Anticancer immunochemotherapy using adjuvants with direct cytotoxic effects

Tyrosinase-Related Protein2 Peptide with Replacement of N-Terminus Residue by Cysteine Binds to H-2Kb and Induces Antigen-Specific Cytotoxic T Lymphocytes after Conjugation with CpG-DNA

Recent studies have shown the potent efficacy of peptide-based vaccines for cancer immunotherapy. Immunological performance is optimized through the co-delivery of adjuvant and antigenic peptide molecules to antigen-presenting cells simultaneously. In our previous study, we showed that a conjugate consisting of 40-mer CpG-DNA and an antigenic ovalbumin peptide through disulfide bonding could efficiently induce ovalbumin-specific cytotoxic T lymphocyte (CTL) responses in vivo. In this study, based on the conjugation design, we prepared a conjugate consisting of 30-mer CpG-DNA (CpG30) and a cancer antigenic peptide of Tyrosinase-related protein 2 (TRP2_180-188) using a cysteine residue attached at the N-terminus of TRP2_180-188. However, the immunization of mice with this conjugate did not induce efficient TRP2_180-188-specific immune responses. It was thought that the resultant peptide (10-mer) cleaved from the conjugate might be too long to fit into the H-2K^b molecule because the optimal length for binding to it is 8-9 amino acids. We newly designed a conjugate consisting of CpG30 and the C-TRP2_181-188 peptide (9-mer), in which the N-terminal serine residue of TRP2_180-188 is replaced by a cysteine. By adjusting the peptide length, we succeeded in inducing strong TRP2_180-188 peptide-specific CTL activity upon immunization with the CpG30-C-TRP2_181-188 conjugate. Furthermore, various CpG30-C-TRP2_181-188 conjugates having other CpG-DNA sequences or cysteine analogues also induced the same level of CTL activity. Therefore, CpG-C-peptide conjugates prepared by replacement of the amino acid residue at the N-terminus with a cysteine residue could be a new and effective platform for peptide vaccines for targeting specific antigens of cancers and infectious diseases.

Effect of Chemotherapeutics on In Vitro Immune Checkpoint Expression in Non-Small Cell Lung Cancer

Objectives: Immune checkpoint (ICP) expression in tumor cells could directly or indirectly affect the results of immunotherapy. ICP ligands on tumor cells usually bind their immune cell receptors to inhibit the activity, resulting in tumor immune escape. Thus, the purpose of this study was to ascertain the impact of various chemotherapeutic drugs on ICP expression in non-small cell lung cancer (NSCLC) cell lines with different pathological subtypes to provide a basis for the development of a superior regimen of chemotherapy combined with ICP blockade. Methods: Several first-line chemotherapy agents (cisplatin, carboplatin, paclitaxel, gemcitabine, vinorelbine, and pemetrexed) were selected to treat different NSCLC cell lines (squamous carcinoma H1703, adenocarcinoma A549, and large cell cancer H460) for 72 hours, and then the changes in ICP expression in the tumor cells were observed through flow cytometry. Results: Cisplatin, carboplatin, and paclitaxel upregulated the expressions of programmed cell death ligand 1 (PD-L1) and programmed cell death ligand 2 (PD-L2) in A549 and H460 cell lines. Meanwhile, vinorelbine and pemetrexed upregulated PD-L1 and PD-L2 in H1703, A549, and H460 cell lines. Paclitaxel, gemcitabine, vinorelbine, and pemetrexed significantly upregulated the expressions of both galectin-9 and high-mobility group box protein 1 (HMGB1) in the A549 cell line. Cisplatin and paclitaxel significantly upregulated the expressions of major histocompatibility complex-II (MHC-II), galectin-3, α-synuclein, and fibrinogen-like protein 1 (FGL1) in A549 and H460 cell lines. In addition, cisplatin and vinorelbine significantly upregulated the expressions of both CD155 and CD112 in the H460 cell line. Vinorelbine upregulated MHC-I in all three cell lines. Conclusion: Chemotherapy agents have different effects on the expression of ICP ligands in tumor cells with different pathological types, and this may affect the efficacy of combined immunotherapy. These results provide a theoretical basis for further selection and optimization of the combination of chemotherapy and immunotherapy.

Cancer Vaccine in Cold Tumors: Clinical Landscape, Challenges, and Opportunities

The idea of cancer immunotherapy is to stimulate the immune system to fight tumors without destroying normal cells. One of the anticancer therapy methods, among many, is based on the use of cancer vaccines that contain tumor antigens in order to induce immune responses against tumors. However, clinical trials have shown that the use of such vaccines as a monotherapy is ineffective in many cases, since they do not cause a strong immune response. Particular tumors are resistant to immunotherapy due to the absence or insufficient infiltration of tumors with CD8+ T cells, and hence, they are called cold or non-inflamed tumors. Cold tumors are characterized by a lack of CD8+ T cell infiltration, the presence of anti-inflammatory myeloid cells, tumor-associated M2 macrophages, and regulatory T cells. It is very important to understand which stage of the antitumor response does not work properly in order to use the right strategy for the treatment of patients. Applying other therapeutic methods alongside cancer vaccines can be more rational for cold tumors which do not provoke the immune system strongly. Herein, we indicate some combinational therapies that have been used or are in progress for cold tumor treatment alongside vaccines.

