Safety and immunological efficacy of a DNA vaccine encoding prostatic acid phosphatase in patients with stage D0 prostate cancer

From genetic code to global health: the impact of nucleic acid vaccines on disease prevention and treatment

Vaccinology has revolutionized modern medicine, delivering groundbreaking solutions to prevent and control infectious diseases while pioneering innovative strategies to tackle non-infectious challenges, including cancer. Traditional vaccines faced inherent limitations, driving the evolution of next-generation vaccines such as subunit vaccines, peptide-based vaccines, and nucleic acid-based platforms. Among these, nucleic acid-based vaccines, including DNA and mRNA technologies, represent a major innovation. Pioneering studies in the 1990s demonstrated their ability to elicit immune responses by encoding specific antigens. Recent advancements in delivery systems and molecular engineering have overcome initial challenges, enabling their rapid development and clinical success. This review explores nucleic acid-based vaccines, including chemically modified variants, by examining their mechanisms, structural features, and therapeutic potential, while underscoring their pivotal role in modern immunization strategies and expanding applications across contemporary medicine.

Nanoparticle-mediated enhancement of DNA Vaccines: Revolutionizing immunization strategies

DNA vaccines are a novel form of vaccination that aims to harness genetic material to produce targeted immune responses. Nevertheless, their therapeutic application is hampered by low transfection efficacy, immunogenicity, and instability. Nanoparticle (NP) - based delivery systems are beneficial in enhancing DNA stability, increasing DNA uptake by antigen-presenting cells (APCs), and controlling antigen release. Some key progress includes the polymeric, lipid-based, and hybrid NPs and biocompatible carriers with inherent adjuvant effects. These systems have helped to enhance the antigen cross-presentation and T-cell activation significantly. In addition, biocompatible hybrid nanocarriers, antigen cross-presentation strategies, and next-generation sequencing (NGS) technologies are speeding up the identification of new antigens, while AI and machine learning are facilitating the development of efficient delivery systems. This review aims to assess how NPs have contributed to improving the effectiveness of DNA vaccines for treating diseases, cancer, and emerging diseases, as well as advancing the next generation of DNA vaccines.

Plant-derived recombinant macromolecular PAP-IgG Fc as a novel prostate cancer vaccine candidate eliciting robust immune responses

Prostatic acid phosphatase (PAP) is a specific protein that is highly expressed in prostate cancer. In this study, we constructed two recombinant PAP fusion genes: PAP fused to the immunoglobulin G (IgG) Fc fragment (designated PAP-Fc) and PAP-Fc fused to the endoplasmic reticulum retention sequence KDEL (designated PAP-FcK). Transgenic Nicotiana tabacum plants expressing these recombinant macromolecular proteins (MPs) were generated using Agrobacterium-mediated transformation, and the presence of both genes was confirmed through genomic PCR. Western blot analysis validated the expression of PAP-Fc and PAP-FcK MPs, which were successfully purified via protein A affinity chromatography. Size-exclusion high-performance liquid chromatography revealed dimeric peaks for PAP-Fc (PAP-FcP) and PAP-FcK (PAP-FcKP). Bio-transmission electron microscopy demonstrated 'Y'-shaped protein particles resembling antibody structures. Moreover, PAP-FcP and PAP-FcKP exhibited a high association rate with human FcγR and FcRn. Vaccination of mice with both PAP-FcP and PAP-FcKP resulted in increased total IgG against PAP and enhanced activation of CD4+ T cells, comparable to mice immunized with PAP, which served as a positive control. These findings indicate that both plant-derived MPs can effectively induce adaptive immunity, positioning them as promising candidates for prostate cancer vaccines. Overall, plants expressing PAP-Fc and PAP-FcK represent a viable production system for antigenic macromolecule-based prostate cancer vaccines.

Synergistic effects of immunotherapy and adjunctive therapies in prostate cancer management

In recent years, cancer immunotherapy has received widespread attention due to significant tumor clearance in some malignancies. Various immunotherapy approaches, including vaccines, immune checkpoint inhibitors, oncolytic virotherapy, bispecific T cell engagers, and adoptive T cell transfer, have completed or are undergoing clinical trials for prostate cancer. Despite immune checkpoint blockade's extraordinary effectiveness in treating a variety of cancers, targeted prostate cancer treatment using the immune system is still in its infancy. Multiple factors including the heterogeneity of prostate cancer, the cold tumor microenvironment, and a low level of neoantigens, contribute to the poor immunotherapy response. Significant effort is being devoted to improving immune-based prostate cancer therapy. Recently, several key discoveries demonstrate that prostate cancer immunotherapy agents may be used to promise better prognosis for patients as part of combination strategies with other agents targeting tumor-associated immune mechanism of resistance. Here, this review comprehensively examines the recent advancements in immunotherapy for prostate cancer, exploring its potential synergistic effects when combined with other treatment modalities to enhance clinical efficacy.

Advances in nucleic acid-based cancer vaccines

Nucleic acid vaccines have emerged as crucial advancements in vaccine technology, particularly highlighted by the global response to the COVID-19 pandemic. The widespread administration of mRNA vaccines against COVID-19 to billions globally marks a significant milestone. Furthermore, the approval of an mRNA vaccine for Respiratory Syncytial Virus (RSV) this year underscores the versatility of this technology. In oncology, the combination of mRNA vaccine encoding neoantigens and immune checkpoint inhibitors (ICIs) has shown remarkable efficacy in eliciting protective responses against diseases like melanoma and pancreatic cancer. Although the use of a COVID-19 DNA vaccine has been limited to India, the inherent stability at room temperature and cost-effectiveness of DNA vaccines present a viable option that could benefit developing countries. These advantages may help DNA vaccines address some of the challenges associated with mRNA vaccines. Currently, several trials are exploring the use of DNA-encoded neoantigens in combination with ICIs across various cancer types. These studies highlight the promising role of nucleic acid-based vaccines as the next generation of immunotherapeutic agents in cancer treatment. This review will delve into the recent advancements and current developmental status of both mRNA and DNA-based cancer vaccines.

Long-term follow up of patients treated with a DNA vaccine (pTVG-hp) for PSA-recurrent prostate cancer

We have previously reported two single-agent phase I trials, evaluating the dose or schedule, of a DNA vaccine (pTVG-HP) encoding prostatic acid phosphatase (PAP) administered with GM-CSF as the adjuvant. These were in patients with PSA-recurrent, radiographically non-metastatic, prostate cancer (PCa). We report here the long-term safety and overall survival of these patients. Specifically, 22 patients with non-metastatic, castration-sensitive PCa (nmCSPC) were treated with pTVG-HP, 100-1500 µg, administered over 12 weeks and followed for 15 y. 17 patients with non-metastatic castration-resistant PCa (nmCRPC) were treated with 100 µg pTVG-HP with different schedules of administration over 1 y and followed for 5 y. No adverse events were detected in long-term follow-up from either trial that were deemed possibly related to vaccination. Patients with nmCSPC had a median overall survival of 12.3 y, with 5/22 (23%) alive at 15 y. 8/22 (36%) died due to prostate cancer with a median survival of 11.0 y, and 9/22 (41%) died of other causes. Patients with nmCRPC had a median overall survival of 4.5 y, with 8/17 (47%) alive at 5 y. The presence of T-cells specific for the PAP target antigen was detectable in 6/10 (60%) individuals with nmCSPC, and 3/5 (60%) individuals with nmCRPC, many years after immunization. The detection of immune responses to the vaccine target years after immunization suggests durable immunity can be elicited in patients using a DNA vaccine encoding a tumor-associated antigen.Trial Registration: NCT00582140 and NCT00849121.

