Prime/boost immunotherapy of HPV16-induced tumors with E7 protein delivered by Bordetella adenylate cyclase and modified vaccinia virus Ankara

Delivery of Mycobacterium tuberculosis epitopes by Bordetella pertussis adenylate cyclase toxoid expands HLA-E-restricted cytotoxic CD8+ T cells

Introduction

Tuberculosis (TB) remains the first cause of death from infection caused by a bacterial pathogen. Chemotherapy does not eradicate Mycobacterium tuberculosis (Mtb) from human lungs, and the pathogen causes a latent tuberculosis infection that cannot be prevented by the currently available Bacille Calmette Guerin (BCG) vaccine, which is ineffective in the prevention of pulmonary TB in adults. HLA-E-restricted CD8+ T lymphocytes are essential players in protective immune responses against Mtb. Hence, expanding this population in vivo or ex vivo may be crucial for vaccination or immunotherapy against TB.

Methods

The enzymatically inactive Bordetella pertussis adenylate cyclase (CyaA) toxoid is an effective tool for delivering peptide epitopes into the cytosol of antigen-presenting cells (APC) for presentation and stimulation of specific CD8+ T-cell responses. In this study, we have investigated the capacity of the CyaA toxoid to deliver Mtb epitopes known to bind HLA-E for the expansion of human CD8+ T cells in vitro.

Results

Our results show that the CyaA-toxoid containing five HLA-E-restricted Mtb epitopes causes significant expansion of HLA-E-restricted antigen-specific CD8+ T cells, which produce IFN-γ and exert significant cytotoxic activity towards peptide-pulsed macrophages.

Discussion

HLA-E represents a promising platform for the development of new vaccines; our study indicates that the CyaA construct represents a suitable delivery system of the HLA-E-binding Mtb epitopes for ex vivo and in vitro expansion of HLA-E-restricted CD8+ T cells inducing a predominant Tc1 cytokine profile with a significant increase of IFN-γ production, for prophylactic and immunotherapeutic applications against Mtb.

Immunotherapy for HPV Malignancies

Owing to the presence of known tumor-specific viral antigens, human papillomavirus (HPV)-associated cancers are well suited for treatment with immunotherapy designed to unleash, amplify or replace the T cell arm of the adaptive immune system. Immune checkpoint blockade designed to unleash existing T cell immunity is currently Food and Drug Administration approved for certain HPV-associated cancers. More specific immunotherapies such as therapeutic vaccines and T cell receptor-engineered cellular therapy are currently in clinical development. Such therapies may offer more specific immune activation against viral tumor antigens and decrease the risk of immune-related adverse events. Current and planned clinical study of these treatments will determine their utility in the treatment of patients with newly diagnosed advanced stage or relapsed HPV-associated cancer.

Prime-boost therapeutic vaccination in mice with DNA/DNA or DNA/Fowlpox virus recombinants expressing the Human Papilloma Virus type 16 E6 and E7 mutated proteins fused to the coat protein of Potato virus X

The therapeutic antitumor potency of a prime-boost vaccination strategy was explored, based on the mutated, nontransforming forms of the E6 (E6_F47R) and E7 (E7_GGG) oncogenes of Human Papilloma Virus type 16 (HPV16), fused to the Potato virus X (PVX) coat protein (CP) sequence. Previous data showed that CP fusion improves the immunogenicity of tumor-associated antigens and may thus increase their efficacy. After verifying the correct expression of E6_F47RCP and E7_GGGCP inserted into DNA and Fowlpox virus recombinants by Western blotting and immunofluorescence, their combined use was evaluated for therapy in a pre-clinical mouse model of HPV16-related tumorigenicity. Immunization protocols were applied using homologous (DNA/DNA) or heterologous (DNA/Fowlpox) prime-boost vaccine regimens. The humoral immune responses were determined by ELISA, and the therapeutic efficacy evaluated by the delay in tumor appearance and reduced tumor volume after inoculation of syngeneic TC-1* tumor cells. Homologous DNA/DNA genetic vaccines were able to better delay tumor appearance and inhibit tumor growth when DNAE6_F47RCP and DNAE7_GGGCP were administered in combination. However, the heterologous DNA/Fowlpox vaccination strategy was able to delay tumor appearance in a higher number of animals when E6_F47RCP and in particular E7_GGGCP were administered alone.

