Dendritic cell-based xenoantigen vaccination for prostate cancer immunotherapy

Effects of Injectable Solutions on the Quality of Monocyte-Derived Dendritic Cells for Immunotherapy

Therapeutic vaccines based on monocyte-derived dendritic cells have been shown to be promising strategies and may act as complementary treatments for viral infections, cancers, and, more recently, autoimmune diseases. Alpha-type-1-polarized dendritic cells (aDC1s) have been shown to induce type-1 immunity with a high capacity to produce interleukin-12p70 (IL-12p70). In the clinical use of cell-based therapeutics, injectable solutions can affect the morphology, immunophenotypic profile, and viability of cells before delivery and their survival after injection. In this sense, preparing a cell suspension that maintains the quality of aDC1s is essential to ensure effective immunotherapy. In the present study, monocytes were differentiated into aDC1s in the presence of IL-4 and GM-CSF. On day 5, the cells were matured by the addition of a cytokine cocktail consisting of IFN-α, IFN-γ, IL-1β, TNF-α, and Poly I:C. After 48 hr, mature aDC1s were harvested and suspended in two different solutions: normal saline and Ringer's lactate. The maintenance of cells in suspension was evaluated after 4, 6, and 8 hr of storage. Cell viability, immunophenotyping, and apoptosis analyses were performed by flow cytometry. Cellular morphology was observed by electron microscopy, and the production of IL-12p70 by aDC1s was evaluated by ELISA. Compared with normal saline, Ringer's lactate solution was more effective at maintaining DC viability for up to 8 hr of incubation at 4 or 22°C.

Exploring nanocarriers as innovative materials for advanced drug delivery strategies in onco-immunotherapies

In recent years, Onco-immunotherapies (OIMTs) have been shown to be a potential therapy option for cancer. Several immunotherapies have received regulatory approval, while many others are now undergoing clinical testing or are in the early stages of development. Despite this progress, a large number of challenges to the broad use of immunotherapies to treat cancer persists. To make immunotherapy more useful as a treatment while reducing its potentially harmful side effects, we need to know more about how to improve response rates to different types of immunotherapies. Nanocarriers (NCs) have the potential to harness immunotherapies efficiently, enhance the efficiency of these treatments, and reduce the severe adverse reactions that are associated with them. This article discusses the necessity to incorporate nanomedicines in OIMTs and the challenges we confront with current anti-OIMT approaches. In addition, it examines the most important considerations for building nanomedicines for OIMT, which may improve upon current immunotherapy methods. Finally, it highlights the applications and future scenarios of using nanotechnology.

Vaccines as treatments for prostate cancer

Prostate cancer is a leading cause of death in men worldwide. For over 30 years, growing interest has focused on the development of vaccines as treatments for prostate cancer, with the goal of using vaccines to activate immune cells capable of targeting prostate cancer to either eradicate recurrent disease or at least delay disease progression. This interest has been prompted by the prevalence and long natural history of the disease and by the fact that the prostate is an expendable organ. Thus, an immune response elicited by vaccination might not need to target the tumour uniquely but could theoretically target any prostate tissue. To date, different vaccine approaches and targets for prostate cancer have been evaluated in clinical trials. Overall, five approaches have been assessed in randomized phase III trials and sipuleucel-T was approved as a treatment for metastatic castration-resistant prostate cancer, being the only vaccine approved to date by the FDA as a treatment for cancer. Most vaccine approaches showed safety and some evidence of immunological activity but had poor clinical activity when used as monotherapies. However, increased activity has been observed when these vaccines were used in combination with other immune-modulating therapies. This evidence suggests that, in the future, prostate cancer vaccines might be used to activate and expand tumour-specific T cells as part of combination approaches with agents that target tumour-associated immune mechanisms of resistance.

Structure of PAP-IgM FcK fusion protein with J-chain expressed in transgenic plant

Transgenic plants expressing immunoglobulin (Ig) M Fc-fused Prostate acid phosphatase (PAP) antigenic proteins (PAP-IgM FcK) and J-chain proteins were generated by Agrobacterium-mediated transformation. The Fc region was tagged with the ER retention motif (KDEL) to make PAP-IgM FcK. Two transgenic plants were crossed together to generate F1 expressing both PAP-IgM FcK and J-chain proteins (PAP-IgM FcK × J-chain). PCR and RT-PCR analyses confirmed the transgene insertion and mRNA transcription of PAP-IgM FcK and J-chain in leaf tissue of PAP-IgM FcK × J-chain F1 plant. Western blot confirmed the expression of PAP-IgM FcK × J-chain protein. Size exclusion (SEC)-high performance liquid chromatography (HPLC) and Bio-transmission electron microscope (TEM) analyses were performed to show the size and shape of the PAP- IgM FcK × J-chain fusion proteins. These results suggest that PAP-IgM FcK with J-chain can be produced in plant expression system with plant crossing.

Down-Regulation of lncRNA MBNL1-AS1 Promotes Tumor Stem Cell-like Characteristics and Prostate Cancer Progression through miR-221-3p/CDKN1B/C-myc Axis

The recurrence, progression, and drug resistance of prostate cancer (PC) is closely related to the cancer stem cells (CSCs). Therefore, it is necessary to find the key regulators of prostate cancer stem cells (PCSCs). Here, we analyzed the results of a single-class logistic regression machine learning algorithm (OCLR) to identify the PCSC-associated lncRNA MBNL1-AS1. The effects of MBNL1-AS1 on the stemness of CSCs was assessed using qPCR, western blot and sphere-forming assays. The role of MBNL1-AS1 in mediating the proliferation and invasion of the PC cell lines was examined using Transwell, wounding-healing, CCK-8, EdU and animal assays. Dual-luciferase and ChIRP assays were used to examine the molecular mechanism of MBNL1-AS1 in PCSCs. MBNL1-AS1 was shown to be negatively correlated with stemness index (mRNAsi), and even prognosis, tumor progression, recurrence, and drug resistance in PC patients. The knockdown of MBNL1-AS1 significantly affected the stemness of the PC cells, and subsequently their invasive and proliferative abilities. Molecular mechanism studies suggested that MBNL1-AS1 regulates CDKN1B through competitive binding to miR-221-3p, which led to the inhibition of the Wnt signaling pathway to affect PCSCs. In conclusion, our study identified MBNL1-AS1 as a key regulator of PCSCs and examined its mechanism of action in the malignant progression of PC.

