In this study, we observed increased proportions of PD-1+, TIGIT+, and PD-1/TIGIT co-positive cells in nearly all lymphocyte subsets in patients with HLH (Table 2), including CD3+, CD4+, and CD8+ T cells, Tregs, NK cells, and NKT cells (Figures 2A–F). Here, CD4 is linked to hemophagocytic syndrome.