Identification of an immunodominant H-2D(b)-restricted CTL epitope of human PSA

Poxvirus-based active immunotherapy synergizes with CTLA-4 blockade to increase survival in a murine tumor model by improving the magnitude and quality of cytotoxic T cells

The dramatic clinical benefit of immune checkpoint blockade for a fraction of cancer patients suggests the potential for further clinical benefit in a broader cancer patient population by combining immune checkpoint inhibitors with active immunotherapies. The anti-tumor efficacy of MVA-BN-HER2 poxvirus-based active immunotherapy alone or in combination with CTLA-4 checkpoint blockade was investigated in a therapeutic CT26-HER-2 lung metastasis mouse model. MVA-BN-HER2 immunotherapy significantly improved the median overall survival compared to untreated controls or CTLA-4 blockade alone (p < 0.001). Robust synergistic efficacy was achieved with the combination therapy (p < 0.01). Improved survival following MVA-BN-HER2 administration was accompanied by increased tumor infiltration by HER-2-specific cytotoxic T lymphocytes (CTL). These tumor-specific CTL had characteristics similar to antiviral CTL, including strong expression of activation markers and co-expression of IFNγ and TNFα. Combination with CTLA-4 blockade significantly increased the magnitude of HER-2-specific T cell responses, with a higher proportion co-expressing TNFα and/or IL-2 with IFNγ. Furthermore, in mice treated with MVA-BN-HER2 (alone or in combination with CTLA-4 blockade), the inducible T cell co-stimulator (ICOS) protein was expressed predominantly on CD4 and CD8 effector T cells but not on regulatory T cells (T(reg)). In contrast, mice left untreated or treated solely with CTLA-4 blockade harbored elevated ICOS(+) Treg, a phenotype associated with highly suppressive activity. In conclusion, poxvirus-based active immunotherapy induced robust tumor infiltration by highly efficient effector T cells. Combination with CTLA-4 immune checkpoint blockade amplified this response resulting in synergistically improved efficacy. These hypothesis-generating data may help elucidate evidence of enhanced clinical benefit from combining CTLA-4 blockade with poxvirus-based active immunotherapy.

From genome screening to creation of vaccine against Trypanosoma cruzi by use of immunoinformatics

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, and activation of CD8(+) T cells is crucial for a protective immune response. Therefore, the identification of antigens with major histocompatibility complex class I epitopes is a crucial step for vaccine development against T. cruzi. Our aim was to identify novel antigens and epitopes by immunoinformatics analysis of the parasite proteome (12 969 proteins) and to validate their immunotherapeutic potential in infected mice. We identified 172 predicted epitopes, using NetMHC and RANKPEP. The corresponding protein sequences were reanalyzed to generate a consensus prediction, and 26 epitopes were selected for in vivo validation. The interferon γ (IFN-γ) recall response of splenocytes from T. cruzi-infected mice confirmed that 10 of 26 epitopes (38%) induced IFN-γ production. The immunotherapeutic potential of a mixture of all 10 peptides was evaluated in infected mice. The therapeutic vaccine was able to control T. cruzi infection, as evidenced by reduced parasitemia, cardiac tissue inflammation, and parasite burden and increased survival. These findings illustrate the benefits of this approach for the rapid development of a vaccine against pathogens with large genomes. The identified peptides and the proteins from which they are derived are excellent candidates for the development of a vaccine against T. cruzi.

A cytomegalovirus-based vaccine expressing a single tumor-specific CD8+ T-cell epitope delays tumor growth in a murine model of prostate cancer

