Similarly, Sekine et al. conducted an analysis that demonstrated lower CD4+ and CD8+ T-cells in patients with moderate and severe COVID-19 compared to a control group.30 However, they observed an increased expression of activation markers such as CD38, CD69, Ki-67, and programmed cell death protein 1 (PD-1) on CD4+ T-cells and CD38, CD39, CD69, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), HLA-DR, Ki-67, lymphocyte-activation gene 3 (LAG-3), and T-cell immunoglobulin 3 (TIM-3) on CD8+ T-cells. Here, PDCD1 is linked to COVID-19.