Lentiviral vectors transduce proliferating dendritic cell precursors leading to persistent antigen presentation and immunization

Tolerogenic IL-10-engineered dendritic cell-based therapy to restore antigen-specific tolerance in T cell mediated diseases

Tolerogenic dendritic cells play a critical role in promoting antigen-specific tolerance via dampening of T cell responses, induction of pathogenic T cell exhaustion and antigen-specific regulatory T cells. Here we efficiently generate tolerogenic dendritic cells by genetic engineering of monocytes with lentiviral vectors co-encoding for immunodominant antigen-derived peptides and IL-10. These transduced dendritic cells (designated DC^IL-10/Ag) secrete IL-10 and efficiently downregulate antigen-specific CD4⁺ and CD8⁺ T cell responses from healthy subjects and celiac disease patients in vitro. In addition, DC^IL-10/Ag induce antigen-specific CD49b⁺LAG-3⁺ T cells, which display the T regulatory type 1 (Tr1) cell gene signature. Administration of DC^IL-10/Ag resulted in the induction of antigen-specific Tr1 cells in chimeric transplanted mice and the prevention of type 1 diabetes in pre-clinical disease models. Subsequent transfer of these antigen-specific T cells completely prevented type 1 diabetes development. Collectively these data indicate that DC^IL-10/Ag represent a platform to induce stable antigen-specific tolerance to control T-cell mediated diseases.

Editing T cell repertoire by thymic epithelial cell-directed gene transfer abrogates risk of type 1 diabetes development

Insulin is the primary autoantigen (Ag) targeted by T cells in type 1 diabetes (T1D). Although biomarkers precisely identifying subjects at high risk of T1D are available, successful prophylaxis is still an unmet need. Leaky central tolerance to insulin may be partially ascribed to the instability of the MHC-InsB_9-23 complex, which lowers TCR avidity, thus resulting in defective negative selection of autoreactive clones and inadequate insulin-specific T regulatory cell (Treg) induction. We developed a lentiviral vector (LV)-based strategy to engineer thymic epithelial cells (TECs) to correct diabetogenic T cell repertoire. Intrathymic (it) LV injection established stable transgene expression in EpCAM⁺ TECs, by virtue of transduction of TEC precursors. it-LV-driven presentation of the immunodominant portion of ovalbumin allowed persistent and complete negative selection of responsive T cells in OT-II chimeric mice. We successfully applied this strategy to correct the diabetogenic repertoire of young non-obese diabetic mice, imposing the presentation by TECs of the stronger agonist InsulinB_9-23R22E and partially depleting the existing T cell compartment. We further circumscribed LV-driven presentation of InsulinB_9-23R22E by micro-RNA regulation to CD45⁻ TECs without loss of efficacy in protection from diabetes, associated with expanded insulin-specific Tregs. Overall, our gene transfer-based prophylaxis fine-tuned the central tolerance processes of negative selection and Treg induction, correcting an autoimmune prone T cell repertoire.

Cancer vaccines as a targeted immunotherapy approach for breast cancer: an update of clinical evidence

INTRODUCTION

Breast cancer (BC) is the first common neoplastic malignancy and the second leading cause of death in women worldwide. Conventional treatments for BC are often associated with severe side effects and may even lead to late recurrence. For this reason, in recent years, cancer immunotherapy (e.g., cancer vaccines), a novel approach based on the specificity and amplification of acquired immune responses, has been considered as a potential candidate in particular to treat metastatic BC.

AREAS COVERED

In this review, we summarize and discuss the recent development of therapeutic vaccines for BC, use of specific BC cellular antigens, antigen selection, and probable causes for their insufficient effectiveness.

EXPERT OPINION

Despite development of several different BC vaccines strategies including protein/peptide, dendritic cell, and genetic vaccines, until now, no BC vaccine has been approved for clinical use. Most of the current BC vaccines themselves fail to bring clinical benefit to BC patients and are applied in combination with radiotherapy, chemotherapy, or targeted therapy. It is hoped that with advances in our knowledge about tumor microenvironment and the development of novel combination strategies, the tumor immunosuppressive mechanisms can be overcome and prolonged immunologic and effective anti-tumor response can be developed in patients.