Current state in the development of candidate therapeutic HPV vaccines

The identification of human papillomavirus (HPV) as an etiological factor for HPV-associated malignancies creates the opportunity to control these cancers through vaccination. Currently, available preventive HPV vaccines have not yet demonstrated strong evidences for therapeutic effects against established HPV infections and lesions. Furthermore, HPV infections remain extremely common. Thus, there is urgent need for therapeutic vaccines to treat existing HPV infections and HPV-associated diseases. Therapeutic vaccines differ from preventive vaccines in that they are aimed at generating cell-mediated immunity rather than neutralizing antibodies. The HPV-encoded early proteins, especially oncoproteins E6 and E7, form ideal targets for therapeutic HPV vaccines since they are consistently expressed in HPV-associated malignancies and precancerous lesions, playing crucial roles in the generation and maintenance of HPV-associated disease. Our review will cover various therapeutic vaccines in development for the treatment of HPV-associated lesions and cancers. Furthermore, we review strategies to enhance vaccine efficacy and the latest clinical trials on therapeutic HPV vaccines.

Bordetella adenylate cyclase toxin: a unique combination of a pore-forming moiety with a cell-invading adenylate cyclase enzyme

The adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) is a key virulence factor of the whooping cough agent Bordetella pertussis. CyaA targets myeloid phagocytes expressing the complement receptor 3 (CR3, known as αMβ2 integrin CD11b/CD18 or Mac-1) and translocates by a poorly understood mechanism directly across the cytoplasmic membrane into cell cytosol of phagocytes an adenylyl cyclase(AC) enzyme. This binds intracellular calmodulin and catalyzes unregulated conversion of cytosolic ATP into cAMP. Among other effects, this yields activation of the tyrosine phosphatase SHP-1, BimEL accumulation and phagocyte apoptosis induction. In parallel, CyaA acts as a cytolysin that forms cation-selective pores in target membranes. Direct penetration of CyaA into the cytosol of professional antigen-presenting cells allows the use of an enzymatically inactive CyaA toxoid as a tool for delivery of passenger antigens into the cytosolic pathway of processing and MHC class I-restricted presentation, which can be exploited for induction of antigen-specific CD8(+) cytotoxic T-lymphocyte immune responses.

A prime/boost strategy using DNA/fowlpox recombinants expressing the genetically attenuated E6 protein as a putative vaccine against HPV-16-associated cancers

BACKGROUND

Considering the high number of new cases of cervical cancer each year that are caused by human papilloma viruses (HPVs), the development of an effective vaccine for prevention and therapy of HPV-associated cancers, and in particular against the high-risk HPV-16 genotype, remains a priority. Vaccines expressing the E6 and E7 proteins that are detectable in all HPV-positive pre-cancerous and cancer cells might support the treatment of HPV-related lesions and clear already established tumors.

METHODS

In this study, DNA and fowlpox virus recombinants expressing the E6F47R mutant of the HPV-16 E6 oncoprotein were generated, and their correct expression verified by RT-PCR, Western blotting and immunofluorescence. Immunization protocols were tested in a preventive or therapeutic pre-clinical mouse model of HPV-16 tumorigenicity using heterologous (DNA/FP) or homologous (DNA/DNA and FP/FP) prime/boost regimens. The immune responses and therapeutic efficacy were evaluated by ELISA, ELISPOT assays, and challenge with TC-1* cells.

