Intravenous injection of naked DNA encoding secreted flt3 ligand dramatically increases the number of dendritic cells and natural killer cells in vivo

S1PR1-mediated IFNAR1 degradation modulates plasmacytoid dendritic cell interferon-α autoamplification

Blunting immunopathology without abolishing host defense is the foundation for safe and effective modulation of infectious and autoimmune diseases. Sphingosine 1-phosphate receptor 1 (S1PR1) agonists are effective in treating infectious and multiple autoimmune pathologies; however, mechanisms underlying their clinical efficacy are yet to be fully elucidated. Here, we uncover an unexpected mechanism of convergence between S1PR1 and interferon alpha receptor 1 (IFNAR1) signaling pathways. Activation of S1PR1 signaling by pharmacological tools or endogenous ligand sphingosine-1 phosphate (S1P) inhibits type 1 IFN responses that exacerbate numerous pathogenic conditions. Mechanistically, S1PR1 selectively suppresses the type I IFN autoamplification loop in plasmacytoid dendritic cells (pDCs), a specialized DC subset, for robust type I IFN release. S1PR1 agonist suppression is pertussis toxin-resistant, but inhibited by an S1PR1 C-terminal-derived transactivating transcriptional activator (Tat)-fusion peptide that blocks receptor internalization. S1PR1 agonist treatment accelerates turnover of IFNAR1, suppresses signal transducer and activator of transcription 1 (STAT1) phosphorylation, and down-modulates total STAT1 levels, thereby inactivating the autoamplification loop. Inhibition of S1P-S1PR1 signaling in vivo using the selective antagonist Ex26 significantly elevates IFN-α production in response to CpG-A. Thus, multiple lines of evidence demonstrate that S1PR1 signaling sets the sensitivity of pDC amplification of IFN responses, thereby blunting pathogenic immune responses. These data illustrate a lipid G-protein coupled receptor (GPCR)-IFNAR1 regulatory loop that balances effective and detrimental immune responses and elevated endogenous S1PR1 signaling. This mechanism will likely be advantageous in individuals subject to a range of inflammatory conditions.

Enhanced in vivo targeting of murine nonparenchymal liver cells with monophosphoryl lipid A functionalized microcapsules

A broad spectrum of infectious liver diseases emphasizes the need of microparticles for targeted delivery of immunomodulatory substances to the liver. Microcapsules (MCs) are particularly attractive for innovative drug and vaccine formulations, enabling the combination of antigen, drugs, and adjuvants. The present study aimed to develop microcapsules characterized by an enhanced liver deposition and accelerated uptake by nonparenchymal liver cells (NPCs). Initially, two formulations of biodegradable microcapsules were synthesized from either hydroxyethyl starch (HES) or mannose. Notably, HES-MCs accumulated primarily in the liver, while mannose particles displayed a lung preference. Functionalization of HES-MCs with anti-CD40, anti-DEC205, and/or monophosphoryl lipid A (MPLA) enhanced uptake of MCs by nonparenchymal liver cells in vitro. In contrast, only MPLA-coated HES-MCs promoted significantly the in vivo uptake by NPCs. Finally, HES-MCs equipped with MPLA, anti-CD40, and anti-DEC205 induced the secretion of TNF-α, IL-6 by Kupffer cells (KCs), and IFN-γ and IL-12p70 by liver dendritic cells (DCs). The enhanced uptake and activation of KCs by MPLA-HES-MCs is a promising approach to prevent or treat infection, since KCs are exploited as an entry gate in various infectious diseases, such as malaria. In parallel, loading and activating liver DCs, usually prone to tolerance, bears the potential to induce antigen specific, intrahepatic immune responses necessary to prevent and treat infections affecting the liver.

Synergic silencing of costimulatory molecules prevents cardiac allograft rejection

Background

While substantial progress has been made in blocking acute transplant rejection with the advent of immune suppressive drugs, chronic rejection, mediated primarily by recipient antigen presentation, remains a formidable problem in clinical transplantation. We hypothesized that blocking co-stimulatory pathways in the recipient by induction of RNA interference using small interference RNA (siRNA) expression vectors can prolong allogeneic heart graft survival.

Method

Vectors expressing siRNA specifically targeting CD40 and CD80 were prepared. Recipients (BALB/c mice) were treated with CD40 and/or CD80 siRNA expression vectors via hydrodynamic injection. Control groups were injected with a scrambled siRNA vector and sham treatment (PBS). After treatment, a fully MHC-mismatched (BALB/c to C57/BL6) heart transplantation was performed.

Result

Allogeneic heart graft survival (>100 days) was approximately 70% in the mice treated simultaneously with CD40 and CD80 siRNA expression vectors with overall reduction in lymphocyte interstitium infiltration, vascular obstruction, and edema. Hearts transplanted into CD40 or CD80 siRNA vector-treated recipients had an increased graft survival time compared to negative control groups, but did not survive longer than 40 days. In contrast, allogenic hearts transplanted into recipients treated with scrambled siRNA vector and PBS stopped beating within 10–16 days. Real-time PCR (RT-PCR) and flow cytometric analysis showed an upregulation of FoxP3 expression in spleen lymphocytes and a concurrent downregulation of CD40 and CD80 expression in splenic dendritic cells of siRNA-treated mice. Functional suppressive activity of splenic dendritic cells (DCs) isolated from tolerant recipients was demonstrated in a mixed lymphocyte reaction (MLR). Furthermore, DCs isolated from CD40- and CD80-treated recipients promoted CD4 + CD25 + FoxP3+ regulatory T cell differentiation in vitro.

Conclusion

This study demonstrates that the simultaneous silencing of CD40 and CD80 genes has synergistic effects in preventing allograft rejection, and may therefore have therapeutic potential in clinical transplantation.

Fms-like tyrosine kinase 3 receptor ligand (Flt3L)-based vaccination administered with an adenoviral vector prevents tumor growth of colorectal cancer in a BALB/c mouse model

PURPOSE

Colorectal cancer is the third most frequent cancer in industrial nations. Therapeutic strategies to treat metastatic disease and prevent recurrence are needed. Anti-tumor immunity can be induced by dendritic cells. Dendritic cells can be expanded by the fms-like tyrosine kinase 3 ligand (Flt3L) in vivo. The aim of this study was to develop an adenoviral-based immune-gene therapy of colorectal cancer with Flt3L in a BALB/c mouse model.

METHODS

A new Flt3L-encoding adenoviral vector (pAdFlt3L) was administered in two approaches in a CT26 colon cancer model in female BALB/c mice. In the therapeutic approach, pAdFlt3L was injected into the tail vein or directly into subcutaneous CT26 colon carcinoma tumors in BALB/c mice. In the vaccination protocol, mice were vaccinated with CT26 cell lysate and pAdFlt3L subcutaneous prior to subcutaneous application of vital CT26 cells.

RESULTS

Application of pAdFlt3L led to high levels of Flt3L in vitro and in vivo. Significant expansion of dendritic cells after application of pAdFlt3L in vivo was confirmed by the use of CD11c and CD11b surface markers in immunohistochemistry and flow cytometry (p = 0.019). In the therapeutic approach, neither intravenous nor intratumoral treatments with pAdFlt3L lead to regression of CT26 tumors. In the vaccination protocol, vaccination completely prevented tumor growth and resulted in superior survival compared to control mice (p < 0.001).

CONCLUSIONS

Our results demonstrate that immunostimulatory therapy with pAdFlt3L is effective to prevent tumor development through vaccination and may represent a therapeutic tool to prevent metastatic disease.

Liver gene transfer of interkeukin-15 constructs that become part of circulating high density lipoproteins for immunotherapy

Apolipoprotein A-I (Apo A-I) is a major component of high density lipoproteins (HDL) that transport cholesterol in circulation. We have constructed an expression plasmid encoding a chimeric molecule encompassing interleukin-15 (IL-15) and Apo A-I (pApo-hIL15) that was tested by hydrodynamic injections into mice and was co-administered with a plasmid encoding the sushi domain of IL-15Rα (pSushi) in order to enhance IL-15 trans-presentation and thereby bioactivity. The pharmacokinetics of the Apo A-I chimeric protein were much longer than non-stabilized IL-15 and its bioactivity was enhanced in combination with IL-15Rα Sushi. Importantly, the APO-IL-15 fusion protein was incorporated in part into circulating HDL. Liver gene transfer of these constructs increased NK and memory-phenotype CD8 lymphocyte numbers in peripheral blood, spleen and liver as a result of proliferation documented by CFSE dilution and BrdU incorporation. Moreover, the gene transfer procedure partly rescued the NK and memory T-cell deficiency observed in IL-15Rα^−/− mice. pApo-hIL15+ pSushi gene transfer to the liver showed a modest therapeutic activity against subcutaneously transplanted MC38 colon carcinoma tumors, that was more evident when tumors were set up as liver metastases. The improved pharmacokinetic profile and the strong biological activity of APO-IL-15 fusion protein holds promise for further development in combination with other immunotherapies.