Physical and in silico immunopeptidomic profiling of a cancer antigen prostatic acid phosphatase reveals targets enabling TCR isolation

Tissue-specific antigens can serve as targets for adoptive T cell transfer-based cancer immunotherapy. Recognition of tumor by T cells is mediated by interaction between peptide-major histocompatibility complexes (pMHCs) and T cell receptors (TCRs). Revealing the identity of peptides bound to MHC is critical in discovering cognate TCRs and predicting potential toxicity. We performed multimodal immunopeptidomic analyses for human prostatic acid phosphatase (PAP), a well-recognized tissue antigen. Three physical methods, including mild acid elution, coimmunoprecipitation, and secreted MHC precipitation, were used to capture a thorough signature of PAP on HLA-A*02:01. Eleven PAP peptides that are potentially A*02:01-restricted were identified, including five predicted strong binders by NetMHCpan 4.0. Peripheral blood mononuclear cells (PBMCs) from more than 20 healthy donors were screened with the PAP peptides. Seven cognate TCRs were isolated which can recognize three distinct epitopes when expressed in PBMCs. One TCR shows reactivity toward cell lines expressing both full-length PAP and HLA-A*02:01. Our results show that a combined multimodal immunopeptidomic approach is productive in revealing target peptides and defining the cloned TCR sequences reactive with prostatic acid phosphatase epitopes.

A Mutated Prostatic Acid Phosphatase (PAP) Peptide-Based Vaccine Induces PAP-Specific CD8+ T Cells with Ex Vivo Cytotoxic Capacities in HHDII/DR1 Transgenic Mice

BACKGROUND

Current treatments for castrate (hormone)-resistant prostate cancer (CRPC) remain limited and are not curative, with a median survival from diagnosis of 23 months. The PAP-specific Sipuleucel-T vaccine, which was approved by the FDA in 2010, increases the Overall Survival (OS) by 4 months, but is extremely expensive. We have previously shown that a 15 amino accid (AA) PAP sequence-derived peptide could induce strong immune responses and delay the growth of murine TRAMP-C1 prostate tumors. We have now substituted one amino acid and elongated the sequence to include epitopes predicted to bind to several additional HLA haplotypes. Herein, we present the immunological properties of this 42mer-mutated PAP-derived sequence (MutPAP42mer).

METHODS

The presence of PAP-135-143 epitope-specific CD8⁺ T cells in the blood of patients with prostate cancer (PCa) was assessed by flow cytometry using Dextramer™ technology. HHDII/DR1 transgenic mice were immunized with mutated and non-mutated PAP-derived 42mer peptides in the presence of CAF^®09 or CpG ODN1826 (TLR-9 agonist) adjuvants. Vaccine-induced immune responses were measured by assessing the proportion and functionality of splenic PAP-specific T cells in vitro.

RESULTS

PAP-135-143 epitope-specific CD8⁺ T cells were detected in the blood of patients with PCa and stimulation of PBMCs from patients with PCa with mutPAP42mer enhanced their capacity to kill human LNCaP PCa target cells expressing PAP. The MutPAP42mer peptide was significantly more immunogenic in HHDII/DR1 mice than the wild type sequence, and immunogenicity was further enhanced when combined with the CAF^®09 adjuvant. The vaccine induced secretory (IFNγ and TNFα) and cytotoxic CD8⁺ T cells and effector memory splenic T cells.

CONCLUSIONS

The periphery of patients with PCa exhibits immune responsiveness to the MutPAP42mer peptide and immunization of mice induces/expands T cell-driven, wild-type PAP immunity, and therefore, has the potential to drive protective anti-tumor immunity in patients with PCa.

A Double-Edged Sword Role of Cytokines in Prostate Cancer Immunotherapy

Prostate cancer (PC) is one of the most common malignancies among men and is the second leading cause of cancer death. PC immunotherapy has taken relatively successful steps in recent years, and these treatments are still being developed and tested. Evidence suggests that immunotherapy using cytokines as essential mediators in the immune system may help treat cancer. It has been shown that cytokines play an important role in anti-tumor defense. On the other hand, other cytokines can also favor the tumor and suppress anti-tumor responses. Moreover, the dose of cytokine in cancer cytokine-based immunotherapy, as well as the side effects of high doses, can also affect the outcomes of treatment. Cytokines can also be determinative in the outcome of other immunotherapy methods used in PC. In this review, the role of cytokines in the pathogenesis of cancer and their impacts on the main types of immunotherapies in the treatment of PC are discussed.

Semen as a rich source of diagnostic biomarkers for prostate cancer: latest evidence and implications

Prostate cancer (PCa) is one of the most common cancers in men and the cause of numerous cancer deaths in the world. Nowadays, based on diagnostic criteria, prostate-specific antigen (PSA) evaluation and rectal examination are used to diagnose prostate-related malignancies. However, due to the different types of PCa, there are several doubts about the diagnostic value of PSA. On the other hand, semen is considered an appropriate source and contains various biomarkers in non-invasive diagnosing several autoimmune disorders and malignancies. Evidence suggests that analysis of semen biomarkers could be helpful in PCa diagnosis. Therefore, due to the invasiveness of most diagnostic methods in PCa, the use of semen as a biologic sample containing various biomarkers can lead to the emergence of novel and non-invasive diagnostic approaches. This review summarized recent studies on the use of various seminal biomarkers for diagnosis, prognosis and prediction of PCa.

Moving on From Sipuleucel-T: New Dendritic Cell Vaccine Strategies for Prostate Cancer

Tumors evade the immune system though a myriad of mechanisms. Using checkpoint inhibitors to help reprime T cells to recognize tumor has had great success in malignancies including melanoma, lung, and renal cell carcinoma. Many tumors including prostate cancer are resistant to such treatment. However, Sipuleucel-T, a dendritic cell (DC) based immunotherapy, improved overall survival (OS) in prostate cancer. Despite this initial success, further DC vaccines have failed to progress and there has been limited uptake of Sipuleucel-T in the clinic. We know in prostate cancer (PCa) that both the adaptive and the innate arms of the immune system contribute to the immunosuppressive environment. This is at least in part due to dysfunction of DC that play a crucial role in the initiation of an immune response. We also know that there is a paucity of DC in PCa, and that those there are immature, creating a tolerogenic environment. These attributes make PCa a good candidate for a DC based immunotherapy. Ultimately, the knowledge gained by much research into antigen processing and presentation needs to translate from bench to bedside. In this review we will analyze why newer vaccine strategies using monocyte derived DC (MoDC) have failed to deliver clinical benefit, particularly in PCa, and highlight the emerging antigen loading and presentation technologies such as nanoparticles, antibody-antigen conjugates and virus co-delivery systems that can be used to improve efficacy. Lastly, we will assess combination strategies that can help overcome the immunosuppressive microenvironment of PCa.

