Accumulating evidences indicated that a subgroup of severe COVID-19 patients might have a cytokine storm syndrome, characterized by increased IL-2, IFN-γ, IL-7, MIP-1, TNF-alpha, MCP-1, IL-6, etc.31–33 In agreement with the clinical findings, SARS-CoV-2 infection in cynomolgus macaques also resulted in the up-regulation of a large number of cytokines and chemokines (Supplementary Fig. S1). Here, IL2 is linked to COVID-19.