Liver sinusoidal endothelial cells are not permissive for adenovirus type 5

Somatic ablation of IKKβ in liver and leukocytes is not tolerated in obese mice but hepatic IKKβ deletion improves fatty liver and insulin sensitivity

The kinase IKKβ controls pro-inflammatory gene expression, and its activity in the liver and leukocytes was shown to drive metabolic inflammation and insulin resistance in obesity. However, it was also proposed that liver IKKβ signaling protects obese mice from insulin resistance and endoplasmic reticulum (ER) stress by increasing XBP1s protein stability. Furthermore, mice lacking IKKβ in leukocytes display increased lethality to lipopolysaccharides. This study aims at improving our understanding of the role of IKKβ signaling in obesity. We induced IKKβ deletion in hematopoietic cells and liver of obese mice by Cre-LoxP recombination, using an INF-inducible system, or a liver-specific IKKβ deletion in obese mice by adenovirus delivery of the Cre recombinase. The histopathological, immune, and metabolic phenotype of the mice was characterized. IKKβ deletion in the liver and hematopoietic cells was not tolerated in mice with established obesity exposed to the TLR3 agonist poly(I:C) and exacerbated liver damage and ER-stress despite elevated XBP1s. By contrast, liver-specific ablation of IKKβ in obese mice reduced steatosis and improved insulin sensitivity in association with increased XBP1s protein abundance and reduced expression of de-novo lipogenesis genes. We conclude that IKKβ blockage in liver and leukocytes is not tolerated in obese mice exposed to TLR3 agonists. However, selective hepatic IKKβ ablation improves fatty liver and insulin sensitivity in association with increased XBP1s protein abundance and reduced expression of lipogenic genes.

Innate immune surveillance of the circulation: A review on the removal of circulating virions from the bloodstream

Many viruses utilize the lymphohematogenous route for dissemination; however, they may not freely use this highway unchecked. The reticuloendothelial system (RES) is an innate defense system that surveys circulating blood, recognizing and capturing viral particles. Examination of the literature shows that the bulk of viral clearance is mediated by the liver; however, the precise mechanism(s) mediating viral vascular clearance vary between viruses and, in many cases, remains poorly defined. Herein, we summarize what is known regarding the recognition and capture of virions from the circulation prior to the generation of a specific antibody response. We also discuss the consequences of viral capture on viral pathogenesis and the fate of the captor cell. Finally, this understudied topic has implications beyond viral pathogenesis, including effects on arbovirus ecology and the application of virus-vectored gene therapies.

Perforin inhibition protects from lethal endothelial damage during fulminant viral hepatitis

CD8 T cells protect the liver against viral infection, but can also cause severe liver damage that may even lead to organ failure. Given the lack of mechanistic insights and specific treatment options in patients with acute fulminant hepatitis, we develop a mouse model reflecting a severe acute virus-induced CD8 T cell-mediated hepatitis. Here we show that antigen-specific CD8 T cells induce liver damage in a perforin-dependent manner, yet liver failure is not caused by effector responses targeting virus-infected hepatocytes alone. Additionally, CD8 T cell mediated elimination of cross-presenting liver sinusoidal endothelial cells causes endothelial damage that leads to a dramatically impaired sinusoidal perfusion and indirectly to hepatocyte death. With the identification of perforin-mediated killing as a critical pathophysiologic mechanism of liver failure and the protective function of a new class of perforin inhibitor, our study opens new potential therapeutic angles for fulminant viral hepatitis.

CD8 T cells can protect the liver from viral infection, but can also result in severe liver damage and organ failure. Here, the authors develop a mouse model reflecting fulminant CD8 T cell mediated viral hepatitis, which occurs in a perforin-dependent manner that is protected by the use of perforin inhibitors.

Aging-Associated TNF Production Primes Inflammasome Activation and NLRP3-Related Metabolic Disturbances

Accumulating evidence suggests that the activation of the innate branch of the immune system plays a pivotal role in the induction and perpetuation of metabolic and aging-related diseases. In this context, the NLRP3 inflammasome pathway has been identified as an important driver of sterile inflammatory processes. De novo protein synthesis of NLRP3 induced by signals such as TLR ligands or TNF is a prerequisite for sustained NLRP3 mediated caspase-1 cleavage and inflammasome activation. Here, we demonstrate in aged mice that spontaneously elevated TNF represents a critical priming signal that functions to control NLRP3 inflammasome activation. Elevated systemic TNF levels were responsible for increased NLRP3 expression and caspase-1 activity in adipose tissues and liver. TNF dependent, spontaneous inflammasome activity in aged mice resulted in impaired glucose tolerance that could be attributed to peripheral insulin resistance. Altogether, these results implicate that TNF-driven NLRP3 expression constitutes an important checkpoint that regulates inflammasome activation, presumably by additional signals such as aging-associated DAMPs.

