Oral tolerization to adenoviral antigens permits long-term gene expression using recombinant adenoviral vectors

Virus specific tolerance enhanced efficacy of cancer immuno-virotherapy

BACKGROUND

Activation of the immune system to fight cancer is a major goal in immunology and oncology. Although cancer treatment using oncolytic viruses shows promising results, virus mediated oncolysis induces a weak anti-tumor immune response. Upon application of viruses, immune responses against the virus play a significant role in limiting tumor virotherapy. Although suppression of host immunity increases the efficacy of virotherapy against the tumor, but inhibits anti-tumor immune responses. Induction of viral specific tolerance before viral replication may cause the virus to efficiently replicate in tumor cells without affecting the immune responses against tumor antigens. Investigation of the combined strategy of virotherapy and immunotherapy using irradiated tumor cells along with IL-2 and interferon-alpha in virus specific tolerant mice was the goal of this study.

MATERIALS AND METHODS

For tolerance induction, the newborn mice were injected with vesicular stomatitis virus (VSV) subcutaneously. After injection of TC-1 tumor cells to adult tolerant mice and formation of a tumor, irradiated TC-1 cells along with IL-2 and Interferon-alpha expression plasmid were injected twice in mice and followed by virotherapy. Size of tumors and CTL activity against the virus and tumor cells were measured.

RESULT

The results showed increased efficacy of virotherapy in combination with immune-stimulators and tumor cells injection in tolerant mice compared to normal mice.

CONCLUSION

Specific tolerance against the oncolytic virus enhances the efficacy of virotherapy both in monotherapy and in combination with immunotherapy.

Liver-targeted gene therapy: Approaches and challenges

The liver plays a major role in many inherited and acquired genetic disorders. It is also the site for the treatment of certain inborn errors of metabolism that do not directly cause injury to the liver. The advancement of nucleic acid-based therapies for liver maladies has been severely limited because of the myriad untoward side effects and methodological limitations. To address these issues, research efforts in recent years have been intensified toward the development of targeted gene approaches using novel genetic tools, such as zinc-finger nucleases, transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeats as well as various nonviral vectors such as Sleeping Beauty transposons, PiggyBac transposons, and PhiC31 integrase. Although each of these methods uses a distinct mechanism of gene modification, all of them are dependent on the efficient delivery of DNA and RNA molecules into the cell. This review provides an overview of current and emerging therapeutic strategies for liver-targeted gene therapy and gene repair.

GENE THERAPY FOR THE TREATMENT OF PITUITARY TUMORS

Pituitary adenomas constitute the most frequent neuroendocrine pathology in humans. Current therapies include surgery, radiotherapy and pharmacological approaches. Although useful, none of them offers a permanent cure. Current research efforts to implement gene therapy in pituitary tumors include the treatment of experimental adenomas with adenoviral vector-mediated transfer of the suicide gene for thymidine kinase, which converts the prodrug ganciclovir into a toxic metabolite. In some cases, the suicide transgene has been placed under the control of pituitary cell-type specific promoters. Also, regulatable adenoviral vector systems are being assessed in gene therapy approaches for experimental pituitary tumors. Although the efficiency and safety of current viral vectors must be optimized before clinical use, they remain as highly promising therapeutic tools.

Crigler-Najjar syndrome: therapeutic options and consequences of mutations in the UGT1A1 complex

Crigler-Najjar syndrome (CN), a rare inherited disorder characterized by failure of bilirubin glucuronidation, can lead to severe disability and death from kernicterus. Gilbert syndrome is a more common, benign familial unconjugated hyperbilirubinemia. The underlying problem in both conditions is impaired bilirubin conjugation and elimination due to a mutation in uridine 5'-diphosphate glucuronyltransferase. The mainstay of current management of CN is phototherapy, followed by liver transplantation. Here, we review other therapies, including hepatocyte transplantation, that have been successfully used to lessen the phenotype, although long-term engraftment of cells remains elusive. Gene therapy holds hope for the future whereby the patient's hepatocytes are transduced with the wild-type gene. Outstanding issues include safety of the gene vector and establishing immunotolerance to both vector and the new protein. The significant advances in understanding the relevance of mutations in UGT not only in glucuronidation of bilirubin, but other drugs and substances, are also reviewed.

Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

The liver is the site of numerous metabolic inherited diseases. It has unique features that make it compliant to various gene therapy approaches. Many vector types and gene delivery strategies have been evaluated during the past 20 years in a number of animal models of metabolic liver diseases. However, the complete cure of inherited liver deficiencies by gene therapy in relevant animal models were only reported recently. These successes were achieved thanks to major advances in vector technology. In this review, we will focus on Crigler-Najjar disease and hereditary tyrosinemia, two paradigmatic examples of the two categories of enzymatic liver deficiencies: type I, in which the genetic defect does not affect liver histology; and type II, in which liver lesions are present.

Adenovirus-Mediated Gene Therapy to Restore Expression and Functionality of Multiple UDP-Glucuronosyltransferase 1A Enzymes in Gunn Rat Liver

The Gunn rat has been a valuable model for investigating the effect of UDP-glucuronosyltransferase 1A (UGT1A) deficiencies on drug metabolism and toxicity, but it is limited in some aspects. For example, the native Gunn rat model cannot distinguish between hepatic and extrahepatic UGT1A deficiencies in toxicological mechanisms. To extend the model's utility, we investigated the use of replication-defective recombinant UGT1A adenoviruses for the purpose of selectively restoring hepatic UGT1A function. Mycophenolic acid, the active metabolite of the anti-transplant rejection drug mycophenolate mofetil and suspected gastrointestinal toxicant, was used as a model UGT1A-dependent substrate. Treatment with UGT1A adenoviruses normalized the plasma mycophenolic acid and 7-O-mycophenolate glucuronide (MPAG) (concentration-time curves after mycophenolic acid administration (80 mg/kg intraperitoneally). Functional reconstitution was also apparent in the correction of the mycophenolic acid t(1/2alpha) and the area under the curve (AUC)(MPA,0-8 h)/AUC(MPAG,0-8 h) ratio. Twenty-four hours after administration of mycophenolic acid, severe signs of toxicity were noted in the naive Gunn group, including reduced food consumption. The effect on food consumption was reduced but not completely prevented in the UGT adenovirus-treated Gunn rats. In vitro analyses indicated adenovirus dose-dependent reconstitution of mycophenolic acid UGT activities and UGT1A contents in liver but not intestinal microsomes. In the highest adenovirus dose group, the liver microsomal UGT1A markers exceeded those of the heterozygote controls. The ability to selectively manipulate multiple hepatic UGT1A enzymes in Gunn rats should provide a novel way to assess the importance of intestinal or other extrahepatic UGT1A enzymes in toxicities induced by mycophenolic acid and other cytotoxic drugs and dietary agents.

A double-blind clinical trial for treatment of Crohn's disease by oral administration of Alequel, a mixture of autologous colon-extracted proteins: a patient-tailored approach

OBJECTIVES

In this study, we evaluated the safety and efficacy of a personalized mode of treatment for Crohn's disease (CD) by oral administration of Alequel an extract of autologous colonic proteins.

METHODS

Thirty-one patients with moderate to severe CD were enrolled in a 27-wk randomized, double-blind, placebo-controlled trial. Patients were randomized to receive either a placebo or the study drug prepared from autologous colonic extract.

RESULTS

Oral administration of autologous colonic proteins resulted in clinical remission (58% vs 29%; 46.6% vs 26.6%, using an intention to treat analysis, p= NS), clinical response (67% vs 43%; 53.3% vs 40%, using an intention to treat analysis, p= NS) and improved quality of life (Inflammatory Bowel Disease Questionnaire score improvement 43%vs 12%) in the drug study group, compared to placebo group. No treatment-related adverse events were noted. Only in the study-drug-treated cohort who achieved clinical remission (DR), there was a decreased number of subject-specific, antigen-directed, IFNgamma spot-forming colonies. DR subjects had a lower initial C-reactive protein level than DNOR or placebo subjects, an increased percentage of peripheral blood nature killer T cells, and an increased CD4+/CD8+ T-cell ratio throughout the period of drug administration.