Immunization with a prostate cancer xenoantigen elicits a xenoantigen epitope-specific T-cell response

Vaccines encoding xenoantigens, “non-self” proteins that are highly homologous to their autologous counterparts, have been investigated as a means to increase immunogenicity and overcome tolerance to “self” antigens. We have previously shown that DNA vaccines encoding native prostatic acid phosphatase (PAP) were able to elicit PAP-specific T cells in both rats and humans, but required multiple immunization courses. In this study, we investigated in a preclinical model whether immunizations with a DNA vaccine encoding a xenoantigen could elicit a cross-reactive immune response to the native protein, potentially requiring fewer immunizations. Lewis rats were immunized with a DNA vaccine encoding human PAP and splenocytes from immunized rats were screened with a human peptide library containing overlapping, 15-mer PAP-derived peptides using T-cell proliferation and interferon γ (IFNγ) release as measures of the immune response. One dominant PAP-specific, RT1.A^l-restricted, epitope was identified. Direct immunization with the immunodominant peptide (HP_201–215) containing this epitope demonstrated that it included a naturally presented MHC Class I epitope recognized by CD8⁺ T cells in Lewis rats. However, no cross-reactive immune response was elicited to the corresponding rat peptide despite a difference of only three amino acids. Immunization with DNA vaccines encoding rat PAP (rPAP) in which this foreign dominant epitope was included as well as with DNA vaccines coding for a variant of the xenoantigen from which this epitope was deleted, did not elicit responses to the native antigen. Overall, these results indicate that the immunization with a xenoantigen-coding DNA vaccine can lead to an immune response which potentially favors foreign epitopes and hence limits any cross-reactive response to the native antigen.

Oncolytic Adenovirus Type 3 Coding for CD40L Facilitates Dendritic Cell Therapy of Prostate Cancer in Humanized Mice and Patient Samples

Dendritic cell (DC)-based vaccines have shown some degree of success for the treatment of prostate cancer (PC). However, the highly immunosuppressive tumor microenvironment leads to DC dysfunction, which has limited the effectiveness of these vaccines. We hypothesized that use of a fully serotype 3 oncolytic adenovirus (Ad3-hTERT-CMV-hCD40L; TILT-234) could stimulate DCs in the prostate tumor microenvironment by expressing CD40L. Activated DCs would then activate cytotoxic T cells against the tumor, resulting in therapeutic immune responses. Oncolytic cell killing due to cancer cell-specific virus replication adds to antitumor effects but also enhances the immunological effect by releasing tumor epitopes for sampling by DC, in the presence of danger signals. In this study, we evaluated the companion effect of Ad3-hTERT-CMV-hCD40L and DC-therapy in a humanized mouse model and PC histocultures. Treatment with Ad3-hTERT-CMV-hCD40L and DC resulted in enhanced antitumor responses in vivo. Treatment of established histocultures with Ad3-hTERT-CMV-hCD40L induced DC maturation and notable increase in proinflammatory cytokines. In conclusion, Ad3-hTERT-CMV-hCD40L is able to modulate an immunosuppressive prostate tumor microenvironment and improve the effectiveness of DC vaccination in PC models and patient histocultures, setting the stage for clinical translation.

Therapeutic Cancer Vaccination with Ex Vivo RNA-Transfected Dendritic Cells-An Update

Over the last two decades, dendritic cell (DC) vaccination has been studied extensively as active immunotherapy in cancer treatment and has been proven safe in all clinical trials both with respect to short and long-term side effects. For antigen-loading of dendritic cells (DCs) one method is to introduce mRNA coding for the desired antigens. To target the whole antigenic repertoire of a tumor, even the total tumor mRNA of a macrodissected biopsy sample can be used. To date, reports have been published on a total of 781 patients suffering from different tumor entities and HIV-infection, who have been treated with DCs loaded with mRNA. The majority of those were melanoma patients, followed by HIV-infected patients, but leukemias, brain tumors, prostate cancer, renal cell carcinomas, pancreatic cancers and several others have also been treated. Next to antigen-loading, mRNA-electroporation allows a purposeful manipulation of the DCs’ phenotype and function to enhance their immunogenicity. In this review, we intend to give a comprehensive summary of what has been published regarding clinical testing of ex vivo generated mRNA-transfected DCs, with respect to safety and risk/benefit evaluations, choice of tumor antigens and RNA-source, and the design of better DCs for vaccination by transfection of mRNA-encoded functional proteins.

Second-Generation Antiandrogens: From Discovery to Standard of Care in Castration Resistant Prostate Cancer

Prostate cancer is the most commonly diagnosed cancer affecting men in the United States. The prostate is a hormone-dependent gland in which androgen hormones testosterone and dihydrotestosterone bind to and activate the androgen receptor, initiating nuclear translocation of androgen receptor and a subsequent signaling cascade. Due to the androgen dependency of the prostate, androgen deprivation therapies have emerged as first line treatment for aggressive prostate cancer. Such therapies are effective until the point at which prostate cancer, through a variety of mechanisms including but not limited to generation of ligand-independent androgen receptor splice variants, or intratumoral androgen production, overcome hormone deprivation. These cancers are androgen ablation resistant, clinically termed castration resistant prostate cancer (CRPC) and remain incurable. First-generation antiandrogens established androgen receptor blockade as a therapeutic strategy, but these therapies do not completely block androgen receptor activity. Efficacy and potency have been improved by the development of second-generation antiandrogen therapies, which remain the standard of care for patients with CRPC. Four second-generation anti-androgens are currently approved by the Food and Drug Administration (FDA); abiraterone acetate, enzalutamide, and recently approved apalutamide and darolutamide. This review is intended to provide a thorough overview of FDA approved second-generation antiandrogen discovery, treatment application, strategies for combination therapy to overcome resistance, and an insight for the potential future approaches for therapeutic inhibition of androgen receptor.

Induced Pluripotent Stem Cell-Based Cancer Vaccines

Over a century ago, it was reported that immunization with embryonic/fetal tissue could lead to the rejection of transplanted tumors in animals. Subsequent studies demonstrated that vaccination of embryonic materials in animals induced cellular and humoral immunity against transplantable tumors and carcinogen-induced tumors. Therefore, it has been hypothesized that the shared antigens between tumors and embryonic/fetal tissues (oncofetal antigens) are the key to anti-tumor immune responses in these studies. However, early oncofetal antigen-based cancer vaccines usually utilize xenogeneic or allogeneic embryonic stem cells or tissues, making it difficult to tease apart the anti-tumor immunity elicited by the oncofetal antigens vs. graft-vs.-host responses. Recently, one oncofetal antigen-based cancer vaccine using autologous induced pluripotent stem cells (iPSCs) demonstrated marked prophylactic and therapeutic potential, suggesting critical roles of oncofetal antigens in inducing anti-tumor immunity. In this review, we present an overview of recent studies in the field of oncofetal antigen-based cancer vaccines, including single peptide-based cancer vaccines, embryonic stem cell (ESC)- and iPSC-based whole-cell vaccines, and provide insights on future directions.