Chapter eight--Oncolytic adenoviruses for cancer immunotherapy: data from mice, hamsters, and humans

Adenovirus is one of the most commonly used vectors for gene therapy and two products have already been approved for treatment of cancer in China (Gendicine(R) and Oncorine(R)). An intriguing aspect of oncolytic adenoviruses is that by their very nature they potently stimulate multiple arms of the immune system. Thus, combined tumor killing via oncolysis and inherent immunostimulatory properties in fact make these viruses in situ tumor vaccines. When further engineered to express cytokines, chemokines, tumor-associated antigens, or other immunomodulatory elements, they have been shown in various preclinical models to induce antigen-specific effector and memory responses, resulting both in full therapeutic cures and even induction of life-long tumor immunity. Here, we review the state of the art of oncolytic adenovirus, in the context of their capability to stimulate innate and adaptive arms of the immune system and finally how we can modify these viruses to direct the immune response toward cancer.

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).

Constitutive expression of short hairpin RNA in vivo triggers buildup of mature hairpin molecules

RNA interference (RNAi) has become the cornerstone technology for studying gene function in mammalian cells. In addition, it is a promising therapeutic treatment for multiple human diseases. Virus-mediated constitutive expression of short hairpin RNA (shRNA) has the potential to provide a permanent source of silencing molecules to tissues, and it is being devised as a strategy for the treatment of liver conditions such as hepatitis B and hepatitis C virus infection. Unintended interaction between silencing molecules and cellular components, leading to toxic effects, has been described in vitro. Despite the enormous interest in using the RNAi technology for in vivo applications, little is known about the safety of constitutively expressing shRNA for multiple weeks. Here we report the effects of in vivo shRNA expression, using helper-dependent adenoviral vectors. We show that gene-specific knockdown is maintained for at least 6 weeks after injection of 1 × 10(11) viral particles. Nonetheless, accumulation of mature shRNA molecules was observed up to weeks 3 and 4, and then declined gradually, suggesting the buildup of mature shRNA molecules induced cell death with concomitant loss of viral DNA and shRNA expression. No evidence of well-characterized innate immunity activation (such as interferon production) or saturation of the exportin-5 pathway was observed. Overall, our data suggest constitutive expression of shRNA results in accumulation of mature shRNA molecules, inducing cellular toxicity at late time points, despite the presence of gene silencing.

Advances and future challenges in adenoviral vector pharmacology and targeting

Adenovirus is a robust vector for therapeutic applications, but its use is limited by our understanding of its complex in vivo pharmacology. In this review we describe the necessity of identifying its natural, widespread, and multifaceted interactions with the host since this information will be crucial for efficiently redirecting virus into target cells. In the rational design of vectors, the notion of overcoming a sequence of viral "sinks" must be combined with re-targeting to target populations with capsid as well as shielding the vectors from pre-existing or toxic immune responses. It must also be noted that most known adenoviral pharmacology is deduced from the most commonly used serotypes, Ad5 and Ad2. However, these serotypes may not represent all adenoviruses, and may not even represent the most useful vectors for all purposes. Chimeras between Ad serotypes may become useful in engineering vectors that can selectively evade substantial viral traps, such as Kupffer cells, while retaining the robust qualities of Ad5. Similarly, vectorizing other Ad serotypes may become useful in avoiding immunity against Ad5 altogether. Taken together, this research on basic adenovirus biology will be necessary in developing vectors that interact more strategically with the host for the most optimal therapeutic effect.

