NOD2 signaling contributes to the innate immune response against helper-dependent adenovirus vectors independently of MyD88 in vivo

We previously demonstrated that Toll-like receptor/myeloid differentiation primary response gene 88 (MyD88) signaling is required for maximal innate and acquired [T helper cell type 1 (Th1)] immune responses following systemic administration of helper-dependent adenoviral vectors (HDAds). However, MyD88-deficient mice injected with HDAdLacZ exhibited only partial reduction of innate immune cytokine expression compared with wild-type mice, suggesting MyD88-independent pathways also respond to HDAds. We now show that NOD2, a nucleotide-binding and oligomerization domain (NOD)-like receptor known to detect muramyl dipeptides in bacterial peptidoglycans, also contributes to innate responses to HDAds, but not to humoral or Th1 immune responses. We established NOD2/MyD88 double-deficient mice that, when challenged with HDAds, showed a significant reduction of the innate response compared with mice deficient for either gene singly, suggesting that NOD2 signaling contributes to the innate response independently of MyD88 signaling following systemic administration of HDAds. In addition, NOD2-deficient mice exhibited significantly higher transgene expression than did wild-type mice at an early time point (before development of an acquired response), but not at a later time point (after development of an acquired response). These results indicate that the intracellular sensor NOD2 is required for innate responses to HDAds and can limit transgene expression during early phases of infection.     

SR-A and SREC-I Are Kupffer and Endothelial Cell Receptors for Helper-dependent Adenoviral Vectors

Helper-dependent adenoviral (HDAd) vectors can mediate long-term, high-level transgene expression from transduced hepatocytes with no chronic toxicity. However, a toxic acute response with potentially lethal consequences has hindered their clinical applications. Liver sinusoidal endothelial cells (LSECs) and Kupffer cells are major barriers to efficient hepatocyte transduction. Understanding the mechanisms of adenoviral vector uptake by non-parenchymal cells may allow the development of strategies aimed at overcoming these important barriers and to achieve preferential hepatocyte gene transfer with reduced toxicity. Scavenger receptors on Kupffer cells bind adenoviral particles and remove them from the circulation, thus preventing hepatocyte transduction. In the present study, we show that HDAd particles interact in vitro and in vivo with scavenger receptor-A (SR-A) and with scavenger receptor expressed on endothelial cells-I (SREC-I) and we exploited this knowledge to increase the efficiency of hepatocyte transduction by HDAd vectors in vivo through blocking of SR-A and SREC-I with specific fragments antigen-binding (Fabs).     

Efficient, Long-term Hepatic Gene Transfer Using Clinically Relevant HDAd Doses by Balloon Occlusion Catheter Delivery in Nonhuman Primates

Helper-dependent adenoviral vectors (HDAd) are devoid of all viral coding sequences and are thus an improvement over early generation Ad because they can provide long-term transgene expression in vivo without chronic toxicity. However, high vector doses are required to achieve efficient hepatic transduction by systemic intravenous injection, and this unfortunately results in dose-dependent acute toxicity. To overcome this important obstacle, we have developed a minimally invasive method to preferentially deliver HDAd into the liver of nonhuman primates. Briefly, a balloon occlusion catheter was percutaneously positioned in the inferior vena cava to occlude hepatic venous outflow. HDAd was injected directly into the occluded liver via a percutaneously placed hepatic artery catheter. Compared to systemic vector injection, this approach resulted in substantially higher hepatic transduction efficiency using clinically relevant low vector doses and was accompanied by mild-to-moderate acute but transient toxicities. Transgene expression was sustained for up to 964 days. These results suggest that our minimally invasive method of delivery can significantly improve the vector''s therapeutic index and may be a first step toward clinical application of HDAd for liver-directed gene therapy.     

