Impact of preexisting and induced humoral and cellular immune responses in an adenovirus-based gene therapy phase I clinical trial for localized mesothelioma

Impact of preimmunization on adenoviral vector expression and toxicity in a subcutaneous mouse cancer model

Immune responses against adenoviral vectors may influence the toxicity and therapeutic effectiveness of adenovirus-mediated gene transfer and may be a limiting factor in adenovirus-mediated gene therapy. The purpose of this study was to determine the effects of preimmunization on intratumoral adenoviral transduction and systemic spread. The hypothesis was that increased doses of adenoviral vectors could overcome local neutralization without added systemic toxicity. The level and duration of gene expression were assessed as a function of time and dose after intratumoral delivery of adenoviral vector (AdV) encoding the luciferase reporter gene (AdV-luc) in a subcutaneous mouse mammary tumor model. Preimmunization resulted in significantly decreased gene expression in tumor and normal tissues (P < 0.01). The decrease was significantly greater in liver than in tumor. Increased AdV doses could be used to overcome the intratumoral inhibition without a concomitant increase in liver transduction. However, preimmunized animals showed greater toxicity than nai;ve animals (P < 0.001). The preimmunized group developed histologic evidence of grade 2-3 hepatic toxicity and increases in the average values of hepatic enzymes. In addition, there was a significant increase in mortality (P < 0.01) in the preimmunized group (12 of 20 animals) compared with the naive group (3 of 20 animals). These findings suggest that although preimmunity can inhibit systemic expression from adenoviral vectors, at high vector doses it may potentiate hepatotoxicity.

Phase I study of direct administration of a replication deficient adenovirus vector containing the vascular endothelial growth factor cDNA (CI-1023) to patients with claudication

The long-term safety and efficacy of adenoviral delivery of growth factors in patients with peripheral arterial disease (PAD) is unknown. CI-1023 (Ad(GV)VEGF(121.10)) is a replication-deficient adenovirus encoding human vascular endothelial growth factor isoform 121. In this phase I trial, we investigated the safety and efficacy of CI-1023 in subjects with advanced claudication symptoms secondary to infra-inguinal disease. Eighteen subjects >35 years of age with a median ankle brachial index (ABI) at rest of 0.525 (interquartile range 0.4) and angiographic disease involving the infra-inguinal vessels underwent intramuscular injection of CI-1023 (4 x10(8) to 4 x10(10) particle units, n = 15) or placebo (n = 3). Eleven of 15 patients (73%) who received CI-1023 and 1 of 3 subjects (33%) who received placebo, completed 1 year of follow-up. Edema and rash were the most common early adverse event. One infra-inguinal bypass procedure occurred in each of the placebo and CI-1023 groups at days 29 and 104, respectively. One death (day 160) and 1 malignancy (day 274) occurred in the CI-1023 group. Conclusions on efficacy could not be made due to the small number of patients. However, there were encouraging trends in ABI at rest and peak walking time at follow-up.

Malignant mesothelioma: options for management

In the past, there has been a tendency to think of diffuse malignant pleural mesothelioma as one disease in therapeutic terms, regardless of histological type and tumor stage. This does not happen with other tumors, yet it is equally illogical and inappropriate in mesothelioma. As with other tumors, early diagnosis-while the disease is still in stage I, or even at an in situ stage-must be the goal so that therapy can be maximized, particularly if immunotherapy or gene therapy is to be used. Patients with pure epithelial mesothelioma have a better prognosis and respond better to trimodality therapy. Stage I patients who meet fitness criteria should be offered the option of radical surgery in combination with chemotherapy and radiotherapy. Further research is required to determine the optimum neoadjuvant and adjuvant modalities, particularly the timing of individual drugs, use of hyperthermia, and route of administration. The place of immunotherapy and gene therapy as adjunctive treatments also remains to be defined. For example, it may be possible to reduce tumor bulk and perhaps downstage the disease with immunotherapy before radical surgery, if treatment is started early enough. Gene therapy may have a role either preoperatively or in destroying the microscopic disease that remains after radical surgery. These and other combinations of treatment need to be tested in well-designed clinical trials, probably on a multicenter basis (to enroll a sufficient number of patients). Finding the means to improve treatment for sarcomatous and mixed histology mesothelioma remains a challenge. At present, radical surgery does not seem worthwhile for these patients when combined with currently employed chemotherapy and radiotherapy; however, chemotherapy combinations used for treating other sarcomas need to be evaluated as adjunctive therapy before radical surgery is abandoned altogether as a mode of treatment. A collaborative approach involving thoracic surgeons, basic scientists and oncologists, and physicians with experience in treating mesothelioma is essential. Despite its increasing frequency, mesothelioma is still a relatively rare tumor, so treatment should be concentrated in relatively few supraregional centers to maximize expertise and allow innovative treatment combinations to be implemented with the greatest chance of success. Evaluation of new therapeutic approaches will be achieved more rapidly if these supraregional centers collaborate in multicenter trials. The nihilistic approach of simply waiting until the mesothelioma epidemic eventually begins to decline spontaneously in 20 or 30 years is untenable in view of the hundreds of thousands of deaths that will result if no effective treatment is found.

Recombinant adenovirus vectors for gene therapy and clinical trials

In the last decade adenovirus (AdV) vectors have emerged as promising technology in gene therapy. They have been used for genetic modification of a variety of somatic cells in vitro and in vivo. They have been widely used as gene delivery vectors in experiments both with curative and preventive purposes. AdV vectors have been used in the experimental and in some extent in the clinical gene therapy of a variety of cancers. The combination of recombinant AdV technology with chemotherapy (pro drug system) seems to be promising, too. AdV vectors offer several advantages over other vectors. Replication defective vectors can be produced in very high titers (10(11) pfu/ml) thus allowing a substantially greater efficiency of direct gene transfer; they have the capacity to infect both replicating and nonreplicating (quiescent) cells from a variety of tissues and species. Several important limitations of adenovirus mediated gene transfer are also known, such as the relatively short-term (transient) expression of foreign genes, induction of the host humoral and cellular immune response to viral proteins and viral infected cells, which may substantially inhibit the effect of repeated treatment with AdV vectors, the limited cloning capacity and the lack of target cell specificity. However, the well-understood structure, molecular biology and host cell interactions of AdV-s offer some potential solutions to these limitations.

Generating p53-specific cytotoxic T lymphocytes by recombinant adenoviral vector-based vaccination in mice, but not man

Mutations and aberrant expression of the p53 tumor suppressor protein are the most frequent molecular alterations in human malignancy. Peptides derived from the wild-type (wt) p53 protein and presented by major histocompatibility complex (MHC) molecules for T lymphocyte recognition are believed to serve as universal tumor-associated antigens for cancer immunotherapy. We studied the immunogeneicity of a recombinant replication-defective adenoviral vector encoding human full-length wt p53 (rAd/hup53) in human leukocyte antigen (HLA)-A2K(b)-transgenic (Tg) mice and man. The generation of p53 epitope-specific cytotoxic T lymphocytes (CTLs) in p53-proficient and p53-deficient A2K(b)-Tg mice was affected by self-tolerance and a selective inability of rAd/hup53 to induce p53.264-272 peptide-reactive effector cells. To extend this study into a pilot clinical trial, six advanced-stage cancer patients received sequential injections of rAd/hup53. The treatment was well tolerated. To date, no evidence for objective tumor responses was observed. An amplification of humoral and cellular anti-adenoviral immune responses was demonstrated in all patients following rAd/hup53 vaccination. However, p53-reactive antibodies and HLA-A*0201 (A2.1)-restricted CTLs specific for wt p53 epitopes were not generated. Tailoring p53-based cancer immunotherapy thus requires the interference with p53-specific self-tolerance and the induction of the entire repertoire of p53-reactive T lymphocytes.