CONCLUSIONS

Oral administration of Alequel is a safe method for treatment of patients with moderate to severe CD, and its efficacy needs to be proven. Several markers may be applicable as surrogate markers for the clinical effect.

Mixed hematopoietic molecular chimerism results in permanent transgene expression from retrovirally transduced hepatocytes in mice

BACKGROUND

Cytotoxic immune elimination of transduced hepatocytes may limit gene therapy for inherited liver diseases. Using beta-galactosidase as a marker gene, we studied whether creation of mixed beta-galactosidase molecular hematopoietic chimerism could induce tolerance to beta-galactosidase-transduced hepatocytes.

METHODS

Molecular hematopoietic chimerism was established in irradiated recipient mice by transplantation of either a mixture of wild-type and beta-galactosidase-transgenic bone marrow or autologous bone marrow stem cells that were transduced with beta-galactosidase lentiviral vectors. After transplantation, mice were hepatectomized and injected with beta-galactosidase recombinant retroviruses to transduce regenerating hepatocytes. We monitored the presence of beta-galactosidase-expressing hepatocytes as well as the appearance of anti-beta-galactosidase antibodies during the time.

RESULTS

In control animals, anti-beta-galactosidase antibodies and cytotoxic T-lymphocyte (CTL) response developed as early as 3 weeks after gene transfer. Transduced hepatocytes disappeared concomitantly. In bone marrow transplanted mice, tolerance could be observed in a significant proportion of animals. Tolerance resulted in permanent liver transgene expression and was absent unless a chimerism above 1% was achieved, demonstrating a threshold effect.

CONCLUSIONS

Creation of a molecular hematopoietic chimerism can result in transgene tolerance and evade immune rejection of retrovirally transduced hepatocytes. This strategy may be useful for hepatic inherited diseases in which the transgene product behaves as a non-self protein.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.

Therapeutic lentivirus-mediated neonatal in vivo gene therapy in hyperbilirubinemic Gunn rats

Crigler-Najjar type 1 disease (CN-1) is a genetic disorder characterized by high levels of unconjugated bilirubin due to the absence of hepatic UDPglucuronosyltransferase (UGT1) activity. Here we show that in vivo neonatal hepatocyte transduction with a lentiviral vector expressing the defective enzyme resulted in long-term correction in Gunn rats, a model of CN-1. Lentiviral vectors harboring the human UGT1 cDNA (approved symbol UGT1A1) under the control of a liver-specific transthyretin promoter were produced. Two-day-old Gunn rats were injected with 50 microl of vector. Bilirubinemia was monitored at 6 weeks and monthly thereafter. At 6 weeks, bilirubinemia was completely normalized in treated animals, whereas it remained around 100 microM in control rats. The level of correction remained stable for up to 42 weeks. Large amounts of bilirubin conjugates were present in the bile of corrected animals. PCR and Western blots confirmed the presence and expression of UGT1 in liver. The estimated proportion of transduced hepatocytes was 40% and transduced cells were not detected in extrahepatic tissues except bone marrow in some animals. This work represents the first demonstration of a complete and permanent correction of hyperbilirubinemia in Gunn rats using lentiviral vectors.

Successful gene therapy of the Gunn rat by in vivo neonatal hepatic gene transfer using murine oncoretroviral vectors

Crigler-Najjar type 1 disease (CN1) is a rare inherited metabolic disease characterized by complete absence of hepatic UDP-glucuronosyl transferase (UGT1), resulting in high levels of unconjugated bilirubin. CN1 is an attractive candidate disease for gene therapy. Here we show that in vivo neonatal hepatocyte transduction using recombinant oncoretroviral vectors results in long-term and complete phenotype correction in Gunn rats, a model for CN1. Two-day-old newborn Gunn rats were injected via the temporal vein with 200 microL UGT1 or control beta-galactosidase retroviral vectors. In UGT1-injected animals, bilirubinemia was normal at 6 weeks (3 micromol/L) and remained in the normal range (i.e., <10 micromol/L) for more than 34 weeks. In contrast, in beta-galactosidase-injected animals as well as in noninjected controls, bilirubinemia remained at a high level (i.e., >100 micromol/L) during the whole experimental follow-up. Large amounts of bilirubin monoglucuronides and diglucuronides were present in the bile of treated animals. Finally, polymerase chain reaction and reverse transcription polymerase chain reaction analysis as well as Western blot confirmed the presence and expression of UGT1 almost exclusively in the liver. The estimated proportion of transduced hepatocytes was in the range of 5% to 10%. In conclusion, complete and permanent correction of hyperbilirubinemia in newborn Gunn rats using retroviral vectors can be obtained, paving the way for future gene therapy for CN1.

Oral immune regulation using colitis extracted proteins for treatment of Crohn’s disease: Results of a phase I clinical trial

AIM: To evaluate safety and possible efficacy of induction of oral immune regulation using colitis extracted proteins (CEP) in Crohn’s disease (CD) subjects.

METHODS: Ten CDs were treated orally with autologous CEP thrice weekly for 16 wk. Subjects were monitored for CDAI and IBDQ. Immune modulatory effect was assessed by T-lymphocyte FACS analysis, CEP-specific IFNγ ELISPOT assay and cytokine levels.

RESULTS: Induction of oral immune regulation significantly ameliorated disease activity. All (10/10) subjects had clinical response (CDAI ≤ 70) and 7/10 achieved clinical remission (CDAI ≤ 150). Significant increase in mean IBDQ score was noted (134±9 vs 164±12). No treatment-related adverse events were noted. High levels of CEP-specific IFNγ spot forming colonies were detected in five subjects prior to treatment and in all five, a marked decrease was observed. The CD4+/CD8+ lymphocyte ratio and peripheral NKT cell numbers increased significantly, in 7/10 and in 5/10 subjects, respectively. Significant increase in serum IL-10 and IL-4 levels was observed in 7/10 subjects during treatment period.

CONCLUSION: Immune regulation via oral administration of CEP is a safe and possibly effective treatment for subjects with moderate CD and may provide means of antigen-specific immune modulation.

Adoptive transfer of NK 1.1+ lymphocytes in immune-mediated colitis: a pro-inflammatory or a tolerizing subgroup of cells?

T lymphocytes expressing NK1.1 marker (NKT) have been suggested to play crucial roles in immune modulation.

AIM

To determine the role of NK1.1+ cells in induction and maintenance of pro-inflammatory and/or tolerizing responses.

METHODS

Colitis was induced in C57/B6 donor mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Donor mice received five oral doses of colonic proteins extracted from TNBS-colitis colonic wall. Depletion of NK1.1+ lymphocytes was performed before lymphocyte harvesting. Splenocytes were harvested and separated into T-cell subpopulations, and transplanted into recipient mice before intracolonic instillation of TNBS. Standard clinical, macroscopic, and microscopic scores, and intracellular staining, flow cytometry, and cytotoxicity assays were performed.

RESULTS

The adoptive transfer of CD4+ and NK1.1+ cells harvested from tolerized mice markedly ameliorated the colitis in recipient mice. In contrast, the adoptive transfer of CD8+ and double negative lymphocytes failed to transfer the tolerance. Recipients of splenocytes from tolerized mice exhibited an increase in CD4+ IL4+/CD4+ IFNgamma+ ratio. In contrast, recipients of splenocytes from NK1.1-depleted-tolerized mice exhibited severe colitis with a significant decrease of the CD4+ IL4+/CD4+ IFNgamma+ ratio. However adoptive transfer of splenocytes from non-tolerized NKT-depleted mice led to an alleviation of colitis with a relative increase of the CD4+ IL4+/CD4+ IFNgamma+ ratio.

