LAG3-MHCII interaction induces a tight cell-cell interface at the immunological synapse

Area of Science:

• Immunology
• Molecular Biology
• Cancer Research

Background:

• Lymphocyte activation gene 3 (LAG3) is an immune checkpoint protein that inhibits T cell activity.
• LAG3 binds to major histocompatibility complex class II (MHCII), but the precise mechanisms of immunosuppression are not fully understood.
• Understanding LAG3-MHCII interactions is crucial for developing effective cancer immunotherapies.

Purpose of the Study:

• To investigate the molecular mechanisms by which LAG3 binding to MHCII suppresses T cell function.
• To characterize the structural and functional consequences of the LAG3-MHCII interaction at the immunological synapse.
• To explore therapeutic strategies targeting the LAG3-MHCII pathway for cancer immunotherapy.

Main Methods:

• Reconstituted cell conjugation assay to study LAG3-MHCII binding.
• Correlative light and electron microscopy to visualize the immunological synapse architecture.
• Use of LAG3 antibodies (whole IgG and Fab fragments) to probe the interaction.

Main Results:

• LAG3 directly binds to MHCII independently of T cell receptor signaling.
• The LAG3-MHCII interaction remodels the immunological synapse, forming a tight interface that excludes certain molecules.
• LAG3-MHCII interaction facilitates MHCII trogocytosis and can be blocked by LAG3 Fab fragments to enhance T cell responses.

Conclusions:

• The LAG3-MHCII interaction creates a selective physical barrier at the immunological synapse, contributing to immunosuppression.
• These findings provide new mechanistic insights into LAG3-mediated immune evasion in cancer.
• Targeting the LAG3-MHCII interaction with specific antibody fragments presents a promising strategy for enhancing cancer immunotherapy.