Vaccine Therapies for Prostate Cancer: Current Status and Future Outlook

Prostate cancer is a prevalent cancer in elderly men, and immunotherapy has emerged as a promising treatment approach in recent years. The aim of immunotherapy is to stimulate the body's immune system to target and destroy cancer cells. Cancer vaccines that are highly specific, safe, and capable of creating long-lasting immune responses are a key focus in cancer immunotherapy research. Despite progress in clinical trials showing positive results, the practical use of cancer vaccines still encounters various obstacles. The complexity of the immune microenvironment and variations in the immune systems of individual patients have hindered the progress of research on prostate cancer vaccines. This review examines the history and mechanisms of cancer vaccines, summarizes recent clinical research findings, and explores future directions in the development of prostate cancer vaccines.

Unlocking Immunity: Innovative prostate cancer vaccine strategies

OBJECTIVE

Prostate Cancer (PCa) is a leading cause of cancer-related mortality in men, especially in Western societies. The objective of this research is to address the unmet need for effective treatments in advanced or recurrent PCa, where current strategies fall short of offering a cure. The focus is on leveraging immunotherapy and cancer vaccines to target the tumor's unique immunological microenvironment.

MAIN RESULTS

Despite immunotherapy's success in other cancers, its effectiveness in PCa has been limited by the tumor's immunosuppressive characteristics. However, cancer vaccines that engage Tumor-Specific Antigens (TSA) and Tumor-Associated Antigens (TAA) have emerged as a promising approach. Preclinical and clinical investigations of Dendritic Cell (DC) vaccines, DNA vaccines, mRNA vaccines, peptide vaccines, and viral vectors have shown their potential to elicit anti-tumor immune responses. The exploration of combination therapies with immune checkpoint inhibitors and the advent of novel adjuvants and oral microparticle vaccines present innovative strategies to improve efficacy and compliance.

CONCLUSION

The development of cancer vaccines for PCa holds significant potential. Future directions include optimizing vaccine design, refining combination therapy strategies, and creating patient-friendly administration methods. The integration of interdisciplinary knowledge and innovative clinical trial designs is essential for advancing personalized and precision immunotherapy for PCa.

New insights for the development of efficient DNA vaccines

Despite the great potential of DNA vaccines for a broad range of applications, ranging from prevention of infections, over treatment of autoimmune and allergic diseases to cancer immunotherapies, the implementation of such therapies for clinical treatment is far behind the expectations up to now. The main reason is the poor immunogenicity of DNA vaccines in humans. Consequently, the improvement of the performance of DNA vaccines in vivo is required. This mini-review provides an overview of the current state of DNA vaccines and the various strategies to enhance the immunogenic potential of DNA vaccines, including (i) the optimization of the DNA construct itself regarding size, nuclear transfer and transcriptional regulation; (ii) the use of appropriate adjuvants; and (iii) improved delivery, for example, by careful choice of the administration route, physical methods such as electroporation and nanomaterials that may allow cell type-specific targeting. Moreover, combining nanoformulated DNA vaccines with other immunotherapies and prime-boost strategies may help to enhance success of treatment.

The Immune Microenvironment in Prostate Cancer: A Comprehensive Review

BACKGROUND

Prostate cancer (PCa) is a malignancy with significant immunosuppressive properties and limited immune activation. This immunosuppression is linked to reduced cytotoxic T cell activity, impaired antigen presentation, and elevated levels of immunosuppressive cytokines and immune checkpoint molecules. Studies demonstrate that cytotoxic CD8+ T cell infiltration correlates with improved survival, while increased regulatory T cells (Tregs) and tumor-associated macrophages (TAMs) are associated with worse outcomes and therapeutic resistance. Th1 cells are beneficial, whereas Th17 cells, producing interleukin-17 (IL-17), contribute to tumor progression. Tumor-associated neutrophils (TANs) and immune checkpoint molecules, such as PD-1/PD-L1 and T cell immunoglobulin-3 (TIM-3) are also linked to advanced stages of PCa. Chemotherapy holds promise in converting the "cold" tumor microenvironment (TME) to a "hot" one by depleting immunosuppressive cells and enhancing tumor immunogenicity.

SUMMARY

This comprehensive review examines the immune microenvironment in PCa, focusing on the intricate interactions between immune and tumor cells in the TME. It highlights how TAMs, Tregs, cytotoxic T cells, and other immune cell types contribute to tumor progression or suppression and how PCa's low immunogenicity complicates immunotherapy.

KEY MESSAGES

The infiltration of cytotoxic CD8+ T cells and Th1 cells correlates with better outcomes, while elevated T regs and TAMs promote tumor growth, metastasis, and resistance. TANs and natural killer (NK) cells exhibit dual roles, with higher NK cell levels linked to better prognoses. Immune checkpoint molecules like PD-1, PD-L1, and TIM-3 are associated with advanced disease. Chemotherapy can improve tumor immunogenicity by depleting T regs and myeloid-derived suppressor cells, offering therapeutic promise.

Transdermal microarrayed electroporation for enhanced cancer immunotherapy based on DNA vaccination

Despite the tremendous clinical potential of nucleic acid-based vaccines, their efficacy to induce therapeutic immune response has been limited by the lack of efficient local gene delivery techniques in the human body. In this study, we develop a hydrogel-based organic electronic device (μEPO) for both transdermal delivery of nucleic acids and in vivo microarrayed cell electroporation, which is specifically oriented toward one-step transfection of DNAs in subcutaneous antigen-presenting cells (APCs) for cancer immunotherapy. The μEPO device contains an array of microneedle-shaped electrodes with pre-encapsulated dry DNAs. Upon a pressurized contact with skin tissue, the electrodes are rehydrated, electrically triggered to release DNAs, and then electroporate nearby cells, which can achieve in vivo transfection of more than 50% of the cells in the epidermal and upper dermal layer. As a proof-of-concept, the μEPO technique is employed to facilitate transdermal delivery of neoantigen genes to activate antigen-specific immune response for enhanced cancer immunotherapy based on a DNA vaccination strategy. In an ovalbumin (OVA) cancer vaccine model, we show that high-efficiency transdermal transfection of APCs with OVA-DNAs induces robust cellular and humoral immune responses, including antigen presentation and generation of IFN-γ+ cytotoxic T lymphocytes with a more than 10-fold dose sparing over existing intramuscular injection (IM) approach, and effectively inhibits tumor growth in rodent animals.

CRISPR editing to mimic porphyria combined with light: A new preclinical approach for prostate cancer

Thanks to its very high genome-editing efficiency, CRISPR-Cas9 technology could be a promising anticancer weapon. Clinical trials using CRISPR-Cas9 nuclease to ex vivo edit and alter immune cells are ongoing. However, to date, this strategy still has not been applied in clinical practice to directly target cancer cells. Targeting a canonical metabolic pathway essential to good functioning of cells without potential escape would represent an attractive strategy. We propose to mimic a genetic metabolic disorder in cancer cells to weaken cancer cells, independent of their genomic abnormalities. Mutations affecting the heme biosynthesis pathway are responsible for porphyria, and most of them are characterized by an accumulation of toxic photoreactive porphyrins. This study aimed to mimic porphyria by using CRISPR-Cas9 to inactivate UROS, leading to porphyrin accumulation in a prostate cancer model. Prostate cancer is the leading cancer in men and has a high mortality rate despite therapeutic progress, with a primary tumor accessible to light. By combining light with gene therapy, we obtained high efficiency in vitro and in vivo, with considerable improvement in the survival of mice. Finally, we achieved the preclinical proof-of-principle of performing cancer CRISPR gene therapy.