Type I IFN signaling in CD8– DCs impairs Th1-dependent malaria immunity

Many pathogens, including viruses, bacteria, and protozoan parasites, suppress cellular immune responses through activation of type I IFN signaling. Recent evidence suggests that immune suppression and susceptibility to the malaria parasite, Plasmodium, is mediated by type I IFN; however, it is unclear how type I IFN suppresses immunity to blood-stage Plasmodium parasites. During experimental severe malaria, CD4⁺ Th cell responses are suppressed, and conventional DC (cDC) function is curtailed through unknown mechanisms. Here, we tested the hypothesis that type I IFN signaling directly impairs cDC function during Plasmodium infection in mice. Using cDC-specific IFNAR1-deficient mice, and mixed BM chimeras, we found that type I IFN signaling directly affects cDC function, limiting the ability of cDCs to prime IFN-γ–producing Th1 cells. Although type I IFN signaling modulated all subsets of splenic cDCs, CD8^– cDCs were especially susceptible, exhibiting reduced phagocytic and Th1-promoting properties in response to type I IFNs. Additionally, rapid and systemic IFN-α production in response to Plasmodium infection required type I IFN signaling in cDCs themselves, revealing their contribution to a feed-forward cytokine-signaling loop. Together, these data suggest abrogation of type I IFN signaling in CD8^– splenic cDCs as an approach for enhancing Th1 responses against Plasmodium and other type I IFN–inducing pathogens.     

A Mini-intronic Plasmid (MIP): A Novel Robust Transgene Expression Vector In Vivo and In Vitro

The bacterial backbone (BB) sequences contained within a canonical plasmid DNA dampen exogenous transgene expression by tenfold to 1,000-fold over a period of a few weeks following transfection into quiescent tissues such as the liver. Minicircle DNA vectors devoid of bacterial plasmid backbone sequences overcome transgene silencing providing persistent transgene expression. Because, we recently established that the length rather than sequence of the DNA flanking the transgene expression cassette is the major parameter affecting transgene silencing, we developed an alternative plasmid propagation process in which the essential bacterial elements for plasmid replication and selection are placed within an engineered intron contained within the eukaryotic expression cassette. As with the minicircle vector, the mini-intronic plasmid (MIP) vector system overcomes transgene silencing observed with plasmids but in addition provides between 2 and often 10 times or higher levels of transgene expression compared with minicircle vectors containing the same expression cassette in vivo and in vitro. These improved plasmids will benefit all studies involving gene transfer/therapy approaches.     

Staphylococcus aureus activates type I IFN signaling in mice and humans through the Xr repeated sequences of protein A

The activation of type I IFN signaling is a major component of host defense against viral infection, but it is not typically associated with immune responses to extracellular bacterial pathogens. Using mouse and human airway epithelial cells, we have demonstrated that Staphylococcus aureus activates type I IFN signaling, which contributes to its virulence as a respiratory pathogen. This response was dependent on the expression of protein A and, more specifically, the Xr domain, a short sequence–repeat region encoded by DNA that consists of repeated 24-bp sequences that are the basis of an internationally used epidemiological typing scheme. Protein A was endocytosed by airway epithelial cells and subsequently induced IFN-β expression, JAK-STAT signaling, and IL-6 production. Mice lacking IFN-α/β receptor 1 (IFNAR-deficient mice), which are incapable of responding to type I IFNs, were substantially protected against lethal S. aureus pneumonia compared with wild-type control mice. The profound immunological consequences of IFN-β signaling, particularly in the lung, may help to explain the conservation of multiple copies of the Xr domain of protein A in S. aureus strains and the importance of protein A as a virulence factor in the pathogenesis of staphylococcal pneumonia.     

Sustained phenotypic correction in a mouse model of hypoalphalipoproteinemia with a helper-dependent adenovirus vector

We examined the efficacy and host response to the adenovirus (Ad)-mediated delivery of human apolipoprotein A-I (APOA1) gene to the liver of APOA1(-/-) mice. Administration of a first-generation vector (FGAd-AI) resulted in a transient appearance of APOA1 in plasma and induced an anti-APOA1 antibody titer, whereas treatment with a helper-dependent vector (HDAd-AI) resulted in sustained APOA1 expression without inducing an antibody titer. With these results, we studied the effects of FGAd vectors on APOAI expression by HDAd-AI vector. Co-treatment with an FGAd vector inhibited HDAd-AI- mediated APOA1 expression independent of transgene cassettes, but only FGAd-AI induced a humoral response. Furthermore, APOA1 mRNA levels in mice co-treated with FGAd vectors were much lower than those expected from the vector copy number, suggesting that DNA of FGAd vectors interferes with the HDAd-AI vector's APOA1 promoter. A single treatment with an HDAd-AI vector produced a supraphysiological plasma APOA1 level that gradually declined to about half the normal human level over the course of 2 years, associated with a plasma cholesterol level that is persistently higher than that in controls. This investigation provides the proof of principle that liver-directed HDAd gene delivery is effective for the long-term phenotypic correction of monogenic hypoalphalipoproteinemia.     

Type I interferon inhibits antibody responses induced by a chimpanzee adenovirus vector.