Induction of alloimmune tolerance in heart transplantation through gene silencing of TLR adaptors

Toll-like receptors (TLRs) activate biochemical pathways that evoke activation of innate immunity, which leads to dendritic cell (DC) maturation and initiation of adaptive immune responses that provoke allograft rejection. We aimed to prolong allograft survival by selectively inhibiting expression of the common adaptors of TLR signaling, namely MyD88 and TRIF, using siRNA. In vitro we demonstrated that blocking expression of MyD88 and TRIF led to reduced DC maturation. In vivo treatment of recipients with MyD88 and TRIF siRNA significantly prolonged allograft survival in the BALB/c > C57BL6 cardiac transplant model. Moreover, the combination of MyD88 and TRIF siRNA along with a low dose of rapamycin further extended the allograft survival (88.8 ± 7.1 days). Tissue histopathology demonstrated an overall reduction in lymphocyte interstitium infiltration, vascular obstruction and hemorrhage in mice treated with MyD88 and TRIF siRNA vector plus rapamycin. Furthermore, treatment was associated with an increase in the numbers of CD4(+) CD25(+) FoxP3(+) regulatory T cells and Th2 deviation. To our knowledge, this study is the first demonstration of prolonging the survival of allogeneic heart grafts through gene silencing of TLR signaling adaptors, highlighting the therapeutic potential of siRNA in clinical transplantation.

The vitamin E analogue α-TEA stimulates tumor autophagy and enhances antigen cross-presentation

The semisynthetic vitamin E derivative alpha-tocopheryloxyacetic acid (α-TEA) induces tumor cell apoptosis and may offer a simple adjuvant supplement for cancer therapy if its mechanisms can be better understood. Here we report that α-TEA also triggers tumor cell autophagy and that it improves cross-presentation of tumor antigens to the immune system. α-TEA stimulated both apoptosis and autophagy in murine mammary and lung cancer cells and inhibition of caspase-dependent apoptosis enhanced α-TEA-induced autophagy. Cell exposure to α-TEA generated double-membrane-bound vesicles indicative of autophagosomes, which efficiently cross-primed antigen-specific CD8(+) T cells. Notably, vaccination with dendritic cells pulsed with α-TEA-generated autophagosomes reduced lung metastases and increased the survival of tumor-bearing mice. Taken together, our findings suggest that both autophagy and apoptosis signaling programs are activated during α-TEA-induced tumor cell killing. We suggest that the ability of α-TEA to stimulate autophagy and enhance cross-priming of CD8(+) T cells might be exploited as an adjuvant strategy to improve stimulation of antitumor immune responses.

Peripheral immunization induces functional intrahepatic hepatitis C specific immunity following selective retention of vaccine-specific CD8 T cells by the liver

It is believed that an effective HCV vaccine must induce strong HCV-specific cytotoxic IFN-γ⁺ CD8⁺ T cells able to migrate into and become fully activated within the liver, an organ known to suppress T cell responses and induce tolerance. Given the importance of intrahepatic HCV-specific T cells in the clearance of acute infection, the goal of this present study was to determine if peripheral immunization was able to induce functional intrahepatic HCV-specific T cell based immunity both in the presence and absence of HCV antigen expression within the liver. Using a novel HCV NS3/NS4A DNA vaccine, we show that peripheral immunization of C57BL/6 mice results in the formation of a large pool of fully functional HCV-specific cytotoxic IFN-γ⁺ CD8⁺ T cells within the liver and that these cells were highly enriched within the liver as compared to the spleen. Following hepatic expression of cognate HCV antigen using a previously described liver transfection method, we show that this pool of vaccine-induced HCV-specific CD8⁺ T cells retained its ability to become highly activated as shown by the upregulation of IFN-γ and CCR5 expression, as well as by the clearance of HCV NS3 expressing hepatocytes. Taken together, these findings suggest that T cell effector function is preserved within the liver and that selective recruitment of antigen-specific T cells to the liver may play a previously unappreciated role in the process of immune surveillance, which may be exploited for future T cell based HCV vaccines.

Hydrodynamic delivery of plasmid DNA encoding human FcγR-Ig dimers blocks immune-complex mediated inflammation in mice

Therapeutic use and function of recombinant molecules can be studied by the expression of foreign genes in mice. In this study, we have expressed human Fcgamma receptor –Ig fusion molecules (FcγR-Igs) in mice by administering FcγR-Ig plasmid DNAs hydrodynamically and compared their effectiveness to purified molecules in blocking immune-complex (IC) mediated inflammation in mice. The concentration of hydrodynamically expressed FcγR-Igs (CD16A^F-Ig, CD32A^R-Ig and CD32A^H-Ig) reached a maximum of 130 μg/ml of blood within 24 h after plasmid DNA administration. The in vivo half-life of FcγR-Igs was found to be 9-16 days and Western blot analysis showed that the FcγR-Igs were expressed as a homodimer. The hydrodynamically expressed FcγR-Igs blocked 50-80% of IC-mediated inflammation up to 3 days in a reverse passive Arthus reaction model. Comparative analysis with purified molecules showed that hydrodynamically expressed FcγR-Igs are more efficient than purified molecules in blocking IC-mediated inflammation and had a higher half-life. In summary, these results suggest that the administration of a plasmid vector with a FcγR-Ig gene can be used to study the consequences of blocking IC-binding to FcγRs during the development of inflammatory diseases. This approach may have potential therapeutic value in treating IC-mediated inflammatory autoimmune diseases such as lupus, arthritis and autoimmune vasculitis.

Histone deacetylase inhibition facilitates GM-CSF-mediated expansion of myeloid-derived suppressor cells in vitro and in vivo

Chromatin-modifying HDACi exhibit anti-inflammatory properties that reflect their ability to suppress DC function and enhance regulatory T cells. The influence of HDACi on MDSCs, an emerging regulatory leukocyte population that potently inhibits T cell proliferation, has not been examined. Exposure of GM-CSF-stimulated murine BM cells to HDACi led to a robust expansion of monocytic MDSC (CD11b(+)Ly6C(+)F4/80(int)CD115(+)), which suppressed allogeneic T cell proliferation in a NOS- and HO-1-dependent manner with similar potency to control MDSCs. The increased yield of MDSCs correlated with blocked differentiation of BM cells and an overall increase in HSPCs (Lin(-)Sca-1(+)c-Kit(+)). In vivo, TSA enhanced the mobilization of splenic HSPCs following GM-CSF administration and increased the number of CD11b(+)Gr1(+) cells in BM and spleen. Increased numbers of Gr1(+) cells, which suppressed T cell proliferation, were recovered from spleens of TSA-treated mice. Overall, HDACi enhance MDSC expansion in vitro and in vivo, suggesting that acetylation regulates myeloid cell differentiation. These findings establish a clinically applicable approach to augment this rare and potent suppressive immune cell population and support a novel mechanism underlying the anti-inflammatory action of HDACi.

Tumor-derived autophagosome vaccine: induction of cross-protective immune responses against short-lived proteins through a p62-dependent mechanism

PURPOSE

Tumor-specific antigens of 3-methylcholanthrene (MCA)-induced sarcomas were defined by the narrow immune responses they elicited, which uniquely rejected the homologous tumor, with no cross-reactions between independently derived syngeneic MCA-induced tumors. This study examines whether an autophagosome-enriched vaccine derived from bortezomib-treated sarcomas can elicit an immune response that cross-reacts with other unique sarcomas.