CONCLUSIONS

NK1.1+ lymphocytes play a critical role in immune regulation. They may be accountable for an alteration of the inflammatory response and the CD4+ IL4+/CD4+ IFNgamma ratio immune-mediated colitis and in peripheral tolerance induction.

Lifelong elimination of hyperbilirubinemia in the Gunn rat with a single injection of helper-dependent adenoviral vector

Crigler-Najjar syndrome is a recessively inherited disorder characterized by severe unconjugated hyperbilirubinemia caused by a deficiency of uridine diphospho-glucuronosyl transferase 1A1. Current therapy relies on phototherapy to prevent kernicterus, but liver transplantation presently is the only permanent cure. Gene therapy is a potential alternative, and recent work has shown that helper-dependent adenoviral (HD-Ad) vectors, devoid of all viral coding sequences, induce prolonged transgene expression and exhibit significantly less chronic toxicity than early-generation Ad vectors. We used a HD-Ad vector to achieve liver-restricted expression of human uridine diphospho-glucuronosyl transferase 1A1 in the Gunn rat, a model of the human disorder. Total plasma bilirubin levels were reduced from >5.0 mg/dl to <<1.4 mg/dl for >2 yr after a single i.v. administration of vector expressing the therapeutic transgene at a dose of 3 x 10(12) viral particles per kg. HPLC analysis of bile from treated rats showed the presence of bilirubin glucuronides at normal WT levels >2 yr after one injection of vector, and i.v. injection of bilirubins IIIalpha and XIIIalpha in the same animals revealed excess bilirubin-conjugating capacity. There was no significant elevation of liver enzymes (alanine aminotransferase) and only transient, moderate thrombocytopenia after injection of the vector. A clinically significant reduction in serum bilirubin was observed with a dose as low as 6 x 10(11) viral particles per kg. We conclude that complete, long-term correction of hyperbilirubinemia in the Gunn rat model of Crigler-Najjar syndrome can be achieved with one injection of HD-Ad vector and negligible chronic toxicity.

Immune responses against adenoviral vectors and their transgene products: a review of strategies for evasion

Human adenoviruses have been adopted as attractive vectors for in vivo gene therapy since they have a well-characterized genomic organization, can be grown to high titres and efficiently transduce a wide spectrum of dividing and non-dividing cells. However, the first-generation of adenoviral (Ad) vectors yielded only transient expression of the transgene in most immunocompetent mice. This constituted a major limitation of this early vector type. In contrast, persistent transgene expression can be established in immunodeficient mice. This suggests that the immunogenicity of adenoviral vectors limits the effective period of adenovirus-based gene therapy. Much effort has been put in devising strategies to circumvent the limitations imposed onto gene therapy by the immune system. Improvements in vector design have significantly improved the performance of the adenovirus vectors. Based on these results it is reasonable to anticipate that new modifications of the vectors will overcome some of the immunological barriers and will further expand the applicability of adenovirus-derived vectors.

Oral Immune Regulation toward Disease-Associated Antigens: Results of Phase I Clinical Trials in Crohn's Disease and Chronic Hepatitis

Oral immune regulation is an immune response toward orally administered antigens, and is a balance between several types of responses. Recent studies in animal models have shown that antiviral immunity and the immune response toward colonic proteins can be modulated by oral feeding of these antigens. The effect of oral immune regulation on the outcome of various immune-mediated processes, including infectious, inflammatory, and neoplastic entities, has been the subject of much research and debate in recent years. Two phase I clinical trials have evaluated the effect of oral immune regulation in patients with chronic hepatitis B virus infection and Crohn's disease. Mechanisms and possible future clinical applications of this immune modulatory method are discussed.

Oral immune regulation: a novel method for modulation of anti-viral immunity

Chronic viral infections, including hepatitis B and C and human immunodeficiency virus (HIV) infections, afflict a significant part of the world's population. In many of these diseases, chronicity has been linked to defective anti-viral immunity that damages host tissues without producing viral clearance. Currently available therapeutic measures for chronic viral infections are limited. Oral immune regulation, the manipulation of immune responses towards antigens by their oral administration, is a relatively simple and antigen-specific immune-modulatory tool. Recent evidence suggests that induction of oral immune-regulation towards viral antigens may entail a complex immune effect, characterized by simultaneous enhancement and suppression of different elements of the immune response in a manner that benefits the host. Such manipulation of the immune response towards viruses may achieve a combination of upregulated specific anti-viral immunity and inhibition of immune-mediated damage. Oral immune regulation may prove to be an important addition to the available therapeutic arsenal for chronic viral infections.

Glucuronidation and the UDP-glucuronosyltransferases in health and disease

This article is an updated report of a symposium held at the June 2000 annual meeting of the American Society for Pharmacology and Experimental Therapeutics in Boston. The symposium was sponsored by the ASPET Divisions for Drug Metabolism and Molecular Pharmacology. The report covers research from the authors' laboratories on the structure and regulation of UDP-glucuronosyltransferase (UGT) genes, glucuronidation of xenobiotics and endobiotics, the toxicological relevance of UGTs, the role of UGT polymorphisms in cancer susceptibility, and gene therapy for UGT deficiencies.

Induction of oral immune regulation towards liver-extracted proteins for treatment of chronic HBV and HCV hepatitis: results of a phase I clinical trial

BACKGROUND

Anti-viral immunity can be modulated via oral feeding of viral proteins. Hepatitis B and C viral (HBV, HCV)-associated hepatocellular injury is mediated by a defective host anti-viral immune response.

AIMS

To determine the effect of oral administration of a mixture of liver-extracted proteins with HBV/HCV proteins, on viral load, liver injury, and the anti-viral T-cell response of chronic HBV/HCV patients.

METHODS

Fourteen patients with chronic HBV and 15 patients with chronic HCV were treated orally with hepatocyte-extracted proteins and HBV or HCV viral proteins for 24 weeks, and followed for an additional 26 weeks. Patients were monitored for HBV-DNA or HCV-RNA levels, liver enzymes and liver histology. Viral-directed T-cell immunity was assessed by IFNgamma and IL10 ELISPOT, viral-specific T-cell proliferation, cytotoxicity, and cytokines assays, and followed for peripheral natural killer T-cell (NKT) number.

RESULTS

In both chronic HBV and HCV patients, oral administration of a mixture of selected liver-extracted proteins and viral proteins induced a favorable increase in viral-specific T-cell proliferation, and IFNgamma-secreting clones, along with a significant decrease in the anti-viral IL10-secreting T-cell clones. However, the effects of modulation of the anti-viral immunity differed between the HBV and HCV patients. In both groups, no major adverse events were noted. In chronic HBV patients, a significant decrease in viral load was observed in 5/14 (35.7%) of patients. HB surface antigen/HB nucleocapsid antigen scores on liver biopsy improved in 46.1% and 50%, respectively, and the histological necroinflammatory score improved in 4/13 (30.7%). Forty percent of the patients with elevated liver enzymes showed a favorable biochemical response. In contrast, an improvement in the histological necroinflammatory score was observed in only 2/12 (17%) of the chronic HCV patients. No significant decrease in HCV RNA was noted in any of these patients.

CONCLUSIONS

Immune regulation of the anti-HBV/HCV immune response via oral administration of a mixture of liver-extracted and viral proteins significantly altered the viral-specific immunity. This effect was associated with clinical and virological improvements in chronic HBV patients.

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.

The role of intrahepatic CD8+ T cell trapping and NK1.1+ cells in liver-mediated immune regulation

The liver was previously suggested as a site of lymphocyte clearance. Liver-associated lymphocytes that express NK1.1 marker (NKT LAL) play a role in immune modulation.

AIM

To determine the role of the liver and of NKT LAL in determining the CD4+/CD8+ balance during tolerance induction.

