RIG-I-like helicases induce immunogenic cell death of pancreatic cancer cells and sensitize tumors toward killing by CD8(+) T cells.

Pancreatic cancer is characterized by a microenvironment suppressing immune responses. RIG-I-like helicases (RLH) are immunoreceptors for viral RNA that induce an antiviral response program via the production of type I interferons (IFN) and apoptosis in susceptible cells. We recently identified RLH as therapeutic targets of pancreatic cancer for counteracting immunosuppressive mechanisms and apoptosis induction. Here, we investigated immunogenic consequences of RLH-induced tumor cell death. Treatment of murine pancreatic cancer cell lines with RLH ligands induced production of type I IFN and proinflammatory cytokines. In addition, tumor cells died via intrinsic apoptosis and displayed features of immunogenic cell death, such as release of HMGB1 and translocation of calreticulin to the outer cell membrane. RLH-activated tumor cells led to activation of dendritic cells (DCs), which was mediated by tumor-derived type I IFN, whereas TLR, RAGE or inflammasome signaling was dispensable. Importantly, CD8α(+) DCs effectively engulfed apoptotic tumor material and cross-presented tumor-associated antigen to naive CD8(+) T cells. In comparison, tumor cell death mediated by oxaliplatin, staurosporine or mechanical disruption failed to induce DC activation and antigen presentation. Tumor cells treated with sublethal doses of RLH ligands upregulated Fas and MHC-I expression and were effectively sensitized towards Fas-mediated apoptosis and cytotoxic T lymphocyte (CTL)-mediated lysis. Vaccination of mice with RLH-activated tumor cells induced protective antitumor immunity in vivo. In addition, MDA5-based immunotherapy led to effective tumor control of established pancreatic tumors. In summary, RLH ligands induce a highly immunogenic form of tumor cell death linking innate and adaptive immunity.

Dendritic cell-based cancer vaccination: quo vadis?

Dendritic cells (DCs) play a central role in the initiation and regulation of primary immune responses. DCs loaded with tumor-associated antigens induce anti-tumoral cytotoxic T cells in vitro and in vivo. However, clinical trials using ex vivo-generated DCs have failed to demonstrate clinical efficacy. This review summarizes recent advances in concepts and techniques that are providing new impulses to DC-based cancer vaccination. Improvements in protocols for ex vivo-generation of DCs, innovations in immunomonitoring, strategies to overcome tumor-induced immunosuppression and insights into the mutual beneficial effects of vaccines and chemotherapy are all considered. Furthermore, we highlight novel developments in cell-free vaccines targeting DCs in vivo.

Dendritic cell-based vaccination combined with gemcitabine increases survival in a murine pancreatic carcinoma model.

BACKGROUND: Tumour-specific cytotoxic T lymphocytes (CTLs) can be activated in vivo by vaccination with dendritic cells (DCs). However, clinical responses to DC-based vaccination have only been observed in a minority of patients with solid cancer. Combination with other treatment modalities such as chemotherapy may overcome immunoresistance of cancer cells. It has been shown previously that gemcitabine sensitises human pancreatic carcinoma cells against CTL-mediated lysis. Here, a murine pancreatic carcinoma model was used to investigate whether combination with gemcitabine increases therapeutic efficacy of DC-based vaccination. METHODS: Bone marrow-derived DCs from C57BL/6 mice were loaded with UV-irradiated, syngeneic Panc02 carcinoma cells and were administered subcutaneously. For prophylactic vaccination, mice were vaccinated three times at weekly intervals prior to tumour challenge with Panc02 cells. Therapeutic vaccination was started when tumours formed a palpable nodule. Gemcitabine was administered intraperitoneally twice weekly. RESULTS: Prophylactic DC-based vaccination completely prevented subcutaneous and orthotopic tumour development and induced immunological memory as well as tumour antigen-specific CTLs. In the subcutaneous tumour model, therapeutic DC-based vaccination was equally effective as gemcitabine (14% vs 17% survival at day 58 after tumour challenge; controls, 0%). Combination of the two strategies significantly increased survival of tumour-bearing mice (50% at day 58 after tumour challenge). DC-based vaccination also prevented death from pulmonary metastatisation after intravenous injection of Panc02 cells. CONCLUSION: DC-based immunotherapy may not only be successfully combined with gemcitabine for the treatment of advanced pancreatic carcinoma, but may also be effective in preventing local recurrence or metastatisation in tumour-free patients.

Tumor cell lysate-pulsed human dendritic cells induce a T-cell response against pancreatic carcinoma cells: an in vitro model for the assessment of tumor vaccines.

