Human PBMC-derived dendritic cells transduced with an adenovirus vectorinduce cytotoxic T-lymphocyte responses against a vector-encoded antigen in vitro

Breaking Entry-and Species Barriers: LentiBOOST® Plus Polybrene Enhances Transduction Efficacy of Dendritic Cells and Monocytes by Adenovirus 5

Due to their ability to trigger strong immune responses, adenoviruses (HAdVs) in general and the serotype5 (HAdV-5) in particular are amongst the most popular viral vectors in research and clinical application. However, efficient transduction using HAdV-5 is predominantly achieved in coxsackie and adenovirus receptor (CAR)-positive cells. In the present study, we used the transduction enhancer LentiBOOST^® comprising the polycationic Polybrene to overcome these limitations. Using LentiBOOST^®/Polybrene, we yielded transduction rates higher than 50% in murine bone marrow-derived dendritic cells (BMDCs), while maintaining their cytokine expression profile and their capability to induce T-cell proliferation. In human dendritic cells (DCs), we increased the transduction rate from 22% in immature (i)DCs or 43% in mature (m)DCs to more than 80%, without inducing cytotoxicity. While expression of specific maturation markers was slightly upregulated using LentiBOOST^®/Polybrene on iDCs, no effect on mDC phenotype or function was observed. Moreover, we achieved efficient HAdV5 transduction also in human monocytes and were able to subsequently differentiate them into proper iDCs and functional mDCs. In summary, we introduce LentiBOOST^® comprising Polybrene as a highly potent adenoviral transduction agent for new in-vitro applications in a set of different immune cells in both mice and humans.

Modification of human embryonic stem cell-derived dendritic cells with mRNA for efficient antigen presentation and enhanced potency

AIM

Dendritic cell (DC)-based vaccines are designed to exploit the intrinsic capacity of these highly effective antigen presenting cells to prime and boost antigen-specific T-cell immune responses. Successful development of DC-based vaccines will be dependent on the ability to utilize and harness the full potential of these potent immune stimulatory cells. Recent advances to generate DCs derived from human embryonic stem cells (hESCs) that are suitable for clinical use represent an alternative strategy from conventional approaches of using patient-specific DCs. Although the differentiation of hESC-derived DCs in serum-free defined conditions has been established, the stimulatory potential of these hESC-derived DCs have not been fully evaluated.

METHODS

hESC-derived DCs were differentiated in serum-free defined culture conditions. The delivery of antigen into hESC-derived DCs was investigated using mRNA transfection and replication-deficient adenoviral vector transduction. hESC-derived DCs modified with antigen were evaluated for their capacity to stimulate antigen-specific T-cell responses with known HLA matching. Since IL-12 is a key cytokine that drives T-cell function, further enhancement of DC potency was evaluated by transfecting mRNA encoding the IL-12p70 protein into hESC-derived DCs.

RESULTS

The transfection of mRNA into hESC-derived DCs was effective for heterologous protein expression. The efficiency of adenoviral vector transduction into hESC-derived DCs was poor. These mRNA-transfected DCs were capable of stimulating human telomerase reverse transcriptase antigen-specific T cells composed of varying degrees of HLA matching. In addition, we observed the transfection of mRNA encoding IL-12p70 enhanced the T-cell stimulation potency of hESC-derived DCs.

CONCLUSION

These data provide support for the development and modification of hESC-derived DCs with mRNA as a potential strategy for the induction of T-cell-mediated immunity.

Tumors suppress in situ proliferation of cytotoxic T cells by promoting differentiation of Gr-1(+) conventional dendritic cells through IL-6

Cancers are often accompanied by inflammation, which can promote tumor growth, invasion, and metastases. We show that the tumor microenvironment induces the development of a Gr-1(+) conventional dendritic cell (cDC) subpopulation that is functionally defective. Gr-1(+)cDCs differentiated from recruited immediate precursors of cDCs, a process supported by the inflammatory cytokine milieu in tumors. Inhibition of Gr-1(+)cDC differentiation enhanced intratumor expansion of cytotoxic CD8(+) T cells (CTLs), resulting in suppression of tumor growth. Diphtheria toxin treatment of CD11c-diphtheria toxin receptor chimeras revealed the importance of intratumor cDCs in stimulating CTL proliferation in situ. Our study demonstrates a key role of intratumor cDCs in determining antitumor CTL responses and suggests that they may be an appropriate target for tumor immunotherapy.

Adenoviral-transduced dendritic cells are susceptible to suppression by T regulatory cells and promote interleukin 17 production

Dendritic cell (DC) vaccines offer a robust platform for the development of cancer vaccines, but their effectiveness is thought to be limited by T regulatory cells (Tregs). Recombinant adenoviruses (RAdV) have been used successfully to engineer tumor antigen expression in DCs, but the impact of virus transduction on susceptibility to suppression by Tregs is unknown. We investigated the functional consequences of exposure to adenovirus on interactions between human monocyte-derived DCs and Tregs. Since the development of Tregs is linked to that of pro-inflammatory Th17 cells, the role of Th17 cells and IL-17-producing Tregs in the context of DC-based immunotherapies was also investigated. We found that Tregs potently suppressed the co-stimulatory capacity of RAdV-transduced DCs, regardless of whether the DCs were maturated by inflammatory cytokines or by exposure to Th1 or Th17 cells. Furthermore, exposure of Tregs to RAdV-exposed DCs increased IL-17 production and suppressive capacity, and correlated with enhanced secretion of IL-1β and IL-6 by DCs. The findings that DCs exposed to RAdV are suppressed by Tregs, promote Treg plasticity, and enhance Treg suppression indicates that strategies to limit Tregs will be required to enhance the efficacy of such DC-based immunotherapies.

Evaluation of transduction efficiency in macrophage colony-stimulating factor differentiated human macrophages using HIV-1 based lentiviral vectors

BACKGROUND

Monocyte-derived macrophages contribute to atherosclerotic plaque formation. Therefore, manipulating macrophage function could have significant therapeutic value. The objective of this study was to determine transduction efficiency of two HIV-based lentiviral vector configurations as delivery systems for the transduction of primary human blood monocyte-derived macrophages.

