Immunotherapy for pancreatic cancer: current concepts

Despite advances in chemotherapy and surgical technique, patients with pancreatic cancer often succumb to local recurrence or metastatic spread. The need for new therapeutic strategies for this disease coupled with a better understanding of basic immunology have led to the development of novel anti-tumor vaccines. This review focuses on the historical development of tumor vaccines emphasizing the identification of potential pancreatic tumor antigens. The role of both B-cell and T-cell responses in tumor rejection will be reviewed. Methods for antigen presentation, including peptides, recombinant viral and bacterial vectors, dendritic cells, and whole cell approaches will be discussed. The use of immune adjuvants and improved methods of vaccine delivery will also be explored. The full potential for the immunotherapy of pancreatic cancer awaits the results of early phase clinical trials. The development of pancreatic cancer vaccines represents a useful paradigm for the translation of basic research into the clinical arena.     

Cancer immunotherapy based on recombinant Salmonella enterica serovar Typhimurium aroA strains secreting prostate-specific antigen and cholera toxin subunit B

Prostate cancer is the most common malignant tumor in men and is normally associated with increased serum levels of prostate-specific antigen (PSA). Therefore, PSA is one potential target for a prostate cancer vaccine. In this study we analyzed the functionality of new bacterial PSA vaccines, expressed and secreted via the hemolysin (HlyA) secretion system of Escherichia coli, the prototype of Type I secretion systems (T1SS) using an attenuated Salmonella enterica serovar Typhimurium aroA strain as carrier. The data demonstrate that a bacterial live vaccine encompassing T1SS in combination with cholera toxin subunit B can be successfully used for delivery of PSA to induce cytotoxic CD8+ T-cell responses resulting in an efficient prevention of tumor growth in mice.     

Pox viral vaccine approaches

Recent advances in understanding tumor-specific immunity have introduced new excitement in the clinical development of vaccines for the treatment of cancer. A better understanding of basic immunologic principles has led to a variety of techniques for enhancing tumor-specific immunity through vaccination. Approaches to antigen-specific immunotherapy have included: (1) peptides, usually in combination with various immunological adjuvants; (2) soluble proteins; (3) dendritic cells pulsed with specific antigens; (4) monoclonal antibodies; (5) recombinant plasmid DNA; (6) autologous and allogeneic tumor cells; and (7) recombinant viral vectors. This review will focus on the use of viral vectors, which offer unique advantages as both gene delivery vectors and as agents supplying additional adjuvant activity for vaccination. Viral vectors are particularly attractive for immunotherapy since they mimic natural infection and can induce potent immune responses. Replicating and nonreplicating members of the poxvirus family have been widely studied for expression of tumor antigens and other immunomodulatory genes, such as cytokines and costimulatory molecules. Although a large number of TAAs are available for insertion into viral vectors, this review will discuss the preclinical and clinical development of prostate-specific antigen (PSA) and carcinoembryonic antigen (CEA) poxviral vaccines, as models of the pox viral vaccine approach.     

Unmet need in lung cancer: can vaccines bridge the gap?

Despite recent advances in therapy for lung cancer, median survival remains poor. Cancer vaccines might meet the unmet need for new and effective therapies with low toxicity. A better understanding of the immunology of cancer has led to novel strategies for vaccine delivery, including the use of immunogenic adjuvant agents, genetic modification of tumor cells to produce cytokines, viral vectors, and the use of antigen-presenting cells. A number of these strategies have been studied in clinical trials for lung cancer. This review discusses the rationale for vaccine therapy in lung cancer, strategies for vaccine delivery, and clinical trials of vaccines in lung cancer.     