Comprehensive Review on Recent Strategies for Management of Prostate Cancer: Therapeutic Targets and SAR

Prostate cancer is a disease that is affecting a large population worldwide. Androgen deprivation therapy (ADT) has become a foundation for the treatment of advanced prostate cancer, as used in most clinical settings from neo-adjuvant to metastatic stage. In spite of the success of ADT in managing the disease in the majority of men, hormonal manipulation fails eventually. New molecules are developed for patients with various hormone-refractory diseases. Advancements in molecular oncology have increased understanding of numerous cellular mechanisms which control cell death in the prostate and these insights can lead to the development of more efficacious and tolerable therapies for carcinoma of the prostate. This review is focused on numerous therapies that might be a boon for prostate therapy like signaling inhibitors, vaccines, and inhibitors of androgen receptors. Along with these, various bioactive molecules and their derivatives are highlighted, which act as potential antiprostate cancer agents. This article also emphasized the recent advances in the field of medicinal chemistry of prostate cancer agents.

Phase 2 trial of a DNA vaccine (pTVG-HP) and nivolumab in patients with castration-sensitive non-metastatic (M0) prostate cancer

PURPOSE

We have previously reported that a plasmid DNA vaccine encoding prostatic acid phosphatase (pTVG-HP) had greater clinical activity when given in combination with pembrolizumab to patients with metastatic, castration-resistant prostate cancer. The current trial was conducted to evaluate vaccination with PD-1 blockade, using nivolumab, in patients with early, recurrent (M0) prostate cancer.

METHODS

Patients with M0 prostate cancer were treated with pTVG-HP (100 µg administered intradermally) and nivolumab (240 mg intravenous infusion) every 2 weeks for 3 months, and then every 4 weeks for 1 year of total treatment. Patients were then followed for an additional year off treatment. The primary objectives were safety and complete prostate-specific antigen (PSA) response (PSA<0.2 ng/mL).

RESULTS

19 patients were enrolled. No patients met the primary endpoint of complete PSA response; however, 4/19 (21%) patients had a PSA decline >50%. Median PSA doubling times were 5.9 months pretreatment, 25.6 months on-treatment (p=0.001), and 9.0 months in the subsequent year off-treatment. The overall median radiographic progression-free survival was not reached. Grade 3 or 4 events included adrenal insufficiency, fatigue, lymphopenia, and increased amylase/lipase. 9/19 (47%) patients developed immune-related adverse effects (irAE). The development of irAE and increased CXCL9 were associated with increased PSA doubling time. Quantitative NaF PET/CT imaging showed the resolution of subclinical lesions along with the development of new lesions at each time point.

CONCLUSIONS

In this population, combining nivolumab with pTVG-HP vaccination was safe, and immunologically active, prolonged the time to disease progression, but did not eradicate disease. Quantitative imaging suggested that additional treatments targeting mechanisms of resistance may be required to eliminate tumors.

TRIAL REGISTRATION NUMBER

NCT03600350.

Pembrolizumab in mCRPC - Combination therapies as breakthrough to success?

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICIs) have shown promising antitumor activity in various malignant diseases. This narrative review provides an update on ongoing clinical studies investigating the only FDA-approved ICI programmed death receptor 1 (PD-1) inhibitor pembrolizumab in mono- and combination therapy in patients with metastatic castration-resistant prostate cancer (mCRPC).

RECENT FINDINGS

Although most clinical trials investigating pembrolizumab as mono- or combinational therapy did not meet their primary endpoints, there exist subgroups of patients that demonstrate impressive responses rates justifying further investigation of ICI in prostate cancer. Beside combination of pembrolizumab with approved mCRPC agents, innovative approaches, like combining pembrolizumab with radioligands, deoxyribonucleic acid vaccines or innovative immunotherapeutic agents (i.e., ONC-392, AMG160, BXCL701) are ongoing exerting promising preliminary findings.

SUMMARY

ICI monotherapy seems to be effective in a small biomarker-preselected population, however, there is evidence that especially novel ICI combination approaches can improve patient survival, which could ultimately refocus and revolutionize the treatment of mCRPC.

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.

Targeting neoantigens to APC-surface molecules improves the immunogenicity and anti-tumor efficacy of a DNA cancer vaccine

Introduction

Tumor-specific mutations generate neoepitopes unique to the cancer that can be recognized by the immune system, making them appealing targets for therapeutic cancer vaccines. Since the vast majority of tumor mutations are patient-specific, it is crucial for cancer vaccine designs to be compatible with individualized treatment strategies. Plasmid DNA vaccines have substantiated the immunogenicity and tumor eradication capacity of cancer neoepitopes in preclinical models. Moreover, early clinical trials evaluating personalized neoepitope vaccines have indicated favorable safety profiles and demonstrated their ability to elicit specific immune responses toward the vaccine neoepitopes.

Methods

By fusing in silico predicted neoepitopes to molecules with affinity for receptors on the surface of APCs, such as chemokine (C-C motif) ligand 19 (CCL19), we designed an APC-targeting cancer vaccine and evaluated their ability to induce T-cell responses and anti-tumor efficacy in the BALB/c syngeneic preclinical tumor model.

Results

In this study, we demonstrate how the addition of an antigen-presenting cell (APC) binding molecule to DNA-encoded cancer neoepitopes improves neoepitope-specific T-cell responses and the anti-tumor efficacy of plasmid DNA vaccines. Dose-response evaluation and longitudinal analysis of neoepitope-specific T-cell responses indicate that combining APC-binding molecules with the delivery of personalized tumor antigens holds the potential to improve the clinical efficacy of therapeutic DNA cancer vaccines.

Discussion

Our findings indicate the potential of the APC-targeting strategy to enhance personalized DNA cancer vaccines while acknowledging the need for further research to investigate its molecular mechanism of action and to translate the preclinical results into effective treatments for cancer patients.

Potential of Personalized Dendritic Cell-Based Immunohybridoma Vaccines to Treat Prostate Cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second most common cause of death due to cancer. About 30% of patients with PCa who have been castrated develop a castration-resistant form of the disease (CRPC), which is incurable. In the last decade, new treatments that control the disease have emerged, slowing progression and spread and prolonging survival while maintaining the quality of life. These include immunotherapies; however, we do not yet know the optimal combination and sequence of these therapies with the standard ones. All therapies are not always suitable for every patient due to co-morbidities or adverse effects of therapies or both, so there is an urgent need for further work on new therapeutic options. Advances in cancer immunotherapy with an immune checkpoint inhibition mechanism (e.g., ipilimumab, an anti-CTLA-4 inhibitor) have not shown a survival benefit in patients with CRPC. Other immunological approaches have also not given clear results, which has indirectly prevented breakthrough for this type of therapeutic strategy into clinical use. Currently, the only approved form of immunotherapy for patients with CRPC is a cell-based medicine, but it is only available to patients in some parts of the world. Based on what was gained from recently completed clinical research on immunotherapy with dendritic cell-based immunohybridomas, the aHyC dendritic cell vaccine for patients with CRPC, we highlight the current status and possible alternatives that should be considered in the future.