RESULTS

Human blood monocytes were transduced using two VSV-G pseudotyped HIV-1 based lentiviral vectors containing EGFP expression driven by either native HIV-LTR (VRX494) or EF1α promoters (VRX1090). Lentiviral vectors were added to cultured macrophages at different times and multiplicities of infection (MOI). Transduction efficiency was assessed using fluorescence microscopy and flow cytometry. Macrophages transduced between 2 and 120 hours after culturing showed the highest transduction efficiency at 2-hours transduction time. Subsequently, cells were transduced 2 hours after culturing at various vector concentrations (MOIs of 5, 10, 25 and 50) to determine the amount of lentiviral vector particles required to maximally transduce human monocyte-derived macrophages. On day 7, all transduced cultures showed EGFP-positive cells by microscopy. Flow cytometric analysis showed with all MOIs a peak shift corresponding to the presence of EGFP-positive cells. For VRX494, transduction efficiency was maximal at an MOI of 25 to 50 and ranged between 58 and 67%. For VRX1090, transduction efficiency was maximal at an MOI of 10 and ranged between 80 and 90%. Thus, transductions performed with VRX1090 showed a higher number of EGFP-positive cells than VRX494.

CONCLUSIONS

This report shows that VSV-G pseudotyped HIV-based lentiviral vectors can efficiently transduce human blood monocyte-derived macrophages early during differentiation using low particle numbers that do not interfere with differentiation of monocytes into macrophages.

An Ad5[E1-, E2b-]-HER2/neu vector induces immune responses and inhibits HER2/neu expressing tumor progression in Ad5 immune mice

Immunotherapy is a promising approach for the treatment of cancers. Modified adenovirus 5 (Ad5) vectors have been used as a platform to deliver genes encoding tumor associated antigens (TAA). A major obstacle to Ad5 vector immunotherapy has been the induction of vector immunity following administration or the presence of pre-existing Ad5 immunity, which results in vector mitigation. It has been reported by us that the Ad5[E1-, E2b-] platform with unique deletions in the E1, E2b and E3 regions can induce potent cell mediated immunity (CMI) against delivered transgene products in the presence of pre-existing Ad5 immunity. Here we report the use of an Ad5[E1-, E2b-] vector platform expressing the TAA HER2/neu as a breast cancer immunotherapeutic agent. Ad5[E1-, E2b-]-HER2/neu induced potent CMI against HER2/neu in Ad5 naïve and Ad5 immune mice. Humoral responses were also induced and antibodies could lyse HER2/neu expressing tumor cells in the presence of complement in vitro. Ad5[E1-, E2b-]-HER2/neu prevented establishment of HER2/neu-expressing tumors and significantly inhibited progression of established tumors in Ad5 naïve and Ad5 immune murine models. These data demonstrate that in vivo delivery of Ad5[E1-, E2b-]-HER2/neu can induce anti-TAA immunity and inhibit progression of HER2/neu expressing cancers.

Lentiviral vectors for immunization: an inflammatory field

Lentiviruses are retroviruses that are able to transduce both dividing and nondividing cells. Dendritic cells are key players in the innate and adaptive immune responses, and are natural targets for lentiviruses. Lentiviral vectors (LVs) have recently reached the clinical gene therapy arena, prompting their use as clinical vaccines. In recent years, LVs have emerged as a robust and practical experimental platform for gene delivery and rational genetic reprogramming of dendritic cells. Here, we present the status quo of the LV system for protective or therapeutic vaccine development. This vector system has been extensively evaluated for ex vivo and in vivo (immuno)gene delivery. Improvements of the LV design in order to further grant a higher biosafety profile for vaccine development are presented.

Recruitment and differentiation of conventional dendritic cell precursors in tumors

The origin of dendritic cells (DCs) in tumors remains obscure. Recent studies indicate that conventional DCs (cDCs) in lymphoid tissues arise from a distinct population of committed cDC precursors (pre-cDCs) that originate in bone marrow and migrate via blood. In this study, we show that pre-cDCs are precursors for cDCs in tumors. Pre-cDCs from tumors, bone marrow, and spleen exhibit similar morphologic, immunophenotypic, and functional properties. Adoptive transfer studies show that bone marrow pre-cDCs migrate from blood into the tumor where they generate cDCs. The chemokine CCL3, which is markedly upregulated in tumors, promotes pre-cDC recruitment. Both pre-cDCs and their cDC progeny actively proliferate within the tumor. cDCs that arise from pre-cDCs in tumors express lower levels of CD11c and MHC class II as compared with those in spleen; however, there was no difference in their abilities to respond to maturation stimuli or activate Ag-specific lymphocytes in vitro. Our study provides the first evidence supporting a role for pre-cDCs in DC development in tumors and suggests a potential target for cancer immunotherapy.

Targeted NF-kappaB inhibition of asthmatic serum-mediated human monocyte-derived dendritic cell differentiation in a transendothelial trafficking model

Transendothelial trafficking model mimics in vivo differentiation of monocytes into dendritic cells (DC). The serum from patients with systemic lupus erythematosus promotes the differentiation of monocytes into mature DC. We have shown that selective inhibition of NF-kappaB by adenoviral gene transfer of a novel mutated IkappaBalpha (AdIkappaBalphaM) in DC contributes to T cell tolerance. Here we demonstrated for the first time that asthmatic serum facilitated human monocyte-derived DC (MDDC) maturation associated with increased NF-kappaB activation in this model. Furthermore, selective blockade of NF-kappaB by AdIkappaBalphaM in MDDC led to increased apoptosis, and decreased levels of CD80, CD83, CD86, and IL-12 p70 but not IL-10 in asthmatic serum-stimulated MDDC, accompanied by reduced proliferation of T cells. These results suggest that AdIkappaBalphaM-transferred MDDC are at a more immature stage which is beneficial to augment the immune tolerance in asthma.

