Prostate cancer cells synergistically defend against CD8+ T cells by secreting exosomal PD-L1

Role of exosomes in castration-resistant prostate cancer

Prostate cancer (PCa) is one of the most common urological malignancies in older male patients. Castration-resistant prostate cancer (CRPC) is an aggressive and refractory stage of PCa and is the leading cause of PCa-related deaths. Exosomes are small spherical vesicles with a lipid bilayer membrane structure, secreted by cells, which carry large amounts of nucleic acids, proteins, lipids, and various important reactive small molecules. Numerous studies have demonstrated that exosomes are involved in the development of CRPC by delivering various biomolecules that regulate biological processes in recipient cells. Despite the advancement in treatments, CRPC remains poorly managed, underscoring the urgent need for novel treatment strategies.As research into exosomes continues, they have shown significant potential in the diagnosis and treatment of CRPC.Unlike previous reviews,this review not only provides an overview of exosomes but also comprehensively explores their role in the CRPC tumor microenvironment, angiogenesis, immune escape, metastasis, and drug resistance, with a focus on the potential value of exosomes in the diagnosis and treatment of CRPC.The literature review includes studies published up to June 2024, and the search strategy involved exosomes, CRPC, diagnosis,and treatment using Pubmed.

Bolstering CD8+ T Cells' Antitumor Immunity: A Promising Strategy to Improve the Response to Advanced Prostate Cancer Treatment

Prostate cancer is among the most frequently diagnosed and deadly cancers among men in the Western world. It is typically classified as an immune "cold" tumor due to its sparse immune cell presence and limited immunogenic response. Recent research has revealed the significant role of immune cells, especially CD8+ T cells, in both prostate cancer progression and treatment efficacy. This review integrates recent findings to provide a comprehensive overview of the current understanding of CD8+ T cell dynamics in prostate cancer and discusses emerging strategies to improve treatment outcomes. The ongoing exploration of new molecular targets and the development of innovative immunotherapeutic approaches hold promise for more effective management of prostate cancer, particularly in the context of advanced and resistant forms of the disease.

Small extracellular vesicles: crucial mediators for prostate cancer

Small extracellular vesicles (sEVs) play a critical role in the progression, diagnosis, and treatment of prostate cancer (PCa), particularly within the tumor microenvironment (TME). Acting as novel biomarkers and agents for targeted biological therapy, sEVs contribute significantly to improving patient survival. These vesicles transport a variety of biomolecules, including proteins, nucleic acids, and lipids, which are instrumental in remodeling the TME, facilitating intercellular communication, and influencing key processes such as tumor growth, metastasis, and therapy resistance. A thorough understanding of sEV heterogeneity, including their biogenesis, characteristics, and potential applications, is essential. Recent advances have illuminated the origins, formation processes, and molecular cargo of PCa-derived sEVs (PCa-sEVs), enhancing our understanding of their role in disease progression. Furthermore, sEVs show promise as diagnostic markers, with potential applications in early detection and prognostic assessment in PCa. Therapeutically, natural and engineered sEVs offer versatile applications, including drug delivery, gene therapy, and immunomodulation, underscoring their potential in PCa management. This review delves into the substantial potential of sEVs in clinical practices for PCa.

Establishing a Prognostic Model Correlates to Inflammatory Response Pathways for Prostate Cancer via Multiomic Analysis of Lactylation-Related Genes

