HAVCR2 and COVID-19: The expression of markers associated with T-cell activation, differentiation, proliferation, and senescence are altered in persons with DS [37], which is similar to what has been observed in severe COVID-19, wherein increased expression of exhaustion-related modules (PD-1, CTLA-4, Tim-3, and TIGIT in CD8+ T cells) has been found [38–40], and also reported to be downstream of IFN signaling [41].