Recent studies have indicated that type I interferon (IFN) enhances antibody responses and promotes isotype switching. In this study, we analyzed the role of type I IFN signaling during the generation of transgene product-specific antibody responses elicited by recombinant adenovirus (Ad) vectors. A vector derived from a human Ad serotype (AdHu5) induced low levels of type I IFN following infection of dendritic cells (DCs) and stimulated normal transgene product-specific antibody responses in mice that have a defective type I IFN receptor (IFNAR(-/-)). A vector derived from a chimpanzee Ad serotype (AdC68) induced very high levels of type I IFN following infection of DCs, and surprisingly, primed stronger transgene product-specific antibody responses in IFNAR(-/-) mice compared to wild-type mice. The increased antibody response in IFNAR(-/-) mice vaccinated with the AdC68 vector was mainly due to the generation of IgG1 antibodies that were not elicited in wild-type mice. The induction of IgG1 antibodies correlated with an increase in transgene product expression in IFNAR(-/-) mice and was not associated with an increase in T helper 2 responses. We conclude that type I IFN, when induced at high levels, can downregulate transgene product expression of Ad vectors and inhibit the formation of optimal antibody responses.     

PEGylation improves pharmacokinetic profile, liver uptake and efficacy of Interferon gamma in liver fibrosis

Interferon gamma (IFNγ) is a potent cytokine that displays a variety of anti-viral, anti-proliferative, immunomodulatory, apoptotic and anti-fibrotic functions. However, its clinical use is limited to the treatment of few diseases due to the rapid clearance from the body. PEGylated IFN-alpha formulations are shown to be beneficial in viral hepatitis, but PEGylation of IFNγ to enhance its therapeutic effects in liver fibrosis is not yet explored. Liver fibrosis is characterized by the extensive accumulation of an abnormal extracellular matrix and is the major cause of liver-related morbidity and mortality worldwide. To date, there is no pharmacotherapy available for this disease. We modified IFNγ with different-sized linear PEG molecules (5, 10 and 20 kDa) and assessed the biological activity in vitro and in vivo. All PEGylated IFNγ constructs were biologically active and activated IFNγ signaling in vitro as determined with a nitric oxide release assay and a pGAS-Luc reporter plasmid assay, respectively. Similar to IFNγ, all PEGylated IFNγ induced a significant reduction of fibrotic parameters in mouse NIH3T3 fibroblasts as shown with immunohistochemical staining and quantitative PCR analyses. In vivo, the pharmacokinetic profile of radiolabeled ¹²⁵I-IFNγ-PEG conjugates revealed a decreased renal clearance and an increased plasma half-life with an increase of PEG size. Moreover, the liver accumulation of PEGylated IFNγ constructs was significantly higher than the unmodified IFNγ, which was also confirmed by increased MHC-II expression in the livers. Furthermore, in a CCl₄-induced acute liver injury model in mice, PEGylated constructs reduced the early fibrotic parameters more drastically than unmodified IFNγ. Of note, these effects were stronger with higher PEG-sized IFNγ constructs. These data nicely correlated with the pharmacokinetic data. In conclusion, PEGylation significantly improved the pharmacokinetics, liver uptake and anti-fibrotic effects of IFNγ. This study opens new opportunities to exploit the therapeutic applications of PEGylated IFNγ for the treatment of liver fibrosis and other diseases.     

Correction of hyperbilirubinemia in gunn rats using clinically relevant low doses of helper-dependent adenoviral vectors

Crigler-Najjar syndrome type I is a severe inborn error of bilirubin metabolism caused by a complete deficiency of uridine diphospho-glucuronosyl transferase 1A1 (UGT1A1) and results in life-threatening unconjugated hyperbilirubinemia. Lifelong correction of hyperbilirubinemia by liver-directed gene therapy using a helper-dependent adenoviral (HDAd) vector has been previously reported in the Gunn rat, a model of Crigler-Najjar syndrome, but was only achieved using high doses (≥ 3 × 10(12) viral particles [vp]/kg), which are likely to elicit a severe toxic response in humans. Therefore, in this study, we investigate strategies to achieve correction of hyperbilirubinemia in the Gunn rat using clinically relevant low HDAd doses. We have found that correction of hyperbilirubinemia in the Gunn rat can be achieved with a low dose of 5 × 10(11) vp/kg by using an HDAd vector bearing a more potent UGT1A1 expression cassette. Furthermore, by using hydrodynamic injection of the improved HDAd vector, correction of hyperbilirubinemia in the Gunn rat can be achieved using an even lower dose of 5 × 10(10) vp/kg. Although hydrodynamic injection as performed in rats is not acceptable in humans, clinically attractive, minimally invasive methods have been successfully developed to mimic hydrodynamic injection of HDAd vector in non-human primates. Therefore, using an improved expression cassette combined with a more efficient method of vector delivery permits correction of hyperbilirubinemia in the Gunn rat using clinically relevant low HDAd doses and may thus pave the way to clinical application of HDAd vectors for Crigler-Najjar syndrome gene therapy.     