Cytomegalovirus (CMV) is a highly immunogenic virus that results in a persistent, life-long infection in the host typically with no ill effects. Certain unique features of CMV, including its capacity to actively replicate in the presence of strong host CMV-specific immunity, may give CMV an advantage compared with other virus-based vaccine delivery platforms. In the present study, we tested the utility of mouse CMV (mCMV)-based vaccines expressing human prostate-specific antigen (PSA) for prostate cancer immunotherapy in double-transgenic mice expressing PSA and HLA-DRB1*1501 (DR2bxPSA F1 mice). We assessed the capacity of 2 mCMV-based vectors to induce PSA-specific CD8 T-cell responses and affect the growth of PSA-expressing Transgenic Adenocarcinoma of the Mouse Prostate tumors (TRAMP-PSA). In the absence of tumor challenge, immunization with mCMV vectors expressing either a H2-D(b)-restricted epitope PSA(65-73) (mCMV/PSA(65-73)) or the full-length gene for PSA (mCMV/PSA(FL)) induced comparable levels of CD8 T-cell responses that increased (inflated) with time. Upon challenge with TRAMP-PSA tumor cells, animals immunized with mCMV/PSA(65-73) had delay of tumor growth and increased PSA-specific CD8 T-cell responses, whereas animals immunized with mCMV/PSA(FL) showed progressive tumor growth and no increase in number of splenic PSA(65-73)-specific T cells. The data show that a prototype CMV-based prostate cancer vaccine can induce an effective antitumor immune response in a "humanized" double-transgenic mouse model. The observation that mCMV/PSA(FL) is not effective against TRAMP-PSA is consistent with our previous findings that HLA-DRB1*1501-restricted immune responses to PSA are associated with suppression of effective CD8 T-cell responses to TRAMP-PSA tumors.

Combined immunotherapy with Listeria monocytogenes-based PSA vaccine and radiation therapy leads to a therapeutic response in a murine model of prostate cancer

Radiation therapy (RT) is an integral part of prostate cancer treatment across all stages and risk groups. Immunotherapy using a live, attenuated, Listeria monocytogenes-based vaccines have been shown previously to be highly efficient in stimulating anti-tumor responses to impact on the growth of established tumors in different tumor models. Here, we evaluated the combination of RT and immunotherapy using Listeria monocytogenes-based vaccine (ADXS31-142) in a mouse model of prostate cancer. Mice bearing PSA-expressing TPSA23 tumor were divided to 5 groups receiving no treatment, ADXS31-142, RT (10 Gy), control Listeria vector and combination of ADXS31-142 and RT. Tumor growth curve was generated by measuring the tumor volume biweekly. Tumor tissue, spleen, and sera were harvested from each group for IFN-γ ELISpot, intracellular cytokine assay, tetramer analysis, and immunofluorescence staining. There was a significant tumor growth delay in mice that received combined ADXS31-142 and RT treatment as compared with mice of other cohorts and this combined treatment causes complete regression of their established tumors in 60 % of the mice. ELISpot and immunohistochemistry of CD8+ cytotoxic T Lymphocytes (CTL) showed a significant increase in IFN-γ production in mice with combined treatment. Tetramer analysis showed a fourfold and a greater than 16-fold increase in PSA-specific CTLs in animals receiving ADXS31-142 alone and combination treatment, respectively. A similar increase in infiltration of CTLs was observed in the tumor tissues. Combination therapy with RT and Listeria PSA vaccine causes significant tumor regression by augmenting PSA-specific immune response and it could serve as a potential treatment regimen for prostate cancer.

Dual antigen target-based immunotherapy for prostate cancer eliminates the growth of established tumors in mice

AIMS

We have previously shown that immunization with an adenovirus vector carrying an individual antigen induces antigen-specific CD8 T cells actively engaged in the destruction of tumor cells expressing the cognate antigen. In order to expand the range of antitumor responses beyond an individual antigen, we designed a recombinant adenovirus type 5 (rAd5) carrying a fusion construct of two full-length antigens. We used this adenovirus vector to test the concept that multiantigenic effector T cells could be generated simultaneously following a single immunization.

METHOD

To perform the rAd5 constructs, we selected a combination of prostate-specific antigen (PSA) and prostate stem cell antigen (PSCA) genes based on their restricted distribution within the prostate tissue and their association with the development and progression of prostate cancer.

RESULTS

Immunization of mice with rAd5 vector carrying a fusion construct of PSA and PSCA (Ad5-PSA/PSCA) simultaneously induced the expansion of anti-PSA and anti-PSCA CD8 T cells, as measured by intracellular cytokine staining for IFN-γ. The antigen-specific T-cell responses that developed were efficient in eliminating the target cells expressing cognate antigens measured by an in vivo cytotoxic T-cell assay. The in vivo tumor growth study showed that immunization of mice with Ad5-PSA/PSCA vaccine induced strong antitumor immunity when challenged with mouse prostate tumor cell lines (RM11) expressing human PSA (RM11/PSA). To further analyze the impact on therapeutic efficacy of Ad5-PSA/PSCA vaccine against the tumor cells expressing PSA and PSCA (RM11-PSA/PSCA) antigens, we injected mice with Ad5-PSA/PSCA vaccine. The vaccine inhibited the growth of established tumors with 80% of the mice becoming tumor free. These data provide useful information that antigen-specific effector T cells can be generated simultaneously and that their additive antitumor effect has the potential to eliminate the growth of established tumors. Therefore, the immunotherapy approach of using the simultaneous targeting of dual antigens associated with prostate cancer may have important implications for human clinical trials.