Regulation of antigen presentation machinery in human dendritic cells by recombinant adenovirus

Recombinant adenoviral vectors (AdV) are potent vehicles for antigen engineering of dendritic cells (DC). DC engineered with AdV to express full length tumor antigens are capable stimulators of antigen-specific polyclonal CD8+ and CD4+ T cells. To determine the impact of AdV on the HLA class I antigen presentation pathway, we investigated the effects of AdV transduction on antigen processing machinery (APM) components in human DC. Interactions among AdV transduction, maturation, APM regulation and T cell activation were investigated. The phenotype and cytokine profile of DC transduced with AdV was intermediate, between immature (iDC) and matured DC (mDC). Statistically significant increases in expression were observed for peptide transporters TAP-1 and TAP-2, and HLA class I peptide-loading chaperone ERp57, as well as co-stimulatory surface molecule CD86 due to AdV transduction. AdV transduction enhanced the expression of APM components and surface markers on mDC, and these changes were further modulated by the timing of DC maturation. Engineering of matured DC to express a tumor-associated antigen stimulated a broader repertoire of CD8+ T cells, capable of recognizing immunodominant and subdominant epitopes. These data identify molecular changes in AdV-transduced DC (AdV/DC) that could influence T cell priming and should be considered in design of cancer vaccines.

Immunotherapy opportunities in ovarian cancer

Ovarian cancer is responsible for the majority of gynecologic cancer deaths and despite the highest standard of multimodality therapy with surgery and cytotoxic chemotherapy, long-term survival remains low. With compelling evidence that epithelial ovarian cancer is an immunogenic tumor capable of stimulating an antitumor immune response, renewed efforts to develop immune therapies to augment the efficacy of traditional therapies are underway. Current immunotherapies focus on varied modes of antitumor vaccine development, particularly with the use of dendritic cell vaccines, effective methods for adoptive T-cell transfer and combinatorial approaches with immune modulatory therapy subverting natural tolerance mechanisms or boosting effector mechanisms. Additional combinatorial approaches include the use of cytokines and/or chemotherapy with immune therapy.

Modulation of viability and maturation of human monocyte-derived dendritic cells by oncolytic adenoviruses

Adenoviral oncolysis is a promising new modality for treatment of cancer based on selective viral replication in tumor cells. However, tumor cell killing by adenoviral oncolysis needs to be improved to achieve therapeutic benefit in the clinic. Towards this end, the activation of anti-tumor immunity by adenoviral oncolysis might constitute a potent mechanism for systemic killing of uninfected tumor cells, thereby effectively complementing direct tumor cell killing by the virus. Knowledge of anti-tumor immune induction by adenoviral oncolysis, however, is lacking mostly due to species-specificity of adenovirus replication, which has hampered studies of human oncolytic adenoviruses in animals. We suggest the analysis of interactions of oncolytic adenoviruses with human immune cells as rational basis for the implementation of adenoviral oncolysis-induced anti-tumor immune activation. The goal of our study was to investigate how oncolytic adenoviruses affect human dendritic cells (DCs), key regulators of innate and adoptive immunity that are widely investigated as tumor vaccines. We report that melanoma-directed oncolytic adenoviruses, like replication-deficient adenoviruses but unlike adenoviruses with unrestricted replication potential, are not toxic to monocyte-derived immature DCs and do not block DC maturation by external stimuli. Of note, this is in contrast to reports for other viruses/viral vectors and represents a prerequisite for anti-tumor immune activation by adenoviral oncolysis. Furthermore, we show that these oncolytic adenoviruses alone do not or only partially induce DC maturation. Thus additional signals are required for optimal immune activation. These could be delivered, for example, by inserting immunoregulatory transgenes into the oncolytic adenovirus genome.

Antigen transmission by replicating antigen-bearing dendritic cells

During steady-state conditions, conventional spleen dendritic cells (DC) turn over every 2-3 days. Recent evidence indicates that in situ proliferation of DC arising from immediate conventional DC precursors is an important contributor to their homeostasis. In this study, we report that replication-competent conventional DC precursors and DC can internalize and transfer model particulate and soluble Ags directly to their DC progeny during cell division. Real-time confocal microscopy and flow cytometry indicated that Ag transmission to progeny was symmetrical, and suggested that other mechanisms of inter-DC Ag transfer were not involved. Soluble protein Ags inherited by DC progeny were presented effectively to Ag-specific T lymphocytes. Furthermore, we show that the number of DC, and the proportion that are actively proliferating, expands several-fold during an immune response against a viral infection. Our results point to an unanticipated mechanism in which DC are continuously replaced from Ag-bearing replication-competent precursor cells that pass Ag molecules onto their progeny through successive cell divisions. Our findings help explain how Ag may persist in a population of DC despite the brief lifespan of individual mature DC.

Contrasting effects of human, canine, and hybrid adenovirus vectors on the phenotypical and functional maturation of human dendritic cells: implications for clinical efficacy

Antipathogen immune responses create a balance between immunity, tolerance, and immune evasion. However, during gene therapy most viral vectors are delivered in substantial doses and are incapable of expressing gene products that reduce the host's ability to detect transduced cells. Gene transfer efficacy is also modified by the in vivo transduction of dendritic cells (DC), which notably increases the immunogenicity of virions and vector-encoded genes. In this study, we evaluated parameters that are relevant to the use of canine adenovirus serotype 2 (CAV-2) vectors in the clinical setting by assaying their effect on human monocyte-derived DC (hMoDC). We compared CAV-2 to human adenovirus (HAd) vectors containing the wild-type virion, functional deletions in the penton base RGD motif, and the CAV-2 fiber knob. In contrast to the HAd type 5 (HAd5)-based vectors, CAV-2 poorly transduced hMoDC, provoked minimal upregulation of major histocompatibility complex class I/II and costimulatory molecules (CD40, CD80, and CD86), and induced negligible morphological changes indicative of DC maturation. Functional maturation assay results (e.g., reduced antigen uptake; tumor necrosis factor alpha, interleukin-1beta [IL-1beta], gamma interferon [IFN-gamma], IL-10, IL-12, and IFN-alpha/beta secretion; and stimulation of heterologous T-cell proliferation) were also significantly lower for CAV-2. Our data suggested that this was due, in part, to the use of an alternative receptor and a block in vesicular escape. Additionally, HAd5 vector-induced hMoDC maturation was independent of the aforementioned cytokines. Paradoxically, an HAd5/CAV-2 hybrid vector induced the greatest phenotypical and functional maturation of hMoDC. Our data suggest that CAV-2 and the HAd5/CAV-2 vector may be the antithesis of Adenoviridae immunogenicity and that each may have specific clinical advantages.