METHODS

Colitis was induced in C57 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Immune tolerance was induced via five oral feedings of colitis-extracted proteins (CEP) from TNBS-colitis colonic wall, starting on the day of colitis induction (group A). Control mice were fed with BSA (group B). To determine the role of NKT cells in immune modulation, NK1.1 depletion was performed in nonfed (group C) and fed (group D) mice. To further evaluate the role of NKT cells in this model, mice in group E were tolerized following NKT depletion. To determine the effect of NKT depletion in a tolerized environment, tolerized mice in group F were NKT depleted following tolerance induction. Peripheral and intrahepatic NK1.1+ and CD4+/CD8+ T cells were determined in all groups. Colitis was assessed by standard clinical and histologic scores. Serum cytokines levels were measured by ELISA.

RESULTS

Oral tolerance induction led to a marked alleviation of colitis as manifested by a significant improvement of the clinical, macroscopic, and microscopic scores of colitis (group A vs. group B). NK1.1+ depletion without tolerance induction had a favorable effect on colitis (C). Depletion of NKT LAL prevented the ability to induce tolerance (group D). However, induction of tolerance following NK1.1+ depletion, and NK1.1+ depletion following tolerance induction led to a marked improvement of colitis (groups E and F). Tolerance induction led to a significant increase in NKT LAL numbers. The peripheral CD4+/CD8+ ratio increased up to 3-fold in tolerized vs. non-tolerized mice. A similar increase was observed in NKT-depleted healthy mice in groups C, E, and F (P < 0.005). In contrast, NK1.1+ depletion in the presence of antigen in the bowel led to a reverse effect with a significant decrease in the peripheral CD4+/CD8+ ratio. An opposite effect was observed in the intrahepatic CD4+/CD8+. The peripheral/intrahepatic CD4+/CD8+ ratio increased significantly in tolerized and in healthy mice (A, D, E, F, P < 0.005). In contrast, NK1.1+ depleted fed mice in group C manifested a marked decrease in the peripheral/intrahepatic CD4+/CD8+ ratio. Induction of tolerance led to a marked increase in the IL-10/interferon gamma (IFNgamma) and IL-4/IFNgamma ratios.

CONCLUSIONS

In the experimental colitis model, the liver is an important site for CD8+ accumulation during tolerance induction in a process that is independent of NK1.1+ cells. NK1.1+ cells play a dual role in the pro/anti-inflammatory balance. In the presence of antigen, these lymphocytes may be accountable for keeping an anti-inflammatory lymphocyte balance. However, in the absence of antigen, they may induce a pro-inflammatory shift.

AAV gene transfer to the retina does not protect retrovirally transduced hepatocytes from the immune response

Gene therapy of inherited hepatic disease relies on sustained expression of the therapeutic transgene. In many instances, such expression will require immune tolerization to the non-self therapeutic transgene product. We previously demonstrated that a cytotoxic immune response eliminated hepatocytes after in vivo transduction using recombinant retroviral vectors. In the present study we investigated whether prior gene transfer to the retina, which is suspected to induce immune tolerance, could alleviate the immune response occurring after retrovirus mediated gene transfer to the liver. Retinal cells were transduced using adeno-associated viral vectors harbouring a beta-galactosidase transgene. Sixty days later, regenerating hepatocytes were transduced after partial hepatectomy using a recombinant retrovirus carrying the transgene. Three weeks later, anti beta-galactosidase antibodies were present in all animals. Elimination of the transduced hepatocytes eventually occurred in all animals by 2 months after liver gene transfer, although sustained beta-galactosidase expression was still present in the retina in 66% of the animals. We conclude that although the retina behaves as an immunoprivileged site, gene expression in the subretinal space is not sufficient to induce immune tolerance to a transgene product expressed in the liver.

Segregation of Mechanisms for Cytotoxic T Lymphocyte Killing between Lungs and Regional Lymph Nodes Subsequent to Intratracheal Delivery of Adenovirus 2 Vector

Recombinant adenovirus (Ad) vectors, highly effective for targeting the respiratory epithelium, have been investigated for proposed application in mucosal immunization. For rendering successful use of Ad vectors, it is imperative to understand the host immune responses in affected organs. We investigated the mechanisms of cytotoxic T lymphocyte (CTL) killing following intratracheal instillation with recombinant Ad2/betagal-2 vector. From the analysis of CTL responses, it became apparent that the lung CTLs were more Fas-dependent, whereas pulmonary lymph nodes (LN) and splenic CTLs were more perforin-dependent. Although there was a segregation in the mode of CTL killing, both mechanisms of cytolysis were used in the described tissues, and the observed dominance in CTL killing was maintained irrespective of the target evaluated. Restimulation of LN and spleen cells did not change dominance in the CTL mechanism utilized. Absence or blockage of perforin or Fas did not result in reciprocal compensation by the other effector mechanism except in Fas ligand-deficient LN and spleens. In vitro restimulation of immune lymphocytes from each mouse group tested showed segregation in the types of cytokines generated. Ad2-restimulated cells showed bias toward IL-2 and IFN-gamma, while betagal-restimulated cells showed bias toward IL-4 and IL-10.

Endocytosis of adenovirus and adenovirus capsid proteins

Key proteins of the icosahedral-shaped adenovirus (Ad) capsid mediate infection, and interact with cellular proteins to coordinate stepwise events of cell entry that produce successful gene transfer. Infection is mediated predominantly by the penton and fiber capsid proteins. The fiber initiates cell binding while the penton binds integrin coreceptors, triggering integrin-mediated endocytosis. Penton integrin signaling precedes viral escape from the endosomal vesicle. After cell binding, the virus undergoes stepwise disassembly of the capsid, shedding proteins during cell entry. Intracellular trafficking of the remaining capsid shell is mediated by the interaction of naked particles with the cytoskeleton. The capsid translocates toward the nucleus, with the majority of capsid proteins accumulating at the nuclear periphery, while viral DNA and associated protein VII are extruded through the nuclear pore. This discussion will encompass the current knowledge on Ad cell entry and trafficking, with an emphasis on the contribution of Ad capsid proteins to these processes. A greater understanding of the highly effective Ad cell entry pathway may lend itself to the development of safer drug and gene delivery alternatives utilizing similar pathways.

Treatment of chronic hepatitis B virus infection via oral immune regulation toward hepatitis B virus proteins

OBJECTIVES

Hepatitis B virus (HBV) is a noncytopathic virus, and hepatocellular injury is mediated by a defective host antiviral immune response. We have previously shown that antiviral immunity can be modulated through oral feeding of viral proteins. The aims of this study were to determine the safety and efficacy of treatment of patients with chronic HBV by means of p.o. administration of HBV envelope proteins.

METHODS

A total of 42 chronic HBV patients were treated p.o. with HBV envelope proteins (HBsAg+preS1+preS2), three times/wk for 20-30 wk, and followed for an additional 20 wk. Patients were monitored for HBV-DNA levels, liver enzymes, and liver histology. HBV-directed T cell immune modulation was assessed in vitro by HBV specific T cell-proliferation, cytotoxicity, IFN gamma, and IL10 ELISPOT assays, and reverse transcription-polymerase chain reaction cytokines assay.

RESULTS

Favorable response in one of the primary endpoints was achieved in 28/42 patients (66.6%) by means of p.o. immune regulation. A significant decrease in viral load was observed in 15 patients (35.7%). HBsAg/HBcAg biopsy scores improved in 41% and 57.1% of patients, respectively. Histological improvement in liver necroinflammatory score was noted in 12/40 patients (30%). In all, 80% showed biochemical response. Five of 19 HBeAg positive patients (26.3%) became negative for HBeAg. A favorable augmentation in anti-HBV specific T cell response, with increased HbsAg specific T cell proliferation (78%), cytotoxicity (75%), and IFN gamma positive T cell clones (62.9%) was noted. In addition, a decrease in the IL10 gamma positive T cell clones was achieved (48.1%). Natural killer T (NKT) lymphocytes increased significantly in all treated patients.