Immunostimulatory CpG-DNA and PSA-peptide vaccination elicits profound cytotoxic T cell responses

OBJECTIVE

Novel strategies for the treatment of advanced prostate cancer (CaP), including immunotherapy or gene therapy, are currently under evaluation with Sipuleucel-T as first FDA-approved immunotherapeutic. Here, we examine cytosine-phosphorothioate-guanine (CpG)-DNA oligonucleotides (ODN) to boost cytokine responses and costimulatory molecule expression on murine bone marrow-derived dendritic cells (mBMDC). Furthermore, we evaluate the potency of a PSA-peptide based vaccine in combination with CpG-DNA to elicit specific cytotoxic T cell (CTL) responses.

MATERIALS AND METHODS

mBMDC were stimulated with CpG-DNA (1668: 5'-TCCATGACGTTCCTGATGCT-3') or non-stimulatory control-ODN (1720: 5'-TCCATGAGCTTCCTGATGCT-3'). Subsequently, expression of the costimulatory molecules CD40 and CD86 and induction of proinflammatory cytokines (interleukin (IL)-6 and IL-12) were analyzed. For induction of PSA-peptide specific CTL, female C57BL/6 mice were immunized with PSA-peptide 65-73 (HCIRNKSVI) alone or in combination with 1668 or 1720-ODN. In vivo cytotoxicity assay determined PSA-peptide specific cytotoxicity 1 week after vaccination.

RESULTS

Treatment of mBMDC with stimulatory CpG-DNA ODN resulted in pronounced up-regulation of costimulatory molecule expression on mBMDC in a dose-dependent manner. CpG-ODN significantly increased production of IL-6 and IL-12 in mBMDC (P < 0.001). Induction of PSA-peptide specific CTL responses in mice immunized with PSA-peptide and CpG-DNA were significantly greater than those of PSA-peptide and control-ODN immunized mice or PSA-peptide only vaccination.

CONCLUSIONS

CpG-DNA acts as potent adjuvant for vaccination therapies and elicits profound PSA-peptide specific CTL responses in combination with an immunodominant PSA-peptide. CpG-ODN mediated immunotherapy represents a potentially inexpensive, safe, easy-to-produce, and easy-to-handle treatment alternative. Therefore, further evaluation of CpG-DNA in immunization therapies against CaP is warranted.

Murine polyomavirus virus-like particles carrying full-length human PSA protect BALB/c mice from outgrowth of a PSA expressing tumor

Virus-like particles (VLPs) consist of capsid proteins from viruses and have been shown to be usable as carriers of protein and peptide antigens for immune therapy. In this study, we have produced and assayed murine polyomavirus (MPyV) VLPs carrying the entire human Prostate Specific Antigen (PSA) (PSA-MPyVLPs) for their potential use for immune therapy in a mouse model system. BALB/c mice immunized with PSA-MPyVLPs were only marginally protected against outgrowth of a PSA-expressing tumor. To improve protection, PSA-MPyVLPs were co-injected with adjuvant CpG, either alone or loaded onto murine dendritic cells (DCs). Immunization with PSA-MPyVLPs loaded onto DCs in the presence of CpG was shown to efficiently protect mice from tumor outgrowth. In addition, cellular and humoral immune responses after immunization were examined. PSA-specific CD4⁺ and CD8⁺ cells were demonstrated, but no PSA-specific IgG antibodies. Vaccination with DCs loaded with PSA-MPyVLPs induced an eight-fold lower titre of anti-VLP antibodies than vaccination with PSA-MPyVLPs alone. In conclusion, immunization of BALB/c mice with PSA-MPyVLPs, loaded onto DCs and co-injected with CpG, induces an efficient PSA-specific tumor protective immune response, including both CD4⁺ and CD8⁺ cells with a low induction of anti-VLP antibodies.