RESULTS

In the preventive protocol, while an anti-E6-specific humoral response was just detectable, a specific CD8(+) cytotoxic T-cell response was elicited in immunized mice. After the challenge, there was a delay in cancer appearance and a significant reduction of tumor volume in the two groups of E6-immunized mice, thus confirming the pivotal role of the CD8(+) T-cell response in the control of tumor growth in the absence of E6-specific antibodies. In the therapeutic protocol, in-vivo experiments resulted in a higher number of tumor-free mice after the homologous DNA/DNA or heterologous DNA/FP immunization.

CONCLUSIONS

These data establish a preliminary indication for the prevention and treatment of HPV-related tumors by the use of DNA and avipox constructs as safe and effective immunogens following a prime/boost strategy. The combined use of recombinants expressing both E6 and E7 proteins might improve the antitumor efficacy, and should represent an important approach to control HPV-associated cancers.

Adenylate cyclase toxin-hemolysin relevance for pertussis vaccines

The adenylate cyclase toxin-hemolysin (ACT, AC-Hly or CyaA) is a key virulence factor of Bordetella pertussis. It targets bactericidal activities of phagocytes, such as oxidative burst and complement- or antibody-mediated opsonophagocytic killing of bacteria. Through cAMP signaling, CyaA also skews TLR-triggered maturation of dendritic cells, inhibiting proinflammatory IL-12 and TNF-α secretion and enhancing IL-10 production and Treg expansion, likely hampering induction of adaptive immune responses to Bordetella infections. Non-enzymatic CyaA toxoid is a potent protective antigen and adjuvant that boosts immunogenicity of co-administered B. pertussis antigens and improves potency of acellular pertussis (aP) vaccines in mice. This makes CyaA a prime antigen candidate for inclusion into a next generation of aP vaccines. Moreover, recombinant CyaA toxoids were recently shown to be safe in humans in frame of Phase I clinical evaluation of a CyaA-based immunotherapeutic vaccine that induces Th1-polarized CD8(+) cytotoxic T-lymphocyte responses targeting cervical tumors.

Trial Watch: Toll-like receptor agonists in oncological indications

Toll-like receptors (TLRs) are an evolutionarily conserved group of enzymatically inactive, single membrane-spanning proteins that recognize a wide panel of exogenous and endogenous danger signals. Besides constituting a crucial component of the innate immune response to bacterial and viral pathogens, TLRs appear to play a major role in anticancer immunosurveillance. In line with this notion, several natural and synthetic TLR ligands have been intensively investigated for their ability to boost tumor-targeting immune responses elicited by a variety of immunotherapeutic and chemotherapeutic interventions. Three of these agents are currently approved by the US Food and Drug Administration (FDA) or equivalent regulatory agencies for use in cancer patients: the so-called bacillus Calmette-Guérin, monophosphoryl lipid A, and imiquimod. However, the number of clinical trials testing the therapeutic potential of both FDA-approved and experimental TLR agonists in cancer patients is stably decreasing, suggesting that drug developers and oncologists are refocusing their interest on alternative immunostimulatory agents. Here, we summarize recent findings on the use of TLR agonists in cancer patients and discuss how the clinical evaluation of FDA-approved and experimental TLR ligands has evolved since the publication of our first Trial Watch dealing with this topic.

Chemokine binding protein vCCI attenuates vaccinia virus without affecting the cellular response elicited by immunization with a recombinant vaccinia vector carrying the HPV16 E7 gene

