The role of skin-derived dendritic cells in CD8+ T cell priming following immunization with lentivectors

Treatment with lentiviral vectors encoding shRNA against interleukin 10 modulates the immunosuppressive activity of murine colon carcinoma-associated myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are potent suppressors of antitumor immunity and their accumulation is often associated with poor prognosis. The aim of the present study was to determine the mechanisms of action of lentiviral vectors encoding short hairpin (sh)RNA against interleukin-10 (IL-10), with particular emphasis on their influence on the activity of tumor-derived MDSCs. Lentiviral vectors encoding shRNA against IL-10 (shIL-10 LVs) were utilized to silence the expression of IL-10 either in MDSCs that were generated ex vivo from bone marrow cells cultured in the presence of supernatant from MC38 colon carcinoma cells, or in situ in the MC38 murine colon carcinoma environment. Although monocytic MDSCs (M-MDSCs) transduced with shIL-10 LVs exhibited increased suppressor activity, transduction of polymorphonuclear MDSCs (PMN-MDSCs) appeared to reduce their ability to inhibit T lymphocyte functions. Analysis of EGFP expression in MC38 tumors revealed that intratumorally inoculated shIL-10 LVs transduced tumor-infiltrating myeloid cells with the highest efficiency and, led to a decreased IL-10 level in the tumor microenvironment. However, the effect was accompanied by increased influx of PMN-MDSCs into tumors observed both on the 6th and on the 10th day after shIL-10 LV injections. Nevertheless, it was noted that suppressor activity of myeloid cells isolated from tumors was dependent on the efficiency of tumor-derived PMN-MDSC transduction with shIL-10 LVs. The increased percentage of transduced PMN-MDSCs on the 10th day was associated with diminished immunosuppressive activity of tumor-derived myeloid cells and an elevated ratio of cytotoxic T lymphocytes to M-MDSCs. The obtained data indicated that treatment with shIL-10 LVs may result in modulation of the immunosuppressive activity of MC38 colon carcinoma-derived MDSCs.

Systemic hypoxia inhibits T cell response by limiting mitobiogenesis via matrix substrate-level phosphorylation arrest

Systemic oxygen restriction (SOR) is prevalent in numerous clinical conditions, including chronic obstructive pulmonary disease (COPD), and is associated with increased susceptibility to viral infections. However, the influence of SOR on T cell immunity remains uncharacterized. Here we show the detrimental effect of hypoxia on mitochondrial-biogenesis in activated mouse CD8⁺ T cells. We find that low oxygen level diminishes CD8⁺ T cell anti-viral response in vivo. We reveal that respiratory restriction inhibits ATP-dependent matrix processes that are critical for mitochondrial-biogenesis. This respiratory restriction-mediated effect could be rescued by TCA cycle re-stimulation, which yielded increased mitochondrial matrix-localized ATP via substrate-level phosphorylation. Finally, we demonstrate that the hypoxia-arrested CD8⁺ T cell anti-viral response could be rescued in vivo through brief exposure to atmospheric oxygen pressure. Overall, these findings elucidate the detrimental effect of hypoxia on mitochondrial-biogenesis in activated CD8⁺ T cells, and suggest a new approach for reducing viral infections in COPD.

A Single Dose of NILV-Based Vaccine Provides Rapid and Durable Protection against Zika Virus

Zika virus, a member of the Flaviviridae family, is primarily transmitted by infected Aedes species mosquitoes. In 2016, Zika infection emerged as a global health emergency for its explosive spread and the remarkable neurological defects in the developing fetus. Development of a safe and effective Zika vaccine remains a high priority owing to the risk of re-emergence and limited understanding of Zika virus epidemiology. We engineered a non-integrating lentiviralvector(NILV)-based Zika vaccine encoding the consensus pre-membrane and envelope glycoprotein of circulating Zika virus strains. We further evaluated the immunogenicity and protective efficacy of this vaccine in both immunocompromised and immunocompetent mouse models. A single immunization in both mouse models elicited a robust neutralizing antibody titer and afforded full protection against Zika challenge as early as 7 days post-immunization. This NILV-based vaccine also induced a long-lasting immunity when immunized mice were challenged 6 months after immunization. Altogether, our NILV Zika vaccine provides a rapid yet durable protection through a single dose of immunization without extra adjuvant formulation. Our data suggest a promising Zika vaccine candidate for an emergency situation, and demonstrate the capacity of lentiviral vector as an efficient vaccine delivery platform.