A replicating cytomegalovirus-based vaccine encoding a single Ebola virus nucleoprotein CTL epitope confers protection against Ebola virus

Background

Human outbreaks of Ebola virus (EBOV) are a serious human health concern in Central Africa. Great apes (gorillas/chimpanzees) are an important source of EBOV transmission to humans due to increased hunting of wildlife including the ‘bush-meat’ trade. Cytomegalovirus (CMV) is an highly immunogenic virus that has shown recent utility as a vaccine platform. CMV-based vaccines also have the unique potential to re-infect and disseminate through target populations regardless of prior CMV immunity, which may be ideal for achieving high vaccine coverage in inaccessible populations such as great apes.

Methodology/Principal Findings

We hypothesize that a vaccine strategy using CMV-based vectors expressing EBOV antigens may be ideally suited for use in inaccessible wildlife populations. To establish a ‘proof-of-concept’ for CMV-based vaccines against EBOV, we constructed a mouse CMV (MCMV) vector expressing a CD8⁺ T cell epitope from the nucleoprotein (NP) of Zaire ebolavirus (ZEBOV) (MCMV/ZEBOV-NP_CTL). MCMV/ZEBOV-NP_CTL induced high levels of long-lasting (>8 months) CD8⁺ T cells against ZEBOV NP in mice. Importantly, all vaccinated animals were protected against lethal ZEBOV challenge. Low levels of anti-ZEBOV antibodies were only sporadically detected in vaccinated animals prior to ZEBOV challenge suggesting a role, at least in part, for T cells in protection.

Conclusions/Significance

This study demonstrates the ability of a CMV-based vaccine approach to protect against an highly virulent human pathogen, and supports the potential for ‘disseminating’ CMV-based EBOV vaccines to prevent EBOV transmission in wildlife populations.

Human outbreaks of hemorrhagic disease caused by Ebola virus (EBOV) are a serious health concern in Central Africa. Great apes (gorillas/chimpanzees) are an important source of EBOV transmission to humans. Candidate EBOV vaccines do not spread from the initial vaccinee. In addition to being highly immunogenic, vaccines based on the cytomegalovirus (CMV) platform have the unique potential to re-infect and disseminate through target populations. To explore the utility of CMV-based vaccines against EBOV, we constructed a mouse CMV (MCMV) vector expressing a region of nucleoprotein (NP) of Zaire ebolavirus (ZEBOV) (MCMV/ZEBOV-NP_CTL). MCMV/ZEBOV-NP_CTL induced high levels of long-lasting CD8⁺ T cells against ZEBOV NP in mice. Importantly, all vaccinated animals were protected against lethal ZEBOV challenge. The absence of ZEBOV neutralizing and only low, sporadic levels of total anti-ZEBOV IgG antibodies in protected animals prior to ZEBOV challenge indicate a role, albeit perhaps not exclusive, for CD8⁺ T cells in mediating protection. This study demonstrates the ability of a CMV-based vaccine approach to protect against ZEBOV, and provides a ‘proof-of-concept’ for the potential for a ‘disseminating’ CMV-based EBOV vaccine to prevent EBOV transmission in wild animal populations.

Optimization of skin electroporation in mice to increase tolerability of DNA vaccine delivery to patients

Electroporation has, during the last years, proven to be a very successful delivery method for DNA vaccines and has now reached clinical evaluation. Although intramuscular electroporation is practical in animal models, intradermal electroporation might be more suitable for clinical administration. Skin is the most accessible organ of the body and has professional antigen-presenting cells in large amounts; thus, skin is an ideal target for DNA vaccine delivery. Moreover, intradermal electroporation has clear clinical benefits such as improved safety and tolerability. This article describes improvements for effective and tolerable DNA delivery to skin. The time of pulse delivery has been shortened by 90% and even pulse programs of 240-ms total duration generate robust immune responses. We show that a single vaccination using an optimized gene delivery generates (i) high and consistent protein expression in vivo, (ii) cytotoxic antigen-specific T cells expressing both IFNgamma and CD107a (lysosomal-associated membrane protein 1). Furthermore, application of a topical anesthetic cream prior to vaccination does not affect the number or function of the antigen-specific T cells induced. This suggests that local anesthesia can be used to further decrease the sensation of pulse delivery in patients.