Preclinical safety and biodistribution of adenovirus-based cancer vaccines after intradermal delivery

The recombinant adenoviral (Ad) vector is being considered as a cancer vaccine platform because it efficiently induces immune responses to tumor antigens by intradermal immunization. The aims of this study were to evaluate the potential toxicities and biodistribution after a single dose or six weekly intradermal doses of Ad2/gp100v2 and Ad2/MART-1v2, which encode tumor-associated antigens gp100 and MelanA/MART-1, respectively. The only dose-related toxicities associated with intradermal administration of these Ad vectors were inflammatory cell infiltrates in the draining lymph nodes and injection sites that persisted 83 days after administration. The biodistribution of Ad DNA as detected by real-time polymerase chain reaction was largely confined to the injection sites and draining lymph nodes of mice treated with either a single dose or multiple doses of Ad vector and in the spleens of mice treated with multiple doses of Ad vector. Adenoviral DNA was transiently detected in the bone marrow, lung, or blood of only one animal for each site and was below the limit of assay quantification (<10 copies/microg DNA). The vector persisted in the skin and lymph nodes as long as 92 days after the last dose. We conclude that Ad vectors delivered by intradermal administration provide a safe, genetic vaccine delivery platform that induces desirable immune responses at the immunization sites and the lymph nodes that, ultimately, result in immune responses specific to the tumor antigens.

Immunotherapy for gynaecological malignancies

Gynaecological malignancies, excluding breast cancer, cause approximately 25,000 deaths yearly among women in the US. Therefore, novel approaches for the prevention or treatment of these diseases are urgently required. In the case of cervical cancer, human papillomavirus (HPV) xenoantigens are readily recognised by the immune system, and their targeting has shown great promise in preclinical models of therapeutic vaccination and in clinical studies of preventative vaccination. A growing body of evidence indicates that ovarian cancer is also immunogenic and can thus be targeted through immunotherapy. This review outlines the principles and problems of immunotherapy for cervical and ovarian cancer, including the authors' personal assessment.

Immunolipoplexes: An Efficient, Nonviral Alternative for Transfection of Human Dendritic Cells with Potential for Clinical Vaccination

Genetic manipulation of dendritic cells (DCs) is important in the context of using either mature DCs to immunize patients or immature DCs to induce tolerance. Here, we describe a novel method of transfecting monocyte-derived human DCs using immunolipoplexes containing anti-CD71 or anti-CD205 monoclonal Abs. This results in up to 20% transfection, which can be increased to 20-30% if the immunolipoplexes are used to transfect CD14+ monocytes prior to differentiation into DCs. Transfected DCs can be substantially enriched using a drug-selection protocol during differentiation. Unlike adenoviral transduction, this nonviral transfection does not alter the expression of costimulatory molecules or the production of proinflammatory cytokines by DCs. In addition, DC function is unaltered, as assessed by mixed lymphocyte reactions. To test the feasibility of the immunolipoplexes and selection protocol for therapeutic intervention, we transfected DCs with the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO). Allogeneic T cells exposed to IDO-expressing DCs did not proliferate, secreted more IL-10 and less Th1 and Th2 cytokines, and had a higher amount of apoptosis than T cells incubated with control DCs. Furthermore the remaining T cells were rendered anergic to further stimulation by allogeneic DC. These immunolipoplexes, which can be easily and rapidly assembled, have potential for clinical immunization, in particular for tolerance induction protocols.

Adenovirus as an emerging pathogen in immunocompromised patients

Adenoviruses are non-enveloped, lytic, DNA viruses capable of infecting most animal species. There are 51 different human adenovirus serotypes, which are grouped from A to F on the basis of genome size, composition, homology and organization. Pathogenicity varies according to group and type, but infections are generally well controlled by the host immune system in immunocompetent individuals. However, in the immunosuppressed, adenoviral infections are a frequent cause of morbidity and mortality. To date there is no effective therapy. Adoptive transfer of immune T cells offers a therapeutic option, but this strategy has been hindered by the lack of information on targets of protective cellular immunity, and by the immunological heterogeneity of the 51 human adenoviruses. Nevertheless, until such an approach is implemented, or an effective antiviral agent becomes commercially available, it is likely that adenovirus infections will continue to be responsible for a significant number of virus-associated deaths each year.

An adenoviral type 5 vector carrying a type 35 fiber as a vaccine vehicle: DC targeting, cross neutralization, and immunogenicity

Substituting the coat proteins of adenoviral vector serotype 5 (Ad5) can alter vector tropism and circumvent vector neutralization. Here we report that an Ad5 vector carrying a part of the fiber molecule of human subgroup B adenovirus serotype 35 (Ad5.Fib35) transduces cultured human dendritic cells (DC) and circulating myeloid derived DC with approximately 10-fold greater efficiency than Ad5 in vitro. The improved DC transduction results in increased T-cell activation ex vivo. In vivo however, immunogenicity of the vectors in mice and non-human primates did not correlate with in vitro DC tropism. Ad5.Fib35 was less immunogenic in monkeys than Ad5, despite the improved primate DC tropism of Ad5.Fib35. In mice with high Ad5 vector-specific immunity, Ad5.Fib35 showed no significant difference in anti-insert immunity over Ad5 indicating that fiber exchange alone does not evade pre-existing Ad5 immunity. We thus conclude that, for ex vivo vaccination, Ad5.Fib35 shows promise as vector for loading of DC but is unable to circumvent anti-Ad5 immunity limiting its in vivo utility.