Prostate cancer (PCa) continues to pose substantial clinical challenges, with molecular heterogeneity significantly impacting therapeutic decision-making and disease trajectories. Emerging evidence implicates protein lactylation-a novel epigenetic regulatory mechanism-in oncogenic processes, though its prognostic relevance in PCa remains underexplored. Through integrative bioinformatics interrogation of lactylation-associated molecular signatures, we established prognostic correlations using multivariable feature selection methodologies. Initial screening via differential expression analysis (limma package) coupled with Cox proportional hazards modeling revealed 11 survival-favorable regulators and 16 hazard-associated elements significantly linked to biochemical recurrence. To enhance predictive precision, ensemble machine learning frameworks were implemented, culminating in a 10-gene lactylation signature demonstrating robust discriminative capacity (concordance index = 0.738) across both primary (TCGA-PRAD) and external validation cohorts (DKFZ). Multivariable regression confirmed the lactylation score's prognostic independence, exhibiting prominent associations with clinicopathological parameters including tumor staging and metastatic potential. The developed clinical-molecular nomogram achieved superior predictive accuracy (C - index > 0.7) through the synergistic integration of biological and clinical covariates. Tumor microenvironment deconvolution uncovered distinct immunological landscapes, with high-risk stratification correlating with enriched stromal infiltration and immunosuppressive phenotypes. Pathway enrichment analyses implicated chromatin remodeling processes and cytokine-mediated inflammatory cascades as potential mechanistic drivers of prognostic divergence. Therapeutic vulnerability profiling demonstrated differential response patterns: low-risk patients exhibited enhanced immune checkpoint inhibitor responsiveness, whereas high-risk subgroups showed selective chemosensitivity to docetaxel and mitoxantrone. Functional validation in PC-3 models revealed AK5 silencing induced proapoptotic effects, suppressed metastatic potential of migration and invasion, and modulated immune checkpoint regulation through CD276 coexpression. These multimodal findings position lactylation dynamics, particularly AK5-mediated pathways, as promising therapeutic targets and stratification biomarkers in PCa management.

Extracellular vesicles in tumor immunity: mechanisms and novel insights

Extracellular vesicles (EVs), nanoscale vesicles secreted by cells, have attracted considerable attention in recent years due to their role in tumor immunomodulation. These vesicles facilitate intercellular communication by transporting proteins, nucleic acids, and other biologically active substances, and they exhibit a dual role in tumor development and immune evasion mechanisms. Specifically, EVs can assist tumor cells in evading immune surveillance and attack by impairing immune cell function or modulating immunosuppressive pathways, thereby promoting tumor progression and metastasis. Conversely, they can also transport and release immunomodulatory factors that stimulate the activation and regulation of the immune system, enhancing the body's capacity to combat malignant diseases. This dual functionality of EVs presents promising avenues and targets for tumor immunotherapy. By examining the biological characteristics of EVs and their influence on tumor immunity, novel therapeutic strategies can be developed to improve the efficacy and relevance of cancer treatment. This review delineates the complex role of EVs in tumor immunomodulation and explores their potential implications for cancer therapeutic approaches, aiming to establish a theoretical foundation and provide practical insights for the advancement of future EVs-based cancer immunotherapy strategies.

Exosomes: Key Messengers Mediating the Interaction Between Tumor Cells and CD8+ T Cells in the Tumor Microenvironment

In recent years, with an increasingly profound comprehension of the tumor microenvironment, it has been discovered that the constituent cells within the immune microenvironment, such as macrophages, CD4+T cells, and CD8+T cells, interact with tumor cells in manners conducive to tumorigenesis and progression. Exosomes play a pivotal role as essential mediators for intercellular material exchange and signal transmission in this context. Tumor cell-derived exosomes carrying cargo such as PD-L1 and ncRNAs engage with CD8+T cells to induce cytotoxic responses and facilitate immune evasion, thereby promoting tumor advancement. When combined with current immune checkpoint inhibitors like anti-PD-L1/PD-1 therapy, enhancing CD8+T cell function through exosomal pathways while monitoring and augmenting therapeutic effects can significantly improve efficacy. This review delineates the crucial role of exosomes derived from both tumor cells and CD8+T cells within the tumor microenvironment along with their impact mechanisms on both tumor cells and CD8+T cells. Furthermore, it summarizes the potential for clinical treatment in this realm when integrated with existing immunotherapy methods-particularly exploring the feasibility of clinical translation alongside engineering materials science techniques.

Characterisation of Castration-Resistant Cell-Derived Exosomes and Their Effect on the Metastatic Phenotype

BACKGROUND/OBJECTIVES

Prostate cancer (PCa) is characterised by its progression to a metastatic and castration-resistant phase. Prostate tumour cells release small extracellular vesicles or exosomes which are taken up by target cells and can potentially facilitate tumour growth and metastasis. The present work studies the effect of exosomes from cell lines that are representative of the different stages of the disease on the tumoral phenotype of PC3 cells.

METHODS

Exosomes were isolated by ultracentrifugation from human prostate epithelial cells (RWPE-1) and androgen-dependent PCa cells (LNCaP) and castration-resistant PCa cells (CRPC) with moderate (DU145) or high (PC3) metastatic capacity. The biophysical and biochemical properties of the exosomes were characterised as well as their effects on PC3 cell viability and migration.

