The immunoregulatory effect of DPSCs can inhibit the secretion of TNF-α through the IDO-mediated pathway, promote the polarization of macrophages, regulate the balance of immune homeostasis, and inhibit the occurrence of inflammation by increasing the secretion of cytokines such as IL-10, PGE2, and IL-6 in COVID-19 [49]. Here, TNF is linked to COVID-19.