Advances in cancer vaccines for immunotherapy of prostate cancer

Prostate cancer is currently one of the most common malignancies that endanger the lives and health of elderly men. In recent years, immunotherapy, which exploits the activation of anti-cancer host immune cells to accomplish tumor-killing effects, has emerged as a new study avenue in the treatment of prostate cancer. As an important component of immunotherapy, cancer vaccines have a unique position in the precision treatment of malignant tumors. Monocyte cell vaccines, dendritic cell vaccines, viral vaccines, peptide vaccines, and DNA/mRNA vaccines are the most often used prostate cancer vaccines. Among them, Sipuleucel-T, as a monocyte cell-based cancer vaccine, is the only FDA-approved therapeutic vaccine for prostate cancer, and has a unique position and role in advancing the development of immunotherapy for prostate cancer. However, due to its own limitations, Sipuleucel-T has not been widely adopted. Meanwhile, owing to the complexity of immunotherapy and the specificity of prostate cancer, the remaining prostate cancer vaccines have not shown good clinical benefit in large randomized phase II and phase III trials, and further in-depth studies are still needed.

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.

GM-CSF elicits antibodies to tumor-associated proteins when used as a prostate cancer vaccine adjuvant

Antibody responses to off-target cancer-associated proteins have been detected following immunotherapies for cancer, suggesting these may be the result of antigen spread. We have previously reported that serum antibodies to prostate cancer-associated proteins were detectable using a high-throughput peptide array. We hypothesized that the breadth of antibody responses elicited by a vaccine could serve as a measure of the magnitude of its induced antigen spread. Consequently, sera from patients with prostate cancer, treated prior to or after vaccination in one of four separate clinical trials, were evaluated for antibody responses to an array of 177,604 peptides derived from over 1600 prostate cancer-associated gene products. Antibody responses to the same group of 5680 peptides previously reported were identified following vaccinations in which patients were administered GM-CSF as an adjuvant, but not with vaccine in the absence of GM-CSF. Hence, antibody responses to off-target proteins following vaccination may not necessarily serve as evidence of antigen spread and must be interpreted with particular caution following vaccine strategies that use GM-CSF, as GM-CSF appears to have direct effects on the production of antibodies. The evaluation of T cell responses to non-target antigens is likely a preferred approach for detection of immune-mediated antigen spread.

Phase 2 trial of T-cell activation using MVI-816 and pembrolizumab in patients with metastatic, castration-resistant prostate cancer (mCRPC)

Background

We previously reported a trial using a DNA vaccine encoding prostatic acid phosphatase (MVI-816, pTVG-HP), given over 12 weeks concurrently or sequentially with pembrolizumab, in patients with mCRPC. We report the final analysis of this trial following two additional treatment arms in which patients with mCRPC continued concurrent treatment until progression.

Materials and methods

Patients with mCRPC were treated with MVI-816 and pembrolizumab every 3 weeks (arm 3, n=20) or MVI-816 every 2 weeks and pembrolizumab every 4 weeks (arm 4, n=20). The primary objectives were safety, 6-month progression-free survival (PFS), median time to radiographic progression, and objective response rates. Secondary objectives included immunological evaluations.

Results

In 25 patients with measurable disease, there were no complete response and one confirmed partial response in a patient who subsequently found to have an MSI^hi tumor. 4/40 patients (10%) had a prostate-specific antigen decline >50%. The estimated overall radiographic PFS rate at 6 months was 47.2% (44.4% arm 3, 61.5% arm 4). Accounting for all off-study events, overall median time on treatment was 5.6 months (95% CI: 5.4 to 10.8 months), 5.6 months for arm 3 and 8.1 months for arm 4 (p=0.64). Thirty-two per cent of patients remained on trial beyond 6 months without progression. Median overall survival was 22.9 (95% CI: 16.2 to 25.6) months. One grade 4 event (hyperglycemia) was observed. Immune-related adverse events (irAEs) >grade 1 were observed in 42% of patients overall. Interferon-γ and/or granzyme B immune response to prostatic acid phosphatase was detected in 2/20 patients in arm 3 and 6/20 patients in arm 4. Plasma cytokines associated with immune activation and CD8+ T-cell recruitment were augmented at weeks 6 and 12. The development of irAE was significantly associated with a prolonged time on treatment (HR=0.42, p=0.003). Baseline DNA homologous recombination repair mutations were not associated with longer time to progression.

Conclusions

Findings here demonstrate that combining programmed cell death 1 blockade with MVI-816 is safe, can augment tumor-specific T cells, and can result in a favorable 6-month disease control rate. Correlative studies suggest T-cell activation by vaccination is critical to the mechanism of action of this combination. Future randomized clinical trials are needed to validate these findings.

Trial registration number

NCT02499835.

Specific targeting of cancer stem cells by immunotherapy: A possible stratagem to restrain cancer recurrence and metastasis

Cancer stem cells (CSCs), the tumor-initiating cells playing a crucial role in cancer progression, recurrence, and metastasis, have the intrinsic property of self-renewal and therapy resistance. The tumorigenic properties of these cells include generation of cellular heterogeneity and immuno-suppressive tumor microenvironment (TME), conferring them the capability to resist a variety of anti-cancer therapeutics. Further, CSCs possess several unique immunological properties that help them escape recognition by the innate and adaptive immune system and shape a TME into a pro-tumorigenic and immunosuppressive landscape. In this context, immunotherapy is considered one of the best therapeutic options for eliminating CSCs to halt cancer recurrence and metastasis. In this review, we discuss the various immunomodulatory properties of CSCs and the interaction of CSCs with the immune system enabling immune evasion. In addition, we also highlight the present research update on immunotherapeutic targeting of CSCs and the possible further scope of research on this topic. We believe that a deeper understanding of CSCs' immunological properties and the crosstalk between CSCs and the immune system can develop better innovative immune-therapeutics and enhance the efficacy of current therapy-resistant cancer treatments.

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.

Overcoming Immune Resistance in Prostate Cancer: Challenges and Advances

Simple Summary

Immunotherapy has changed the landscape of treatment modalities available for many different types of malignancies. However, the factors that influence the success of immunotherapeutics have not been as clearly seen in advanced prostate cancer, likely due to immunosuppressive factors that exist within the prostate cancer tumor microenvironment. While there have been many immunotherapeutics used for prostate cancer, the majority have targeted a single immunosuppressive mechanism resulting in limited clinical efficacy. More recent research centered on elucidating the key mechanisms of immune resistance in the prostate tumor microenvironment has led to the discovery of a range of new treatment targets. With that in mind, many clinical trials have now set out to evaluate combination immunotherapeutic strategies in patients with advanced prostate cancer, in the hopes of circumventing the immunosuppressive mechanisms.