Strategies for developing and optimizing cancer vaccines

With the spotlight on cancer immunotherapy and the expanding use of immune checkpoint inhibitors, strategies to improve the response rate and duration of current cancer immunotherapeutics are highly sought. In that sense, investigators around the globe have been putting spurs on the development of effective cancer vaccines in humans after decades of efforts that led to limited clinical success. In more than three decades of research in pursuit of targeted and personalized immunotherapy, several platforms have been incorporated into the list of cancer vaccines from live viral or bacterial agents harboring antigens to synthetic peptides with the hope of stronger and durable immune responses that will tackle cancers better. Unlike adoptive cell therapy, cancer vaccines can take advantage of using a patient's entire immune system that can include more than engineered receptors or ligands in developing antigen-specific responses. Advances in molecular technology also secured the use of genetically modified genes or proteins of interest to enhance the chance of stronger immune responses. The formulation of vaccines to increase chances of immune recognition such as nanoparticles for peptide delivery is another area of great interest. Studies indicate that cancer vaccines alone may elicit tumor-specific cellular or humoral responses in immunologic assays and even regression or shrinkage of the cancer in select trials, but novel strategies, especially in combination with other cancer therapies, are under study and are likely to be critical to achieve and optimize reliable objective responses and survival benefit. In this review, cancer vaccine platforms with different approaches to deliver tumor antigens and boost immunity are discussed with the intention of summarizing what we know and what we need to improve in the clinical trial setting.

Immunological-based approaches for cancer therapy

The immunologic landscape of tumors has been continuously unveiled, providing a new look at the interactions between cancer cells and the immune system. Emerging tumor cells are constantly eliminated by the immune system, but some cells establish a long-term equilibrium phase leading to tumor immunoediting and, eventually, evasion. During this process, tumor cells tend to acquire more mutations. Bearing a high mutation burden leads to a greater number of neoantigens with the potential to initiate an immune response. Although many tumors evoke an immune response, tumor clearance by the immune system does not occur due to a suppressive tumor microenvironment. The mechanisms by which tumors achieve the ability to evade immunologic control vary. Understanding these differences is crucial for the improvement and application of new immune-based therapies. Much effort has been placed in developing in silico algorithms to predict tumor immunogenicity and to characterize the microenvironment via high-throughput sequencing and gene expression techniques. Each sequencing source, transcriptomics, and genomics yields a distinct level of data, helping to elucidate the tumor-based immune responses and guiding the fine-tuning of current and upcoming immune-based therapies. In this review, we explore some of the immunological concepts behind the new immunotherapies and the bioinformatic tools to study the immunological aspects of tumors, focusing on neoantigen determination and microenvironment deconvolution. We further discuss the immune-based therapies already in clinical use, those underway for future clinical application, the next steps in immunotherapy, and how the characterization of the tumor immune contexture can impact therapies aiming to promote or unleash immune-based tumor elimination.

Post-operative unadjuvanted therapeutic xenovaccination with chicken whole embryo vaccine suppresses distant micrometastases and prolongs survival in a murine Lewis lung carcinoma model

Immunotherapy in the form of anticancer vaccination relies on the mobilization of the patient's immune system against specific cancer antigens. Instead of focusing on an autologous cell lysate, which is not always available in clinical practice, the present study investigates vaccines utilizing xenogeneic foetal tissue that are rich in oncofoetal antigens. Lewis lung carcinoma (LLC)-challenged C57BL/6 mice were treated with either a xenogeneic vaccine made from chicken whole embryo, or a xenogeneic vaccine made from rat embryonic brain tissue, supplemented with a Bacillus subtilis protein fraction as an adjuvant. Median and overall survival, size of metastatic foci in lung tissue and levels of circulating CD8a⁺ T cells were evaluated and compared with untreated control mice. Following primary tumour removal, a course of three subcutaneous vaccinations with xenogeneic chicken embryo vaccine led to significant increase in overall survival rate (100% after 70 days of follow-up vs. 40% in untreated control mice), significant increase in circulating CD8a⁺ T cells (18.18 vs. 12.6% in untreated control mice), and a significant decrease in the area and incidence of metastasis foci. The xenogeneic rat brain tissue-based vaccine did not improve any of the investigated parameters, despite promising reports in other models. We hypothesize that the proper selection of antigen source (tissue) can constitute an effective immunotherapeutic product.

Development of Autologous C5 Vaccine Nanoparticles to Reduce Intravascular Hemolysis in Vivo

The complement system is emerging as a new target for treating many diseases. For example, Eculizumab, a humanized monoclonal antibody against complement component 5 (C5), has been approved for paroxysmal nocturnal hemoglobinuria (PNH) in which patient erythrocytes are lysed by complement. In this study, we developed vaccines to elicit autologous anti-C5 antibody production in mice for complement inhibition. Immunization of mice with a conservative C5 xenoprotein raised high titers of IgG's against the xenogenous C5, but these antibodies did not reduce C5 activity in the blood. In contrast, an autologous mouse C5 vaccine containing multiple predicted epitopes together with a tolerance-breaking peptide was found to induce anti-C5 autoantibody production in vivo, resulting in decreased hemolytic activity in the blood. We further validated a peptide epitope within this C5 vaccine and created recombinant virus-like particles (VLPs) displaying this epitope fused with the tolerance breaking peptide. Immunizing mice with these novel nanoparticles elicited strong humoral responses against recombinant mouse C5, reduced hemolytic activity, and protected the mice from complement-mediated intravascular hemolysis in a model of PNH. This proof-of-concept study demonstrated that autologous C5-based vaccines could be an effective alternative or supplement for treating complement-mediated diseases such as PNH.

Implementation of Nanoparticles in Cancer Therapy

Cancer is a wide group of diseases and generally characterized by uncontrolled proliferation of cells whose metabolic activities are disrupted. Conventionally, chemotherapy, radiotherapy, and surgery are used in the treatment of cancer. However, in theory, even a single cancer cell may trigger recurrence. Therefore, these treatments cannot provide high survival rate for deadly types. Identification of alternative methods in treatment of cancers is inevitable because of adverse effects of conventional methods. In the last few decades, nanotechnology developed by scientists working in different disciplines—physics, chemistry, and biology—offers great opportunities. It is providing elimination of both circulating tumor cells and solid cancer cells by targeting cancer cells. In this chapter, inadequate parts of conventional treatment methods, nanoparticle types used in new treatment methods of cancer, and targeting methods of nanoparticles are summarized; furthermore, recommendations of future are provided.