Viral CC chemokine inhibitor (vCCI) of the clone P13 vaccinia virus (VACV) strain PRAHA lacks eight amino acids in the signal peptide sequence. To study the influence of vCCI on virus biology, a virus with the vCCI gene coding for a prolonged signal sequence was prepared. We found that secreted vCCI attenuated the virus in vivo, and that it correlated with decreased levels of RANTES, eotaxin, TARC, and MDC in the blood in comparison with the parental virus. We determined the influence of vCCI on the CTL response against VACV E3((140-148)) (VGPSNSPTF) and HPV16 E7((49-57)) (RAHYNIVTF) H-2D(b)-restricted epitopes. The examination of the specific CTL response elicited by immunization with the recombinant VACV-expressing tumor-associated HPV16 E7 antigen by IFN-γ ELISPOT showed that the immunogenicity of the recombinant VACV-producing secretory vCCI was similar to that of the parent virus or deletion mutant in the C23L/B29R locus. Immunization with the secretory vCCI-producing recombinant virus has a lower therapeutic anti-tumor effect against TC-1 tumors. Viral CCI downregulated the E7-specific response induced by gene gun immunization with the DNA vaccines pBSC-SigE7 LAMP and pBSC-vCCI. We also observed that the immune response against vCCI elicited by the DNA vaccine did not affect the multiplication of VACV in vivo.

Plasmodium berghei sporozoite challenge of vaccinated BALB/c mice leads to the induction of humoral immunity and improved function of CD8(+) memory T cells

Protection against malaria can be achieved by induction of a strong CD8(+) T-cell response against the Plasmodium circumsporozoite protein (CSP), but most subunit vaccines suffer from insufficient memory responses. In the present study, we analyzed the impact of postimmunization sporozoite challenge on the development of long-lasting immunity. BALB/c mice were immunized by a heterologous prime/boost regimen against Plasmodium berghei CSP that induces a strong CD8(+) T-cell response and sterile protection, which is short-lived. Here, we show that protective immunity is prolonged by a sporozoite challenge after immunization. Repeated challenges induced sporozoite-specific antibodies that showed protective capacity. The numbers of CSP-specific CD8(+) T cells were not substantially enhanced by sporozoite infections; however, CSP-specific memory CD8(+) T cells of challenged mice displayed a higher cytotoxic activity than memory T cells of immunized-only mice. CD4(+) T cells contributed to protection as well; but CD8(+) memory T cells were found to be the central mediator of sterile protection. Based on these data, we suggest that prolonged protective immunity observed after immunization and infection is composed of different antiparasitic mechanisms including CD8(+) effector-memory T cells with increased cytotoxic activity as well as CD4(+) memory T cells and neutralizing antibodies.

Delivery of large heterologous polypeptides across the cytoplasmic membrane of antigen-presenting cells by the Bordetella RTX hemolysin moiety lacking the adenylyl cyclase domain

The Bordetella adenylate cyclase toxin-hemolysin (CyaA; also called ACT or AC-Hly) targets CD11b-expressing phagocytes and translocates into their cytosol an adenylyl cyclase (AC) that hijacks cellular signaling by conversion of ATP to cyclic AMP (cAMP). Intriguingly, insertion of large passenger peptides removes the enzymatic activity but not the cell-invasive capacity of the AC domain. This has repeatedly been exploited for delivery of heterologous antigens into the cytosolic pathway of CD11b-expressing dendritic cells by CyaA/AC(-) toxoids, thus enabling their processing and presentation on major histocompatibility complex (MHC) class I molecules to cytotoxic CD8(+) T lymphocytes (CTLs). We produced a set of toxoids with overlapping deletions within the first 371 residues of CyaA and showed that the structure of the AC enzyme does not contain any sequences indispensable for its translocation across target cell membrane. Moreover, replacement of the AC domain (residues 1 to 371) with heterologous polypeptides of 40, 146, or 203 residues yielded CyaAΔAC constructs that delivered passenger CTL epitopes into antigen-presenting cells (APCs) and induced strong antigen-specific CD8(+) CTL responses in vivo in mice and ex vivo in human peripheral blood mononuclear cell cultures. This shows that the RTX (repeats in toxin) hemolysin moiety, consisting of residues 374 to 1706 of CyaA, harbors all structural information involved in translocation of the N-terminal AC domain across target cell membranes. These results decipher the extraordinary capacity of the AC domain of CyaA to transport large heterologous cargo polypeptides into the cytosol of CD11b(+) target cells and pave the way for the construction of CyaAΔAC-based polyvalent immunotherapeutic T cell vaccines.