Abstract

The use of immunotherapy has become a critical treatment modality in many advanced cancers. However, immunotherapy in prostate cancer has not been met with similar success. Multiple interrelated mechanisms, such as low tumor mutational burden, immunosuppressive cells, and impaired cellular immunity, appear to subvert the immune system, creating an immunosuppressive tumor microenvironment and leading to lower treatment efficacy in advanced prostate cancer. The lethality of metastatic castrate-resistant prostate cancer is driven by the lack of therapeutic regimens capable of generating durable responses. Multiple strategies are currently being tested to overcome immune resistance including combining various classes of treatment modalities. Several completed and ongoing trials have shown that combining vaccines or checkpoint inhibitors with hormonal therapy, radiotherapy, antibody–drug conjugates, chimeric antigen receptor T cell therapy, or chemotherapy may enhance immune responses and induce long-lasting clinical responses without significant toxicity. Here, we review the current state of immunotherapy for prostate cancer, as well as tumor-specific mechanisms underlying therapeutic resistance, with a comprehensive look at the current preclinical and clinical immunotherapeutic strategies aimed at overcoming the immunosuppressive tumor microenvironment and impaired cellular immunity that have largely limited the utility of immunotherapy in advanced prostate cancer.

A Guide to Nucleic Acid Vaccines in the Prevention and Treatment of Infectious Diseases and Cancers: From Basic Principles to Current Applications

Faced with the challenges posed by infectious diseases and cancer, nucleic acid vaccines present excellent prospects in clinical applications. Compared with traditional vaccines, nucleic acid vaccines have the characteristics of high efficiency and low cost. Therefore, nucleic acid vaccines have potential advantages in disease prevention and treatment. However, the low immunogenicity and instability of nucleic acid vaccines have limited their development. Therefore, a large number of studies have been conducted to improve their immunogenicity and stability by improving delivery methods, thereby supporting progress and development for clinical applications. This article mainly reviews the advantages, disadvantages, mechanisms, delivery methods, and clinical applications of nucleic acid vaccines.

Considering the potential for gene-based therapy in prostate cancer

Therapeutic gene manipulation has been at the forefront of popular scientific discussion and basic and clinical research for decades. Basic and clinical research applications of CRISPR-Cas9-based technologies and ongoing clinical trials in this area have demonstrated the potential of genome editing to cure human disease. Evaluation of research and clinical trials in gene therapy reveals a concentration of activity in prostate cancer research and practice. Multiple aspects of prostate cancer care - including anatomical considerations that enable direct tumour injections and sampling, the availability of preclinical immune-competent models and the delineation of tumour-related antigens that might provide targets for an induced immune system - make gene therapy an appealing treatment option for this common malignancy. Vaccine-based therapies that induce an immune response and new technologies exploiting CRISPR-Cas9-assisted approaches, including chimeric antigen receptor (CAR) T cell therapies, are very promising and are currently under investigation both in the laboratory and in the clinic. Although laboratory and preclinical advances have, thus far, not led to oncologically relevant outcomes in the clinic, future studies offer great promise for gene therapy to become established in prostate cancer care.

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.

Immunotherapy and Immunotherapy Combinations in Metastatic Castration-Resistant Prostate Cancer

Although most prostate cancers are localized, and the majority are curable, recurrences occur in approximately 35% of men. Among patients with prostate-specific antigen (PSA) recurrence and PSA doubling time (PSADT) less than 15 months after radical prostatectomy, prostate cancer accounted for approximately 90% of the deaths by 15 years after recurrence. An immunosuppressive tumor microenvironment (TME) and impaired cellular immunity are likely largely responsible for the limited utility of checkpoint inhibitors (CPIs) in advanced prostate cancer compared with other tumor types. Thus, for immunologically "cold" malignancies such as prostate cancer, clinical trial development has pivoted towards novel approaches to enhance immune responses. Numerous clinical trials are currently evaluating combination immunomodulatory strategies incorporating vaccine-based therapies, checkpoint inhibitors, and chimeric antigen receptor (CAR) T cells. Other trials evaluate the efficacy and safety of these immunomodulatory agents' combinations with standard approaches such as androgen deprivation therapy (ADT), taxane-based chemotherapy, radiotherapy, and targeted therapies such as tyrosine kinase inhibitors (TKI) and poly ADP ribose polymerase (PARP) inhibitors. Here, we will review promising immunotherapies in development and ongoing trials for metastatic castration-resistant prostate cancer (mCRPC). These novel trials will build on past experiences and promise to usher a new era to treat patients with mCRPC.

The Tumor Microenvironment and Immunotherapy in Prostate and Bladder Cancer

Bladder cancer has been successfully treated with immunotherapy, whereas prostate cancer is a cold tumor with inadequate immune-related treatment response. A greater understanding of the tumor microenvironment and methods for harnessing the immune system to address tumor growth will be needed to improve immunotherapies for both prostate and bladder cancer. Here, we provide an overview of prostate and bladder cancer, including fundamental aspects of the disease and treatment, the elaborate cellular makeup of the tumor microenvironment, and methods for exploiting relevant pathways to develop more effective treatments.

Antibody profiling of patients with prostate cancer reveals differences in antibody signatures among disease stages

BACKGROUND

Previous studies of prostate cancer autoantibodies have largely focused on diagnostic applications. So far, there have been no reports attempting to more comprehensively profile the landscape of prostate cancer-associated antibodies. Specifically, it is unknown whether the quantity of antibodies or the types of proteins recognized change with disease progression.

METHODS

A peptide microarray spanning the amino acid sequences of the gene products of 1611 prostate cancer-associated genes was synthesized. Serum samples from healthy male volunteers (n=15) and patients with prostate cancer (n=85) were used to probe the array. These samples included patients with various clinical stages of disease: newly diagnosed localized prostate cancer (n=15), castration-sensitive non-metastatic prostate cancer (nmCSPC, n=40), castration-resistant non-metastatic prostate cancer (n=15) and castration-resistant metastatic disease (n=15). The patients with nmCSPC received treatment with either standard androgen deprivation therapy (ADT) or an antitumor DNA vaccine encoding prostatic acid phosphatase. Serial sera samples from these individuals were also used to probe the array, to secondarily determine whether this approach could be used to detect treatment-related changes.

RESULTS

We demonstrated that this peptide array yielded highly reproducible measurements of serum IgG levels. We found that the overall number of antibody responses did not increase with disease burden. However, the composition of recognized proteins shifted with clinical stage of disease. Our analysis revealed that the largest difference was between patients with castration-sensitive and castration-resistant disease. Patients with castration-resistant disease recognized more proteins associated with nucleic acid binding and gene regulation compared with men in other groups. Our longitudinal data showed that treatments can elicit antibodies detectable by this array, and notably vaccine-treated patients developed increased responses to more proteins over the course of treatment than did ADT-treated patients.

CONCLUSIONS

This study represents the largest survey of prostate cancer-associated antibodies to date. We have been able to characterize the classes of proteins recognized by patients and determine how they change with disease burden. Our findings further demonstrate the potential of this platform for measuring antigen spread and studying responses to immunomodulatory therapies.