Enhanced Immune Responses Conferring Cross-Protection by Skin Vaccination With a Tri-Component Influenza Vaccine Using a Microneedle Patch

Skin vaccination using biodegradable microneedle patch (MNP) technology in vaccine delivery is a promising strategy showing significant advantages over conventional flu shots. In this study, we developed an MNP encapsulating a 4M2e-tFliC fusion protein and two types of whole inactivated influenza virus vaccines (H1N1 and H3N2) as a universal vaccine candidate. We demonstrated that mice receiving this tri-component influenza vaccine via MNP acquired improved IgG1 antibody responses with more balanced IgG1/IgG2a antibody responses and enhanced cellular immune responses, including increased populations of IL-4 and IFN-γ producing cells and higher frequencies of antigen-specific plasma cells compared with intramuscular injection. In addition, stronger germinal center reactions, increased numbers of Langerin-positive migratory dendritic cells, and increased cytokine secretion were observed in the skin-draining lymph nodes after immunization with the tri-component influenza MNP vaccine. The MNP-immunized group also possessed enhanced protection against a heterologous reassortant A/Shanghai/2013 H7N9 (rSH) influenza virus infection. Furthermore, the sera collected from 4M2e-tFliC MNP-immunized mice were demonstrated to have antiviral efficacy against reassortant A/Vietnam/1203/2004 H5N1 (rVet) and A/Shanghai/2013 H7N9 (rSH) virus challenges. The immunological advantages of skin vaccination with this tri-component MNP vaccine could offer a promising approach to develop an easily applicable and broadly protective universal influenza vaccine.

Reprogramming the murine colon cancer microenvironment using lentivectors encoding shRNA against IL-10 as a component of a potent DC-based chemoimmunotherapy

Background

The excessive amounts of immunosuppressive factors present in a tumor microenvironment (TME) reduce the effectiveness of cancer vaccines. The main objective of our research was to improve the effectiveness of dendritic cell (DC)-based immunotherapy or chemoimmunotherapy composed of cyclophosphamide (CY) and DCs by application of lentivectors encoding shRNA specific to IL-10 (shIL10 LVs) in murine colon carcinoma MC38 model.

Methods

The efficacy of shIL10 LVs in silencing of IL-10 expression was measured both in vitro and in vivo using Real-Time PCR and ELISA assays. In addition, the influence of intratumorally inoculated lentivectors on MC38 tumor microenvironment was examined using flow cytometry method. The effect of applied therapeutic schemes was determined by measurement of tumor growth inhibition and activation state of local and systemic immune response.

Results

We observed that intratumorally inoculated shIL10 LVs transduced tumor and TME-infiltrating cells and reduced the secretion of IL-10. Application of shIL10 LVs for three consecutive weeks initiated tumor growth inhibition, whereas treatment with shIL10 LVs and BMDC/TAg did not enhance the antitumor effect. However, when pretreatment with CY was introduced to the proposed scheme, we noticed high MC38 tumor growth inhibition accompanied by reduction of MDSCs and Tregs in TME, as well as activation of potent local and systemic Th1-type antitumor response.

Conclusions

The obtained data shows that remodeling of TME by shIL10 LVs and CY enhances DC activity and supports them during regeneration and actuation of a potent antitumor response. Therefore, therapeutic strategies aimed at local IL-10 elimination using lentiviral vectors should be further investigated in context of combined chemoimmunotherapies.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0799-y) contains supplementary material, which is available to authorized users.

Dissolving Microneedles as Skin Allergy Test Device

The possibility of using dissolving microneedles (DMs) as a skin allergy test device was studied in rats. Poly-L-arginine was used as a model allergen. Dextran was used to prepare three kinds of DM array chips containing different doses of poly-L-arginine: 17.1±0.5 µg (low-dose DM), 42.2±0.8 µg (medium-dose DM), and 87.4±1.1 µg (high-dose DM); each 1.0 cm² chip contained 300 DMs. The mean lengths of the low-, medium-, and high-dose DM were 489±3, 485±3, and 492±1 µm and mean diameters of the base were 301±2, 299±1, and 299±2 µm, respectively. Furthermore, for the low-, medium-, and high-dose DM, the administered doses of poly-L-arginine were estimated to be 9.3±1.9, 31.1±1.3, and 61.9±4.7 µg and the scratching behavior per 30 min was 9.8±3.4, 60.4±8.3, and 95.7±10.6 times, respectively. These results demonstrate the dose dependence of the immunoreactivity of the poly-L-arginine DMs, suggesting that DMs can be used an alternative skin allergy device.