Brain cross-protection against SARS-CoV-2 variants by a lentiviral vaccine in new transgenic mice

COVID-19 vaccines already in use or in clinical development may have reduced efficacy against emerging SARS-CoV-2 variants. In addition, although the neurotropism of SARS-CoV-2 is well established, the vaccine strategies currently developed have not taken into account protection of the central nervous system. Here, we generated a transgenic mouse strain expressing the human angiotensin-converting enzyme 2, and displaying unprecedented brain permissiveness to SARS-CoV-2 replication, in addition to high permissiveness levels in the lung. Using this stringent transgenic model, we demonstrated that a non-integrative lentiviral vector, encoding for the spike glycoprotein of the ancestral SARS-CoV-2, used in intramuscular prime and intranasal boost elicits sterilizing protection of lung and brain against both the ancestral virus, and the Gamma (P.1) variant of concern, which carries multiple vaccine escape mutations. Beyond induction of strong neutralizing antibodies, the mechanism underlying this broad protection spectrum involves a robust protective T-cell immunity, unaffected by the recent mutations accumulated in the emerging SARS-CoV-2 variants.

Dendritic cell-targeted lentiviral vector immunization uses pseudotransduction and DNA-mediated STING and cGAS activation

Dendritic cell (DC) activation and antigen presentation are critical for efficient priming of T cell responses. Here, we study how lentiviral vectors (LVs) deliver antigen and activate DCs to generate T cell immunization in vivo. We report that antigenic proteins delivered in vector particles via pseudotransduction were sufficient to stimulate an antigen-specific immune response. The delivery of the viral genome encoding the antigen increased the magnitude of this response in vivo but was irrelevant in vitro. Activation of DCs by LVs was independent of MyD88, TRIF, and MAVS, ruling out an involvement of Toll-like receptor or RIG-I-like receptor signaling. Cellular DNA packaged in LV preparations induced DC activation by the host STING (stimulator of interferon genes) and cGAS (cyclic guanosine monophosphate-adenosine monophosphate synthase) pathway. Envelope-mediated viral fusion also activated DCs in a phosphoinositide 3-kinase-dependent but STING-independent process. Pseudotransduction, transduction, viral fusion, and delivery of cellular DNA collaborate to make the DC-targeted LV preparation an effective immunogen.

Dendritic Cells Cross-Present Immunogenic Lentivector-Encoded Antigen from Transduced Cells to Prime Functional T Cell Immunity

Recombinant lentiviral vectors (LVs) are highly effective vaccination vehicles that elicit protective T cell immunity in disease models. Dendritic cells (DCs) acquire antigen at sites of vaccination and migrate to draining lymph nodes, where they prime vaccine-specific T cells. The potency with which LVs activate CD8+ T cell immunity has been attributed to the transduction of DCs at the immunization site and durable presentation of LV-encoded antigens. However, it is not known how LV-encoded antigens continue to be presented to T cells once directly transduced DCs have turned over. Here, we report that LV-encoded antigen is efficiently cross-presented by DCs in vitro. We have further exploited the temporal depletion of DCs in the murine CD11c.DTR (diphtheria toxin receptor) model to demonstrate that repopulating DCs that were absent at the time of immunization cross-present LV-encoded antigen to T cells in vivo. Indirect presentation of antigen from transduced cells by DCs is sufficient to prime functional effector T cells that control tumor growth. These data suggest that DCs cross-present immunogenic antigen from LV-transduced cells, thereby facilitating prolonged activation of T cells in the absence of circulating LV particles. These are findings that may impact on the future design of LV vaccination strategies.

Tissue-resident dendritic cells and diseases involving dendritic cell malfunction

Dendritic cells (DCs) control immune responses and are central to the development of immune memory and tolerance. DCs initiate and orchestrate immune responses in a manner that depends on signals they receive from microbes and cellular environment. Although DCs consist mainly of bone marrow-derived and resident populations, a third tissue-derived population resides the spleen and lymph nodes (LNs), different subsets of tissue-derived DCs have been identified in the blood, spleen, lymph nodes, skin, lung, liver, gut and kidney to maintain the tolerance and control immune responses. Tissue-resident DCs express different receptors for microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs), which were activated to promote the production of pro- or anti-inflammatory cytokines. Malfunction of DCs contributes to diseases such as autoimmunity, allergy, and cancer. It is therefore important to update the knowledge about resident DC subsets and diseases associated with DC malfunction.