RESULTS

The study of the exosomes of prostate cell lines shows heterogeneity in their size, presenting in some of them two types of populations; in both populations, a larger size in those derived from PC3 cells and a smaller size in those derived from non-tumourigenic prostate cells were detected. Differences were found in the physical properties of those derived from healthy and PCa cells, as well as between cells representative of the most aggressive stages of the disease. The highest gamma-glutamyl transferase (GGT) activity was observed in androgen-dependent cells and differences in the pro-metalloproteinases (MMP) activity were detected in healthy cells and in castration-resistant cells with moderate metastatic capacity with respect to PC3 cells. The treatment of PC3 cells with their own exosomes increased PC3 cell viability and migration.

CONCLUSION

Exosomes represent a promising field of research in the diagnosis, prognosis, and treatment of prostate cancer.

Exosome-Derived Cargos in Immune Microenvironment in Esophageal Carcinoma: A Mini-Review

Esophageal carcinoma, a lethal malignancy with limited treatment options and poor prognosis, necessitates understanding its underlying mechanisms and identifying novel therapeutic targets. Recent studies have highlighted the critical role of the immune microenvironment in esophageal carcinoma, particularly the interplay between tumor cells and immune cells mediated by exosomes and their cargos. Exosomes, small extracellular vesicles secreted by various cells, including tumor cells, facilitate intercellular communication by transferring bioactive molecules such as proteins, nucleic acids, and lipids to recipient cells. In the context of esophageal carcinoma, tumor-derived exosomes have been shown to play a significant role in shaping the immune microenvironment. In esophageal carcinoma, exosomal cargos have been found to modulate immune cell function and impact tumor progression. These cargos can carry immune inhibitory molecules, such as programmed death-ligand 1 (PD-L1), to suppress T-cell activity and promote immune evasion by tumor cells. Furthermore, exosomal cargos can activate antigen- presenting cells, enhancing their ability to present tumor-specific antigens to T cells and thereby promoting anti-tumor immune responses. Additionally, the cargos of exosomes have been implicated in the induction of immune regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) within the esophageal carcinoma microenvironment. These immunosuppressive effectors inhibit the activity of T cells, contributing to tumor immune evasion and resistance to immune therapies. In summary, exosomes and their cargo play a crucial role in the immune microenvironment of esophageal carcinoma. Understanding the mechanisms by which exosomal cargos regulate immune cell function and tumor progression may reveal novel therapeutic targets for this devastating disease.

Exosomes are the mediators between the tumor microenvironment and prostate cancer (Review)

Prostate cancer poses a serious threat to the well-being of men worldwide, with the leading cause of mortality being primarily through metastasis. Prostate cancer metastasis is dependent on cell communication, which is an essential component of this process; yet its exact mechanism remains obscure. Nonetheless, cell-to-cell communication plays a critical part in prostate cancer metastasis. Exosomes play an indispensable role in the development of metastatic growth by promoting intercellular communication. They are pivotal regulatory agents for both prostate cancer cells as well as their microenvironment. The present study investigated the makeup and function of exosomes in the tumor microenvironment, highlighting their significance to prostate cancer metastasis.

The biological function of extracellular vesicles in prostate cancer and their clinical application as diagnostic and prognostic biomarkers

Prostate cancer (PCa) is one of the most commonly diagnosed malignancies and main causes of cancer-related deaths worldwide. It is characterized by high heterogeneity, ranging from slow-growing tumor to metastatic disease. Since both therapy selection and outcome strongly rely on appropriate patient stratification, it is crucial to differentiate benign from more aggressive conditions using new and improved diagnostic and prognostic biomarkers. Extracellular vesicles (EVs) are membrane-coated particles carrying a specific biological cargo composed of nucleic acids, proteins, and metabolites. Here, we provide an overview of the role of EVs in PCa, focusing on both their biological function and clinical value. Specifically, we summarize the oncogenic role of EVs in mediating the interactions with PCa microenvironment as well as the horizontal transfer of metastatic traits and drug resistance between PCa cells. Furthermore, we discuss the potential usage of EVs as innovative tools for PCa diagnosis and prognosis.