Therapeutic Efficacy of Delta-Like Ligand 4 Gene Vaccine Overexpression on Liver Cancer in Mice

Delta-like ligand 4 is a notch ligand that is predominantly expressed in the endothelial tip cells and plays essential roles in the regulation of angiogenesis. In this study, we explored the therapeutic effects of delta-like ligand 4 gene vaccine overexpression on the syngeneic model mouse model of liver cancer and the underlying mechanisms. Mouse hepatocellular carcinoma cell line H22-H8D8 was used to generate subcutaneous syngeneic model liver cancer in Kunming mice, and the effects of recombinant plasmid pVAX1 containing delta-like ligand 4 vaccine on tumor growth was examined. Compared to controls, delta-like ligand 4 vaccination reduced syngeneic model tumor size by 70.31% (from 17.11 ± 9.30 cm³ to 5.08 ± 2.75 cm³, P = .035) and tumor weight by 34.19% (from 6.26 ± 3.01 g to 4.12 ± 2.52 g, P = .102), while the mouse survival was significantly increased (from 27.7 ± 6.0 days to 33.1 ± 6.1 days, P = .047). High level of delta-like ligand 4 antibody, together with a significantly increased number of CD4⁺ and decreased CD8⁺ cells were identified in the mouse peripheral blood serum samples after delta-like ligand 4 immunization. In addition, elevated serum levels of interleukin 2, interleukin 4, and interferon γ were detected in the delta-like ligand 4-vaccinated mice when compared to the controls. Further studies have revealed increased CD31 and decreased Ki67 expression in the syngeneic model tumor tissues of vaccinated mice. Taken together, our studies suggest that delta-like ligand 4 gene vaccine can inhibit the growth of hepatocellular carcinoma in mice through inhibiting tumor angiogenesis and boosting antitumor immune responses. Hence, delta-like ligand 4 gene vaccination may be a promising strategy for the treatment of transplanted liver cancer.

The Potential Role for Immunotherapy in Biochemically Recurrent Prostate Cancer

Biochemically recurrent prostate cancer represents a stage of prostate cancer where conventional (continued on next page) computed tomography and technetium Tc 99m bone scan imaging are unable to detect disease after curative intervention despite rising prostate-specific antigen. There is no clear standard of care and no systemic therapy has been shown to improve survival. Immunotherapy-based treatments potentially are attractive options relative to androgen deprivation therapy due to the generally more favorable side-effect profile. Biochemically recurrent prostate cancer patients have a low tumor burden and likely lymph node-based disease, which may make them more likely to respond to immunotherapy.

Treatment Combinations with DNA Vaccines for the Treatment of Metastatic Castration-Resistant Prostate Cancer (mCRPC)

Simple Summary

The only vaccine approved by FDA as a treatment for cancer is sipuleucel-T, a therapy for patients with metastatic castration-resistant prostate cancer (mCRPC). Most investigators studying anti-tumor vaccines believe they will be most effective as parts of combination therapies, rather than used alone. Unfortunately, the cost and complexity of sipuleucel-T makes it difficult to feasibly be used in combination with many other agents. In this review article we discuss the use of DNA vaccines as a simpler vaccine approach that has demonstrated efficacy in several animal species. We discuss the use of DNA vaccines in combination with traditional treatments for mCRPC, and other immune-modulating treatments, in preclinical and early clinical trials for patients with mCRPC.

Abstract

Metastatic castration-resistant prostate cancer (mCRPC) is a challenging disease to treat, with poor outcomes for patients. One antitumor vaccine, sipuleucel-T, has been approved as a treatment for mCRPC. DNA vaccines are another form of immunotherapy under investigation. DNA immunizations elicit antigen-specific T cells that cause tumor cell lysis, which should translate to meaningful clinical responses. They are easily amenable to design alterations, scalable for large-scale manufacturing, and thermo-stable for easy transport and distribution. Hence, they offer advantages over other vaccine formulations. However, clinical trials with DNA vaccines as a monotherapy have shown only modest clinical effects against tumors. Standard therapies for CRPC including androgen-targeted therapies, radiation therapy and chemotherapy all have immunomodulatory effects, which combined with immunotherapies such as DNA vaccines, could potentially improve treatment. In addition, many investigational drugs are being developed which can augment antitumor immunity, and together with DNA vaccines can further enhance antitumor responses in preclinical models. We reviewed the literature available prior to July 2020 exploring the use of DNA vaccines in the treatment of prostate cancer. We also examined various approved and experimental therapies that could be combined with DNA vaccines to potentially improve their antitumor efficacy as treatments for mCRPC.

Immunotherapy in prostate cancer: current state and future perspectives

Metastatic castrate resistant prostate cancer (PCa) remains an incurable entity. In the era of immunotherapy, the complex PCa microenvironment poses a unique challenge to the successful application of this class of agents. However, in the last decade, a tremendous effort has been made to explore this field of therapeutics. In this review, the physiology of the cancer immunity cycle is highlighted in the context of the prostate tumor microenvironment, and the current evidence for use of various classes of immunotherapy agents including vaccines (dendritic cell based, viral vector based and DNA/mRNA based), immune checkpoint inhibitors, Chimeric antigen receptor T cell therapy, antibody-mediated radioimmunotherapy, antibody drug conjugates, and bispecific antibodies, is consolidated. Finally, the future directions for combinatorial approaches to combat PCa are discussed.

Multicenter Phase I Trial of a DNA Vaccine Encoding the Androgen Receptor Ligand-binding Domain (pTVG-AR, MVI-118) in Patients with Metastatic Prostate Cancer

PURPOSE

Preclinical studies demonstrated that a DNA vaccine (pTVG-AR, MVI-118) encoding the androgen receptor ligand-binding domain (AR LBD) augmented antigen-specific CD8⁺ T cells, delayed prostate cancer progression and emergence of castration-resistant disease, and prolonged survival of tumor-bearing mice. This vaccine was evaluated in a multicenter phase I trial.

PATIENTS AND METHODS

Patients with metastatic castration-sensitive prostate cancer (mCSPC) who had recently begun androgen deprivation therapy were randomly assigned to receive pTVG-AR on one of two treatment schedules over one year, and with or without GM-CSF as a vaccine adjuvant. Patients were followed for 18 months. Primary objectives were safety and immune response. Secondary objectives included median time to PSA progression, and 18-month PSA-PFS (PPFS).

RESULTS

Forty patients were enrolled at three centers. Twenty-seven patients completed treatment and 18 months of follow-up. Eleven patients (28%) had a PSA progression event before the 18-month time point. No grade 3 or 4 adverse events were observed. Of 30 patients with samples available for immune analysis, 14 (47%) developed Th1-type immunity to the AR LBD, as determined by IFNγ and/or granzyme B ELISPOT. Persistent IFNγ immune responses were observed irrespective of GM-CSF adjuvant. Patients who developed T-cell immunity had a significantly prolonged PPFS compared with patients without immunity (HR = 0.01; 95% CI, 0.0-0.21; P = 0.003).

CONCLUSIONS

pTVG-AR was safe and immunologically active in patients with mCSPC. Association between immunity and PPFS suggests that treatment may delay the time to castration resistance, consistent with preclinical findings, and will be prospectively evaluated in future trials.See related commentary by Shenderov and Antonarakis, p. 5056.

Safety and immunogenicity of novel 5T4 viral vectored vaccination regimens in early stage prostate cancer: a phase I clinical trial

BACKGROUND

Prostate cancer (PCa) has been under investigation as a target for antigen-specific immunotherapies in metastatic disease settings for the last two decades leading to a licensure of the first therapeutic cancer vaccine, Sipuleucel-T, in 2010. However, neither Sipuleucel-T nor other experimental PCa vaccines that emerged later induce strong T-cell immunity.