Transgenic interleukin 2 secreted by CML dendritic cells stimulates autologous T(H)1 T cells

BACKGROUND

We investigated if dendritic cells (DC), derived from patients suffering from chronic myeloid leukemia (CML) could be modified by recombinant replication-defective adenoviruses to express functional interleukin 2 (IL-2). Such modification might confer onto antigen-presenting cells the ability to stimulate expansion of effector cells.

METHODS

To quantify the infection efficiency of CML dendritic cells (CML-DC) by recombinant adenovirus, we measured the expression of green fluorescent protein (GFP) gene contained in the virus. In CML-DC infected with an adenovirus containing the IL-2 gene, we evaluated their ability to secrete IL-2 and stimulate proliferation of autologous T cells.

RESULTS

Uninfected CML-DC and normal DC secreted similar amounts of IL-12 and stimulated similarly efficient autologous mixed leukocyte reaction. Immature CML-DC infected by an adenovirus containing the gene for IL-2 secreted large amounts of IL-2 and stimulated proliferation of autologous T cells more efficiently than the corresponding CML-DC alone. High levels of interferon eta, but not of IL-4, in cell culture supernates indicated that the proliferating cells were T(H)1. Infected mature CML-DC were more effective than infected immature CML-DC, showing that T cell stimulation by mature DC and by IL-2 was additive.

DISCUSSION

CML-DC can be modified genetically and functionally by recombinant replication-defective adenoviruses, providing new possibilities for clinical trials in dendritic cell-based immunotherapy.

Gene therapy for lung neoplasms

The field of gene therapy is still in its infancy, but significant accomplishments have been achieved. The ability to transfer genes safely and successfully into animals and patients clearly has been established. It is highly likely that in the near future, gene therapy will be shown to have clear therapeutic efficacy in diseases such as the treatment of hemophilia (using adeno-associated virus vectors) and the stimulation of angiogenesis in peripheral vascular disease and myocardial ischemia. Although only Phase 1 cancer gene therapy trials for thoracic malignancy have been conducted (usually in patients with large tumor burdens and at submaximal doses), there are some hints of efficacy at higher doses of vector in trials for localized malignancy. The studies reviewed in this article demonstrate the first attempts to use gene therapy vectors for lung cancer and mesothelioma. Although none of the diseases studied was "cured," valuable lessons have been learned from these trials, especially in defining the challenges of relatively inefficient and transient delivery of transgene in vivo. Using this knowledge, the second phase of gene therapy research has begun, with a strong focus on developing improved vector technology. Given the progress so far, there is little doubt that gene therapy will become a key approach for the treatment of thoracic malignancies in the near future.

Interaction of large DNA viruses with dendritic cells

Dendritic cells (DC) with their unique capacity to prime naïve T cells are crucial in the induction of immunological responses, including anti-tumoral and anti-viral immunity. DC based immunotherapies are thus currently considered a particularly promising approach for cellular immunotherapy. The cloning of tumor associated antigens (TAAs) together with the possibility of manipulating viral genomes by biotechnological techniques has sparked the interest of using genetically modified viruses to transduce DC in order to achieve antigenic expression of TAA with the aim of inducing a protective immune response. An increasing number of modified viral vectors has been designed for gene therapy purposes and consecutively has been used for the ex vivo transduction of DC. It has been shown that viral vectors genetically engineered to express TAA or immune modifiers like cytokines or costimulatory molecules can lead to a high level of transgene expression. Furthermore, these studies have also revealed that viruses have developed several immune evasion mechanisms specifically targeting DC. Therefore, analysing the interactions of viruses with DC is crucial for the development of new viral vectors suitable for the transduction of DC. In this report we describe the interaction of two large DNA viruses, herpes simplex virus type 1 (HSV-1) and vaccinia virus (VV), with DC generated from peripheral blood mononuclear cells.

Adenovirus-mediated transfer of heme oxygenase-1 cDNA attenuates severe lung injury induced by the influenza virus in mice

Heme oxygenase-1 (HO-1) is an inducible heat shock protein that regulates heme metabolism to form bilirubin, ferritin and carbon monoxide. Based on recent evidence that HO-1 is involved in the resolution of inflammation by modulating apoptotic cell death or cytokine expression, the present study examined whether overexpression of exogenous HO-1 gene transfer provides a therapeutic effect on a murine model of acute lung injury caused by the type A influenza virus. We demonstrate herein that the transfer of HO-1 cDNA resulted in (1) suppression of both pathological changes and intrapulmonary hemorrhage; (2) enhanced survival of animals; and (3) a decrease of inflammatory cells in the lung. TUNEL analysis revealed that HO-1 gene transfer reduced the number of respiratory epithelial cells with DNA damage, and caspase assay suggested that HO-1 suppressed lung injury via a caspase-8-mediated pathway. These findings suggest the feasibility of HO-1 gene transfer to treat lung injury induced by a pathogen commonly seen in the clinical setting. Since oxidative stress and lung injury are involved in many lung disorders, such as pneumonia induced by a variety of microorganisms and pulmonary fibrosis, HO-1 may be useful for wider clinical applications in gene therapy targeting lung disorders including acute pneumonia and pulmonary fibrosis.

An adenovirus with enhanced infectivity mediates molecular chemotherapy of ovarian cancer cells and allows imaging of gene expression

The adenovirus (Ad) is a useful vector for cancer gene therapy due to its unparalleled gene transfer efficiency to dividing and quiescent cells. Primary cancer cells, however, often have highly variable or low levels of the requisite coxsackie-adenovirus receptor (CAR). Also, assessment of gene transfer and vector persistence has been logistically difficult in human clinical trials. We describe here two novel bicistronic adenoviral (Ad) vectors, AdTKSSTR and RGDTKSSTR, which contain the herpes simplex virus thymidine kinase gene (TK) for molecular chemotherapy and bystander effect. In addition, the viruses contain the human somatostatin receptor subtype-2 gene (SSTR2), the expression of which can be noninvasively imaged. We enhanced the infectivity of RGDTKSSTR by genetically incorporating the RGD-4C motif into the HI-loop of the fiber. This allows the virus to circumvent CAR deficiency by binding to alpha(v)beta(3) and alpha(v)beta(5) integrins, which are highly expressed on most ovarian cancers. The expanded tropism of RGDTKSSTR results in increased infectivity of purified primary ovarian cancer cells and allows enhanced gene transfer in the presence of malignant ascites containing anti-Ad antibodies. RGDTKSSTR may be a useful agent for treating ovarian cancer in clinical trials.

