Lymphocyte Activation Gene (LAG)-3 Is Associated With Mucosal Inflammation and Disease Activity in Ulcerative Colitis
Slevin SM., Garner LC., Lahiff C., Tan M., Wang LM., Ferry H., Greenaway B., Lynch K., Geremia A., Hughes S., Leavens K., Krull D., Marks DJB., Nevin K., Page K., Srinivasan N., Tarzi R., Klenerman P., Travis S., Arancibia-Cárcamo CV., Keshav S.
<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background and Aims</jats:title> <jats:p>Lymphocyte activation gene [LAG]-3 is an immune checkpoint and its expression identifies recently activated lymphocytes that may contribute to inflammation. We investigated the role of LAG-3 by analysing its expression and function in immune cells from blood and tissue of patients with ulcerative colitis [UC].</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>The phenotypic properties of LAG-3+ T cells were determined by flow cytometry, qRT-PCR and single-cell RNA-sequencing. LAG-3+ cells were quantified and correlated with disease activity. The functional effects of LAG-3+ cells were tested using a depleting anti-LAG-3 monoclonal antibody [mAb] in a mixed lymphocyte reaction [MLR].</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>LAG-3+ cells in the blood were negligible. LAG-3+ lymphocytes were markedly increased in inflamed mucosal tissue and both frequencies of LAG-3+ T cells and transcript levels of LAG3 correlated with endoscopic severity. LAG-3 expression was predominantly on effector memory T cells, and single-cell RNA-sequencing revealed LAG3 expression in activated and cytokine-producing T cell subsets. Foxp3+CD25hi Tregs also expressed LAG-3, although most mucosal Tregs were LAG-3−. Mucosal LAG-3+ cells produced mainly interferon γ [IFNγ] and interleukin-17A. LAG-3+ cell numbers decreased in patients who responded to biologics, and remained elevated in non-responders. Treatment with a depleting anti-LAG-3 mAb led to a reduction in proliferation and IFNγ production in an MLR.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>LAG-3+ cells are increased in the inflamed mucosa, predominantly on effector memory T cells with an activated phenotype and their cell numbers positively correlate with disease activity. Depleting LAG-3 eliminates activated proliferating T cells, and hence LAG-3 could be a therapeutic target in UC.</jats:p> </jats:sec>