Other major immunological breakthroughs in sepsis, such as the characterization of immunosuppressive cells (e.g., regulatory T-cells, Tregs; and myeloid-derived suppressor cells, MDSCs) and immune checkpoints (e.g., programmed cell death protein-1, PD-1; and cytotoxic T-lymphocyte antigen 4, CTLA-4), occurred initially in models, before further verification of their importance in human sepsis (69–71). The gene discussed is PDCD1; the disease is Sepsis.