EXPERIMENTAL DESIGN

Mice were vaccinated with either MCA-induced sarcomas or autophagosomes derived from those tumors and later challenged with either homologous or nonhomologous sarcomas. In addition, 293 cells expressing a model antigen were used to understand the necessity of short-lived proteins (SLiP) in this novel vaccine. These findings were then tested in the sarcoma model. Autophagosomes were characterized by Western blotting and fluorescent microscopy, and their ability to generate immune responses was assessed in vitro by carboxyfluorescein succinimidyl ester dilution of antigen-specific T cells and in vivo by monitoring tumor growth.

RESULTS

In contrast to a whole-cell tumor vaccine, autophagosomes isolated from MCA-induced sarcomas treated with a proteasome inhibitor prime T cells that cross-react with different sarcomas and protect a significant proportion of vaccinated hosts from a nonhomologous tumor challenge. Ubiquitinated SLiPs, which are stabilized by proteasome blockade and delivered to autophagosomes in a p62/sequestosome-dependent fashion, are a critical component of the autophagosome vaccine, as their depletion limits vaccine efficacy.

CONCLUSION

This work suggests that common short-lived tumor-specific antigens, not physiologically available for cross-presentation, can be sequestered in autophagosomes by p62 and used as a vaccine to elicit cross-protection against independently derived sarcomas.

Involvement of activated transcriptional process in efficient gene transfection using unmodified and mannose-modified bubble lipoplexes with ultrasound exposure

Recently, our group developed ultrasound (US)-responsive and mannose-modified gene carriers (Man-PEG(2000) bubble lipoplexes), and successfully obtained a high level of gene expression in mannose receptor-expressing cells following gene transfection using Man-PEG(2000) bubble lipoplexes and US exposure. We also reported that large amounts of plasmid DNA (pDNA) were transferred into the cytoplasm of the targeted cells in the gene transfection using this method. In the present study, we investigated the involvement of transcriptional processes on enhanced gene expression obtained by unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. The transcriptional process related to activator protein-1 (AP-1) and nuclear factor-κB (NFκB) was activated by US exposure, and was founded to be involved in enhanced gene expression obtained by gene transfection using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. On the other hand, activation of AP-1 and NFκB pathways followed by US exposure was hardly involved in the inflammatory responses in the gene transfection using this method. These findings suggest that activation of AP-1 and NFκB followed by US exposure is involved in the enhanced gene expression using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure, and the selection of pDNAs activated by US exposure is important in this gene transfection method.

Antigen encoded by vaccine vectors derived from human adenovirus serotype 5 is preferentially presented to CD8+ T lymphocytes by the CD8α+ dendritic cell subset

Different subsets of dendritic cells (DC) elicit qualitatively different immune responses. In mice, two lymphoid tissue-resident subsets, CD8α(+) and CD8α(-), have been implicated in the induction of T helper 1 (Th1) or Th2 responses, respectively. Moreover, CD8α(+) DC appear to play a major role in priming CD8(+) T lymphocyte responses to viral antigens in the course of diverse viral infections. These considerations have been less extensively explored for vaccine vectors derived from viruses. Despite inefficient ex vivo transduction of DC, vectored vaccines derived from human adenoviruses of serotype 5 (Ad5) elicit robust immune responses, predominantly of the Th1 orientation, in humans and mice. At present it is unknown whether Ad5 interacts with DC subsets in a differential manner, thereby influencing the quality of the elicited IR. To address this issue, successive steps (attachment, transgene expression, MHC class I antigen presentation and activation of antigen-specific T lymphocytes) involved in induction of immune responses by Ad5-based vectors have been examined in CD8α(+) and CD8α(-) murine DC subsets. Although in both ex vivo and in vivo experiments CD8α(+) and CD8α(-) DC subsets captured an Ad5-based vector to a similar extent, transgene expression and subsequent MHC class I display of a transgene-encoded antigen were more efficient in CD8α(+) DC. Moreover, following in vivo and ex vivo transduction with an Ad5-based vaccine, antigen-specific CD8(+) T lymphocytes were more efficiently activated by CD8α(+) DC than by CD8α(-) DC. Thus, superior antigen expression and MHC class I display in CD8α(+) DC may contribute to preferred priming of antigen-specific CD8(+) lymphocytes by Ad5-transduced CD8α(+) DC.

Ethanol inhibits antigen presentation by dendritic cells

Previous studies suggest that altered virus-specific T-cell responses observed during chronic ethanol exposure may be due to abnormal functioning of dendritic cells (DCs). Here we explored the effects of ethanol on exogenous antigen presentation by DCs. BALB/c, C57BL/6, and CBA/caj mice were fed ethanol or an isocaloric control diet for 8 weeks. The splenic DC population was expanded using an Flt3L expression plasmid via tail vein injection. DCs were purified and assessed for antigen presentation and processing and for peptide-major histocompatibility complex class I and II (MHCI and MHCII) formation on the cell surface. Interleukin-2 (IL-2) was measured as an indicator of antigen-specific T-cell activation by DCs in coculture. Antigen processing and peptide-MHCII complexes were evaluated by flow cytometry. We observed that ethanol not only suppressed allogeneic peptide presentation to T cells by DCs but also altered presentation of exogenous ovalbumin (OVA) peptide 323-339 to an OVA-specific DO11 T-cell line as well as to OVA-sensitized primary T cells. Smaller amounts of peptide-MHCII complexes were found on the DCs isolated from the spleens of ethanol-fed mice. In contrast to MHCII presentation, cross-presentation of exogenous OVA peptide via MHCI by DCs remained intact. More importantly, ethanol-exposed DCs had reduced B7-DC and enhanced ICOS-L (inhibitory) costimulatory molecule expression. Ethanol inhibits exogenous and allogeneic antigen presentation and affects the formation of peptide-MHCII complexes, as well as altering costimulatory molecule expression on the cell surface. Therefore, DC presentation of peptides in a favorable costimulatory protein environment is required to subsequently activate T cells and appears to be a critical target for the immunosuppressive effects of ethanol.

Dendritic cells in alcoholic liver injury and fibrosis

Alcohol consumption impairs the development of innate and adaptive immune responses, however the exact mechanism by which alcohol leads to immune defects remains to be established. Dendritic cells (DCs) form a heterogeneous population of hematopoietic cells that are present in all tissues including the liver. DC are initially described playing a key role in the induction of innate and adaptive immune response against specific antigens. In our presentation, we discussed few new aspects of DC development, critical assessment of DC in non-lymphoid organs and the impact of alcohol consumption on DC function. Understanding the mechanism by which DC modulate liver function after alcohol consumption may help uncover novel therapeutic strategies for the treatment of these conditions.

Generation of cellular immune responses to HCV NS5 protein through in vivo activation of dendritic cells

Chronic hepatitis C (HCV) infection is a substantial medical problem that leads to progressive liver disease, cirrhosis, and hepatocellular carcinoma (HCC). The aim of this study was to achieve sustained cellular immune responses in vivo to a HCV nonstructural protein using dendritic cell (DC)-based immunization approach. We targeted the HCV NS5 protein to DCs in vivo by injecting microparticles loaded with this antigen. The DC population was expanded in BALB/C mice (H-2(d) ) by hydrodynamic injection of a plasmid pUMVC3-hFLex expressing the secreted portion of the human Fms-like tyrosine kinase receptor-3 ligand (hFlt3). Mice were subsequently injected with microparticles coated with HCV NS5 protein via the tail vein. Cellular immune responses were determined with respect to secretion of INFγ and IL2 by CD4(+) cells and cytotoxic T-lymphocyte (CTL) assays in vitro; inhibition of tumour cell growth was employed for the assessment of CD8(+) generated activity in vivo. We found that Flt3L treatment expanded the DC population in the spleen to 43%, and such cells displayed a striking upregulation of CD86 as well as CD80 and CD40 co-stimulating molecules. Viral antigen-specific T(H) 1 cytokine secretion by splenocytes was generated, and CTL activity against syngeneic NS5 expressing myeloma target cells was observed. In addition, these cells inhibited tumour growth indicating that NS5-specific robust CTL activity was operative in vivo. Thus, the capability of activating DCs in vivo using the methods described is valuable as a therapeutic vaccine strategy for chronic HCV infection.