Tn-MUC1 DC Vaccination of Rhesus Macaques and a Phase I/II Trial in Patients with Nonmetastatic Castrate-Resistant Prostate Cancer

MUC1 is a glycoprotein expressed on the apical surface of ductal epithelial cells. Malignant transformation results in loss of polarization and overexpression of hypoglycosylated MUC1 carrying truncated carbohydrates known as T or Tn tumor antigens. Tumor MUC1 bearing Tn carbohydrates (Tn-MUC1) represent a potential target for immunotherapy. We evaluated the Tn-MUC1 glycopeptide in a human phase I/II clinical trial for safety that followed a preclinical study of different glycosylation forms of MUC1 in rhesus macaques, whose MUC1 is highly homologous to human MUC1. Either unglycosylated rhesus macaque MUC1 peptide (rmMUC1) or Tn-rmMUC1 glycopeptide was mixed with an adjuvant or loaded on autologous dendritic cells (DC), and responses were compared. Unglycosylated rmMUC1 peptide induced negligible humoral or cellular responses compared with the Tn-rmMUC1 glycopeptide. Tn-rmMUC1 loaded on DCs induced the highest anti-rmMUC1 T-cell responses and no clinical toxicity. In the phase I/II clinical study, 17 patients with nonmetastatic castrate-resistant prostate cancer (nmCRPC) were tested with a Tn-MUC1 glycopeptide-DC vaccine. Patients were treated with multiple intradermal and intranodal doses of autologous DCs, which were loaded with the Tn-MUC1 glycopeptide (and KLH as a positive control for immune reactivity). PSA doubling time (PSADT) improved significantly in 11 of 16 evaluable patients (P = 0.037). Immune response analyses detected significant Tn-MUC1-specific CD4⁺ and/or CD8⁺ T-cell intracellular cytokine responses in 5 out of 7 patients evaluated. In conclusion, vaccination with Tn-MUC1-loaded DCs in nmCRPC patients appears to be safe, able to induce significant T-cell responses, and have biological activity as measured by the increase in PSADT following vaccination. Cancer Immunol Res; 4(10); 881-92. ©2016 AACR.

Optimized tumor cryptic peptides: the basis for universal neo-antigen-like tumor vaccines

The very impressive clinical results recently obtained in cancer patients treated with immune response checkpoint inhibitors boosted the interest in immunotherapy as a therapeutic choice in cancer treatment. However, these inhibitors require a pre-existing tumor specific immune response and the presence of tumor infiltrating T cells to be efficient. This immune response can be triggered by cancer vaccines. One of the main issues in tumor vaccination is the choice of the right antigen to target. All vaccines tested to date targeted tumor associated antigens (TAA) that are self-antigens and failed to show a clinical efficacy because of the immune self-tolerance to TAA. A new class of tumor antigens has recently been described, the neo-antigens that are created by point mutations of tumor expressing proteins and are recognized by the immune system as non-self. Neo-antigens exhibit two main properties: they are not involved in the immune self-tolerance process and are immunogenic. However, the majority of the neo-antigens are patient specific and their use as cancer vaccines requires their previous identification in each patient individualy that can be done only in highly specialized research centers. It is therefore evident that neo-antigens cannot be used for patient vaccination worldwide. This raises the question of whether we can find neo-antigen like vaccines, which would not be patient specific. In this review we show that optimized cryptic peptides from TAA are neo-antigen like peptides. Optimized cryptic peptides are recognized by the immune system as non-self because they target self-cryptic peptides that escape self-tolerance; in addition they are strongly immunogenic because their sequence is modified in order to enhance their affinity for the HLA molecule. The first vaccine based on the optimized cryptic peptide approach, Vx-001, which targets the widely expressed tumor antigen telomerase reverse transcriptase (TERT), has completed a large phase I clinical study and is currently being tested in a randomized phase II trial in non-small cell lung cancer (NSCLC) patients.

Induced Pluripotent Stem Cell as a New Source for Cancer Immunotherapy

The immune system consists of cells, proteins, and other molecules that beside each other have a protective function for the host against foreign pathogens. One of the most essential features of the immune system is distinguishability between self- and non-self-cells. This function has an important role in limiting development and progression of cancer cells. In this case, the immune system can detect tumor cell as a foreign pathogen; so, it can be effective in elimination of tumors in their early phases of development. This ability of the immune system resulted in the development of a novel therapeutic field for cancer treatment using host immune components which is called cancer immunotherapy. The main purpose of cancer immunotherapy is stimulation of a strong immune response against the tumor cells that can result from expressing either the immune activator cytokines in the tumor area or gene-modified immune cells. Because of the problems of culturing and manipulating immune cells ex vivo, in recent years, embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) have been used as new sources for generation of modified immune stimulatory cells. In this paper, we reviewed some of the progressions in iPSC technology for cancer immunotherapy.

Treatment with cyclophosphamide supported by various dendritic cell-based vaccines induces diversification in CD4⁺ T cell response against MC38 colon carcinoma

The present study shows that an application of cyclophosphamide (CY) supported by dendritic cell (DC)-based vaccines affected differentiation of the activity of CD4⁺ T cell subpopulations accompanied by an alteration in CD8⁺ cell number. Vaccines were composed of bone marrow-derived DCs activated with tumor cell lysate (BM-DC/TAg^TNF-α) and/or genetically modified DCs of JAWS II line (JAWS II/ Neo or JAWS II/IL-2 cells). Compared to untreated or CY-treated mice, the combined treatment of MC38 colon carcinoma-bearing mice resulted in significant tumor growth inhibition associated with an increase in influx of CD4⁺ and CD8⁺ T cells into tumor tissue. Whereas, the division of these cell population in spleen was not observed. Depending on the nature of DC-based vaccines and number of their applications, both tumor infiltrating cells and spleen cells were able to produce various amount of IFN-γ, IL-4 and IL-10 after mitogenic ex vivo stimulation. The administration of CY followed by BM-DC/TAg^TNF-α and genetically modified JAWS II cells, increased the percentage of CD4⁺T-bet⁺ and CD4⁺GATA3⁺ cells and decreased the percentage of CD4⁺RORγt⁺ and CD4⁺FoxP3⁺ lymphocytes. However, the most intensive response against tumor was noted after the ternary treatment with CY + BM-DC/TAg^TNF-α + JAWS II/IL-2 cells. Thus, the administration of various DC-based vaccines was responsible for generation of the diversified antitumor response. These findings demonstrate that the determination of the size of particular CD4⁺ T cell subpopulations may become a prognostic factor and be the basis for future development of anticancer therapy.