Comparative Study of Anti-hepatitis B Virus RNA Interference by Double-stranded Adeno-associated Virus Serotypes 7, 8, and 9

Using a hepatitis B virus (HBV) transgenic mouse model, we previously showed that a single dose of double-stranded adeno-associated virus (dsAAV) vector serotype 8 carrying a small hairpin RNA (shRNA) effectively reduces HBV replication and gene expression, but the effect gradually decreases with time. In this report, we compared the anti-HBV RNA interference (RNAi) effect of dsAAV8 with those of dsAAV7 and dsAAV9, two other hepatotropic AAV vectors, and examined whether the sequential use of these heterologous AAV vectors could prolong the anti-HBV effect. Our results showed that shRNA delivered by each of the three dsAAV vectors profoundly reduced the serum HBV titer and liver HBV mRNA and DNA levels in the transgenic mice for up to 22 weeks, with dsAAV8 having the greatest inhibitory effect, followed by dsAAV9 and dsAAV7. The potency of dsAAV8 correlated with the presence of higher levels of vector DNA and anti-HBV shRNA in the liver. An in vivo cross-administration experiment showed that preexisting anti-AAV8 antibody completely blocked the anti-HBV RNAi effect of dsAAV8, but had no effect on the potency of dsAAV7 and dsAAV9. Moreover, we demonstrated that a longer anti-HBV effect could be achieved by the sequential use of dsAAV8 and dsAAV9. These results indicate that effective and persistent HBV suppression might be achieved by a combination of the power of RNAi silencing effect and multiple treatments with different AAV serotypes.     

A type I interferon autocrine-paracrine loop is involved in Toll-like receptor-induced interleukin-12p70 secretion by dendritic cells

Dendritic cells (DC) produce interleukin-12 (IL-12) in response to Toll-like receptor (TLR) activation. Two major TLR signaling pathways participate in the response to pathogens: the nuclear factor-kappaB (NF-kappaB)-dependent pathway leading to inflammatory cytokine secretion including IL-12 and the interferon (IFN)-dependent pathway inducing type I IFN and IFN-regulated genes. Here we show that the two pathways cooperate and are likely both necessary for inducing an optimal response to pathogens. R-848/Resiquimod (TLR7 ligand in the mouse and TLR7/8 ligand in human) synergized with poly(I:C) (TLR3 ligand) or lipopolysaccharide (LPS; TLR4 ligand) in inducing high levels of bioactive IL-12p70 secretion and IFN-beta mRNA accumulation by mouse bone marrow-derived DC (BM-DC). Strikingly, IL-12p70 but not IL-12p40 secretion was strongly reduced in BM-DC from STAT1(-/-) and IFNAR(-/-) mice. STAT1 tyrosine-phosphorylation, IL-12p35, and IFN-beta mRNA accumulation were strongly inhibited in IFNAR(-/-) BM-DC activated with the TLR ligand combinations. Similar observation were obtained in human TLR8-expressing monocyte-derived DC (moDC) using neutralizing anti-IFNAR2 antibodies, although results also pointed to a possible involvement of IFN-lambda1 (also known as IL-29). This suggests that TLR engagement on DC induces endogenous IFNs that further synergize with the NF-kappaB pathway for optimal IL-12p70 secretion. Moreover, analysis of interferon regulatory factors (IRF) regulation in moDC suggests a role for IRF7/8 in mediating IRF3-independent type I IFN and possibly IL-12p35 synthesis in response to TLR7/8.     