Bioluminescence imaging allows measuring CD8 T cell function in the liver

In vivo evaluation of CD8 T cell effector (cytotoxic T lymphocyte [CTL]) function in peripheral organs such as the liver is currently not possible but would greatly improve our understanding of local immune regulation, because simple determination of antigen-specific CTL numbers does not predict the outcome of immune responses. In particular, measurement of alanine aminotransferase serum levels is not sensitive enough to detect T cell immunity against low numbers of target hepatocytes. We developed a procedure that detects virus-specific effector function of CTLs in the liver after simultaneous adenoviral transfer of reporter and immune target genes into hepatocytes, followed by bioluminescence imaging of reporter genes. Bioluminescence imaging enabled detection of as few as 10,000 infected hepatocytes in vivo, and even more importantly, quantification of antiviral effector function of as few as 50,000 CTLs.

CONCLUSION

Our results provide evidence that low numbers of antigen-specific CTLs are sufficient to control viral gene expression and eliminate viral infection from hepatocytes. The experimental system established here is a highly sensitive method to simultaneously detect viral infection of hepatocytes and to quantify antiviral CTL function in the liver in vivo and will help in characterizing principles of hepatic immune regulation.

Virally infected mouse liver endothelial cells trigger CD8+ T-cell immunity

BACKGROUND & AIMS

Dendritic cell activation through ligation of pattern recognition receptors leading to full functional maturation causes induction of CD8(+) T-cell immunity through increased delivery of costimulatory signals instead of tolerance. Here we investigate whether organ-resident antigen-presenting cells, such as liver sinusoidal endothelial cells (LSECs), also switch from tolerogenic to immunogenic CD8(+) T-cell activation upon such stimulation.

METHODS

Murine LSECs were isolated by immunomagnetic separation and analyzed for functional maturation upon triggering pattern recognition receptors or viral infection employing gene expression analysis and T cell coculture assays. In vivo relevance of the findings was confirmed with bone-marrow chimeric animals.

RESULTS

LSECs expressed numerous pattern recognition receptors that allowed for sentinel function, but ligand-induced activation of these receptors was not sufficient to overcome tolerance induction of CD8(+) T cells. Importantly, viral infection with murine cytomegalovirus caused functional maturation of antigen-presenting LSECs and was sufficient to promote antigen-specific differentiation into effector CD8(+) T cells in the absence of dendritic cells and independent of CD80/86.

CONCLUSIONS

These results shed new light on the generation of organ-specific immunity and may contribute to overcoming tolerance in relevant situations, such as cancer.

In vitro and in vivo analysis of expression cassettes designed for vascular gene transfer

Increasing the level and duration of transgene expression and restricting expression to vascular cells are important goals for clinically useful gene therapy vectors. We evaluated several promoters, enhancers and introns in endothelial, smooth muscle and liver cells in tissue culture and in vivo, comparing local delivery to the carotid artery with intravenous delivery to the liver. A 1800-bp fragment of the oxidized LDL receptor (LOX-1) promoter showed highest in vivo activity in the carotid artery, achieving 39% the activity of the reference cytomegalovirus promoter, with 188-fold greater specificity for carotid artery over liver. An enhancer from the Tie2 gene in combination with the intracellular adhesion molecule-2 promoter improved endothelial specificity of plasmid vectors, increased the expression from adenoviral vectors in cultured endothelial cells and doubled the specificity for carotid artery over liver in vivo. Adding a short intron to expression cassettes increased expression in both endothelial and smooth muscle cells in vitro; however, the eNOS enhancer failed to consistently increase the expression or endothelial specificity of the vector. In conclusion, elements from the LOX-1 promoter and Tie2 enhancer together with an intron can be used to improve vectors for vascular gene transfer.

Recombinant adenovirus as a methodology for exploration of physiologic functions of growth factor pathways

The use of recombinant adenoviruses (Ad) to express secreted antagonists of growth factors represents a powerful strategy for studying physiologic functions of growth factor pathways in experimental animals. Indeed, a single adenoviral injection can produce characteristic high-level and persistent plasma expression of soluble receptor ectodomains or secreted protein antagonists, allowing highly stringent conditional inactivation of target pathways in vivo. In this review, we describe our experience using recombinant Ad to inactivate growth factor pathways in vivo and discuss their advantages and limitations. Using our studies on vascular endothelial growth factor and Wnt systems as examples, we further describe how recombinant Ad can unveil previously unknown physiological roles of signaling pathways. Finally, we discuss the potential physiological and therapeutic relevance of our findings.

