Dendritic cells transduced with HSV-1 amplicons expressing prostate-specific antigen generate antitumor immunity in mice

Anti-tumor effect of the alphavirus-based virus-like particle vector expressing prostate-specific antigen in a HLA-DR transgenic mouse model of prostate cancer

The goal of this study was to determine if an alphavirus-based vaccine encoding human Prostate-Specific Antigen (PSA) could generate an effective anti-tumor immune response in a stringent mouse model of prostate cancer. DR2bxPSA F1 male mice expressing human PSA and HLA-DRB1(*)1501 transgenes were vaccinated with virus-like particle vector encoding PSA (VLPV-PSA) followed by the challenge with Transgenic Adenocarcinoma of Mouse Prostate cells engineered to express PSA (TRAMP-PSA). PSA-specific cellular and humoral immune responses were measured before and after tumor challenge. PSA and CD8 reactivity in the tumors was detected by immunohistochemistry. Tumor growth was compared in vaccinated and control groups. We found that VLPV-PSA could infect mouse dendritic cells in vitro and induce a robust PSA-specific immune response in vivo. A substantial proportion of splenic CD8 T cells (19.6 ± 7.4%) produced IFNγ in response to the immunodominant peptide PSA(65-73). In the blood of vaccinated mice, 18.4 ± 4.1% of CD8 T cells were PSA-specific as determined by the staining with H-2D(b)/PSA(65-73) dextramers. VLPV-PSA vaccination also strongly stimulated production of IgG2a/b anti-PSA antibodies. Tumors in vaccinated mice showed low levels of PSA expression and significant CD8+ T cell infiltration. Tumor growth in VLPV-PSA vaccinated mice was significantly delayed at early time points (p=0.002, Gehan-Breslow test). Our data suggest that TC-83-based VLPV-PSA vaccine can efficiently overcome immune tolerance to PSA, mediate rapid clearance of PSA-expressing tumor cells and delay tumor growth. The VLPV-PSA vaccine will undergo further testing for the immunotherapy of prostate cancer.

Murine Bone Marrow-Derived Dendritic Cells Transduced by Light-Helper-Dependent Herpes Simplex Virus-1 Amplicon Vector Acquire a Mature Dendritic Cell Phenotype

Dendritic cells (DCs) turn into the most potent antigen-presenting cells following a complex transforming process, which leads to their maturation. Herpes simplex virus-1 (HSV-1) amplicon vectors represent highly versatile viral vector platforms with the ability to transduce immature DCs at exceedingly high efficiencies, while the efficiency of infection of mature DCs is significantly low. However, the bacterial artificial chromosome (BAC)-dependent (BD) amplicon vectors tested so far do not result in the maturation of mouse bone marrow-derived DCs (BMDCs) in vitro. In this study we investigated the effects of light-helper-dependent (LHD) amplicon vectors produced with the replication-defective HSV-1 LaLΔJ helper virus system. First, we observed that transgene expression in BMDC cultures was equally potent between the LHD and the BD amplicon vectors. We determined that the percentage of transduced cells and the duration of transgene expression were negatively influenced by the presence of increasing levels of helper virus. Second, infection by the LHD amplicon vector as well as the helper HSV-1 LaLΔJ virus alone resulted in the phenotypic maturation of BMDCs and the expression of both interferon-stimulated genes and proinflammatory cytokines. Further comparisons of the gene expression of infected DCs showed that while interferon-stimulated genes such as Ifit1, Ifit3, Mx2, Isg15, and Cxcl10 were induced by both BD and LHD amplicon vectors, early proinflammatory cytokine gene expression (Tnfa, Il1a, Il1b, Il6, Il10, Il12b, Cxcl1, and Cxcl16) and DC maturation were mediated only by the LHD amplicons.

A novel IgE antibody targeting the prostate-specific antigen as a potential prostate cancer therapy

BACKGROUND

Prostate cancer (PCa) is the second leading cause of cancer deaths in men in the United States. The prostate-specific antigen (PSA), often found at high levels in the serum of PCa patients, has been used as a marker for PCa detection and as a target of immunotherapy. The murine IgG1 monoclonal antibody AR47.47, specific for human PSA, has been shown to enhance antigen presentation by human dendritic cells and induce both CD4 and CD8 T-cell activation when complexed with PSA. In this study, we explored the properties of a novel mouse/human chimeric anti-PSA IgE containing the variable regions of AR47.47 as a potential therapy for PCa. Our goal was to take advantage of the unique properties of IgE in order to trigger immune activation against PCa.

METHODS

Binding characteristics of the antibody were determined by ELISA and flow cytometry. In vitro degranulation was determined by the release of β-hexosaminidase from effector cells. In vivo degranulation was monitored in human FcεRIα transgenic mice using the passive cutaneous anaphylaxis assay. These mice were also used for a vaccination study to determine the in vivo anti-cancer effects of this antibody. Significant differences in survival were determined using the Log Rank test. In vitro T-cell activation was studied using human dendritic cells and autologous T cells.

