IL15 and COVID-19: In the setting of COVID-19, NicheNet has been applied to identify persistent IFN-α signaling in NK cells from patients with severe COVID-19 [140], IFN-γ and TNF-α as ligands driving monocyte dysfunction in post-acute sequelae of COVID-19 (PASC) [141], and IL-15 and IL-18 as macrophage-expressed ligands predicted to enhance functional activity of SARS-CoV-2 antigen-reactive CD4 and CD8 T cells [63].