Generation of immune responses against hepatitis C virus by dendritic cells containing NS5 protein-coated microparticles

Dendritic cells (DCs) internalize and process antigens as well as activate cellular immune responses. The aim of this study was to determine the capacity of DCs that contain antigen-coated magnetic beads to induce immunity against the nonstructural hepatitis C virus (HCV) antigen 5 (NS5). Splenocytes derived from Fms-like tyrosine kinase receptor 3 (Flt3) ligand-pretreated BALB/c mice were incubated with magnetic beads coated with HCV NS5, lipopolysaccharide (LPS), and/or anti-CD40; purified; and used for immunization. Cellular immunity was measured using cytotoxic T-lymphocyte (CTL) and T-cell proliferation assays, intracellular cytokine staining, and a syngeneic tumor challenge using NS5-expressing SP2/0 myeloma cells in vivo. Splenocytes isolated from animals vaccinated with DCs containing beads coated with NS5, LPS, and anti-CD40 secreted elevated levels of interleukin-2 (IL-2) and gamma interferon in the presence of NS5. The numbers of CD4(+), IL-2-producing cells were increased >5-fold in the group immunized with DCs containing beads coated with NS5, LPS, and anti-CD40, paralleled by an enhanced splenocyte proliferative response. Immunization promoted antigen-specific CTL activity threefold compared to the level for control mice and significantly reduced the growth of NS5-expressing tumor cells in vivo. Thus, strategies that employ NS5-coated beads induce cellular immune responses in mice, which correlate well with the natural immune responses that occur in individuals who resolve HCV.

Efficient cross-presentation depends on autophagy in tumor cells

Cross-presentation of antigens is critical for the induction of adaptive immunity against tumor cells and infectious pathogens. Currently, it is not known how cross-presentation of tumor antigens is regulated by autophagy. Using both HEK 293T cells that expressed the model antigen OVA and melanoma cells as antigen donors, we show that macroautophagy in tumor cells is essential for cross-presentation by dendritic cells both in vitro and in vivo. Inhibition of autophagy abolished cross-presentation almost completely, whereas induction of autophagy dramatically enhanced the cross-presentation of tumor antigens. Moreover, purified autophagosomes were found to be efficient antigen carriers for cross-presentation. Our findings not only identified a novel role for autophagy as an active process in antigen sequestration and delivery to dendritic cells for cross-presentation, but also suggested, for the first time, that isolated autophagosomes may have potential as potent vaccines for immunotherapy against cancer and infectious diseases.

Intercellular adhesion molecule-1-dependent stable interactions between T cells and dendritic cells determine CD8+ T cell memory

The initiation of cytotoxic immune responses requires the direct interaction between naive CD8+ T lymphocytes and dendritic cells (DCs). Multiphoton imaging in intact lymph nodes (LNs) showed that during priming, naive T cells and DCs establish sequentially brief (i.e., minutes) and long (hours) antigen-specific contacts. We show here that the expression of the Intercellular Adhesion Molecule-1 (ICAM-1) by mature DCs is critical for long-lasting contacts with CD8+ T cells but dispensable for short-lived antigen-specific interactions. Serial brief DC-T cell contacts induced early CD8+ T cell activation, proliferation, and differentiation into effector cytotoxic T lymphocytes in the first few days after immunization. ICAM-1-deficient mature DCs, however, failed to induce fully effective priming, because CD8+ T cells produced reduced amounts of interferon gamma and were clonally depleted after 2 weeks. In addition, Icam1(-/-) mice failed to respond to rechallenge. We conclude that ICAM-1-dependent long-lasting interactions between mature DCs and naive CD8+ T cells determine the survival of activated CD8+ T cells and the establishment of effective memory.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

Generation and characterization of an immunogenic dendritic cell population

Dendritic cells (DCs) capture, internalize and process antigens leading to the induction of antigen-specific immune responses. The aim of this study was to develop, implement and characterize an efficient approach for DC-based immunization. Dendritic cells were expanded in vivo by hydrodynamic delivery of a human flt3 ligand expression plasmid. Splenic DCs were isolated and purified with magnetic beads linked to hepatitis C virus (HCV) nonstructural protein-5 (NS5), anti-CD40 and/or LPS. The DCs that contained beads were purified by passage over a magnetic column and subsequently phenotyped. Enrichment resulted in a population consisting of 80% CD11c(+) cells. Uptake of uncoated microparticles promoted DC maturation and the expression of CD80, CD86, and MHC-II molecules; beads coated with LPS and anti-CD40 further increased the expression of these co-stimulatory molecules, as well as the secretion of IL-12. Mice immunized subcutaneously with DCs containing beads coated with HCV NS5 protein, anti-CD40 and LPS exhibited significant antigen-specific, increases in IFN-gamma-producing CD4(+) T cells and CTL activity. This approach combines three critical elements necessary for efficient DC-based immunization that include DC enrichment, maturation and antigen targeting.

The combined actions of NK and T lymphocytes are necessary to reject an EGFP+ mesenchymal tumor through mechanisms dependent on NKG2D and IFN gamma

Better understanding of the mechanisms that mediate spontaneous immune rejections ought to be important in the quest for improvements in immunotherapy of cancer. A set of intraperitoneal tumors of mesenchymal origin that had been chemically induced in ubiquitously expressing EGFP transgenic mice provided a model in which both T and NK cells were absolutely required for tumor rejection. Tumor cells were traceable because of being fluorescent and readily grafted in RAG1(-/-) immunodeficient mice, whereas they were rejected in a majority of syngeneic C57BL/6 and EGFP-transgenic mice. Tumor-cell clones with the highest EGFP expression tended to be rejected, but a direct involvement of EGFP as the antigen recognized for the immune rejections was ruled out. Rejections were absolutely dependent on NK cells as well as on CD4(+) and CD8(+) T lymphocytes according to selective depletion studies. Furthermore, CD8(+) and CD4(+) T lymphocytes as well as NK cells were detected in the inflammatory infiltrate that mediates tumor rejection along with some DC. The effects of IFN gamma, produced at the tumor site by T and NK lymphocytes, were only required at the malignant cell level and were necessary for tumor eradication. NK recognition of tumor cells was mediated by the NKG2D-activating receptor and blocking its function in vivo partially interfered with rejection. Therefore, complete rejection of these mesenchymal tumors requires a concerted set of activities including direct tumor-cell destruction and IFN gamma production that are mediated by both NK and T cells.

Flt3-L gene therapy enhances immunocytokine-mediated antitumor effects and induces long-term memory

Therapeutic treatment with hu14.18-IL-2 immunocytokine (IC) or Flt3-L (FL) protein is initially effective at resolving established intradermal NXS2 neuroblastoma tumors in mice. However, many treated animals develop recurrent disease. We previously found that tumors recurring following natural killer (NK) mediated IC treatment show augmented MHC class I expression, while the tumors that recurred following T cell dependent Flt3-L treatment exhibited decreased MHC class I expression. We hypothesized that this divergent MHC modulation on recurrent tumors was due to therapy-specific immunoediting. We further postulated that combining IC and Flt3-L treatments might decrease the likelihood of recurrent disease by preventing MHC modulation as a mechanism for immune escape. We now report that combinatorial treatment of FL plus hu14.18-IL-2 IC provides greater antitumor benefit than treatment with either alone, suppressing development of recurrent disease. We administered FL by gene therapy using a clinically relevant approach: hydrodynamic limb vein (HLV) delivery of DNA for transgene expression by myofibers. Delivery of FL DNA by HLV injection in mice resulted in systemic expression of >10 ng/ml of FL in blood at day 3, and promoted up to a fourfold and tenfold increase in splenic NK and dendritic cells (DCs), respectively. Furthermore, the combination of FL gene therapy plus suboptimal IC treatment induced a greater expansion in the absolute number of splenic NK and DCs than achieved by individual component treatments. Mice that received combined FL gene therapy plus IC exhibited complete and durable resolution of established NXS2 tumors, and demonstrated protection from subsequent rechallenge with NXS2 tumor.

Spleen but not tumor infiltration by dendritic and T cells is increased by intravenous adenovirus-Flt3 ligand injection

Dendritic cell (DC) expansion is regulated by the hematopoietic growth factor fms-like tyrosine kinase 3 ligand (Flt3L). DCs are critical to the control of tumor growth and metastasis, and there is a positive correlation between intratumoral DC infiltration and clinical outcome. In this report, we first demonstrate that single intravenous (i.v.) injections of adenovirus (Adv)-Flt3L significantly increased splenic dendritic, B, T and natural killer (NK) cell numbers in both normal and mammary tumor-bearing mice. In contrast, the numbers of DCs and T cells infiltrating the tumors were not increased. Consistent with the minimal effect on immune cell infiltration, i.v. Adv-Flt3L injections had no therapeutic activity against orthotopic mammary tumors. In addition, we noted tumor and Adv-Flt3L expansion of Gr1(+)CD11b(+) immature myeloid suppressor cells (IMSCs), which may inhibit the therapeutic efficacy of Adv-Flt3L-expanded DCs.