Oncolytic virotherapy using herpes simplex virus: how far have we come?

Oncolytic virotherapy exploits the properties of human viruses to naturally cytolysis of cancer cells. The human pathogen herpes simplex virus (HSV) has proven particularly amenable for use in oncolytic virotherapy. The relative safety of HSV coupled with extensive knowledge on how HSV interacts with the host has provided a platform for manipulating HSV to enhance the targeting and killing of human cancer cells. This has culminated in the approval of talimogene laherparepvec for the treatment of melanoma. This review focuses on the development of HSV as an oncolytic virus and where the field is likely to head in the future.

DNA vaccination for prostate cancer: key concepts and considerations

While locally confined prostate cancer is associated with a low five year mortality rate, advanced or metastatic disease remains a major challenge for healthcare professionals to treat and is usually terminal. As such, there is a need for the development of new, efficacious therapies for prostate cancer. Immunotherapy represents a promising approach where the host's immune system is harnessed to mount an anti-tumour effect, and the licensing of the first prostate cancer specific immunotherapy in 2010 has opened the door for other immunotherapies to gain regulatory approval. Among these strategies DNA vaccines are an attractive option in terms of their ability to elicit a highly specific, potent and wide-sweeping immune response. Several DNA vaccines have been tested for prostate cancer and while they have demonstrated a good safety profile they have faced problems with low efficacy and immunogenicity compared to other immunotherapeutic approaches. This review focuses on the positive aspects of DNA vaccines for prostate cancer that have been assessed in preclinical and clinical trials thus far and examines the key considerations that must be employed to improve the efficacy and immunogenicity of these vaccines.

A vaccine strategy with multiple prostatic acid phosphatase-fused cytokines for prostate cancer treatment

Immunotherapy is one of the attractive treatment strategies for advanced prostate cancer. The US Food and Drug Administration (FDA) previously approved the therapeutic vaccine, sipuleucel-T, which is composed of autologous antigen-presenting cells cultured with a fusion protein [prostatic acid phosphatase (PAP) and granulocyte-macrophage colony-stimulating factor (GMCSF)]. Although sipuleucel-T has been shown to prolong the median survival of patients for 4.1 months, more robust therapeutic effects may be expected by modifying the vaccination protocol. In the present study, we aimed to develop and validate a novel vaccination strategy using multiple PAP-fused cytokines for prostate cancer treatment. Using a super gene expression (SGE) system that we previously established to amplify the production of a recombinant protein, significant amounts of PAP-fused cytokines [human GMCSF, interleukin-2 (IL2), IL4, IL7 and mouse GMCSF and IL4] were obtained. We examined the activity of the fusion proteins in vitro to validate their cytokine functions. A significant upregulation of dendritic cell differentiation from monocytes was achieved by PAP-GMCSF when used with the other PAP-fused cytokines. The PAP-fused human IL2 significantly increased the proliferation of lymphocytes, as determined by flow cytometry. We also investigated the in vivo therapeutic effects of multiple PAP-fused cytokines in a mouse prostate cancer model bearing prostate-specific antigen (PSA)- and PAP-expressing tumors. The simultaneous intraperitoneal administration of PAP-GMCSF, -IL2, -IL4 and -IL7 significantly prevented tumor induction and inhibited the tumor growth in the PAP-expressing tumors, yet not in the PSA-expressing tumors. The in vivo therapeutic effects with the multiple PAP-fused cytokines were superior to the effects of PAP-GMCSF alone. We thus demonstrated the advantages of the combined use of multiple PAP-fused cytokines including PAP-GMCSF, and propose a promising prostatic antigen-vaccination strategy to enhance the therapeutic effects.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Activated lymphocyte recruitment into the tumor microenvironment following preoperative sipuleucel-T for localized prostate cancer

Background

Sipuleucel-T is a US Food and Drug Administration–approved immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Its mechanism of action is not fully understood. This prospective trial evaluated the direct immune effects of systemically administered sipuleucel-T on prostatic cancer tissue in the preoperative setting.

Methods

Patients with untreated localized prostate cancer were treated on an open-label Phase II study of sipuleucel-T prior to planned radical prostatectomy (RP). Immune infiltrates in RP specimens (posttreatment) and in paired pretreatment biopsies were evaluated by immunohistochemistry (IHC). Correlations between circulating immune response and IHC were assessed using Spearman rank order.

Results

Of the 42 enrolled patients, 37 were evaluable. Adverse events were primarily transient, mild-to-moderate and infusion related. Patients developed T cell proliferation and interferon-γ responses detectable in the blood following treatment. Furthermore, a greater-than-three-fold increase in infiltrating CD3⁺, CD4⁺ FOXP3^-, and CD8⁺ T cells was observed in the RP tissues compared with the pretreatment biopsy (binomial proportions: all P < .001). This level of T cell infiltration was observed at the tumor interface, and was not seen in a control group consisting of 12 concurrent patients who did not receive any neoadjuvant treatment prior to RP. The majority of infiltrating T cells were PD-1⁺ and Ki-67⁺, consistent with activated T cells. Importantly, the magnitude of the circulating immune response did not directly correlate with T cell infiltration within the prostate based upon Spearman’s rank order correlation.

Conclusions

This study is the first to demonstrate a local immune effect from the administration of sipuleucel-T. Neoadjuvant sipuleucel-T elicits both a systemic antigen-specific T cell response and the recruitment of activated effector T cells into the prostate tumor microenvironment.

A transient increase in eosinophils is associated with prolonged survival in men with metastatic castration-resistant prostate cancer who receive sipuleucel-T

Sipuleucel-T is an autologous cellular immunotherapy used to treat asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Traditional short-term indicators of clinical response commonly used with chemotherapy have not correlated with survival in patients treated with sipuleucel-T. This retrospective study aimed to evaluate laboratory parameters as possible early biomarkers associated with clinical benefit following sipuleucel-T treatment. Patients treated with sipuleucel-T from three randomized, controlled, phase III clinical trials in mCRPC were considered: IMPACT (NCT00065442; n = 512), D9901 (NCT00005947; n = 127), and D9902A (NCT01133704; n = 98). Patients from these trials were included in this study if their samples were analyzed by the central laboratory and if data were available from baseline and ≥ 1 posttreatment time point (n = 377). We found that sipuleucel-T treatment was associated with a transient increase in serum eosinophil count at week 6 that resolved by week 14 in 28% of patients (105 of 377). This eosinophil increase correlated with induced immune response, longer prostate cancer-specific survival [HR, 0.713; 95% confidence interval (CI), 0.525-0.970; P = 0.031], and a trend in overall survival (HR, 0.753; 95% CI, 0.563-1.008; P = 0.057). Median serum globulin protein levels also increased transiently, which was associated with antigen-specific antibody responses; however, this finding did not correlate with longer survival. We conclude that transient increases in eosinophils at week 6 may be a useful, objective, short-term indicator of global immune activation and survival benefit with sipuleucel-T in patients with mCRPC. This observation warrants prospective evaluation in future clinical trials.

