PS1303 CHRONIC TCR STIMULATION PROMOTES PERIPHERAL T‐CELL LYMPHOMAGENESIS AND INDUCES ADDICTION TO SYK AND NK RECEPTOR SIGNALING
Authors: S. Carras, D. Chartoire, A. Marcais, M. Heiblig, L. Courtois, A. Verney, R. Robinot, M. Urb, G. Salles, A. Traverse‐Glehen, L. De Leval, P. Gaulard, T. Walzer, E. Bachy, L. Genestier
Journal: HemaSphere (2019)

Background: Peripheral T cell lymphomas (PTCL) represent about 10% of non‐Hodgkin lymphomas and are associated with poor prognosis. T‐cell receptor (TCR) signaling is the major growth‐regulatory machinery of normal T cells. Although its involvement in T‐cell lymphomagenesis has not been extensively investigated, various genes coding components of the TCR signaling are found altered in human PTCL and several reports indicates a predominant role of chronic antigenic stimulation in some PTCL. Aims: This study was conducted to investigate the role of TCR chronic stimulation in T‐cell lymphomagenesis and to identify crucial survival factors for lymphoma cells. Methods: To mimic chronic TCR stimulation, we took advantage of a phenomenon called homeostatic proliferation, which is known to be driven by TCR signaling generated by self‐MHC/TCR interactions. To this end, purified mature T cells from p53‐deficient mice were transferred into CD3epsilon‐deficient mice. Peripheral T‐cell lymphomas generated were analyzed using different approaches; flow cytometry, transcriptomic analysis, kinome, western blot, immunohistochemistry and by various in vitro or in vivo functional experiments. Human PTCL cases from Grenoble, Lyon and Tenomic or CeVi collections were analyzed using flow cytometry and immunochemistry. Results: Sixty percent of mice died from PTCL originating from conventional alpha‐beta T cells with an effector‐memory (CD44 hi , CD62L lo , CD122 hi ) and exhausted (PD1 hi ) phenotype. Transcriptomic analysis reveals a chronic TCR activation signature, showing the role of TCR in lymphomagenesis. To study signals involved in lymphoma survival, we performed a kinome analysis showing a constitutive activation of the Syk kinase. Syk expression and activation was confirmed by western blot and constitutive activation of downstream targets of Syk such as PLCg1&amp;2 and the PI3K‐Akt‐mTOR pathway was demonstrated. However, using in vivo experiments, we demonstrated that TCR signaling is not required for PTCL survival, suggesting that Syk may be involved in other signaling pathways. Interestingly, transcriptomic analyses of both mouse and human PTCLs showed an upregulation of a subset of genes involved in Natural Killer (NK) cells biology, such as NK receptors (NKRs) and signaling effectors of NKR, compared to normal T‐cells. This suggests that PTCL acquire “innate‐like” features during chronic TCR stimulation that would be implicated in cell survival and we next show that activatory NKRs are functional and signalize through SYK in murine PTCL. We also demonstrate that activatory NKRs participate to murine PTCL survival as in vivo NKR blockade delays PTCL evolution as well as Syk inhibition. We studied NKRs and Syk expression in a large subset of human PTCL and confirmed their various expression by many PTCL entities. Summary/Conclusion: Using a murine model, we show that chronic TCR stimulation is crucial for T‐cell lymphomagenesis and is associated with an ”innate like“ reprogramming. We characterized potential novel mechanisms of PTCL survival involving NKR and Syk signaling in murine PTCL that could lead to new therapeutic strategy development as a large proportion of human PTCL shares some common features with this murine PTCL generated in this experimental model.