Molecular analysis of T cell differentiation and memory formation
Project leader: Monika Wolkers
The molecular regulation of T cell memory
CD8 memory T cells are crucial to protect us from recurring infections. When they re-encounter the pathogen, T cells get swiftly reactivated which allows for rapid generation of effector molecules and clearance of infected cells. For the generation of proficient CD8 T cell memory, survival signals from CD4 T helper cells are required. Lack of CD4 T cell help results in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated cell death of CD8 T cells upon reactivation. In our recent studies, we have dissected the molecular mechanisms on how Interleukin-2 rescues ‘helpless’ CD8 T cells (Wolkers et al., Immunol Lett 2011). Importantly, we found that ‘help’ is imprinted in CD8 T cells through the transcriptional regulator Nab2, which suppresses TRAIL expression in helped CD8 T cells, thereby allowing for the development of proficient secondary CD8 T cell responses (Wolkers et al., Blood 2011).
Regulation of TRAIL expression in plasmacytoid DCs and NK cells
Given that TRAIL is also employed by immune cells to specifically kill virally infected and cancer cells, we addressed whether Nab2 also affects TRAIL expression in other cell types. Our preliminary data showed that TRAIL expression in natural killer (NK) cells is also regulated by Nab2 (Balzarolo et al. manuscript in preparation). Conversely, we found that Nab2 is required for TRAIL expression in plasmacytoid dendritic cells (pDCs). We further unraveled the Nab2-mediated TRAIL induction and established that activated pDCs require the engagement of two signaling pathways for optimal TRAIL expression, i.e. for optimal target cell killing: PI3K-Nab2 signaling and type I IFN-R engagement (Balzarolo et al., manuscript under review).
The molecular regulation of T cell effector functions
One hallmark of CD8 memory T cells is that massive production of effector molecules is ensured within a few hours upon reactivation. This high responsiveness of memory T cells correlates with elevated levels of cytokine transcripts that allow for rapid generation of the effector molecules. Strikingly, regardless of these high mRNA levels, cytokine production is blocked unless the cognate antigen is recognized, thereby preventing uncontrolled protein production of otherwise toxic molecules. We have recently developed a model system to study how this translational block is mediated, and found that both in vitro and in vivo, the effector molecule interferon (IFN) γ is regulated through translational regulation. We have identified the sequences required for this translational block (Salerno et al.; manuscript in preparation). We are currently investigating which proteins are involved in the translational regulation and aim to understand the functional consequence for this translational regulation.
- Hennies CM, Reboulet RA, Garcia Z, Nierkens S, Wolkers MC, Janssen EM. Selective expansion of merocytic dendritic cells and CD8DCs confers anti-tumor effect of Fms-like tyrosine kinase 3-ligand treatment in vivo. Clin Exp Immunol 2011; 163:381-91.
- Wolkers MC, Bensinger SJ, Green DR, Schoenberger SP, Janssen EM. Interleukin-2 rescues helpless effector CD8+ T cells by diminishing the susceptibility to TRAIL- mediated death. Immunol Lett 2011; 139(1-2):25-32.
- Wolkers MC, Gerlach C, Arens R, Janssen EM, Fitzgerald P, Schumacher TN, Medema JP, Green DR, Schoenberger SP. Nab2 regulates secondary CD8+ T-cell responses through control of TRAIL expression. Blood 2012; 119(3):798-804.
Balzarolo M, Watzl C, Medema JP, Wolkers MC. NAB2 and EGR-1 exert opposite roles in regulating TRAIL expression in human Natural Killer cells. Immunol Lett 2013; 151(1-2):61-67.
Karrich JJ, Jachimowski LC, Nagasawa M, Kamp A, Balzarolo M, Wolkers MC, Uittenbogaart CH, van Ham SM, Blom B. IL-21 stimulated human plasmacytoid dendritic cells secrete Granzyme B, which impairs their capacity to induce T cell proliferation. Blood 2013; 121(16):3103-3111.
Balzarolo M, Karrich JJ, Engels S, Blom B, Medema JP, Wolkers MC. The transcriptional regulator NAB2 reveals a two-step induction of TRAIL in activated plasmacytoid DCs. Eur J Immunol 2012; 423019-3027.
Karrich JJ, Balzarolo M, Schmidlin H, Libouban M, Nagasawa M, Gentek R, Kamihira S, Maeda T, Amsen D, Wolkers MC, Blom B. The transcription factor Spi-B regulates human plasmacytoid dendritic cell survival through direct induction of the anti-apoptotic gene BCL2-A1. Blood 2012; 119(22):5191-5200.