RESULTS

The anti-PSA IgE, expressed in murine myeloma cells, is properly assembled and secreted, and binds the antigen and FcεRI. In addition, this antibody is capable of triggering effector cell degranulation in vitro and in vivo when artificially cross-linked, but not in the presence of the natural soluble antigen, suggesting that such an interaction will not trigger systemic anaphylaxis. Importantly, the anti-PSA IgE combined with PSA also triggers immune activation in vitro and in vivo and significantly prolongs the survival of human FcεRIα transgenic mice challenged with PSA-expressing tumors in a prophylactic vaccination setting.

CONCLUSIONS

The anti-PSA IgE exhibits the expected biological properties and is capable of triggering immune activation and anti-tumor protection. Further studies on this antibody as a potential PCa therapy are warranted.

HSV-1 amplicon vectors launch the production of heterologous rotavirus-like particles and induce rotavirus-specific immune responses in mice

Virus-like particles (VLPs) are promising vaccine candidates because they represent viral antigens in the authentic conformation of the virion and are therefore readily recognized by the immune system. As VLPs do not contain genetic material they are safer than attenuated virus vaccines. In this study, herpes simplex virus type 1 (HSV-1) amplicon vectors were constructed to coexpress the rotavirus (RV) structural genes VP2, VP6, and VP7 and were used as platforms to launch the production of RV-like particles (RVLPs) in vector-infected mammalian cells. Despite the observed splicing of VP6 RNA, full-length VP6 protein and RVLPs were efficiently produced. Intramuscular injection of mice with the amplicon vectors as a two-dose regimen without adjuvants resulted in RV-specific humoral immune responses and, most importantly, immunized mice were partially protected at the mucosal level from challenge with live wild-type (wt) RV. This work provides proof of principle for the application of HSV-1 amplicon vectors that mediate the efficient production of heterologous VLPs as genetic vaccines.

CD4+ T cell effects on CD8+ T cell location defined using bioluminescence

T lymphocytes of the CD8+ class are critical in delivering cytotoxic function and in controlling viral and intracellular infections. These cells are “helped” by T lymphocytes of the CD4+ class, which facilitate their activation, clonal expansion, full differentiation and the persistence of memory. In this study we investigated the impact of CD4+ T cells on the location of CD8+ T cells, using antibody-mediated CD4+ T cell depletion and imaging the antigen-driven redistribution of bioluminescent CD8+ T cells in living mice. We documented that CD4+ T cells influence the biodistribution of CD8+ T cells, favoring their localization to abdominal lymph nodes. Flow cytometric analysis revealed that this was associated with an increase in the expression of specific integrins. The presence of CD4+ T cells at the time of initial CD8+ T cell activation also influences their biodistribution in the memory phase. Based on these results, we propose the model that one of the functions of CD4+ T cell “help” is to program the homing potential of CD8+ T cells.

Herpes simplex virus type 1/adeno-associated virus hybrid vectors

Herpes simplex virus type 1 (HSV-1) amplicons can accommodate foreign DNA of any size up to 150 kbp and, therefore, allow extensive combinations of genetic elements. Genomic sequences as well as cDNA, large transcriptional regulatory sequences for cell type-specific expression, multiple transgenes, and genetic elements from other viruses to create hybrid vectors may be inserted in a modular fashion. Hybrid amplicons use genetic elements from HSV-1 that allow replication and packaging of the vector DNA into HSV-1 virions, and genetic elements from other viruses that either direct integration of transgene sequences into the host genome or allow episomal maintenance of the vector. Thus, the advantages of the HSV-1 amplicon system, including large transgene capacity, broad host range, strong nuclear localization, and availability of helper virus-free packaging systems are retained and combined with those of heterologous viral elements that confer genetic stability to the vector DNA. Adeno-associated virus (AAV) has the unique capability of integrating its genome into a specific site, designated AAVS1, on human chromosome 19. The AAV rep gene and the inverted terminal repeats (ITRs) that flank the AAV genome are sufficient for this process. HSV-1 amplicons have thus been designed that contain the rep gene and a transgene cassette flanked by AAV ITRs. These HSV/AAV hybrid vectors direct site-specific integration of transgene sequences into AAVS1 and support long-term transgene expression.

The role of dendritic cells in alphaherpesvirus infections: archetypes and paradigms

Dendritic cells (DCs) play a critical role in orchestrating both innate and adaptive components of the immune system and are therefore of pivotal importance in the initiation of immune responses to control and eliminate viral infections. A major focus of this review is to give an overview on the recent findings that point out the importance of DCs in controlling alphaherpesvirus infections, but also indicate that these viruses have evolved several strategies to inhibit and/or exploit DC functions to delay or escape elimination by the immune system. In addition, we point out the common features and interspecies differences between DCs from man and animal, and discuss the potential use of animal alphaherpesvirus homologues to gain further insights into the interaction between alphaherpesviruses and DCs in their natural virus-host environment. Finally, recent knowledge on the potential of alphaherpesviruses as vectors for DC stimulation and their use for immunotherapy is presented.