therapeutic vaccines for colorectal cancer

A number of cancer vaccine strategies for the treatment of colorectal cancer have entered clinical trials. Whole tumor cell vaccines have been developed from both patients’ autologous tumor cells as well as established allogeneic tumor cell lines. A vaccine consisting of autologous tumor cells along with bacillus Calmette-Guerin (BCG) has shown a potential clinical benefit in patients with stage II colon cancer. Other approaches using autologous tumor cells have involved transfection of primary tumor cells with cytokine genes. Allogeneic tumor cell vaccines have also been modified to express cytokine genes. Vectors have been studied extensively as a means of vaccine strategy. One tumor-associated antigen (TAA) that has been extensively studied in viral vector vaccines is carcinoembryonic antigen (CEA). A recombinant vaccinia virus containing the CEA transgene (rV-CEA) has been shown to elicit CEA-specific immune responses in advanced carcinoma patients. However, patients receiving multiple vaccinations had limited increases in CEA-specific responses by the third vaccination. This problem may be overcome by the use of non-replicating poxviruses, which have been shown in clinical trials to be safe and to elicit CEA-specific responses. However, recent clinical studies have shown that the optimal use of poxviruses is to prime with vaccinia, followed by boosts with avipox vectors. A recent randomized clinical trial showed that patients primed with rV-CEA and boosted with avipox-CEA had greater immune responses compared with patients receiving three 1-monthly avipox-CEA vaccinations followed by an rV-CEA vaccination. Furthermore, a statistically significant survival advantage was noted in the prime/boost arm. Ongoing studies are now incorporating the genes for costimulatory molecules along with TAA in these vectors. Another vaccine strategy involving TAA that is currently in clinical trials for colorectal cancer is the peptide vaccine. Dendritic cells (DCs) are considered to be the most potent antigen-presenting cell, thus providing an attractive modality for cancer vaccines. In addition to using DCs for peptide-based vaccines, a number of other strategies, including transfection with messenger RNA, have produced specific T-cell responses in clinical trials. In addition, several clinical trials using murine anti-idiotype antibodies as vaccines for patients with advanced colorectal cancer have shown both immunologic responses as well as clinical responses.     

应用病毒治疗结直肠癌的研究进展*

基于病毒的抗肿瘤治疗是一种新兴的生物治疗方式,病毒载体感染肿瘤组织,引起溶瘤效应,制成疫苗激活体内抗肿瘤免疫,搭载基因行癌症的基因治疗。随着对病毒的不断改造,各类病毒治疗肿瘤更趋于安全和高效,同时,病毒载体与现有的抗肿瘤疗法合理联用,可提高治疗效果。因此,基于病毒的抗肿瘤治疗将作为极具潜力的方法而逐渐引起人们的重视。本文就近些年各种病毒在治疗结直肠癌中的研究进展做一综述。      

Improvement of different vaccine delivery systems for cancer therapy

Cancer vaccines are the promising tools in the hands of the clinical oncologist. Many tumor-associated antigens are excellent targets for immune therapy and vaccine design. Optimally designed cancer vaccines should combine the best tumor antigens with the most effective immunotherapy agents and/or delivery strategies to achieve positive clinical results. Various vaccine delivery systems such as different routes of immunization and physical/chemical delivery methods have been used in cancer therapy with the goal to induce immunity against tumor-associated antigens. Two basic delivery approaches including physical delivery to achieve higher levels of antigen production and formulation with microparticles to target antigen-presenting cells (APCs) have demonstrated to be effective in animal models. New developments in vaccine delivery systems will improve the efficiency of clinical trials in the near future. Among them, nanoparticles (NPs) such as dendrimers, polymeric NPs, metallic NPs, magnetic NPs and quantum dots have emerged as effective vaccine adjuvants for infectious diseases and cancer therapy. Furthermore, cell-penetrating peptides (CPP) have been known as attractive carrier having applications in drug delivery, gene transfer and DNA vaccination. This review will focus on the utilization of different vaccine delivery systems for prevention or treatment of cancer. We will discuss their clinical applications and the future prospects for cancer vaccine development.     

Cancer Gene Therapy Goes Viral: Viral Vector Platforms Come of Age

BackgroundSince the advent of viral vector gene therapy in 1990s, cancer treatment with viral vectors promised to revolutionize the field of oncology. Notably, viral vectors offer a unique combination of efficient gene delivery and engagement of the immune system for anti-tumour response. Despite the early potential, viral vector-based cancer treatments are only recently making a big impact, most prominently as gene delivery devices in approved CAR-T cell therapies, cancer vaccines and targeted oncolytic therapeutics. To reach this broad spectrum of applications, a number of challenges have been overcome – from our understanding of cancer biology to vector design, manufacture and engineering. Here, we take an overview of viral vector usage in cancer therapy and discuss the latest advancements. We also consider production platforms that enable mainstream adoption of viral vectors for cancer gene therapy.ConclusionsViral vectors offer numerous opportunities in cancer therapy. Recent advances in vector production platforms open new avenues in safe and efficient viral therapeutic strategies, streamlining the transition from lab bench to bedside. As viral vectors come of age, they could become a standard tool in the cancer treatment arsenal.Key words: viral vector, gene therapy, oncolytic virus, immunotherapy, bioprocess platform     