Immunogenicity of targeted lentivectors

To increase the safety and possibly efficacy of HIV-1 derived lentivectors (LVs) as an anti-cancer vaccine, we recently developed the Nanobody (Nb) display technology to target LVs to antigen presenting cells (APCs). In this study, we extend these data with exclusive targeting of LVs to conventional dendritic cells (DCs), which are believed to be the main cross-presenting APCs for the induction of a TH1-conducted antitumor immune response. The immunogenicity of these DC-subtype targeted LVs was compared to that of broad tropism, general APC-targeted and non-infectious LVs. Intranodal immunization with ovalbumin encoding LVs induced proliferation of antigen specific CD4+ T cells, irrespective of the LVs' targeting ability. However, the cytokine secretion profile of the restimulated CD4+ T cells demonstrated that general APC targeting induced a similar TH1-profile as the broad tropism LVs while transduction of conventional DCs alone induced a similar and less potent TH1 profile as the non-infectious LVs. This observation contradicts the hypothesis that conventional DCs are the most important APCs and suggests that the activation of other APCs is also meaningful. Despite these differences, all targeted LVs were able to stimulate cytotoxic T lymphocytes, be it to a lesser extent than broad tropism LVs. Furthermore this induction was shown to be dependent on type I interferon for the targeted and non-infectious LVs, but not for broad tropism LVs. Finally we demonstrated that the APC-targeted LVs were as potent in therapy as broad tropism LVs and as such deliver on their promise as safer and efficacious LV-based vaccines.

4-1BB ligand activates bystander dendritic cells to enhance immunization in trans

Expression of the costimulatory receptor 4-1BB is induced by TCR recognition of Ag, whereas 4-1BB ligand (4-1BBL) is highly expressed on activated APC. 4-1BB signaling is particularly important for survival of activated and memory CD8(+) T cells. We wished to test whether coexpression of Ag and 4-1BBL by dendritic cells (DC) would be an effective vaccine strategy. Therefore, we constructed lentiviral vectors (LV) coexpressing 4-1BBL and influenza nucleoprotein (NP). Following s.c. immunization of mice, which targets DC, we found superior CD8(+) T cell responses against NP and protection from influenza when 4-1BBL was expressed. However, functionally superior CD8(+) T cell responses were obtained when two LV were coinjected: one expressing 4-1BBL and the other expressing NP. This surprising result suggested that 4-1BBL is more effective when expressed in trans, acting on adjacent DC. Therefore, we investigated the effect of LV expression of 4-1BBL in mouse DC cultures and observed induced maturation of bystander, untransduced cells. Maturation was blocked by anti-4-1BBL Ab, required cell-cell contact, and did not require the cytoplasmic signaling domain of 4-1BBL. Greater maturation of untransduced cells could be explained by LV expression of 4-1BBL, causing downregulation of 4-1BB. These data suggest that coexpression of 4-1BBL and Ag by vaccine vectors that target DC may not be an optimal strategy. However, 4-1BBL LV immunization activates significant numbers of bystander DC in the draining lymph nodes. Therefore, transactivation by 4-1BBL/4-1BB interaction following DC-DC contact may play a role in the immune response to infection or vaccination.

Anti-melanoma vaccines engineered to simultaneously modulate cytokine priming and silence PD-L1 characterized using ex vivo myeloid-derived suppressor cells as a readout of therapeutic efficacy

Efficacious antitumor vaccines strongly stimulate cancer-specific effector T cells and counteract the activity of tumor-infiltrating immunosuppressive cells. We hypothesised that combining cytokine expression with silencing programmed cell death ligand 1 (PD-L1) could potentiate anticancer immune responses of lentivector vaccines. Thus, we engineered a collection of lentivectors that simultaneously co-expressed an antigen, a PD-L1-silencing shRNA, and various T cell-polarising cytokines, including interferon γ (IFNγ), transforming growth factor β (TGFβ) or interleukins (IL12, IL15, IL23, IL17A, IL6, IL10, IL4). In a syngeneic B16F0 melanoma model and using tyrosinase related protein 1 (TRP1) as a vaccine antigen, we found that simultaneous delivery of IL12 and a PD-L1-silencing shRNA was the only combination that exhibited therapeutically relevant anti-melanoma activities. Mechanistically, we found that delivery of the PD-L1 silencing construct boosted T cell numbers, inhibited in vivo tumor growth and strongly cooperated with IL12 cytokine priming and antitumor activities. Finally, we tested the capacities of our vaccines to counteract tumor-infiltrating myeloid-derived suppressor cell (MDSC) activities ex vivo. Interestingly, the lentivector co-expressing IL12 and the PD-L1 silencing shRNA was the only one that counteracted MDSC suppressive activities, potentially underlying the observed anti-melanoma therapeutic benefit. We conclude that (1) evaluation of vaccines in healthy mice has no significant predictive value for the selection of anticancer treatments; (2) B16 cells expressing xenoantigens as a tumor model are of limited value; and (3) vaccines which inhibit the suppressive effect of MDSC on T cells in our ex vivo assay show promising and relevant antitumor activities.