Repositioning of Antiparasitic Drugs for Tumor Treatment

Drug repositioning is a strategy for identifying new antitumor drugs; this strategy allows existing and approved clinical drugs to be innovatively repurposed to treat tumors. Based on the similarities between parasitic diseases and cancer, recent studies aimed to investigate the efficacy of existing antiparasitic drugs in cancer. In this review, we selected two antihelminthic drugs (macrolides and benzimidazoles) and two antiprotozoal drugs (artemisinin and its derivatives, and quinolines) and summarized the research progresses made to date on the role of these drugs in cancer. Overall, these drugs regulate tumor growth via multiple targets, pathways, and modes of action. These antiparasitic drugs are good candidates for comprehensive, in-depth analyses of tumor occurrence and development. In-depth studies may improve the current tumor diagnoses and treatment regimens. However, for clinical application, current investigations are still insufficient, warranting more comprehensive analyses.

High-throughput approaches to discover novel immunomodulatory agents for cancer

The clinical success of immunomodulatory thalidomide derivatives has renewed the general interest in immunomodulatory anticancer compounds and prompted us to develop a high-throughput system to quantify immune effector-cell activity. We documented that the interaction between cancer cells, their stroma, anticancer agents and cells from the innate system are critical for determining the response of tumors to immunomodulatory strategies.

Immune Responses and Antitumor Effect through Delivering to Antigen Presenting Cells by Optimized Conjugates Consisting of CpG-DNA and Antigenic Peptide

Immunotherapy using antigen-specific cytotoxic T lymphocytes (CTLs) has become one of the most attractive strategies for cancer treatment. For the induction of antigen-specific CTLs in vivo, the co-delivery of CpG-DNAs and antigens to the same antigen-presenting cells (APCs) is a promising strategy. In this study, we prepared conjugates consisting of 40mer of CpG-DNA (CpG40) and antigenic peptide (OVA_257-264), which have the following distinctive features: (1) multiple CpG motifs in a molecule; (2) cleavage in the cytosol because of the disulfide bonding via cysteine residue between peptide and CpG-DNA; (3) conjugation designed to induce antigen presentation on MHC class I molecules. Immunization with the conjugate CpG40-C-OVA_257-264 at the mouse tail base induced strong CTL activity at a very low peptide dose of 20 ng/head. It was found that the conjugates were internalized into C-type mannose receptor 1 (MRC1)-expressing cells in inguinal lymph nodes, indicating that the CpG portion in the conjugate acts as not only an adjuvant for the activation of TLR9 but also a carrier to APCs expressing MRC1. In a tumor-bearing mice model, mice immunized with CpG40-C-OVA_257-264 conjugates exhibited long delays in tumor growth compared with those treated with PBS, OVA_257-264 alone, or a mixture of CpG40 and OVA_257-264. Therefore, CpG-C-peptide conjugates could be a new and effective platform for peptide vaccine for the treatment of cancers and infectious diseases.

Building a Bridge between Chemotherapy and Immunotherapy in Malignant Pleural Mesothelioma: Investigating the Effect of Chemotherapy on Immune Checkpoint Expression

In light of the promising results of immune checkpoint blockade (ICPB) in malignant pleural mesothelioma (MPM), we investigated the effect of different chemotherapeutic agents on the expression of immune checkpoints (ICPs) in order to rationally design a good treatment schedule for their combination with ICP blocking antibodies. Cisplatin, oxaliplatin and pemetrexed are interesting chemotherapeutic agents to combine with immunotherapy given their immunomodulatory capacities. We looked into cisplatin and pemetrexed because their combination is used as first-line treatment of MPM. Additionally, the effect of the immunogenic chemotherapeutic agent, oxaliplatin, was also studied. Three different MPM cell lines were used for representation of both epithelioid and sarcomatoid subtypes. The desired inhibitory concentrations of the chemotherapeutic agents were determined with the SRB-assay. Allogeneic co-cultures of MPM cells with healthy donor peripheral blood mononuclear cells (PBMC) were set up to assess the effect of these chemotherapeutic agents on the expression of ICPs (PD-1, LAG-3, TIM-3) and their ligands (PD-L1, PD-L2, galectin-9). Cisplatin might be a promising treatment to combine with ICP blocking antibodies since our MPM cell lines were most susceptible to this stand-alone treatment. We found that the expression of ICPs and their ligands on both MPM cells and PBMC was mostly downregulated or unaltered when treated with chemotherapeutic agents, though no clear trend could be determined.