Human dendritic cell maturation by adenovirus transduction enhances tumor antigen-specific T-cell responses

Dendritic cells (DCs) have been shown to require a degree of maturation to stimulate antigen-specific, type 1 cytotoxic T lymphocytes in numerous murine models. Limited data in humans suggest that immature DCs (DC) can induce tolerance, yet a variety of nonmatured DC used clinically have induced antigen-specific type 1 T cells in vivo to various tumor-associated antigens. Use of adenovirus to engineer DCs is an efficient method for delivery of entire genes to DC, but the data on the biologic effects of viral transduction are contradictory. The authors demonstrate that DCs transduced with adenovirus (AdV) clearly become more mature by the phenotypic criterion of upregulation of CD83 and downregulation of CD14. Transduced DCs also decrease production of IL-10, and a subset of transduced DCs produce increased levels of IL-12 p70. This level of maturation is superior to that achieved by treatment of these cells with tumor necrosis factor-alpha or interferon-alpha but less pronounced than with CD40L trimer or CD40L + interferon-gamma. Maturation by AdV transduction alone leads to efficient stimulation of antigen-specific T cells from both healthy donors and patients with advanced cancer using two defined human tumor-associated antigens, MART-1 and AFP. Given the pivotal role of DCs in immune activation, it is important to understand the direct biologic effects of AdV on DCs, as well as the impact these biologic changes have on the stimulation of antigen-specific T cells. This study has important implications for the design of DC-based clinical trials.

Adoptive immunotherapy for posttransplantation viral infections

Viral diseases are a major cause of morbidity and mortality after hemopoietic stem cell transplantation. Because viral complications in these patients are clearly associated with the lack of recovery of virus-specific cellular immune responses, reconstitution of the host with in vitro expanded cytotoxic T lymphocytes is a potential approach to prevent and treat these diseases. Initial clinical studies of cytomegalovirus and Epstein-Barr virus in human stem cell transplant patients have shown that adoptively transferred donor-derived virus-specific T cells may restore protective immunity and control established infections. Preclinical studies are evaluating this approach for other viruses while strategies for generating T cells specific for multiple viruses to provide broader protection are being evaluated in clinical trials. The use of genetically modified T cells or the use of newer suicide genes may result in improved safety and efficacy.

Adenoviral Transgene Ubiquitination Enhances Mouse Immunization and Class I Presentation by Human Dendritic Cells

Therapeutic vaccination aims at a strong stimulation of antigen-specific CD8(+) T-cells, so that they differentiate into effectors active in vivo against antigenic targets. Two adenovirus vectors (Ad) encoding two HLA-A*0201-restricted HIV epitope sequences (pol 476 and pol 589) were constructed. The Ad differ by the presence or absence of a ubiquitin monomer sequence (AdUb(+) and AdUb(-)). The effect of transgene product ubiquitination was analyzed on (1) in vivo, the immunization of Ad vaccinated HLA-A*0201 humanized HHD mice and (2) in vitro, the presentation of the transgene encoded peptides by transduced human dendritic cells (DC). In vivo, we found that immunization of humanized HHD mice with AdUb(+) elicited a transgene product-specific interferon (INF)-gamma CD8(+) T-cell response detectable by enzyme-linked immunospot (ELISPOT), whereas the AdUb(-) construction did not. Antigen-specific cytotoxic T lymphocytes (CTL) were also generated in HHD mice immunized with AdUb(+) and not with AdUb(-). In vitro, using human AdUb(+)-transduced DC, a sizeable expansion of pol 476 and pol 589 tetramer positive CD8(+) T cells as well as CD8(+) CTL were obtained in healthy donors. Compared to AdUb(-)-transduced DC, AdUb(+)-transduced DC triggered a higher number of pol 476-specific IFN-gamma-secreting CD8(+) T cells. In agreement, AdUb(+) transduced DC, used as target in a (51)Cr-release assay, were more efficiently lysed by peptide-specific CTL than AdUb(-)-transduced DC. In conclusion, the addition of an ubiquitin sequence to the adenoviral transgene, used as an antigen source, resulted in both in vivo enhanced CD8(+) T-cell immunogenicity in HHD mice and in vitro increased HLA class I-restricted presentation of encoded peptides by human DC.

Viral vectors for dendritic cell-based immunotherapy

Dendritic cells (DCs) constitute a specialised system of antigen-presenting cells with a high capacity to induce and to modulate the immune response against microbial, tumour and self-antigens. New techniques to generate large amounts of DCs together with the molecular identification of human tumour-associated antigens (TAA) have opened new ways for antigen-specific cancer immunotherapies. DCs loaded either with TAA-derived MHC class I-specific synthetic peptides or with whole tumour cell preparations have been used in numerous clinical trials evaluating the efficacy of DCs in patients with cancer. However, the disadvantages of DCs pulsed with synthetic peptides from TAA include the uncertainty regarding the longevity of antigen presentation, the restriction by the patient's haplotype and the relatively low number of known MHC class I and in particular of MHC class II helper cell-related epitopes. Whole tumour cell preparations are difficult to standardise, and they depend on the availability of tumour cells. Thus the utilisation of viral vectors genetically modified to express TAA for the ex vivo transduction of DCs is an attractive alternative to achieve a MHC I- and MHC II-restricted presentation of tumoural antigens. To induce protective anti-tumoural immune response an increasing number of modified viral vectors have been used to transduce DCs. Although high transduction efficacies were reported for several viruses, analysis of the interaction of viral vectors with DCs has revealed several viral mechanisms that interfere with main functions of DCs, dampening somewhat the initial optimism in the field of DC transduction. However, promising results with different vectors have been achieved. In this review we summarise available data and discuss advantages and drawbacks of currently available vectors.

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Efficient transduction of human monocyte-derived dendritic cells by chimpanzee-derived adenoviral vector

Using recombinant adenoviruses (Ads) to target host dendritic cells (DCs) presents an attractive prospect for immunization. The efficacy of commonly used human Ad-derived gene transfer vectors for antigen delivery in humans is often compromised by preexisting anti-Ad immunity, acquired by the majority of human population as a result of frequent naturally occurring virus infections. As an alternative vector we propose chimpanzee-derived recombinant adenoviruses, which are poorly neutralized by human sera. In the present study we examine the ability of one such vector, AdC68, to transduce and activate human monocyte-derived DCs in culture. We found that AdC68 could efficiently transduce both immature and mature DCs at levels similar to those by the human serotype 5 Ad recombinant. Exposure of immature DCs to AdC68 did not alter the expression of activation and maturation marker molecules on the cell surface. Nevertheless, the transduction induced DCs to secrete interferon alpha and interleukin (IL)-6, but not IL-12 or tumor necrosis factor alpha. In addition, AdC68-transduced immature DCs could stimulate proliferation of autologous T lymphocytes. This is the first report describing a chimpanzee-derived recombinant Ad as a vector for transduction of human DCs.