Specific depletion of human anti-adenovirus antibodies facilitates transduction in an in vivo model for systemic gene therapy

Recombinant adenoviral (rAd) vectors are capable of mediating high-efficiency gene transfer in vivo. Under conditions requiring systemic administration, however, the use of rAd vectors can be problematic due to the presence of circulating anti-adenovirus antibodies developed either through natural infection or during the course of treatment. We developed a passive immunization model in SCID/Beige mice to assess the effect of human and mouse anti-adenovirus antibodies on systemic administration of a rAd vector expressing beta-galactosidase (rAd-betagal). In this model, the in vitro neutralizing activity of human or mouse antibodies used for passive immunization correlated well with inhibition of transduction of the liver following i.v. administration of rAd-betagal. Depletion of antibodies to individual adenovirus structural proteins (hexon, penton, fiber) by affinity chromatography demonstrated that antibodies to each of the three virion components contributed to neutralization of infectivity in vitro and to inhibition of transduction in vivo. Depletion of antibodies against all three structural proteins from human or mouse immune serum prior to passive immunization restored in vivo transduction activity to levels comparable to those obtained with nonimmune serum. Our data suggest that depletion of both murine and human anti-adenoviral antibodies can restore transduction in vivo during systemic rAd gene therapy in hosts previously exposed to adenovirus.

An improved helper-dependent adenoviral vector allows persistent gene expression after intramuscular delivery and overcomes preexisting immunity to adenovirus

Helper-dependent adenoviral vectors deleted of all viral coding sequences have shown an excellent gene expression profile in a variety of animal models, as well as a reduced toxicity after systemic delivery. What is still unclear is whether long-term expression and therapeutic dosages of these vectors can be obtained also in the presence of a preexisting immunity to adenovirus, a condition found in a high proportion of the adult human population. In this study we performed intramuscular delivery of helper-dependent vectors carrying mouse erythropoietin as a marker transgene. We found that low doses of helper-dependent adenoviral vectors can direct long-lasting gene expression in the muscles of fully immunocompetent mice. The best performance-i.e., 100% of treated animals showing sustained expression after 4 months-was achieved with the latest generation helper-dependent backbones, which replicate and package at high efficiency during vector propagation. Moreover, efficient and prolonged transgene expression after intramuscular injection was observed with limited vector load also in animals previously immunized against the same adenovirus serotype. These data suggest that human gene therapy by intramuscular delivery of helper-dependent adenoviral vectors is feasible.

Immunotherapy of established tumors in mice by intratumoral injection of an adenovirus vector harboring the human IL-2 cDNA: induction of CD8(+) T-cell immunity and NK activity

Intratumoral (i.t.) injections of an adenovirus encoding the human interleukin-2 (IL-2) under the control of the RSV (Ad-pRSV-IL-2) or CMV (Ad-pCMV-IL-2) promoter were performed in established mastocytoma P815 tumors in B6D2 mice. Both early and long-term survival were found increased in mice treated with Ad-pCMV-IL-2 as compared with those obtained with Ad-pRSV-IL-2: tumor regression was observed in 30--50% of mice for the former and 5--15% for the latter. Difference in efficacy between the two vectors was directly correlated to the amount of IL-2 produced i.t. between 24 and 48 hours postinjection, which reached 10--20 ng/tumor for Ad-pCMV-IL-2 and 0.3--0.5 ng/tumor for Ad-pRSV-IL-2. In both cases, expression in the tumor was clearly detectable for a period of 7--10 days postinjection. Serum IL-2 was not detectable in mice treated with Ad-pRSV-IL-2, whereas expression peaked at a total of 1--2 ng at 24 hours but declined very rapidly in the Ad-pCMV-IL-2-treated group. Constant production of IL-2 inside the tumor was necessary for successful therapy because i.t. injections of recombinant IL-2 at levels up to 1 microg for five consecutive days did not lead to antitumoral activity. Evidence of induced systemic immunity following Ad-pCMV-IL-2 injections was obtained from rechallenge experiments in which tumor-free mice after treatment rejected a subsequent contralateral injection of a lethal dose of P815 tumor cells and from the observation that regression of nontreated tumors occurred in animals bearing bilateral tumors that were treated i.t. in a single tumor with Ad-pCMV-IL-2. P815-specific cytotoxic T lymphocytes (CTL) were found specifically in spleen cells from cured mice or rechallenged mice but not in control mice. Interestingly, limiting dilution analysis of anti-P815 CTL precursor (CTLp) frequency revealed a significant increase in mice cured of their tumor as compared to that obtained in naive mice or control mice treated or not with Ad-IL-2 but whose tumor was growing. In vivo depletion of T-cell subsets, as well as natural killer cells at the time of i.t. injections with Ad-pCMV-IL-2, demonstrated that both CD8(+) T cells and natural killer cells, but not CD4(+) T cells, were required for successful therapy. Finally, mice preimmunized with Ad-null viruses were severely compromised in their capacity to eradicate established P815 tumors after Ad-pCMV-IL-2 therapy, at least when neutralizing antibody titers reached a critical level.

Tumor suppression and therapy sensitization of localized and metastatic breast cancer by adenovirus p53

We have examined the effects of a replication-defective adenovirus encoding p53 (RPR/INGN 201 [Ad5CMV-p53]; Adp53), alone or in combination with the breast cancer therapeutic doxorubicin (Adriamycin), to suppress growth and induce apoptosis in breast cancer cells in vitro. We have also examined the in vivo effect of intratumoral administration of Adp53, alone or in combination with doxorubicin, to suppress the growth of established subcutaneous MDA-MB-435 breast cancer tumors. Finally, using the MDA-MB-435 orthotopic model of metastatic breast cancer, we have examined the effect of systemic administration of Adp53, alone or in combination with doxorubicin, to reduce the incidence of metastases. We find that whereas in vitro treatment of cells with Adp53 reduces [(3)H]thymidine incorporation by about 90% at 48 hr, cell viability at 6 days is reduced by only some 50% relative to controls. Although apoptosis is detectable in Adp53-treated cultures, these results suggest that a large fraction of Adp53-treated cells merely undergo reversible cell cycle arrest. Combined treatment with Adp53 and doxorubicin results in a greater than additive loss of viability in vitro and increased apoptosis. In vivo, locally administered Adp53 suppresses growth of established subcutaneous tumors in nude mice and suppression is enhanced by doxorubicin. In the metastatic breast cancer model, systemic administration of Adp53 plus doxorubicin leads to a significant reduction in the incidence of metastases relative to Adp53 or doxorubicin alone. Taken together, these data indicate an additive to synergistic effect of Adp53 and doxorubicin for the treatment of primary and metastatic breast cancer.

Molecular therapy in a model neuroendocrine disease: developing clinical gene therapy for pituitary tumours

The main objectives of pituitary tumour treatment are to restore normal function of the pituitary gland and prevent tumour recurrences. In spite of the success of current therapies in the treatment of relatively small tumours, new therapeutic alternatives need to be explored for large invasive tumours, tumour recurrences postsurgery, and when intolerance to drug treatment develops. Gene therapy, which uses nucleic acids as drugs, is a very attractive alternative to classic therapeutic modalities. With the development of efficient gene delivery vectors, which allow widespread distribution and long-term transgene expression with limited side effects, the clinical implementation of gene therapy for the treatment of pituitary tumours will become a reality within the next five to ten years.