Intratumoral Lentivector-Mediated TGF-β1 Gene Downregulation As a Potent Strategy for Enhancing the Antitumor Effect of Therapy Composed of Cyclophosphamide and Dendritic Cells

Vaccination with dendritic cells (DCs) stimulated with tumor antigens can induce specific cellular immune response that recognizes a high spectrum of tumor antigens. However, the ability of cancer cells to produce immunosuppressive factors drastically decreases the antitumor activity of DCs. The main purpose of the study was to improve the effectiveness of DC-based immunotherapy or chemoimmunotherapy composed of cyclophosphamide (CY) and DCs by application of lentivectors (LVs)-encoding short hairpin RNA specific for TGF-β1 (shTGFβ1 LVs). We observed that s.c. inoculation of both MC38 cells with silenced expression of TGF-β1 (MC38/shTGF-β1) and direct intratumoral application of shTGFβ1 LVs contributed to reduction of suppressor activity of myeloid cells and Tregs in tumor. Contrary to expectations, in mice bearing wild tumor, the application of shTGFβ1 LVs prior to vaccination with bone marrow-derived DC stimulated with tumor antigens (BMDC/TAg) did not influence myeloid-derived suppressor cell (MDSC) infiltration into tumor. As a result, we observed only minor MC38 tumor growth inhibition (TGI) accompanied by systemic antitumor response activation comparable to that obtained for negative control (shN). However, when the proposed scheme was complemented by pretreatment with a low dose of CY, we noticed high MC38 TGI together with decreased number of MDSCs in tumor and induction of Th1-type response. Moreover, in both schemes of treatment, LVs (shTGFβ1 as well as shN) induced high influx of CTLs into tumor associated probably with the viral antigen introduction into tumor microenvironment. Concluding, the application of shTGFβ1 LVs alone or in combination with DC-based vaccines is not sufficient for long-lasting elimination of suppression in tumor. However, simultaneous reduction of TGF-β1 in tumor microenvironment and its remodeling by pretreatment with a low dose of CY facilitates the settlement of peritumorally inoculated DCs and supports them in restoration and activation of a potent antitumor response.

Fibered Confocal Fluorescence Microscopy for the Noninvasive Imaging of Langerhans Cells in Macaques

Purpose

We developed a new approach to visualize skin Langerhans cells by in vivo fluorescence imaging in nonhuman primates.

Procedures

Macaques were intradermally injected with a monoclonal, fluorescently labeled antibody against HLA-DR molecule and were imaged for up to 5 days by fibered confocal microscopy (FCFM).

Results

The network of skin Langerhans cells was visualized by in vivo fibered confocal fluorescence microscopy. Quantification of Langerhans cells revealed no changes to cell density with time. Ex vivo experiments confirmed that injected fluorescent HLA-DR antibody specifically targeted Langerhans cells in the epidermis.

Conclusions

This study demonstrates the feasibility of single-cell, in vivo imaging as a noninvasive technique to track Langerhans cells in nontransgenic animals.

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.

Lentiviral vector encoding ubiquitinated hepatitis B core antigen induces potent cellular immune responses and therapeutic immunity in HBV transgenic mice

Predominant T helper cell type 1 (Th1) immune responses accompanied by boosted HBV-specific cytotoxic T lymphocyte (CTL) activity are essential for the clearance of hepatitis B virus (HBV) in chronic hepatitis B (CHB) patients. Ubiquitin (Ub) serves as a signal for the target protein to be recognized and degraded through the ubiquitin-proteasome system (UPS). Ubiquitinated hepatitis B core antigen (Ub-HBcAg) has been proved to be efficiently degraded into the peptides, which can be presented by major histocompatibility complex (MHC) class I resulting in stimulating cell-mediated responses. In the present study, lentiviral vectors encoding Ub-HBcAg (LV-Ub-HBcAg) were designed and constructed as a therapeutic vaccine for immunotherapy. HBcAg-specific cellular immune responses and anti-viral effects induced by LV-Ub-HBcAg were evaluated in HBV transgenic mice. We demonstrated that immunization with LV-Ub-HBcAg promoted the secretion of cytokines interleukin-2 (IL-2), interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), generated remarkably high percentages of IFN-γ-secreting CD8(+) T cells and CD4(+) T cells, and enhanced HBcAg-specific CTL activity in HBV transgenic mice. More importantly, vaccination with LV-Ub-HBcAg could efficiently decreased the levels of serum hepatitis B surface antigen (HBsAg), HBV DNA and the expression of HBsAg and HBcAg in liver tissues of HBV transgenic mice. In addition, LV-Ub-HBcAg could upregulate the expression of T cell-specific T-box transcription factor (T-bet) and downregulate the expression of GATA-binding protein 3 (GATA-3) in spleen T lymphocytes. The therapeutic vaccine LV-Ub-HBcAg could break immune tolerance, and induce potent HBcAg specific cellular immune responses and therapeutic effects in HBV transgenic mice.