Priming of T cells with Ad-transduced DC followed by expansion with peptide-pulsed DC significantly enhances the induction of tumor-specific CD8+ T cells: implications for an efficient vaccination strategy

In recent years, vaccination strategies using antigen-presenting cells (APC) have been under investigation. Antigen delivery using genetic immunization through ex vivo transduction of dendritic cells (DC) is supposed to enhance the induction of antitumor responses in humans by activating a broad range of peptide-specific CD8+ T cells. In this study, we compared the potential of adenoviral (Ad)-transduced versus peptide-pulsed DC to induce melanoma-antigen (Ag)-specific T-cell responses in vitro. Whereas gp100-peptide-pulsed DC induced long-lasting specific CD8+ T-cell responses against single peptides, Ad-transduced DC induced broad and strong, specific immunity against various peptides of the gp100-Ag. Surprisingly, several restimulations led to decreasing gp100-specific and in parallel to increasing anti-adenoviral T-cell responses. Nevertheless, those anti-adenoviral T-cell responses provided an "adjuvant" effect by inducing an early release of high amounts of IL-2/IFN-gamma, therewith enhancing CTL induction in the initiation phase. Based on these data, we suggest a prime/boost vaccination strategy in melanoma patients--combining the use of Ad-DC and peptide-pulsed DC--to obtain efficient and long-term antitumor T-cell responses.

Nonviral and viral gene transfer into different subsets of human dendritic cells yield comparable efficiency of transfection

Among the many promising cancer immunotherapeutic strategies, dendritic cells (DC) have become of particular interest. This study aims to optimize a clinical grade protocol for culture and transfection of human DC. Monocytes and CD34(+) hematopoietic stem cells (HSC) from same donor were differentiated under serum-free conditions and analyzed for their susceptibility to several recently described nonviral transfection methods as compared with established virally mediated gene transfer. Nonviral gene transfer methods studied were square-wave electroporation, lipofection, and particle-mediated transfer of plasmid DNA or in vitro transcribed mRNA. We conclude that DNA is not suitable for transduction of DC using nonviral methods. In contrast, mRNA and square-wave electroporation reproducibly yields 60% and 50% transfected monocyte- and CD34(+)-derived DC, respectively, measured at protein level, without affecting the cell viability. Thus, the transfection efficiency of this method is comparable with the 40-90% transgene expression obtained using retroviral (RV) or adenoviral (AdV) vectors in CD34(+)- and monocyte-derived DC, respectively. In monocyte-derived DC, however, the amount of protein expressed per-cell basis was higher after AdV (MOI = 1000) compared with mRNA electroporation-mediated transfer. This is the first study directly demonstrating side-by-side that mRNA electroporation into DC of different origin indeed results in a comparable number of transduced cells as when using virus-mediated gene transfer.

Helper-dependent adenoviral vectors efficiently express transgenes in human dendritic cells but still stimulate antiviral immune responses

Adenoviral (AdV) vectors can be used to transduce a wide range of human cells and tissues. However, pre-existing immunity to AdV, and enhancement of this immunity after repeated administration, limits their clinical application. This may be especially relevant when vectors are loaded into APCs. Helper-dependent AdV (Hd-AdV), in which viral coding regions are replaced by human stuffer DNA, offers a new approach for limiting antiviral responses. To evaluate their immunogenicity, human dendritic cells (DCs) were infected with either an Hd-AdV or a conventional replication-deficient E1-deleted AdV (E1-AdV) and were evaluated for their capacity to stimulate antiviral T cell responses. Hd-AdV proved to be 50- to 275-fold more effective than E1-AdV at expressing the lacZ transgene in human DCs. PCR demonstrated similar transduction efficiencies, but RT-PCR revealed much higher expression of transgene mRNA after transduction with Hd-AdV. Functionally, DCs transduced with Hd-AdV stimulated the proliferation of autologous T cells to the same level as DCs transduced with E1-AdV. Identical viral-specific T cell responder frequencies were observed and T cells stimulated with either type of AdV-transduced DC lysed viral-infected target cells. Disrupting transcription of vector-based genes had no effect on T cell activation, suggesting that responses against both vectors were directed against preformed components of the viral capsid. We conclude that Hd-AdV vectors can be used to obtain higher transgene expression in human DCs but that they still evoke a vector-related immune response similar to that generated by E1-AdV.

Intratumoral injection of dendritic cells after treatment of anticancer drugs induces tumor-specific antitumor effect in vivo

We investigated the in vivo antitumor effects of intratumoral (i.t.) administration of dendritic cells (DC) after low-dose chemotherapy using cisplatin + 5-FU. Combination of i.t. injection of DC and systemic chemotherapy induced complete rejection of the treated tumor, MC38 murine adenocarcinoma. Furthermore, the antitumor effects were also observed on a distant tumor inoculated in the contralateral flank of the animal. When 10x the number of tumor cells were inoculated, the antitumor effect of the combination of DC after chemotherapy was also confirmed and in comparison to that of DC or chemotherapy alone, thereafter contributed to a greater prolongation of survival. To analyze the mechanisms of the systemic antitumor effect generated in this system, we assessed the cytolytic activity against inoculated tumors. The cytolytic activity of effector cells from treated animals was shown to be tumor-specific and was mainly CD8 and MHC Class-I (p < 0.01) restricted. CD4 and MHC Class-II treatment marginally inhibited the cytolytic activity but not significantly (p = 0.07, 0.08 respectively). The cytolysis of effector cells was enhanced more significantly by the treatment of both DC and chemotherapy, than that of either DC or chemotherapy alone. Our study suggests that the strategy of i.t. injection of DC after low-dose chemotherapy could be a powerful weapon to treat patients with cancer in the clinical settings.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.