Effects of herpes simplex virus amplicon transduction on murine dendritic cells

The herpes simplex virus (HSV)-based amplicon is a versatile vaccine platform that has been preclinically vetted as a gene-based immunotherapeutic for cancer, HIV, and neurodegenerative disorders. Although it is well known that injection of dendritic cells (DCs) transduced ex vivo with helper virus-free HSV amplicon vectors expressing disease-relevant antigens induces antigen-specific immune responses, the cellular receptor(s) by which the amplicon virion gains entry into DCs, as well as the effects that viral vector transduction impinges on the physiological status of these cells, is less understood. Herein, we examine the effects of amplicon transduction on mouse bone marrow-derived DCs. We demonstrate that HSV-1 cellular receptors HveC and HveA are expressed on the cell surface of murine DCs, and that HSV amplicons transduce DCs at high efficiency (>90%) with minimal effects on cell viability. Transduction of dendritic cells with amplicons induces a transient DC maturation phenotype as represented by self-limited upregulation of MHCII and CD11c markers. Mature DCs are less sensitive to HSV amplicon transduction than immature DCs regarding DC-related surface marker maintenance. From this and our previous work, we conclude that HSV amplicons transduce DCs efficiently, but impart differential and transient physiological effects on mature and immature DC pools, which will facilitate fine-tuning of this vaccination platform and further exploit its potential in immunotherapy.

Herpes Virus Amplicon Vectors

Since its emergence onto the gene therapy scene nearly 25 years ago, the replication-defective Herpes Simplex Virus Type-1 (HSV-1) amplicon has gained significance as a versatile gene transfer platform due to its extensive transgene capacity, widespread cellular tropism, minimal immunogenicity, and its amenability to genetic manipulation. Herein, we detail the recent advances made with respect to the design of the HSV amplicon, its numerous in vitro and in vivo applications, and the current impediments this virus-based gene transfer platform faces as it navigates a challenging path towards future clinical testing.

Dysfunctional memory CD8+ T cells after priming in the absence of the cell cycle regulator E2F4

The transcriptional repressor E2F4 is important for cell cycle exit and terminal differentiation in epithelial cells, neuronal cells and adipocytes but its role in T lymphocytes proliferation and memory formation is not known. Herein, we investigated the function of E2F4 protein for the formation of functional murine memory T cells. Murine transgenic CD8+ T cells were infected in vitro with lentivirus vector expressing a shRNA targeted against E2F4 followed by in vitro stimulation with SIINFEKL antigenic peptide. For in vivo assays, transduced cells were injected into congenic mice which were then infected with HSV-OVA. The primary response, memory formation and secondary stimulation were determined for CD8+ lentivirus transduced cells. In the absence of E2F4 cell cycle repressor, activated CD8+ T cells underwent intensive proliferation in vitro and in vivo. These cells had the ability to differentiate into memory cells in vivo, but they were defective in recall proliferation. We show that transient suppression of E2F4 during CD8+ T cell priming enhances primary proliferation and has a negative effect on secondary stimulation. These findings demonstrate that the cell cycle repressor E2F4 is essential for the formation of functional memory T cells. A decrease in CD8+ T-lymphocyte compartment would diminish our capacity to control viral infections.

HSV-1 amplicon vectors elicit polyfunctional T cell responses to HIV-1 Env, and strongly boost responses to an adenovirus prime

HSV-1 amplicon vectors elicit strong T-cell responses to encoded antigens but the qualitative nature of these responses is poorly understood. Antigen-specific CD4(+) and CD8(+) T-cell responses to amplicon and adenovirus (rAd5) vectors encoding HIV-1 gp120 were assessed following immunization of mice, by performing intracellular cytokine staining for IFNgamma, IL2 and TNFalpha, following stimulation of splenocytes with a HIV-1 Env peptide pool. The quality of the primary T-cell response to amplicon and rAd5 vectors was strikingly similar, but there were qualitative differences in responses to amplicon vectors that incorporated different promoters upstream of gp120 - suggesting that promoters can significantly influence immune response quality. When prime-boost combinations were studied, a rAd5 prime and amplicon boost elicited the highest T-cell response. Furthermore, protocols that incorporated a rAd5 prime consistently elicited a greater proportion of polyfunctional CD4(+) T-cells-regardless of boost. This suggests that initial priming can shape immune response quality after a boost. Overall, these findings provide insight into effective vector combinations for HIV-1 vaccine development.