Knockdown of IGF-1R Triggers Viral RNA Sensor MDA5- and RIG-I-Mediated Mitochondrial Apoptosis in Colonic Cancer Cells

The important role of insulin-like growth factor-1 receptor (IGF-1R) in tumorigenesis has been well established. The classical model involves IGF-1R binding to IGF-1/2, the following activation of PI3K-Akt-signaling cascades, driving cell proliferation and apoptosis inhibition. Here we report a new signal transduction pathway of IGF-1R in the intestinal epithelium. Using heterozygous knockout mice (Igf1r^+/-), we analyzed the expressions of viral RNA sensors MDA5 and RIG-I in the intestinal epithelium. Igf1r^+/- mice exhibited higher MDA5 and RIG-I than wild-type (WT) mice, indicating that knockdown of IGF-1R could trigger MDA5 and RIG-I. IGF-1R knockdown-triggered MDA5 and RIG-I were further investigated in human colonic cancer cells. Increased MDA5 and RIG-I were clearly seen in the cytoplasm in cancer cells as well as normal human colonic cells with silenced IGF-1R. Notably, the upregulations of MDA5 and RIG-I was not affected by blockage of the PI3K-Akt pathway with LY294002. These results suggested a new signal transduction pathway of IGF-1R. Importantly, IGF-1R knockdown-triggered MDA5 and RIG-I resulted in colorectal cancer apoptosis through activation of the mitochondrial pathway. These in vitro observations were evidenced in the azoxymethane (AOM)-dextran sulfate sodium (DSS) colorectal cancer model of mice. In conclusion, knockdown of IGF-1R triggers viral RNA sensor MDA5- and RIG-I-mediated mitochondrial apoptosis in cancer cells.

Next Generation Cancer Vaccines-Make It Personal!

Dramatic success in cancer immunotherapy has been achieved over the last decade with the introduction of checkpoint inhibitors, leading to response rates higher than with chemotherapy in certain cancer types. These responses are often restricted to cancers that have a high mutational burden and show pre-existing T-cell infiltrates. Despite extensive efforts, therapeutic vaccines have been mostly unsuccessful in the clinic. With the introduction of next generation sequencing, the identification of individual mutations is possible, enabling the production of personalized cancer vaccines. Combining immune check point inhibitors to overcome the immunosuppressive microenvironment and personalized cancer vaccines for directing the host immune system against the chosen antigens might be a promising treatment strategy.

Combined roles of ATP and small hairpin RNA in the activation of RIG-I revealed by solution-based analysis

RIG-I (retinoic acid inducible gene-I) is a cytosolic innate immune protein that senses viral dsRNA with a 5'-triphosphate overhang. Upon interaction with dsRNA a de-repression of the RIG-I CARD domains takes place that ultimately leads to the production of type I interferons and pro-inflammatory cytokines. Here we investigate the RIG-I conformational rearrangement upon interaction with an activating 5'-triphosphate-10-base pair dsRNA hairpin loop (10bp) compared with a less active 5'-triphosphate-8-base pair dsRNA hairpin loop (8bp). We use size-exclusion chromatography-coupled small-angle X-ray scattering (SAXS) and limited tryptic digest experiments to show that that upon binding to 10 bp, but not 8 bp, RIG-I becomes extended and shows greater flexibility, reflecting the release of its CARDs. We also examined the effect of different ATP analogues on the conformational changes of RIG-I/dsRNA complexes. Of the analogues tested, the addition of ATP transition state analogue ADP-AlFx further assisted in the complete activation of RIG-I in complex with 10bp and also to some extent RIG-I bound to 8bp. Together these data provide solution-based evidence for the molecular mechanism of innate immune signaling by RIG-I as stimulated by short hairpin RNA and ATP.

Peripheral and local predictive immune signatures identified in a phase II trial of ipilimumab with carboplatin/paclitaxel in unresectable stage III or stage IV melanoma

BACKGROUND

Checkpoint blockade with ipilimumab provides long-term survival to a significant proportion of patients with metastatic melanoma. New approaches to increase survival and to predict which patients will benefit from treatment are needed. This phase II trial combined ipilimumab with carboplatin/paclitaxel (CP) to assess its safety, efficacy, and to search for peripheral and tumor-based predictive biomarkers.

METHODS

Thirty patients with untreated unresectable/metastatic melanoma were treated with ipilimumab and CP. Adverse events (AEs) were monitored and response to treatment was evaluated. Tumor tissue and peripheral blood were collected at specified time points to characterize tumor immune markers by immunohistochemistry and systemic immune activity by multiplex assays and flow cytometry.

RESULTS

Eighty three percent of patients received all 5 cycles of CP and 93% completed ipilimumab induction. Serious AEs occurred in 13% of patients, and no treatment-related deaths were observed. Best Overall Response Rate (BORR) and Disease Control Rate (DCR) were 27 and 57%, respectively. Median overall survival was 16.2 months. Response to treatment was positively correlated with a higher tumor CD3+ infiltrate (immune score) at baseline. NRAS and BRAF mutations were less frequent in patients who experienced clinical benefit. Assessment of peripheral blood revealed that non-responders had elevated baseline levels of CXCL8 and CCL4, and a higher proportion of circulating late differentiated B cells. Pre-existing high levels of chemokines (CCL3, CCL4 and CXCL8) and advanced B cell differentiation were strongly associated with worse patient overall survival. Elevated proportions of circulating CD8+/PD-1+ T cells during treatment were associated with worse survival.

CONCLUSIONS

The combination of ipilimumab and CP was well tolerated and revealed novel characteristics associated with patients likely to benefit from treatment. A pre-existing systemic inflammatory state characterized by elevation of selected chemokines and advanced B cell differentiation, was strongly associated with poor patient outcomes, revealing potential predictive circulating biomarkers.

TRIAL REGISTRATION

Clinicaltrials.gov , NCT01676649 , registered on August 29, 2012.

