Other co-inhibitory receptors, including TIGIT (counteracts the co-stimulatory function of CD226), BTLA (CD272, B/T lymphocyte attenuator), VISTA (T-cell activation V-domain Ig Inhibitor), and SIGLEC9, have been reported to show synergistic anti-tumor effects after co-blockade with PD-1 (13). This evidence concerns the gene BTLA and neoplasm.