The signaling pathways regulating metabolic processes, including the TGF-beta signaling pathway, HIF-1 signaling pathway, FoxO signaling pathway, cAMP signaling pathway, and PI3K-Akt signaling pathway, were mostly downregulated in the subsets of CD4+ and CD8+ T cells in COVID-19 patients (Figure 2A). Here, CD8A is linked to COVID-19.