CONCLUSIONS

Immune regulation of the anti-HBV immune response via p.o. administration of HBV envelope proteins alleviated the immune-mediated liver injury while augmenting the effective antiviral immunity.

Adoptive transfer of ex vivo immune-programmed NKT lymphocytes alleviates immune-mediated colitis

T lymphocyte-expressing natural killer (NK) cell markers (NKT cells) play a role in immune regulation. Our aim was to evaluate the in vivo effect of adoptive transfer of immune-programmed NKT cells. Colitis was induced in C57/B6 mice by 2,4,6-trinitrobenzenesulfonic acid. NKT, CD4, CD8 lymphocytes, and dendritic cells (DC) were prepared from spleens of naive mice, animals with colitis, and animals with colitis that were orally tolerized. Subsets of splenocytes, NKT, CD4, and CD8 and NKT+CD4, NKT+CD8, and NKT+DC lymphocytes were prepared. Assessment of the T helper cell type 1 (Th1)/Th2 cytokine secretion paradigm in vitro was performed before and following exposure to the antigen. Adoptive transfer of ex vivo immune-programmed lymphocytes from each group was performed into recipient mice, followed by colitis induction. Ex vivo exposure of NKT cells harvested from mice with colitis-to-colitis proteins [colitis-extracted proteins (CEP)] led to a Th2 cytokine shift. The interleukin (IL)-4/interferon-gamma (IFN-gamma) ratio increased for NKT harvested from colitis-harboring mice following exposure to CEP. Adoptive transfer of NKT lymphocytes harvested from colitis-harboring mice, which were ex vivo-educated, significantly alleviated experimental colitis in vivo. Intrahepatic NKT lymphocytes increased significantly in mice transplanted with NKT lymphocytes harvested from colitis-harboring donor mice, which were ex vivo-exposed to CEP, similar to mice transplanted with NKT lymphocytes harvested from tolerized donors. Exposure of NKT cells to the disease-target antigen induced a significant increase in the IL-4/IFN-gamma cytokine ratio. Adoptive transfer of a relatively small number of immune-programmed NKT cells induced a systemic Th1 to Th2-immune shift and alleviated immune-mediated colitis.

Immunological basis of septal fibrosis of the liver in Capillaria hepatica-infected rats

Rats infected with the helminth Capillaria hepatica regularly develop septal fibrosis of the liver similar to that induced by repeated ip injections of pig serum. Fibrosis starts when the focal parasitic lesions begin to show signs of resorption, thus suggesting an immunologically mediated pathogenesis of this fibrosis. To explore this possibility, the development of C. hepatica-related hepatic fibrosis was observed in rats exposed to worm antigens from the first neonatal day onward. Wistar rats (150 g) were either injected ip with an extract of C. hepatica eggs (protein concentration: 1 mg/ml) or received immature eggs by gavage from the first neonatal day until adult life and were then infected with 500 embryonated eggs. Changes were monitored on the basis of serum levels of anti-worm antibodies and hepatic histopathology. Rats submitted to immunological oral tolerance markedly suppressed C. hepatica-related serum antibodies and septal fibrosis of the liver when infected with the helminth later on. Tolerance trials with ip injections of worm antigens gave essentially negative results. The partial suppression of septal fibrosis of the liver after the induction of immunological tolerance to C. hepatica antigens in rats indicates an immunological basis for the fibrosis and emphasizes the importance of immunological factors in the pathogenesis of hepatic fibrosis.

Induction of oral tolerance in bone marrow transplantation recipients suppresses graft-versus-host disease in a semiallogeneic mouse model

Graft-versus-host disease (GVHD) is the major obstacle for successful allogeneic stem cell transplantation (SCT). Morbidity and mortality are high, and novel therapeutic strategies are required. Current therapy, which is based mainly on immunosuppression, is associated with a high degree of complications. Immune hyporesponsiveness induced by oral antigen administration has recently been shown to prevent the development of chronic GVHD (cGVHD) in a murine model. The aim of the present study was to evaluate whether it is possible to induce tolerance and to alleviate GVHD in a semiallogeneic transplantation model in mice. GVHD was generated by infusing 2 x 10(7) splenocytes from C57BL/6 donor mice into (C57BL/6 x Balb/c)F1 recipient mice, which received 7 Gy (60)Co total body irradiation (TBI) prior to transplantation. Oral tolerance was induced by feeding recipient F1 mice with five oral doses of proteins, 50 micro g/mouse, extracted from C57BL/6 splenocytes on alternate days following transplantation. In vitro mixed lymphocyte reaction (MLR) from tolerized and nontolerized mice was performed. Recipient mice were followed for chimerism, and for clinical and histological parameters of GVHD. Induction of tolerance was documented by a significant reduction in MLR response of tolerated vs nontolerated splenocytes. A significant alleviation of the clinical and pathological manifestation of GVHD was observed in the liver, small bowel, and skin. Tolerance induction did not jeopardize engraftment. These results may constitute a step towards reducing the frequency of GVHD via manipulation of the immune system.

Early expression of interferon gamma following oral antigen administration is associated with peripheral tolerance induction

Oral tolerance is the induction of immune hyporesponsiveness to orally administered antigens. It was described in association with a decrease in interferon gamma (IFNgamma) production by activated T cells. To determine the role of IFNgamma and IL10 in immunemodulation via oral tolerization. Colitis was induced by intracolonic instillation of trinitrobenzene sulfonic acid. Treated mice received five oral doses of colitis-extracted proteins (CEPs) every other day, starting immediately after colitis induction. Control mice received similar doses of bovine serum albumin. Colitis was assessed in both groups by standard clinical, micro- and macroscopic scores. IFNgamma and IL10 expression in splenic lymphocytes from both groups was tested by RT-PCR immediately after oral feeding, 1, 4, 8, 12, and 24 h thereafter and then every 24 h for 2 weeks. Feeding of CEPs markedly ameliorated experimental colitis. These mice gained weight and showed markedly improved macro- and microscopic parameters of colitis. Tolerized mice exhibited IFNgamma expression in splenic lymphocytes starting immediately following oral CEP immunization and up to 14 d thereafter. IL10 was expressed starting 1 h after CEP feeding and during the first 48 h thereafter. In contrast, non-tolerized control mice manifested IFNgamma expression starting on day 6 and had no IL10 expression. Early induction of IFNgamma expression by oral antigen may be associated with systemic tolerance in the experimental colitis setting. In contrast, late expression of IFNgamma is associated with a pro-inflammatory response in non-tolerized controls.

Immunological hurdles to lung gene therapy

Gene delivery has the potential to offer effective treatment to patients with life-threatening lung diseases such as cystic fibrosis, alpha1-antitrypsin deficiency and lung cancer. Phase I/II clinical trials have shown that, in principle, gene transfer to the lung is feasible and safe. However, gene expression from both viral and non-viral gene delivery systems has been inefficient. In addition to extra- and intracellular barriers, the host innate and acquired immune system represents a major barrier to successful gene transfer to the lung. Results from studies in experimental animals and clinical trials have shown that inflammatory, antibody and T cell responses can limit transgene expression duration and readministration of the gene transfer vector. We will review here how the development of pharmacological and/or immunological agents can modulate the host immune system and the limitations of these strategies. A better understanding of the immunological barriers which exist in the lung might allow for a more sustained expression of the transgene and importantly help overcome the problem of readministration of viral vectors.