METHODS

In this first-in-man study, VANCE, we evaluated a novel vaccination platform based on two replication-deficient viruses, chimpanzee adenovirus (ChAd) and MVA (Modified Vaccinia Ankara), targeting the oncofetal self-antigen 5T4 in early stage PCa. Forty patients, either newly diagnosed with early-stage PCa and scheduled for radical prostatectomy or patients with stable disease on an active surveillance protocol, were recruited to the study to assess the vaccine safety and T-cell immunogenicity. Secondary and exploratory endpoints included immune infiltration into the prostate, prostate-specific antigen (PSA) change, and assessment of phenotype and functionality of antigen-specific T cells.

RESULTS

The vaccine had an excellent safety profile. Vaccination-induced 5T4-specific T-cell responses were measured in blood by ex vivo IFN-γ ELISpot and were detected in the majority of patients with a mean level in responders of 198 spot-forming cells per million peripheral blood mononuclear cells. Flow cytometry analysis demonstrated the presence of both CD8+ and CD4+ polyfunctional 5T4-specific T cells in the circulation. 5T4-reactive tumor-infiltrating lymphocytes were isolated from post-treatment prostate tissue. Some of the patients had a transient PSA rise 2-8 weeks following vaccination, possibly indicating an inflammatory response in the target organ.

CONCLUSIONS

An excellent safety profile and T-cell responses elicited in the circulation and also detected in the prostate gland support the evaluation of the ChAdOx1-MVA 5T4 vaccine in efficacy trials. It remains to be seen if this vaccination strategy generates immune responses of sufficient magnitude to mediate clinical efficacy and whether it can be effective in late-stage PCa settings, as a monotherapy in advanced disease or as part of multi-modality PCa therapy. To address these questions, the phase I/II trial, ADVANCE, is currently recruiting patients with intermediate-risk PCa, and patients with advanced metastatic castration-resistant PCa, to receive this vaccine in combination with nivolumab.

TRIAL REGISTRATION

The trial was registered with the U.S. National Institutes of Health (NIH) Clinical Trials Registry (ClinicalTrials.gov identifier NCT02390063).

Opportunities for Conventional and in Situ Cancer Vaccine Strategies and Combination with Immunotherapy for Gastrointestinal Cancers, A Review

Survival of gastrointestinal cancer remains dismal, especially for metastasized disease. For various cancers, especially melanoma and lung cancer, immunotherapy has been proven to confer survival benefits, but results for gastrointestinal cancer have been disappointing. Hence, there is substantial interest in exploring the usefulness of adaptive immune system education with respect to anti-cancer responses though vaccination. Encouragingly, even fairly non-specific approaches to vaccination and immune system stimulation, involving for instance influenza vaccines, have shown promising results, eliciting hopes that selection of specific antigens for vaccination may prove useful for at least a subset of gastrointestinal cancers. It is widely recognized that immune recognition and initiation of responses are hampered by a lack of T cell help, or by suppressive cancer-associated factors. In this review we will discuss the hurdles that limit efficacy of conventional cancer therapeutic vaccination methods (e.g., peptide vaccines, dendritic cell vaccination). In addition, we will outline other forms of treatment (e.g., radiotherapy, chemotherapy, oncolytic viruses) that also cause the release of antigens through immunogenic tumor cell death and can thus be considered unconventional vaccination methods (i.e., in situ vaccination). Finally, we focus on the potential additive value that vaccination strategies may have for improving the effect immunotherapy. Overall, a picture will emerge that although the field has made substantial progress, successful immunotherapy through the combination with cancer antigen vaccination, including that for gastrointestinal cancers, is still in its infancy, prompting further intensification of the research effort in this respect.

Immunotherapy: Newer Therapeutic Armamentarium against Cancer Stem Cells

Mounting evidence from the literature suggests the existence of a subpopulation of cancer stem cells (CSCs) in almost all types of human cancers. These CSCs possessing a self-renewal capacity inhabit primary tumors and are more defiant to standard antimitotic and molecularly targeted therapies which are used for eliminating actively proliferating and differentiated cancer cells. Clinical relevance of CSCs emerges from the fact that they are the root cause of therapy resistance, relapse, and metastasis. Earlier, surgery, chemotherapy, and radiotherapy were established as cancer treatment modalities, but recently, immunotherapy is also gaining importance in the management of various cancer patients, mostly those of the advanced stage. This review abridges potential off-target effects of inhibiting CSC self-renewal pathways on immune cells and some recent immunological studies specifically targeting CSCs on the basis of their antigen expression profile, even though molecular markers or antigens that have been described till date as expressed by cancer stem cells are not specifically expressed by these cells which is a major limitation to target CSCs. We propose that owing to CSC stemness property to mediate immunotherapy response, we can apply a combination therapy approach by targeting CSCs and tumor microenvironment (TME) along with conventional treatment strategies as an effective means to eradicate cancer cells.

Immunological Complexity of the Prostate Cancer Microenvironment Influences the Response to Immunotherapy

Prostate cancer is one of the most common cancers in men and a leading cause of cancer-related death. Recent advances in the treatment of advanced prostate cancer, including the use of more potent and selective inhibitors of the androgen signaling pathway, have provided significant clinical benefit for men with metastatic castration-resistant prostate cancer (mCRPC). However, most patients develop progressive lethal disease, highlighting the need for more effective treatments. One such approach is immunotherapy, which harness the power of the patient's immune system to identify and destroy cancer cells through the activation of cytotoxic CD8 T cells specific for tumor antigens. Although immunotherapy, particularly checkpoint blockade, can induce significant clinical responses in patients with solid tumors or hematological malignancies, minimal efficacy has been observed in men with mCRPC. In the current review, we discuss our current understanding of the immunological complexity of the immunosuppressive prostate cancer microenvironment, preclinical models of prostate cancer, and recent advances in immunotherapy clinical trials to improve outcomes for men with mCRPC.

Phase II Trial of a DNA Vaccine Encoding Prostatic Acid Phosphatase (pTVG-HP [MVI-816]) in Patients With Progressive, Nonmetastatic, Castration-Sensitive Prostate Cancer

PURPOSE

We previously reported the safety and immunologic effects of a DNA vaccine (pTVG-HP [MVI-816]) encoding prostatic acid phosphatase (PAP) in patients with recurrent, nonmetastatic prostate cancer. The current trial evaluated the effects of this vaccine on metastatic progression.

PATIENTS AND METHODS

Ninety-nine patients with castration-sensitive prostate cancer and prostate-specific antigen (PSA) doubling time (DT) of less than 12 months were randomly assigned to treatment with either pTVG-HP co-administered intradermally with 200 μg granulocyte-macrophage colony-stimulating factor (GM-CSF) adjuvant or 200 μg GM-CSF alone six times at 14-day intervals and then quarterly for 2 years. The primary end point was 2-year metastasis-free survival (MFS). Secondary and exploratory end points were median MFS, changes in PSA DT, immunologic effects, and changes in quantitative ¹⁸F-sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) imaging.