Influencing immunity: role of extracellular vesicles in tumor immune checkpoint dynamics

Immune checkpoint proteins (ICPs) serve as critical regulators of the immune system, ensuring protection against damage due to overly activated immune responses. However, within the tumor environment, excessive ICP activation weakens antitumor immunity. Despite the development of numerous immune checkpoint blockade (ICB) drugs in recent years, their broad application has been inhibited by uncertainties about their clinical efficacy. A thorough understanding of ICP regulation in the tumor microenvironment is essential for advancing the development of more effective and safer ICB therapies. Extracellular vesicles (EVs), which are pivotal mediators of cell-cell communication, have been extensively studied and found to play key roles in the functionality of ICPs. Nonetheless, a comprehensive review summarizing the current knowledge about the crosstalk between EVs and ICPs in the tumor environment is lacking. In this review, we summarize the interactions between EVs and several widely studied ICPs as well as their potential clinical implications, providing a theoretical basis for further investigation of EV-related ICB therapeutic approaches.

Role of tumor-derived exosomes mediated immune cell reprograming in cancer

Tumor-derived exosomes (TDEs), as topologies of tumor cells, not only carry biological information from the mother, but also act as messengers for cellular communication. It has been demonstrated that TDEs play a key role in inducing an immunosuppressive tumor microenvironment (TME). They can reprogram immune cells indirectly or directly by delivering inhibitory proteins, cytokines, RNA and other substances. They not only inhibit the maturation and function of dendritic cells (DCs) and natural killer (NK) cells, but also remodel M2 macrophages and inhibit T cell infiltration to promote immunosuppression and create a favorable ecological niche for tumor growth, invasion and metastasis. Based on the specificity of TDEs, targeting TDEs has become a new strategy to monitor tumor progression and enhance treatment efficacy. This paper reviews the intricate molecular mechanisms underlying the immunosuppressive effects induced by TDEs to establish a theoretical foundation for cancer therapy. Additionally, the challenges of TDEs as a novel approach to tumor treatment are discussed.

Tumor Microenvironment-Derived Exosomes: A Double-Edged Sword for Advanced T Cell-Based Immunotherapy

The tumor microenvironment (TME) plays a crucial role in cancer progression and immune evasion, partially mediated by the activity of the TME-derived exosomes. These extracellular vesicles are pivotal in shaping immune responses through the transfer of proteins, lipids, and nucleic acids between cells, facilitating a complex interplay that promotes tumor growth and metastasis. This review delves into the dual roles of exosomes in the TME, highlighting both their immunosuppressive functions and their emerging therapeutic potential. Exosomes can inhibit T cell function and promote tumor immune escape by carrying immune-modulatory molecules, such as PD-L1, yet they also hold promise for cancer therapy as vehicles for delivering tumor antigens and costimulatory signals. Additionally, the review discusses the intricate crosstalk mediated by exosomes among various cell types within the TME, influencing both cancer progression and responses to immunotherapies. Moreover, this highlights current challenges and future directions. Collectively, elucidating the detailed mechanisms by which TME-derived exosomes mediate T cell function offers a promising avenue for revolutionizing cancer treatment. Understanding these interactions allows for the development of targeted therapies that manipulate exosomal pathways to enhance the immune system's response to tumors.

The Role of Extracellular Vesicles in the Treatment of Prostate Cancer

Prostate cancer (PCa) has become a public health concern in elderly men due to an ever-increasing number of estimated cases. Unfortunately, the available treatments are unsatisfactory because of a lack of a durable response, especially in advanced disease states. Extracellular vesicles (EVs) are lipid-bilayer encircled nanoscale vesicles that carry numerous biomolecules (e.g., nucleic acids, proteins, and lipids), mediating the transfer of information. The past decade has witnessed a wide range of EV applications in both diagnostics and therapeutics. First, EV-based non-invasive liquid biopsies provide biomarkers in various clinical scenarios to guide treatment; EVs can facilitate the grading and staging of patients for appropriate treatment selection. Second, EVs play a pivotal role in pathophysiological processes via intercellular communication. Targeting key molecules involved in EV-mediated tumor progression (e.g., proliferation, angiogenesis, metastasis, immune escape, and drug resistance) is a potential approach for curbing PCa. Third, EVs are promising drug carriers. Naïve EVs from various sources and engineered EV-based drug delivery systems have paved the way for the development of new treatment modalities. This review discusses the recent advancements in the application of EV therapies and highlights EV-based functional materials as novel interventions for PCa.

