The effect of a therapeutic dendritic cell-based cancer vaccination depends on the blockage of CTLA-4 signaling

Dendritic cell-based cancer immunotherapy in the era of immune checkpoint inhibitors: From bench to bedside

Dendritic cells (DCs) can present tumoral antigens to T-cells and stimulate T-cell-mediated anti-tumoral immune responses. In addition to uptaking, processing, and presenting tumoral antigens to T-cells, co-stimulatory signals have to be established between DCs with T-cells to develop anti-tumoral immune responses. However, most of the tumor-infiltrated immune cells are immunosuppressive in the tumor microenvironment (TME), paving the way for immune evasion of tumor cells. This immunosuppressive TME has also been implicated in suppressing the DC-mediated anti-tumoral immune responses, as well. Various factors, i.e., immunoregulatory cells, metabolic factors, tumor-derived immunosuppressive factors, and inhibitory immune checkpoint molecules, have been implicated in developing the immunosuppressive TME. Herein, we aimed to review the biology of DCs in developing T-cell-mediated anti-tumoral immune responses, the significance of immunoregulatory cells in the TME, metabolic barriers contributing to DCs dysfunction in the TME, tumor-derived immunosuppressive factors, and inhibitory immune checkpoint molecules in DC-based cell therapy outcomes. With reviewing the ongoing clinical trials, we also proposed a novel therapeutic strategy to increase the efficacy of DC-based cell therapy. Indeed, the combination of DC-based cell therapy with monoclonal antibodies against novel immune checkpoint molecules can be a promising strategy to increase the response rate of patients with cancers.

Innovative lipoplexes formulations with enhanced siRNA efficacy for cancer treatment: Where are we now?

Over the past two decades, RNA interference has become an extensively studied mechanism to silence gene and treat diseases including cancer. siRNA appears as a promising strategy that could avoid some side effects related to traditional chemotherapy. Considering the weak stability of naked siRNA in blood, vectors like cationic liposomes or Lipid Nanoparticles (LNPs) are widely used to carry and protect siRNA until it reaches the tumor targeted. Despite extensive research, only three RNAi drugs are currently approved by the Food and Drug Administration, including only one LNP formulation of siRNA to treat hereditary ATTR amyloidosis. This shows the difficulty of lipoplexes clinical translation, in particular in cancer therapy. To overcome the lipoplexes limitations, searches are made on innovative lipoplexes formulations with enhanced siRNA efficacy. The present review is focusing on the recent use of pH-sensitive lipids, peptides and cell-penetrating peptides or polymers. The incorporation of some of these components in the lipoplex formulation induces a fusogenic property or an enhanced endosomal escape, an enhanced cellular uptake, an enhanced tumor targeting, an improved stability in the blood stream …These innovations appear critical to obtain an efficient siRNA accumulation in tumor cells with effective antitumor effect considering the complex tumor environment.

Envisioning the immune system to determine its role in pancreatic ductal adenocarcinoma: Culprit or victim?

Pancreatic ductal adenocarcinoma has a poor 5-year survival rate that makes it one of the most fatal human malignancies. Unfortunately, despite the serious improvement in the survival of most cancers, there has been a minor advance in pancreatic cancer (PC). Major advances in PC treatment have been assessed over the bygone twenty-year time span, yet some complications make the survival of the patients shorter. Getting to know the PC tumor microenvironment (TME) and the immunosuppression that happens during the pathogenesis of this malignancy could be a great help to understand the nature of the immune system and find better treatment modalities based on it. Although many immune cells are present in PC, immunosuppression of the TME leads to severe immune dysfunction in the patients, therefore immune effectors fail to do their functions. Lately, immunotherapy has been presented as one of the promising treatment strategies for different malignancies including hepatocellular carcinoma, melanoma, non-small cell lung cancer, and kidney cancer. In PC, there has been shown promising results centered around the TME, immune checkpoint inhibitors, cancer vaccines, and other approaches especially when used as combinational therapy. Here we dig a little deeper into the role of the immune system and possible therapeutic options in the treatment of PC.

Personalized neoantigen pulsed dendritic cell vaccine for advanced lung cancer

Neoantigens are considered to be ultimate target of tumor immunotherapy due to their high tumor specificity and immunogenicity. Dendritic cell (DCs) vaccines based on neoantigens have exciting effects in treatment of some malignant tumors and are a promising therapeutic modality. Lung cancer is a lethal disease with the highest morbidity and mortality rate in the world. Despite the rapid development of targeted therapy and immune checkpoint inhibitors for lung cancer in recent years, their efficacy is still unsatisfactory overall. Therefore, there is an urgent unmet clinical need for lung cancer treatment. Here, we attempted to treat lung cancer using a personalized neoantigen peptide-pulsed autologous DC vaccine and conducted a single-arm, 2 medical centers, pilot study initiated by the investigator (ChiCTR-ONC-16009100, NCT02956551). The patients enrolled were patients with heavily treated metastatic lung cancer. Candidate neoantigens were derived from whole-exome sequencing and RNA sequencing of fresh biopsy tissues as well as bioinformatics analysis. A total of 12 patients were enrolled in this study. A total of 85 vaccine treatments were administered with a median value of 5 doses/person (range: 3-14 doses/person). In total, 12-30 peptide-based neoantigens were selected for each patient. All treatment-related adverse events were grade 1-2 and there were no delays in dosing due to toxic effects. The objective effectiveness rate was 25%; the disease control rate was 75%; the median progression-free survival was 5.5 months and the median overall survival was 7.9 months. This study provides new evidence for neoantigen vaccine therapy and new therapeutic opportunities for lung cancer treatment.