Dendritic cells (DCs) are potent antigen-presenting cells and play a pivotal role in T cell-mediated immunity. DCs have been shown to induce strong antitumor immune responses in vitro and in vivo, and their efficacy is being investigated in clinical trials. Compared with vaccination strategies directed against a single tumor antigen, tumor-cell lysate as the source of antigen offers the potential advantage of inducing a broad T-cell response against multiple known, as well as unknown, tumor-associated antigens expressed by the individual tumor. We used pancreatic carcinoma cell lines to develop an in vitro model for monitoring T-cell responses induced by lysate-pulsed DCs. Monocyte-derived DCs of HLA-A2(+) donors were pulsed with lysate generated from the HLA-A2(+) pancreatic carcinoma cell line Panc-1. In some experiments, the immunogenic protein keyhole limpet hemocyanin (KLH) was added to the lysate. Subsequently, the antigen-loaded DCs were activated with tumor necrosis factor-alpha and prostaglandin E(2). Autologous mononuclear cells were cocultured with DCs in the presence of low-dose interleukin (IL)-2 and IL-7 and were restimulated weekly with new DCs. High levels of IL-12 and IFN-gamma could be detected in the supernatants, indicating a T-helper type 1-type immune response. This cytokine profile was associated with the expression of the activation marker CD69 on both T helper and CTLs and with an antigen-induced proliferative T-cell response. After 4 weeks, CTL-mediated cytotoxicity was assessed. Tumor cell lysis was specific for Panc-1 tumor cells and was MHC class I-restricted. Cytokine secretion, CD69 expression of T cells, and antigen-induced T-cell proliferation correlated with the cytotoxic activity and were more pronounced when KLH was added to the lysate. This is the first study to show that T cells specific for pancreatic carcinoma cells can be generated in vitro by lysate-pulsed DCs and that the T-cell response can be enhanced by KLH. This in vitro model can be applied to compare different strategies in the development of DC-based tumor vaccines.

Extracellular ATP and TNF-alpha synergize in the activation and maturation of human dendritic cells.

Extracellular ATP mediates numerous biological activities by interacting with plasma membrane P2 purinergic receptors. Recently, P2 receptors have been described on dendritic cells (DC), but their functional role remains unclear. Proposed functions include improved Ag presentation, cytokine production, chemotaxis, and induction of apoptosis. We investigated the effects of ATP and of other P2 receptor agonists on endocytosis, phenotype, IL-12 secretion, and T cell stimulatory capacity of human monocyte-derived DC. We found that in the presence of extracellular ATP, DC transiently increase their endocytotic activity. Subsequently, DC up-regulate CD86, CD54, and MHC-II; secrete IL-12; and exhibit an improved stimulatory capacity for allogeneic T cells. These effects were more pronounced when chemically modified ATP derivatives with agonistic activity on P2 receptors, which are resistent to degradation by ectonucleotidases, were applied. Furthermore, ATP and TNF-alpha synergized in the activation of DC. Stimulated with a combination of ATP and TNF-alpha, DC expressed the maturation marker CD83, secreted large amounts of IL-12, and were potent stimulators of T cells. In the presence of the P2 receptor antagonist suramin, the effects of ATP were completely abolished. Our results suggest that extracellular ATP may play an important immunomodulatory role by activating DC and by skewing the immune reaction toward a Th1 response through the induction of IL-12 secretion.

Nonrandom chromosomal abnormalities in bovine lymphoma.

Despite detailed knowledge of the genetic map of the bovine leukemia virus (BLV), the mechanism whereby BLV infection results in transformation and B-lineage restriction of tumors is poorly understood. The aim of this study was to gain new insight into pathogenetic mechanisms of BLV-induced tumorigenesis by determining the karyotypes of BLV-associated lymphomas in cattle. Metaphases in cells from lymphoid tumors from 20 mature dairy cows were banded and analyzed after short-term, unstimulated culture. Nineteen out of twenty cases exhibited clonal abnormalities, 17 cases were hyperdiploid, and 16 cases had extremely complex chromosomal changes. Recurrent chromosomal anomalies were identified and there was clear evidence for the evolution of increasing chromosomal instability in 12 cases. The most common abnormalities were the acquisition of additional small chromosomes (23-29); trisomy of chromosomes 5 and 7, and Robertsonian translocations and isochromosome rearrangements involving chromosomes 10, 12, 23, and 26. Monosomy X, trisomy X, and translocations involving the X chromosome were also detected. Chromosomes 2, 3, 4, 6, 8, 9, 11, 13, 14, 19, and 21 were infrequently involved in either structural or numerical changes. Structural rearrangements of chromosomes 10, 12, 23, and 26 may reflect primary abnormalities occurring relatively early in transformation, whereas trisomy 5 may be an extremely common secondary abnormality. While comparison of these findings with the current bovine gene map raises intriguing possibilities for pathogenetic mechanisms, further studies are needed before hypothetical mechanisms linking chromosomal abnormalities with BLV-induced transformation can be made.

Determination of oxolinic acid residues in salmon muscle tissue by liquid chromatography with fluorescence detection.

The present paper describes a method for determination of oxolinic acid in salmon muscle tissue. Tissue (0.5-2 g) mixed with 2 g anhydrous sodium sulfate is extracted twice with ethyl acetate, centrifuged, and the extract evaporated. The residue is partitioned in a mixture of hexane and 0.01M oxalic acid and the aqueous phase chromatographed using fluorescence detection at 327 nm excitation and 369 nm emission. Calibration and standard curves are linear from 10-200 ppb and 100-2000 ppb at different sensitivity settings. Recoveries ranged from 71-83% in spiked blanks, with a CV of 4-10.3% over a 2-week period. Preliminary results in treated salmon were variable, possibly because some fish refused to eat medicated feed.