Shedding Light on the Role of Exosomal PD-L1 (ExoPD-L1) in Cancer Progression: an Update

Exosomes are the primary category of extracellular vesicles (EVs), which are lipid-bilayer vesicles with biological activity spontaneously secreted from either normal or tansformed cells. They serve a crucial role for intercellular communication and affect extracellular environment and the immune system. Tumor-derived exosomes (TEXs) enclose high levels of immunosuppressive proteins, including programmed death-ligand 1 (PD-L1). PD-L1 and its receptor PD-1 act as crucial immune checkpoint molecules, thus facilitating tumor advancement by inhibiting immune responses. PDL-1 is abundantly present on tumor cells and interacts with PD-1 on activated T cells, resulting in T cell suppression and allowing immune evasion of cancer cells. Various FDA-approved monoclonal antibodies inhibiting the PD-1/PD-L1 interaction are commonly used to treat a diverse range of tumors. Although the achieved results are significant, some individuals have a poor reaction to PD-1/PD-L1 blocking. PD-L1-enriched TEXs may mimic the impact of cell-surface PD-L1, consequently potentiating tumor resistance to PD1/PD-L1 based therapy. In light of this, a strong correlation between circulating exosomal PD-L1 levels and response rate to anti-PD-1/PD-L1 antibody treatment has been evinced. This article inspects the function of exosomal PDL-1 in developing resistance to anti-PD-1/PD-L1 therapy for opening new avenues for overcoming tumor resistance to such modalities and development of more favored combination therapy.

Targeting IL-8 and Its Receptors in Prostate Cancer: Inflammation, Stress Response, and Treatment Resistance

This review delves into the intricate roles of interleukin-8 (IL-8) and its receptors, CXCR1 and CXCR2, in prostate cancer (PCa), particularly in castration-resistant (CRPC) and metastatic CRPC (mCRPC). This review emphasizes the crucial role of the tumour microenvironment (TME) and inflammatory cytokines in promoting tumour progression and response to tumour cell targeting agents. IL-8, acting through C-X-C chemokine receptor type 1 (CXCR1) and type 2 (CXCR2), modulates multiple signalling pathways, enhancing the angiogenesis, proliferation, and migration of cancer cells. This review highlights the shift in PCa research focus from solely tumour cells to the non-cancer-cell components, including vascular endothelial cells, the extracellular matrix, immune cells, and the dynamic interactions within the TME. The immunosuppressive nature of the PCa TME significantly influences tumour progression and resistance to emerging therapies. Current treatment modalities, including androgen deprivation therapy and chemotherapeutics, encounter persistent resistance and are complicated by prostate cancer's notably "immune-cold" nature, which limits immune system response to the tumour. These challenges underscore the critical need for novel approaches that both overcome resistance and enhance immune engagement within the TME. The therapeutic potential of inhibiting IL-8 signalling is explored, with studies showing enhanced sensitivity of PCa cells to treatments, including radiation and androgen receptor inhibitors. Clinical trials, such as the ACE trial, demonstrate the efficacy of combining CXCR2 inhibitors with existing treatments, offering significant benefits, especially for patients with resistant PCa. This review also addresses the challenges in targeting cytokines and chemokines, noting the complexity of the TME and the need for precision in therapeutic targeting to avoid side effects and optimize outcomes.

The correlation between TRIM28 expression and immune checkpoints in CRPC

This study delves into the unexplored realm of castration-resistant prostate cancer (CRPC) by investigating the role of TRIM28 and its intricate molecular mechanisms using high-throughput single-cell transcriptome sequencing and advanced bioinformatics analysis. Our comprehensive examination unveiled dynamic TRIM28 expression changes, particularly in immune cells such as macrophages and CD8+ T cells within CRPC. Correlation analyses with TCGA data highlighted the connection between TRIM28 and immune checkpoint expression and emphasized its pivotal influence on the quantity and functionality of immune cells. Using TRIM28 knockout mouse models, we identified differentially expressed genes and enriched pathways, unraveling the potential regulatory involvement of TRIM28 in the cGAS-STING pathway. In vitro, experiments further illuminated that TRIM28 knockout in prostate cancer cells induced a notable anti-tumor immune effect by inhibiting M2 macrophage polarization and enhancing CD8+ T cell activity. This impactful discovery was validated in an in situ transplant tumor model, where TRIM28 knockout exhibited a deceleration in tumor growth, reduced proportions of M2 macrophages, and enhanced infiltration of CD8+ T cells. In summary, this study elucidates the hitherto unknown anti-tumor immune role of TRIM28 in CRPC and unravels its potential regulatory mechanism via the cGAS-STING signaling pathway. These findings provide novel insights into the immune landscape of CRPC, offering promising directions for developing innovative therapeutic strategies.