Cutting edge: permissive MHC class II allele changes the pattern of antitumor immune response resulting in failure of tumor rejection

We studied the growth of transgenic adenocarcinoma of mouse prostate (TRAMP)-C1 tumor cells expressing human prostate-specific Ag (PSA) in HLA-DRB1*1501 (DR2b) transgenic mice. TRAMP-PSA tumors were frequently rejected by HLA-DR2b(-) mice but had increased incidence in HLA-DR2b(+) littermates. The levels of PSA-specific CD8 T cell responses were significantly higher in the HLA-DR2b(-) mice that rejected TRAMP-PSA tumors compared with HLA-DR2b(+) tumor-bearing littermates. In contrast, Ab responses to PSA were strong in HLA-DR2b(+) mice bearing TRAMP-PSA tumors and were virtually undetectable in HLA-DR2b(-) littermates. The analysis of CD4 T cell responses to PSA revealed the presence of several CD4 T cell epitopes in HLA-DR2b(+) mice but failed to identify strong I-A(b)-restricted epitopes in HLA-DR2b(-) mice. Our data demonstrate that the expression of a permissive HLA class II allele can change the pattern of the immune response to a tumor Ag, resulting in the failure of tumor rejection.

A modified epitope identified for generation and monitoring of PSA-specific T cells in patients on early phases of PSA-based immunotherapeutic protocols

Efficacy of vaccination in cancer patients on immunotherapeutic protocols can be difficult to evaluate. The aim of this study was therefore to identify a single natural or modified epitope in prostate-specific antigen (PSA) with the ability to generate high levels of PSA-specific T cells to facilitate monitoring in patients after vaccination against prostate cancer. To the best of our knowledge, this study describes for the first time the peptide specificity of T cells stimulated by endogenously processed PSA antigen. The peptide specificity of HLA-A*0201-restricted CD8(+) T cells against human and rhesus PSA was investigated both in vivo after DNA vaccination in HLA-A*0201-transgenic mice and in vitro after repetitive stimulation of human T cells with DNA-transfected human dendritic cells (DCs). One of seven native PSA peptides, psa53-61, was able to activate high levels of PSA-specific CD8(+) T cells in HLA-A*0201-transgenic mice after PSA DNA vaccination. Psa53-61 was also the only peptide that induced human T cells to produce IFNgamma after stimulation with PSA transfected DCs, however not in all donors. Therefore, plasmids encoding modified epitopes in predicted HLA-A*0201 sequences were constructed. One of these modified PSA plasmids consistently induced IFNgamma producing CD8(+) T cells to the corresponding modified peptide as well as to the corresponding native peptide, in all murine and human T cell cultures. This study demonstrates a novel concept of introducing a modified epitope within a self-tumor antigen, with the purpose of eliciting a reliable T cell response from the non-tolerized immune repertoire, to facilitate monitoring of vaccine efficacy in cancer patients on immunotherapeutic protocols. The purpose of such a modified epitope is thus not to induce therapeutically relevant T cells but rather to, in case of weak or divergent T cell responses to self antigens/peptides, help answer questions about efficacy of vaccine delivery and about the possibility to induce immune responses in the selected and often immunosuppressed cancer patients.

Construction and characterization of an attenuated Listeria monocytogenes strain for clinical use in cancer immunotherapy

Listeria monocytogenes has been exploited previously as a vaccine vector for the delivery of heterologous proteins such as tumor-specific antigens for active cancer immunotherapy. However, for effective use of live vector in clinics, safety is a major concern. In the present study, we describe an irreversibly attenuated and highly immunogenic L. monocytogenes platform, the L. monocytogenes dal-, dat-, and actA-deleted strain that expresses the human prostate-specific antigen (PSA) using an antibiotic resistance marker-free plasmid (the dal dat DeltaactA 142 strain expressing PSA). Despite limited in vivo survival, the dal dat DeltaactA 142 strain was able to elicit efficient immune responses required for tumor clearance. Our results showed that immunization of mice with the dal dat DeltaactA 142 strain caused the regression of the tumors established by the prostate adenocarcinoma cell line expressing PSA. An evaluation of immunologic potency indicated that the dal dat DeltaactA 142 strain elicits a high frequency of PSA-specific immune responses. Interestingly, immunization with the dal dat DeltaactA 142 strain induced significant infiltration of PSA-specific T cells in the intratumoral milieu. Collectively, our data suggest that the dal dat DeltaactA 142 strain is a safe and potent vector for clinical use and that this platform may be further exploited as a potential candidate to express other single or multiple antigens for cancer immunotherapy.