RESULTS

Two-year MFS was not different between study arms (41.8% vaccine v 42.3%; P = .97). Changes in PSA DT and median MFS were not different between study arms (18.9 v 18.3 months; hazard ratio [HR], 1.6; P = .13). Preplanned subset analysis identified longer MFS in vaccine-treated patients with rapid (< 3 months) pretreatment PSA DT (12.0 v 6.1 months; n = 21; HR, 4.4; P = .03). PAP-specific T cells were detected in both cohorts, including multifunctional PAP-specific T-helper 1-biased T cells. Changes in total activity (total standardized uptake value) on ¹⁸F-NaF PET/CT from months 3 to 6 increased 50% in patients treated with GM-CSF alone and decreased 23% in patients treated with pTVG-HP (n = 31; P = .07).

CONCLUSION

pTVG-HP treatment did not demonstrate an overall increase in 2-year MFS in patients with castration-sensitive prostate cancer, with the possible exception of a subgroup with rapidly progressive disease. Prespecified ¹⁸F-NaF PET/CT imaging conducted in a subset of patients suggests that vaccination had detectable effects on micrometastatic bone disease. Additional trials using pTVG-HP in combination with PD-1 blockade are under way.

Past, Current, and Future of Immunotherapies for Prostate Cancer

Prostate cancer (PCa) is the most common cancer in men, and the second leading cause of cancer related death in men in Western countries. The standard therapy for metastatic PCa is androgen suppression therapy (AST). Men undergoing AST eventually develop metastatic castration-resistant prostate cancer (mCRPC), of which there are limited treatment options available. Immunotherapy has presented substantial benefits for many types of cancer, but only a marginal benefit for mCRPC, at least in part, due to the immunosuppressive tumor microenvironment (TME). Current clinical trials are investigating monotherapies or combination therapies involving adoptive cellular therapy, viral, DNA vaccines, oncolytic viruses, and immune checkpoint inhibitors (ICI). Immunotherapies are also being combined with chemotherapy, radiation, and AST. Additionally, preclinical investigations show promise with the recent description of alternative ways to circumvent the immunosuppressive nature of the prostate tumor microenvironment, including harnessing the immune stimulatory NKG2D pathway, inhibiting myeloid derived suppressor cells, and utilizing immunomodulatory oncolytic viruses. Herein we provide an overview of recent preclinical and clinical developments in cancer immunotherapies and discuss the perspectives for future immunotherapies in PCa.

Immune-based therapies for metastatic prostate cancer: an update

Prostate cancer (PC) is a common malignancy among elderly males and is noncurable once it becomes metastatic. In recent years, a number of antigen-delivery systems have emerged as viable and promising immunotherapeutic agents against PC. The approval of sipuleucel-T by the US FDA for the treatment of males with asymptomatic or minimally symptomatic castrate resistant PC was a landmark in cancer immunotherapy, making this the first approved immunotherapeutic. A number of vaccines are under clinical investigation, each having its own set of advantages and disadvantages. Here, we discuss the basic technologies underlying these different delivery modes, we discuss the completed and current human clinical trials, as well as the use of vaccines in combination with immune checkpoint inhibitors.

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.

Cytolytic Perforin as an Adjuvant to Enhance the Immunogenicity of DNA Vaccines

DNA vaccines present one of the most cost-effective platforms to develop global vaccines, which have been tested for nearly three decades in preclinical and clinical settings with some success in the clinic. However, one of the major challenges for the development of DNA vaccines is their poor immunogenicity in humans, which has led to refinements in DNA delivery, dosage in prime/boost regimens and the inclusion of adjuvants to enhance their immunogenicity. In this review, we focus on adjuvants that can enhance the immunogenicity of DNA encoded antigens and highlight the development of a novel cytolytic DNA platform encoding a truncated mouse perforin. The application of this innovative DNA technology has considerable potential in the development of effective vaccines.

Prostate cancer: updates on current strategies for screening, diagnosis and clinical implications of treatment modalities

Prostate cancer is the most common cancer in men by way of diagnosis and a leading cause of cancer-related deaths. Early detection and intervention remains key to its optimum clinical management. This review provides the most updated information on the recent methods of prostate cancer screening, imaging and treatment modalities. Wherever possible, clinical trial data has been supplemented to provide a comprehensive overview of current prostate cancer research and development. Considering the recent success of immunotherapy in prostate cancer, we discuss cell, DNA and viruses based, as well as combinatorial immunotherapeutic strategies in detail. Furthermore, the potential of nanotechnology is increasingly being realized, especially in prostate cancer research, and we provide an overview of nanotechnology-based strategies, with special emphasis on nanotheranostics and multifunctional nanoconstructs. Understanding these recent developments is critical to the design of future therapeutic strategies to counter prostate cancer.

Autophagosome-based strategy to monitor apparent tumor-specific CD8 T cells in patients with prostate cancer

The immune system plays an essential role in eradicating cancer in concert with various treatment modalities. In the absence of autologous tumor material, no standardized method exists to assess T cell responses against the many antigens that may serve as cancer rejection antigens. Thus, development of methods to screen for therapy-induced anti-tumor responses is a high priority that could help tailor therapy. Here we tested whether a tumor-derived antigen source called DRibbles®, which contain a pool of defective ribosomal products (DRiPs), long-lived and short-lived proteins (SLiPs) and danger-associated molecular patterns (DAMPs), can be used to identify tumor-associated antigen (TAA)-specific responses in patients before or after immunotherapy treatment. Protein content, gene expression and non-synonymous - single nucleotide variants (ns-SNVs) present in UbiLT3 DRibbles were compared with prostate adenocarcinomas and the prostate GVAX vaccine cell lines (PC3/LNCaP). UbiLT3 DRibbles were found to share proteins, as well as match tumor sequences for ns-SNVs with prostate adenocarcinomas and with the cell lines PC3 and LNCaP. UbiLT3 DRibbles were used to monitor anti-tumor responses in patients vaccinated with allogeneic prostate GVAX. UbiLT3-DRibble-reactive CD8+ T-cell responses were detected in post-vaccine PBMC of 6/12 patients (range 0.85-22% of CD8+ cells) after 1 week in vitro stimulation (p = 0.007 vs. pre-vaccine). In conclusion, a cancer-derived autophagosome-enriched preparation, packaging over 100 proteins over-expressed in prostate cancer into microvesicles containing DAMPs, could be used to identify CD8+ T cells in peripheral blood from patients after prostate GVAX vaccination and may represent a general method to monitor anti-cancer T cell responses following immunotherapy.

Therapeutic Cancer Vaccines: How Much Closer Are We?

The promise of immune-based therapies to treat cancer has been realized over the last several years with several breakthrough therapies, including T-cell checkpoint inhibitors and chimeric antigen receptor (CAR)-T cell therapies. While cancer vaccines have been investigated for many decades, to date only one has been approved in the USA as a treatment for existing cancer. The failure of several anti-tumor vaccines in large phase III trials has led many to question their future role in cancer treatment. Trials to date have demonstrated that many cancer vaccines can elicit tumor-specific T cells, but these T cells may be insufficient to mediate substantial anti-tumor effects without concurrent blockade of tumor-resistance mechanisms. Emerging data from preclinical models and clinical trials demonstrate that cancer vaccines have greater activity in low-volume disease and in combination with other immune-modulating therapies, including T-cell checkpoint blockade, targeting these resistance mechanisms. Because T-cell checkpoint therapies likely require the presence or activity of tumor-specific T cells, cancer vaccines may be optimal agents to use in combination to enable these therapies to work for greater numbers of patients. Future trials will explore optimal vaccine approaches and antigens that work best in combination treatment approaches and in earlier stages of disease.