Development and immunological evaluation of HLA-specific chronic myeloid leukemia polyepitope vaccine in Chinese population

BACKGROUND

BCR/ABL and Wilms' tumor 1 (WT1) are an ideal tumor associated antigens which can be used to develop a potential chronic myeloid leukemia (CML) dentritic cell (DC) vaccine. Here, we constructed a novel polyepitope vaccine which used recombinant lentiviral vector carrying BCR/ABL and WT1 genes, and determined the immunological effects of this vaccine in vitro.

METHODS

The DC vaccine was constructed using lentiviral vector transduced DCs. T lymphocytes were stimulated with DC vaccine and then co-cultured in vitro with peripheral blood mononuclear cells (PBMCs) from CML or ALL patients, respectively. The cytotoxicity of proliferous cytotoxic T lymphocytes (CTLs) was determined by the LDH assay. The IFN-γ production of CTLs was detected using ELISPOT assay.

RESULTS

We constructed an lentiviral vector encoding 50 different epitopes from BCR/ABL and WT1 antigens, and transferred it into DCs to prepare the DC vaccine successfully. The in vivo stimulation of CTLs with this DC vaccine were proved to show strong cytotoxicity and produce high level of IFN-γ.

CONCLUSIONS

The novel recombinant lentiviral polyepitope DC vaccine is a promising candidate for clinical trials and may be an effective approach for CML immunotherapy.

Vaccination with lentiviral vector expressing the nfa1 gene confers a protective immune response to mice infected with Naegleria fowleri

Naegleria fowleri, a pathogenic free-living amoeba, causes fatal primary amoebic meningoencephalitis (PAM) in humans and animals. The nfa1 gene (360 bp), cloned from a cDNA library of N. fowleri, produces a 13.1-kDa recombinant protein which is located on pseudopodia, particularly the food cup structure. The nfa1 gene plays an important role in the pathogenesis of N. fowleri infection. To examine the effect of nfa1 DNA vaccination against N. fowleri infection, we constructed a lentiviral vector (pCDH) expressing the nfa1 gene. For the in vivo mouse study, BALB/c mice were intranasally vaccinated with viral particles of a viral vector expressing the nfa1 gene. To evaluate the effect of vaccination and immune responses of mice, we analyzed the IgG levels (IgG, IgG1, and IgG2a), cytokine induction (interleukin-4 [IL-4] and gamma interferon [IFN-γ]), and survival rates of mice that developed PAM. The levels of both IgG and IgG subclasses (IgG1 and IgG2a) in vaccinated mice were significantly increased. The cytokine analysis showed that vaccinated mice exhibited greater IL-4 and IFN-γ production than the other control groups, suggesting a Th1/Th2 mixed-type immune response. In vaccinated mice, high levels of Nfa1-specific IgG antibodies continued until 12 weeks postvaccination. The mice vaccinated with viral vector expressing the nfa1 gene also exhibited significantly higher survival rates (90%) after challenge with N. fowleri trophozoites. Finally, the nfa1 vaccination effectively induced protective immunity by humoral and cellular immune responses in N. fowleri-infected mice. These results suggest that DNA vaccination using a viral vector may be a potential tool against N. fowleri infection.

Induction of broadly neutralising HCV antibodies in mice by integration-deficient lentiviral vector-based pseudotyped particles

Introduction

Integration-deficient lentiviral vectors (IDLVs) are a promising platform for immunisation to elicit both humoral immunity and cellular mediated immunity (CMI). Here, we compared the specific immunity in mice immunised via different regimens (homologous and cocktail) with IDLV-based HCV pseudoparticles (HCVpps) carrying pseudotyped glycoproteins E1E2 and bearing the HCV NS3 gene. Humoral and cell-mediated immune responses were also evaluated after IDLV-HCVpp immunisation combined with heterologous rAd5-CE1E2 priming protocols. Sera from the mice effectively elicited anti-E1, -E2, and -NS3 antibody responses, and neutralised various HCVpp subtypes (1a, 1b, 2a, 3a and 5a). No significant CMI was detected in the groups immunised with IDLV-based HCVpps. In contrast, the combination of rAd5-CE1E2 priming and IDLV-based HCVpp boosting induced significant CMI against multiple antigens (E1, E2, and NS3).

Conclusion

IDLV-based HCVpps are a promising vaccination platform and the combination of rAd5-CE1E2 and IDLV-based HCVpp prime-boost strategy should be further explored for the development of a cross-protective HCV vaccine.