VEGF modulates erythropoiesis through regulation of adult hepatic erythropoietin synthesis

Vascular endothelial growth factor (VEGF) exerts crucial functions during pathological angiogenesis and normal physiology. We observed increased hematocrit (60-75%) after high-grade inhibition of VEGF by diverse methods, including adenoviral expression of soluble VEGF receptor (VEGFR) ectodomains, recombinant VEGF Trap protein and the VEGFR2-selective antibody DC101. Increased production of red blood cells (erythrocytosis) occurred in both mouse and primate models, and was associated with near-complete neutralization of VEGF corneal micropocket angiogenesis. High-grade inhibition of VEGF induced hepatic synthesis of erythropoietin (Epo, encoded by Epo) >40-fold through a HIF-1alpha-independent mechanism, in parallel with suppression of renal Epo mRNA. Studies using hepatocyte-specific deletion of the Vegfa gene and hepatocyte-endothelial cell cocultures indicated that blockade of VEGF induced hepatic Epo by interfering with homeostatic VEGFR2-dependent paracrine signaling involving interactions between hepatocytes and endothelial cells. These data indicate that VEGF is a previously unsuspected negative regulator of hepatic Epo synthesis and erythropoiesis and suggest that levels of Epo and erythrocytosis could represent noninvasive surrogate markers for stringent blockade of VEGF in vivo.

Delivery of viral vectors to tumor cells: extracellular transport, systemic distribution, and strategies for improvement

It is a challenge to deliver therapeutic genes to tumor cells using viral vectors because (i) the size of these vectors are close to or larger than the space between fibers in extracellular matrix and (ii) viral proteins are potentially toxic in normal tissues. In general, gene delivery is hindered by various physiological barriers to virus transport from the site of injection to the nucleus of tumor cells and is limited by normal tissue tolerance of toxicity determined by local concentrations of transgene products and viral proteins. To illustrate the obstacles encountered in the delivery and yet limit the scope of discussion, this review focuses only on extracellular transport in solid tumors and distribution of viral vectors in normal organs after they are injected intravenously or intratumorally. This review also discusses current strategies for improving intratumoral transport and specificity of viral vectors.

Dendritic cells take up viral antigens but do not support the early steps of hepatitis B virus infection

Dendritic cells (DC) of hepatitis B virus (HBV) carriers have been reported to exhibit functional impairment. Possible explanations for this phenomenon are infection of HBV by DC or alteration of DC function by HBV. We therefore analyzed whether DC support the different steps of HBV infection and replication: uptake, deposition of the HBV genome in the nucleus, antigen expression, and progeny virus release. When HBV genomes were artificially introduced into monocyte-derived DC by adenoviral vectors, low-level expression of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) but no HBV replication was detected. When monocyte-derived DC were subjected to wild-type HBV or a recombinant HBV expressing Renilla luciferase under a non-liver-specific promoter, intracellular HBV DNA was detected in a low percentage of cells. However, neither nuclear cccDNA was formed nor luciferase activity was detected, indicating that either uncoating or nucleocytoplasmic transport were blocked. To verify our observation in the in vivo situation, myeloid and plasmacytoid DC were isolated from blood of high viremic HBV carriers, and analyzed by quantitative polymerase chain reaction (PCR) and electron microscopy. Although circulating DC had in vivo been exposed to more than 10(4) HBV virions per cell, HBV genomic DNA was hardly detected, and no nuclear cccDNA was detected at all. By using electron microscopy, subviral particles were found in endocytic vesicles, but virions were undetectable as were viral capsids in the cytoplasm. In conclusion, circulating DC may take up HBV antigens, but neither support nucleocytoplasmic transport nor replication of HBV.

Adenoviral gene transfer of ABIN-1 protects mice from TNF/galactosamine-induced acute liver failure and lethality