In vitro activation of CMV-specific human CD8(+) T cells by adenylate cyclase toxoids delivering pp65 epitopes

Human CMV infects between 50-85% of healthy individuals and can cause live-threatening infections in immunocompromised patients. Therefore, peptide vaccination is being developed as a promising immunotherapeutic approach for treatment of patients at risk of CMV disease. The enzymatically inactive toxoid of Bordetella adenylate cyclase (CyaA-AC(-)) was shown to be an efficient tool for delivery of peptide epitopes and stimulation of Ag-specific T-cell immune responses. We investigated here the capacity of two CyaA-AC(-) constructs to deliver epitopes derived from the CMV phosphoprotein pp65 for activation of human T cells in vitro. Expansion of γ-IFN-secreting CMV-specific CD8(+) T cells, as well as increase of total IFN-γ and TNF-α production by PBMCs from CMV-seropositive donors were observed after in vitro stimulation with CyaA-AC(-) constructs carrying CMV epitopes, whereas limited activation of immune response occurred with free peptides. The activation of immune response was confirmed by expansion of CMV-specific T-cell clones and anti-CMV cytotoxic effect of stimulated PBMCs. These data open the way to clinical evaluation of CyaA-AC(-) constructs as tools for detection and expansion of CMV-specific T-cell immune responses for diagnostic and immunotherapeutic applications against CMV-associated diseases.

RTX proteins: a highly diverse family secreted by a common mechanism

Repeats-in-toxin (RTX) exoproteins of Gram-negative bacteria form a steadily growing family of proteins with diverse biological functions. Their common feature is the unique mode of export across the bacterial envelope via the type I secretion system and the characteristic, typically nonapeptide, glycine- and aspartate-rich repeats binding Ca²⁺ ions. In this review, we summarize the current state of knowledge on the organization of rtx loci and on the biological and biochemical activities of therein encoded proteins. Applying several types of bioinformatic screens on the steadily growing set of sequenced bacterial genomes, over 1000 RTX family members were detected, with the biological functions of most of them remaining to be characterized. Activities of the so far characterized RTX family members are then discussed and classified according to functional categories, ranging from the historically first characterized pore-forming RTX leukotoxins, through the large multifunctional enzymatic toxins, bacteriocins, nodulation proteins, surface layer proteins, up to secreted hydrolytic enzymes exhibiting metalloprotease or lipase activities of industrial interest.

Immunotherapy for cervical cancer: Research status and clinical potential

The high-risk types of human papillomavirus (HPV) have been found to be associated with most cervical cancers and play an essential role in the pathogenesis of the disease. Despite recent advances in preventive HPV vaccine development, such preventive vaccines are unlikely to reduce the prevalence of HPV infections within the next few years, due to their cost and limited availability in developing countries. Furthermore, preventive HPV vaccines may not be capable of treating established HPV infections and HPV-associated lesions, which account for high morbidity and mortality worldwide. Thus, it is important to develop therapeutic HPV vaccines for the control of existing HPV infection and associated malignancies. Therapeutic vaccines are quite different from preventive vaccines in that they require the generation of cell-mediated immunity, particularly T cell-mediated immunity, instead of the generation of neutralizing antibodies. The HPV-encoded early proteins, the E6 and E7 oncoproteins, form ideal targets for therapeutic HPV vaccines, since they are consistently expressed in HPV-associated cervical cancer and its precursor lesions and thus play crucial roles in the generation and maintenance of HPV-associated disease. Our review covers the various therapeutic HPV vaccines for cervical cancer, including live vector-based, peptide or protein-based, nucleic acid-based, and cell-based vaccines targeting the HPV E6 and/or E7 antigens. Furthermore, we review the studies using therapeutic HPV vaccines in combination with other therapeutic modalities and review the latest clinical trials on therapeutic HPV vaccines.