Nanomaterial-based delivery vehicles for therapeutic cancer vaccine development

Nanomaterial-based delivery vehicles such as lipid-based, polymer-based, inorganics-based, and bio-inspired vehicles often carry distinct and attractive advantages in the development of therapeutic cancer vaccines. Based on various delivery vehicles, specifically designed nanomaterials-based vaccines are highly advantageous in boosting therapeutic and prophylactic antitumor immunities. Specifically, therapeutic vaccines featuring unique properties have made major contributions to the enhancement of antigen immunogenicity, encapsulation efficiency, biocompatibility, and stability, as well as promoting antigen cross-presentation and specific CD8⁺ T cell responses. However, for clinical applications, tumor-associated antigen-derived vaccines could be an obstacle, involving immune tolerance and deficiency of tumor specificities, in achieving maximum therapeutic indices. However, when using bioinformatics predictions with emerging innovations of in silico tools, neoantigen-based therapeutic vaccines might become potent personalized vaccines for tumor treatments. In this review, we summarize the development of preclinical therapeutic cancer vaccines and the advancements of nanomaterial-based delivery vehicles for cancer immunotherapies, which provide the basis for a personalized vaccine delivery platform. Moreover, we review the existing challenges and future perspectives of nanomaterial-based personalized vaccines for novel tumor immunotherapies.     

Combination of docetaxel and recombinant vaccine enhances T-cell responses and antitumor activity: effects of docetaxel on immune enhancement

PURPOSE: Taxanes comprise some of the most widely used cancer chemotherapeutic agents. Members of this drug family, including docetaxel, are commonly used to treat breast, prostate, and lung cancers, among others. This study was designed to determine if this taxane has the ability to modulate components of the immune system independent of antitumor activity and to investigate the potential synergistic activities of the combination of docetaxel and vaccine therapy. EXPERIMENTAL DESIGN: We examined the in vivo effects of docetaxel on immune-cell subsets and on the function of CD4+, CD8+, and regulatory T-cell (Treg) populations in response to antigen-specific vaccination. We also examined the antitumor effects of the combination of docetaxel and vaccine in a preclinical model in which docetaxel has no observable effect on tumor growth. RESULTS: These studies show for the first time that (a) docetaxel modulates CD4+, CD8+, CD19+, natural killer cell, and Treg populations in non-tumor-bearing mice; (b) unlike cyclophosphamide, docetaxel does not inhibit the function of Tregs; (c) docetaxel enhances CD8+ but not CD4+ response to CD3 cross-linking; (d) docetaxel given after vaccination provides optimal enhancement of immune response to recombinant viral vaccines; (e) docetaxel combined with recombinant viral vaccine is superior to either agent alone at reducing tumor burden; and (f) docetaxel plus vaccine increases antigen-specific T-cell responses to antigen in the vaccine, as well as to cascade antigens derived from the tumor. CONCLUSIONS: These findings suggest potential clinical benefit for the combined use of docetaxel and recombinant cancer vaccines.     

Novel recombinant alphaviral and adenoviral vectors for cancer immunotherapy

Although cellular immunotherapy based on autolgous dendritic cells (DCs) targeting antigens expressed by metastatic cancer has demonstrated clinical efficacy, the logistical challenges in generating an individualized cell product create an imperative to develop alternatives to DC-based cancer vaccines. Particularly attractive alternatives include in situ delivery of antigen and activation signals to resident antigen-presenting cells (APCs), which can be achieved by novel fusion molecules targeting the mannose receptor and by recombinant viral vectors expressing the antigen of interest and capable of infecting DCs. A particular challenge in the use of viral vectors is the well-appreciated clinical obstacles to their efficacy, specifically vector-specific neutralizing immune responses. Because heterologous prime and boost strategies have been demonstrated to be particularly potent, we developed two novel recombinant vectors based on alphaviral replicon particles and a next-generation adenovirus encoding an antigen commonly overexpressed in many human cancers, carcinoembryonic antigen (CEA). The rationale for developing these vectors, their unique characteristics, the preclinical studies and early clinical experience with each, and opportunities to enhance their effectiveness will be reviewed. The potential of each of these potent recombinant vectors to efficiently generate clinically active anti-tumor immune response alone, or in combination, will be discussed.     