Second-generation Langerhans cells originating from epidermal precursors are essential for CD8+ T cell priming

In vivo studies questioned the ability of Langerhans cells (LCs) to mediate CD8(+) T cell priming. To address this issue, we used intradermal immunization with plasmid DNA, a system in which activation of CD8(+) T cells depends on delayed kinetics of Ag presentation. We found that dendritic cells (DCs) located in the skin at the time of immunization have limited ability to activate CD8(+) T cells. This activity was mediated by a second generation of DCs that differentiated in the skin several days after immunization, as well as by lymph node-resident DCs. Intriguingly, CD8(+) T cell responses were not affected following treatment with clodronate liposomes, immunization of CCR2(-/-) mice, or local neutralization of CCL20. This suggests that local, rather than blood-derived, DC precursors mediate CD8(+) T cell priming. Analysis of DC differentiation in the immunized skin revealed a gradual increase in the number of CD11c(+) cells, which reached their maximum 2 wk after immunization. A similar differentiation kinetics was observed for LCs, with the majority of differentiating LCs proliferating in situ from epidermal precursors. By using B6/Langerin-diphtheria toxin receptor chimeric mice and LC ablation, we demonstrated that epidermal LCs were crucial for the elicitation of CD8(+) T cell responses in vivo. Furthermore, LCs isolated from lymph nodes 2 wk after immunization contained the immunization plasmid and directly activated Ag-specific CD8(+) T cells ex vivo. Thus, these results indicate that second-generation Ag-expressing LCs differentiating from epidermal precursors directly prime CD8(+) T cells and are essential for optimal cellular immune responses following immunization with plasmid DNA.

Dendritic cells of the oral mucosa

The oral cavity contains distinct mucosal surfaces, each with its own unique distribution of dendritic cell (DC) subsets. In addition to tissue-specific properties, such organization might confer differential immune outcomes guided by tissue-resident DCs, which translate in the lymph node into an overall immune response. This process is further complicated by continual exposure and colonization of the oral cavity with enormous numbers of diverse microbes, some of which might induce destructive immunity. As a central cell type constantly monitoring changes in oral microbiota and orchestrating T-cell function, oral DCs are of major importance in deciding whether to induce immunity or tolerance. In this review, an overview of the phenotype and distribution of DCs in the oral mucosa is provided. In addition, the role of the various oral DC subsets in inducing immunity vs. tolerance, as well as their involvement in several oral pathologies is discussed.

Diminished Memory T-Cell Expansion Due to Delayed Kinetics of Antigen Expression by Lentivectors

Memory CD8⁺ T lymphocytes play a central role in protective immunity. In attempt to increase the frequencies of memory CD8⁺ T cells, repeated immunizations with viral vectors are regularly explored. Lentivectors have emerged as a powerful vaccine modality with relatively low pre-existing and anti-vector immunity, thus, thought to be ideal for boosting memory T cells. Nevertheless, we found that lentivectors elicited diminished secondary T-cell responses that did not exceed those obtained by priming. This was not due to the presence of anti-vector immunity, as limited secondary responses were also observed following heterologous prime-boost immunizations. By dissecting the mechanisms involved in this process, we demonstrate that lentivectors trigger exceptionally slow kinetics of antigen expression, while optimal activation of lentivector-induced T cells relays on durable expression of the antigen. These qualities hamper secondary responses, since lentivector-encoded antigen is rapidly cleared by primary cytotoxic T cells that limit its presentation by dendritic cells. Indeed, blocking antigen clearance by cytotoxic T cells via FTY720 treatment, fully restored antigen presentation. Taken together, while low antigen expression is expected during secondary immunization with any vaccine vector, our results reveal that the intrinsic delayed expression kinetics of lentiviral-encoded antigen, further dampens secondary CD8⁺ T-cell expansion.