Maturation of dendritic cells infected by recombinant adenovirus can be delayed without impact on transgene expression

Adenovirus-mediated gene transfer to dendritic cells is highly efficient and often used, but the relationship among cell maturation, viral infection and expression of a transferred gene remains unclear. To study this relationship, we introduced a recombinant replication-defective adenovirus encoding the gene for green fluorescent protein to normal human immature myeloid dendritic cells. We induced maturation by the addition of TNF-alpha, IL-1beta, IL-6 and prostaglandin E2 to the medium and assessed cell maturity by the levels of the secreted p40 subunit of IL-12 and of membrane-bound CD83. We quantified the efficiency of gene expression by GFP fluorescence and analyzed the data by a mixed-model analysis of variance; the model explained more than 97% of the effects. CD83 expression and p40 secretion depended solely on incubation time and maturation medium. The cells cultured in the absence of maturation medium remained immature and maintained the ability to respond to the later addition of the maturation irrespective of adenovirus infection and transferred gene expression. This expression was independent of cell maturation. In comparison with mature cells, the transferred gene was expressed in immature dendritic cells with a lag compatible with the less effective initial step (infection and/or gene transfer) in the absence of the maturation medium rather than less effective later GFP synthesis. Expression of CD83 and p40 were unaffected by adenovirus infection and transferred gene expression. Thus, immature dendritic cells infected with recombinant adenoviruses can be matured when desired after transferred gene expression.

Idiotype-encoding recombinant adenoviruses provide protective immunity against murine B-cell lymphomas

Vaccination with tumor-specific immunoglobulin or idiotype (Id) is a promising new form of immunotherapy for B-cell malignancies. Id protein vaccination has demonstrated clinical activity in B-cell lymphomas, yet it requires the laborious and time-consuming procedures of tumor-myeloma cell hybridization, large-scale in vitro culture, and protein purification. Recombinant adenoviruses are highly efficient and immunogenic gene transfer vehicles from which individualized vaccines can be rapidly assembled using polymerase chain reaction-amplified tumor Id genes. Id-encoding adenoviruses were evaluated as vaccines in 2 murine B-cell lymphoma models. A single injection of recombinant Id adenovirus provided protection from subsequent tumor challenge that was equivalent or superior to that afforded by Id protein vaccination. Protected mice had substantial serum titers of Id-specific antibodies. When used in conjunction with chemotherapy, vaccination also prolonged the survival of mice bearing pre-existing tumor. Mechanistic studies demonstrated that tumor protection was not dependent upon T cells. Importantly, in mice prevaccinated with an irrelevant adenovirus, tumor protection following vaccination with Id adenovirus was not significantly impaired. These findings have implications for the design of future lymphoma immunotherapy trials.

Viral vectors for dendritic cell-based immunotherapy

Transduction of dendritic cells (DCs) by viral vectors genetically engineered to express tumor-associated antigens (TAAs) or cytokines can produce a high level of transgene expression and is an attractive approach for DC-based immunotherapy. Ex vivo transduction allows the control of DC quality, antigen quantity and site of DC reinjection. This review evaluates the viral vectors currently being developed for use in DC-based immunotherapy.

Efficacy of repeated adenoviral suicide gene therapy in a localized murine tumor model

BACKGROUND

Gene therapy using adenovirus to deliver herpes simplex virus thymidine kinase (Ad.HSVtk) followed by the administration of the prodrug ganciclovir has been an effective anticancer therapy in models of localized tumor (including malignant mesothelioma) and is currently being evaluated in clinical trials. To optimize this approach, we studied the effects of repeated injections of Ad.HSVtk in an animal model of localized tumor in both naive and immunized mice.

METHODS

Immunocompetent animals with established abdominal tumor were treated with either one or three (given weekly) intraperitoneal injections of Ad.HSVtk (10(9) plaque-forming units) followed by daily ganciclovir and monitored for survival. Survival studies were also performed in mice previously immunized with adenovirus.

RESULTS

Animals treated with multiple courses of Ad.HSVtk showed significantly improved survival versus singly injected animals and control animals with some long-term survivors in the multiple injected group. Preexisting neutralizing immunity did not diminish this survival advantage.

CONCLUSIONS

Multiple treatments using an adenoviral vector to deliver HSVtk significantly improves survival in a murine intraperitoneal tumor model. The presence of preexisting neutralizing antibodies does not blunt this effect. Repeat Ad.HSVtk is a feasible approach and may be a useful strategy in human cancer gene therapy.

Gene therapy in wound repair and regeneration

The potential use of gene therapy to treat human disease increases with the development of various physical, chemical, and biological methods to deliver genes to mammalian cells, and with our rapidly expanding knowledge of the human genome. One area of therapeutic interest for gene therapy is the treatment of wound healing disorders. Most recently, recombinant human growth factor therapy has been examined as a means to treat problem wounds. However, this approach suffers from the difficulty in providing an accurate dose of growth factor and the expense of the recombinant proteins. Delivery of a gene that could be expressed within the wound is an attractive alternative to application of the protein. This review discusses several methods that have been used to deliver genes encoding growth factor proteins into wounds and the advantages/disadvantages of each approach. Novel methods to regulate the expression of the transgene are also presented, highlighting the ability of these unique vector systems to adjust gene dose as the wound heals. We expect that gene therapy will become a significant treatment modality for those wound healing pathologies refractory to other wound management approaches in the years ahead.

Using a tropism-modified adenoviral vector to circumvent inhibitory factors in ascites fluid

Peritoneal compartmentalization of advanced stage ovarian cancer provides a rational scenario for gene therapy strategies. Several groups are exploring intraperitoneal administration of adenoviral (Ad) vectors for this purpose. We examined in vitro gene transfer in the presence of ascites fluid from ovarian cancer patients and observed significant inhibition of Ad-mediated gene transfer. The inhibitory activity was not identified as either complement or cellular factors, but depletion of IgG from ascites removed the inhibitory activity, implicating neutralizing anti-Ad antibodies. A wide range of preexisting anti-Ad antibody titers in patient ascites fluid was measured by ELISA. Western blot analysis demonstrated that the antibodies were directed primarily against the Ad fiber protein. To circumvent inhibition by neutralizing antibodies, a genetically modified adenoviral vector was tested. The Ad5Luc.RGD vector has an Arg-Gly-Asp (RGD) peptide sequence inserted into the fiber knob domain and enters cells through a nonnative pathway. Compared with the conventional Ad5 vector, Ad5Luc.RGD directed efficient gene transfer to cell lines and primary ovarian cancer cells in the presence of ascites fluid containing high-titer neutralizing anti-Ad antibodies. These results suggest that such modified Ad vectors will be needed to achieve efficient gene transfer in the clinical setting.

Targetable gene delivery vectors

Adenoviral vectors, which have targeting ligands for tumor cells on the capsid, no natural tropism, and carry a therapeutic payload should be constructed soon and tested in pre-clinical models. Nevertheless, there are still important considerations for the design and therapeutic use of targetable vectors. Perhaps the single greatest challenge in the future, as it was in the past, will be finding ligands that have a higher apparent affinity for tumor and/or tumor endothelial cells then normal cells. However, the advent of many rapidly advancing technologies and information including the sequencing of the human genome, in vivo and in vitro phage display, rapid analysis of gene and protein expression in any context, and new cellular targets such as angiogenic endothelial cells, may provide many opportunities for the discovery of novel and useful ligands. In addition, the interests in targeting vectors are rapidly growing with new journals and meetings solely devoted to this subject increasing annually. Within the next 5 years, we should have meaningful clinical data on targetable vectors to reassess our progress.