Cancer vaccines: Enhanced immunogenic modulation through therapeutic combinations

Therapeutic cancer vaccines have gained significant popularity in recent years as new approaches for specific oncologic indications emerge. Three therapeutic cancer vaccines are FDA approved and one is currently approved by the EMA as monotherapy with modest treatment effects. Combining therapeutic cancer vaccines with other treatment modalities like radiotherapy (RT), hormone therapy, immunotherapy, and/or chemotherapy have been investigated as a means to enhance immune response and treatment efficacy. There is growing preclinical and clinical data that combination of checkpoint inhibitors and vaccines can induce immunogenic intensification with favorable outcomes. Additionally, novel methods for identifying targetable neoantigens hold promise for personalized vaccine development. In this article, we review the rationale for various therapeutic combinations, clinical trial experiences, and future directions. We also highlight the most promising developments that could lead to approval of novel therapeutic cancer vaccines.

Vaccine adjuvants as potential cancer immunotherapeutics

Accumulated evidence obtained from various clinical trials and animal studies suggested that cancer vaccines need better adjuvants than those that are currently licensed, which include the most commonly used alum and incomplete Freund's adjuvant, because of either a lack of potent anti-tumor immunity or the induction of undesired immunity. Several clinical trials using immunostimulatory adjuvants, particularly agonistic as well as non-agonistic ligands for TLRs, C-type lectin receptors, retinoic acid-inducible gene I-like receptors and stimulator of interferon genes, have revealed their therapeutic potential not only as vaccine adjuvants but also as anti-tumor agents. Recently, combinations of such immunostimulatory or immunomodulatory adjuvants have shown superior efficacy over their singular use, suggesting that seeking optimal combinations of the currently available or well-characterized adjuvants may provide a better chance for the development of novel adjuvants for cancer immunotherapy.

Tumor suppressor activity of RIG-I

Retinoic acid inducible gene-I (RIG-I), named for the observation that its mRNA expression is highly upregulated in the progression of all-trans retinoic acid (ATRA)-induced maturation of acute promyelocytic leukemia (APL) cells, has been well documented as a pivotal virus-associated molecular pattern recognition receptor (PRR) responsible for triggering innate immunity. Upon recognizing viral RNA ligands, RIG-I experiences a series of programmed conformational changes and modifications that unleash its activity through the formation of complexes with various binding partners. Such partners include the mitochondria membrane-anchored protein IPS-1 (also named MAVS/VISA/Cardif) that activates both the IRF3/7 and NF-κB pathways. These partnerships and resulting pathway activations underlie the synthesis of type I interferon and other inflammatory factors. Recent studies have demonstrated that RIG-I is also involved in the regulation of basic cellular processes outside of innate immunity against viral infections, such as hematopoietic proliferation and differentiation, maintenance of leukemic stemness, and tumorigenesis of hepatocellular carcinoma. In this review, we will highlight recent studies leading up to the recognition that RIG-I performs an essential function as a tumor suppressor and try to reconcile this activity of RIG-I with its well-known role in protecting cells against viral infection.

Potentiation of immunomodulatory antibody therapy with oncolytic viruses for treatment of cancer

Identification of the immune suppressive mechanisms active within the tumor microenvironment led to development of immunotherapeutic strategies aiming to reverse the immunosuppression and to enhance the function of tumor-infiltrating lymphocytes. Of those, cancer therapy with antibodies targeting the immune costimulatory and coinhibitory receptors has demonstrated significant promise in the recent years, with multiple antibodies entering clinical testing. The responses to these agents, however, have not been universal and have not been observed in all cancer types, calling for identification of appropriate predictive biomarkers and development of combinatorial strategies. Pre-existing immune infiltration in tumors has been demonstrated to have a strong association with response to immunotherapies, with the type I interferon (IFN) pathway emerging as a key player in tumor innate immune recognition and activation of adaptive immunity. These findings provide a rationale for evaluation of strategies targeting the type I IFN pathway as a means to enhance tumor immune recognition and infiltration, which could potentially make them susceptible to therapeutics targeting the cosignaling receptors. To this end in particular, oncolytic viruses (OVs) have been demonstrated to enhance tumor recognition by the immune system through multiple mechanisms, which include upregulation of major histocompatibility complex and costimulatory molecules on cancer cells, immunogenic cell death and antigen release, and activation of the type I IFN pathway. Evidence is now emerging that combination therapies using OVs and agents targeting immune cosignaling receptors such as 4-1BB, PD-1, and CTLA-4 may work in concert to enhance antitumor immunity and therapeutic efficacy. Our evolving understanding of the interplay between OVs and the immune system demonstrates that the virus-induced antitumor immune responses can be harnessed to drive the efficacy of the agents targeting cosignaling receptors and provides a strong rationale for integration of such therapies in clinic.