Activating the Antitumor Immune Response in Non-Hodgkin Lymphoma Using Immune Checkpoint Inhibitors

Non-Hodgkin lymphomas comprise a heterogenous group of disorders which differ in biology. Although response rates are high in some groups, relapsed disease can be difficult to treat, and newer approaches are needed for this patient population. It is increasingly apparent that the immune system plays a significant role in the propagation and survival of malignant cells. Immune checkpoint blocking agents augment cytotoxic activity of the adaptive and innate immune systems and enhance tumor cell killing. Anti-PD-1 and anti-CTLA-4 antibodies have been tested as both single agents and combination therapy. Although success rates with anti-PD-1 antibodies are high in patients with Hodgkin lymphoma, the results are yet to be replicated in those with non-Hodgkin lymphomas. Some lymphoma histologies, such as primary mediastinal B cell lymphoma (PMBL), central nervous system, and testicular lymphomas and gray zone lymphoma, respond favorably to PD-1 blockade, but the response rates in most lymphoma subtypes are low. Other agents including those targeting the adaptive immune system such as TIM-3, TIGIT, and BTLA and innate immune system such as CD47 and KIR are therefore in trials to test alternative ways to activate the immune system. Patient selection based on tumor biology is likely to be a determining factor in treatment response in patients, and further research exploring optimal patient populations, newer targets, and combination therapy as well as identifying biomarkers is needed.

Blockade of CTLA-4 increases anti-tumor response inducing potential of dendritic cell vaccine

The immunosuppressive state of the tumor microenvironment diminishes the efficacy of dendritic cell (DC)-based cancer immunotherapy. Inhibitory immune checkpoint molecules expressed on tumor-infiltrating T lymphocytes, such as cytotoxic T-lymphocyte antigen 4 (CTLA-4) molecules are one of the main barriers in priming T cells by DCs. Therefore, it seems that blockade of such molecules facilitates the T cells activation by the DC vaccine. In this study, we intended to suppress the expression of CTLA-4 molecule on tumor-infiltrating T cells by siRNA-loaded chitosan-lactate (CL) nanoparticles to facilitate priming anti- tumor T cells by tumor lysate-loaded DC vaccine. Nanoparticles (NPs) have also provided an opportunity for specific drug delivery into the tumor site. CL NPs exhibited favorable physicochemical characteristics (size about 75 nm, polydispersive index<0.2, and a zeta potential about 14), which were associated with a high transfection rate and low toxicity. Moreover, the administration of anti-CTLA-4 siRNA-loaded NPs into CT26 and 4 T1 tumor -bearing mice led to the downregulation of CTLA-4 on tumor -infiltrating T cells, which was associated with tumor regression and increased mice survival. Moreover, while the treatment of tumor -bearing mice with DC vaccine had mild therapeutic outcomes, its combination with siRNA-loaded NPs may exhibit synergistic anti- tumor effects. This possible synergistic ameliorating effect is achieved through the reduction of immunosuppressive cells, the improved cytotoxicity of T lymphocytes, decreased inhibitory and increased inflammatory cytokines, and reduced angiogenesis and metastasis processes. These results indicate that the silencing of CTLA-4 can potentiate the T cell priming capacity of the DC vaccine, proposing a practical anti-cancer therapeutic approach.

Safety, immunogenicity, and clinical efficacy of durvalumab in combination with folate receptor alpha vaccine TPIV200 in patients with advanced ovarian cancer: a phase II trial

BACKGROUND

Immune checkpoint inhibitors (ICIs) to date have demonstrated limited activity in advanced ovarian cancer (OC). Folate receptor alpha (FRα) is overexpressed in the majority of OCs and presents an attractive target for a combination immunotherapy to potentially overcome resistance to ICI in OCs. The current study sought to examine clinical and immunologic responses to TPIV200, a multiepitope FRα vaccine administered with programmed death ligand 1 (PD-L1) inhibitor durvalumab in patients with advanced platinum-resistant OC.

METHODS

Following Simon two-stage phase II trial design, 27 patients were enrolled. Treatment was administered in 28-day cycles (intradermal TPIV200 and granulocyte-macrophage colony-stimulating factor (GM-CSF) for 6 cycles and intravenous durvalumab for 12 cycles). Primary endpoints included overall response rate and progression-free survival at 24 weeks. Translational parameters focused on tumor microenvironment, PD-L1 and FRα expression, and peripheral vaccine-specific immune responses.

RESULTS

Treatment was well tolerated, with related grade 3 toxicity rate of 18.5%. Increased T cell responses to the majority of peptides were observed in all patients at 6 weeks (p<0.0001). There was one unconfirmed partial response (3.7%) and nine patients had stable disease (33.3%). Clinical benefit was not associated with baseline FRα or PD-L1 expression. One patient with prolonged clinical benefit demonstrated loss of FRα expression and upregulation of PD-L1 in a progressing lesion. Despite the low overall response rate, the median overall survival was 21 months (13.5-∞), with evidence of benefit from postimmunotherapy regimens.

CONCLUSIONS

Combination of TPIV200 and durvalumab was safe and elicited robust FRα-specific T cell responses in all patients. Unexpectedly durable survival in this heavily pretreated population highlights the need to investigate the impact of FRα vaccination on the OC biology post-treatment.

microRNAs in the Antitumor Immune Response and in Bone Metastasis of Breast Cancer: From Biological Mechanisms to Therapeutics

Breast cancer is the most common type of cancer in women, and the occurrence of metastasis drastically worsens the prognosis and reduces overall survival. Understanding the biological mechanisms that regulate the transformation of malignant cells, the consequent metastatic transformation, and the immune surveillance in the tumor progression would contribute to the development of more effective and targeted treatments. In this context, microRNAs (miRNAs) have proven to be key regulators of the tumor-immune cells crosstalk for the hijack of the immunosurveillance to promote tumor cells immune escape and cancer progression, as well as modulators of the metastasis formation process, ranging from the preparation of the metastatic site to the transformation into the migrating phenotype of tumor cells. In particular, their deregulated expression has been linked to the aberrant expression of oncogenes and tumor suppressor genes to promote tumorigenesis. This review aims at summarizing the role and functions of miRNAs involved in antitumor immune response and in the metastasis formation process in breast cancer. Additionally, miRNAs are promising targets for gene therapy as their modulation has the potential to support or inhibit specific mechanisms to negatively affect tumorigenesis. With this perspective, the most recent strategies developed for miRNA-based therapeutics are illustrated.