Molecular pathology of head and neck cancer: implications for diagnosis, prognosis, and treatment

The prototypic head and neck squamous cell carcinoma (HNSCC) arises from the mucosal lining of the upper aerodigestive tract, demonstrates squamous differentiation microscopically, involves older men with a long history of cigarette smoking and alcohol consumption, and is treated by multimodality therapy. HNSCC has long been regarded as a uniform disease process requiring a methodical and unwavering therapeutic approach. Divergence in epidemiologic trends among HNSCCs arising from different anatomic sites has introduced a view that, morphologic repetition aside, head and neck cancers form a heterogeneous group. This view has been supported at the molecular genetic level. A more complete understanding of the molecular genetics of head and neck cancer is providing new insights into long-held but poorly comprehended concepts such as field cancerization and is introducing various biomarkers with potential application for diagnosing, staging, monitoring, and prognosticating HNSCC.

Antigen-specific immunotherapy of cervical and ovarian cancer

We contrast the efforts to treat ovarian cancer and cervical cancer through vaccination because of their different pathobiology. A plethora of approaches have been developed for therapeutic vaccination against cancer, many of which target defined tumor-associated antigens (TAAs). Persistent infection with oncogenic human papillomavirus (HPV) types causes cervical cancer. Furthermore, cervical cancer patients frequently mount both humoral and T-cell immune responses to the HPV E6 and E7 oncoproteins, whose expression is required for the transformed phenotype. Numerous vaccine studies target these viral TAAs, including recent trials that may enhance clearance of pre-malignant disease. By contrast, little is known about the etiology of epithelial ovarian cancer. Although it is clear that p53 mutation or loss is a critical early event in the development of epithelial ovarian cancer, no precursor lesion has been described for the most common serous histotype, and even the location of its origin is debated. These issues have complicated the selection of appropriate ovarian TAAs and the design of vaccines. Here we focus on mesothelin as a promising ovarian TAA, because it is overexpressed and immunogenic at high frequency in patients, is displayed on the cell surface, and potentially contributes to ovarian cancer biology.

Complete protection against P. berghei malaria upon heterologous prime/boost immunization against circumsporozoite protein employing Salmonella type III secretion system and Bordetella adenylate cyclase toxoid

Sterile immunity against malaria can be achieved by the induction of IFNgamma-producing CD8(+) T cells that target infected hepatocytes presenting epitopes of the circumsporozoite protein (CSP). In the present study we evaluate the protective efficacy of a heterologous prime/boost immunization protocol based on the delivery of the CD8(+) epitope of Plasmodium berghei CSP into the MHC class I presentation pathway, by either a type III secretion system of live recombinant Salmonella and/or by direct translocation of a recombinant Bordetella adenylate cyclase toxoid fusion (ACT-CSP) into the cytosol of professional antigen-presenting cells (APCs). A single intraperitoneal application of the recombinant ACT-CSP toxoid, as well as a single oral immunization with the Salmonella vaccine, induced a specific CD8(+) T cell response, which however conferred only a partial protection on mice against a subsequent sporozoite challenge. In contrast, a heterologous prime/boost vaccination with the live Salmonella followed by ACT-CSP led to a significant enhancement of the CSP-specific T cell response and induced complete protection in all vaccinated mice.

Therapeutic human papillomavirus vaccines: current clinical trials and future directions

BACKGROUND

Cervical cancer is the second largest cause of cancer deaths in women worldwide. It is now evident that persistent infection with high-risk human papillomavirus (HPV) is necessary for the development and maintenance of cervical cancer. Thus, effective vaccination against HPV represents an opportunity to restrain cervical cancer and other important cancers. The FDA recently approved the HPV vaccine Gardasil for the preventive control of HPV, using HPV virus-like particles (VLP) to generate neutralizing antibodies against major capsid protein, L1. However, prophylactic HPV vaccines do not have therapeutic effects against pre-existing HPV infections and HPV-associated lesions. Furthermore, due to the considerable burden of HPV infections worldwide, it would take decades for preventive vaccines to affect the prevalence of cervical cancer. Thus, in order to speed up the control of cervical cancer and treat current infections, the continued development of therapeutic vaccines against HPV is critical. Therapeutic HPV vaccines can potentially eliminate pre-existing lesions and malignant tumors by generating cellular immunity against HPV-infected cells that express early viral proteins such as E6 and E7.

