The immunological synapses (IS) is the specialized contact between a T cell and antigen presenting cell that serves effector function for helper and cytotoxic T cells. A key feature of the IS is the transport of TCR microclusters to the centre, where signaling is terminated. We discovered using correlative light and electron microscopy that TCR were ectocytosed in the centre of the synapse. These vesicles also serve as an antigen specific carrier for CD40-ligand, a critical signal delivered by helper T cells1. We next adapted our technology to investigate how CD8 cytotoxic T cells (CTL) and NK cells use nanoscale protein “bombs” with a core of cytotoxic perforin and granzymes and a shell of thrombospondin-1 (TSP-1) that are secreted into the synaptic cleft to kill target cells 2. We have referred to these “bombs” as supramolecular attack particles (SMAPs).

While the radially symmetric synapse has clear benefits for effector function, the control of proliferation is less clear. Work led by Alexander Leithner has recently developed a new method to selectively control the lateral mobility of one component in a synthetic bilayer at a time, which has revealed new requirements for costimulatory signaling by the ICAM1 integrin ligand based on mechanical feedback. The impact of mixtures of mobile and immobile ICAM1 is currently being investigated.

With Jemma Larson in the lab of Bruce Blazar, Ewoud Compeer and Olga Margaritaki have investigated the cytotoxic mechanisms of chimeric antigen receptor expressing CD8+ iTreg 3, as a novel approach to immunotherapy for B cell leukemias. The CAR CD8 iTreg have similar cytotoxicity to CD8 CTL, but produce lower levels of inflammatory cytokines and thus have less toxicity. They have found that CD8 iTreg make SMAPs with a shell of TSP-4 rather than TSP-1. Nagaja Capitani and Cosima Baldari, collaborators at the University of Siena have also found that culture human CD8 CTL also switch from TSP-1 to TSP-4 during in vitro expansion. The importance of this change in the composition of the SMAP shell from trimeric TSP-1 to pentameric TSP-4 is under study.

References:
1 Cespedes, P. F. et al. T-cell trans-synaptic vesicles are distinct and carry greater effector content than constitutive extracellular vesicles. Nat Commun 13, 3460 (2022). doi.org:10.1038/s41467-022-31160-3
2 Balint, S. et al. Supramolecular attack particles are autonomous killing entities released from cytotoxic T cells. Science 368, 897-901 (2020). doi.org:10.1126/science.aay9207
3 Bolivar-Wagers, S., Larson, J. H., Jin, S. & Blazar, B. R. Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease. Frontiers in Immunology 13 (2022). doi.org:10.3389/fimmu.2022.864748