Re-induction using whole cell melanoma vaccine genetically modified to melanoma stem cells-like beyond recurrence extends long term survival of high risk resected patients - updated results

BACKGROUND

AGI-101H is an allogeneic gene modified whole cell therapeutic melanoma vaccine, evaluated in over 400 melanoma patients in the adjuvant and therapeutic settings. We present updated long-term survival results from two single-arm, phase II adjuvant trials (Trial 3 and Trial 5) with the focus on treatment beyond recurrence of the disease.

METHODS

Patients with resected high-risk melanoma (stage IIIB-IV) were enrolled to Trial 3 (n = 99) and Trial 5 (n = 97). The primary endpoint was disease-free survival (DFS), and the secondary was overall survival (OS). In the induction phase, the vaccine was administered every 2 weeks (eight times), followed by the maintenance phase every month until progression. At progression, maintenance was continued or re-induction was applied with or without surgery.

RESULTS

In Trial 3, the 10-year DFS was equal to 33.0% overall and to 52.4, 25.0, and 8.7% for stage IIIB, IIIC, and stage IV patients, respectively. In Trial 5, the overall 10-year DFS was equal to 24.2%, and to 37.5, 18.0, and 17.6% for stage IIIB, IIIC, and stage IV patients, respectively. In Trial 3, the 10-year OS was equal to 42.3% overall, and to 59.5, 37.5, and 17.4% for stage IIIB, IIIC, and stage IV patients, respectively. In Trial 5, the 10-year OS was equal to 34.3% overall and to 46.9, 28.0, and 29.4% for stage IIIB, IIIC, and stage IV patients, respectively. Among the 65 patients of Trial 3 who developed progression, 43 received re-induction with (n = 22) or without (n = 21) surgery. Two patients received surgery without re-induction. All the 22 progressing patients, who did not receive re-induction, died. Among the 75 patients of Trial 5 who experienced progression, 39 received re-induction with (n = 21) or without (n = 18) surgery. Among the 36 progressing patients who did not receive the re-induction, 35 died. Surgery and re-induction reduced (independently) the increase of mortality after progression in both trials, with the effect of re-induction reaching statistical significance in Trial 5.

CONCLUSIONS

Vaccination beyond recurrence of the disease with additional re-induction combined with surgery or alone increased long term survival of melanoma patients. However, further studies on larger patient cohorts are required.

TRIAL REGISTRATION

Central Evidence of Clinical Trials (EudraCT Number 2008-003373-40 ).

Physical activation of innate immunity by spiky particles

Microbial biochemicals have been indicated as the primary stimulators of innate immunity, the first line of the body's defence against infections. However, the influence of topological features on a microbe's surface on immune responses remains largely unknown. Here we demonstrate the ability of TiO₂ microparticles decorated with nanospikes (spiky particles) to activate and amplify the immune response in vitro and in vivo. The nanospikes exert mechanical stress on the cells, which results in potassium efflux and inflammasome activation in macrophages and dendritic cells during phagocytosis. The spiky particles augment antigen-specific humoral and cellular immune responses in the presence of monophosphoryl lipid A and elicit protective immunity against tumour growth and influenza viral infection. The study offers insights into how surface physical cues can tune the activation of innate immunity and provides a basis for engineering particles with increased immunogenicity and adjuvanticity.

Phosphoinositide 3-kinase δ inhibition promotes antitumor responses but antagonizes checkpoint inhibitors

Multiple modes of immunosuppression restrain immune function within tumors. We previously reported that phosphoinositide 3-kinase δ (PI3Kδ) inactivation in mice confers resistance to a range of tumor models by disrupting immunosuppression mediated by regulatory T cells (Tregs). The PI3Kδ inhibitor idelalisib has proven highly effective in the clinical treatment of chronic lymphocytic leukemia and the potential to extend the use of PI3Kδ inhibitors to nonhematological cancers is being evaluated. In this work, we demonstrate that the antitumor effect of PI3Kδ inactivation is primarily mediated through the disruption of Treg function, and correlates with tumor dependence on Treg immunosuppression. Compared with Treg-specific PI3Kδ deletion, systemic PI3Kδ inactivation is less effective at conferring resistance to tumors. We show that PI3Kδ deficiency impairs the maturation and reduces the capacity of CD8+ cytotoxic T lymphocytes (CTLs) to kill tumor cells in vitro, and to respond to tumor antigen-specific immunization in vivo. PI3Kδ inactivation antagonized the antitumor effects of tumor vaccines and checkpoint blockade therapies intended to boost the CD8+ T cell response. These findings provide insights into mechanisms by which PI3Kδ inhibition promotes antitumor immunity and demonstrate that the mechanism is distinct from that mediated by immune checkpoint blockade.

Regulation of cancer immune escape: The roles of miRNAs in immune checkpoint proteins

Immune checkpoint proteins (ICPs) are regulators of immune system. The ICP dysregulation silences the host immune response to cancer-specific antigens, contributing to the occurrence and progress of various cancers. MiRNAs are regulatory molecules and function in mRNA silencing and post-transcriptional regulation of gene expression. MiRNAs that modulate the immunity via ICPs have received increasing attention. Many studies have shown that the expressions of ICPs are directly or indirectly repressed by miRNAs in multiple types of cancers. MiRNAs are also subject to regulation by ICPs. In this review, recent studies of the relationship between miRNAs and ICPs (including the PD-1, PD-L1, CTLA-4, ICOS, B7-1, B7-2, B7-H2, B7-H3, CD27, CD70, CD40, and CD40L) in cancer immune escape are comprehensively discussed, which provide critical detailed mechanistic insights into the functions of the miRNA-ICP axes and their effects on immune escape, and will be beneficial for the potential applications of immune checkpoint therapy and miRNA-based guidance for personalized medicine as well as for predicting the prognosis.