Tumor necrosis factor (TNF) is a proinflammatory cytokine that plays a central role in acute and chronic hepatitis B and C infection and alcoholic liver disease as well as fulminant liver failure. TNF-induced liver failure is characterized by parenchymal cell apoptosis and inflammation leading to liver cell necrosis. The transcription factor NF-kappaB is believed to mediate at least part of the proinflammatory effects of TNF, and is therefore a favorite drug target. However, NF-kappaB also suppresses TNF-mediated hepatocyte apoptosis, implicating a potential cytotoxic effect of NF-kappaB inhibitors in the liver. This dual function of NF-kappaB emphasizes the need for therapeutics that can inhibit both TNF-induced NF-kappaB activation and cell death. Here we describe that adenoviral expression of the NF-kappaB inhibitory protein ABIN-1, but not an IkappaBalpha superrepressor (IkappaBalpha(s)), completely prevents lethality in the TNF/D-(+)-galactosamine-induced model of liver failure. Protection was associated with a significant decrease in TNF-induced leukocyte infiltration as well as hepatocyte apoptosis. The differential effects of ABIN-1 and IkappaBalpha(s) suggest a role for an NF-kappaB independent function of ABIN-1. Indeed, ABIN-1 was found to prevent not only NF-kappaB activation, but also apoptosis of cultured hepatocytes in response to TNF, explaining its protective effect against TNF-induced liver failure. In conclusion, ABIN-1 has a dual NF-kappaB inhibitory and anti-apoptotic activity in the liver, which might be of considerable interest for the treatment of inflammatory liver diseases.

A hemodynamic response to intravenous adenovirus vector particles is caused by systemic Kupffer cell-mediated activation of endothelial cells

Intravascular injection of adenoviral vectors may result in a toxic and potentially lethal reaction, the mechanism of which is poorly understood. We noted that mice demonstrated a transient change in behavior that was characterized by inactivity and lethargy within minutes after intravenous injection of relatively low doses of adenoviral vectors (including high-capacity gutless vectors). Moreover, immediately after vector injection a significant drop in blood pressure was measured that most probably was caused by the systemic activation of endothelial cells as monitored by detection of phosphorylated Akt/PKB kinase, activated endothelial nitric oxide synthase (eNOS), and nitrotyrosine. The activation of the endothelium was the result of the interaction of viral particles with Kupffer cells, which are resident macrophages of the liver representing the first line of defense of the innate immune system. Surprisingly, the uptake of vector particles by Kupffer cells not only resulted in their strong activation, but also in their nearly complete disappearance from the liver. Our results suggest that the toxicity of intravenously injected adenoviral vectors may be directly linked to the activation and destruction of Kupffer cells.

Reduction of natural adenovirus tropism to mouse liver by fiber-shaft exchange in combination with both CAR- and alphav integrin-binding ablation

The primary receptor, the coxsackievirus and adenovirus receptor (CAR), and the secondary receptor, alphav integrins, are the tropism determinants of adenovirus (Ad) type 5. Inhibition of the interaction of both the fiber with CAR and the penton base with the alphav integrin appears to be crucial to the development of targeted Ad vectors, which specifically transduce a given cell population. In this study, we developed Ad vectors with ablation of both CAR and alphav integrin binding by mutating the fiber knob and the RGD motif of the penton base. We also replaced the fiber shaft domain with that derived from Ad type 35. High transduction efficiency in the mouse liver was suppressed approximately 130- to 270-fold by intravenous administration of the double-mutant Ad vectors, which mutated two domains each of the fiber knob and shaft and the RGD motif of the penton base compared with those of conventional Ad vectors (type 5). Most significantly, the triple-mutant Ad vector containing the fiber knob with ablation of CAR binding ability, the fiber shaft of Ad type 35, and the penton base with a deletion of the RGD motif mediated a >30,000-fold lower level of mouse liver transduction than the conventional Ad vectors. This triple-mutant Ad vector also mediated reduced transduction in other organs (the spleen, kidney, heart, and lung). Viral DNA analysis showed that systemically delivered triple-mutant Ad vector was primarily taken up by liver nonparenchymal cells and that most viral DNAs were easily degraded, resulting in little gene expression in the liver. These results suggest that the fiber knob, fiber shaft, and RGD motif of the penton base each plays an important role in Ad vector-mediated transduction to the mouse liver and that the triple-mutant Ad vector exhibits little tropism to any organs and appears to be a fundamental vector for targeted Ad vectors.