Suppression of the immune response against exogenous desmoglein 3 in desmoglein 3 knockout mice: an implication for gene therapy

Gene therapies for recessive genetic diseases may provoke unwanted immune responses against the introduced gene product because patients, especially those with null mutation of a certain protein, have no tolerance for the protein of interest. This study used desmoglein 3 knockout (Dsg3-/-) mice as a disease model for a genetic defect in DSG3, to investigate whether nonviral gene therapy induces an immune response against Dsg3 and whether the reaction against Dsg3 can be prevented. When mouse Dsg3 cDNA was injected in the skin of Dsg3-/- mice, 50% of treated Dsg3-/- mice developed anti-Dsg3 IgG, which can bind native Dsg3 in vivo. To prevent this response, we used an anti-CD40L monoclonal antibody, MR1, which blocks the costimulatory interaction between CD40 and CD40L. To evaluate the effect of MR1, we grafted Dsg3+/+skin on Dsg3-/- mice, to mimic stable gene transfer of Dsg3. After skin grafting, all the recipient Dsg3-/- mice were treated with either MR1 (n=8) or control hamster IgG (n=8). All of the control IgG-treated mice developed circulating anti-Dsg3 IgG about 2 wk after grafting, and IgG deposition was observed on the surfaces of keratinocytes in the grafted Dsg3+/+skin. Such anti-Dsg3 IgG production was significantly prevented, however, when the recipient mice were treated with MR1. These findings suggested that gene therapies for recessive diseases may provoke an immune response against the transgene product, and that the CD40-CD40L interaction might be a reasonable target for effective prevention of such undesirable immune responses, leading, in turn, to a successful gene therapy.

Role of NK1.1+ and AsGm-1+ cells in oral immunoregulation of experimental colitis

NK1.1 and AsGm-1 expressing cells play a role in immunomodulation. Our purpose was to determine the role of NK1.1+ and AsGm-1+ expressing cells in the inflammatory/tolerance paradigm in experimental colitis. Oral tolerance towards colitis-extracted proteins had previously been shown to alleviate experimental colitis. Colitis was induced in C57/B6 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Oral tolerance was induced via five oral doses of proteins extracted from TNBS-colitis colonic wall. Clinical, macroscopic, and microscopic scores were used for colitis assessment. To evaluate the putative role of AsGm-1 in tolerance induction, depletion of AsGm-1 expressing cells was performed. To evaluate the mechanism of tolerance induction, liver-associated NKT lymphocytes were harvested 14 days following tolerance induction, and cultured with concanavalin A (con A) and colitis-extracted proteins. T cell subsets were measured by flow cytometry. Cytokine expression was measured by intracellular staining and enzyme-linked immunosorbent assay (ELISA). Orally tolerized mice exhibited significant alleviation of the clinical, macroscopic, and microscopic parameters of colitis, with increased CD4+ILA+/CD4+IFNgamma+ lymphocyte ratio, increased IL-4, and decreased IFNgamma and IL-12 serum levels. In contrast, orally fed mice that were AsGm-1 depleted showed evidence of severe colitis. These mice exhibited significant decreased CD4 +IL4+/CD4+IFNgamma+ ratios, and an increase in IFNgamma and IL-12, with decreased IL-4 levels. NKT cells harvested from tolerized mice secreted high levels of antiinflammatory cytokines. In contrast, in nontolerized mice, NKT cells mainly secreted proinflammatory cytokines. In a tolerized environment, both NK1.1 and AsGm-1 expressing cells are essential for disease alleviation. In contrast, in a nontolerized environment, AsGm-1 expressing cells support an antiinflammatory immune paradigm, while NKT lymphocytes support a proinflammatory shift.

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.

Transfer of the interleukin-1 receptor antagonist gene into rat liver abrogates hepatic ischemia-reperfusion injury

BACKGROUND

The anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1Ra) is known to reduce hepatic ischemia-reperfusion injury. Therefore, we wished to examine the effect of IL-1Ra gene delivery into the rat liver on hepatic ischemia-reperfusion injury.

METHODS

IL-1Ra cDNA was delivered into the rat liver by a single injection of the transgene vector into the portal vein using either the plasmid-cationic liposome or the recombinant adenoviral vector. At 24 hours after the gene delivery, rats were subjected to partial liver ischemia for 90 minutes followed by reperfusion. Liver tissue and serum samples were taken at 180 minutes of reperfusion, and the degree of the liver injury as well as the expression level of pro-inflammatory cytokines in the serum and tissue were investigated. In addition, we assessed the effect of IL-1Ra gene delivery on the 7-day survival rate when the nonischemic liver lobe was partially excised immediately following reperfusion.

RESULTS

In both cases of delivery methods, gene transfer of IL-1Ra resulted in significant elevation of serum IL-1Ra concentration, which reached maximal levels at 24 hours following the delivery. However, the highest serum concentration with the adenoviral vector was 1,000-fold of that in the liposome-treated animals. In the IL-1Ra delivered rats, liver damage, as well as production of pro-inflammatory cytokines, at 180 minutes of reperfusion was significantly reduced in a concentration-dependent manner of the circulating IL-1Ra protein. Rats subjected to the adenoviral vector gene delivery had higher 7-day survival rates compared with control animals.

CONCLUSIONS

IL-1Ra gene delivery into the liver may be of therapeutic use for abrogating hepatic ischemia-reperfusion injury after transplantation.

Immune downregulation leads to upregulation of an antiviral response: a lesson from the hepatitis B virus

Induction of tolerance towards antigens that drive susceptibility or pathology may be considered a new mode of treatment for several infections. Hepatitis B virus is a non-cytopathic virus, and oral immune regulation was shown to be effective in modulation of the immune-mediated liver injury.

NK 1.1+ T cell: a two-faced lymphocyte in immune modulation of the IL-4/IFN-gamma paradigm

T lymphocytes expressing NK1.1 marker (NK1.1+) have been suggested as being important in peripheral immune modulation. Alteration of the balance between Th1 proinflammatory and Th2 anti-inflammatory cytokine-producing cells can ameliorate immune-mediated disorders. The aim of the study was to determine the role of NK1.1+ lymphocytes in the pathogenesis of tolerance and proinflammatory states and to determine their role in altering the Th1/Th2 balance in experimental colitis. Colitis was induced in C57/B6 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Mice received five oral doses of colonic proteins extracted from TNBS colitis colonic wall. Standard clinical, macroscopic, and microscopic scores were used for colitis assessment. Liver-associated lymphocytes and splenocytes were harvested 14 days following tolerance induction. Depletion of NK 1.1+ lymphocytes was performed 36 hr before lymphocyte harvesting. Lymphocytes were cultured for 12 hr with Con A and colitis extracted proteins. To evaluate the role of NK1.1+ lymphocytes in keeping a balance between immunogenic and tolerogenic subsets of cells, intracellular staining and flow cytometry assays were performed in tolerized and nontolerized mice. IL-4, IL-12, and IFN-gamma levels were measured by ELISA. Administration of mouse-derived colitis-extracted proteins ameliorated experimental colitis. Tolerized mice exhibited significant improvement in all macroscopic and microscopic parameters for colitis. Depletion of NK1.1 following tolerance induction significantly decreased the CD4(+)IL-4(+)/CD4(+)IFN-gamma(+) ratio in tolerized mice. However, depletion of NK1.1 lymphocytes in nontolerized mice increased the CD4(+)IL-4(+)/CD4(+)IFN-gamma(+) ratio, compared with nondepleted nontolerized mice. Induction of tolerance led to an increase in IL4 and a decrease in IFN-gamma levels. In the experimental colitis model NK1.1+ lymphocytes play a dual role: In the presence of peripheral tolerance they may be accountable for keeping the high CD4(+)IL-4(+)/CD4(+)IFN-gamma(+) ratio and disease alleviation. However, in nontolerized conditions they may induce a proinflammatory shift.