Ipilimumab for the treatment of metastatic prostate cancer

INTRODUCTION

Immunotherapy with checkpoint inhibitors is beginning to be recognized as a valid weapon for the treatment of metastatic prostate cancer (PCa) when chemotherapy fails. Ipilimumab (ipi) is a fully humanized monoclonal antibody that blocks the activity of CTLA4. It also has a molecular weight of 148 kDa and is water-soluble at physiological pH. Ipi was first approved by the FDA for the treatment of malignant melanoma and is currently being studied in metastatic castration-resistant prostate cancer, with promising early results. Areas covered: The aim of this review is to collate the most significant preclinical and clinical studies available that look at ipi to propose new strategies for the future. Expert opinion: Additional studies are required to reduce toxicity and increase the activity of ipi in PCa. A possible strategy is to combine ipi with standard anti-cancer therapeutics such as vaccines, PDL1 inhibitors, antiandrogen drugs, and chemotherapy agents. Several initial results have suggested that combination strategies are useful to increase the activity in mCRPC, even if the toxicity of the treatment can increase. The activity of combined treatments is still not predictable, but considering the ongoing studies, we believe that they have good potential that will lead to the discovery of an optimal therapeutic strategy.

New Combination Strategies Using Programmed Cell Death 1/Programmed Cell Death Ligand 1 Checkpoint Inhibitors as a Backbone

The discovery of immune checkpoints and subsequent clinical development of checkpoint inhibitors have revolutionized the field of oncology. The durability of the antitumor immune responses has raised the hope for long-term patient survival and potential cure; however, currently, only a minority of patients respond. Combination strategies to help increase antigen release and T-cell priming, promote T-cell activation and homing, and improve the tumor immune microenvironment, all guided by predictive biomarkers, can help overcome the tumor immune-evasive mechanisms and maximize efficacy to ultimately benefit the majority of patients. Great challenges remain because of the complex underlying biology, unpredictable toxicity, and accurate assessment of response. Carefully designed clinical trials guided by translational studies of paired biopsies will be key to develop reliable predictive biomarkers to choose which patients would most likely benefit from each strategy.

Immune checkpoint inhibitor combinations in solid tumors: opportunities and challenges

The emergence of immune 'checkpoint inhibitors' such as cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed death receptor 1 (PD-1) has revolutionized treatment of solid tumors including melanoma, lung cancer, among many others. The goal of checkpoint inhibitor combination therapy is to improve clinical response and minimize toxicities. Rational design of checkpoint combinations considers immune-mediated mechanisms of antitumor activity: immunogenic cell death, antigen release and presentation, activation of T-cell responses, lymphocytic infiltration into tumors and depletion of immunosuppression. Potential synergistic combinations include checkpoint blockade with conventional (radiation, chemotherapy and targeted therapies) and newer immunotherapies (cancer vaccines, oncolytic viruses, among others). Reliable biomarkers are necessary to define patients who will achieve best clinical benefit with minimal toxicity in combination therapy.

Is There Still Room for Cancer Vaccines at the Era of Checkpoint Inhibitors

Checkpoint inhibitor (CPI) blockade is considered to be a revolution in cancer therapy, although most patients (70%–80%) remain resistant to this therapy. It has been hypothesized that only tumors with high mutation rates generate a natural antitumor T cell response, which could be revigorated by this therapy. In patients with no pre-existing antitumor T cells, a vaccine-induced T cell response is a rational option to counteract clinical resistance. This hypothesis has been validated in preclinical models using various cancer vaccines combined with inhibitory pathway blockade (PD-1-PDL1-2, CTLA-4-CD80-CD86). Enhanced T cell infiltration of various tumors has been demonstrated following this combination therapy. The timing of this combination appears to be critical to the success of this therapy and multiple combinations of immunomodulating antibodies (CPI antagonists or costimulatory pathway agonists) have reinforced the synergy with cancer vaccines. Only limited results are available in humans and this combined approach has yet to be validated. Comprehensive monitoring of the regulation of CPI and costimulatory molecules after administration of immunomodulatory antibodies (anti-PD1/PD-L1, anti-CTLA-4, anti-OX40, etc.) and cancer vaccines should help to guide the selection of the best combination and timing of this therapy.

Immune Cells in Cancer Therapy and Drug Delivery

Recent studies indicate the critical role of tumour associated macrophages, tumour associated neutrophils, dendritic cells, T lymphocytes, and natural killer cells in tumourigenesis. These cells can have a significant impact on the tumour microenvironment via their production of cytokines and chemokines. Additionally, products secreted from all these cells have defined specific roles in regulating tumour cell proliferation, angiogenesis, and metastasis. They act in a protumour capacity in vivo as evidenced by the recent studies indicating that macrophages, T cells, and neutrophils may be manipulated to exhibit cytotoxic activity against tumours. Therefore therapy targeting these cells may be promising, or they may constitute drug or anticancer particles delivery systems to the tumours. Herein, we discussed all these possibilities that may be used in cancer treatment.

Phase II Study of Autologous Monocyte-Derived mRNA Electroporated Dendritic Cells (TriMixDC-MEL) Plus Ipilimumab in Patients With Pretreated Advanced Melanoma

Purpose

Autologous monocyte-derived dendritic cells (DCs) electroporated with synthetic mRNA (TriMixDC-MEL) are immunogenic and have antitumor activity as a monotherapy in patients with pretreated advanced melanoma. Ipilimumab, an immunoglobulin G1 monoclonal antibody directed against the cytotoxic T-lymphocyte-associated protein 4 receptor that counteracts physiologic suppression of T-cell function, improves the overall survival of patients with advanced melanoma. This phase II study investigated the combination of TriMixDC-MEL and ipilimumab in patients with pretreated advanced melanoma.

Patients and Methods

Thirty-nine patients were treated with TriMixDC-MEL (4 × 106 cells administered intradermally and 20 × 106 cells administered intravenously) plus ipilimumab (10 mg/kg every 3 weeks for a total of four administrations, followed by maintenance therapy every 12 weeks in patients who remained progression free). Six-month disease control rate according to the immune-related response criteria served as the primary end point.

Results

The 6-month disease control rate was 51% (95% CI, 36% to 67%), and the overall tumor response rate was 38% (including eight complete and seven partial responses). Seven complete responses and one partial tumor response are ongoing after a median follow-up time of 36 months (range, 22 to 43 months). The most common treatment-related adverse events (all grades) consisted of local DC injection site skin reactions (100%), transient post–DC infusion chills (38%) and flu-like symptoms (84%), dermatitis (64%), hepatitis (13%), hypophysitis (15%), and diarrhea/colitis (15%). Grade 3 or 4 immune-related adverse events occurred in 36% of patients. There was no grade 5 adverse event.