Inherited STING-activating mutation underlies a familial inflammatory syndrome with lupus-like manifestations

Innate immunity to viral infection involves induction of the type I IFN response; however, dysfunctional regulation of this pathway leads to inappropriate inflammation. Here, we evaluated a nonconsanguineous family of mixed European descent, with 4 members affected by systemic inflammatory and autoimmune conditions, including lupus, with variable clinical expression. We identified a germline dominant gain-of-function mutation in TMEM173, which encodes stimulator of type I IFN gene (STING), in the affected individuals. STING is a key signaling molecule in cytosolic DNA-sensing pathways, and STING activation normally requires dimerization, which is induced by 2′3′ cyclic GMP-AMP (cGAMP) produced by the cGAMP synthase in response to cytosolic DNA. Structural modeling supported constitutive activation of the mutant STING protein based on stabilized dimerization. In agreement with the model predictions, we found that the STING mutant spontaneously localizes in the Golgi of patient fibroblasts and is constitutively active in the absence of exogenous 2′3′-cGAMP in vitro. Accordingly, we observed elevated serum IFN activity and a type I IFN signature in peripheral blood from affected family members. These findings highlight the key role of STING in activating both the innate and adaptive immune responses and implicate aberrant STING activation in features of human lupus.     

Triptolide-Mediated Inhibition of Interferon Signaling Enhances Vesicular Stomatitis Virus-Based Oncolysis

Preclinical and clinical trials demonstrated that use of oncolytic viruses (OVs) is a promising new therapeutic approach to treat multiple types of cancer. To further improve their viral oncolysis, experimental strategies are now combining OVs with different cytotoxic compounds. In this study, we investigated the capacity of triptolide – a natural anticancer molecule – to enhance vesicular stomatitis virus (VSV) oncolysis in OV-resistant cancer cells. Triptolide treatment increased VSV replication in the human prostate cancer cell line PC3 and in other VSV-resistant cells in a dose- and time-dependent manner in vitro and in vivo. Mechanistically, triptolide (TPL) inhibited the innate antiviral response by blocking type I interferon (IFN) signaling, downstream of IRF3 activation. Furthermore, triptolide-enhanced VSV-induced apoptosis in a dose-dependent fashion in VSV-resistant cells, as measured by annexin-V, cleaved caspase-3, and B-cell lymphoma 2 staining. In vivo, using the TSA mammary adenocarcinoma and PC3 mouse xenograft models, combination treatment with VSV and triptolide delayed tumor growth and prolonged survival of tumor-bearing animals by enhancing viral replication. Together, these results demonstrate that triptolide inhibition of IFN production sensitizes prostate cancer cells to VSV replication and virus-mediated apoptosis.     

Expression of Apolipoprotein A-I in Rabbit Carotid Endothelium Protects Against Atherosclerosis

Expression of atheroprotective genes in the blood vessel wall is potentially an effective means of preventing or reversing atherosclerosis. Development of this approach has been hampered by lack of a suitable gene-transfer vector. We used a helper-dependent adenoviral (HDAd) vector to test whether expression of apolipoprotein A-I (apoA-I) in the artery wall could retard the development of atherosclerosis in hyperlipidemic rabbits. Carotid arteries were infused with an HDAd expressing rabbit apoA-I or a “null” HDAd and harvested 2 and 4 weeks later. ApoA-I mRNA and protein were detected only in HDAdApoAI arteries. Lesion size, lipid and macrophage content, and adhesion molecule expression were similar in both groups at 2 weeks. Between 2 and 4 weeks, most of these measures of atherosclerosis increased in HDAdNull arteries, but were stable or decreased in HDAdApoAI arteries (P ≤ 0.04 for all end points in 4-week HDAdApoAI versus HDAdNull arteries). A longer-term study in chow-fed rabbits revealed persistence of HDAd vector DNA and apoA-I expression for ≥48 weeks, with stable vector DNA content and apoA-I expression from 4 to 48 weeks. Expression of apoA-I in arterial endothelium significantly retards atherosclerosis. HDAd provides prolonged, stable expression of a therapeutic transgene in the artery wall.     

Increased hepatic transduction with reduced systemic dissemination and proinflammatory cytokines following hydrodynamic injection of helper-dependent adenoviral vectors.

Hydrodynamic injection of helper-dependent adenoviral vectors (HDAd) in mice results in increased hepatic transduction, reduced splenic and pulmonary transduction, and reduced levels of the proinflammatory cytokines IL-6 and IL-12 compared to conventional injection. These results indicate that hepatic transduction by HDAd, at least alone, does not necessarily provoke a severe innate inflammatory response. Instead, they suggest that systemic vector dissemination may play a major role in the severity of the innate inflammatory response. These results further suggest that the safety and efficacy of HDAd-mediated, liver-directed gene therapy may be improved if the vector could be preferentially, if not exclusively, targeted to liver.