Genetic vaccination with Flt3-L and GM-CSF as adjuvants: Enhancement of cellular and humoral immune responses that results in protective immunity in a murine model of hepatitis C virus infection

AIM: To investigate whether transfection of plasmid DNA encoding these cytokines enhances both humoral and cellular immune responses to hepatitis C virus (HCV) in a murine model.

METHODS: We established a tumor model of HCV infection using syngenic mouse myeloma cells stably transfected with NS5. Co-vaccination of DNA encoding granulocyte macrophage colony-stimulating factor (GM-CSF) and Flt-3 ligand together with a plasmid encoding for the HCV NS5 protein was carried out. Mice were sacrificed 14 d after the last immunization event with collection of spleen cells and serum to determine humoral and cellular immune responses.

RESULTS: Co-vaccination of DNA encoding GM-CSF and Flt-3 ligand together with a plasmid encoding for the HCV NS5 protein induced increased antibody responses and CD4+ T cell proliferation to this protein. Vaccination with DNA encoding GM-CSF and Flt-3L promoted protection against tumor formation and/or reduction in mice co-immunized with cytokine-encoding DNA constructs. This suggests this strategy is capable of generating cytotoxic T lymphocyte activity in vivo. Following inoculation with plasmid DNA encoding Flt-3L, no increase in spleen size or in dendritic cell (DC) and natural killer cell numbers was observed. This was in contrast to a dramatic increase of both cell types after administration of recombinant Flt3-L in vivo. This suggests that vaccination with plasmid DNA encoding cytokines that regulate DC generation and mobilization may not promote unwanted side effects, such as autoimmunity, splenic fibrosis or hematopoietic malignancies that may occur with administration of recombinant forms of these proteins.

CONCLUSION: Our data support the view that plasmid DNA vaccination is a promising approach for HCV immunization, and may provide a general adjuvant vaccination strategy against malignancies and other pathogens.

Hydrodynamics-based gene delivery of naked DNA encoding fetal liver kinase-1 gene effectively suppresses the growth of pre-existing tumors

Antiangiogenic gene therapy is a promising strategy for cancer treatment, which generally requires highly efficient delivery systems. To date, success of this strategy has depended almost exclusively on the delivery of high titers of viral vectors, which can result in effective transgene expression. However, their cytotoxicity and immunogenicity are a major concern for clinical applications. Recent advances in delivery efficiency of naked DNA could potentially meet the requirement for both high transgene expression and minimal side effects. To investigate whether naked DNA can be used for antiangiogenic cancer therapy, an expression plasmid was generated that encodes a soluble form of fetal liver kinase-1 (Flk-1) gene, a receptor for vascular endothelial growth factor (VEGF). Hydrodynamic injection of this plasmid resulted in close to 0.1 mg/ml of soluble Flk-1 protein in mouse serum and blocked VEGF-driven angiogenesis in matrigel in vivo. The same delivery significantly suppressed the growth of two different pre-existing subcutaneous tumors, Renca renal cell carcinoma and 3LL lung carcinoma. CD31 immunohistochemistry revealed that the tumor-associated angiogenesis was also highly attenuated in soluble Flk-1-treated mice. Thus, expression of genes by hydrodynamics-based gene delivery of naked DNA appears to be a promising approach for antiangiogenic cancer gene therapy.

Recombinant adenoviral vectors turn on the type I interferon system without inhibition of transgene expression and viral replication

Recombinant adenovirus administration gives rise to transgene-independent effects caused by the ability of the vector to activate innate immunity mechanisms. We show that recombinant adenoviruses encoding reporter genes trigger IFN-alpha and IFN-beta transcription from both plasmacytoid and myeloid mouse dendritic cells. Interestingly, IFN-beta and IFN-alpha5 are the predominant transcribed type I IFN genes both in vitro and in vivo. In human peripheral blood leukocytes type I IFNs are induced by adenoviral vectors, with a preponderance of IFN-beta together with IFN-alpha1 and IFN-alpha5 subtypes. Accordingly, functional type I IFN is readily detected in serum samples from human cancer patients who have been treated intratumorally with a recombinant adenovirus encoding thymidine kinase. Despite inducing functional IFN-alpha release in both mice and humans, gene transfer by recombinant adenoviruses is not interfered with by type I IFNs either in vitro or in vivo. Moreover, IFN-alpha does not impair replication of wild-type adenovirus. As a consequence, cancer gene therapy strategies with defective or replicative-competent adenoviruses are not expected to be hampered by the effect of the type I IFNs induced by the vector itself. However, type I IFN might modulate antitumor and antiadenoviral immune responses and thus influence the outcome of gene immunotherapy.

Augmenting the immunogenicity of DNA vaccines: role of plasmid-encoded Flt-3 ligand, as a molecular adjuvant in genetic vaccination

In this study, we have taken advantage of the unique property of a potent dendritic cell (DC) growth factor, Flt-3 ligand (FL), which could act as a vaccine adjuvant. Accordingly, a single injection of plasmid DNA coding for soluble FL (FLex) was shown to induce large numbers of DCs in various tissue compartments and was critical for generating high frequencies of antigen-specific (HIV gp120 and LCMV NP) immune responses in mice. Interestingly, this enhanced level of immune response is strictly dependent on the co-delivery (i.m.) of the DNA vaccines and hFLex DNA to mice harboring large numbers of DCs. The high frequencies of antigen-specific CD8(+) T cells were largely associated with the expansion phase of DCs in vivo. However, DC expansion and immune enhancement have not reciprocally maintained a linear correlation, suggesting that other factors, cytokines/chemokines, which have the potential to modulate the microenvironment of DCs, could influence immunological outcome in this vaccination modality.

Vaccination with protein-transduced dendritic cells elicits a sustained response to hepatitis C viral antigens

BACKGROUND & AIMS

Professional antigen-presenting dendritic cells are capable of eliciting a vigorous antiviral response in naive T cells. The administration of antigen-loaded dendritic cells offers a potential approach to induce high-level immunity against hepatitis C virus.

METHODS

The dendritic cell population in mice was expanded in vivo by hydrodynamic delivery of naked DNA that encoded the secreted form of human fms-like tyrosine kinase 3 ligand. The CD11c-enriched dendritic cell population obtained from the spleen was transduced in vitro with recombinant hepatitis C virus core and nonstructural 5 proteins by using macromolecular-based protein delivery. Vaccine efficacy was assessed with a cytotoxic T-lymphocyte assay, cytokine enzyme-linked immunosorbent assays, and intracellular cytokine staining in vitro and by a tumor challenge model in vivo.

RESULTS

Relative to mice inoculated with nontransduced dendritic cells, splenocytes derived from mice immunized with either hepatitis C virus core-transduced or nonstructural 5-transduced dendritic cells showed 3- to 5-fold greater antigen-specific cytotoxic T lymphocyte activity. The CD4(+) T cells obtained from mice immunized with nonstructural 5-transduced dendritic cells produced interferon gamma, but not interleukin 4, when stimulated with nonstructural 5. In contrast, T cells derived from mice immunized with hepatitis C virus core-transduced dendritic cells produced neither interferon gamma nor interleukin 4 when stimulated with core protein. Mice vaccinated with nonstructural 5-transduced dendritic cells, but not a nonstructural 5-expressing plasmid, showed a sustained antiviral response to nonstructural 5 as evidenced by reduced growth of nonstructural 5-expressing tumor cells inoculated 10 weeks after vaccination.

CONCLUSIONS

These findings suggest that vaccination with protein-transduced dendritic cells may constitute an important antiviral strategy for hepatitis C virus.

Enhancement of radiation effects by pXLG-mEndo in a lung carcinoma model

PURPOSE

Endostatin is a potent antiangiogenesis protein with little or no toxicity that has potential to enhance radiotherapy. The major goal of this study was to evaluate the combination of radiation and endostatin gene therapy in a preclinical lung cancer model.