Uptake of biodegradable poly(γ-glutamic acid) nanoparticles and antigen presentation by dendritic cells in vivo

Poly(γ-glutamic acid) (γ-PGA) nanoparticles (NPs) carrying antigens have been shown to induce potent antigen-specific immune responses. However, in vivo delivery of γ-PGA NPs to dendritic cells (DCs), a key regulator of immune responses, still remains unclear. In this study, γ-PGA NPs were examined for their uptake by DCs and subsequent migration from the skin to the regional lymph nodes (LNs) in mice. After subcutaneous injection of fluorescein 5-isothiocyanate (FITC)-labeled NPs or FITC-ovalbumin (OVA)-carrying NPs (FITC-OVA-NPs), DCs migrated from the skin to the LNs and maturated, resulting in the upregulation of the costimulatory molecules CD80 and CD86 and the chemokine receptor CCR7. However, the migrated DCs were not detected in the spleen. FITC-OVA-NPs were found to be taken up by skin-derived CD103(+) DCs, and the processed antigen peptides were cross-presented by the major histocompatibility complex (MHC) class I molecule of DCs. Furthermore, significant activation of antigen-specific CD8(+) T cells was observed in mice immunized with OVA-carrying NPs (OVA-NPs) but not with OVA alone or OVA with an aluminum adjuvant. The antigen-specific CD8(+) T cells were induced within 7 days after immunization with OVA-NPs. Thus, γ-PGA NPs carrying various antigens may have great potential as an antigen-delivery system and vaccine adjuvant in vivo.

A nonintegrative lentiviral vector-based vaccine provides long-term sterile protection against malaria

Trials testing the RTS,S candidate malaria vaccine and radiation-attenuated sporozoites (RAS) have shown that protective immunity against malaria can be induced and that an effective vaccine is not out of reach. However, longer-term protection and higher protection rates are required to eradicate malaria from the endemic regions. It implies that there is still a need to explore new vaccine strategies. Lentiviral vectors are very potent at inducing strong immunological memory. However their integrative status challenges their safety profile. Eliminating the integration step obviates the risk of insertional oncogenesis. Providing they confer sterile immunity, nonintegrative lentiviral vectors (NILV) hold promise as mass pediatric vaccine by meeting high safety standards. In this study, we have assessed the protective efficacy of NILV against malaria in a robust pre-clinical model. Mice were immunized with NILV encoding Plasmodium yoelii Circumsporozoite Protein (Py CSP) and challenged with sporozoites one month later. In two independent protective efficacy studies, 50% (37.5-62.5) of the animals were fully protected (p = 0.0072 and p = 0.0008 respectively when compared to naive mice). The remaining mice with detectable parasitized red blood cells exhibited a prolonged patency and reduced parasitemia. Moreover, protection was long-lasting with 42.8% sterile protection six months after the last immunization (p = 0.0042). Post-challenge CD8+ T cells to CSP, in contrast to anti-CSP antibodies, were associated with protection (r = -0.6615 and p = 0.0004 between the frequency of IFN-g secreting specific T cells in spleen and parasitemia). However, while NILV and RAS immunizations elicited comparable immunity to CSP, only RAS conferred 100% of sterile protection. Given that a better protection can be anticipated from a multi-antigen vaccine and an optimized vector design, NILV appear as a promising malaria vaccine.

Transdermal insulin application system with dissolving microneedles

BACKGROUND

The aim of this report was to develop a dissolving microneedle (DM) application system, where 225-300 insulin-loaded DMs were formed on a chip. After the heat-sealed sheet is removed, the system covered with the press-through package layer is put on the skin. By pressing with the hand, insulin DMs were inserted into the skin.

MATERIALS AND METHODS

Factors affecting the penetration depth of DM were studied using applicator in vitro and in vivo experiments. The penetration depth was determined for rat and human skin. Two-layered DM array chips were prepared to obtain complete absorption of insulin and administered to the rat abdominal skin. Plasma glucose levels were measured for 6 h. By comparing the hypoglycemic effect with that obtained after subcutaneous injection, relative pharmacological availability (RPA) was determined.

