Dr. Donna Farber Research
Signaling pathways for memory CD4 T cell recall and homeostasis
The two distinguishing features of memory T cells that enable them to mediate efficacious responses--are their rapid recall following TCR engagement, and their ability to persist longterm by perpetual homeostatic turnover. The biochemical signaling pathways regulating the functional responses and maintenance of memory T cells remain undefined. My laboratory has taken novel approaches to dissect the pathways and mechanisms by which TCR-coupled signaling pathways trigger rapid effector responses in memory CD4 T cells, and also to define how both TCR and cytokine signaling pathways contribute and regulate memory T cell survival and homeostasis.
To dissect how TCR-coupled signaling events are coupled to rapid recall, we recently implemented multiparameter analysis of signaling and function on the single cell level using flow cytometry. From these analyses, we found that resting memory CD4 T cells exhibit a strikingly elevated expression of the ZAP-70 tyrosine kinase, and that there are two pathways controlling IFN-γ production at rapid and later times, respectively after TCR triggering (1-3). By analysis of transcription factor expression, IFN-γ production and also chromatin immunoprecipitation studies, we found that the early IFN-γ production is independent of the T-bet transcription factor and requires NFκB, which is engaged on the IFN-γ promoter at early times after activation (4). Based on these findings we have proposed a model whereby memory CD4 T cells use an innate signaling pathway for NFκB-mediated control of rapid effector function (5) . We are currently analyzing memory T cell recall in T cells with conditional deletion of regulators of the NFkB pathway to further dissect how NFkB activation controls rapid recall.
We have also used novel mouse models for conditional ablation of the key TCR-coupled adaptor molecule SLP-76 to investigate TCR signaling requirements for memory CD4 T cell generation and maintenance/homeostasis. We found that conditional ablation of SLP-76 following CD4 T-cell priming, enabled the generation of memory CD4 T cells, yet significantly inhibited their homeostatic turnover and persistence in vivo (6). SLP-76-deficient memory CD4 T cells were further impaired in their ability to proliferate in response to IL-7 in vivo, revealing a dominant requirements for TCR engagement and signaling in memory CD4 T cell homeostasis in vivo. These studies have important implications for promoting memory T cell persistence in vaccines and understanding mechanisms for altered T cell functions in aging. We are also examining mechanisms for how T cells are reconstituted during lymphopenic conditions, including T cell depletional therapies typically administered to transplant patients.
1. Chandok, M. R., and D. L. Farber. 2004. Signaling control of memory T cell generation and function. Semin Immunol 16:285-293.
2. Chandok, M. R., F. I. Okoye, M. P. Ndejembi, and D. L. Farber. 2007. A biochemical signature for rapid recall of memory CD4 T cells. J Immunol 179:3689-3698.
3. Okoye, F. I., S. Krishnan, M. R. Chandok, G. C. Tsokos, and D. L. Farber. 2007. Proximal signaling control of human effector CD4 T cell function. Clin Immunol 125:5-15.
4. Lai, W., M. Yu, M.-N. Huang, F. I. Okoye, A. D. Keegan, and D. L. Farber. 2010. Transcriptional Control of rapid recall by memory CD4 T cells. submitted.
5. Farber, D. L. 2009. Biochemical signaling pathways for memory T cell recall. Semin Immunol 21:84-91.
6. Bushar, N. D., E. Corbo, M. Schmidt, J. S. Maltzman, and D. L. Farber. 2010. Ablation of SLP-76 signaling after T cell priming generates memory CD4 T cells impaired in steady-state and cytokine-driven homeostasis. Proc. Nat'l Acad. Sci. U.S.A. 107:827-831.