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Cytomegalovirus (CMV) is widespread in humans and has been implicated in glioblastoma (GBM) and other tumors. However, the role of CMV in GBM remains poorly understood and the mechanisms involved are not well-defined. The goal of this study was to identify candidate pathways relevant to GBM that may be modulated by CMV. Analysis of RNAseq data after CMV infection of patient-derived GBM cells showed significant upregulation of GBM-associated transcripts including the MET oncogene, which is known to play a role in a subset of GBM patients. These findings were validated in vitro in both mouse and human GBM cells. Using immunostaining and RT-PCR in vivo, we confirmed c-MET upregulation in a mouse model of CMV-driven GBM progression and in human GBM. siRNA knockdown showed that MET upregulation was dependent on CMV-induced upregulation of NF-κB signaling. Finally, proneural GBM xenografts overexpressing c-MET grew much faster in vivo than controls, suggesting a mechanism by which CMV infection of tumor cells could induce a more aggressive mesenchymal phenotype. These studies implicate the CMV-induced upregulation of c-MET as a potential mechanism involved in the effects of CMV on GBM growth.

Efficient resolution of acute cytopathogenic cytomegalovirus infection through innate and adaptive host immune mechanisms is followed by lifelong maintenance of the viral genome in host tissues in a state of replicative latency, which is interrupted by episodes of virus reactivation for transmission. The establishment of latency is the result of aeons of co-evolution of cytomegaloviruses and their respective host species. Genetic adaptation of a particular cytomegalovirus to its specific host is reflected by private gene families not found in other members of the cytomegalovirus group, whereas basic functions of the viral replicative cycle are encoded by public gene families shared between different cytomegaloviruses or even with herpesviruses in general. Private genes include genes coding for immunoevasins, a group of glycoproteins specifically dedicated to dampen recognition by the host's innate and adaptive immune surveillance to protect the virus against elimination. Recent data in the mouse model of cytomegalovirus latency have indicated that viral replicative latency established in the immunocompetent host is a dynamic state characterized by episodes of viral gene desilencing and immune sensing of reactivated presentation of antigenic peptides at immunological checkpoints by CD8 T cells. This sensing maintains viral replicative latency by triggering antiviral effector functions that terminate the viral gene expression program before infectious viral progeny are assembled. According to the immune sensing hypothesis of latency control, immunological checkpoints are unique for each infected individual in reflection of host MHC (HLA) polymorphism and the proteome(s) of the viral variant(s) harbored in latency.

Purpose/Objective: Memory T cell formation is the result of an intricate balance between extracellular cues and intracellular signaling components. PI3K-signaling is associated extensively with effector cell differentiation, but its inhibition during T cell activation results in apoptosis of all cells, including memory precursors. This suggests a vital role for PI3K-signaling in memory cell formation. NKG2D is an activating receptor which potentiates cytotoxic cell function by stimulating the PI3K pathway. On CD8 T cells its expression is induced after activation, but long before target tissues are encountered. In this study, we investigated whether NKG2D is involved in the formation and maintenance of CD8 memory T cells. Materials and methods: In order to specifically study the function of NKG2D on T cells, mice deficient for NKG2D and Dap10 were used, on a wild type or T cell receptor transgenic background. Full knockout mice were used, as well as mixed bone marrow chimeric mice and adoptive transfer models of transgenic T cells. T cell responses were assessed in vivo using LCMV, mCMV and Listeria monocytogenes infection models. In addition, a novel in vitro memory cell differentiation model dependent on IL-15, was developed to specifically study intracellular signaling. Results: We show that upon viral infection NKG2D does not only enhance cytotoxicity of effector cells, but also mediates memory CD8 T cell formation. In vivo, NKG2D requires Dap10 to promote memory cell formation in a process that involves IL-15. In vitro, we demonstrate that NKG2D potentiates IL-15 mediated PI3K signaling in a narrow timeframe after activation, early during memory cell differentiation. Inhibition of PI3K or NKG2D signaling during this stage resulted in cell death of memory precursor cells and impaired memory formation. Ablation of NKG2D was accompanied by enhanced T-bet expression, effector cell differentiation and reduced survival. Conclusions: Here, we show a novel and crucial role for PI3Kmediated survival signaling early during memory cell differentiation, which is controlled by the IL-15/NKG2D axis. Our findings provide new insights in how these receptors may control both cytotoxicity and memory T cell differentiation. Moreover, it provides an important new therapeutic window for enhancing T cell based immunotherapy.