HSV-1 amplicon vectors: a promising and versatile tool for gene delivery

Amplicons are defective and non-integrative vectors derived from herpes simplex virus type 1. They carry no virus genes in the vector genome and are, therefore, not toxic to the infected cells or pathogenic for the transduced organisms, making these vectors safe. In addition, the large transgenic capacity of amplicons, which allow delivery of < or = 150 Kbp of foreign DNA, make these vectors one of the most powerful, interesting and versatile gene delivery platforms. Here, the authors present recent technological developments that have significantly improved and extended the use of amplicons, both in cultured cells and in living organisms. In addition, this review illustrates the many possible applications that are presently being developed with amplicons and discuss the many difficulties still pending to be solved in order to achieve stable and physiologically regulated transgenic expression.

Imaging CD8+ T cell dynamics in vivo using a transgenic luciferase reporter

After activation, populations of antigen-specific T cells flow between sites of antigen expression, local lymphoid structures and other lymphoid and non-lymphoid organs. In this study, we documented the in vivo dynamics of a CD8(+) T cell response to antigen delivered using herpes simplex virus amplicon vectors and revealed several unexpected features. First, the T cells localized to the site of vector injection, as well as the draining lymph node within 24-48 h. Second, the major site to which T cells later redistributed were intra-abdominal lymphoid organs, including milky spots, mesenteric and lumbar lymph nodes. We determined the relationship between bioluminescent signal and antigen-specific T cell numbers in various lymphoid organs, and concluded that bioluminescent signal is a valid surrogate measure of T cell abundance in superficial lymph nodes, but not in deeper structures such as the spleen.

Spatial and temporal expression of herpes simplex virus type 1 amplicon-encoded genes: implications for their use as immunization vectors

There is great interest in developing new immunization vectors. Helper virus-free herpes amplicons, plasmid-based vectors that encode no viral gene products and have an extremely large coding capacity, are attractive viral vaccine candidates for expressing recombinant proteins in vivo for immunization. Earlier studies in mice, using amplicons encoding the gp120 protein of human immunodeficiency virus (HIV), resulted in strikingly robust cellular immune responses as measured by cytotoxicity and interferon gamma enzyme-linked immunospot assays. To begin to understand how such vectors function in vivo to generate an immune response, we used amplicons encoding reporter constructs including green fluorescent protein (GFP) and luciferase to examine the duration of expression after administration to mice. Luciferase expression, measured with the IVIS system from Xenogen/Caliper Life Sciences (Hopkinton, MA) and by enzymatic assays of tissue extracts, revealed that expression after injection of the HSVluc amplicons peaked earlier than 24 hr after injection into mice. HSVegfp injection resulted in peak accumulation of GFP 24 hr after administration in vivo. Thus, both reporter genes revealed a rather rapid and robust expression pattern of short duration. The short period of expression appears in part to be due to gene silencing. Examination of the cells transduced by amplicons encoding GFP and human B7.1 suggested that the amplicons transduce a variety of cells, including professional antigen-presenting cells. From this and previous work, we conclude that amplicons may engender a potent immune response by directly transducing dendritic cells as well as by cross-priming of antigen produced by other transduced host cells.

Effect of promoter strength on protein expression and immunogenicity of an HSV-1 amplicon vector encoding HIV-1 Gag

Helper-free herpes simplex virus type-1 (HSV-1) amplicon vectors elicit robust immune responses to encoded proteins, including human immunodeficiency virus type-1 (HIV-1) antigens. To improve this vaccine delivery system, seven amplicon vectors were constructed, each encoding HIV-1 Gag under the control of a different promoter. Gag expression levels were analyzed in murine and human cell lines, as well as in biopsied tissue samples from injected mice; these data were then compared with Gag-specific T cell responses in BALB/c mice. The magnitude of the amplicon-induced immune response was found to correlate strongly with the level of Gag production both in vitro and in vivo. Interestingly, the best correlation of the strength of the amplicon-induced immune response was with antigen expression in cultured DC rather than expression at the tissue site of injection or in cultured cell lines. These findings may have implications for the generation of improved HSV-1 amplicon vectors for HIV-1 vaccine delivery.

Activation of antigen-presenting cells by DNA delivery vectors

Gene-based modulation of immune functions is a promising means of eliciting protective immunity and induction of tolerance. Novel viral and non-viral DNA delivery systems are being investigated to achieve efficient gene transfer into mammalian cells. Antigen-presenting cells (APCs), in particular dendritic cells, are crucial targets in this context due to their capacity to initiate and direct effector functions. The increasing relevance of APCs as targets of DNA vectors calls for an assessment of vector-driven activation of these cells. For viral vectors, a putative pathway of APC activation would be Toll-like receptor signalling for certain RNA genome viruses. On the other hand, non-viral vectors appear to mature APCs by interaction of polymeric particulates or bioactive lipids with cellular mechanisms. The rational design of DNA-based therapies is possible only when the intrinsic effects of the vector and immune modulation originating from the DNA are delineated. This paper will summarise recent reports of adjuvant properties of viral and non-viral delivery systems.