RESULTS

The penetration depth increased from 21 ± 3 μm to 63 ± 2 μm in proportion to application speed to isolated rat skin, at 0.8-2.2 m/s. Human skin showed similar results in the penetration depth. The in vivo penetration depth was dependent on the force (0.5-2.5 N) and duration (1-10 min), as the secondary application force. The penetration depth was 211 ± 3 μm with a duration of 3 min in the in vivo rat experiment. DM array chips having an insulin-loaded space of 181.2 ± 4.2 and 209 ± 3.9 μm were evaluated in the rat. RPA values of insulin from DMs were 98.1 ± 0.8% and 98.1 ± 3.1%, respectively.

CONCLUSIONS

These results suggest the usefulness of the two-layered DM application system for the transdermal delivery of insulin.

Immunoglobulin Fc fragment tagging allows strong activation of endogenous CD4 T cells to reshape the tumor milieu and enhance the antitumor effect of lentivector immunization

A major problem with current cancer vaccines is that the induction of CD8 immune responses is rarely associated with antitumor benefits, mainly owing to multiple immune suppressions in established tumor lesions. In this study, we investigated if and how activation of endogenous CD4 T cells could be achieved to influence the suppressive tumor milieu and antitumor effect. We engineered a lentivector (lv) to express a nominal fusion Ag composed of hepatitis B surface protein and IgG2a Fc fragment (HBS-Fc-lv) to increase the magnitude of CD8 response but, more importantly, to induce effective coactivation of CD4 T cells. We found that, remarkably, immunization with HBS-Fc-lv caused significant regression of established tumors. Immunologic analysis revealed that, compared with HBS-lv without Fc fragment, immunization with HBS-Fc-lv markedly increased the number of functional CD8 and CD4 T cells and the level of Th1/Tc1-like cytokines in the tumor while substantially decreasing the regulatory T cell ratio. The favorable immunologic changes in tumor lesions and the improvement of antitumor effects from HBS-Fc-lv immunization were dependent on the CD4 activation, which was Fc receptor mediated. Adoptive transfer of CD4 T cells from the HBS-Fc-lv-immunized mice could activate endogenous CD8 T cells in an IFN-γ-dependent manner. We conclude that endogenous CD4 T cells can be activated by lv expressing Fc-tagged Ag to provide another layer of help--that is, creating a Th1/Tc1-like proinflammatory milieu within the tumor lesion to boost the effector phase of immune responses in enhancing the antitumor effect.

A TLR4 agonist synergizes with dendritic cell-directed lentiviral vectors for inducing antigen-specific immune responses

TLR4 agonists can be used as adjuvants to trigger innate immune responses of antigen-presenting cells (APCs) such as dendritic cells (DCs) to enhance vaccine-specific immunity. Adjuvant effects of TLR4 agonists are mediated by downstream signaling controlled by both MyD88 and TRIF adapter proteins. In this study, we investigated the adjuvanting capacity of glucopyranosyl lipid A (GLA), a chemically synthesized TLR4 agonist, to boost antigen-specific immunity elicited by DC-directed lentiviral vectors (DC-LV). We found that stimulation by this agonist in vitro can activate DCs in a TLR4-dependent manner. The agonist can significantly boost DC-LV-induced humoral and cellular immune responses, resulting in better antitumor reactions in response to tumor challenges. We observed that the adjuvant-mediated enhancement of cytotoxic CD8(+) T cell responses is CD4(+) T cell-dependent and determined that in vitro the agonist stimulation involves the participation of both MyD88 and TRIF pathways to activate DCs. In vivo immunization study however revealed that adjuvant effects depend more on the MyD88 signaling as TRIF(-/-) mice but not MyD88(-/-) mice were able to maintain the enhanced CD8(+) T cell responses upon DC-LV immunization. Thus, our study supports the use of this TLR4 agonist as a potent adjuvant candidate for boosting DC-LV immunization.

