# Mixed-mobility supported lipid bilayers uncover the role of immobilized ICAM1 on T cell activation and immune synapse organization

## TL;DR

This study shows that anchoring ICAM1 on a surface increases T cell activation and killing ability, offering insights for improving immune therapies.

## Contribution

The study introduces mixed-mobility supported lipid bilayers to separately control the mobility of TCR agonists and ICAM1.

## Key findings

- Immobilized ICAM1 disrupts F-actin flow and shifts TCR signaling to peripheral microclusters.
- Anchored ICAM1 enhances T cell activation, degranulation, and cytotoxicity.
- Findings were validated in a cell-cell system with cytoskeleton-anchored ICAM1.

## Abstract

This research explores how the mobility of a key immune ligand, intercellular adhesion molecule 1 (ICAM1), influences T cell activation. T cells have a receptor that specifically binds to ICAM1, triggering events that contribute to T cell activation. By creating a system where ICAM1 is selectively immobilized or mobile on a surface, this study shows that when ICAM1 is anchored, T cells become more activated and increase their ability to kill target cells. These findings reveal that the physical anchoring of molecules in immune interactions can significantly impact how T cells respond. This could help design better strategies for enhancing immune responses, such as in cancer therapies, by modulating how immune receptors and ligands are anchored during interactions.

The immunological synapse (IS) integrates antigen recognition and adhesion to control T cell activation and effector functions. Reductionist systems have been instrumental in dissecting IS organization, but conventional systems constrain all ligands to be either mobile or immobile, unlike antigen-presenting cells where intercellular adhesion molecule 1 (ICAM1) is cytoskeletally anchored while T cell receptor (TCR) ligands remain mobile. Here, we establish mixed-mobility supported lipid bilayers (SLBs) that simultaneously present mobile TCR agonists and immobile ICAM1. Selective immobilization of ICAM1 disrupts centripetal F-actin flow, prevents centralization of TCR microclusters and shifts signaling to peripheral microclusters. This attenuates TCR downregulation through ectocytosis while maintaining recycling, and enhances integrin mechanotransduction, reflected in increased phosphorylation of Focal Adhesion Kinase, Paxillin, and the stretch-sensitive adaptor CasL. Functionally, immobilized ICAM1 augments T cell activation, degranulation, Perforin release, and cytotoxicity. Importantly, these findings were recapitulated in a cell–cell system engineered to express either full-length, cytoskeleton-anchored ICAM1 or a truncated form lacking cytoskeletal association, with full-length ICAM1 consistently promoting stronger effector responses. These findings identify ligand mobility as a key biophysical parameter that shapes IS organization and T cell effector responses and establish mixed-mobility SLBs as a powerful tool for probing receptor mechanics in immunity.