Development of a Listeria monocytogenes based vaccine against prostate cancer

Prostate specific antigen (PSA) is a likely immunotherapeutic target antigen for prostate cancer, the second leading cause of cancer-related death in American men. Previously, we demonstrated that attenuated strains of Listeria monocytogenes (Lm) can be used as effective vaccine vectors for delivery of tumor antigens causing regression of established tumors accompanied by strong immune responses toward these antigens in murine models of cancer. In the present study, we have developed and characterized a recombinant live attenuated L. monocytogenes/PSA (Lm-LLO-PSA) vaccine with potential use for the treatment of pCa. Human PSA gene was cloned into and expressed by an attenuated Lm strain. This recombinant bacterial vaccine, Lm-LLO-PSA was tested for stability, virulence, immunogenicity and anti-tumor effects in a murine model for pCa. Immunization with Lm-LLO-PSA was shown to lower the number of tumor infiltrating T regulatory cells and cause complete regression of over 80% of tumors formed by an implanted genetically modified mouse prostate adenocarcinoma cell line, which expressed human PSA. Lm-LLO-PSA was immunogenic in C57BL/6 mice and splenocytes from mice immunized with Lm-LLO-PSA showed significantly higher number of IFN-gamma secreting cells over that of the naïve animals in response to a PSA H2Db-specific peptide, as measured by both, ELISpot and intracellular cytokine staining. In addition, using a CTL assay we show that the T cells specific for PSA were able to recognize and lyse PSA-peptide pulsed target cells in vitro. In a comparison study with two other PSA-based vaccines (a pDNA and a vaccinia vaccine), Lm-LLO-PSA was shown to be more efficacious in regressing established tumors when used in a homologues prime/boost regimen. Together, these results indicate that Lm-LLO-PSA is a potential candidate for pCa immunotherapy and should be further developed.

DNA vaccination for prostate cancer

DNA-based cancer vaccines have been used successfully in mice to induce cytotoxic T lymphocytes (CTLs) specific for prostate antigens. Translation of a prostate-specific antigen (PSA) DNA vaccine into a phase I clinical trial demonstrated that PSA-specific immune responses could be induced but at a significantly lower level compared with those in mice. To enhance the efficacy of DNA vaccination against prostate cancer, we have explored and optimized intradermal electroporation as an effective way of delivering a PSA DNA vaccine. The results demonstrated that intradermal DNA vaccination using low amounts of DNA, followed by two sets of electrical pulses of different length and voltage, effectively induced PSA-specific T cells. Here we describe in detail how to perform intradermal DNA electroporation to induce high gene expression in skin and, more important, how to induce and analyze PSA-specific T cell responses.

Clonal expansions of pathogenic CD8+ effector cells in the CNS of myelin mutant mice

Tissue damage in the CNS is critically influenced by the adaptive immune system. Primary oligodendrocyte damage (by overexpression of PLP) leads to low-grade inflammation of high pathological impact, which is mediated by CD8+ T cells. To yield further insight into pathogenesis and nature of immune responses in myelin mutated mice, we here apply a detailed immunological characterization of CD8+ T cells in PLP-transgenic and aged wild type mice. We provide evidence that T effector cells accumulate in the CNS of PLP-transgenic and wild-type mice and show a higher level of activation in mutant mice, indicated by surface markers and clonal expansions, as demonstrated by T cell receptor CDR3-spectratype analysis. Vbeta-Jbeta similarities suggest specificity against a common antigen, albeit we could not find specific responses against myelin-antigen-derived peptides. The association of primary oligodendrocyte damage with secondary expansions of pathogenic cells underlines the role of adaptive immune reactions in neurodegenerative and neuroinflammatory diseases.

HLA class II antigen presentation by prostate cancer cells

Prostate cancer is the second most commonly diagnosed cancer in men. Recent evidence suggests that reduced expression of target protein antigens and human leukocyte antigen (HLA) molecules is the predominant immune escape mechanism of malignant prostate tumor cells. The purpose of this study was to investigate the prospect of antigen specific immunotherapy against prostate cancer via the HLA class II pathway of immune recognition. Here, we show for the first time that prostate cancer cells express HLA class II proteins that are recognized by CD4+ T cells. Prostate tumor cells transduced with class II molecules efficiently presented tumor-associated antigens/peptides to CD4+ T cells. This data suggests that malignant prostate tumors can be targeted via the HLA class II pathway, and that class II-positive tumors could be employed for direct antigen presentation, and CD4+ T-cell mediated tumor immunotherapy.Prostate Cancer and Prostatic Diseases (2008) 11, 334-341; doi:10.1038/sj.pcan.4501021; published online 16 October 2007.