Intradermal naked plasmid DNA immunization: mechanisms of action

Plasmid DNA is a promising vaccine modality that is regularly examined in prime-boost immunization regimens. Recent advances in skin immunity increased our understanding of the sophisticated cutaneous immune network, which revived scientific interest in delivering vaccines to the skin. Intradermal administration of plasmid DNA via needle injection is a simple and inexpensive procedure that exposes the plasmid and its encoded antigen to the dermal immune surveillance system. This triggers unique mechanisms for eliciting local and systemic immunity that can confer protection against pathogens and tumors. Understanding the mechanisms of intradermal plasmid DNA immunization is essential for enhancing and modulating its immunogenicity. With regard to vaccination, this is of greater importance as this routine injection technique is highly desirable for worldwide immunization. This article will focus on the current understanding of the mechanisms involved in antigen expression and presentation during primary and secondary syringe and needle intradermal plasmid DNA immunization.

Intradermal immunization triggers epidermal Langerhans cell mobilization required for CD8 T-cell immune responses

The potential of the skin immune system for the generation of both powerful humoral and cellular immune responses is now well established. However, the mechanisms responsible for the efficacy of skin antigen-presenting cells (APCs) during intradermal (ID) vaccination still remain to be elucidated. We have previously demonstrated in clinical trials that preferential targeting of Langerhans cells (LCs) by transcutaneous immunization shapes the immune response toward vaccine-specific CD8 T cells. Others have shown that ID inoculation of a vaccine, which targets dermal APCs, mobilizes both the cellular and humoral arms of immunity. Here, we investigated the participation of epidermal LCs in response to ID immunization. When human or mouse skin was injected ID with a particle-based vaccine, we observed significant modifications in the morphology of epidermal LCs and their mobilization to the dermis. We further established that this LC recruitment after ID administration was essential for the induction of antigen-specific CD8 T cells, but was, however, dispensable for the generation of specific CD4 T cells and neutralizing antibodies. Thus, epidermal and dermal APCs shape the outcome of the immune responses to ID vaccination. Their combined potential provides new avenues for the development of vaccination strategies against infectious diseases.

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.

Lentivector prime and vaccinia virus vector boost generate high-quality CD8 memory T cells and prevent autochthonous mouse melanoma

Most cancer vaccines, to date, fail to control established tumors. However, their application in preventing tumors is another question that is understudied. In the current study, we investigated the CD8 memory T cell responses of lentivector (lv) immunization and its potential to prevent melanoma using both transplantable B16 tumor and autochthonous melanoma models. We found that lv-expressing xenogenic human gp100 could induce potent CD8 responses that cross-react with mouse gp100. Importantly, the lv-primed CD8 response consisted of a high number of memory precursors and could be further increased by recombinant vaccinia virus vector (vv) boost, resulting in enhanced CD8 memory response. These long-lasting CD8 memory T cells played a critical role in immune surveillance and could rapidly respond and expand after sensing B16 tumor cells to prevent tumor establishment. Although CD8 response plays a dominant role after lv immunization, both CD4 and CD8 T cells are responsible for the immune prevention. In addition, we surprisingly found that CD4 help was not only critical for generating primary CD8 responses, but also important for secondary CD8 responses of vv boost. CD4 depletion prior to lv prime or prior to vv boost substantially reduced the magnitude of secondary CD8 effector and memory responses, and severely compromised the effect of cancer immune prevention. More importantly, the CD8 memory response from lv-vv prime-boost immunization could effectively prevent autochthonous melanoma in tumor-prone transgenic mice, providing a strong evidence that lv-vv prime-boost strategy is an effective approach for cancer immune prevention.

Complexity of dendritic cell subsets and their function in the host immune system

Dendritic cells (DCs) are professional antigen-presenting cells that are critical for induction of adaptive immunity and tolerance. Traditionally DCs have been divided into two discrete subtypes, which comprise conventional and non-conventional DCs. They are distributed across various organs in the body and comprise a heterogeneous population, which has been shown to display differences in terms of surface marker expression, function and origins. Recent studies have shed new light on the process of DC differentiation and distribution of DC subtypes in various organs. Although monocytes, macrophages and DCs share a common macrophage-DC progenitor, a common DC progenitor population has been identified that exclusively gives rise to DCs and not monocytes or macrophages. In this review, we discuss the recent advances in our understanding of DC differentiation and subtypes and provide a comprehensive overview of various DC subtypes with emphasis on their function and origins. Furthermore, in light of recent developments in the field of DC biology, we classify DCs based on the precursor populations from which the various DC subsets originate. We classify DCs derived from common DC progenitor and pre-DC populations as conventional DCs, which includes both migratory and lymphoid-resident DC subsets and classify monocyte-derived DCs and plasmacytoid DCs as non-conventional DCs.