OBJECTIVE

This review discusses the future directions of therapeutic HPV vaccine approaches for the treatment of established HPV-associated malignancies, with emphasis on current progress of HPV vaccine clinical trials.

METHODS

Relevant literature is discussed.

RESULTS/CONCLUSION

Though their development has been challenging, many therapeutic HPV vaccines have been shown to induce HPV-specific antitumor immune responses in preclinical animal models and several promising strategies have been applied in clinical trials. With continued progress in the field of vaccine development, HPV therapeutic vaccines may provide a potentially promising approach for the control of lethal HPV-associated malignancies.

Immunotherapy for head and neck cancer

Head and neck cancer represents a challenging disease. Despite recent treatment advances, which have improved functional outcomes, the long-term survival of head and neck cancer patients has remained unchanged for the past 25 years. One of the goals of adjuvant cancer therapy is to eradicate local regional microscopic and micrometastatic disease with minimal toxicity to surrounding normal cells. In this respect, antigen-specific immunotherapy is an attractive therapeutic approach. With the advances in molecular genetics and fundamental immunology, antigen-specific immunotherapy is being actively explored using DNA, bacterial vector, viral vector, peptide, protein, dendritic cell, and tumor-cell based vaccines. Early phase clinical trials have demonstrated the safety and feasibility of these novel therapies and the emphasis is now shifting towards the development of strategies, which can increase the potency of these vaccines. As the field of immunotherapy matures and as our understanding of the complex interaction between tumor and host develops, we get closer to realizing the potential of immunotherapy as an adjunctive method to control head and neck cancer and improve long-term survival in this patient population.

Prostate stem cell antigen vaccination induces a long-term protective immune response against prostate cancer in the absence of autoimmunity

Prostate stem cell antigen (PSCA) is an attractive antigen to target using therapeutic vaccines because of its overexpression in prostate cancer, especially in metastatic tissues, and its limited expression in other organs. Our studies offer the first evidence that a PSCA-based vaccine can induce long-term protection against prostate cancer development in prostate cancer-prone transgenic adenocarcinoma mouse prostate (TRAMP) mice. Eight-week-old TRAMP mice displaying prostate intraepithelial neoplasia were vaccinated with a heterologous prime/boost strategy consisting of gene gun-delivered PSCA-cDNA followed by Venezuelan equine encephalitis virus replicons encoding PSCA. Our results show the induction of an immune response against a newly defined PSCA epitope that is mediated primarily by CD8 T cells. The prostates of PSCA-vaccinated mice were infiltrated by CD4-positive, CD8-positive, CD11b-positive, and CD11c-positive cells. Vaccination induced MHC class I expression and cytokine production [IFN-gamma, tumor necrosis factor-alpha, interleukin 2 (IL-2), IL-4, and IL-5] within prostate tumors. This tumor microenvironment correlated with low Gleason scores and weak PSCA staining on tumor cells present in hyperplastic zones and in areas that contained focal and well-differentiated adenocarcinomas. PSCA-vaccinated TRAMP mice had a 90% survival rate at 12 months of age. In contrast, all control mice had succumbed to prostate cancer or had heavy tumor loads. Crucially, this long-term protective immune response was not associated with any measurable induction of autoimmunity. The possibility of inducing long-term protection against prostate cancer by vaccination at the earliest signs of its development has the potential to cause a dramatic paradigm shift in the treatment of this disease.