Combinational adenovirus-mediated gene therapy and dendritic cell vaccine in combating well-established tumors

Recent developments in tumor immunology and biotechnology have made cancer gene therapy and immunotherapy feasible. The current efforts for cancer gene therapy mainly focus on using immunogenes, chemogenes and tumor suppressor genes. Central to all these therapies is the development of efficient vectors for gene therapy. By far, adenovirus (AdV)-mediated gene therapy is one of the most promising approaches, as has confirmed by studies relating to animal tumor models and clinical trials. Dendritic cells (DCs) are highly efficient, specialized antigen-presenting cells, and DC-based tumor vaccines are regarded as having much potential in cancer immunotherapy. Vaccination with DCs pulsed with tumor peptides, lysates, or RNA, or loaded with apoptotic/necrotic tumor cells, or engineered to express certain cytokines or chemokines could induce significant antitumor cytotoxic T lymphocyte (CTL) responses and antitumor immunity. Although both AdV-mediated gene therapy and DC vaccine can both stimulate antitumor immune responses, their therapeutic efficiency has been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or to growth inhibition of small tumors. However, this approach has been unsuccessful in combating well-established tumors in animal models. Therefore, a major strategic goal of current cancer immunotherapy has become the development of novel therapeutic strategies that can combat well-established tumors, thus resembling real clinical practice since a good proportion of cancer patients generally present with significant disease. In this paper, we review the recent progress in AdV-mediated cancer gene therapy and DC-based cancer vaccines, and discuss combined immunotherapy including gene therapy and DC vaccines. We underscore the fact that combined therapy may have some advantages in combating well-established tumors vis-a-vis either modality administered as a monotherapy.

HSV-1-based amplicon vectors: design and applications

Amplicons are defective, helper-dependent herpes simplex virus type 1 (HSV-1)-based vectors able to convey more than 100 kbp of foreign DNA to the nucleus of mammalian cells. This unique feature make amplicons very appealing for preventive or therapeutic gene transfer requiring the transduction of very large pieces of DNA, as well as for upstream fundamental studies, such as functional genomics. Several recent achievements in amplicon technology have allowed to produce relatively large amounts of essentially helper-free amplicons, as well as to expand the host range of these vectors. In this review, we will update the current know-how concerning design, construction, and recent applications, as well as the potential and current limitations, of this interesting and promising class of vectors.

Human dendritic cells transduced with herpes simplex virus amplicons encoding human immunodeficiency virus type 1 (HIV-1) gp120 elicit adaptive immune responses from human cells engrafted into NOD/SCID mice and confer partial protection against HIV-1 challenge

Small-animal models are needed to test human immunodeficiency virus (HIV) vaccine efficacy following viral challenge. To this end, we examined HIV-1-specific immune responses following immunization of nonobese diabetic-severe combined immunodeficient mice that were repopulated with human peripheral blood lymphocytes (hu-PBL-NOD/SCID mice). Autologous dendritic cells (DC) were transduced ex vivo with replication-defective, helper virus-free, herpes simplex virus type 1 (HSV-1) amplicons that expressed HIV-1 gp120 and were then injected into the hu-PBL-NOD/SCID mice. This resulted in primary HIV-1-specific humoral and cellular immune responses. Serum samples from vaccinated animals contained human immunoglobulin G that reacted with HIV-1 Env proteins by enzyme-linked immunosorbent assay and neutralized the infectivity of HIV-1 LAI and ADA strains. T cells isolated from the mice responded to viral antigens by producing gamma interferon when analyzed by enzyme-linked immunospot assay. Importantly, exposure of the vaccinated animals to infectious HIV-1 demonstrated partial protection against infectious HIV-1 challenge. This was reflected by a reduction in HIV-1(ADA) and by protection of the engrafted human CD4(+) T lymphocytes against HIV-1(LAI)-induced cytotoxicity. These data demonstrate that transduction of DC by HSV amplicon vectors expressing HIV-1 gp120 induce virus-specific immune responses in hu-PBL-NOD/SCID mice. This mouse model may be a useful tool to evaluate human immune responses and protection against viral infection following vaccination.

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

BACKGROUND

Human prostate specific antigen (PSA) is expressed selectively in prostate epithelium and is a potential target for the immunotherapy against prostate cancer. Various PSA-based vaccines have been reported to induce cytotoxic T lymphocyte (CTL) responses in animal models. Here, we present the identification and validation of an immunodominant CTL epitope of PSA in C57Bl/6 mice (H-2(b)).

METHODS

PSA-specific CTLs were induced by immunization with a plasmid expressing PSA. Epitope specificity of the CTLs was determined by their reactivity against a panel of C-terminus truncated or mutated PSA proteins and use of bioinformatical prediction with the SYFPEITHI algorithm.

RESULTS

The majority of PSA-specific CTLs were directed against a single H-2D(b) restricted epitope corresponding to the amino acid residues 65-74 (HCIRNKSVIL) of the protein. The CTLs had similar functional avidity against two putative H-2D(b) binding peptides: a 9-aa-long psa65-73 (HCIRNKSVI) and a 10-aa-long psa65-74 (HCIRNKSVIL).