Complementary induction of immunogenic cell death by oncolytic parvovirus H-1PV and gemcitabine in pancreatic cancer

Novel therapies employing oncolytic viruses have emerged as promising anticancer modalities. The cure of particularly aggressive malignancies requires induction of immunogenic cell death (ICD), coupling oncolysis with immune responses via calreticulin, ATP, and high-mobility group box protein B1 (HMGB1) release from dying tumor cells. The present study shows that in human pancreatic cancer cells (pancreatic ductal adenocarcinoma [PDAC] cells n=4), oncolytic parvovirus H-1 (H-1PV) activated multiple interconnected death pathways but failed to induce calreticulin exposure or ATP release. In contrast, H-1PV elevated extracellular HMGB1 levels by 4.0±0.5 times (58%±9% of total content; up to 100 ng/ml) in all infected cultures, whether nondying, necrotic, or apoptotic. An alternative secretory route allowed H-1PV to overcome the failure of gemcitabine to trigger HMGB1 release, without impeding cytotoxicity or other ICD activities of the standard PDAC medication. Such broad resistance of H-1PV-induced HMGB1 release to apoptotic blockage coincided with but was uncoupled from an autocrine interleukin-1β (IL-1β) loop. That and the pattern of viral determinants maintained in gemcitabine-treated cells suggested the activation of an inflammasome/caspase 1 (CASP1) platform alongside DNA detachment and/or nuclear exclusion of HMGB1 during early stages of the viral life cycle. We concluded that H-1PV infection of PDAC cells is signaled through secretion of the alarmin HMGB1 and, besides its own oncolytic effect, might convert drug-induced apoptosis into an ICD process. A transient arrest of cells in the cyclin A1-rich S phase would suffice to support compatibility of proliferation-dependent H-1PV with cytotoxic regimens. These properties warrant incorporation of the oncolytic virus H-1PV, which is not pathogenic in humans, into multimodal anticancer treatments.

IMPORTANCE

The current therapeutic concepts targeting aggressive malignancies require an induction of immunogenic cell death characterized by exposure of calreticulin (CRT) as well as release of ATP and HMGB1 from dying cells. In pancreatic tumor cells (PDAC cells) infected with the oncolytic parvovirus H-1PV, only HMGB1 was released by all infected cells, whether nondying, necrotic, or succumbing to one of the programmed death pathways, including contraproductive apoptosis. Our data suggest that active secretion of HMGB1 from PDAC cells is a sentinel reaction emerging during early stages of the viral life cycle, irrespective of cell death, that is compatible with and complements cytotoxic regimens. Consistent induction of HMGB1 secretion raised the possibility that this reaction might be a general "alarming" phenomenon characteristic of H-1PV's interaction with the host cell; release of IL-1β points to the possible involvement of a danger-sensing inflammasome platform. Both provide a basis for further virus-oriented studies.

Clinical Implications of Co-Inhibitory Molecule Expression in the Tumor Microenvironment for DC Vaccination: A Game of Stop and Go

The aim of therapeutic dendritic cell (DC) vaccines in cancer immunotherapy is to activate cytotoxic T cells to recognize and attack the tumor. T cell activation requires the interaction of the T cell receptor with a cognate major-histocompatibility complex-peptide complex. Although initiated by antigen engagement, it is the complex balance between co-stimulatory and co-inhibitory signals on DCs that results in T cell activation or tolerance. Even when already activated, tumor-specific T cells can be neutralized by the expression of co-inhibitory molecules on tumor cells. These and other immunosuppressive cues in the tumor microenvironment are major factors currently hampering the application of DC vaccination. In this review, we discuss recent data regarding the essential and complex role of co-inhibitory molecules in regulating the immune response within the tumor microenvironment. In particular, possible therapeutic intervention strategies aimed at reversing or neutralizing suppressive networks within the tumor microenvironment will be emphasized. Importantly, blocking co-inhibitory molecule signaling, often referred to as immune checkpoint blockade, does not necessarily lead to an effective activation of tumor-specific T cells. Therefore, combination of checkpoint blockade with other immune potentiating therapeutic strategies, such as DC vaccination, might serve as a synergistic combination, capable of reversing effector T cells immunosuppression while at the same time increasing the efficacy of T cell-mediated immunotherapies. This will ultimately result in long-term anti-tumor immunity.

Deciphering and reversing tumor immune suppression

Generating an anti-tumor immune response is a multi-step process that is executed by effector T cells that can recognize and kill tumor targets. However, tumors employ multiple strategies to attenuate the effectiveness of T-cell-mediated attack. They achieve this by interfering with nearly every step required for effective immunity, from deregulation of antigen-presenting cells to establishment of a physical barrier at the vasculature that prevents homing of effector tumor-rejecting cells and the suppression of effector lymphocytes through the recruitment and activation of immunosuppressive cells such as myeloid-derived suppressor cells, tolerogenic monocytes, and T regulatory cells. Here, we review the ways in which tumors exert immune suppression and highlight the new therapies that seek to reverse this phenomenon and promote anti-tumor immunity. Understanding anti-tumor immunity, and how it becomes disabled by tumors, will ultimately lead to improved immune therapies and prolonged survival of patients.

Deciphering and reversing tumor immune suppression

Generating an anti-tumor immune response is a multi-step process that is executed by effector T cells that can recognize and kill tumor targets. However, tumors employ multiple strategies to attenuate the effectiveness of T-cell-mediated attack. They achieve this by interfering with nearly every step required for effective immunity, from deregulation of antigen-presenting cells to establishment of a physical barrier at the vasculature that prevents homing of effector tumor-rejecting cells and the suppression of effector lymphocytes through the recruitment and activation of immunosuppressive cells such as myeloid-derived suppressor cells, tolerogenic monocytes, and T regulatory cells. Here, we review the ways in which tumors exert immune suppression and highlight the new therapies that seek to reverse this phenomenon and promote anti-tumor immunity. Understanding anti-tumor immunity, and how it becomes disabled by tumors, will ultimately lead to improved immune therapies and prolonged survival of patients.

