Cancer control by adaptive immunity involves a number of defined death and clearance mechanisms. However, efficient inhibition of exponential cancer growth by T cells and interferon-γ (IFN-γ) requires additional undefined mechanisms that arrest cancer cell proliferation. Here we show that the combined action of the T-helper-1-cell cytokines IFN-γ and tumour necrosis factor (TNF) directly induces permanent growth arrest in cancers. To safely separate senescence induced by tumour immunity from oncogene-induced senescence, we used a mouse model in which the Simian virus 40 large T antigen (Tag) expressed under the control of the rat insulin promoter creates tumours by attenuating p53- and Rb-mediated cell cycle control. When combined, IFN-γ and TNF drive Tag-expressing cancers into senescence by inducing permanent growth arrest in G1/G0, activation of p16INK4a (also known as CDKN2A), and downstream Rb hypophosphorylation at serine 795. This cytokine-induced senescence strictly requires STAT1 and TNFR1 (also known as TNFRSF1A) signalling in addition to p16INK4a. In vivo, Tag-specific T-helper 1 cells permanently arrest Tag-expressing cancers by inducing IFN-γ- and TNFR1-dependent senescence. Conversely, Tnfr1(-/-)Tag-expressing cancers resist cytokine-induced senescence and grow aggressively, even in TNFR1-expressing hosts. Finally, as IFN-γ and TNF induce senescence in numerous murine and human cancers, this may be a general mechanism for arresting cancer progression.

Conserved molecular patterns derived from pathogenic microorganisms prime antigen-presenting dendritic cells (DC) to induce adaptive T cell responses. In contrast, virus-infected or tumor cells that express low levels of major histocompatibility complex (MHC) class I activate natural killer (NK) cells for direct killing. It is unknown whether NK cell recognition of MHC class I(low) targets can also induce adaptive T cell responses. Here, we show that MHC class I(low) targets initiate a cascade of immune responses, starting with the immediate activation of NK cells. The activated NK cells then prime DC to produce IL-12 and to induce highly protective CD8 T cell memory responses. Therefore, sensing of MHC class I(low) targets by NK cells can link innate and adaptive immunity to induce protective T cell responses and may alarm the immune system during early infection with noncytopathic viruses.

No therapeutic cancer vaccine has yet shown sufficient efficacy to be approved in the U.S., in part because of the complex immune response to vaccination. A study in Cancer Cell helps refine the tactics for developing pancreatic cancer vaccines, showing that local activity by tumor-seeking helper T cells can retard-or promote-tumor development. 1 The study, conducted by a team led by Martin Röcken, professor of dermatology at Eberhard Karls University, could help cancer vaccine makers design therapies that direct T cells to the right place and elicit the right kind of immune response. The group used an established mouse model in which overexpression of a viral oncoprotein called T antigen (TAG) promotes islet cell adeno-mas and, eventually, carcinomas in the pancreas. 2 Such tumors develop extensive vascular structures that facilitate tumor growth. The researchers raised helper T cells that recognized a TAG fragment in cell culture. The T cells were labeled with a fluorescent dye and injected into mice. Within days, the TAG-seeking T cells migrated to pancreatic lymph nodes in TAG-expressing mice but not in wild-type controls. Once on the scene, the T cells prevented both the appearance of new tumors and the expansion of existing ones beyond the adenoma stage. Compared with mock-treated controls, mice that received TAG-specific T cell transfusions had fewer and smaller pancreatic tumors with less extensive vascularization. T cell-treated mice, including those treated after tumors started to form, lived longer than mock-treated controls. "We show that T cells can induce tumor dormancy, " Röcken told SciBX. Playing TAG with tumors According to conventional wisdom, helper T cells act indirectly in cancer vaccines by secreting cytokines that prompt cytotoxic T cells to attack tumors. This principle is the basis of several therapeutic cancer vaccines. 3 However, Röcken's team found that mice lacking most of their cytotoxic T cells still could benefit from TAG-specific helper T cells. Although the pancreatic tumors of these T cell-treated mice showed no signs of apoptosis, which would be indicative of cytotoxic T cell attack, the researchers did see a decrease in the pancreatic incorporation of bro-modeoxyuridine (BrdU) compared with that seen in wild-type controls. BrdU labels newly replicated DNA in proliferating tumors.

It is generally accepted that priming of antitumor CD8 ؉ cytotoxic T lymphocytes (CTLs) needs help that can be provided by CD4 ؉ T cells. We show that interactions between dendritic cells (DCs) and natural killer (NK) cells can bypass the T helper arm in CTL induction. Bone marrow-derived DCs caused rejection of the A20 lymphoma and induced tumor-specific long-term memory, although they were not loaded with tumor-derived antigen. Experiments using CD40 ؊ knock-out mice and cell depletion showed that this effect did not require CD4 ؉ cells. Both primary rejection and long-term CTL memory were the result of NK cell activation by DCs. NK cytotoxicity, which was necessary for primary rejection, was dependent on expression of natural killer group 2 D (NKG2D) ligands on tumor cells. Blocking of these ligands using NKG2D tetramers abrogated tumor killing in vitro and in vivo. The long-term response was due to CTLs directed against antigen(s) expressed on A20 and in vitrodifferentiated DCs. The mechanism leading to CD4 ؉ helper cell-independent CTL responses was elucidated as a cascade that was initiated by NK cell activation. This pathway was dependent on interferon-␥ expression and involved priming endogenous DCs for interleukin-12 production. Our data suggest a novel pathway linking innate and adaptive immunity. ( IntroductionInduction of efficient immune responses requires a coordinated interplay between innate and adaptive immune effector systems. Dendritic cells (DCs) are components of the innate immune system that activate specific effectors of adaptive immunity. 1,2 In an immature state, DCs are able to ingest antigen (Ag). Following a maturation process that involves migration to lymphoid tissues, down-regulation of Ag uptake and upregulation of major histocompatibility complex (MHC) and costimulatory molecules, DCs present antigenic peptides to T lymphocytes. 1 Exogenous proteins are taken up and processed by DCs and presented to CD4 ϩ cells in association with MHC class II molecules, whereas intracellular Ags are presented by MHC class I molecules to CD8 ϩ cytotoxic T lymphocytes (CTLs). There is, however, emerging evidence that exogenous proteins can also be directed to the endogenous presentation pathway, thus leading to CTL induction, a process referred to as cross-presentation. Efficient generation of CTLs from naive CD8 ϩ T cells needs help from CD4 ϩ T cells. [3][4][5] This help involves secretion of cytokines and CD40/CD40L interactions that lead to increased expression of costimulatory molecules on DCs and to induction of interleukin-12 (IL-12). 6 As shown in mouse models, CD4 ϩ T cells are pivotal for protection against tumors and can even mediate tumor rejection independently of CD8 ϩ T lymphocytes, if they are biased toward a T helper 1 (Th1) response. 7 Expression of CD40 by DCs is crucial for the production of Th1 cytokines such as IL-12 and for tumor protection. 7,8 Natural killer (NK) cells are effector cells of the innate immune system that exert direct cytotoxic functions. 9 These are determ...