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Retinoic acid-inducible gene-I (RIG-I) is a cytoplasmic immune receptor sensing viral RNA. It triggers the release of type I interferons (IFN) and proinflammatory cytokines inducing an adaptive cellular immune response. We investigated the therapeutic potential of systemic RIG-I activation by short 5'-triphosphate-modified RNA (ppp-RNA) for the treatment of acute myeloid leukemia (AML) in the syngeneic murine C1498 AML tumor model. ppp-RNA treatment significantly reduced tumor burden, delayed disease onset and led to complete remission including immunological memory formation in a substantial proportion of animals. Therapy-induced tumor rejection was dependent on CD4 + and CD8 + T cells, but not on NK or B cells, and relied on intact IFN and mitochondrial antiviral signaling protein (MAVS) signaling in the host. Interestingly, ppp-RNA treatment induced programmed death ligand 1 (PD-L1) expression on AML cells and established therapeutic sensitivity to anti-PD-1 checkpoint blockade in vivo. In immune-reconstituted humanized mice, ppp-RNA treatment reduced the number of patient-derived xenografted (PDX) AML cells in blood and bone marrow while concomitantly enhancing CD3 + T cell counts in the respective tissues. Due to its ability to establish a state of full remission and immunological memory, our findings show that ppp-RNA treatment is a promising strategy for the immunotherapy of AML.

Pancreatic cancer is one of the most aggressive malignancies and has been considered poorly immunogenic for decades. However, this characterization might be over-simplistic. A more sophisticated approach is needed in order to develop new treatment strategies. In this review, we will focus on T cell exhaustion as a phenomenon of immune failure that is a useful paradigm to characterize immunosuppressive effects. Cancer creates an environment of constant antigen exposure and inflammation. In this setting, T cells transform into a differentiation state that has been termed T cell exhaustion, which is characterized by upregulation of inhibitory receptors, resulting in loss of effector function. The discovery of receptor-mediated immune checkpoints, which prevent uncontrolled T cell reactions, led to the development of a new class of antibodies termed checkpoint inhibitors. Unprecedented results in patients with metastatic melanoma and lung cancer have renewed interest in the immunotherapy of other solid tumor entities, including pancreatic cancer. Data on the efficacy of checkpoint inhibitors in pancreatic cancer are still sparse and indicate limited efficacy as single agents. Combination of checkpoint inhibitors with other immune-activating strategies or cytotoxic drugs might be a way to overcome therapy resistance in the treatment of pancreatic cancer., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Background: A number of new drugs for tumor immunotherapy have been approved in the past few years. They work by activating T cells to combat tumors., Methods: This review is based on publications on recently approved T-cell-activating drugs that were retrieved by a selective search in PubMed., Results: Randomized, controlled trials of "checkpoint" inhibitors, i.e., inhibitory antibodies for use against tumors, have shown that the cytotoxic T-lymphocyte antigen 4 (CTLA-4) inhibitor ipilimumab can prolong the survival of patients with advanced melanoma by 2 to 4 months. No data on median overall survival are yet available for the two programmed-death-1 (PD-1) inhibitors pembrolizumab und nivolumab; the endpoint "tumor response" was achieved in 24% and 32% of patients receiving these drugs, respectively. Grade 3 or 4 adverse effects occurred in 50% of patients receiving ipilimumab and in 12 to 13% of those taking either of the two PD-1-inhibitors. Nivolumab prolonged the median survival of patients with metastatic non-small-cell lung cancer from 6 to 9 months. In refractory or recurrent Philadelphia-chromosome-negative pre-B acute lymphoblastic leukemia (pre-B-ALL), treatment with the bispecific antibody construct blinatumomab led to complete remission in 43% of the patients, while grade 3, 4 or 5 toxicities occurred in 83%., Conclusion: T-cell-directed strategies have been established as a new pillar of treatment in medical oncology. As these drugs have frequent and severe adverse effects, therapeutic decision-making will have to take account not only of the predicted prolongation of survival, but also of the potential for an impaired quality of life while the patient is under treatment.

Despite continuous progress in the understanding of deregulated pathways in pancreatic cancer cells and development of targeted therapies, therapeutic advances with clinical benefit have been scarce over the last decades. The recent success of immunotherapy for some solid cancers has fueled optimism that this approach might also work for pancreatic cancer. However, a highly immunosuppressive microenvironment mediated by tumor, stromal and immune cells creates a major hurdle for immunotherapy. Mouse models have helped to unravel critical immunosuppressive mechanisms that could serve as novel therapeutic targets. Here we review new promising strategies that alone or in combination with other modalities, such as chemotherapy or irradiation, have the potential to lead to tumor immune control and finally better clinical outcome.

Vaccines based on immune stimulatory complexes (ISCOM) induce T-cell responses against tumor antigen (Ag). However, immune responses are impaired in pancreatic cancer patients. We investigated the efficacy of an ISCOM vaccine in a murine pancreatic carcinoma model. Panc02 cells expressing OVA as a model Ag were induced subcutaneously or orthotopically in the pancreas of C57BL/6 mice. Treatment consisted of an OVA containing ISCOM vaccine, either used alone or in combination with the TLR9 agonist CpG. The ISCOM vaccine effectively induced Ag-specific CTL capable of killing tumor cells. However, in mice with established tumors CTL induction by the vaccine was inefficient and did not affect tumor growth. Lack of efficacy correlated with increased numbers of Treg. Depletion of Treg with anti-CD25 mAb restored CTL induction and prolonged survival. Adding low-dose CpG to the ISCOM vaccine reduced Treg numbers, enhanced CTL responses and induced regression of pancreatic tumors in a CD8(+) T cell-dependent manner. Mice cured from the primary tumor mounted a memory T-cell response against wild-type Panc02 tumors, indicative of epitope spreading. Combining ISCOM vaccines with TLR agonists is a promising strategy for breaking tumor immune evasion and deserves further evaluation for the treatment of pancreatic carcinoma., (Copyright © 2010 UICC.)