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.

Lentivector expressing HBsAg and immunoglobulin Fc fusion antigen induces potent immune responses and results in seroconversion in HBsAg transgenic mice

Even though hepatitis B virus(HBV) vaccines effectively prevent new cases of HBV infection, with approximately 350 million patients worldwide, chronic HBV infection remains a major health problem because of the associated complications (such as liver cirrhosis and hepatocellular carcinoma) and the limited treatment options. Immunotherapy has the potential to effectively control HBV replication. In this current study, we found that recombinant lentivectors could induce potent HBV surface antigen (HBsAg) specific T cell responses and humoral immune responses. Tagging the HBsAg with immunoglobulin Fc fragment further substantially increased the HBsAg specific immune responses. Remarkably, the HBS-Fc-lv lentivector could effectively break immune tolerance and induce potent HBsAg specific adaptive immune responses in HBsAg transgenic (Tg) mice with low serum level of HBsAg. More importantly, the induction of HBsAg specific immune responses in Tg mice accompanied seroconversion from HBsAg to anti-HBsAg antibody (anti-HBsAb). Our study demonstrated the potential of utilizing lentivector to treat chronic HBV infection following reduction of viral load with antiviral drug therapy.

Conventional dendritic cells are required for the activation of helper-dependent CD8 T cell responses to a model antigen after cutaneous vaccination with lentiviral vectors

Cutaneous vaccination with lentiviral vectors generates systemic CD8 T cell responses that have the potential to eradicate tumors for cancer immunotherapy. However, although s.c. immunization with <1 million lentiviral particles clearly primes cytotoxic T cells, vaccination with much higher doses has routinely been used to define the mechanisms of T cell activation by lentiviral vectors. In particular, experiments to test presentation of lentiviral Ags by dendritic cells (DC) require injection of high viral titers, which may result in aberrant transduction of different DC populations. We exploited inducible murine models of DC depletion to investigate which DC prime the lentiviral response after s.c. immunization with low doses of lentiviral particles. In this article, we demonstrate that conventional DC are required to present Ag to CD8 T cells in draining lymph nodes. Langerhans cells are not required to activate the effector response, and neither Langerhans cells nor plasmacytoid DC are sufficient to prime Ag-specific T cells. Immunization drives the generation of endogenous long-lived memory T cells that can be reactivated to kill Ag-specific targets in the absence of inflammatory challenge. Furthermore, lentiviral vaccination activates expansion of endogenous CD4 Th cells, which are required for the generation of effector CD8 T cells that produce IFN-γ and kill Ag-specific targets. Collectively, we demonstrate that after cutaneous immunization with lentiviral particles, CD4-licensed lymph node conventional DC present Ag to CD8 T cells, resulting in the generation of protective endogenous antitumor immunity that may be effective for cancer immunotherapy.

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.

Directly transfected langerin+ dermal dendritic cells potentiate CD8+ T cell responses following intradermal plasmid DNA immunization

Dendritic cells (DCs) play a critical role in CD8(+) T cell priming following DNA vaccination. In contrast to other DNA injection routes or immunization with viral vectors, Ag presentation is delayed following needle injection of plasmid DNA into the skin. The contribution of various skin DC subsets to this process is not known. In this study, we show that dermal CD11c(+) cells are the most important transgene-expressing cells following immunization. Using langerin- diphtheria toxin receptor mice we demonstrated that langerin(+) dermal DCs (Ln(+) dDCs) were crucial for generating an optimal CD8(+) T cell response. Blocking migration of skin cells to the lymph node (LN) ablated immunogenicity, suggesting that migration of dDC subsets to the LN is essential for generating immunity. This migration generated a weak Ag-presenting activity in vivo until day 5 postimmunization, which then increased dramatically. We further found that Ln(+) dDCs and dDCs were the only DC populations directly presenting Ag to CD8(+) T cells ex vivo during the initial 8-d period postimmunization. This activity changed on the following days, when both skin DCs and LN-resident DCs were able to present Ag to CD8(+) T cells. Taken together, our in vivo and ex vivo results suggest that activation of CD8(+) T cells following intradermal plasmid DNA immunization depends on directly transfected Ln(+)dDCs and dDCs. Moreover, the type of DCs presenting Ag changed over time, with Ln(+)dDCs playing the major role in potentiating the initial CD8(+) T cell response.