Patients with cystic fibrosis have inducible IL-17+IL-22+ memory cells in lung draining lymph nodes

BACKGROUND

IL-17 is an important cytokine signature of the TH differentiation pathway TH17. This T-cell subset is crucial in mediating autoimmune disease or antimicrobial immunity in animal models, but its presence and role in human disease remain to be completely characterized.

OBJECTIVE

We set out to determine the frequency of TH17 cells in patients with cystic fibrosis (CF), a disease in which there is recurrent infection with known pathogens.

METHODS

Explanted lungs from patients undergoing transplantation or organ donors (CF samples=18; non-CF, nonbronchiectatic samples=10) were collected. Hilar nodes and parenchymal lung tissue were processed and examined for TH17 signature by using immunofluorescence and quantitative real-time PCR. T cells were isolated and stimulated with antigens from Pseudomonas aeruginosa and Aspergillus species. Cytokine profiles and staining with flow cytometry were used to assess the reactivity of these cells to antigen stimulation.

RESULTS

We found a strong IL-17 phenotype in patients with CF compared with that seen in control subjects without CF. Within this tissue, we found pathogenic antigen-responsive CD4+IL-17+ cells. There were double-positive IL-17+IL-22+ cells [TH17(22)], and the IL-22+ population had a higher proportion of memory characteristics. Antigen-specific TH17 responses were stronger in the draining lymph nodes compared with those seen in matched parenchymal lungs.

CONCLUSION

Inducible proliferation of TH17(22) with memory cell characteristics is seen in the lungs of patients with CF. The function of these individual subpopulations will require further study regarding their development. T cells are likely not the exclusive producers of IL-17 and IL-22, and this will require further characterization.

Intravenous delivery of HIV-based lentiviral vectors preferentially transduces F4/80+ and Ly-6C+ cells in spleen, important target cells in autoimmune arthritis

Antigen presenting cells (APCs) play an important role in arthritis and APC specific gene therapeutic targeting will enable intracellular modulation of cell activity. Viral mediated overexpression is a potent approach to achieve adequate transgene expression levels and lentivirus (LV) is useful for sustained expression in target cells. Therefore, we studied the feasibility of lentiviral mediated targeting of APCs in experimental arthritis. Third generation VSV-G pseudotyped self-inactivating (SIN)-LV were injected intravenously and spleen cells were analyzed with flow cytometry for green fluorescent protein (GFP) transgene expression and cell surface markers. Collagen-induced arthritis (CIA) was induced by immunization with bovine collagen type II in complete Freund's adjuvant. Effect on inflammation was monitored macroscopically and T-cell subsets in spleen were analyzed by flow cytometry. Synovium from arthritic knee joints were analyzed for proinflammatory cytokine expression. Lentiviruses injected via the tail vein preferentially infected the spleen and transduction peaks at day 10. A dose escalating study showed that 8% of all spleen cells were targeted and further analysis showed that predominantly Ly6C+ and F4/80+ cells in spleen were targeted by the LV. To study the feasibility of blocking TAK1-dependent pathways by this approach, a catalytically inactive mutant of TAK1 (TAK1-K63W) was overexpressed during CIA. LV-TAK1-K63W significantly reduced incidence and arthritis severity macroscopically. Further histological analysis showed a significant decrease in bone erosion in LV-TAK1-K63W treated animals. Moreover, systemic Th17 levels were decreased by LV-TAK1-K63W treatment in addition to diminished IL-6 and KC production in inflamed synovium. In conclusion, systemically delivered LV efficiently targets monocytes and macrophages in spleen that are involved in autoimmune arthritis. Moreover, this study confirms efficacy of TAK1 targeting in arthritis. This approach may provide a valuable tool in targeting splenic APCs, to unravel their role in autoimmune arthritis and to identify and validate APC specific therapeutic targets.

Dendritic cell modification as a route to inhibiting corneal graft rejection by the indirect pathway of allorecognition

Dendritic cell (DC) modification is a potential strategy to induce clinical transplantation tolerance. We compared two DC modification strategies to inhibit allogeneic T-cell proliferation. In the first strategy, murine DCs were transduced with a lentiviral vector expressing CTLA4-KDEL, a fusion protein that prevents surface CD80/86 expression by retaining the co-stimulatory molecules within the ER. In the second approach, DCs were transduced to express the tryptophan-catabolising enzyme IDO. CTLA4-KDEL-expressing DCs induced anergy in alloreactive T cells and generated both CD4⁺CD25⁺ and CD4⁺CD25⁻ Treg cells (with direct and indirect donor allospecificity and capacity for linked suppression) both in vitro and in vivo. In contrast, T-cell unresponsiveness induced by IDO⁺ DCs lacked donor specificity. In the absence of any immunosuppressive treatment, i.v. administration of CTLA4-KDEL-expressing DCs resulted in long-term survival of corneal allografts only when the DCs were capable of indirect presentation of alloantigen. This study demonstrates the therapeutic potential of CTLA4-KDEL-expressing DCs in tolerance induction.