Human cytomegalovirus gene products US2 and US11 differ in their ability to attack major histocompatibility class I heavy chains in dendritic cells

Human cytomegalovirus (HCMV) encodes several proteins that inhibit major histocompatibility complex (MHC) class I-dependent antigen presentation. The HCMV products US2 and US11 are each sufficient for causing the dislocation of human and murine MHC class I heavy chains from the lumen of the endoplasmic reticulum to the cytosol, where the heavy chains are readily degraded. The apparent redundancy of US2 and US11 has been probed predominantly in cultured cell lines, where differences in their specificities were shown for murine and human MHC class I locus products. Here, we expressed US11 and US2 via adenovirus vectors and show that US11 exhibits a superior ability to degrade MHC class I molecules in primary human dendritic cells. MHC class II complexes are unaffected by US2- and US11-mediated attack. We suggest that multiple HCMV-encoded immunoevasions have evolved complementary functions in response to diverse host cell types and tissues.

Adenovirus type 5 vectors induce dendritic cell differentiation in human CD14(+) monocytes cultured under serum-free conditions

To determine whether infection by a model virus is capable of initiating dendritic cell (DC) differentiation, human CD14(+) peripheral blood monocytes were infected with replication-defective type 5 adenovirus. Under serum-free conditions, this resulted in differentiation of a majority of cells toward a DC phenotype within 36 to 48 hours, without the need for cytokine-induced predifferentiation. Infection induced DC morphology and altered the expression of surface markers, including loss of CD14, de novo induction of CD83 and CD25, and strongly augmented expression of CD86, CD80, CD40, and HLA-DR and HLA class I molecules. Differentiated cells maintained immunophenotype without loss of viability for at least 2 days after removal of the differentiation agent and cytokines. A greatly enhanced capacity to stimulate T-lymphocyte alloproliferation and increased expression of the DC-associated transcription factor RelB were observed. Virus without transgene was found to induce changes similar to transgene-expressing viruses. RelB up-regulation and DC immunophenotype were sensitive to the antioxidant N-acetylcysteine, suggesting a critical role for nuclear factor kappaB. RNAse protection assays revealed elevated levels of messenger RNA for a number of chemokines and cytokines associated with DCs. Finally, during differentiation, adenovirus-infected monocytes were shown to secrete chemokines and cytokines, including tumor necrosis factor-alpha (TNF-alpha). Furthermore, a TNF-alpha-neutralizing antibody inhibited the expression of some DC surface markers, indicating a contributing role for this cytokine in the adenovirus-induced differentiation of DC from monocytes. These findings have implications for the biology of monocytes as precursors to DCs and also for the use of recombinant adenovirus in vaccines or gene therapy.

Adenoviral gene transfer into dendritic cells efficiently amplifies the immune response to LMP2A antigen: a potential treatment strategy for Epstein-Barr virus--positive Hodgkin's lymphoma

The EBV-encoded LMP2A protein is consistently expressed in EBV(+) Hodgkin's lymphoma and can be targeted by CTLs. CTLs stimulated conventionally by LCLs have little activity against LMP2A(+) target cells. Here, we describe an alternative approach, based on the in vitro stimulation of CTLs with DCs genetically modified with 2 E1/E3-deleted recombinant adenoviruses, AdGFPLMP2A, encoding a fusion gene of GFP and LMP2A, and AdLMP2A, encoding LMP2A only. Transduction of DCs with AdGFPLMP2A at MOI 1,000 resulted in LMP2A expression in up to 88% of DCs. LMP2A protein was expressed in 40% of DCs transduced with AdLMP2A at an MOI of 100. Higher MOI resulted in DC death. CTL lines activated by transduced DCs had a higher frequency of LMP2A tetramer-specific CTLs than CTL lines activated by LCLs. CTLs stimulated with transduced DCs lysed both autologous fibroblasts infected with vaccinia virus LMP2A (FBvaccLMP2A) and autologous LCLs, which express LMP2A at lower levels. In contrast, CTLs generated from the same donors by stimulation with autologous LCLs showed minimal lysis of FBvaccLMP2A. Moreover, 1 donor who did not respond to LMP2A when CTLs were stimulated with LCLs became a responder when LMP2A was expressed by transduced DCs. Hence, recombinant adenoviruses encoding LMP2A effectively transduce DCs and direct the generation of LMP2A-specific CTLs. This approach will be a potent strategy in Hodgkin's lymphoma immunotherapy.

Dendritic cells for specific cancer immunotherapy

The characterization of tumor-associated antigens recognized by human T lymphocytes in a major histocompatibility complex (MHC)-restricted fashion has opened new possibilities for immunotherapeutic approaches to the treatment of human cancers. Dendritic cells (DC) are professional antigen presenting cells that are well suited to activate T cells toward various antigens, such as tumor-associated antigens, due to their potent costimulatory activity. The availability of large numbers of DC, generated either from hematopoietic progenitor cells or monocytes in vitro or isolated from peripheral blood, has profoundly changed pre-clinical research as well as the clinical evaluation of these cells. Accordingly, appropriately pulsed or transfected DC may be used for vaccination in the field of infectious diseases or tumor immunotherapy to induce antigen-specific T cell responses. These observations led to pilot clinical trials of DC vaccination for patients with cancer in order to investigate the feasibility, safety, as well as the immunologic and clinical effects of this approach. Initial clinical studies of human DC vaccines are generating encouraging preliminary results demonstrating induction of tumor-specific immune responses and tumor regression. Nevertheless, much work is still needed to address several variables that are critical for optimizing this approach and to determine the role of DC-based vaccines in tumor immunotherapy.

HIV gag mRNA transfection of dendritic cells (DC) delivers encoded antigen to MHC class I and II molecules, causes DC maturation, and induces a potent human in vitro primary immune response

Dendritic cells (DC) are the major APCs involved in naive T cell activation making them prime targets of vaccine research. We observed that mRNA was efficiently transfected, resulting in superior translation in DC compared with other professional APCs. A single stimulation of T cells by HIV gag-encoded mRNA-transfected DC in vitro resulted in primary CD4(+) and CD8(+) T cell immune responses at frequencies of Ag-specific cells (5-12.5%) similar to primary immune responses observed in vivo in murine models. Additionally, mRNA transfection also delivered a maturation signal to DC. Our results demonstrated that mRNA-mediated delivery of encoded Ag to DC induced potent primary T cell responses in vitro. mRNA transfection of DC, which mediated efficient delivery of antigenic peptides to MHC class I and II molecules, as well as delivering a maturation signal to DC, has the potential to be a potent and effective anti-HIV T cell-activating vaccine.

