cytokines associated with cytokine release syndrome (CRS)40 such as IL-15, IL-6, IL-8, IP-10, IL-10, GM-CSF, Eotaxin-3, IL-1β, IL-1RA, IL-18, MCP-2, MCP-1, VEGF, IL-1α, IL-7, TNF-α, IL-12p70, and IL-17A in SOTRs with COVID-19 (Fig. 7c). Here, IL6 is linked to COVID-19.