METHODS

Plasmid pXLG-mEndo, constructed in our laboratory, includes the mouse endostatin gene cloned into the pWS4 vector. The kinetics of endostatin expression and efficacy of the pXLG-mEndo and radiation ((60)Co gamma-rays) combination was evaluated in the C57BL/6 mouse-Lewis lung carcinoma (LLC) model. The LLC cells were implanted s.c. and pXLG-mEndo was injected intratumorally 12-14 days later without any transfection agent; a dose of 10 Gy radiation was applied approximately 16 h thereafter. Some groups received each modality twice. Endostatin, vascular endothelial growth factor (VEGF), and transforming growth factor-beta1 (TGF-beta1) were quantified in plasma and tumors, and tumor vasculature was examined.

RESULTS

Endostatin expression within LLC tumors peaked on Day 7 after pXLG-mEndo injection. Addition of radiation to pXLG-mEndo significantly enhanced the level of tumor endostatin compared with plasmid alone (p < 0.05). Tumor growth was significantly delayed in mice receiving pXLG-mEndo plus radiation compared with no treatment (p < 0.005), radiation (p < 0.05), and control plasmid (p < 0.05). The number of LLC tumor vessels was reduced after combined treatment (p < 0.05), and significant treatment-related changes were observed in both VEGF and TGF-beta1.

CONCLUSIONS

The data demonstrate that delivery of endostatin by pXLG-mEndo as an adjuvant to radiation can significantly enhance the antitumor efficacy of radiotherapy in the LLC mouse tumor model and support further investigation of this unique combination therapy.

In Vivo Hydrodynamic Delivery of cDNA Encoding IL-2: Rapid, Sustained Redistribution, Activation of Mouse NK Cells, and Therapeutic Potential in the Absence of NKT Cells

In the present study, we have tested the ability of hydrodynamically delivered IL-2 cDNA to modulate the number and function of murine leukocyte subsets in different organs and in mice of different genetic backgrounds, and we have evaluated effects of this mode of gene delivery on established murine tumor metastases. Hydrodynamic administration of the IL-2 gene resulted in the rapid and transient production of up to 160 ng/ml IL-2 in the serum. The appearance of IL-2 was followed by transient production of IFN-gamma and a dramatic and sustained increase in NK cell numbers and NK-mediated cytolytic activity in liver and spleen leukocytes. In addition, significant increases in other lymphocyte subpopulations (e.g., NKT, T, and B cells) that are known to be responsive to IL-2 were observed following IL-2 cDNA plasmid delivery. Finally, hydrodynamic delivery of only 4 mug of the IL-2 plasmid to mice bearing established lung and liver metastases was as effective in inhibiting progression of metastases as was the administration of large amounts (100,000 IU/twice daily) of IL-2 protein. Studies performed in mice bearing metastatic renal cell tumors demonstrated that the IL-2 cDNA plasmid was an effective treatment against liver metastasis and moderately effective against lung metastasis. Collectively, these results demonstrate that hydrodynamic delivery of relatively small amounts of IL-2 cDNA provides a simple and inexpensive method to increase the numbers of NK and NKT cells, to induce the biological effects of IL-2 in vivo for use in combination with other biological agents, and for studies of its antitumor activity.

Treatment with Flt3 ligand plasmid reverses allergic airway inflammation in ovalbumin-sensitized and -challenged mice

We have previously reported that fms-like tyrosine kinase 3 ligand (Flt3-L) prevents and reverses established allergic airway inflammation in an ovalbumin (OVA) induced mouse model of asthma. In this study, we investigated the effect of pUMVC3-hFLex, a plasmid, mammalian expression vector for the secretion of Flt3-L on the same mouse model as well as the duration of the effect of the treatment. Allergic airway inflammation to OVA was established in BALB/c mice. OVA-sensitized mice received three intramuscular (i.m.) injections of 200 mug pUMVC3-hFLex over 10 days. The response to pUMVC3-hFLex therapy was assessed based on airway hyperresponsiveness (AHR) to methacholine and inflammation, measured as serum cytokine and immunoglobulins (Ig) levels, and the total and differential cells in bronchoalveolar lavage fluid (BALF). pUMVC3-hFLex treatment completely reversed established AHR (P<0.01) and this effect lasted for at least 24 days after the last treatment injection (P<0.001). pUMVC3-hFLex treatment significantly increased BALF interferon-gamma (IFN-gamma) (P<0.01), serum interleukin (IL)-10 (P<0.01) and anti-OVA IgG2a levels (P<0.01). In contrast, serum IL-4 and IgE levels were significantly reduced (P<0.05). Total BALF cellularity, eosinophiles counts and BALF IL-5 levels were also reduced (P<0.01). pUMVC3-hFLex treatment can reverse established experimental asthma and might provide a novel approach for treating asthma.

The hydrodynamics-based procedure for controlling the pharmacokinetics of gene medicines at whole body, organ and cellular levels

Hydrodynamics-based gene delivery, involving a large-volume and high-speed intravenous injection of naked plasmid DNA (pDNA), gives a significantly high level of transgene expression in vivo. This has attracted a lot of attention and has been used very frequently as an efficient, simple and convenient transfection method for laboratory animals. Until recently, however, little information has been published on the pharmacokinetics of the injected DNA molecules and of the detailed mechanisms underlying the efficient gene transfer. We and other groups have very recently demonstrated that the mechanism for the hydrodynamics-based gene transfer would involve, in part, the direct cytosolic delivery of pDNA through the cell membrane due to transiently enhanced permeability. Along with the findings in our series of studies, this article reviews the cumulative reports and other intriguing information on the controlled pharmacokinetics of naked pDNA in the hydrodynamics-based gene delivery. In addition, we describe various applications reported so far, as well as the current attempts and proposals to develop novel gene medicines for future gene therapy using the concept of the hydrodynamics-based procedure. Furthermore, the issues associated with the clinical feasibility of its seemingly invasive nature, which is probably the most common concern about this hydrodynamics-based procedure, are discussed along with its future prospects and challenges.

Murine mammary adenocarcinoma cells transfected with p53 and/or Flt3L induce antitumor immune responses

Transfection of tumors with tumor-associated antigens (Ags) or cytokines can increase immunogenicity and slow down tumor growth. However, the effect of cotransfection with genes that encode a tumor-associated Ag, such as the tumor suppressor gene p53, and a cytokine has been rarely investigated. We report that transfection of 4T1 mammary tumor cells (p53-null) with the dendritic cell (DC) growth factor, fms-like tyrosine kinase 3 ligand (Flt3L), significantly delayed their growth in vivo, resulting in the rejection of 100% of the tumors formed by injection of tumor cells cotransfected with Flt3L and p53. Immunization with irradiated 4T1 cells transfected with Flt3L induced DC infiltration of the immunization site and significantly increased the antitumor T-cell responses. Further, immunization with irradiated 4T1 cells cotransfected with p53 and Flt3L significantly increased p53-specific immune responses, as compared to vaccination with 4T1 cells transfected with either Flt3L or p53 alone. These responses included increased activity against clone 66 (Cl-66), a sister tumor to 4T1 with high murine mutant p53 expression levels. Challenge with Cl-66 revealed that immunization with irradiated 4T1-Flt3L-p53 cells significantly slowed growth, prolonged survival, and resulted in complete remissions. Further, immunization with irradiated 4T1-Flt3L also slowed Cl-66 growth, although to a lesser extent than 4T1-Flt3L-p53. We suggest that immunization with DCs transfected with the Flt3L transgene and a tumor Ag may potentially heighten T-cell responses and therapeutic activity.

Hydrodynamic Delivery

Hydrodynamic delivery has emerged as a near-perfect method for intracellular DNA delivery in vivo. For gene delivery to parenchymal cells, only essential DNA sequences need to be injected via a selected blood vessel, eliminating safety concerns associated with current viral and synthetic vectors. When injected into the bloodstream, DNA is capable of reaching cells in the different tissues accessible to the blood. Hydrodynamic delivery employs the force generated by the rapid injection of a large volume of solution into the incompressible blood in the circulation to overcome the physical barriers of endothelium and cell membranes that prevent large and membrane-impermeable compounds from entering parenchymal cells. In addition to the delivery of DNA, this method is useful for the efficient intracellular delivery of RNA, proteins, and other small compounds in vivo. This review discusses the development, current application, and clinical potential of hydrodynamic delivery.