A non-immunogenic adenoviral vector, coexpressing CTLA4Ig and bilirubin-uridine-diphosphoglucuronateglucuronosyltransferase permits long-term, repeatable transgene expression in the Gunn rat model of Crigler-Najjar syndrome

Host immune responses limit the duration of expression of transgenes introduced by recombinant adenoviruses, preclude gene transfer upon vector readministration and cause liver injury. CTLA4Ig inhibits immune response by blocking the co-stimulatory interaction between CD28 on T cells and B7 on antigen-presenting cells. We have constructed a recombinant adenovirus, Ad-hUGT1A1-CTLA4Ig that coexpresses human bilirubin-uridinediphosphoglucuronate glucuronosyltransferase (hUGT1A1) and soluble murine CTLA4Ig, both driven by CMV immediate-early promoters. After intravenous injection of this vector (6 x 10(11) p.f.u.) into UGT1A1-deficient jaundiced Gunn rats, serum CTLA4Ig levels peaked at 1.8-2.0 mg/ml on day 7 and declined thereafter to 0.2 mg/ml by day 180. Serum bilirubin declined from mean preinjection levels of 8.0 mg/dl to 0.48-0.6 mg/dl in 3 days, remained normal for 28 weeks, and then gradually increased to 8 mg/dl by day 350. A second injection of Ad-hUGT1A1-CTLA4Ig normalized serum bilirubin. In two rats in this group that were followed longer, serum bilirubin increased to 3.1 and 3.5 mg/dl in 40 weeks, but was normalized again after a third injection. The antibody and cytotoxic lymphocyte (CTL) responses were negligible, and liver biopsy showed no inflammatory cell infiltration. Rats receiving a tertiary challenge with Ad-LacZ (expressing E. coli beta-galactosidase) (5 x 10(11) p.f.u.), 2 months after the second dose of Ad-hUGT1A1-CTLA4Ig, showed beta-galactosidase expression in over 80% of hepatocytes. In contrast, after Ad-hUGT1A1 (which expresses UGT1A1 alone) injection, serum bilirubin remained normal for only 4 weeks, and returned to preinjection levels by day 120. Bilirubin levels did not decline upon reinjection, and beta-galactosidase was not expressed after Ad-LacZ. High levels of adenovirus-specific antibodies and CTL, and hepatic inflammation were found. This is the first demonstration that coexpression of CTLA4Ig permits prolonged expression and repeatable gene transfer by an adenoviral vector.

Inhibition of rat hepatocellular carcinoma tumor growth after multiple infusions of recombinant Ad.AFPtk followed by ganciclovir treatment

BACKGROUND/AIMS

The antitumor efficiency of thymidine kinase (tk) in Herpes Simplex virus-tk-based gene therapy of rat hepatocellular carcinoma (HCC) was examined by specific transcriptional targeting of tk to tumor cells by the alpha-fetoprotein (AFP) gene promoter and by multiple infusions of recombinant adenovirus Ad.AFPtk.

METHODS

We developed a surgical procedure that allows efficient, non-invasive delivery (during 2 months) of recombinant Ad via the intra-hepatic artery (IHA) route.

RESULTS

Treatment of tumor-bearing rats with either three or five doses of 5x10(9)pfu Ad.AFPtk, administered every 3 days, and followed by intra-peritoneal treatment with ganciclovir (GCV), resulted in tumor growth inhibition and apoptosis, when compared to untreated tumor-bearing rats or animals treated with Ad.AFPlacZ or buffered saline. No treatment-related toxicity was noted. Antitumor efficacy, based on tumor size and number of tumors, was demonstrated in more than 50% of Ad.AFPtk+GCV-treated rats, as compared to control rats (P<0.0005).

CONCLUSIONS

Our results demonstrate the safety and potential of multiple Ad.AFPtk administrations by the IHA route to inhibit HCC tumor growth, and support further clinical investigation of Ad.AFPtk gene therapy for treatment of multifocal tumor lesions in most primary liver cancers.

Cells as vehicles for cancer gene therapy: the missing link between targeted vectors and systemic delivery?

Systemic administration of currently manufactured viral stocks has not so far achieved sufficient circulating titers to allow therapeutic targeting of metastatic disease. This is due to low initial viral titers, immune inactivation, nonspecific adhesion, and loss of particles. One way to exploit the elegant molecular manipulations that have been made to increase vector targeting is to protect these vectors until they reach the local sites of tumor growth. Various cell types home preferentially to tumors and can be loaded with the constructs required to produce targeted vectors. Here we discuss the potential of using such cell carriers to chaperone precious vectors directly to the tumors. The vectors can incorporate mechanisms to achieve tumor site-inducible expression, along with tumor cell-specific expression of the therapeutic gene and/or replicating viral genomes that would be released at the tumor. In this way, the great advances that have so far been made with the engineering of vector tropisms might be genuinely exploited and converted into clinical benefit.

Adenoviral-mediated transfer of a lysostaphin gene into the goat mammary gland

As a step toward preventing and curing Staphylococcus aureus mastitis, an adenoviral-mediated gene transfer technique was used to enable mammary cells to synthesize and secrete lysostaphin, an anti-staphylococcal protein. A lysostaphin gene, modified for eukaryotic expression of the bioactive variant, Gln125,232-lysostaphin, was inserted into a replication deficient adenovirus by homologous recombination in 293 cells. The resulting adenoviral vector containing the modified lysostaphin gene (Ad-lys) was used to infect bovine mammary epithelial cells in vitro and caprine mammary cells in vivo. A similar adenoviral vector containing the Escherichia coli gene encoding beta-galactosidase (Ad-lacZ) was also evaluated. Transduction of cultured bovine cells by Ad-lacZ was confirmed by the presence of beta-galactosidase in fixed cells 48 h postinfection. Bovine cells transduced by Ad-lys secreted immunoreactive Gln125,232-lysostaphin (0.8 microg/ml) into media that had approximately 20% bioactivity compared with native lysostaphin. To evaluate transduction in vivo, udder halves of four nonlactating goats were exposed to 10(10) plaque-forming units (pfu) ofAd-lacZ by two intramammary infusions given 48 h apart. The animals were euthanized 24 h later, and extensive expression of beta-galactosidase was detected in cells lining the teat canals, with more moderate expression observed in adjoining mammary parenchyma. Udder halves of two other nonlactating goats were infused with 10(10) pfu of Ad-lys while contralateral udder halves received Ad-lacZ. The animals were euthanized 48 h postinfusion. In both animals, extensive expression of beta-galactosidase was detected in Ad-lacZ exposed teats. Immunoreative Gln125,232-lysostaphin was detectable in secretions from Ad-lys exposed glands 24 h postinfusion, increasing to approximately 1 microg/ml at 48 h postinfusion. As with cultured bovine mammary epithelial cells, the bioactivity of goat-derived Gln125,232-lysostaphin was approximately 20% of native lysostaphin. These results demonstrate that an adenoviral vector can be used to introduce a gene into the ruminant mammary gland, enabling the secretion of a bioactive form of lysostaphin.

The adenovirus capsid protein hexon contains a highly conserved human CD4+ T-cell epitope

The immunogenicity of adenovirus vectors remains a major obstacle to their safe and efficacious use for gene therapy. In order to identify T-cell epitopes directly from adenoviruses, four viral protein sequences were screened for the well-characterized 9-mer HLA-A2 binding motif. Peripheral blood mononuclear cells (PBMC) from healthy adults were tested for responses to 17 selected viral peptides using a short-term interferon-gamma ELISPOT assay. Memory T-cell responses were identified to a single peptide derived from the major capsid protein hexon in 5 of 6 HLA-A2-positive donors. Unexpectedly, responses to this hexon peptide were also detected in 4 of 6 HLA-A2-negative donors, and responder cells were identified as CD4(+) T cells by immunomagnetic depletion experiments. A longer 15-mer peptide, H910-924, was identified as the optimal CD4(+) T-cell epitope. This hexon epitope induces strong proliferative T-cell responses that can be blocked by a monoclonal antibody against HLA-DR, and molecular HLA typing of donors suggests that the peptide response is restricted by multiple HLA-DR alleles. Additionally, quantitative analysis of responses to H910-924 and whole adenovirus reveals that the frequency of circulating CD4(+) T cells specific for this single hexon epitope (mean = 61 per 10(6) PBMC) represents up to one third of the total adenovirus-specific T-cell response. Finally, comparison of hexon sequences from over 20 different human adenovirus serotypes indicates that H910-924 is highly conserved. In most individuals, therefore, T-cell responses to this hexon epitope will be induced by all adenovirus vectors, including "gutted" vectors packaged with capsid proteins and vectors based on different serotypes.

