Membrane Association Transforms an Inert Anti-TCRβ Fab' Ligand into a Potent T Cell Receptor Agonist

Area of Science:

• Immunology
• Cellular Biology
• Biophysics

Background:

• T-cell receptor (TCR) activation by natural peptide-major histocompatibility complex (pMHC) ligands occurs at the cell membrane, not in solution.
• TCR activation involves complex mechanisms like steric phosphatase exclusion and mechanical forces.
• Current methods using cross-linked pMHC or multivalent antibodies activate TCRs non-physiologically.

Purpose of the Study:

• To develop a strictly monovalent ligand system for TCR activation that mimics natural pMHC interactions.
• To investigate the threshold of TCR engagement required for T-cell activation.
• To compare the activation profiles of monovalent membrane-associated ligands with existing methods.

Main Methods:

• Utilized a monovalent anti-TCRβ H57 Fab' fragment.
• Immobilized the Fab' fragment to a supported lipid bilayer using DNA complementation.
• Measured T-cell activation, including nuclear translocation of NFAT, in primary murine T-cells.

Main Results:

• The monovalent Fab'-DNA ligand, when membrane-coupled, triggered TCRs and activated NFAT translocation with potency similar to pMHC.
• TCR activation by Fab'-DNA required membrane association, unlike soluble ligands.
• Approximately 100 monovalent Fab':TCR interactions were sufficient for early T-cell activation.

Conclusions:

• Membrane-associated monovalent ligands can physiologically activate T-cells.
• This system provides a tool to study TCR activation thresholds and mechanisms.
• The findings differentiate from non-physiological activation induced by multivalent ligands.