Modulation of T-effector function by imatinib at the level of cytokine secretion

OBJECTIVE

Recently, evidence was provided, that the selective tyrosine kinase inhibitor imatinib mesylate (imatinib) has immunomodulatory or suppressive effects. However, the discussion about imatinib's influence on immune cells is still controversial. The aim of this study was to clarify the effect of imatinib on CD8+ and CD4+ T-cell effector functions.

MATERIALS AND METHODS

For analyzing T-cell effector functions T-cell receptor-transgenic ovalbumin-specific CD8+ T cells and in vivo primed CD4+ Th1 cells were used. T-cell effector functions were analyzed on the level of antigen responsiveness by intracellular cytokine staining, by measuring cytokine secretion in an interferon-gamma (IFN-gamma) enzyme-linked immunosorbent assay and by detecting cytotoxicity using the fluorescein-activated cell sorting-based fluorometric assessment of T-lymphocyte antigen-specific lysis assay.

RESULTS

It was demonstrated that imatinib inhibits antigen-specific IFN-gamma secretion of both CD4+ and CD8+ T-effector cells at therapeutically relevant concentrations, while T cells remain responsive. The decrease of IFN-gamma production was not due to the loss of T-cell viability. Further, it was shown that the effector T cells are modulated rather than suppressed, because the cytolytic functions of CD8+ cytotoxic T cells were not altered. Residual cytolytic activity in the presence of imatinib was not due to FasL interaction.

CONCLUSIONS

These experiments provide evidence for a therapeutically relevant modulation of T-cell effector functions by imatinib. This might open a possible applicability of imatinib in various autoimmune and inflammatory diseases, including multiple sclerosis and rheumatoid arthritis.

Priming of CD8+ T-cell responses after DNA immunization is impaired in TLR9- and MyD88-deficient mice

The plasmid DNA vaccine not only provides expression of the antigen in vivo, but also activates cells of the innate immune system via unmethylated CpG-containing DNA sequences that are recognized by Toll like receptor 9 (TLR9). The requirement of such immunostimulatory activity for induction of CD8+ T-cell responses after DNA immunization is still controversial. In the present study we assessed induction of CD8+ T-cell responses against an immunodominant H-2D(b)-restricted epitope of human prostate-specific antigen in C57Bl/6 (wild-type), TLR9- and MyD88-deficient mice. A single DNA immunization resulted in efficient priming of CD8+ T responses in wild-type mice but not in TLR9- or MyD88-deficient mice. However, priming of CD8+ T cell responses was observed in TLR9-deficient but not in MyD88-deficient mice after multiple DNA immunizations. Moreover, induction of CD8+ T cell responses in TLR9-deficient mice was dependent on the presence of endotoxin contamination in plasmid DNA preparations. Collectively, these results demonstrate that TLR9-dependent immunostimulatory activity of plasmid DNA is essential for priming of CD8+ T-cell responses and that other bacterial compounds present in plasmid DNA preparations and acting via MyD88-dependent pathway could provide alternative signals necessary for priming of CD8+ T cells.

Enhancement of cellular immune response to a prostate cancer DNA vaccine by intradermal electroporation

Recently it has become clear that more potent methods for DNA vaccine delivery need to be developed to enhance the efficacy of DNA vaccines. In vivo electroporation has emerged as a potent method for DNA vaccine delivery. In a mouse model, we evaluated the CD8(+) T lymphocyte response to a prostate cancer DNA vaccine encoding prostate-specific antigen (PSA) after intradermal electroporation. A significantly increased gene expression (100- to 1000-fold) and higher levels of PSA-specific T cells, compared to DNA delivery without electroporation, was demonstrated. Interestingly, investigation of a panel of different electroporation conditions showed that only some conditions that induce high levels of gene expression additionally induced cellular immunity. This suggests that electroporation parameters should be carefully optimized, not only to enhance transfection efficiency, but also to enhance the immune response to the vaccine. This study demonstrates the applicability of intradermal electroporation as a delivery method for genetic cancer vaccines and other DNA vaccines relying on antigen-specific T cell induction.