A caspase-3 'death-switch' in colorectal cancer cells for induced and synchronous tumor apoptosis in vitro and in vivo facilitates the development of minimally invasive cell death biomarkers

Novel anticancer drugs targeting key apoptosis regulators have been developed and are undergoing clinical trials. Pharmacodynamic biomarkers to define the optimum dose of drug that provokes tumor apoptosis are in demand; acquisition of longitudinal tumor biopsies is a significant challenge and minimally invasive biomarkers are required. Considering this, we have developed and validated a preclinical 'death-switch' model for the discovery of secreted biomarkers of tumour apoptosis using in vitro proteomics and in vivo evaluation of the novel imaging probe [(18)F]ML-10 for non-invasive detection of apoptosis using positron emission tomography (PET). The 'death-switch' is a constitutively active mutant caspase-3 that is robustly induced by doxycycline to drive synchronous apoptosis in human colorectal cancer cells in vitro or grown as tumor xenografts. Death-switch induction caused caspase-dependent apoptosis between 3 and 24 hours in vitro and regression of 'death-switched' xenografts occurred within 24 h correlating with the percentage of apoptotic cells in tumor and levels of an established cell death biomarker (cleaved cytokeratin-18) in the blood. We sought to define secreted biomarkers of tumor apoptosis from cultured cells using Discovery Isobaric Tag proteomics, which may provide candidates to validate in blood. Early after caspase-3 activation, levels of normally secreted proteins were decreased (e.g. Gelsolin and Midkine) and proteins including CD44 and High Mobility Group protein B1 (HMGB1) that were released into cell culture media in vitro were also identified in the bloodstream of mice bearing death-switched tumors. We also exemplify the utility of the death-switch model for the validation of apoptotic imaging probes using [(18)F]ML-10, a PET tracer currently in clinical trials. Results showed increased tracer uptake of [(18)F]ML-10 in tumours undergoing apoptosis, compared with matched tumour controls imaged in the same animal. Overall, the death-switch model represents a robust and versatile tool for the discovery and validation of apoptosis biomarkers.

The role of tumour-stromal interactions in modifying drug response: challenges and opportunities

The role of stromal cells and the tumour microenvironment in general in modulating tumour sensitivity is increasingly becoming a key consideration for the development of active anticancer therapeutics. Here, we discuss how these tumour-stromal interactions affect tumour cell signalling, survival, proliferation and drug sensitivity. Particular emphasis is placed on the ability of stromal cells to confer - to tumour cells - resistance or sensitization to different classes of therapeutics, depending on the specific microenvironmental context. The mechanistic understanding of these microenvironmental interactions can influence the evaluation and selection of candidate agents for various cancers, in both the primary site as well as the metastatic setting. Progress in in vitro screening platforms as well as orthotopic and 'orthometastatic' xenograft mouse models has enabled comprehensive characterization of the impact of the tumour microenvironment on therapeutic efficacy. These recent advances can hopefully bridge the gap between preclinical studies and clinical trials of anticancer agents.

Duplex RNA activated ATPases (DRAs): platforms for RNA sensing, signaling and processing

Double-stranded RNAs are an important class of functional macromolecules in living systems. They are usually found as part of highly specialized intracellular machines that control diverse cellular events, ranging from virus replication, antiviral defense, RNA interference, to regulation of gene activities and genomic integrity. Within different intracellular machines, the RNA duplex is often found in association with specific RNA-dependent ATPases, including Dicer, RIG-I and DRH-3 proteins. These duplex RNA-activated ATPases represent an emerging group of motor proteins within the large and diverse super family 2 nucleic acid-dependent ATPases (which are historically defined as SF2 helicases). The duplex RNA-activated ATPases share characteristic molecular features for duplex RNA recognition, including motifs (e.g., motifs IIa and Vc) and an insertion domain (HEL2i), and they require double-strand RNA binding for their enzymatic activities. Proteins in this family undergo large conformational changes concomitant with RNA binding, ATP binding and ATP hydrolysis in order to achieve their functions, which include the release of signaling domains and the recruitment of partner proteins. The duplex RNA-activated ATPases represent a distinct and fascinating group of nanomechanical molecular motors that are essential for duplex RNA sensing and processing in diverse cellular pathways.

Strategies for enhancing vaccine-induced CTL antitumor immune responses

Vaccine-induced cytotoxic T lymphocytes (CTLs) play a critical role in adaptive immunity against cancers. An important goal of current vaccine research is to induce durable and long-lasting functional CTLs that can mediate cytotoxic effects on tumor cells. To attain this goal, there are four distinct steps that must be achieved. To initiate a vaccine-induced CTL antitumor immune response, dendritic cells (DCs) must capture antigens derived from exogenous tumor vaccines in vivo or autologous DCs directly loaded in vitro with tumor antigens must be injected. Next, tumor-antigen-loaded DCs must activate CTLs in lymphoid organs. Subsequently, activated CTLs must enter the tumor microenvironment to perform their functions, at which point a variety of negative regulatory signals suppress the immune response. Finally, CTL-mediated cytotoxic effects must overcome the tolerance induced by tumor cells. Each step is a complex process that may be impeded in many ways. However, if these steps happen under appropriate regulation, the vaccine-induced CTL antitumor immune response will be more successful. For this reason, we should gain a better understanding of the basic mechanisms that govern the immune response. This paper, based on the steps necessary to induce an immune response, discusses current strategies for enhancing vaccine-induced CTL antitumor immune responses.

