Projects & Publications
Mechanobiology of the Immunological Synapse
Research from our lab has revealed the existence of a tug-of-war that takes place at the immunological synapse, the cell-cell interface between T cells and dendritic cells. We found that centripetal actin flow on the T cell side of the synapse exerts force on the integrin LFA-1, inducing conformational changes that promote adhesion and promote T cell activation. Though the dendritic cell actin network is less dynamic, it restrains ligand mobility and stiffens the signaling platform, both of which augment T cell activation by resisting the forces exerted by the T cell. Ongoing work on this project is aimed at understanding how the cytoskeletal networks of the two cells contribute to receptor activation and signal integration.
Representative Papers:
Comrie WA, Babich A, Burkhardt JK. F-actin flow drives affinity maturation and spatial organization of LFA-1 at the immunological synapse. J Cell Biol. 2015 208:475-91. PMCID: PMC4332248.
Comrie WA, Li S, Boyle S, Burkhardt JK. The dendritic cell cytoskeleton promotes T cell adhesion and activation by constraining ICAM-1 mobility. J Cell Biol. 2015 208:457-73. PMCID: PMC4332244.
Jankowska KI, Williamson EK, Roy NH, Blumenthal D, Chandra V, Baumgart T, Burkhardt JK. Integrins Modulate T Cell Receptor Signaling by Constraining Actin Flow at the Immunological Synapse. Front. Immunol. 2018. DOI: 10.3389/fimmu.2018.00025 PMCID: PMC29403502
Blumenthal D, Chandra V, Burkhardt JK. T-cell priming is enhanced by maturation-dependent stiffening of the dendritic cell cortex. eLife 2020;9:e55995. DOI: 10.7554/eLife.55995 PMCID: PMC7417170
T-Cell Migratory Versatility
Typically, T cell migration is thought to involve actin polymerization at the leading edge and myosin contractility within a trailing uropod. This model is appropriate for cells stimulated by conventional chemokines, especially when migrating on integrin ligands. Indeed, we found that engagement of ICAM-1 promotes action polymerization at the leading edge, allowing upstream migration under shear flow conditions. However, we found that stimulation with the lipid chemoattractant sphingosine-1-phosphate (S1P) undergo bleb based motility, a process that requires increased intracellular pressure coupled to localized changes in the actin cortex. This mode of motility allows cells to move through confined spaces, even in the absence of adhesive ligands. Current research on this project is aimed at delineating the distinct signaling pathways activated by conventional chemokines and S1P, and at testing the idea that these two migratory mechanisms allow T cells to navigate complex environmental obstacles.
Representative Papers:
Roy, NH, MacKay, JL, Robertson, TF, Hammer, DA, Burkhardt, JK. Crk adaptor proteins mediate actin-dependent T cell migration and mechanosensing induced by the integrin LFA-1. Science Signaling. 2018 11:560. PMCID: PMC6333317
Roy NH, Kim SHJ, Buffone A Jr, Blumenthal D, Huang B, Agarwal S, Schwartzberg PL, Hammer DA, Burkhardt JK. LFA-1 signals to promote actin polymerization and upstream migration in T cells. J Cell Sci. 2020 133(17):jcs248328. doi: 10.1242/jcs.248328. PMCID: PMC7502589
Robertson, TF, Chengappa, P, Gomez Atria D, Wu CF, Avery L, Roy NH, Maillard I, Petrie RJ, Burkhardt JK. Lymphocyte Egress Signal Sphingosine-1-Phosphate Promotes ERM-Guided, Bleb-Based Migration. J. Cell Biol 220:6: e20200718, 2021. PMCID: PMC8006814
Actin-Based Immunodeficiency
Since the lab’s inception, we have been interested in understanding how mutations in actin regulatory proteins lead to immune dysregulation. Proteins of interest include WASp and the WAVE component Hem-1, mutations in which lead to primary immunodeficiency disease, as well as the Lupus-linked protein HS1. Recently, we have focused on a newly-defined primary immunodeficiency disease termed X-linked moesin-associated immunodeficiency (X-MAID). Unlike the other diseases that we have studies, which involve defects in actin polymerization, X-MAID is caused by mutations moesin, a protein that links the actin cortex to the cell membrane. We generated mice bearing the human X-MAID mutation and showed that these mice are severely lymphopenic due to defects in cell migration and lymphoid development. Ongoing research on this project is aimed at understanding how the X-MAID mutation perturbs moesin activity and determining how this influences immune cell function.
Representative Papers:
Bendell, A.C., Williamson, E.K., Chen, C.S., Burkhardt, J.K., and Hammer, D.A.: The Arp 2/3 Complex Binding Protein HS1 is Required for Dendritic Cell Random Migration and Force Generation. Integrat. Biol. 9(8): 695-708, Aug 2017 PMCID: PMC5830129.
Cook SA, Comrie WA, et al. HEM1 deficiency disrupts mTORC2 and F-actin control in inherited immunodysregulatory disease. Science 2020. 369(6500): 202-207.
Avery L, Robertson TF, Wu CF, Roy NH, Chauvin SD, Perkey E, Vanderbeck A, Maillard I, Burkhardt JK: A Murine Model of X-Linked Moesin-Associated Immunodeficiency (X-MAID) Reveals Defects in T Cell Homeostasis and Migration. Front Immunol. 2022. 12:726406. doi: 10.3389/fimmu.2021.726406. eCollection 2021. PMCID: PMC8770857
Enhancing Immunotherapy
We use the lessons we learn about basic cell biology to make rational improvements to immunotherapy. In one set of studies, we drew upon our discovery that the adapter molecule CrkL is needed for integrin-dependent T cell migration. Interestingly, we discovered that these cells traffic normally to lymphoid tissues, but fail to efficiently enter inflamed tissues. In a murine model of acute allogeneic hematopoietic stem cell transplant, these cells could eliminate lymphoma cells while causing little or no GVHD. In other translational work, we have collaborated with several labs to understand receptor dynamics at the immunological synapse formed by CAR T cells.