Lymphocytopenia and modulation in lymphocyte balance associated with a decrease in levels of CD4+ cells, CD8+ cells, Th1, and Th2 cells and increased circulating CD4+ T cells, CD8+ T cells, Th2, PD-1, Tim-3, and LAG-3 in severe COVID-19. The gene discussed is HAVCR2; the disease is COVID-19.