Plasmid DNA and viral vector-based vaccines for the treatment of cancer

Plasmid DNA and viral vector-based cancer vaccines have many inherent features that make them promising cancer vaccine candidates. This review focuses on the use of plasmid DNA and viral vector vaccines to deliver tumour-specific antigens to induce a tumour-specific immune response. Examples of different antigen delivery systems that have been tested in recent clinical trials are summarised and advantages and disadvantages of a number of delivery systems and approaches are discussed. Finally, an outlook on how plasmid DNA and viral vectors might be developed further as cancer vaccines is provided.

In vivo effects of vaccination with six-transmembrane epithelial antigen of the prostate: a candidate antigen for treating prostate cancer

Immunotherapy may provide an alternative treatment for cancer patients, especially when tumors overexpress antigens that can be recognized by immune cells. The identification of markers and therapeutic targets that are up-regulated in prostate cancer has been important to design new potential treatments for prostate cancer. Among them, the recently identified six-transmembrane epithelial antigen of the prostate (STEAP) is considered attractive due to its overexpression in human prostate cancer tissues. Our study constitutes the first assessment of the in vivo effectiveness of STEAP-based vaccination in prophylactic and therapeutic mouse models. Two delivery systems, cDNA delivered by gene gun and Venezuelan equine encephalitis virus-like replicon particles (VRP), both encoding mouse STEAP (mSTEAP) and three vaccination strategies were used. Our results show that mSTEAP-based vaccination was able to induce a specific CD8 T-cell response against a newly defined mSTEAP epitope that prolonged the overall survival rate in tumor-challenged mice very significantly. This was achieved without any development of autoimmunity. Surprisingly, CD4 T cells that produced IFNgamma, tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2) played the main role in tumor rejection in our model as shown by using CD4- and CD8-deficient mice. In addition, the presence of high IL-12 levels in the tumor environment was associated with a favorable antitumor response. Finally, the therapeutic effect of STEAP vaccination was also assessed and induced a modest but significant delay in growth of established, 31 day old tumors. Taken together, our data suggest that vaccination against mSTEAP is a viable option to delay tumor growth.

An increase in antimycobacterial Th1-cell responses by prime-boost protocols of immunization does not enhance protection against tuberculosis

Bordetella pertussis adenylate cyclase (CyaA) toxoid is a powerful nonreplicative immunization vector targeting dendritic cells, which has already been used successfully in prophylactic and therapeutic vaccination in various preclinical animal models. Here, we investigated the potential of CyaA, harboring strong mycobacterial immunogens, i.e., the immunodominant regions of antigen 85A or the complete sequence of the 6-kDa early secreted antigenic target (ESAT-6) protein, to induce antimycobacterial immunity. By generating T-cell hybridomas or by using T cells from mice infected with mycobacteria, we first demonstrated that the in vitro delivery of 85A or ESAT-6 to antigen-presenting cells by CyaA leads to processing and presentation, by major histocompatibility complex class II molecules, of the same epitopes as those displayed upon mycobacterial infection. Importantly, compared to the recombinant protein alone, the presentation of ESAT-6 in vitro was 100 times more efficient upon its delivery to antigen-presenting cells in fusion to CyaA. Immunization with CyaA-85A or CyaA-ESAT-6 in the absence of any adjuvant induced strong antigen-specific lymphoproliferative, interleukin-2 (IL-2) and gamma interferon (IFN-gamma) cytokine responses, in the absence of any IL-4 or IL-5 production. When used as boosters after priming with a BCG expressing ESAT-6, the CyaA-85A and CyaA-ESAT-6 proteins were able to strikingly increase the sensitivity and intensity of proliferative and Th1-polarized responses and notably the frequency of antigen-specific IFN-gamma-producing CD4+ T cells. However, immunization with these CyaA constructs as subunit vaccines alone or as boosters did not allow induction or improvement of protection against Mycobacterium tuberculosis infection. These results question the broadly admitted correlation between the frequency of IFN-gamma-producing CD4+ T cells and the level of protection against tuberculosis.