Induction of potent TRAIL-mediated tumoricidal activity by hFLEX/Furin/TRAIL recombinant DNA construct

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to exert selectively cytotoxic activity against many tumor cells but not normal cells. On the other hand, the ligand for the receptor tyrosine kinase Fms-like tyrosine kinase 3 (Flt3L) is a growth factor for hematopoietic progenitors and is a potent stimulating factor for dendritic and NK cells. Previously, we have demonstrated that it is possible to inhibit the outgrowth of primary tumors by the administration of an hFlex (the extracellular domain of the Flt3L) and TRAIL (amino acid residues 95-281) secreted fusion protein. Here, we report that by the insertion of a linker sequence encoding the cleavage site for the Golgi-expressed endoprotease furin between the DNA sequences encoding hFlex and TRAIL, the tumoricidal activity of the cleaved TRAIL protein generated was greatly enhanced in comparison to the hFlex/TRAIL fusion protein. Furthermore, we demonstrate that intratumoral injection of the hFlex/furin/TRAIL DNA, in conjunction with cationic liposomes, significantly suppressed the outgrowth of the human CNE-2 nasopharyngeal tumor xenografts in SCID mice. In situ histological examinations confirmed the expression of TRAIL in the treated tumor nodules and the induction of apoptosis was also evidenced by the presence of numerous pyknotic nuclei.

Role of natural killer cells in innate protection against lethal ebola virus infection

Ebola virus is a highly lethal human pathogen and is rapidly driving many wild primate populations toward extinction. Several lines of evidence suggest that innate, nonspecific host factors are potentially critical for survival after Ebola virus infection. Here, we show that nonreplicating Ebola virus-like particles (VLPs), containing the glycoprotein (GP) and matrix protein virus protein (VP)40, administered 1-3 d before Ebola virus infection rapidly induced protective immunity. VLP injection enhanced the numbers of natural killer (NK) cells in lymphoid tissues. In contrast to live Ebola virus, VLP treatment of NK cells enhanced cytokine secretion and cytolytic activity against NK-sensitive targets. Unlike wild-type mice, treatment of NK-deficient or -depleted mice with VLPs had no protective effect against Ebola virus infection and NK cells treated with VLPs protected against Ebola virus infection when adoptively transferred to naive mice. The mechanism of NK cell-mediated protection clearly depended on perforin, but not interferon-gamma secretion. Particles containing only VP40 were sufficient to induce NK cell responses and provide protection from infection in the absence of the viral GP. These findings revealed a decisive role for NK cells during lethal Ebola virus infection. This work should open new doors for better understanding of Ebola virus pathogenesis and direct the development of immunotherapeutics, which target the innate immune system, for treatment of Ebola virus infection.

Hydrodynamic delivery of DNA

Hydrodynamic delivery is an efficient and inexpensive procedure to deliver a wide range of nucleic acids to hepatic tissues and other organs in vivo. The successful application of hydrodynamic delivery is dependent on the rapid injection of a large aqueous volume containing DNA, RNA or other molecules into the vasculature of the liver. In this review, the development of the procedures for hydrodynamic delivery will be described and the parameters necessary for attaining maximal gene expression will be highlighted. A review of the mechanisms for transfecting hepatocytes, as well as potential uses of this approach in various research and clinical applications, will also be discussed.

Regional, but not systemic recruitment/expansion of dendritic cells by a pluronic-formulated Flt3-ligand plasmid with vaccine adjuvant activity

Regional recruitment of dendritic cells (DCs) by the local administration of granulocyte macrophage-colony stimulating factor (GM-CSF) or Flt3-ligand (Flt3L) has vaccine adjuvant activity. However, Flt3L, with its DC growth factor activity, has not been extensively studied as a vaccine adjuvant, particularly as a plasmid vector. We report that the intramuscular (IM) injection of a Flt3L plasmid (pNGVL-hFlex), when formulated in a pluronic carrier (SP1017, Supratek Pharma, Inc., Laval, Que., Canada), recruits DC to the injection site and regional lymph nodes (LNs) and augments immune responses to a p17 HIV plasmid vaccine to a greater extent than the injection of a naked DNA vaccine alone. Following IM administration of pNGVL-hFlex, Flt3L mRNA, Flt3L protein and infiltrating DC accumulate at the injection site. The number of DC in the draining LNs are also significantly increased with the greatest increase observed following injection of 2.5 microg of pNGVL-hFlex formulated in 0.01% SP1017. Flow cytometric studies demonstrate that the LN-infiltrating DC is mainly of the CD11c(+)CD11b(-) phenotype (IL-12 producing). Further, the co-injection of pNGVL3-hFlex and p17 HIV plasmids, formulated in SP1017, significantly increases the immune responses to the plasmid vaccine (pVAX-gag). The co-injection of pVAX-gag and pNGVL3-hFlex, formulated in SP1017, significantly increase delayed-type hypersensitivity responses and the numbers of antigen (Ag)-specific interferon-gamma secreting T cells in the spleen (Enzyme Linked Immune Spot (ELISpot) assay), compared to mice immunized with pVAX-gag formulated in SP1017 alone. We conclude that the IM injection of pNGVL-hFlex with SP1017 can increase the number of DC in draining LN and at the site of injection, thereby providing adjuvant activity for a plasmid vaccine resulting in a significantly increased, Ag-specific T cell response.

Long-term maintenance of gp120-specific immune responses by genetic vaccination with the HIV-1 envelope genes linked to the gene encoding Flt-3 ligand

DNA vaccines target dendritic cells (DC) to induce Ag-specific immune responses in animals. Potent HIV-specific immunity could be achieved by efficient priming of the immune system by DNA vaccines. We investigated a novel DNA vaccine approach based on the role of growth factors in DC expansion and differentiation. To this end, we constructed chimeric genes encoding the HIV envelope glycoproteins physically linked to the extracellular domain of Fms-like tyrosine kinase receptor-3 ligand (FLex; a DC growth factor; both mouse (m)FLex and human (h)FLex). These chimeric gene constructs synthesized biologically active, oligomeric FLex:gp120 fusion proteins and induced DC expansion (CD11c(+)CD11b(+)) when injected i.v. into mice. This DC expansion is comparable to that achieved by FLex DNA encoding native FLex protein. When delivered intramuscularly as DNA vaccines, hFLex:gp120 induced high frequencies of gp120-specific CD8(+) T cells in the presence or absence of FLex DNA-induced DC expansion, but gp120 and mFLex:gp120 elicited only low to moderate levels of Ag-specific CD8(+) T cells. In contrast, mFLex:gp120 induced high levels of anti-gp120 Abs under identical conditions of DNA vaccination. However, the Ab levels in mice immunized with DNA vaccines encoding hFLex:gp120 and gp120 proteins were low without DC expansion, but reached high levels comparable to that elicited by mFLex:gp120 only after the second boost in the presence of DC expansion. Importantly, the gp120-specific CD8(+) T cells persisted at high frequency for 114 days (16 wk) after a booster injection. These experiments provide insight into the importance of modulating DC function in vivo for effective genetic vaccination in animals.

In vivo generation of dendritic cells by intramuscular codelivery of FLT3 ligand and GM-CSF plasmids

Dendritic cells (DCs) are the major cells responsible for the uptake and the transport of antigens to regional lymphoid tissues and for the presentation of antigenic peptides to T cells. They are highly effective in immunotherapy. However, in lymphoid and other tissues, DCs constitute only a small population and are difficult to isolate in large numbers. Our objective was to devise a method with which to rapidly expand splenic DCs in vivo. We accomplished this by intramuscular injection of plasmids encoding mouse granulocyte-macrophage colony stimulating factor (GM-CSF) and fms-like tyrosine kinase 3-ligand (FLT3-L). Gene transfer was amplified by electroporation. Both cytokine vectors significantly increased DC numbers, but they were more effective in combination. When either control plasmid (Blank), or FLT3-L or GM-CSF expression plasmids were injected individually, the mean numbers of CD11c(+)/MHC II(+) DCs in spleen cell suspensions were, respectively, 6, 11, and 23 million. When FLT3-L and GM-CSF plasmids were codelivered, this increased to 36 million. Peak levels occurred 7 days postinjection of DNA. To further characterize these DCs, we stained them with myeloid (CD11b, F4/80)- and lymphoid (CD8alpha)-related markers. FLT3-L cDNA favored lymphoid DC expansion and GM-CSF cDNA favored myeloid DC expansion, whereas combined treatment expanded both types with a myeloid predominance. We confirm the ability of these DCs to present antigen to CD4(+) T cells and to stimulate in mixed lymphocyte cultures. We demonstrate that DCs can be rapidly expanded by this simple gene transfer method, which has numerous potential applications.