Xenogeneic therapeutic cancer vaccines as breakers of immune tolerance for clinical application: to use or not to use?

Accumulation of firm evidence that clinically apparent cancer develops only when malignant cells manage to escape immunosurveillance led to the introduction of tumor immunotherapy strategies aiming to reprogramm the cancer-dysbalanced antitumor immunity and restore its capacity to control tumor growth. There are several immunotherapeutical strategies, among which specific active immunotherapy or therapeutic cancer vaccination is one of the most promising. It targets dendritic cells (DCs) which have a unique ability of inducing naive and central memory T cell-mediated immune response in the most efficient manner. DCs can be therapeutically targeted either in vivo/in situ or by ex vivo manipulations followed by their re-injection back into the same patient. The majority of current DC targeting strategies are based on autologous or allogeneic tumor-associated antigens (TAAs) which possess various degrees of inherent tolerogenic potential. Therefore still limited efficacy of various tumor immunotherapy approaches may be attributed, among various other mechanisms, to the insufficient immunogenicity of self-protein-derived TAAs. Based on such an idea, the use of homologous xenogeneic antigens, derived from different species was suggested to overcome the natural immune tolerance to self TAAs. Xenoantigens are supposed to differ sufficiently from self antigens to a degree that renders them immunogenic, but at the same time preserves an optimal homology range with self proteins still allowing xenoantigens to induce cross-reactive T cells. Here we discuss the concept of xenogeneic vaccination, describe the cons and pros of autologous/allogeneic versus xenogeneic therapeutic cancer vaccines, present the results of various pre-clinical and several clinical studies and highlight the future perspectives of integrating xenovaccination into rapidly developing tumor immunotherapy regimens.

Immunotherapy for prostate cancer: lessons from responses to tumor-associated antigens

Prostate cancer (PCa) is the most common cancer in men and the second most common cause of cancer-related death in men. In recent years, novel therapeutic options for PCa have been developed and studied extensively in clinical trials. Sipuleucel-T is the first cell-based immunotherapeutic vaccine for treatment of cancer. This vaccine consists of autologous mononuclear cells stimulated and loaded with an immunostimulatory fusion protein containing the prostate tumor antigen prostate acid posphatase. The choice of antigen might be key for the efficiency of cell-based immunotherapy. Depending on the treatment strategy, target antigens should be immunogenic, abundantly expressed by tumor cells, and preferably functionally important for the tumor to prevent loss of antigen expression. Autoimmune responses have been reported against several antigens expressed in the prostate, indicating that PCa is a suitable target for immunotherapy. In this review, we will discuss PCa antigens that exhibit immunogenic features and/or have been targeted in immunotherapeutic settings with promising results, and we highlight the hurdles and opportunities for cancer immunotherapy.

DNA vaccines encoding altered peptide ligands for SSX2 enhance epitope-specific CD8+ T-cell immune responses

Plasmid DNA serves as a simple and easily modifiable form of antigen delivery for vaccines. The USDA approval of DNA vaccines for several non-human diseases underscores the potential of this type of antigen delivery method as a cost-effective approach for the treatment or prevention of human diseases, including cancer. However, while DNA vaccines have demonstrated safety and immunological effect in early phase clinical trials, they have not consistently elicited robust anti-tumor responses. Hence many recent efforts have sought to increase the immunological efficacy of DNA vaccines, and we have specifically evaluated several target antigens encoded by DNA vaccine as treatments for human prostate cancer. In particular, we have focused on SSX2 as one potential target antigen, given its frequent expression in metastatic prostate cancer. We have previously identified two peptides, p41-49 and p103-111, as HLA-A2-restricted SSX2-specific epitopes. In the present study we sought to determine whether the efficacy of a DNA vaccine could be enhanced by an altered peptide ligand (APL) strategy wherein modifications were made to anchor residues of these epitopes to enhance or ablate their binding to HLA-A2. A DNA vaccine encoding APL modified to increase epitope binding elicited robust peptide-specific CD8+ T cells producing Th1 cytokines specific for each epitope. Ablation of one epitope in a DNA vaccine did not enhance immune responses to the other epitope. These results demonstrate that APL encoded by a DNA vaccine can be used to elicit increased numbers of antigen-specific T cells specific for multiple epitopes simultaneously, and suggest this could be a general approach to improve the immunogenicity of DNA vaccines encoding tumor antigens.

Chimeric DNA Vaccines: An Effective Way to Overcome Immune Tolerance

The fact that cancer immunotherapy is considered to be a safe and successful weapon for use in combination with surgery, radiation, and chemotherapy treatments means that it has recently been chosen as Breakthrough of the Year 2013 by Science editors. Anticancer vaccines have been extensively tested, in this field, both in preclinical cancer models and in the clinic. However, tumor-associated antigens (TAAs) are often self-tolerated molecules and cancer patients suffer from strong immunosuppressive effects, meaning that the triggering of an effective anti-tumor immune response is difficult. One possible means to overcome immunological tolerance to self-TAAs is of course the use of vaccines that code for xenogeneic proteins. However, a low-affinity antibody response against the self-homologous protein expressed by cancer cells is generally induced by xenovaccination. This issue becomes extremely limiting when working with tumors in which the contribution of the humoral rather than the cellular immune response is required if tumor growth is to be hampered. A possible way to avoid this problem is to use hybrid vaccines which code for chimeric proteins that include both homologous and xenogeneic moieties. In fact, a superior protective anti-tumor immune response against ErbB2⁺ transplantable and autochthonous mammary tumors was observed over plasmids that coded for the fully rat or fully human proteins when hybrid plasmids that coded for chimeric rat/human ErbB2 protein were tested in ErbB2 transgenic mice. In principle, these findings may become the basis for a new rational means of designing effective vaccines against TAAs.

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.

Immunotherapy and immune evasion in prostate cancer

Metastatic prostate cancer remains to this day a terminal disease. Prostatectomy and radiotherapy are effective for organ-confined diseases, but treatment for locally advanced and metastatic cancer remains challenging. Although advanced prostate cancers treated with androgen deprivation therapy achieves debulking of disease, responses are transient with subsequent development of castration-resistant and metastatic disease. Since prostate cancer is typically a slowly progressing disease, use of immune-based therapies offers an advantage to target advanced tumors and to induce antitumor immunity. This review will discuss the clinical merits of various vaccines and immunotherapies in castrate resistant prostate cancer and challenges to this evolving field of immune-based therapies.

