Binding of LAG-3 to stable peptide-MHC class II limits T cell function and suppresses autoimmunity and anti-cancer immunity

• DOI: 10.1016/j.immuni.2022.03.013
• Publication Date: 2022-04-11T14:28:56Z
• Authors: Takumi Maruhashi; Daisuke Sugiura; Il-mi Okazaki; Kenji Shimizu; Takeo K. Maeda; Jun Ikubo; Harunori Yoshikawa; Katsumi Maenaka; Naozumi Ishimaru; Hidetaka Kosako; Tatsuya Takemoto; Taku Okazaki
• Keywords: 0303 health sciences; T-Lymphocytes; Histocompatibility Antigens Class II; Autoimmunity; Ligands; Lymphocyte Activation Gene 3 Protein; 3. Good health; Mice, Inbred C57BL; Mice; 03 medical and health sciences; Antigens, CD; Mice, Inbred NOD; Neoplasms; Animals; Peptides

Lymphocyte activation gene-3 (LAG-3) is a potent inhibitory co-receptor; yet, its functional ligand remains elusive, with distinct potential ligands identified. Here, we investigated the relative contribution of potential ligands, stable peptide-MHC class II complexes (pMHCII) and fibrinogen-like protein 1 (FGL1), to LAG-3 activity in vitro and in vivo. Binding of LAG-3 to stable pMHCII but not to FGL1 induced T cell suppression in vitro. Consistently, LAG-3 mutants lacking FGL1-binding capacity but not those lacking stable pMHCII-binding capacity retained suppressive activity in vitro. Accordingly, targeted disruption of stable pMHCII- but not FGL1-binding capacity of LAG-3 in NOD mice recapitulated diabetes exacerbation by LAG-3 deficiency. Additionally, the loss of stable pMHCII-binding capacity of LAG-3 augmented anti-cancer immunity comparably with LAG-3 deficiency in C57BL/6 mice. These results identify stable pMHCII as a functional ligand of LAG-3 both in autoimmunity and anti-cancer immunity. Thus, stable pMHCII-LAG-3 interaction is a potential therapeutic target in human diseases.