Immunotherapy: a useful strategy to help combat multidrug resistance

Multidrug resistance (MDR) renders cancer cells relatively invulnerable to treatment with many standard cytotoxic anti-cancer agents. Cancer immunotherapy could be an important adjunct for other strategies to treat MDR positive cancers, as resistance to immunotherapy generally is unrelated to mechanisms of resistance to cytotoxic agents. Immunotherapy to combat MDR positive tumors could use any of the following strategies: direct immune attack against MDR positive cells, using MDR as an immune target to deliver cytotoxic agents, capitalization on other immune properties of MDR positive cells, or conditional immunotoxins expressed under MDR control. Additional insights into the immunogenic potential of some cytotoxic agents can also be brought to bear on these strategies. This review will highlight key concepts in cancer immunotherapy and illustrate immune principles and strategies that have been or could be used to help destroy MDR positive tumor cells, either alone or in rational combinations.

Compartment-Specific Bioluminescence Imaging platform for the high-throughput evaluation of antitumor immune function

Conventional assays evaluating antitumor activity of immune effector cells have limitations that preclude their high-throughput application. We adapted the recently developed Compartment-Specific Bioluminescence Imaging (CS-BLI) technique to perform high-throughput quantification of innate antitumor activity and to show how pharmacologic agents (eg, lenalidomide, pomalidomide, bortezomib, and dexamethasone) and autologous BM stromal cells modulate that activity. CS-BLI-based screening allowed us to identify agents that enhance or inhibit innate antitumor cytotoxicity. Specifically, we identified compounds that stimulate immune effector cells against some tumor targets but suppressed their activity against other tumor cells. CS-BLI offers rapid, simplified, and specific evaluation of multiple conditions, including drug treatments and/or cocultures with stromal cells and highlights that immunomodulatory pharmacologic responses can be heterogeneous across different types of tumor cells. This study provides a framework to identify novel immunomodulatory agents and to prioritize compounds for clinical development on the basis of their effect on antitumor immunity.

The chemotherapeutic drug oxaliplatin differentially affects blood DC function dependent on environmental cues

It has become evident that the tumor microenvironment plays a pivotal role in the maintenance of cancerous growth. One of the acquired functions of the tumor microenvironment is the suppression of immune responses. Indeed, blocking the inhibitory pathways operational in the microenvironment results in enhanced T-cell-dependent, anti-tumor immunity. Chemotherapeutic drugs not only directly kill tumor cells but also shape the tumor microenvironment and potentiate anti-tumor immunity. Here, we demonstrate that the chemotherapeutic compound oxaliplatin acts as a double-edged sword. Besides killing tumor cells, oxaliplatin bolsters immunosuppressive pathways, resulting in decreased activation of T cells by human plasmacytoid dendritic cells (pDCs). Exposure to oxaliplatin markedly increased expression of the T-cell inhibitory molecule programmed death receptor-ligand 1 (PD-L1) on human pDCs and also TLR9-induced IFNα secretion. Furthermore, oxaliplatin decreased TLR-induced STAT1 and STAT3 expression, and NF-κB-mediated responses. The oxaliplatin induced upregulation of PD-L1 and downregulation of costimulatory molecules CD80 and CD86 resulted in decreased T-cell proliferation. Our results demonstrate that platinum-based anticancer drugs adapt TLR-induced signaling in human pDCs and myeloid DCs (mDCs), thereby downgrading their immunostimulatory potential.

Cancer immunotherapy comes of age

Activating the immune system for therapeutic benefit in cancer has long been a goal in immunology and oncology. After decades of disappointment, the tide has finally changed due to the success of recent proof-of-concept clinical trials. Most notable has been the ability of the anti-CTLA4 antibody, ipilimumab, to achieve a significant increase in survival for patients with metastatic melanoma, for which conventional therapies have failed. In the context of advances in the understanding of how tolerance, immunity and immunosuppression regulate antitumour immune responses together with the advent of targeted therapies, these successes suggest that active immunotherapy represents a path to obtain a durable and long-lasting response in cancer patients.

Cancer immunotherapy comes of age

Activating the immune system for therapeutic benefit in cancer has long been a goal in immunology and oncology. After decades of disappointment, the tide has finally changed due to the success of recent proof-of-concept clinical trials. Most notable has been the ability of the anti-CTLA4 antibody, ipilimumab, to achieve a significant increase in survival for patients with metastatic melanoma, for which conventional therapies have failed. In the context of advances in the understanding of how tolerance, immunity and immunosuppression regulate antitumour immune responses together with the advent of targeted therapies, these successes suggest that active immunotherapy represents a path to obtain a durable and long-lasting response in cancer patients.