Messenger RNA vaccine based on recombinant MS2 virus‐like particles against prostate cancer

Prostate cancer (PCa) is the most diagnosed cancer in the western male population with high mortality. Recently, alternative approaches based on immunotherapy including mRNA vaccines for PCa have shown therapeutic promise. However, for mRNA vaccine, several disadvantages such as the instability of mRNA, the high cost of gold particles, the limited production scale for mRNA‐transfected dendritic cells in vitro, limit their development. Herein, recombinant bacteriophage MS2 virus‐like particles (VLPs), which based on the interaction of a 19‐nucleotide RNA aptamer and the coat protein of bacteriophage MS2, successfully addressed these questions, in which target mRNA was packaged by MS2 capsid. MS2 VLP‐based mRNA vaccines were easily prepared by recombinant protein technology, nontoxic and RNase‐resistant. We show the packaged mRNA was translated into protein as early as 12 hr after phagocytosed by macrophages. Moreover, MS2 VLP‐based mRNA vaccines induced strong humoral and cellular immune responses, especially antigen‐specific cytotoxic T‐lymphocyte (CTL) and balanced Th1/Th2 responses without upregulation of CD4⁺ regulatory T cells, and protected C57BL/6 mice against PCa completely. As a therapeutic vaccine, MS2 VLP‐based mRNA vaccines delayed tumor growth. Our results provide proof of concept on the efficacy and safety of MS2 VLP‐based mRNA vaccine, which provides a new delivery approach for mRNA vaccine and implies important clinical value for the prevention and therapy of PCa.     

Contribution of viral recombinants to the study of the immune response against the Epstein-Barr virus

Over the past two decades, Epstein-Barr virus (EBV) mutants have become valuable tools for the analysis of viral functions. Several experimental strategies are currently used to generate recombinant mutant genomes that carry alterations in one or several viral genes. The probably most versatile approach utilizes bacterial artificial chromosomes (BAC) carrying parts or the whole EBV genome, which permits extensive genetic manipulations in Escherichia coli cells. The 'mini-EBVs', for example, which contain roughly half of the wild type viral information, efficiently transform primary B cells and have been used as gene vectors for foreign antigens. After expression in lymphoblastoid cell lines (LCLs), these antigens are efficiently presented on MHC molecules and recognized by antigen-specific T cells. These vectors, however, cannot undergo lytic replication and require a helper cell line for efficient replication and DNA packaging. Further experimental systems include the complete viral genome cloned onto a BAC. These mutants can typically be complemented by expression plasmids, some of which are expressed on EBV-derived vectors and can be propagated without requirement of a helper cell line. Over the last years, these viral recombinants have been utilized increasingly to analyse different aspects of the immune response against EBV. Immunological applications are manifold and steadily growing and include crude screening of T cell clones for their specificity towards latent versus lytic antigens, or more detailed analyses in which the exact specificity of T cells is determined using EBV mutants that lack a single viral antigen. Other applications include detailed analysis of protein domains important for immune recognition, e.g. Gly-Ala repeats in the EBV nuclear antigen 1 (EBNA1) protein, expansion of T cell clones directed against virion structures using virus-like particles and phenotypic analysis of virus mutants defective in infection. Future developments might include the genetic identification and characterization of viral proteins involved in the modulation of the immune response and, in particular, immune evasion. Recombinant viral strains are already being used experimentally for the expansion of T cells in vitro prior to in vivo cellular therapy and have been proposed as potential prophylactic vaccines.     