Pre-existent adenovirus antibody inhibits systemic toxicity and antitumor activity of CN706 in the nude mouse LNCaP xenograft model: implications and proposals for human therapy

Pre-existent humoral antibody to adenovirus potentially confounds human clinical trials involving intravascular administration of adenovirus. Using the LNCaP prostate cancer xenograft model in BALB/c nu/nu mice and the prostate-specific attenuated replication-competent adenovirus (ARCATM) CN706, we developed an animal model that systematically controls both the dose of intravascularly administered adenovirus and the titer of the pre-existent anti-Ad5 antibody, and then measures the virus-induced toxicity as well as antitumor activity. We prepared hyperimmune sera to adenovirus in rabbits, passively injected the purified rabbit anti-Ad5 antibody into tumor-bearing mice, and established measurable humoral anti-Ad5 antibody titers. CN706 was intravenously injected into the tail vein of animals 24 hr after passive anti-Ad5 antibody administration. In the absence of pre-existent antibody, the lethal dose (LD100) for BALB/c nu/nu mice was 2.5x10(11) CN706 particles, whereas 1x10(11) CN706 particles was not lethal. However, in the presence of a 1:80 pre-existent titer of Ad5 neutralizing antibody (NAb), intravenous injection of 5x10(11) CN706 particles was no longer lethal. In addition, pre-existent antibody also prevented antitumor activity in a dose-dependent manner: 1x 10(11) CN706 particles prevented LNCaP xenograft tumor progression, but antitumor activity was eliminated by a pre-existent 1:80 NAb titer. These results led us to propose transient removal of pre-existent adenovirus antibody by immunoapheresis. An affinity column of cloned virus capsid proteins was constructed that was able to specifically remove adenovirus antibody from human clinical serum samples. A 5-min disposable immunoassay was also developed to monitor the level of pre-existent antibody in sera before and after immunoapheresis. Clinically, this approach may enable controlled clinical studies of intravenously administered adenovirus in patients with pre-existent anti-adenovirus antibody.

Expression of an antigenic adenovirus epitope in a group B coxsackievirus

Group B coxsackieviruses (CVB) cause human myocarditis, while human adenovirus type 2 (Ad2) is implicated as an agent of this disease. The L1 loop of the Ad2 hexon protein has been demonstrated to be antigenic in rabbits. To evaluate the feasibility of a multivalent vaccine strain against the CVB and Ad2, we cloned the sequence encoding the Ad2 hexon L1 loop, flanked by dissimilar sequences encoding the protease 2A (2Apro) recognition sites, into the genome of an attenuated strain of CVB type 3 (CVB3/0) at the junction of 2Apro and the capsid protein 1D. Progeny virus (CVB3-PL2-Ad2L1) was obtained following transfection of the construct into HeLa cells. Replication of CVB3-PL2-Ad2L1 in diverse cell cultures demonstrated that the yield of the chimeric virus was between 0.5 to 2 log units less than the parental strain. Western blot analyses of the CVB3 capsid protein 1D in CVB3-PL2-Ad2L1-infected HeLa cells demonstrated production of the expected capsid protein. Viral proteins were detected earlier and in approximately fourfold greater amounts in CVB3-PL2-Ad2L1-infected HeLa cells than in CVB3/0-infected cells. Cleavage of the CVB3-PL2-Ad2L1 polyprotein by 2Apro was slowed, accompanied by an accumulation of the fusion 1D-L1 loop protein. Reverse transcription-PCR sequence analysis of CVB3-PL2-Ad2L1 RNA demonstrated that the Ad2 hexon polypeptide coding sequence was maintained in the chimeric viral genome through at least 10 passages in HeLa cells. Mice inoculated with CVB3-PL2-Ad2L1 demonstrated a brief viremia with no replication detectable in the heart but prolonged replication of virus in the pancreas in the absence of pathologic changes in either organ. CVB3-PL2-Ad2L1 induced binding and neutralizing anti-Ad2 antibodies, in addition to antibodies against CVB3 in mice. CVB3-PL2-Ad2L1 was used to challenge mice previously inoculated with CVB3/0 and with preexisting anti-CVB3 neutralizing-antibody titers; anti-Ad2 neutralizing and binding antibodies were induced in these mice at higher levels than in mice without anti-CVB3 immunity. The data demonstrate that a CVB vector can stably express an antigenic polypeptide of Ad2 from within the CVB open reading frame that results in the induction of protective immune responses against both viruses.

Adenoviral gene transfer is inhibited by soluble factors in malignant pleural effusions

Direct in vivo gene delivery is a prerequisite for many gene therapy strategies; however, efficacy has been limited by a lack of therapeutic gene transfer. In studying intrapleural malignancy as a model for the gene therapy of non-small cell lung cancer, we previously identified soluble chondroitin sulfate-proteoglycans/glycosaminoglycans (CS-PG/GAGs) in malignant pleural effusions (MPE) as factors that inhibit retroviral vector (RV) transduction. Similarly, we have observed inhibition to gene transfer in the fluid component of MPE using adenoviral (Ad) vectors. Analyses indicate that the factors responsible for the block are filterable, soluble, titrable, and heat stable (56 degrees C). Passage through microporous membranes fractionates the inhibitory factors into large (> 100 kD) components of the effusions. In contrast to RV transduction, hyaluronic acid or CS-PG/GAGs are not the inhibitors because the block is not reversed by pretreatment of the effusions with mammalian hyaluronidase, and exogenous addition of GAGs into the transduction media does not diminish Ad transduction. In considering the mechanism of action of the inhibitory factors, we observe that Ad entry, and specifically the binding of radiolabeled Ad to its target cell, is inhibited in the presence of MPE. Ad internalization may also be impaired; however, these studies exclude soluble fibronectin in MPE as a competitive inhibitor of Ad transduction. Lastly, sepharose A- mediated immunoglobulin depletion of MPE only partially reverses the block, and significant inhibition to Ad gene transfer persists at lower adenovirus:target cell ratios. Identifying the structural and functional basis for inhibition to Ad gene transfer may yield specific strategies to enable better in vivo translation of gene therapy approaches.

Gene therapy for lung disease: hype or hope?

Gene therapy, the treatment of any disorder or pathophysiologic state on the basis of the transfer of genetic information, was a high-priority goal in the 1990s. The lung is a major target of gene therapy for genetic disorders, such as cystic fibrosis and alpha1-antitrypsin deficiency, and for other diseases, including lung cancer, malignant mesothelioma, pulmonary inflammation, surfactant deficiency, and pulmonary hypertension. This paper examines general concepts in gene therapy, summarizes the results of published clinical trials, and highlights areas of research aimed at overcoming challenges in the field. Although progress has been slower than anticipated, gene transfer has been safely achieved in patients with lung diseases. Recent advancements in understanding of the molecular basis of lung disease and the development of improved vector systems make it likely that gene therapy will be an important tool for the 21st-century clinician.

Immune responses against replication-deficient adenovirus inhibit ovalbumin-specific allergic reactions in mice

Replication-deficient adenovirus vector (Ad) is one of the most efficient gene transfer vehicles for human gene therapy. However, Ad is antigenic, known to evoke prominent inflammatory responses in vivo, and there are concerns that using Ad in patients with immune-mediated disorders (allergy and autoimmune diseases) may affect the status of the diseases. To evaluate this concept in a manner close to clinical scenarios, a mouse model of airway eosinophilic inflammation was developed by administering intraperitoneal injections and inhalations of chicken ovalbumin (OA), with Ad administered intranasally 5 days after the OA sensitization. The administration of Ad resulted in a significant suppression of eosinophil counts in peripheral blood as well as in the bronchoalveolar lavage fluid (BALF), and a decrease in OA-specific IgE. The decrease in the number of eosinophils in BALF was associated with a marked upregulation of interferon gamma (IFN-gamma) expression. In contrast, the Ad-specific, delayed-type hypersensitivity response and efficacy of reporter gene expression mediated by Ad were only marginally affected in animals sensitized with OA. Together, these data support the idea that Ad administration in patients with Th2-mediated immune disorders does not exacerbate the parameters of ongoing inflammations or gene transfer efficiency, and with its ability to induce prominent type 1 immune response to the antigen in vivo, Ad could potentially be used as an efficient adjuvant to control immune disorders where Th2 cell-mediated mechanisms are involved.