Structural insights into RNA recognition by RIG-I

Intracellular RIG-I-like receptors (RLRs, including RIG-I, MDA-5, and LGP2) recognize viral RNAs as pathogen-associated molecular patterns (PAMPs) and initiate an antiviral immune response. To understand the molecular basis of this process, we determined the crystal structure of RIG-I in complex with double-stranded RNA (dsRNA). The dsRNA is sheathed within a network of protein domains that include a conserved "helicase" domain (regions HEL1 and HEL2), a specialized insertion domain (HEL2i), and a C-terminal regulatory domain (CTD). A V-shaped pincer connects HEL2 and the CTD by gripping an α-helical shaft that extends from HEL1. In this way, the pincer coordinates functions of all the domains and couples RNA binding with ATP hydrolysis. RIG-I falls within the Dicer-RIG-I clade of the superfamily 2 helicases, and this structure reveals complex interplay between motor domains, accessory mechanical domains, and RNA that has implications for understanding the nanomechanical function of this protein family and other ATPases more broadly.

Platinum-based drugs disrupt STAT6-mediated suppression of immune responses against cancer in humans and mice

Tumor microenvironments feature immune inhibitory mechanisms that prevent T cells from generating effective antitumor immune responses. Therapeutic interventions aimed at disrupting these inhibitory mechanisms have been shown to enhance antitumor immunity, but they lack direct cytotoxic effects. Here, we investigated the effect of cytotoxic cancer chemotherapeutics on immune inhibitory pathways. We observed that exposure to platinum-based chemotherapeutics markedly reduced expression of the T cell inhibitory molecule programmed death receptor-ligand 2 (PD-L2) on both human DCs and human tumor cells. Downregulation of PD-L2 resulted in enhanced antigen-specific proliferation and Th1 cytokine secretion as well as enhanced recognition of tumor cells by T cells. Further analysis revealed that STAT6 controlled downregulation of PD-L2. Consistent with these data, patients with STAT6-expressing head and neck cancer displayed enhanced recurrence-free survival upon treatment with cisplatin-based chemoradiation compared with patients with STAT6-negative tumors, demonstrating the clinical relevance of platinum-induced STAT6 modulation. We therefore conclude that platinum-based anticancer drugs can enhance the immunostimulatory potential of DCs and decrease the immunosuppressive capability of tumor cells. This dual action of platinum compounds may extend their therapeutic application in cancer patients and provides a rationale for their use in combination with immunostimulatory compounds.

The oncogenic BRAF kinase inhibitor PLX4032/RG7204 does not affect the viability or function of human lymphocytes across a wide range of concentrations

PURPOSE

PLX4032 (RG7204), an oncogenic BRAF kinase inhibitor undergoing clinical evaluation, has high response rates in early clinical trials in patients with advanced BRAF(V600E) mutant melanoma. Combining PLX4032 with immunotherapy may allow expanding the durability of responses. The effects of PLX4032 on immune cells were studied to explore the feasibility of future combinatorial approaches with immunotherapy for melanoma.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells (PBMC) and BRAF(V600E) mutant melanoma cells were exposed to increasing concentrations of PLX4032 and the cell viability, proliferation, cell cycle, apoptosis, and phosphorylation of signaling proteins were analyzed. Effects of PLX4032 on antigen-specific T-cell function were analyzed by specific cytokine release and cytotoxicity activity.

RESULTS

The 50% inhibition concentration (IC(50)) of PLX4032 for resting human PBMC was between 50 and 150 μmol/L compared with an IC(50) below 1 μmol/L for sensitive BRAF(V600E) mutant melanoma cell lines. Activated lymphocytes were even more resistant with no growth inhibition up to concentrations of 250 μmol/L. PLX4032 had a marginal effect on cell-cycle arrest, apoptotic cell changes or alteration of phosphorylated signaling molecules in lymphocytes. Functional analysis of specific antigen recognition showed preserved T-cell function up to 10-μmol/L concentration of PLX4032, whereas the cytotoxic activity of PLX4032 was maintained up to high concentrations of 50 μmol/L.

CONCLUSIONS

The preserved viability and function of lymphocytes exposed to high concentrations of PLX4032 suggest that this agent could be a potential candidate for combining with immunotherapy strategies for the treatment of patients with BRAF(V600)(E) mutant melanoma.

Pattern recognition of viral nucleic acids by RIG-I-like helicases

Recognition of pathogenic microbes by the innate immune system is based on the principle of pathogen-associated molecular patterns (PAMPs). These are conserved molecular structures that are present in the pathogen but not in the host. Cells of the innate immune system or, in some cases, virtually all cells of our body express receptors that are able to specifically recognize PAMPs and trigger the appropriate responses including the production of cytokines. In the case of viruses, an interesting complication exists: Viruses use the host's cellular metabolism and building blocks to replicate. As a consequence, protein modifications, lipid or carbohydrate configurations restricted to viruses do not exist. Instead, parts of the innate immune system have evolved to detect viral nucleic acids mainly by virtue of their (non-physiological) localization and structure. Understanding the molecules involved in anti-viral defence and the patterns they recognize will allow harnessing them for therapeutic strategies targeting viral and autoimmune diseases and tumours. This review presents important recent advances in understanding intracellular recognition of nucleic acid patterns by the innate immune system.