Conclusion

The combination of TriMixDC-MEL and ipilimumab is tolerable and results in an encouraging rate of highly durable tumor responses in patients with pretreated advanced melanoma.

Leveraging immunotherapy for the treatment of gynecologic cancers in the era of precision medicine

During the past decade significant progress in the understanding of stimulatory and inhibitory signaling pathways in immune cells has reinvigorated the field of immuno-oncology. In this review we outline the current immunotherapy based approaches for the treatment of gynecological cancers, and focus on the emerging clinical data on immune checkpoint inhibitors, adoptive cell therapies, and vaccines. It is anticipated that in the coming years biomarker-guided clinical trials, will provide for a better understanding of the mechanisms of response and resistance to immunotherapy, and guide combination treatment strategies that will extend the benefit from immunotherapy to patients with gynecologic cancers.

Coinhibitory Pathways in Immunotherapy for Cancer

The immune system is capable of recognizing tumors and eliminates many early malignant cells. However, tumors evolve to evade immune attack, and the tumor microenvironment is immunosuppressive. Immune responses are regulated by a number of immunological checkpoints that promote protective immunity and maintain tolerance. T cell coinhibitory pathways restrict the strength and duration of immune responses, thereby limiting immune-mediated tissue damage, controlling resolution of inflammation, and maintaining tolerance to prevent autoimmunity. Tumors exploit these coinhibitory pathways to evade immune eradication. Blockade of the PD-1 and CTLA-4 checkpoints is proving to be an effective and durable cancer immunotherapy in a subset of patients with a variety of tumor types, and additional combinations are further improving response rates. In this review we discuss the immunoregulatory functions of coinhibitory pathways and their translation to effective immunotherapies for cancer.

Checkpoint Blockade for the Treatment of Advanced Melanoma

Immunotherapy with immune checkpoint inhibition has been improving the outcomes of patients with many different types of malignancies. Immune checkpoint inhibition has been most extensively studied in patients with advanced melanoma and there are three FDA approved antibodies already widely used in clinical practice (ipilimumab, nivolumab, and pembrolizumab). In this chapter, we review the mechanistic basis behind the development of immune checkpoint blocking antibodies. We then discuss specifics regarding each agent, unique clinical considerations in treating patients with this approach, and future directions, including combination strategies. This chapter is focused on melanoma, but the principles related to this immunotherapy approach are applicable to patients with many types of malignancies.

Immune checkpoint blockade: Releasing the brake towards hematological malignancies

Tumor cells utilize co-inhibitory molecules to avoid host immune destruction. Checkpoint blockade has emerged as a promising approach to treat cancer by restoring T cell effector function and breaking a tumor permissive microenvironment. Patients with hematological malignancies often have immune dysregulation, thus the role of checkpoint blockade in treatment of these neoplasms is particularly intriguing. In early trials, antibodies targeting cytotoxic T lymphocyte antigen 4 (CTLA-4) or the programmed death 1 (PD-1) signaling pathway have displayed significant efficacy with minimal toxicity in patients with relapsed and refractory hematological neoplasms. In this review, we provide evidence of dysregulation of CTLA-4 and PD-1/PD-Ls in the context of several major types of hematological neoplasms and summarize relevant clinical practice points for checkpoint blockade. The preclinical rationale and preliminary clinical data of potential combination approaches designed to optimize checkpoint antagonists are well presented.

Lymphoma Immunotherapy: Current Status

The rationale to treat lymphomas with immunotherapy comes from long-standing evidence on their distinctive immune responsiveness. Indolent B-cell non-Hodgkin lymphomas, in particular, establish key interactions with the immune microenvironment to ensure prosurvival signals and prevent antitumor immune activation. However, reports of spontaneous regressions indicate that, under certain circumstances, patients develop therapeutic antitumor immunity. Several immunotherapeutic approaches have been thus developed to boost these effects in all patients. To date, targeting CD20 on malignant B cells with the antibody rituximab has been the most clinically effective strategy. However, relapse and resistance prevent to cure approximately half of B-NHL patients, underscoring the need of more effective therapies. The recognition of B-cell receptor variable regions as B-NHL unique antigens promoted the development of specific vaccines to immunize patients against their own tumor. Despite initial promising results, this strategy has not yet demonstrated a sufficient clinical benefit to reach the regulatory approval. Several novel agents are now available to stimulate immune effector functions or counteract immunosuppressive mechanisms, such as engineered antitumor T cells, co-stimulatory receptor agonist, and immune checkpoint-blocking antibodies. Thus, multiple elements can now be exploited in more effective combinations to break the barriers for the induction of anti-lymphoma immunity.

Vaccination strategies in lymphoproliferative disorders: Failures and successes

Anti-tumor vaccines in lymphoproliferative disorders hold out the prospect of effective tumor therapies with minimal side effects. The addition of immunotherapy to old and new chemotherapy regimens has improved both response rates and disease-free survival, leading in many cases to an extended overall survival. Ideally, an antigen that is used for vaccination would be specifically expressed in the tumor; it must have an important, causal part in the multifactorial process that leads to cancer, and it must be expressed stably even after it is attacked by the immune system. Immunotherapies, which aim to activate the immune system to kill cancer cells, include strategies to increase the frequency or potency of antitumor T cells, to overcome suppressive factors in the tumor microenvironment, and to reduce T-cell suppression systemically. In this review, we focus on the results of clinical trials of vaccination in lymphoma, and discuss potential strategies to enhance the efficacy of immunotherapy in the future.

