Abstract
Immune checkpoint inhibitors (antibodies that block the T cell co‐inhibitory receptors PD‐1/PD‐L1 or CTLA‐4) have revolutionized the treatment of some forms of cancer. Importantly, combination approaches using drugs that target both pathways have been shown to boost the efficacy of such treatments. Subsequently, several other T cell inhibitory receptors have been identified for the development of novel immune checkpoint inhibitors. Included in this list is the co‐inhibitory receptor lymphocyte activation gene‐3 (LAG‐3), which is upregulated on T cells extracted from tumor sites that have suppressive or exhausted phenotypes. However, the molecular rules that govern the function of LAG‐3 are still not understood. Using surface plasmon resonance combined with a novel bead‐based assay (AlphaScreenTM), we demonstrate that LAG‐3 can directly and specifically interact with intact human leukocyte antigen class II (HLA‐II) heterodimers. Unlike the homologue CD4, which has an immeasurably weak affinity using these biophysical approaches, LAG‐3 binds with low micromolar affinity. We further validated the interaction at the cell surface by staining LAG‐3+ cells with pHLA‐II‐multimers. These data provide new insights into the mechanism by which LAG‐3 initiates T cell inhibition.
Highlights
Immune checkpoint inhibitors (ICIs; antibodies that block T cell co-inhibitory receptors such as PD-1 and CTLA-4) have revolutionized the treatment of some cancers [1,2,3]
Direct Lymphocyte activation gene-3 (LAG-3):Fc binding to peptide-human leukocyte antigen class II · Response units (RU) (pHLA-II) detected by AlphaScreenTM
Soluble LAG-3 was generated as a LAG-3:Fc fusion protein, expressed in glycosylation-sufficient Chinese hamster ovary (CHO) cells to form a functionally viable and stable protein dimer as previously reported [19]
Summary
Immune checkpoint inhibitors (ICIs; antibodies that block T cell co-inhibitory receptors such as PD-1 and CTLA-4) have revolutionized the treatment of some cancers [1,2,3]. LAG-3 mediated suppression of T cell signaling has been shown to be dependent on the three intracellular regions in the cytoplasmic tail [7], the signaling pathway remains unknown.
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