Retroviral and lentiviral vectors for the induction of immunological tolerance

Retroviral and lentiviral vectors have proven to be particularly efficient systems to deliver genes of interest into target cells, either in vivo or in cell cultures. They have been used for some time for gene therapy and the development of gene vaccines. Recently retroviral and lentiviral vectors have been used to generate tolerogenic dendritic cells, key professional antigen presenting cells that regulate immune responses. Thus, three main approaches have been undertaken to induce immunological tolerance; delivery of potent immunosuppressive cytokines and other molecules, modification of intracellular signalling pathways in dendritic cells, and de-targeting transgene expression from dendritic cells using microRNA technology. In this review we briefly describe retroviral and lentiviral vector biology, and their application to induce immunological tolerance.

Delivery of antigens by viral vectors for vaccination

Viral vectors have been developed as vaccine platforms for a number of pathogens and tumors. In particular, adenovirus (Ad)-based vectors expressing genes coding for pathogen or tumor antigens have proven efficacious to induce protective immunity. Major challenges in the use of Ad vectors are the high prevalence of anti-Ad immunity and the recent observation during an Ad-based HIV vaccine trial that led to increased HIV-1 acquisition in the presence of circulating anti-Ad5 neutralizing antibodies. In this review we summarize strategies to address these challenges and focus on modifications of the Ad capsid to enhance the adjuvant effect of anti-Ad immunogenicity and to circumvent pre-existing immunity. In addition, we summarize the current status and potential of other viral vector vaccines based on adeno-associated viruses, lentiviruses and poxviruses.

Lentiviral vector followed by protein immunisation breaks tolerance against the self-antigen Her1 and results in lung cancer immunotherapy

BACKGROUND

Lung cancer remains a leading cause of cancer mortality, and so the aim of the present study was to develop a therapeutic vaccine protocol.

METHODS

We constructed a lentiviral vector (LV) expressing the extracellular domain (ECD) of murine Her1, an antigen associated with poor prognosis in lung cancer.

RESULTS

A single LV injection, followed by two Her1 protein boosts, was effective in reducing the metastatic burden of Lewis lung carcinoma in mice. The Her1 LV immunisation generated CD8+ T cells that recognised Her1 ECD presented by dendritic cells, and that also homed to Her1-expressing tumours. Protein boosting further increased the CD8+ T cell response and generated anti-Her1 antibodies; in the antibody response, Her1 LV priming increased Th1-dependent immunoglobulin G2c production.

CONCLUSIONS

The ability of this vaccine protocol to break both T cell and B cell tolerance to a self-antigen likely explains its effectiveness.

Tumour-derived IL-10 within tumour microenvironment represses the antitumour immunity of Socs1-silenced and sustained antigen expressing DCs

It has been shown that silencing of suppressor of cytokine signalling 1 (Socs1) or stably expressing transgenic protein Ags in antigen-presenting dentritic cells (DCs) strongly enhances antigen-specific anti-tumour immunity. However, whether the strong and long-lasting T cell responses induced by the modified DCs could modulate the immunosuppressive tumour microenvironment has not been clarified. In this study, we explored the anti-tumour immunity of DCs modified by Socs1-shRNA lentiviral transduction combined with sustained expression of TRP2 in different tumour models. We showed that transfer Socs1-silenced or tumour antigen TRP2 persistent expressed DCs, or DCs modified by combination of Socs1-silencing and sustaining TRP2 expression prior to inoculation of tumour cells delayed B16 tumour cell growth, prolonged mouse survival and increased the ratio of CD8+ T/Treg as well as the CTL activity in tumours. However, there was no significant effect on tumour growth and mouse survival rate upon tumour established. Further, we showed that tumour cell secreted IL-10 counteracted the immunity of modified DCs in established tumour model, injection of Socs1-shRNA and TRP2 antigen modified significantly inhibited growth of the established B16-IL-10(-/-) tumours. These data indicated that the high level of IL-10 within tumour microenvironment is one of factors that compromise DC vaccine functions.

