COVID-19 patients had profound lymphopenia compared with healthy controls, including the median total number of lymphocytes: 1100 (800–1500) vs. 1846 (1585–2129) cells/μL (p < 0.001), the CD4+ T cells: 636 (416–708) vs. 783 (664–1099) cells/μL (p = 0.012) and CD8+ T cells: 296 (185–477) vs. 404 (285–524) cells/μL (p = 0.022) (Table 2). This evidence concerns the gene CD4 and COVID-19.