In 2019, Wang et al. identified fibrinogen-like protein 1 (FGL1) as the ligand for Lag-3.181 It was found to bind to Lag-3 to form a new PD-1/PD-L1-independent immune checkpoint pathway, leading to T-cell exhaustion, dysfunction, and tumor cell evasion of immune surveillance. The gene discussed is PDCD1; the disease is neoplasm.