Mechanisms Underlying LAG3 Immune Checkpoint Function 2330007

Abstract

Abstract Introduction Immune checkpoint blockade was recognized with the 2018 Nobel Prize in Physiology or Medicine for its revolutionary impact on cancer therapy. LAG3 has emerged as a promising target in cancer immunotherapy, with the FDA approval of relatlimab establishing it as the third immune checkpoint blockade with demonstrated clinical efficacy. However, the molecular mechanisms underlying LAG3-mediated T cell inhibition remain incompletely understood. Methods We employed a multidisciplinary strategy to investigate LAG3 signaling, integrating site-directed mutagenesis, biochemical assays, and mass spectrometry. The functional consequences of LAG3 signaling were assessed through T cell proliferation and ELISA measurement of IL-2, while membrane binding properties were evaluated using FRET and NMR. Finally, these mechanistic insights were validated in a clinical context through analysis of single-cell RNA sequencing (scRNA-seq) and immunohistochemistry (IHC) data from patient cohorts treated with PD-1/LAG3 dual blockade. Results OUR RECENT STUDIES demonstrated that LAG3 undergoes robust non-K48-linked polyubiquitination upon ligand engagement, which promotes its inhibitory function through disruption of membrane binding by the juxtamembrane basic residue-rich sequence (Cell 2025). Building upon this foundation, our ongoing investigations are uncovering the downstream signaling mechanisms by which LAG3 suppresses T cell function. Through comprehensive proteomic analysis, we have identified novel LAG3-interacting proteins that mediate its immunosuppressive effects. Furthermore, we have discovered additional post-translational modifications on LAG3 that regulate its checkpoint activity in a context-dependent manner. Conclusion Collectively, our findings reveal a multi-layered regulatory network controlling LAG3 checkpoint signaling, which may provide new therapeutic opportunities for optimizing LAG3-targeted cancer immunotherapy. Funding Source n/a Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)