Modified vaccinia virus ankara recombinants are as potent as vaccinia recombinants in diversified prime and boost vaccine regimens to elicit therapeutic antitumor responses

Cancer vaccine regimens use various strategies to enhance immune responses to specific tumor-associated antigens (TAAs), including the increasing use of recombinant poxviruses [vaccinia (rV) and fowlpox (rF)] for delivery of the TAA to the immune system. However, the use of replication competent vectors with the potential of adverse reactions have made attenuation a priority for next-generation vaccine strategies. Modified vaccinia Ankara (MVA) is a replication defective form of vaccinia virus. Here, we investigated the use of MVA encoding a tumor antigen gene, carcinoembryonic antigen (CEA), in addition to multiple costimulatory molecules (B7-1, intercellular adhesion molecule-1, and lymphocyte function-associated antigen-3 designated TRICOM). Vaccination of mice with MVA-CEA/TRICOM induced potent CD4+ and CD8+ T-cell responses specific for CEA. MVA-CEA/TRICOM could be administered twice in vaccinia na?ve mice and only a single time in vaccinia-immune mice before being inhibited by antivector-immune responses. The use of MVA-CEA/TRICOM in a diversified prime and boost vaccine regimen with rF-CEA/TRICOM, however, induced significantly greater levels of both CD4+ and CD8+ T-cell responses specific for CEA than that seen with rV-CEA/TRICOM prime and rF-CEA/TRICOM boost. In a self-antigen tumor model, the diversified MVA-CEA/TRICOM/rF-CEA/ TRICOM vaccination regimen resulted in a significant therapeutic antitumor response as measured by increased survival, when compared with the diversified prime and boost regimen, rV-CEA/TRICOM/rF-CEA/TRICOM. The studies reported here demonstrate that MVA, when used as a prime in a diversified vaccination, is clearly comparable with the regimen using the recombinant vaccinia in both the induction of cellular immune responses specific for the "self"-TAA transgene and in antitumor activity.     

Induction of P815 tumor immunity by DNA-based recombinant Semliki Forest virus or replicon DNA expressing the P1A gene

AIM: To compare the prophylactic and therapeutic effects of alphaviruses in the same tumor model, we used a DNA-based approach to generate a replicon DNA and recombinant Semliki Forest virus (rSFV) particles expressing P1A, the P815 mastocytoma tumor associated antigen, and compared the immune effect of each vaccine. METHODS: Six to eight-week-old female DBA/2 mice were inoculated with P1A plasmid or viral vaccines. Spleen cells were assayed for antigen-specific cytotoxic T cell activity. Tumor growth or survival rate was observed in preventive and therapeutic experiments, respectively. RESULTS: We found that the rSFV particles prevented tumor growth when delivered prior to innoculation of mice with P815 cells, and more importantly, improved survival when delivered after the initiation of tumor growth. Naked P1A replicon DNA also functioned as a protective and therapeutic vaccine, although with less potency than rSFV particles. Virus particles also elicited a stronger cellular immune response as measured by target cell lysis. CONCLUSION: rSFV particles have stronger specific prophylactic and therapeutic immune effects in mice than replicon DNA-based DNA vaccines, though the latter is more effective than traditional plasmid vectors (e.g. pCI-neo vector).     

New approaches to the development of live attenuated rabies vaccines

In the United States, extensive reservoirs of the rabies virus exist in many diverse wild animal species, which continue to pose a serious risk of lethal infection of humans and cause an economic burden exceeding $1 billion annually. Previous experience with rabies control in foxes in Europe has clearly demonstrated that oral immunization with live vaccines is the only practical approach to eradicate rabies in free-ranging animals. However, unlike Europe where vulpine rabies was the only major reservoir, the Americas harbor a variety of species including raccoons, skunks, coyotes, and bats that serve as the primary reservoirs of rabies. Each of these animal reservoirs carries an antigenically distinct virus variant. The currently available modified-live rabies virus vaccines have either safety problems or do not induce sufficient protective immunity in particular wildlife species. Therefore, there is a need for the development of new live rabies virus vaccines that are very safe and highly effective in particular wildlife species. Based on previous observations indicating that the potency of a vaccine is significantly increased if the G protein of the vaccine strain is identical to that of the target virus, we have used a reverse genetics approach to engineer viruses that contain G proteins from virus strains associated with relevant wildlife species. Furthermore, because our recent data also indicate that the pathogenicity of a particular rabies virus strain is inversely proportional to its ability to induce apoptosis and that low-level apoptosis-inducing ability is associated with low anti-viral immune responses, we inserted genes encoding pro-apoptotic proteins to stimulate immunity or otherwise interfere with viral pathogenesis into these recombinant viruses to enhance their efficacy and safety.     

