The study showed that the absolute numbers of T-lymphocytes, CD4+T cells, and CD8+T cells were decreased in almost all COVID-19 patients, with significantly lower numbers in patients with severe COVID-19 (294.0, 177.5, and 89.0× 106/L) than in patients with moderate COVID-19 (640.5, 381.5, and 254.0× 106/L). This evidence concerns the gene CD4 and COVID-19.