CONCLUSIONS

We demonstrate that the psa65-73 peptide can be used for reactivation of PSA-specific CTLs in vitro and ex vivo, and H-2D(b) pentamers assembled with this peptide are an efficient tool for monitoring of PSA-specific CTL responses after DNA vaccination.

Gene therapy meets vaccine development

Therapeutic vaccines such as those used to combat cancer or persistent viral infection are required to reprogramme a downregulated immune system. This presents a difficult challenge for vaccine design and merits the development of novel immunization protocols. Currently, we know that mobilization of dendritic cells (DCs) to present antigens to T lymphocytes is crucial for effective immunization. Our increasing understanding of DC biology, coupled with the growing sophistication of viral vectors developed for gene therapy, makes more rational vaccine design an exciting possibility. Here we propose that engineering viral vectors to express antigens in activated DCs will provide the most effective vaccines for priming an immune response.

HSV amplicon-mediated Aβ vaccination in Tg2576 mice: differential antigen-specific immune responses

Given the participation of amyloid beta (Abeta) in Alzheimer's disease (AD) pathogenesis the derivation of experimental therapeutics to prevent Abeta fibrillogenesis and/or enhance removal of parenchymal amyloid deposits represent viable disease-modifying approaches. Active Abeta-based immunotherapies have shown promise in mouse AD models, but application in human trials was accompanied by moderate brain inflammation in a subset of patients. Immune-shaping vaccine platforms may mitigate adverse effects. Herein, we describe the use of herpes simplex virus (HSV)-derived amplicons to elicit distinctive immune responses against Abeta. Two vaccine vectors were constructed: one expressing Abeta1-42 alone (HSVAbeta), and a second expressing Abeta1-42 fused with the molecular adjuvant tetanus toxin Fragment C (HSVAbeta/TtxFC). Peripheral administration of these vaccines augmented humoral responses to Abeta and reduced CNS Abeta deposition in Tg2576 AD mice. Interestingly and unexpectedly, HSVAbeta vaccination was uniquely toxic and incited the expression of pro-inflammatory molecule transcripts within the hippocampi of Tg2576 mice, suggesting that this paradigm may serve as a relevant model to study Abeta vaccine-elicited CNS inflammatory syndromes.

Exploiting dendritic cells for cancer immunotherapy: genetic modification of dendritic cells

Dendritic cells (DCs) are pivotal regulators of immune reactivity and immune tolerance. The observation that DCs can recruit naive T cells has invigorated cancer immunology and led to the proposal of DCs as the basis for vaccines designed for the treatment of cancer. Designing effective strategies to load DCs with antigens is a challenging field of research. The successful realization of gene transfer to DCs will be highly dependent on the employed vector system. Here, we review various viral and non-viral gene transfer systems, and discuss their distinct characteristics and possible advantages and disadvantages in respect to their use in DC-based immunotherapy.

Improved packaging system for generation of high-level noncytotoxic HSV-1 amplicon vectors using Cre-loxP site-specific recombination to delete the packaging signals of defective helper genomes

Amplicons are promising helper-dependent HSV-1-derived vectors that allow the transfer and expression of very large foreigner DNA into dividing and quiescent cells. We had already described an approach to prepare large amounts of high-titer amplicon vectors, using Cre-loxP site-specific recombination system to delete the packaging ("a") signals of an HSV-1 recombinant helper virus (HSV-1 LaL). Amplicon vectors prepared using such a system showed a level of contamination with helper particles lower than 1%. The residual helper particles generated by this system are, however, replication-competent, thus precluding their use in gene therapy. To avoid such potential spread of residual particles, we present here the development of a defective Cre-loxP-based helper virus (HSV-1 LaL Delta J), deleted of the genes encoding ICP4 and ICP34.5 proteins from the helper genome, in addition to the native "a" signals. HSV-1 LaL Delta J carries a single floxed "a" signal in gC locus. To produce HSV-1 LaL Delta J and to prepare the amplicon vectors, we have constructed two novel cell lines expressing the essential ICP4 protein, either alone or in combination with Cre recombinase. These cell lines were conceived to complement ICP4 while minimizing the probability of generating replication-competent particles. In this paper we present results demonstrating that the novel helper system allows ready production of large amounts of high-titer amplicon vectors. Residual helper particles generated still do not exceed 0.5% of the viral population and can grow only in cells expressing ICP4. Amplicon vectors produced with this method showed no cytotoxicty for infected cells.