Adenoviral transduction of human 'clinical grade' immature dendritic cells enhances costimulatory molecule expression and T-cell stimulatory capacity

The therapeutic use of dendritic cells (DC) in antigen-specific anti-tumor vaccines, requires sufficient numbers of functional DC, the preparation of which should comply with the code of Good Manufacturing Practice. In addition, the expression of tumor specific antigen should be possible in these DC. As a preclinical step, the method reported here was developed in healthy volunteers. Monocytes (Mo) were isolated by leukapheresis from 12 donors, purified by elutriation and then cultured for 6 days in sealed bags in AIM-V serum free medium with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-13 (IL-13). Between 6x10(8) and 1x10(9) immature DC (iDC) could be differentiated from one leukapheresis. Cells displayed a characteristic iDC phenotype (CD1a(+), CD14(-), CD80(+), CD86(+), HLA DR(+), CD83(-)), and had potent allogeneic and antigen dependent autologous T cell-stimulatory capacity. Moreover, iDC could be further differentiated into mature DC by CD40 ligation as assessed by CD83 expression and the upregulation of HLA-DR and costimulatory molecules. After infection with a recombinant adenovirus encoding for beta-galactosidase (betaGal), 50% to 80% of iDC expressed betaGal without toxicity. Adenovirus infection increased the expression of both costimulatory molecules and CD83, and also increased allogeneic stimulatory capacity. Thus, the method developed here allows us to use large numbers of functional iDC as will be required for therapeutic uses in man. These DC can express a transgenic protein.

Efficient transduction of mature CD83+ dendritic cells using recombinant adenovirus suppressed T cell stimulatory capacity

We have developed a culture method for the foreign serum-free generation of highly immunostimulatory, CD83+ human dendritic cells (DC). In this study, we evaluated the feasibility and consequences of endogenously expressing antigens in mature DC using adenoviral vectors. Transduction of DC with Ad-EGFP demonstrated endogenous fluorescence in 50-85% of CD83+ DC. Ad-transduced DC stimulated the proliferation of allogeneic CD8+ and CD4+ T cells at low DC: T cell ratios. However, at high DC: T cell ratios the stimulatory capacity of Ad-transduced DC was suppressed. This immunosuppressive effect was confirmed by demonstrating that the stimulatory function of untreated DC could be suppressed in a dose-dependent manner by addition of Ad-transduced DC. Furthermore, transwell experiments suggested that direct cell contact was required. Taken together, our results demonstrate the feasibility of efficiently expressing antigens in CD83+ DC using adenoviruses. However, immunosuppressive effects must be considered and carefully studied before Ad-transduced DC are employed for clinical trials. Gene Therapy (2000) 7, 249-254.

Transduction of human PBMC-derived dendritic cells and macrophages by an HIV-1-based lentiviral vector system

Professional antigen-presenting cells, such as dendritic cells (DCs) and macrophages, are target cells for gene therapy of infectious disease and cancer. However, transduction of DCs and macrophages has proved difficult by most currently available gene transfer methods. Several recent studies have shown that lentiviral vector systems can efficiently transduce many nondividing and differentiated cell types. In this study, we examined the gene transfer to DCs and macrophages using a lentiviral vector system. Human DCs were propagated from the adherent fraction of peripheral blood mononuclear cells (PBMCs) by culture in medium containing GM-CSF, IL-4, and TNF-alpha. Human macrophages were propagated from adherent PBMCs in medium containing GM-CSF. High titers of a replication-defective vesicular stomatitis virus glycoprotein G pseudotyped HIV-1-based vector encoding the enhanced yellow fluorescent protein were produced. In immature DCs (culture days 3 and 5), transduction efficiencies of 25 to 35% were achieved at a multiplicity of infection of 100. However, the transduction efficiency was decreased in more mature DCs (culture day 8 or later). Furthermore, monocyte-derived macrophages were also transduced by the lentiviral vector system. In addition, Alu-LTR PCR demonstrated the integration of the HIV-1 provirus into the cellular genome of the transduced DCs and macrophages. Allogeneic mixed lymphocyte reactions revealed similar antigen-presenting functions of untransduced and lentivirally transduced DCs. Thus, the results of this study demonstrate that both PBMC-derived DCs and macrophages can be transduced by lentiviral vectors.

Human Fibroblasts Transduced with CD80 or CD86 Efficiently trans-Costimulate CD4+ and CD8+ T Lymphocytes in HLA-Restricted Reactions: Implications for Immune Augmentation Cancer Therapy and Autoimmunity

Augmenting immunogenicity by genetically modifying tumor cells to express costimulatory molecules has proven to be a promising therapeutic strategy in murine tumor models and is currently under investigation in human clinical trials for metastatic cancer. However, there are significant technical and logistic problems associated with implementing strategies requiring direct gene modification of primary tumor cells. In an effort to circumvent these problems, we are developing a strategy in which the costimulatory signal required for tumor-specific T lymphocyte activation is provided by a genetically modified human fibroblast (trans-costimulation). We have evaluated the efficiency of CD80- and CD86-mediated trans-costimulation in the activation of human CD8+ and CD4+ T lymphocytes in MHC class I- and class II-restricted lymphoproliferation reactions. Our studies demonstrate that the efficiency of CD80- or CD86-mediated trans-costimulation of purified human CD8+ and CD4+ T lymphocytes is comparable to cis-costimulation under defined conditions. Moreover, a dose-response relationship consistent with the predicted two-hit kinetics of the reaction was evident in trans-costimulation reactions in which the ratio of target cells expressing either signal 1 or signal 2 was varied incrementally from 1:10 to 10:1. Importantly, the level of cell-surface CD86 required for trans-costimulation is equivalent to that constitutively expressed by human peripheral blood monocytes. These results may have significant implications for the clinical implementation of this type of cancer immunotherapy and also raise questions about the possibility of trans-costimulating autoreactive T lymphocytes in vivo.