Combination of Id2 Knockdown Whole Tumor Cells and Checkpoint Blockade: A Potent Vaccine Strategy in a Mouse Neuroblastoma Model

Tumor vaccines have held much promise, but to date have demonstrated little clinical success. This lack of success is conceivably due to poor tumor antigen presentation combined with immuno-suppressive mechanisms exploited by the tumor itself. Knock down of Inhibitor of differentiation protein 2 (Id2-kd) in mouse neuroblastoma whole tumor cells rendered these cells immunogenic. Id2-kd neuroblastoma (Neuro2a) cells (Id2-kd N2a) failed to grow in most immune competent mice and these mice subsequently developed immunity against further wild-type Neuro2a tumor cell challenge. Id2-kd N2a cells grew aggressively in immune-compromised hosts, thereby establishing the immunogenicity of these cells. Therapeutic vaccination with Id2-kd N2a cells alone suppressed tumor growth even in established neuroblastoma tumors and when used in combination with immune checkpoint blockade eradicated large established tumors. Mechanistically, immune cell depletion studies demonstrated that while CD8+ T cells are critical for antitumor immunity, CD4+ T cells are also required to induce a sustained long-lasting helper effect. An increase in number of CD8+ T-cells and enhanced production of interferon gamma (IFNγ) was observed in tumor antigen stimulated splenocytes of vaccinated mice. More importantly, a massive influx of cytotoxic CD8+ T-cells infiltrated the shrinking tumor following combined immunotherapy. These findings show that down regulation of Id2 induced tumor cell immunity and in combination with checkpoint blockade produced a novel, potent, T-cell mediated tumor vaccine strategy.

Immuno-regulatory antibodies for the treatment of cancer

INTRODUCTION

After years of limited success, progress of anti-cancer immuno-therapeutics has been considerable over the past decade. Key to this progress has been the application of new biological insights around the importance and nature of immune checkpoints that are able to reverse down-regulation of anti-tumor immunity.

AREAS COVERED

An overview of the preclinical and recent clinical trial data on key immuno-regulatory agents currently in development, including antibody targeting of cytotoxic T-lymphocyte antigen 4 (CTLA-4), programmed death receptor 1 (PD-1) on T-lymphocytes and its principal ligand (PD-L1) on tumor cells as well as immune agonists (e.g., anti-CD40).

EXPERT OPINION

Durable long-term responses in some patients with advanced melanoma, initially with ipilimumab (anti-CTLA-4) and more recently antibodies targeting either PD-1 or PD-L1 in patients with melanoma and renal cancer, non-small-cell lung, bladder and head and neck cancers with less toxicity, have provided real optimism that immunotherapeutic approaches can improve outcomes in a wide range of cancer. The manageable tolerability of PD-1-pathway blockers and their unique mechanism of action are encouraging combination approaches. Current efforts focus on registration trials of single agents plus combinations in many different tumor types and treatment settings and identifying and developing predictive biomarkers of immunological response.

Cytotoxic T lymphocyte-associated antigen 4 inhibition increases the antitumor activity of adoptive T-cell therapy when carried out with naïve rather than differentiated T cells

Although treatment with an antibody against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) combined with multiple therapeutic interventions has been explored, the effect of combination therapy with CTLA-4 inhibition and adoptive T-cell therapy has not been determined. In the present study, our aim was to determine whether CTLA-4 inhibition, combined with adoptive transfer of T cells at different stages of differentiation, exhibits synergistic antitumor effects in a murine colon cancer model. Mice bearing subcutaneous tumors were administered adoptive T-cell transfer of CD62Lhigh or CD62Llow cells combined with an anti-CTLA-4 antibody (α-CTLA-4) or control immunoglobulin G. Subcutaneous tumors were harvested, and the antitumor effects and helper T-cell polarization were analyzed. CTLA-4 inhibition combined with CD62Lhigh cell administration showed the strongest antitumor effect. Combination therapy increased the number of CD3+ cells within the tumor. Moreover, CTLA-4 inhibition induced polarization of T cells infiltrating the tumor toward the T helper 1 lineage, and suppressed the frequency of regulatory T cells within the tumor, particularly in combination with CD62Lhigh T-cell transfer. This is the first report demonstrating that the efficacy of α-CTLA-4 and adoptive T-cell transfer combination therapy depends on the state of differentiation of the transferred T cells. Our data support the notion that a combination of α-CTLA-4 and adoptive T-cell transfer containing an abundance of naïve phenotype cells could potentially exert antitumor effects in a clinical setting.

Immune checkpoint modulation: rational design of combination strategies

Immune recognition and elimination of malignant cells require a series of steps orchestrated by the innate and the adaptive arms of the immune system. The majority of tumors have evolved mechanisms that allow for successful evasion of these immune responses. Recognition of these evasive processes led to the development of immunotherapeutic antibodies targeting the co-stimulatory and co-inhibitory receptors on T cells, with the goal of enhancement of T cell activation or reversal of tumor-induced T cell inhibition. Several of these agents, such as antibodies targeting cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed death receptor 1 (PD-1) have already demonstrated significant promise in clinical trials. Clinical benefit of these antibodies as single agents, however, has been limited to a subset of patients and has not been observed in all tumor types. These limitations call for the development of rational combination strategies aiming to extend therapeutic benefit to a broader range of patients. These include: 1) modalities that enhance antigen presentation, such as radiation, cryotherapy, chemotherapy, targeted agents, vaccines, toll-like receptor (TLR) agonists, type I interferon, and oncolytic viruses; 2) additional agents aiming to reverse T cell dysfunction, such as other immune checkpoint inhibitors; and 3) agents targeting other immune inhibitory mechanisms, such as inhibitors of indoleamine dioxygenase (IDO), regulatory T cells, and myeloid-derived suppressor cells (MDSCs). It is becoming increasingly evident that the efficacy of specific combinations will likely not be universal and that the choice of a treatment modality may need to be tailored to fit the needs of each individual patient.