Xenogeneic human p53 DNA vaccination by electroporation breaks immune tolerance to control murine tumors expressing mouse p53

The pivotal role of p53 as a tumor suppressor protein is illustrated by the fact that this protein is found mutated in more than 50% of human cancers. In most cases, mutations in p53 greatly increase the otherwise short half-life of this protein in normal tissue and cause it to accumulate in the cytoplasm of tumors. The overexpression of mutated p53 in tumor cells makes p53 a potentially desirable target for the development of cancer immunotherapy. However, p53 protein represents an endogenous tumor-associated antigen (TAA). Immunization against a self-antigen is challenging because an antigen-specific immune response likely generates only low affinity antigen-specific CD8⁺ T-cells. This represents a bottleneck of tumor immunotherapy when targeting endogenous TAAs expressed by tumors. The objective of the current study is to develop a safe cancer immunotherapy using a naked DNA vaccine. The vaccine employs a xenogeneic p53 gene to break immune tolerance resulting in a potent therapeutic antitumor effect against tumors expressing mutated p53. Our study assessed the therapeutic antitumor effect after immunization with DNA encoding human p53 (hp53) or mouse p53 (mp53). Mice immunized with xenogeneic full length hp53 DNA plasmid intramuscularly followed by electroporation were protected against challenge with murine colon cancer MC38 while those immunized with mp53 DNA were not. In a therapeutic model, established MC38 tumors were also well controlled by treatment with hp53 DNA therapy in tumor bearing mice compared to mp53 DNA. Mice vaccinated with hp53 DNA plasmid also exhibited an increase in mp53-specific CD8⁺ T-cell precursors compared to vaccination with mp53 DNA. Antibody depletion experiments also demonstrated that CD8⁺ T-cells play crucial roles in the antitumor effects. This study showed intramuscular vaccination with xenogeneic p53 DNA vaccine followed by electroporation is capable of inducing potent antitumor effects against tumors expressing mutated p53 through CD8⁺ T cells.

Identification of prostatic acid phosphatase (PAP) specific HLA-DR1-restricted T-cell epitopes

BACKGROUND

Prostatic acid phosphatase (PAP) is a prostate cancer tumor antigen and is an immunological target in several active immunotherapy clinical trials for the treatment of prostate cancer. We and others have demonstrated that PAP-specific T-cell responses can be elicited and augmented following antigen-specific immunization in both humans and animal models. We have previously reported that prostate cancer patients immunized with a DNA vaccine encoding PAP (pTVG-HP) developed both CD4+ and CD8+ T-cell responses. PAP-specific, CD4+ T-cell proliferative responses were generated in three out of four HLA-DRB1*0101 patients suggesting the possibility that DR1-restricted epitopes exist.

METHODS

To identify PAP-specific HLA-DRB1*0101 restricted epitopes, we immunized HLA-A2.01/HLA-DRB1*0101 (A2/DR1) transgenic mice with the pTVG-HP DNA vaccine. To map DRB1*0101-restricted epitopes, splenocytes from immunized mice were screened against a library of overlapping 15-residue, PAP-derived peptides using an IFNγ ELISPOT assay.

RESULTS

We identified four HLA-DRB1*0101 epitopes for PAP in A2/DR1 mice (PAP(161-175) , PAP(181-195) , PAP(191-205) , and PAP (351-365) ). T cells specific for one epitope (PAP(181-195) ) were found to be augmented after immunization in a HLA-DRB1*0101+ prostate cancer patient.

CONCLUSIONS

The identification of MHC class II epitopes may provide tools to directly monitor immune responses after vaccination and may be important for the design of future prostate cancer vaccines.

A phase 1 study of a vaccine targeting preferentially expressed antigen in melanoma and prostate-specific membrane antigen in patients with advanced solid tumors

Preferentially expressed antigen in melanoma (PRAME) and prostate-specific membrane antigen (PSMA) are tumor-associated antigens implicated in cellular differentiation, genetic stability, and angiogenesis. MKC1106-PP is an immunotherapeutic regimen cotargeting PRAME and PSMA, comprised of a recombinant plasmid (pPRA-PSM encoding fragments derived from both antigens) and 2 peptides (E-PRA and E-PSM derived from PRAME and PSMA, respectively). This multicenter study evaluated MKC1106-PP with a fixed plasmid dose and 2 different peptide doses, administered by intralymph node injection in a prime-boost sequence in human leukocyte antigen-A*0201 and tumor-antigen-positive patients with progressing metastatic solid tumors who had failed standard therapy. Immune monitoring was done by tetramer and enzymatic-linked immune spot analysis. The treatment was well tolerated, with no significant differences in safety, immune response, and clinical outcome relative to peptide doses. Fifteen of 24 evaluable patients showed an immune response, as defined by the expansion of PRAME-specific or PSMA-specific T cells in the blood. There were no partial or complete responses by the Response Evaluation Criteria in Solid Tumors. Seven patients showed stable disease (SD) for 6 months or longer, or prostate specific antigen decline: 4 of 10 with prostate carcinoma, 2 of 2 with renal clear cell carcinoma, and 1 of 10 with metastatic melanoma. In addition, there was an association between the induction and persistence of antigen-specific T cells in blood above baseline levels and disease control, defined as SD for 6 months or longer. These results support further development of MKC1106-PP in specific clinical indications.

Immunotherapy for prostate cancer: biology and therapeutic approaches

Although prostate cancer was not historically considered to be a particularly immune-responsive cancer, recent clinical trials have demonstrated that immunotherapy for prostate cancer can lead to improvements in overall survival (OS). These studies include randomized controlled trials with sipuleucel-T and another with PROSTVAC-VF, both of which rely on stimulating the immune system to target prostate proteins. This review discusses the most promising developments over the past year in immune-based therapy for prostate cancer and the opportunities that lie ahead. Recent randomized immunotherapy trials in prostate cancer have demonstrated improvements in OS but without the concomitant improvements in progression-free survival. This uncoupling of survival from clinical response poses challenges to clinical management, because conventional measures of objective response cannot be used to identify patients benefiting from treatment. There is a significant need to identify immunologic or clinical surrogates for survival so that clinical benefit can be assessed in a timely manner. Immunotherapy is now an established treatment approach for prostate cancer, with multiple clinical trials demonstrating improvements in OS. Significant challenges to this modality remain, including determining best clinical setting for immunotherapy, identifying patients who benefit, and defining relevant clinical and immunologic end points. Nevertheless, the broader availability of novel immunotherapies will provide opportunities not only to target different components of the immune system but also to combine immunotherapies with other treatments for improved clinical efficacy.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.