Characterization of in vitro and in vivo gene transfer properties of adenovirus serotype 35 vector

We have recently developed a replication-defective, recombinant adenovirus (Ad) vector composed of the whole Ad serotype 35 (Ad35), a member of subgroup B. We describe herein the in vitro and in vivo gene transfer properties of Ad35 vector in comparison with Ad serotype 5 (Ad5) and the Ad5F35 vector, which is a fiber-substituted Ad5 vector containing Ad35 fiber proteins. In vitro, Ad35 vector efficiently transduced not only human CAR-positive cells but also CAR-negative cells. Following intravenous administration into mice, both Ad5 and Ad35 vectors were rapidly cleared from the bloodstream with a half-life of approximately 3 min. Ad5 vector-mediated transgene expression predominantly occurred in liver parenchymal cells, although the Ad5 vector was delivered to both liver parenchymal and nonparenchymal cells. In contrast, Ad35 vector was efficiently taken up by liver nonparenchymal cells and mediated transduction efficiency in the liver on a level 4 log orders lower than the Ad5 vector. These findings demonstrate that Ad35 vector is an attractive vehicle for gene transfer into human cells, while the biodistribution profile of Ad35 vector in mice is much different from that of the Ad5 vector.

Selective depletion or blockade of Kupffer cells leads to enhanced and prolonged hepatic transgene expression using high-capacity adenoviral vectors

Tissue macrophages, in particular hepatic Kupffer cells (KCs), contribute to early inflammatory responses following adenoviral vector administration. This study evaluates the effect of selective and transient (3 days) depletion of KCs by a single injection of clodronate liposomes on the in vivo performance of high-capacity adenoviral (HC-Ad) vectors. In KC-depleted C57BL/6 and C3H mice increased and stabilized hAAT levels were observed following intravenous injection of HC-Ad vectors expressing human alpha-1 anti-trypsin (hAAT) either from the hAAT promoter or from the human cytomegalovirus promoter. Comparable increases in hAAT levels were obtained in mice preinjected with a transcriptionally silent HC-Ad vector. Interestingly, in the majority of animals of both strains depletion of KCs was sufficient to prevent the generation of anti-hAAT antibodies, resulting in prolonged transgene expression. Thus, short-term and selective depletion of hepatic macrophages at the same time significantly increased hepatic transgene expression and reduced the humoral immune response to the transgenic protein.

Intratumoral adenovirus-mediated suicide gene transfer for hepatic metastases from colorectal adenocarcinoma: results of a phase I clinical trial

Animal studies have shown that direct injection of an adenoviral vector (Adv.RSV-tk) expressing the herpes thymidine kinase gene into established tumors in the liver, followed by systemic ganciclovir administration, was effective in inducing tumor necrosis. Toxicities were minimal at therapeutically effective vector doses, although severe hepatic necroinflammation was seen at much higher supratherapeutic doses. We conducted a clinical phase I trial in patients with metastatic colorectal adenocarcinoma in the liver to assess the safety of intratumoral Adv.RSV-tk injection (escalating doses) followed by intravenous ganciclovir (fixed dose). The vector was injected into a metastatic tumor in the liver under local anesthesia by percutaneous needle placement with concurrent ultrasonographic monitoring to prevent injection or leakage into adjacent normal liver structures. We treated 16 patients in five dose level cohorts of Adv.RSV-tk, from 1.0x10(10) to 1.0x10(13) virus particles per patient. Hepatic toxicities were low, with transient grade 1 elevations in serum aminotransferase levels in 3 of 16 patients. Other toxicities were also transient: grade 2-3 fevers in 5 of 16 patients, grade 3 thrombocytopenia in 1 of 16 patients, and grade 2 leucopenia in 3 of 16 patients. These results indicate that Adv.RSV-tk can be safely administered by percutaneous intratumoral injection in patients with hepatic metastases at doses up to 1.0x10(13) virus particles per patient, and can provide the basis for future clinical trials involving intratumoral adenoviral vector injection.

CAR-binding ablation does not change biodistribution and toxicity of adenoviral vectors

Intravenous administration of adenoviral vectors results mostly in hepatocyte transduction and subsequent hepatotoxicity. Because hepatocytes express high levels of the primary adenovirus receptor CAR, untargeting hepatocytes requires CAR-binding ablation. The amino acid residues of the viral fiber responsible for CAR-binding are known. We have constructed a mutant adenoviral vector unable to bind CAR and studied vector biodistribution and hepatotoxicity after intravenous administration. In contrast to a vector with wild-type fiber, the infectivity of the CAR-ablated vector is greatly reduced and not susceptible to inhibition with wild-type knob. Biodistribution and hepatotoxicity are, however, not affected by CAR-binding ablation. A possible explanation could be related to an increased blood persistence detected for the CAR-ablated vectors combined with their residual infectivity through other receptors.