Induction of Bcl-xL-specific cytotoxic T lymphocytes in mice

The induction of active immunity against tumour-associated antigens to prevent relapse of cancer is a promising approach but has so far shown only low efficacy. This low efficacy may in part be due to clonal escape of tumour cell variants by the downregulation of antigen expression or inflammation-induced dedifferentiation. Identification of novel tumour-associated antigens that at the same time are essential for continued tumour cell survival is thus critical for the development of active cancer vaccinations. At the same time, identification of novel endogenous murine tumour antigens will help improve preclinical development of cancer immunotherapy. The anti-apoptotic protein Bcl-xL has been suggested to be such an essential tumour antigen, but the lack of well-defined murine epitopes have delayed preclinical studies of Bcl-xL-targeting cancer vaccines. Here, we report the identification of two novel murine tumour-associated epitopes TAYQSFEQV and AFFSFGGAL derived from mouse Bcl-xL. Dendritic cell (DC)-based vaccination induced CD8(+) T cells capable of producing IFN-γ upon restimulation with these epitopes. Thus, our data may benefit the design of future immunotherapy strategies by providing a preclinical model for cancer vaccination with an endogenous tumour antigen that can be combined with other cancer treatments.

Anti-CD40-mediated cancer immunotherapy: an update of recent and ongoing clinical trials

The costimulatory molecule CD40 is a member of the tumor necrosis factor (TNF) receptor superfamily and is expressed on various antigen presenting cells (APCs) as well as some tumor cells. The binding to the natural ligand CD40L, which is expressed on T helper cells, leads to APC activation and thus enhancement of immune responses. Treatment with anti-CD40 monoclonal antibodies has been exploited in several cancer immunotherapy studies in mice and led to the development of anti-CD40 antibodies for clinical use. Here, Dacetuzumab and Lucatumumab are in the most advanced stage and are being tested as treatment for malignancies such as chronic lymphatic leukemia (CLL), Multiple Myeloma (MM), and non-Hodgkin's lymphoma (NHL). The promising results from these early clinical trials have encouraged clinical drug development in order to investigate the effect of CD40 mAbs in combination with other cancer immunotherapies, in particular interleukin (IL)-2. An in-depth analysis of this immunotherapy is provided elsewhere. In the present review, we provide an update of the most recent clinical trials with anti-CD40 antibodies. We present and discuss recent and ongoing clinical trials in this field, including clinical studies which combine anti-CD40 treatment with other cancer-treatments, such as Rituximab and Tremelimumab.

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.

Immunomodulatory therapy for melanoma: ipilimumab and beyond

In 2011, the U.S. Food and Drug Administration approved the first new therapy for melanoma in more than a decade, ipilimumab (Yervoy). Ipilimumab is a novel antibody that blocks cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), a regulatory molecule expressed on activated T cells. Blockade of this important immune checkpoint can lead to durable tumor regression, and phase III studies show an overall survival benefit for patients with advanced melanoma. During the clinical development of ipilimumab, several unique features of this immunotherapy were identified, including the remarkable durability of responses and a distinct side-effects profile. We review the preclinical and clinical development of CTLA-4-blocking antibodies and describe current practices using ipilimumab for the treatment of advanced melanoma. Unique clinical issues related to ipilimumab will be summarized. Lastly, we will briefly preview combination therapies that incorporate ipilimumab and new checkpoint-targeting antibodies currently in clinical development.

Immunomodulatory therapy for melanoma: ipilimumab and beyond

In 2011, the U.S. Food and Drug Administration approved the first new therapy for melanoma in more than a decade, ipilimumab (Yervoy). Ipilimumab is a novel antibody that blocks cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), a regulatory molecule expressed on activated T cells. Blockade of this important immune checkpoint can lead to durable tumor regression, and phase III studies show an overall survival benefit for patients with advanced melanoma. During the clinical development of ipilimumab, several unique features of this immunotherapy were identified, including the remarkable durability of responses and a distinct side-effects profile. We review the preclinical and clinical development of CTLA-4-blocking antibodies and describe current practices using ipilimumab for the treatment of advanced melanoma. Unique clinical issues related to ipilimumab will be summarized. Lastly, we will briefly preview combination therapies that incorporate ipilimumab and new checkpoint-targeting antibodies currently in clinical development.

Active immunotherapy: current state of the art in vaccine approaches for NHL

Immune therapy of cancer is a rapidly evolving field, with long-deserved successes now finally achieved. As new pathways triggered by the immune synapsis are elucidated, and new molecules responsible for immune checkpoints are being discovered, it is becoming clear that vaccination against a single antigen aided by non-specific immune stimulation is not sufficient for an efficient, long term, immune response. Though lymphoma is a highly curable malignancy, there is still a subset of patients that is at very high risk of disease relapse even after successfully completing chemotherapy or a stem cell transplant. Patients with minimal residual disease are particularly suitable for vaccination. Over the past 3 decades, the classic model of lymphoma-specific idiotype vaccine has evolved and recent data on vaccination with nonspecific oligodeoxynucleotides has provided very encouraging results. Furthermore, the introduction of checkpoint blockade via agonist or antagonist monoclonal antibodies holds the promise of significant improvement in the efficacy of future vaccines. What follows is a brief summary of the historical highlights in lymphoma immunotherapy as well as an update on the most recently published clinical trials and a look at future developments.

Coinhibitory molecules in hematologic malignancies: targets for therapeutic intervention

The adaptive immune system can be a potent defense mechanism against cancer; however, it is often hampered by immune suppressive mechanisms in the tumor microenvironment. Coinhibitory molecules expressed by tumor cells, immune cells, and stromal cells in the tumor milieu can dominantly attenuate T-cell responses against cancer cells. Today, a variety of coinhibitory molecules, including cytotoxic T lymphocyte–associated antigen-4, programmed death-1, B and T lymphocyte attenuator, LAG3, T-cell immunoglobulin and mucin domain 3, and CD200 receptor, have been implicated in immune escape of cancer cells. Sustained signaling via these coinhibitory molecules results in functional exhaustion of T cells, during which the ability to proliferate, secrete cytokines, and mediate lysis of tumor cells is sequentially lost. In this review, we discuss the influence of coinhibitory pathways in suppressing autologous and allogeneic T cell–mediated immunity against hematologic malignancies. In addition, promising preclinical and clinical data of immunotherapeutic approaches interfering with negative cosignaling, either as monotherapy or in conjunction with vaccination strategies, are reviewed. Numerous studies indicate that coinhibitory signaling hampers the clinical benefit of current immunotherapies. Therefore, manipulation of coinhibitory networks is an attractive adjuvant immunotherapeutic intervention for hematologic cancers after standard treatment with chemotherapy and hematopoietic stem cell transplantation.