Neutralisation of adenovirus infectivity by ascitic fluid from ovarian cancer patients

Animal models and phase I clinical trials have shown that repeat virus delivery and subsequent transgene expression is limited by the generation of humoral and cellular immune responses directed towards the therapeutic vector. The presence of a pre-existing immune response may even prevent initial delivery. In order to determine the presence of pre-existing anti-adenovirus humoral immunity we analysed ascitic fluid, collected from the peritoneal cavity of patients with advanced ovarian cancer. Twelve ascitic fluid and four matched serum samples were examined. The titre and isotype of anti-adenovirus antibodies was determined by ELISA, and Western blotting identified the molecular basis of the immune response, which was primarily directed towards fibre and penton base. Neutralisation of virus infectivity was assessed in vitro by measurement of green fluorescent protein reporter gene expression. We found that the ascitic fluid samples contain antibodies that recognise both adenovirus types 2 and 5, were predominantly IgG and directed towards the viral antigens responsible for cell adhesion, and had virus neutralising activity.

Latest developments in gene transfer technology: achievements, perspectives, and controversies over therapeutic applications

Over the last decade, more than 300 phase I and phase II gene-based clinical trials have been conducted worldwide for the treatment of cancer and monogenic disorders. Lately, these trials have been extended to the treatment of AIDS and, to a lesser extent, cardiovascular diseases. There are 27 currently active gene therapy protocols for the treatment of HIV-1 infection in the USA. Preclinical studies are currently in progress to evaluate the possibility of increasing the number of gene therapy clinical trials for cardiopathies, and of beginning new gene therapy programs for neurologic illnesses, autoimmuno diseases, allergies, regeneration of tissues, and to implement procedures of allogeneic tissues or cell transplantation. In addition, gene transfer technology has allowed for the development of innovative vaccine design, known as genetic immunization. This technique has already been applied in the AIDS vaccine programs in the USA. These programs aim to confer protective immunity against HIV-1 transmission to individuals who are at risk of infection. Research programs have also been considered to develop therapeutic vaccines for patients with AIDS and generate either preventive or therapeutic vaccines against malaria, tuberculosis, hepatitis A, B and C viruses, influenza virus, La Crosse virus, and Ebola virus. The potential therapeutic applications of gene transfer technology are enormous. However, the effectiveness of gene therapy programs is still questioned. Furthermore, there is growing concern over the matter of safety of gene delivery and controversy has arisen over the proposal to begin in utero gene therapy clinical trials for the treatment of inherited genetic disorders. From this standpoint, despite the latest significant achievements reported in vector design, it is not possible to predict to what extent gene therapeutic interventions will be effective in patients, and in what time frame.

Recent developments in the virus therapy of cancer

Cancer is one of the leading causes of death in the United States. Although there has been significant progress in the areas of cancer etiology, diagnostic techniques, and cancer prevention, adequate therapeutic approaches for many cancers have lagged behind. One promising line of investigation is the virus therapy of cancer. This approach entails the use of viruses, such as retroviruses, adenovirus, and vaccinia virus, to modify tumor cells so that they become more susceptible to being killed by the host immune response, chemotherapeutic agents, or programmed cell death. This review discusses recent advances in the virus therapy of cancer from both basic science and clinical perspectives. Given the potential of viruses to kill tumor cells directly or transduce desired gene products to allow a vigorous host antitumor immune response, the virus therapy of cancer holds great promise in the treatment of cancer.

Gene therapy for carcinoma of the breast: Pro-apoptotic gene therapy

The dysregulation of apoptosis contributes in a variety of ways to the malignant phenotype. It is increasingly recognized that the alteration of pro-apoptotic and anti-apoptotic molecules determines not only escape from mechanisms that control cell cycle and DNA damage, but also endows the cancer cells with the capacity to survive in the presence of a metabolically adverse milieu, to resist the attack of the immune system, to locally invade and survive despite a lack of tissue anchorage, and to evade the otherwise lethal insults induced by drugs and radiotherapy. A multitude of apoptosis mediators has been identified in the past decade, and the roles of several of them in breast cancer have been delineated by studying the clinical correlates of pathologically documented abnormalities. Using this information, attempts are being made to correct the fundamental anomalies at the genetic level. Fundamental to this end are the design of more efficient and selective gene transfer systems, and the employment of complex interventions that are tailored to breast cancer and that are aimed concomitantly towards different components of the redundant regulatory pathways. The combination of such genetic modifications is most likely to be effective when combined with conventional treatments, thus robustly activating several pro-apoptotic pathways.

Combined therapy with chemotherapeutic agents and herpes simplex virus type 1 ICP34.5 mutant (HSV-1716) in human non-small cell lung cancer

A replication-selective herpes simplex virus type 1 ICP34.5 mutant (HSV-1716) has shown efficacy both in vitro and in vivo against human non-small cell lung cancer (NSCLC) cell lines but complete eradication of tumor has not been accomplished with a single viral treatment in our murine xenograft models. Therefore, strategies to enhance the efficacy of this treatment were investigated. We determined the oncolytic activity of HSV-1716 in NCI-H460 cells in combination with each of four chemotherapeutic agents: mitomycin C (MMC), cis-platinum II (cis-DDP), methotrexate (MTX), or doxorubicin (ADR). Isobologram analysis was performed to evaluate the interaction between the viral and chemotherapeutic agents. The oncolytic effect of HSV-1716 in combination with MMC was synergistic in two of five NSCLC cell lines. In the other three cell lines, the combined effect appeared additive. No antagonism was observed. The in vivo effect of this combination was then examined in a murine xenograft model. NCI-H460 flank tumors were directly injected with HSV-1716 (4 x 106 PFU) followed by intravenous MMC administration (0.17 mg/kg) 24 hr later. After 3 weeks, the mean tumor weight in the combined treatment group was significantly less than either individual treatment in an additive manner. The synergistic dose of MMC neither augmented nor inhibited viral replication in vitro and HSV-1716 infection did not upregulate DT-diaphorase, which is the primary enzyme responsible for MMC activation. In summary, the combination of HSV-1716 with common chemotherapeutic agents may augment the effect of HSV-based therapy in the treatment of NSCLC.

