A T cell is a type of white blood cell that is central to adaptive immunity. T cells rapidly recognize and destroy virus-infected cells and cancer cells to prevent disease. This recognition must be highly specific to prevent T cells from inappropriately destroying healthy cells.
The activation of T cells critically depends on triggering of the T cell receptor (TCR) by a peptide antigen bound to the major histocompatibility complex (pMHC) on the target cell. This extracellular binding event initiates a series of enzymatic reactions and protein-protein interactions that propagate the signal from the plasma membrane to the nucleus, causing changes in gene transcription that are required for T cell effector functions.
Our lab uses our strength in microscopy and reconstitution to uncover the molecular mechanisms regulating T cell activation and specificity. We have developed single molecule imaging techniques and membrane-bound reconstitution platforms to uncover the spatial organization of signaling components at the T cell interface. We are now expanding our signaling expertise to other immune cell lineages, including macrophages.
Selected References:
Morrissey MA*, Williamson AP*, Steinbach AM, Roberts EW, Kern N, Headley MB, Vale RD. Chimeric antigen receptors that trigger phagocytosis. Elife. 2018 Jun 4;7. pii: e36688. doi: 10.7554/eLife.36688. PMID: 29862966
(link) – Carbone CB, Kern N, Fernandes RA, Hui E, Su X, Garcia KC, Vale RD. In vitro reconstitution of T cell receptor-mediated segregation of the CD45 phosphatase. Proc Natl Acad Sci USA. 2017 Oct 17. doi: 10.1073/pnas.1710358114
(link) –Taylor M.J., Husain K, Gartner ZJ, Mayor S, Vale RD. A DNA-Based T Cell Receptor Reveals a Role for Receptor Clustering in Ligand Discrimination. Cell. 2017 Mar 23;169(1):108-119.e20. doi: 10.1016/j.cell.2017.03.006. PMID: 28340336
- Using a synthetic DNA-based receptor, we examined how the TCR discriminates between high-affinity and low-affinity ligands. We found that higher affinity receptor-ligand pairs have longer dwell times, and are dramatically more likely to be converted from a single receptor-ligand interaction to a signaling cluster that recruits downstream effector proteins. These data support a ‘kinetic proof-reading’ model where molecules with longer dwell times have disproportionately greater signaling outputs.
(link) – Hui E, Cheung J, Zhu J, Su X, Taylor M.J., Wallweber HA, Sasmal DK, Huang J, Kim JM, Mellman I, Vale RD. T cell costimulatory receptor CD28 is a primary target for PD-1-mediated inhibition. Science. 2017 Mar 31;355(6332):1428-1433. doi: 10.1126/science.aaf1292. Epub 2017 Mar 9. PMID: 28280247
(link) Su X*, Ditlev JA*, Hui E, Xing W, Banjade S, Okrut J, King DS, Taunton J, Rosen MK, Vale RD. (2016). Phase separation of signaling molecules promotes T cell receptor signal transduction. Science. 2016 Apr 29;352(6285):595-9.
- We developed an in vitro reconstitution system that allows monitoring signal transduction at high spatial and temporal resolutions. By building up a TCR signaling pathway using 12 purified proteins on supported lipid bilayers, we demonstrated that T cell microclusters are liquid-like phase separated structures. The microclusters are formed through multivalent protein-protein interactions. They promote tyrosine phosphorylation, actin polymerization, and MAPK activation. This work showed that phase separated cellular structures can promote cell signaling.
(pdf) – Hui, E. and Vale, R.D. (2014) In vitro membrane reconstitution of the T-cell receptor proximal signaling network. Nat Struct Mol Biol 21: 133-142. PMCID: PMC4062301.
- By reconstituting the TCR/kinase/phosphatase signaling network into lipid bilayers, the network can be studied in a reduced, well-defined membrane system, where both concentrations and spatial relationships of these proteins can be readily manipulated. This work revealed that there is switch like transition from the quiescent to the phosphorylated state of the TCR. It also demonstrated that manipulating the spatial distribution of signaling molecules (co-clustering TCR and Lck or detaching Csk from the membrane) can trigger TCR phosphorylation.
(pdf) – James, J.R., and Vale, R.D. (2012) Biophysical mechanism of T-cell receptor triggering in a reconsistuted system. Nature 487: 64-69.
- By reconstituting the minimal signaling apparatus in non-immune cells (HEK-293T) we found that the binding energy of the TCR-pMHC interaction generates an exclusion force for membranes proteins with large and/or unligated extracellular domains. Because T cells have having an inhibitory phosphatase activity linked to a transmembrane protein (CD45) that is subject to the exclusion force and an activating kinase linked to the inner leaflet of the membrane (Lck) that is not, the TCR-pMHC mediated exclusion shifts the kinase-phosphatase balance and thus triggers the TCR, as first suggested by the kinetic segregation model.
(pdf) – Yudushkin, I.A., and Vale, R.D. (2010) Imaging T-cell receptor activation reveals accumulation of tyrosine-phosphorylated CD3{zeta} in the endosomal compartment. Proc Natl Acad Sci USA 107: 22128-22133
- We developed an imaging based FRET sensor for the TCR that can be used to examine its phosphorylation in living cells. Somewhat surprisingly, this study revealed considerable phosphorylation of the TCR in endosomes in addition to the plasma membrane.
(pdf) – Yu, C.H., Wu, H.J., Kaizuka, Y., Vale, R.D. & Grove. J.T. (2010) Altered actin centripetal retrograde flow in physically restricted immunological synapses. PLoS One 5: e11878.
(pdf) – Kaizuka, Y., Douglass, A.D., Vardhana, S., Dustin, M.L. and Vale, R.D. (2009) The coreceptor CD2 uses plasma membrane microdomains to transduce signals in T cells. J Cell Biol 185: 521-534.
(pdf) – Douglass, A.D. and Vale, R.D. (2008) Single-molecule imaging of fluorescent proteins. Methods Cell Biol 85: 113-125.
(pdf) – Kaizuka, Y., Douglass, A.D., Varma, R., Dustin, M L. and Vale, R.D. (2007) Mechanisms for segregating T cell receptor and adhesion molecules during immunological synapse formation in Jurkat T cells. Proc Natl Acad Sci USA 104: 20296-20301.
(pdf) – Douglass, A.D. and Vale, R.D. (2005) Single-molecule microscopy reveals plasma membrane microdomains created by protein-protein networks that exclude or trap signaling molecules in T cells. Cell 121: 937-950.
- The study was initially motivated to look for lipid rafts although we did not find evidence for them (at our temporal, spatial resolution) in this study. However, the work did reveal the formation of clusters of signaling proteins in the T cell membrane and that work suggested that these clusters were held together by multi-valent protein-protein interactions. In addition, single molecule work suggested that these signaling clusters could trap some molecules and acted as diffusion barriers and excluded other molecules.