Intramuscular co-injection of naked DNA encoding HBV core antigen and Flt3 ligand suppresses anti-HBc antibody response

Flt3 ligand, a recently described growth factor affecting early hematopoietic progenitor cells, can also support the expansion of dendritic cells secreting IL-12. Its potential use in a clinical setting has been suggested. Here, we studied the effect of in situ delivery of Flt3 ligand plasmid (FL) on the antibody response induced by DNA vaccine encoding wild-type hepatitis B virus core antigen (HBc/w). Intramuscular injection of FL increased the expression of DEC205 and the size of splenocytes, and immunization with HBc/w or HBc/w-transfected EL-4 cells induced strong anti-HBc antibody responses in mice. However, intramuscular injection of FL with HBc/w significantly suppressed HBc/w-induced antibody response in a dose-dependent manner. Suppression of immune response by FL injection was the most prominent when FL and HBc/w were co-injected at the same time and the same site. These results suggest that FL may inhibit humoral response induced by DNA-type vaccination, and DC locally expanded by FL may not have proper functions for induction of humoral response.

Lymphocyte activation with localized pGL1-TNF-alpha gene therapy in a glioma model

The major goal of this study was to evaluate the effects of tumor necrosis factor-alpha (TNF-alpha), delivered as pGL1-TNF-alpha, on hematological variables, as well as C6 tumor growth in athymic mice treated with and without radiation. pGL1-TNF-alpha was administered intratumorally at low to high doses (15, 150 and 450 microg) in all three phases of this study. In phase A, pGL1-TNF-alpha expression within tumors was dose dependent and transient, with highest levels seen at 18 h after injection, whereas no TNF-alpha protein was detected in plasma. Low erythrocyte counts, hemoglobin, and hematocrit were associated with tumor presence, but the reduction in these variables was most striking in the group receiving 450 microg of pGL1-TNF-alpha, the group that also exhibited thrombocytopenia at 72 h. In phase B, treatment with pGL1-TNF-alpha at 15 or 150 microg resulted in the greatest degree of splenomegaly, increased spontaneous blastogenesis by splenocytes, and high leukocyte and lymphocyte numbers in the spleen. In these same two groups, flow cytometry analyses of spleen cells showed that high levels of natural killer (panNK+) cells, B (CD19+) lymphocytes, and cells expressing the CD71 and CD25 activation markers were present (p < 0.05). An enhancing effect was also noted in some of the measurements with parental plasmid p WS4 and tumor presence. In phase C, the slowest tumor progression was observed in the groups receiving 15 and 150 microg pGL1-TNF-alpha together with radiation; tumor volumes were 51 and 43% smaller, respectively, than for PBS-injected controls by the end of the study. Collectively, these results show that localized treatment with pGL1-TNF-alpha is hematologically nontoxic at low doses and support the premise that activation of lymphocytes may contribute to the antitumor effects of radiation against a highly aggressive brain tumor.

Systemic administration of naked DNA encoding interleukin 12 for the treatment of human papillomavirus DNA-positive tumor

Interleukin 12 (IL-12) is one of the most effective and promising cytokines for cancer therapy. Its therapeutic effects have been demonstrated in a variety of tumors in animal models when it is administrated locally or systemically. We describe here a systemic delivery of naked murine IL-12 (mIL-12) gene in vivo. Dose-dependent systemic production of mIL-12, with a serum level up to approximately 20 microg/ml, was observed 24 hr after systemic gene delivery. The apparent half-life in the circulation was about 5 hr. The result of a bioactivity assay (in vitro interferon gamma [IFN-gamma] release) indicated that the gene product in mice was as active as the purified recombinant murine IL-12 protein (rmIL-12). The circulating mIL-12 activated natural killer cells and stimulated IFN-gamma production in vivo. A single administration of mIL-12 gene resulted in prominent regression of established subcutaneous tumor in a human papillomavirus (HPV) DNA-positive tumor model (TC-1) in C57BL/6J mice. The antitumor effect of the single gene dose was comparable to repeated intraperitoneal administration of rmIL-12 (0.5 microg/day for consecutive 5 days). This systemic gene delivery is simple, economical, and highly efficient for the production of large amounts of cytokine in vivo. With this gene delivery method, we have demonstrated the therapeutic potential of IL-12 for the treatment of HPV DNA-positive tumor and the usefulness of the systemic gene delivery for assessing the therapeutic effect of a candidate gene.

Flt3 ligand: a novel cytokine prevents allergic asthma in a mouse model

Flt-3 ligand (FL), a recently described growth factor affecting early hematopoietic progenitor cells, can also support the expansion of dendritic cells secreting IL-12. Since type 2 T cells predominate in asthma and IL-12 prevents the differentiation of naive T lymphocytes to a type 2 phenotype, we hypothesized that FL could prevent the development of asthma-like conditions in the ovalbumin mouse model. We found that co-administration of FL during ovalbumin sensitization abrogated late allergic responses, but had no effect on early allergic responses. Airway hyperresponsiveness to methacholine was also blocked by FL treatment. Analysis of bronchoalveolar lavage (BAL) fluid demonstrated a significant reduction in eosinophils, with concomitant decreases in IL-5 and increases in IFN-gamma levels. However, there was no change in BAL fluid IL-4 and serum IgE levels. These data suggest that FL treatment prevents ovalbumin-induced asthma in the mouse and may provide a useful adjuvant in the treatment of human asthma.

Highly efficient gene transfer into murine liver achieved by intravenous administration of naked Epstein-Barr virus (EBV)-based plasmid vectors

Naked plasmid DNA (pDNA) injection could become an alternative procedure to viral and nonviral gene delivery systems. We have previously shown that Epstein-Barr virus (EBV)-based plasmid vectors containing the EBV nuclear antigen 1 (EBNA1) gene and the oriP sequence enable quite high and long-lasting expression in various in vitro and in vivo transfection systems. The EBV-based plasmids were intravenously injected into mice via their tail vein under high pressure. A large amount of the marker gene product was expressed in the liver; as much as 320 microg of luciferase was demonstrated per gram of liver at 8 to 24 h after a single injection with 10 microg of DNA. More than 70% of liver cells stained with X-gal when beta-gal gene was transferred. The expression level was significantly higher than that obtained by conventional pDNA lacking the EBNA1 gene and oriP. On day 35 after the transfection, the expression from the EBV-based plasmid was approximately 100-fold stronger than the conventional pDNA gene expression. Both the EBNA1 gene and oriP are a prerequisite for the augmentation of the transfection efficiency. These results suggest that the intravascular transfection with naked EBV-based plasmid may provide a quite efficient, simple and convenient means to transduce therapeutic genes in vivo into the liver.

Systemic administration of naked plasmid encoding hepatocyte growth factor ameliorates chronic renal fibrosis in mice

The progression of chronic renal diseases is considered as an irreversible process that eventually leads to end-stage renal failure characterized by extensive tissue fibrosis. At present, chronic renal fibrosis is incurable and the incidence of affected patients is on the rise worldwide. In this study, we demonstrate that delivery of hepatocyte growth factor (HGF) gene via systemic administration of naked plasmid vector markedly ameliorated renal fibrosis in an animal model of chronic renal disease induced by unilateral ureteral obstruction. A high level of exogenous HGF protein was detected in the obstructed kidneys following intravenous injection of naked plasmid encoding human HGF. Delivery of human HGF gene induced a sustained activation of extracellular signal-regulated kinases-1 and -2 in the obstructed kidneys. Exogenous HGF expression dramatically inhibited alpha-smooth muscle actin expression, attenuated renal interstitial accumulation and deposition of collagen I and fibronectin. In addition, exogenous HGF suppressed renal expression of pro-fibrogenic cytokine TGF-beta1 and its type I receptor in vivo. These results suggest that systemic administration of naked plasmid vector introduces a high level of exogenous HGF to the diseased kidneys, and that HGF gene transfer may provide a novel therapeutic strategy for amelioration of chronic renal fibrosis in vivo.