Dendritic cells transduced with an adenovirus vector encoding Epstein-Barr virus latent membrane protein 2B: a new modality for vaccination

Epstein-Barr virus (EBV) is a herpesvirus commonly associated with several malignancies, particularly in immunocompromised hosts. As a strategy for stimulating immunity against EBV for the treatment of EBV-associated tumors, we have genetically engineered dendritic cells (DC) to express EBV antigens, such as latent membrane protein 2B (LMP2B), using recombinant adenovirus vectors. CD8(+) T lymphocytes from HLA-A2.1(+), EBV-seropositive healthy donors were cultured with autologous DC infected with recombinant adenovirus vector AdEGFP, encoding an enhanced green fluorescent protein (EGFP), or AdLMP2B at a multiplicity of infection of 250. After 48 h, >95% of the DC were positive for EGFP expression as assessed by fluorescence-activated cell sorting analysis, indicating efficient gene transfer. AdLMP2-transduced DC were used to stimulate CD8(+) T cells. Responder CD8(+) T cells were tested for gamma interferon (IFN-gamma) release by enzyme-linked spot (ELISPOT) assay and cytotoxic activity. Prior to in vitro stimulation, the frequencies of T-cells directed against two HLA-A2-presented LMP2 peptides (LMP2 329-337 and LMP2 426-434) were very low as assessed by IFN-gamma spot formation (T-cell frequency, <0.003%). IFN-gamma ELISPOT assays performed at day 14 showed a significant (2-log) increase of the day 0 frequency of T cells reactive against the LMP2 329-337 peptide, from 0.003 to 0.3 (P < 0.001). Moreover, specific cytolytic activity was observed against the autologous EBV B-lymphoblastoid cell lines after 21 days of stimulation of T-cell responders with AdLMP2-transduced DC (P < 0.01). In summary, autologous mature DC genetically modified with an adenovirus encoding EBV antigens stimulate the generation of EBV-specific CD8(+) effector T cells in vitro, supporting the potential application of EBV-based adenovirus vector vaccination for the immunotherapy of the EBV-associated malignancies.

Cellular immune responses of healthy individuals to intradermal administration of an E1-E3- adenovirus gene transfer vector

In animals, Ad-mediated gene transfer initiates anti-Ad host immune responses that vary, depending on vector design, dose, host, and transgene. To begin to understand whether the anti-Ad vector responses in humans simulate those in animals, Ad(GV)CD.10, an E1-E3- Ad5 vector encoding the E. coli cytosine deaminase gene, was administered by the intradermal route to six normal individuals (8 x 10(7) to 8 x 10(9) particle units, each dose administered to two sites; n = 2 per group). No adverse events were observed. Polymerase chain reaction/Southern analysis demonstrated vector genome in the skin through 28 days in all individuals except one of two at the lowest dose. Local induration, independent of vector dose and baseline systemic anti-Ad5 neutralizing antibodies, developed in all subjects (6 to 17 mm, peak by day 3). Biopsies revealed a mild to moderate T cell (CD3+, CD4+, CD8+), B cell, and macrophage infiltrate at day 3, all decreased by day 28. Langerhans cells accumulated primarily in the papillary dermis. The day 3 cellular response was dose independent. On day 28, CD4+ and CD8+ T lymphocytes and macrophages showed dose dependency. There was minimal systemic Ad5-specific lymphocyte proliferation induced by Ad vector administration in three individuals studied, and no Ad5-specific cytotoxic T lymphocytes (evaluated in two subjects) could be detected. Thus, intradermal administration of an E1-E3- Ad vector to normal subjects induces mild/moderate local cellular responses, even in Ad-immunized individuals. These observations provide a baseline to determine if these human anti-Ad vector host responses can be circumvented by using "stealth" vectors and/or immunosuppression.

Oncolytic therapy using a mutant type-1 herpes simplex virus and the role of the immune system

BACKGROUND

Herpes simplex virus (HSV)-1716, a replication-restricted herpes simplex virus type 1, has shown efficacy as an oncolytic treatment for central nervous system tumors, breast cancer, ovarian cancer, and malignant mesothelioma. We evaluated the efficacy of HSV-1716 in a murine lung cancer model, Lewis lung carcinoma.

METHODS

Lewis lung carcinoma cells were infected with HSV-1716 and implanted in the flanks of mice at varying ratios of infected to uninfected cells. Tumor burden was assessed by measurement of the weight of the tumor nodule. The role of the immune system was examined by performing experiments in both immunocompetent and SCID mice. Tumors were implanted in the opposite flank to evaluate the vaccine effect.

RESULTS

In immunocompetent and SCID animals, ratio of 1:10 (infected-to-uninfected) cells completely prevented tumor formation and ratio of 1:100 suppressed tumor growth. Established tumors at a distant site in the groups receiving HSV-1716 infected cells showed no difference in size versus control, suggesting absence of a vaccine effect.

CONCLUSIONS

We conclude that HSV-1716 may provide a oncolytic therapy for lung cancer even in the absence of immune system induction and a "carrier" cell could potentially deliver this vector.

Immune responses to adenovirus and adeno-associated virus in humans

Vectors based on human adenovirus (Ad) and adeno-associated virus (AAV) are being evaluated for human gene therapy. The response of the host to the vector, in terms of antigen-specific immunity, will play a substantial role in clinical outcome. We have surveyed cohorts of normal subjects and cystic fibrosis patients for pre-existing immunity to these viruses, caused by naturally acquired infections. A number of humoral and cellular assays to adenovirus serotype 5 (Ad5) and adeno-associated virus serotype 2 (AAV2) were performed from serum and peripheral blood mononuclear cells. Virtually all subjects had Ig to Ad5 although only 55% of these antibodies neutralized virus (NAB). Approximately two of three patients demonstrated CD4+ T cells that proliferated to Ad antigens of which most were of the TH1 subset, based on cytokine secretion. A substantially different pattern of immune responses was observed to AAV2. Although virtually all patients had Ig to AAV2, most of these antibodies were not neutralizing (32% NAB) and only 5% of patients had peripheral blood lymphocytes that proliferated in response to AAV2 antigens. These studies demonstrate marked heterogeneity in pre-existing immunity to Ad5 and AAV2 in human populations. The impact of these findings on outcome following gene therapy will require further study.

Rapid infection of oral mucosal-associated lymphoid tissue with simian immunodeficiency virus

The early events during infection with an immunodeficiency virus were followed by application of pathogenic simian immunodeficiency virus atraumatically to the tonsils of macaques. Analyses by virologic assays and in situ hybridization revealed that the infection started locally in the tonsils, a mucosal-associated lymphoid organ, and quickly spread to other lymphoid tissues. At day 3, there were few infected cells, but then the number increased rapidly, reaching a high plateau between days 4 and 7. The infection was not detected in the dendritic cell-rich squamous epithelium to which the virus was applied; instead, it was primarily in CD4+ tonsillar T cells, close to the specialized antigen-transporting epithelium of the tonsillar crypts. Transport of the virus and immune-activating stimuli across this epithelium would allow mucosal lymphoid tissue to function in the atraumatic transmission of immunodeficiency viruses.

Immune responses to adenoviruses: viral evasion mechanisms and their implications for the clinic

Adenoviruses encode proteins that block responses to interferons, intrinsic cellular apoptosis, killing by CD8(+) cytotoxic T lymphocytes and killing by the death ligands TNF, Fas ligand and TRAIL. The viral proteins are believed to prolong acute and persistent adenovirus infections. The proteins may prove useful in protecting adenovirus gene therapy vectors and transplanted cells from the immune system.

Advances in the treatment of malignant pleural mesothelioma

Malignant pleural mesothelioma is a neoplasm that is commonly fatal and for which there are no widely accepted curative approaches. Mesothelioma is unresponsive to most chemotherapy and radiotherapy regimens, and it typically recurs even after the most aggressive attempts at surgical resection. Multimodality approaches have been of some benefit in prolonging survival of very highly selected subgroups of patients, but they have had a relatively small impact on the majority of the patients diagnosed with this disease. As the incidence of pleural mesothelioma peaks in the United States and Europe over the next 10 to 20 years, new therapeutic measures will be necessary. This review will discuss the roles of chemotherapy, radiotherapy, surgery, and combined modality approaches in the treatment of pleural mesothelioma, as well as scientific advances made in the past decade that have led to the development of experimental techniques, such as photodynamic therapy, immunotherapy, and gene therapy, that are currently undergoing human clinical trials. These promising new avenues may modify the therapeutic nihilism that is rampant among clinicians dealing with mesothelioma.