以减毒沙门菌为载体的肿瘤疫苗研究

减毒沙门菌不但能用于疫苗的构建,而且可作为外源基因的载体.减毒沙门菌作为细菌载体使目的基因在肿瘤组织内表达,可刺激机体发生特异性的抗肿瘤免疫应答,从而抑制肿瘤生长,为疫苗的研制提供了新的思路.     

A novel strategy for the discovery of MHC class II-restricted tumor antigens: identification of a melanotransferrin helper T-cell epitope

CD4+ helper T cells play a critical role in orchestrating host immune responses, including antitumor immunity. The limited availability of MHC class II-associated tumor antigens is still viewed as a major obstacle in the use of CD4+ T cells in cancer vaccines. Here, we describe a novel approach for the identification of MHC class II tumor-associated antigens (TAAs). By combining two-dimensional liquid chromatography and nanoelectrospray ionization tandem mass spectrometry, we developed a highly sensitive method for the detection of human leukocyte antigen (HLA)-DR-associated peptides of dendritic cells upon exposure to necrotic tumor cells. This approach led to the identification of a novel MHC class II-restricted TAA epitope derived from melanotransferrin. The epitope stimulated T cells derived from melanoma patients and healthy individuals and displayed promiscuity in HLA-DR restriction. Moreover, the same peptide was also presented by MHC class II-positive melanoma cells. This strategy may contribute to increase the number of tumor epitopes presented by MHC class II molecules and may support the development of more efficacious vaccines against cancer.     

肿瘤疫苗的临床研究新进展

肿瘤疫苗包括多肽疫苗、基因疫苗、重组病毒疫苗、肿瘤细胞疫苗、多肽冲击的树突细胞疫苗等。肿瘤疫苗是应用其表达特异性的肿瘤抗原,来激活、恢复或加强机体抗肿瘤的免疫反应,进而杀伤、清除肿瘤细胞。研制一种肿瘤疫苗需先进行动物实验,再行Ⅲ期的临床试验,研究其安全性和有效性。肿瘤疫苗在多种肿瘤临床试验中的效果是可喜的。已有相当多的肿瘤疫苗试验在患者体内能检测出有意义的免疫应答,且患者通常对肿瘤疫苗有很好的耐受性。很多新的肿瘤疫苗临床试验正在进行,一些Ⅲ期临床试验已经结束,但由于还没有达到预期的安全性和有效性,肿瘤疫苗治疗肿瘤仍然属于试验研究性质的。目前,更多新的有应用前景的肿瘤疫苗已经进入了临床试验,人们正在期待出现更理想的结果。本文就肿瘤疫苗临床研究进展及应用前景作一综述。     

Dendritic cell-directed lentivector vaccine induces antigen-specific immune responses against murine melanoma

Lentivectors are potential vaccine delivery vehicles because they can efficiently transduce a variety of non-dividing cells, including antigen-presenting cells, and do not cause expression of extra viral proteins. To improve safety while retaining efficiency, a dendritic cell (DC)-specific lentivector was constructed by pseudotyping the vector with an engineered viral glycoprotein derived from Sindbis virus. We assessed the level of anti-tumor immunity conferred by this engineered lentivector encoding the melanoma antigen gp100 in a mouse model. Footpad injection of the engineered lentivectors results in the best antigen-specific immune response as compared with subcutaneous and intraperitoneal injections. A single prime vaccination of the engineered lentivectors can elicit a high frequency (up to 10%) of gp100-specific CD8(+) T cells in peripheral blood 3 weeks after the vaccination and this response will be maintained at around 5% for up to 8 weeks. We found that these engineered lentivectors elicited relatively low levels of anti-vector neutralizing antibody responses. Importantly, direct injection of this engineered lentivector inhibited the growth of aggressive B16 murine melanoma. These data suggest that DC-specific lentivectors can be a novel and alternative vaccine carrier with the potential to deliver effective anti-tumor immunity for cancer immunotherapy.