Murine cytomegalovirus abortively infects human dendritic cells, leading to expression and presentation of virally vectored genes

Dendritic cells (DC) are potent antigen-presenting cells that play a crucial role in antigen-specific immune responses. Thus, the targeting of exogenous antigens to DC has become a popular approach for cancer immunotherapy and vaccine development. In this report, we studied the interplay between murine cytomegalovirus (MCMV) and human monocyte-derived DC. The results showed that an enhanced green fluorescent protein (EGFP)-encoding, replication-competent MCMV vector underwent abortive infection in human DC; this was accompanied by the efficient expression of EGFP. Infection of human DC by this vector resulted in a modest increase in the expression of cell surface proteins associated with DC maturation and has no significant effect on the immunostimulatory function of the cells, as reflected by their ability to support T-cell proliferation in a mixed-lymphocyte reaction. Finally, an MCMV vector encoding the human immunodeficiency virus type 1 (HIV-1) gp120 envelope glycoprotein was constructed and used to infect cultured human DC. The infected DC were shown to be capable of stimulating the expansion of autologous, gp120-specific, class I-restricted T lymphocytes from an HIV-1-negative donor, as determined by tetramer staining and enzyme-linked immunospot analysis. Taken together, these results suggest that MCMV may have potential utility as a vector for human vaccine development.

Immune responses to replication-defective HSV-1 type vectors within the CNS: implications for gene therapy

Herpes simplex virus (HSV) is a naturally occurring double-stranded DNA virus that has been adapted into an efficient vector for in vivo gene transfer. HSV-based vectors exhibit wide tropism, large transgene size capacity, and moderately prolonged transgene expression profiles. Clinical implementation of HSV vector-based gene therapy for prevention and/or amelioration of human diseases eventually will be realized, but inherently this goal presents a series of significant challenges, one of which relates to issues of immune system involvement. Few experimental reports have detailed HSV vector-engendered immune responses and subsequent resolution events primarily within the confines of the central nervous system. Herein, we describe the immunobiology of HSV and its derived vector platforms, thus providing an initiation point from where to propose requisite experimental investigation and potential approaches to prevent and/or counter adverse antivector immune responses.

Advances in dendritic cell-based vaccine of cancer

Dendritic cells (DCs) are potent antigen presenting cells that exist in virtually every tissue, and from which they capture antigens and migrate to secondary lymphoid organs where they activate naïve T cells. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have allowed the development of methods to generate large numbers of these cells in vitro. Because of their immunoregulatory capacity, vaccination with tumor antigen-presenting DCs has been proposed as a treatment modality for cancer. In animal models, vaccination with DCs pulsed with tumor peptides, lysates, or RNA or loaded with apoptotic/necrotic tumor cells could induce significant antitumor CTL responses and antitumor immunity. However, the results from early clinical trails pointed to a need for additional improvement of DC-based vaccines before they could be considered as practical alternatives to the existing cancer treatment strategies. In this regard, subsequent studies have shown that DCs that express transgenes encoding tumor antigens are more potent primers of antitumor immunity both in vitro and in vivo than DCs simply pulsed with tumor peptides. Furthermore, DCs that have been engineered to express certain cytokines or chemokines can display a substantially improved maturation status, capacity to migrate to secondary lymphoid organs in vivo, and abilities to stimulate tumor-specific T cell responses and induce tumor immunity in vivo. In this review we also discuss a number of factors that are important considerations in designing DC vaccine strategies, including (i) the type and concentrations of tumor peptides used for pulsing DCs; (ii) the timing and intervals for DC vaccination/boostable data on DC vaccination portends bright prospects for this approach to tumor immune therapy, either alone or in conjunction with other therapies.

Genetically modified dendritic cells--a new, promising cancer treatment strategy?

Dendritic cells (DCs), the most potent antigen-presenting cells (APCs), were discovered almost 30 years ago. Due to the priming of antigen-specific immune responses mediated by CD4+ and CD8+ lymphocytes, DCs are crucial for the induction of adaptive immunity against cancer. Therefore, vaccination of cancer patients with DCs presenting tumour-associated antigens (TAAs) have been believed to be a promising anticancer strategy. Multiple clinical trials have been carried out in order to evaluate the safety and efficacy of cancer vaccines based on antigen-pulsed DCs. However, pulsing of DCs with particular peptides has several disadvantages: i) short-time duration of antigen-major histocompatability complex (MHC) complexes, ii) a requirement for matching defined peptides with MHC complexes and iii) exclusive presentation of single antigen epitopes. Application of gene transfer technologies in the field of DC-based vaccines made possible the development of novel, anticancer immunisation strategies. In several animal models, DCs modified with genes encoding TAA or immunostimulatory proteins have been shown to be effective in the induction of antitumour immune responses. Based on these encouraging results, a first clinical trial of prostate cancer patients vaccinated with gene modified DCs has recently been initiated. In this article, methods used for genetic modification of DCs and anticancer vaccination strategies based on genetically modified DCs are reviewed.