Variability of human systemic humoral immune responses to adenovirus gene transfer vectors administered to different organs

Administration of adenovirus (Ad) vectors to immunologically naive experimental animals almost invariably results in the induction of systemic anti-Ad neutralizing antibodies. To determine if the human systemic humoral host responses to Ad vectors follow a similar pattern, we evaluated the systemic (serum) anti-Ad serotype 5 (Ad5) neutralizing antibodies in humans after administration of first generation (E1(-) E3(-)) Ad5-based gene transfer vectors to different hosts. AdGVCFTR.10 (carrying the normal human cystic fibrosis [CF] transmembrane regulator cDNA) was sprayed (8 x 10(7) to 2 x 10(10) particle units [PU]) repetitively (every 3 months or every 2 weeks) to the airway epithelium of 15 individuals with CF. AdGVCD.10 (carrying the Escherichia coli cytosine deaminase gene) was administered (8 x 10(8) to 8 x 10(9) PU; once a week, twice) directly to liver metastasis of five individuals with colon cancer and by the intradermal route (8 x 10(7) to 8 x 10(9) PU, single administration) to six healthy individuals. AdGVVEGF121.10 (carrying the human vascular endothelial growth factor 121 cDNA) was administered (4 x 10(8) to 4 x 10(9.5) PU, single administration) directly to the myocardium of 11 individuals with ischemic heart disease. Ad vector administration to the airways of individuals with CF evoked no or minimal serum neutralizing antibodies, even with repetitive administration. In contrast, intratumor administration of an Ad vector to individuals with metastatic colon cancer resulted in a robust antibody response, with anti-Ad neutralizing antibody titers of 10(2) to >10(4). Healthy individuals responded to single intradermal Ad vector variably, from induction of no neutralizing anti-Ad antibodies to titers of 5 x 10(3). Likewise, individuals with ischemic heart disease had a variable response to single intramyocardial vector administration, ranging from minimal neutralizing antibody levels to titers of 10(4). Evaluation of the data from all trials showed no correlation between the peak serum neutralizing anti-Ad response and the dose of Ad vector administered (P > 0.1, all comparisons). In contrast, there was a striking correlation between the peak anti-Ad5 neutralizing antibody levels evoked by vector administration and the level of preexisting anti-Ad5 antibodies (P = 0.0001). Thus, unlike the case for experimental animals, administration of Ad vectors to humans does not invariably evoke a systemic anti-Ad neutralizing antibody response. In humans, the extent of the response is dictated by preexisting antibody titers and modified by route of administration but is not dose dependent. Since the extent of anti-Ad neutralizing antibodies will likely modify the efficacy of administration of Ad vectors, these observations are of fundamental importance in designing human gene therapy trials and in interpreting the efficacy of Ad vector-mediated gene transfer.

PEGylation of adenovirus with retention of infectivity and protection from neutralizing antibody in vitro and in vivo

Replication-defective recombinant adenovirus (Ad) vectors are under development for a wide variety of gene therapy indications. A potential limiting factor associated with virus gene therapy requiring repeated treatment is the development of a humoral immune response to the vector by the host. In animal models, there is a dose-dependent rise in neutralizing antibodies after primary vector administration, which can preclude effective repeat administration. The strategy we have developed to circumvent the neutralization of adenovirus vectors by antibodies is to mask their surface by covalent attachment of the polymer polyethylene glycol (PEG). Covalent attachment of PEG to the surface of the adenovirus was achieved primarily by using activated PEG tresylmonomethoxypolyethylene glycol (TMPEG), which reacts preferentially with the epsilon-amino terminal of lysine residues. We show that the components of the capsid that elicit a neutralizing immune response, i.e., hexon, fiber, and penton base, are also the main targets for PEGylation. Several protocols for PEGylation of an adenovirus vector were evaluated with respect to retention of virus infectivity and masking from antibody neutralization. We show that covalent attachment of polymer to the surface of the adenovirus can be achieved with retention of infectivity. We show further that PEG-modified adenovirus can be protected from antibody neutralization in the lungs of mice with high antibody titers to adenovirus, suggesting that PEGylation will improve the ability to administer Ad vectors on a repeated basis.

Recombinant adenovirus is an efficient and non-perturbing genetic vector for human dendritic cells

Recombinant adenoviral vectors have promise for human gene therapy because of efficient transgene expression in nondividing primary cell types. Dendritic cells (DC) have potential as adjuvants for immune therapy, since they are specialized to capture antigens to form MHC-peptide complexes, migrate to T cell areas in the lymph node, and activate T cells including CD4+ helpers and CD8+ cytotoxic T lymphocytes (CTL). We show that several current chemical and physical transfection methods allow < 2 % of DC to express reporter genes but that recombinant adenoviruses, encoding the reporter genes green fluorescent protein and LacZ, efficiently transfect monocyte-derived human DC. Immature DC, generated with IL-4 and GM-CSF, are transfected to 95% efficiency, while mature DC show reduced transfection (50%) and gene expression. Adenovirus-transfected, immature DC exhibit several critical functions. The DC can differentiate in the presence of lipopolysaccharide or a monocyte-conditioned medium to express the surface markers of mature, T cell stimulatory DC including CD25, CD83, and high levels of CD86 and HLA-DR. Transfected DC can also secrete high levels of IL-12 and are potent inducers of T cell growth. Transgene expression in DC is stable for at least 6 days in the presence of the DC survival factor, TRANCE. Therefore adenoviral infection does not perturb the maturation and function of DC. The efficiency of adenoviral-mediated gene transfer prompts the evaluation of this vector in studies of DC biology, including the expression of antigens for active immune therapy.

Recombinant adenovirus is an efficient and non-perturbing genetic vector for human dendritic cells

Recombinant adenoviral vectors have promise for human gene therapy because of efficient transgene expression in nondividing primary cell types. Dendritic cells (DC) have potential as adjuvants for immune therapy, since they are specialized to capture antigens to form MHC-peptide complexes, migrate to T cell areas in the lymph node, and activate T cells including CD4+ helpers and CD8+ cytotoxic T lymphocytes (CTL). We show that several current chemical and physical transfection methods allow < 2 % of DC to express reporter genes but that recombinant adenoviruses, encoding the reporter genes green fluorescent protein and LacZ, efficiently transfect monocyte-derived human DC. Immature DC, generated with IL-4 and GM-CSF, are transfected to 95% efficiency, while mature DC show reduced transfection (50%) and gene expression. Adenovirus-transfected, immature DC exhibit several critical functions. The DC can differentiate in the presence of lipopolysaccharide or a monocyte-conditioned medium to express the surface markers of mature, T cell stimulatory DC including CD25, CD83, and high levels of CD86 and HLA-DR. Transfected DC can also secrete high levels of IL-12 and are potent inducers of T cell growth. Transgene expression in DC is stable for at least 6 days in the presence of the DC survival factor, TRANCE. Therefore adenoviral infection does not perturb the maturation and function of DC. The efficiency of adenoviral-mediated gene transfer prompts the evaluation of this vector in studies of DC biology, including the expression of antigens for active immune therapy.