Targeting lentiviral vectors for cancer immunotherapy

Delivery of tumour-associated antigens (TAA) in a way that induces effective, specific immunity is a challenge in anti-cancer vaccine design. Circumventing tumour-induced tolerogenic mechanisms in vivo is also critical for effective immunotherapy. Effective immune responses are induced by professional antigen presenting cells, in particular dendritic cells (DC). This requires presentation of the antigen to both CD4(+) and CD8(+) T cells in the context of strong co-stimulatory signals. Lentiviral vectors have been tested as vehicles, for both ex vivo and in vivo delivery of TAA and/or activation signals to DC, and have been demonstrated to induce potent T cell mediated immune responses that can control tumour growth. This review will focus on the use of lentiviral vectors for in vivo gene delivery to DC, introducing strategies to target DC, either targeting cell entry or gene expression to improve safety of the lentiviral vaccine or targeting dendritic cell activation pathways to enhance performance of the lentiviral vaccine. In conclusion, this review highlights the potential of lentiviral vectors as a generally applicable 'off-the-shelf' anti-cancer immunotherapeutic.

Ten years of progress in vaccination against cancer: the need to counteract cancer evasion by dual targeting in future therapies

Although cancer immunology has made vigorous progress over the last decade, its future remains uncertain. Tumors have clearly proved subject to immune surveillance, leading to antigenic editing, and means of activating both T and B arms of the immune system have been devised. Therapeutic vaccination and monoclonal antibody therapy have so far proved disappointing, because tumors prove adept at evasion from immune control. Dual targeting could well counteract evasion, provided that the two targets are independent and are attacked simultaneously. This stage has nearly but not quite been reached in several forms of immunotherapy, particularly of B-cell cancers, although such treatment also carries hazards.

Immunization delivered by lentiviral vectors for cancer and infectious diseases

The increasing level of understanding of the lentivirus biology has been instrumental in shaping the design strategy of creating therapeutic lentiviral delivery vectors. As a result, lentiviral vectors have become one of the most powerful gene transfer vehicles. They are widely used for therapeutic purposes as well as in studies of basic biology, due to their unique characteristics. Lentiviral vectors have been successfully employed to mediate durable and efficient antigen expression and presentation in dendritic cells both in vitro and in vivo, leading to the activation of cellular immunity and humoral responses. This capability makes the lentiviral vector an ideal choice for immunizations that target a wide range of cancers and infectious diseases. Further advances into optimizing the vector system and understanding the relationship between the immune system and diseases pathogenesis will only augment the potential benefits and utility of lentiviral vaccines for human health.

Integrase-defective lentiviral-vector-based vaccine: a new vector for induction of T cell immunity

INTRODUCTION

The development of new strategies for the induction of potent and broad immune responses is of high priority in the vaccine field. In this setting, integrase-defective lentiviral vectors (IDLV) represent a new and promising delivery system for immunization purposes.

AREAS COVERED

In this review we describe the development and application of IDLV for vaccination. IDLV are turning out to be a new class of vectors endowed with peculiar characteristics, setting them apart from the parental integration-competent lentiviral vectors. Recent data suggest that IDLV are able to induce strong antigen-specific immune responses in terms of quantity, persistence and quality of CD8(+) T cell response following a single immunization in mice.

EXPERT OPINION

IDLV are a recent acquisition in the field of genetic immunization, thus allowing for the opportunity of further upgrading, including increasing antigen expression and potency of immune response. Based on recent reports showing the potential of IDLV for immunization in mouse models, further development and validation of IDLV, including comparison with other vaccine protocols and use in non-human primate models, are warranted.

Lentiviral vectors targeted to MHC II are effective in immunization

Abstract vectors (LVs) that are targeted to APC using a chimeric measles virus (MV) hemagglutinin (H). The MV H protein is mutated to prevent binding to MV receptors and incorporates a single-chain antibody that recognizes murine major histocompatibility complex class II (MHC II). This targeted LV is highly efficient in transduction of freshly isolated mouse B cells and dendritic cells. MHC II-positive cells in spleen are transduced after intravenous injection, and a robust immune response to an antigen transgene is generated.