Immunocombination therapy for high-risk neuroblastoma

Neuroblastoma (NBL) is an aggressive malignancy of the sympathetic nervous system. Advanced-stage NBLs prove fatal in approximately 50% of patients within 5 years. Therefore, new treatment modalities are urgently needed. Immunotherapy is a treatment modality that can be combined with established forms of treatment. Administration of monoclonal antibodies or dendritic cell-based therapies alone can lead to favorable clinical outcomes in individual cancer patients; for example patients with melanoma, lymphoma and NBL. However, clinical benefit is still limited to a minority of patients, and further improvements are clearly needed. In this article, we review the most commonly used approaches to treat patients with NBL and highlight the prerequisites and opportunities of cell-based immunotherapy, involving both innate and adaptive immune-effector cells. Furthermore, we discuss the potential of the combined application of immunotherapy and novel tumor-targeted therapies for the treatment of both cancer in general and NBL in particular.

Combination immunotherapy with 4-1BBL and CTLA-4 blockade for the treatment of prostate cancer

Immune regulation has been shown to be involved in the progressive growth of some murine tumours. Interruption of immune regulatory pathways via activation of 4-1BB or cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) blockade appears to be a promising strategy for cancer immunotherapy. In this study, we examined the effectiveness of 4-1BBL-expressing tumor cell vaccine in combination with CTLA-4 blockade on rejection of murine prostate cancer RM-1. We found that the combination of both a vaccine consisting of 4-1BBL-expressing RM-1 cells and CTLA-4 blockade resulted in regression of RM-1 tumors and a significant increase in survival of the tumour cell recipients, compared to that of either treatment alone. The combined vaccination resulted in higher CTL against RM-1 cells and increased secretion of IFN-γ, TNF-α, and IL-2 in the mix-cultured supernatant. These results suggest that combining activation of 4-1BB and blockade of CTLA-4 may offer a new strategy for prostate cancer immunotherapy.

Immune modulation by chemotherapy or immunotherapy to enhance cancer vaccines

Chemotherapy has been a mainstay in cancer treatment for many years. Despite some success, the cure rate with chemotherapy remains unsatisfactory in some types of cancers, and severe side effects from these treatments are a concern. Recently, understanding of the dynamic interplay between the tumor and immune system has led to the development of novel immunotherapies, including cancer vaccines. Cancer vaccines have many advantageous features, but their use has been hampered by poor immunogenicity. Many developments have increased their potency in pre-clinical models, but cancer vaccines continue to have a poor clinical track record. In part, this could be due to an inability to effectively overcome tumor-induced immune suppression. It had been generally assumed that immune-stimulatory cancer vaccines could not be used in combination with immunosuppressive chemotherapies, but recent evidence has challenged this dogma. Chemotherapies could be used to condition the immune system and tumor to create an environment where cancer vaccines have a better chance of success. Other types of immunotherapies could also be used to modulate the immune system. This review will discuss how immune modulation by chemotherapy or immunotherapy could be used to bolster the effects of cancer vaccines and discuss the advantages and disadvantages of these treatments.

Adenoviral vaccination combined with CD40 stimulation and CTLA-4 blockage can lead to complete tumor regression in a murine melanoma model

Therapeutic vaccination with replication deficient adenovirus expressing a viral antigen linked to invariant chain was recently found to markedly delay the growth of B16.F10 melanomas expressing the same antigen; however, complete regression of the tumors was never observed. Here we show that the delay in tumor growth can be converted to complete regression and long-term survival in 30-40% of the mice by a booster vaccination plus combinational treatment with agonistic anti-CD40 monoclonal antibodies (mAb) and anti-CTLA-4 mAb. Regarding the mechanism underlying the improved clinical effect, analysis of the tumor-specific response revealed a significantly prolonged tumor-specific CD8 T cell response in spleens of the mice receiving the combinational treatment compared with mice receiving either treatment individually. Matching this, CD8 T cell depletion completely prevented tumor control. These results indicate that even with a strong tumor vaccine candidate, combinatorial treatment may be required to obtain clinically relevant results.

CTLA-4 blockade during dendritic cell based booster vaccination influences dendritic cell survival and CTL expansion

Dendritic cells (DCs) are potent antigen-presenting cells and critical for the priming of CD8+ T cells. Therefore the use of these cells as adjuvant cells has been tested in a large number of experimental and clinical vaccination studies, in particular cancer vaccine studies. A number of protocols are emerging that combine vaccination with CTL expanding strategies, such as e.g. blockade of CTLA-4 signalling. On the other hand, the lifespan and in vivo survival of therapeutic DCs have only been addressed in a few studies, although this is of importance for the kinetics of CTL induction during vaccination. We have previously reported that DCs loaded with specific antigens are eliminated by antigen specific CTLs in vivo and that this elimination affects the potential for in vivo CTL generation. We now show that CTLA-4 blockade increases the number of DC vaccine induced LCMV gp33 specific CTLs and the lysis of relevant in vivo targets. However, the CTLA-4 blockage dependent expansion of CTLs also affect DC survival during booster DC injections and our data suggest that during a booster DC vaccine, the largest increase in CTL levels is already obtained during the first vaccination.

Treatment of transplanted CT26 tumour with dendritic cell vaccine in combination with blockade of vascular endothelial growth factor receptor 2 and CTLA-4

We investigated the anti CT26 tumour effect of dendritic cell based vaccination with the MuLV gp70 envelope protein-derived peptides AH1 and p320-333. Vaccination lead to generation of AH1 specific cytotoxic lymphocytes (CTL) and some decrease in tumour growth of simultaneously inoculated CT26 cells. After combination with an antibody against VEGF receptor 2 (DC101), a significant increase in survival of the tumour cell recipients was observed. Also, monotherapy with an antibody against CTLA-4 (9H10), led to approximately 100% survival of tumour cell recipients. However, effective treatment of mice with already established tumours was only obtained after combination of vaccination, DC101 and 9H10 treatment in which setting 80% of the mice rejected their tumours.