Role of extracellular vesicles in castration-resistant prostate cancer

Prostate cancer (PCa) is a common health threat to men worldwide, and castration-resistant PCa (CRPC) is the leading cause of PCa-related deaths. Extracellular vesicles (EVs) are lipid bilayer compartments secreted by living cells that are important mediators of intercellular communication. EVs regulate the biological processes of recipient cells by transmitting heterogeneous cargoes, contributing to CRPC occurrence, progression, and drug resistance. These EVs originate not only from malignant cells, but also from various cell types within the tumor microenvironment. EVs are widely dispersed throughout diverse biological fluids and are attractive biomarkers derived from noninvasive liquid biopsy techniques. EV quantities and cargoes have been tested as potential biomarkers for CRPC diagnosis, progression, drug resistance, and prognosis; however, technical barriers to their clinical application continue to exist. Furthermore, exogenous EVs may provide tools for new therapies for CRPC. This review summarizes the current evidence on the role of EVs in CRPC.

Extracellular vesicles and prostate cancer management: a narrative review

Background and Objective

Prostate cancer (PCa) is the second most common male cancer in the United States. Although new drugs have recently been approved, clinical challenges remain, notably the precise detection and prognostic implications of drug-resistant PCa. Extracellular vesicles (EVs), nanoscale lipid membrane vesicles, are actively secreted into the extracellular milieu by a variety of cell types. Over the past decade, interest in EVs has grown, and emerging evidence suggests that EVs play pivotal roles in cancer biology. In this review, we would like to summarize recent reports on EVs in PCa and discuss the potential clinical applications.

Methods

We performed a non-systematic literature review using the PubMed database to identify articles specifically related to EVs and PCa management.

Key Content and Findings

EVs contain pathogenic components, such as proteins, DNA fragments, mRNA, non-coding RNA, and lipids, all of which can trigger intercellular signaling within tumor microenvironments. Thereby, EVs exert significant effects on several stages of cancer progression, influencing the immune system, angiogenesis, and the establishment of pre-metastatic niches. Furthermore, as EVs are encapsulated, their contents are stable in bodily fluids, and thus EVs have recently attracted attention as a novel kind of liquid biopsy.

Conclusions

We have summarized recent research on how EVs may aid PCa management. To date, we have discovered only the tip of the iceberg. We anticipate that further research will yield innovative therapeutic modalities, thereby aiding all PCa patients.

TLR9 Monotherapy in Immune-Competent Mice Suppresses Orthotopic Prostate Tumor Development

Prostate cancer is ranked second in the world for cancer-related deaths in men, highlighting the lack of effective therapies for advanced-stage disease. Toll-like receptors (TLRs) and immunity have a direct role in prostate cancer pathogenesis, but TLR9 has been reported to contribute to both the progression and inhibition of prostate tumorigenesis. To further understand this apparent disparity, we have investigated the effect of TLR9 stimulation on prostate cancer progression in an immune-competent, syngeneic orthotopic mouse model of prostate cancer. Here, we utilized the class B synthetic agonist CPG-1668 to provoke a TLR9-mediated systemic immune response and demonstrate a significant impairment of prostate tumorigenesis. Untreated tumors contained a high abundance of immune-cell infiltrates. However, pharmacological activation of TLR9 resulted in smaller tumors containing significantly fewer M1 macrophages and T cells. TLR9 stimulation of tumor cells in vitro had no effect on cell viability or its downstream transcriptional targets, whereas stimulation in macrophages suppressed cancer cell growth via type I IFN. This suggests that the antitumorigenic effects of CPG-1668 were predominantly mediated by an antitumor immune response. This study demonstrated that systemic TLR9 stimulation negatively regulates prostate cancer tumorigenesis and highlights TLR9 agonists as a useful therapeutic for the treatment of prostate cancer.