HIV-1-derived lentiviral vectors directly activate plasmacytoid dendritic cells, which in turn induce the maturation of myeloid dendritic cells

Lentiviral vectors (LV) can induce type I interferon (IFN I) production from murine plasmacytoid dendritic cells (pDC), but not myeloid (my)DC. Here, we investigated whether this mechanism is conserved in human DC. MyDC and pDC were isolated from peripheral blood and transduced with increasing vector concentrations. Compared with in vitro differentiated monocyte-derived DC, the transduction efficiency of peripheral blood DC was low (ranging from <1% to 45%), with pDC showing the lowest susceptibility to LV transduction. Phenotype and function of myDC were not directly modified by LV transduction; by contrast, pDC produced significant levels of IFN-α and tumor necrosis factor-α. pDC activation was dependent on functional vector particles and was mediated by Toll-like receptor 7/9 triggering. Coculture of myDC with pDC in the presence of LV resulted in myDC activation, with CD86 up-regulation and interleukin-6 secretion. These findings demonstrate that the induction of transgene-specific immunity is triggered by an innate immune response with pDC activation and consequent myDC maturation, a response that closely resembles the one induced by functional viruses. This information is important to design strategies aimed at using LV in humans for gene therapy, where adverse immune responses must be avoided, or for cancer immunotherapy, where inducing immunity is the goal.

Emerging applications of lentiviral vectors in dendritic cell-based immunotherapy

Dendritic cells are professional antigen-presenting cells that initiate, regulate and shape the induction of specific immune responses. The ability to use dendritic cells in the induction of antigen-specific tolerance, antigen-specific immunity or specific differentiation of T-helper subsets holds great promise in dendritic cell-based immunotherapy of various diseases such as cancer, viral infections, allergy, as well as autoimmunity. Replication-incompetent HIV-1-based lentiviral vector is now emerging as a promising delivery system to genetically modify dendritic cells through antigen recognition, costimulatory molecules and/or polarization signals for the manipulation of antigen-specific immunity in vivo. This article discusses some of the recent advances in the uses of lentiviral vectors in dendritic cell-based immunotherapy.

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.

The evolving role of dendritic cells in cancer therapy

IMPORTANCE OF THE FIELD

Dendritic cells (DC) are a clear choice for use in cancer immunotherapy, and much research has focused on generating DC for clinical use. Although DC therapy has been successful in inducing specific anti-tumour immune responses, these have rarely translated into clinical efficacy.

AREAS COVERED IN THIS REVIEW

We examine some of the components of generating DC for therapy, including their culture, antigen loading and delivery, and discuss why DC therapy has not yet delivered substantial clinical benefit. We also examine more novel approaches, such as the potential for combination DC-based immunomodulatory strategies.

WHAT THE READER WILL GAIN

Given the highly immunosuppressive tumour environment, many of the approaches to DC vaccination are unlikely to result in effective therapy, as even successfully primed T cells may fail to infiltrate tumours or be anergized after entry. Broader approaches against multiple tumour-associated antigens in the context of overcoming tumour immune suppression are likely to prove more successful. The combination of oncolytic viral therapy with DC vaccines may promote an inflammatory tumour environment, inducing optimal DC activation, T cell priming and effective therapy.

TAKE HOME MESSAGE

Evolving DC-based therapeutic strategies addressing multiple components of tumour-immune system interactions may yield substantial benefits for patients.

HIV-1 lentiviral vector immunogenicity is mediated by Toll-like receptor 3 (TLR3) and TLR7

Lentiviral vectors are promising vaccine vector candidates that have been tested extensively in preclinical models of infectious disease and cancer immunotherapy. They are also used in gene therapy clinical trials both for the ex vivo modification of cells and for direct in vivo injection. It is therefore critical to understand the mechanism(s) by which such vectors might stimulate the immune system. We evaluated the effect of lentiviral vectors on myeloid dendritic cells (DC), the main target of lentiviral transduction following subcutaneous immunization. The activation of DC cultures was independent of the lentiviral pseudotype but dependent on cell entry and reverse transcription. In vivo-transduced DC also displayed a mature phenotype, produced tumor necrosis factor alpha (TNF-alpha), and stimulated naive CD8(+) T cells. The lentiviral activation of DC was Toll-like receptor (TLR) dependent, as it was inhibited in TRIF/MyD88 knockout (TRIF/MyD88(-/-)) DC. TLR3(-/-) or TLR7(-/-) DC were less activated, and reverse transcription was important for the activation of TLR7(-/-) DC. Moreover, lentivirally transduced DC lacking TLR3 or TLR7 had an impaired capacity to induce antigen-specific CD8(+) T-cell responses. In conclusion, we demonstrated TLR-dependent DC activation by lentiviral vectors, explaining their immunogenicity. These data allow the rational development of strategies to manipulate the host's immune response to the transgene.