Transfer of hepatitis B virus genome by adenovirus vectors into cultured cells and mice: crossing the species barrier

For the study of hepatitis B virus infection, no permissive cell line or small animal is available. Stably transfected cell lines and transgenic mice which contain hepadnavirus genomes produce virus, but--unlike in natural infection--from an integrated viral transcription template. To transfer hepadnavirus genomes across the species barrier, we developed adenovirus vectors in which 1.3-fold-overlength human and duck hepatitis B virus genomes were inserted. The adenovirus-mediated genome transfer efficiently initiated hepadnavirus replication from an extrachromosomal template in established cell lines, in primary hepatocytes from various species, and in the livers of mice. Following the transfer, hepatitis B virus proteins, genomic RNA, and all replicative DNA intermediates were detected. Detection of covalently closed circular DNA in hepatoma cell lines and in primary hepatocytes indicated that an intracellular replication cycle independent from the transferred linear viral genome was established. High-titer hepatitis B virions were released into the culture medium of hepatoma cells and the various primary hepatocytes. In addition, infectious virions were secreted into the sera of mice. In conclusion, adenovirus-mediated genome transfer initiated efficient hepatitis B virus replication in cultured liver cells and in the experimental animals from an extrachromosomal template. This will allow development of small-animal systems of hepatitis B virus infection and will facilitate study of pathogenicity of wild-type and mutant viruses as well as of virus-host interaction and new therapeutic approaches.

A dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN)-related protein is highly expressed on human liver sinusoidal endothelial cells and promotes HIV-1 infection

The discovery of dendritic cell (DC)-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin (DC-SIGN) as a DC-specific ICAM-3 binding receptor that enhances HIV-1 infection of T cells in trans has indicated a potentially important role for adhesion molecules in AIDS pathogenesis. A related molecule called DC-SIGNR exhibits 77% amino acid sequence identity with DC-SIGN. The DC-SIGN and DC-SIGNR genes map within a 30-kb region on chromosome 19p13.2-3. Their strong homology and close physical location indicate a recent duplication of the original gene. Messenger RNA and protein expression patterns demonstrate that the DC-SIGN-related molecule is highly expressed on liver sinusoidal cells and in the lymph node but not on DCs, in contrast to DC-SIGN. Therefore, we suggest that a more appropriate name for the DC-SIGN-related molecule is L-SIGN, liver/lymph node-specific ICAM-3-grabbing nonintegrin. We show that in the liver, L-SIGN is expressed by sinusoidal endothelial cells. Functional studies indicate that L-SIGN behaves similarly to DC-SIGN in that it has a high affinity for ICAM-3, captures HIV-1 through gp120 binding, and enhances HIV-1 infection of T cells in trans. We propose that L-SIGN may play an important role in the interaction between liver sinusoidal endothelium and trafficking lymphocytes, as well as function in the pathogenesis of HIV-1.

Immortalized bone-marrow derived pig endothelial cells

Primary cultures of porcine endothelial cells (EC) can only be maintained for a limited number of passages. To facilitate studies of xenogeneic human anti-pig immune responses in vitro, pig microvascular bone-marrow (BM) and macrovascular aortic EC were obtained from our herd of partially inbred miniature swine, homozygous for the major histocompatibility locus, and immortalized with a modified SV40 large T vector. The resulting BM-derived (2A2) and aortic (PEDSV.15) immortalized EC lines showed unlimited growth and EC phenotype as indicated by expression of von Willebrand Factor (vWF) and low density lipoprotein (LDL) receptors as well as by formation of typical cobblestone monolayers. Ultrastructural studies revealed morphological similarities in primary and immortalized EC. Flow cytometry analysis demonstrated constitutive SLA class I expression by all lines whereas SLA class II was only expressed after stimulation with porcine IFNgamma. Furthermore, pig CD34 mRNA was detected by Northern blot analysis in primary and immortalized aortic EC but not in 2A2. Both EC lines expressed a number of myeloid markers, adhesion molecules and xenoantigens, the latter being determined by binding of human natural antibodies. Gene transfer into the porcine EC lines was successfully performed by electroporation or calcium-phosphate transfection, as well as by adenoviral infection. Finally, the functional similarity between primary and immortalized EC was demonstrated in adhesion and cytotoxicity assays. Together, these results suggest that 2A2 and PEDSV. 15 represent valuable tools to study both human cellular and humoral immune responses in vitro against pig EC derived from microvascular and large vessels.