Analysis of CD4+ T cells from Foxp3YFPCreNUMBΔ/Δ mice revealed that their activation phenotype recapitulated that of CD4+ T cells from patients with MIS-C, including increased memory markers (CD44+CD62L–) and heightened IFN-γ production by Tconv cells (Supplemental Figure 9, E and F). This evidence concerns the gene CD44 and COVID-19–associated multisystem inflammatory syndrome in children.