Age-dependent effects of repeated immunization with a first generation adenovirus vector on the immune response and transgene expression in young and old rats

We evaluated the kinetics of transgene expression and humoral and cellular immune responses against viral antigens and the product of the reporter gene LacZ in young (4 months) and old (20 months) Wistar rats. Animals received the intramuscular injection of a recombinant E1-deleted human type 5 adenovirus encoding beta-gal (Ad-LacZ) on days 0 and 30. The transgene expression evaluated on day 2 after infection revealed a significantly higher beta-gal activity in young than in old animals (1.9-fold increase, p<0.05). beta-gal expression decreased on day 6, and on day 15 transgene activity was undetectable in muscles from both groups. Ad-LacZ inoculation was repeated on day 30 in both animal groups. However, after the second adenovirus administration, no increase in beta-gal activity was observed. Humoral and cellular immune responses, evaluated after the first and second Ad-LacZ injection, developed with similar kinetics in young and old rats. In particular, the antigen specific antibodies were able to kill adenovirus-infected tumor cells in both complement-dependent cytotoxicity (CDC) and antibody-mediated cell-dependent cytotoxicity (ADCC) assays. Lymphocyte proliferation in response to the in vitro stimulation with specific antigens was significantly lower in old than in young animals whereas no difference was found in cytotoxic T lymphocyte activity against adenovirus-infected tumor cells. Our results demonstrate that repeated immunization with AdCMV.LacZ induces minor age-related differences in immune response which precludes gene expression both in young and old animals.

Cancer gene therapy: scientific basis

Gene therapy of cancer has been one of the most exciting and elusive areas of therapeutic research in the past decade. Critical developments have occurred in gene therapy targeting cancer cells, cancer vasculature, the immune system, and the bone marrow, itself often the target for severe toxicity from therapeutic agents. We review some recent developments in the field. In each instance, clear preclinical models validated the therapeutic approach and efforts have been made to evaluate the target impact in both preclinical and early clinical trials. Although no cures can consistently be expected from today's cancer gene therapy, the rapid progress may imply that such cures are a few short years away.

Inducing oral immune regulation of hepatitis B virus envelope proteins suppresses the growth of hepatocellular carcinoma in mice

BACKGROUND

Hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC) expresses hepatitis B surface antigen (HBsAg) on its cell surface, and this may serve as a tumor-associated antigen. It was shown previously that adoptive transfer of immunity against HBsAg facilitates the suppression of experimental human HCC-expressing HBsAg in athymic mice. The authors recently showed that it was possible to augment the anti-HBV immune response through induction of oral immune regulation for HBV-associated antigens. The objective of this study was to evaluate the effect of oral immune regulation for HBV antigens on the growth of HBsAg-expressing HCC.

METHODS

Recipient athymic Balb/c mice were irradiated sublethally and injected with 10(7) human hepatoma cells followed by the adoptive transfer of 2 x 10(6) splenocytes from donor mice. Four groups of donor Balb/c mice were studied: Two groups were immune modulated through oral administration of HBV antigens (HBsAg, PreS1, and Pre S2) or bovine serum albumin (BSA). Two control groups were immunized for HBsAg and fed HBV antigens or BSA. Recipient mice were followed for tumor volume and serum alpha-fetoprotein (aFP) levels. The humoral immune response was determined by measuring serum HBs antibodies. HBV specific T-cell immune modulation was assessed in vitro by HBV specific T-cell proliferation and interferon gamma (IFNgamma) ELISPOT assays as well as cytokine expression by reverse transcriptase-polymerse chain reaction assays.

RESULTS

The adoptive transfer of orally immune modulated HBV splenocytes induced complete tumor suppression in recipient mice compared with control mice transplanted with nonimmune modulated cells (BSA), which showed significant tumor growth (serum aFP levels were 3.5 ng/mL and 2320.0 ng/mL, respectively). Control mice transplanted with anti-HBs immunized cells (with or without oral immune modulation) manifested similar tumor suppression (3.5 ng/mL and 0.5 ng/mL, respectively). Immunoregulation for HBV antigens augmented the HBV specific T-cell immune response, as manifested by an increase in HBV specific T-cell proliferation and IFNgamma ELISPOT assays in mice orally immune regulated with HBV proteins compared with naïve mice. Tumor suppression was mediated through increased IFNgamma production in immune regulated and immunized mice.

CONCLUSIONS

The induction of oral immune regulation for HBV antigens modulated the antitumor immune response, thus suppressing the growth of HCC in mice. This effect was mediated by the enhancement of anti-HBV specific T-cell immunity.

Toxicity of a first-generation adenoviral vector in rhesus macaques

We constructed a first-generation adenovirus vector (AVC3FIX5) that we used to assess the rhesus macaque as a nonhuman primate model for preclinical testing of hemophilia B gene therapy vectors. Although we succeeded in our primary objective of demonstrating expression of human factor IX we encountered numerous toxic side effects that proved to be dose limiting. Following intravenous administration of AVC3FIX5 at doses of 3.4 x 10(11) vector particles/kg to 3.8 x 10(12) vector particles/kg, the animals in our study developed antibodies against human factor IX, and dose-dependent elevations of enzymes specific for liver, muscle, and lung injury. In addition, these animals showed dose-dependent prolongation of clotting times as well as acute, dose-dependent decreases in platelet counts and concomitant elevation of fibrinogen and von Willebrand factor. These abnormalities may be caused by the direct toxic effects of the adenovirus vector itself, or may result indirectly from the accompanying acute inflammatory response marked by elevations in IL-6, a key regulator of the acute inflammatory response. The rhesus macaque may be a useful animal model in which to evaluate mechanisms of adenovirus toxicities that have been encountered during clinical gene therapy trials.

Induction of immune tolerance toward tumor-associated-antigens enables growth of human hepatoma in mice

Adoptive transfer of immunity against hepatitis B surface antigen (HBsAg) was previously shown to facilitate suppression of experimental human hepatocellular carcinoma (HCC) expressing HBsAg in athymic mice. We have shown that oral tolerance induces antigen-specific immune suppression of HBsAg by feeding hepatitis B virus (HBV) antigens. In the present study we evaluated the effect of oral tolerance induction toward HBV or HCC antigens on the growth of experimental HCC-expressing HBsAg in mice. Tolerance induction was induced in mice by 5 oral feedings of 1 microg HBV antigens or HCC-extracted proteins (50 microg protein) before vaccination with recombinant HBsAg. Splenocytes (2 x 10(6)) from these mice were transferred to sublethally irradiated athymic BALB/c mice previously transplanted subcutaneously with 10(7) human hepatoma Hep3B cells. Adoptive transfer of splenocytes immunized toward HBsAg prevented tumor growth. At 4 weeks after splenocyte transplantation, tumor volume and serum alpha-fetoprotein (AFP) levels in athymic mice transplanted with splenocytes immunized to HBsAg were undetectable as compared with 1,048 +/- 738 mm(3) and 2,500 +/- 1,431 ng/ml in recipients of naïve splenocytes (p < 0.0001). Mice receiving splenocytes tolerized toward Hep3B cells, as manifested by reduced serum HBs antibody levels, reduced HBV-specific stimulation index and reduced HBV-specific-IFN gamma spot-forming cells, had early tumor growth evident by elevated AFP serum levels, weight loss and mortality, which were suppressed at 6 weeks. Mice transplanted with splenocytes tolerized toward HBV antigens did not have direct evidence of tumor growth. Induction of oral tolerance toward HCC-extracted proteins enabled transient tumor growth in this model. This effect was mediated through downregulation of the anti-HBV immune response.