Herpes simplex virus type 1/adeno-associated virus hybrid vectors mediate site-specific integration at the adeno-associated virus preintegration site, AAVS1, on human chromosome 19

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors have a large transgene capacity and can efficiently infect many different cell types. One disadvantage of HSV-1 vectors is their instability of transgene expression. By contrast, vectors based on adeno-associated virus (AAV) can either persist in an episomal form or integrate into the host cell genome, thereby supporting long-term gene expression. AAV expresses four rep genes, rep68, -78, -40, and -52. Of those, rep68 or rep78 are sufficient to mediate site-specific integration of the AAV DNA into the host cell genome. The major disadvantage of AAV vectors is the small transgene capacity ( approximately 4.6 kb). In this study, we constructed HSV/AAV hybrid vectors that contained, in addition to the standard HSV-1 amplicon elements, AAV rep68, rep78, both rep68 and -78, or all four rep genes and a reporter gene that was flanked by the AAV inverted terminal repeats (ITRs). Southern blots of Hirt DNA from cells transfected with the hybrid vectors and HSV-1 helper DNA demonstrated that both the AAV elements and the HSV-1 elements were functional in the context of the hybrid vector. All hybrid vectors could be packaged into HSV-1 virions, although those containing rep sequences had lower titers than vectors that did not. Site-specific integration at AAVS1 on human chromosome 19 was directly demonstrated by PCR and sequence analysis of ITR-AAVS1 junctions in hybrid vector-transduced 293 cells. Cell clones that stably expressed the transgene for at least 12 months could easily be isolated without chemical selection. In the majority of these clones, the transgene cassette was integrated at AAVS1, and no sequences outside the ITR cassette, rep in particular, were present as determined by PCR, ITR rescue/replication assays, and Southern analysis. Some of the clones contained random integrations of the transgene cassette alone or together with sequences outside the ITR cassette. These data indicate that the long-term transgene expression observed following transduction with HSV/AAV hybrid vectors is, at least in part, supported by chromosomal integration of the transgene cassette, both randomly and site specifically.

Expression of human immunodeficiency virus type 1 gp120 from herpes simplex virus type 1-derived amplicons results in potent, specific, and durable cellular and humoral immune responses

Herpes simplex virus type 1 (HSV-1) infects a wide range of cells, including dendritic cells. Consequently, HSV-1 vectors may be capable of eliciting strong immune responses to vectored antigens. To test this hypothesis, an HSV-1 amplicon plasmid encoding human immunodeficiency virus type 1 gp120 was constructed, and murine immune responses to helper virus-free amplicon preparations derived from this construct were evaluated. Initial studies revealed that a single intramuscular (i.m.) injection of 10(6) infectious units (i.u.) of HSV:gp120 amplicon particles (HSV:gp120) elicited Env-specific cellular and humoral immune responses. A potent, CD8(+)-T-cell-mediated response to an H-2D(d)-restricted peptide from gp120 (RGPGRAFVTI) was measured by a gamma interferon ELISPOT and was confirmed by standard cytotoxic-T-lymphocyte assays. Immunoglobulin G enzyme-linked immunosorbent assay analysis showed the induction of a strong, Env-specific antibody response. An i.m. or an intradermal administration of HSV:gp120 at the tail base elicited a more potent cellular immune response than did an intraperitoneal (i.p.) inoculation, although an i.p. introduction generated a stronger humoral response. The immune response to HSV:gp120 was durable, with robust cellular and humoral responses persisting at 171 days after a single 10(6)-i.u. inoculation. The immune response to HSV:gp120 was also found to be dose dependent: as few as 10(4) i.u. elicited a strong T-cell response. Finally, HSV:gp120 elicited significant Env-specific cellular immune responses even in animals that had been previously infected with wild-type HSV-1. Taken together, these data strongly support the use of helper-free HSV-1 amplicon particles as vaccine delivery vectors.

Prostate-specific antigen vaccines for prostate cancer

Prostate cancer is the most common malignant tumour in men and there are few treatment options available once the tumour becomes refractory to hormonal manipulation. Prostate-specific antigen (PSA) is a secretory glycoprotein that is commonly expressed by prostatic epithelial cells and is found in elevated levels in the serum of men with prostate cancer. The identification of T cell specific epitopes within the coding sequence of PSA has led to the development of various vaccine strategies that target PSA in an attempt to treat established prostate cancer. These strategies have included human leukocyte antigen-restricted PSA peptides, dendritic cells pulsed with PSA, recombinant viruses expressing PSA and combinations of different vectors. In addition to PSA, several other antigens have been described that may be useful for targeting prostate tumours by vaccines. Animal studies have established the feasibility and safety for many of these agents and clinical trials are now in progress to evaluate the immunological and clinical responses of PSA vaccines. Further research in manipulating anti-PSA immunity with cytokines, costimulatory molecules and other immune modulating agents will likely improve the therapeutic effectiveness of PSA vaccines. Clinical trials designed to evaluate the effects of vaccination in different stages of disease and through different routes of administration need to be performed to define the optimal schedule for PSA vaccines in patients with prostate cancer, or for those at high risk of developing the disease.