The long-term consequences of adenovirus-mediated conditional cytotoxic gene therapy for gliomas remain uncharacterized. We report here detection of active brain inflammation 3 months after successful inhibition of syngeneic glioma growth. The inflammatory infiltrate consisted of activated macrophages/microglia and astrocytes, and T lymphocytes positive for leucosyalin, CD3 and CD8, and included secondary demyelination. We detected strong widespread herpes simplex virus 1 thymidine kinase immunoreactivity and vector genomes throughout large areas of the brain. Thus, patient evaluation and the design of clinical trials in ongoing and future gene therapy for brain glioblastoma must address not only tumor-killing efficiency, but also long-term active brain inflammation, loss of myelin fibers and persistent transgene expression.

Epithelial-mesenchymal transition (EMT) events occur during embryonic development and are important for the metastatic spread of epithelial tumors. We show here that spontaneous differentiation of mouse embryonic stem (ES) cells is associated with an E-to N-cadherin switch, up-regulation of E-cadherin repressor molecules (Snail and Slug proteins), gelatinase activity (matrix metalloproteinase [MMP]-2 and -9), and increased cellular motility, all characteristic EMT events. The 5T4 oncofetal antigen, previously shown to be associated with very early ES cell differentiation and altered motility, is also a part of this coordinated process. E-and N-cadherin and 5T4 proteins are independently regulated during ES cell differentiation and are not required for induction of EMT-associated transcripts and proteins, as judged from the study of the respective knockout ES cells. Further, abrogation of E-cadherin-mediated cell-cell contact in undifferentiated ES cells using neutralizing antibody results in a reversible mesenchymal phenotype and actin cytoskeleton rearrangement that is concomitant with translocation of the 5T4 antigen from the cytoplasm to the cell surface in an energy-dependent manner. E-cadherin null ES cells are constitutively cell surface 5T4 positive, and although forced expression of E-cadherin cDNA in these cells is sufficient to restore cell-cell contact, cell surface expression of 5T4 antigen is unchanged. 5T4 and N-cadherin knockout ES cells exhibit significantly decreased motility during EMT, demonstrating a functional role for these proteins in this process. We conclude that E-cadherin protein stabilizes cortical actin cytoskeletal arrangement in ES cells, and this can prevent cell surface localization of the promigratory 5T4 antigen.

Tissue- and tumour-specific approaches to the modulation of MGMT together with other DNA repair functions and in combination with immuno- or radiotherapy are promising strategies to improve alkylating agent therapy.

5T4 oncofetal molecules are highly expressed during development and upregulated in cancer while showing only low levels in some adult tissues. Upregulation of 5T4 expression is a marker of loss of pluripotency in the early differentiation of embryonic stem (ES) cells and forms an integrated component of an epithelial-mesenchymal transition, a process important during embryonic development and metastatic spread of epithelial tumors. Investigation of the transcriptional changes in early ES differentiation showed upregulation of CXCL12 and down-regulation of a cell surface protease, CD26, which cleaves this chemokine. CXCL12 binds to the widely expressed CXCR4 and regulates key aspects of development, stem cell motility and tumour metastasis to tissues with high levels of CXCL12. We show that the 5T4 glycoprotein is required for optimal functional cell surface expression of the chemokine receptor CXCR4 and CXCL12 mediated chemotaxis in differentiating murine embryonic stem cells and embryo fibroblasts (MEF). Cell surface expression of 5T4 and CXCR4 molecules is co-localized in differentiating ES cells and MEF. By contrast, differentiating ES and MEF derived from 5T4 knockout (KO) mice show only intracellular CXCR4 expression but infection with adenovirus encoding mouse 5T4 restores CXCL12 chemotaxis and surface co-localization with 5T4 molecules. A series of chimeric constructs with interchanged domains of 5T4 and the glycoprotein CD44 were used to map the 5T4 sequences relevant for CXCR4 membrane expression and function in 5T4KO MEF. These data identified the 5T4 transmembrane domain as sufficient and necessary to enable CXCR4 cell surface expression and chemotaxis. Furthermore, some monoclonal antibodies against m5T4 can inhibit CXCL12 chemotaxis of differentiating ES cells and MEF which is not mediated by simple antigenic modulation. Collectively, these data support a molecular interaction of 5T4 and CXCR4 occurring at the cell surface which directly facilitates the biological response to CXCL12. The regulation of CXCR4 surface expression by 5T4 molecules is a novel means to control responses to the chemokine CXCL12 for example during embryogenesis but can also be selected to advantage the spread of a 5T4 positive tumor from its primary site.

Gene therapy using Fas ligand (FasL) for treatment of tumours and protection of transplant rejection is hampered because of the systemic toxicity of FasL. In the present study, recombinant replication-defective adenovirus vectors (RAds) encoding FasL under the control of either the neuronal-specific neuronal-specific enolase (NSE) promoter or the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter have been constructed. The cell type-specific expression of FasL in both neurons and glial cells in primary cultures, and in neuronal and glial cell lines is demonstrated. Furthermore, transgene expression driven by the neuronal and glial promoter was not detected in fibroblastic or epithelial cell lines. Expression of FasL driven by a major immediate early human cytomegalovirus promoter (MIEhCMV) was, however, achieved in all cells tested. As a final test of the stringency of transgene-specific expression, the RAds were injected directly into the bloodstream of mice. The RAds encoding FasL under the control of the non-cell type-specific MIEhCMV promoter induced acute generalized liver haemorrhage with hepatocyte apoptosis, while the RAds containing the NSE or GFAP promoter sequences were completely non-toxic. This demonstrates the specificity of transgene expression, enhanced safety during systemic administration, and tightly regulated control of transgene expression of highly cytotoxic gene products, encoded within transcriptionally targeted RAds.

Adenovirus-mediated gene transfer into the brain is associated with significant inflammation and activation of anti-vector and anti-transgene immune responses that curtail the gene delivery of adenoviruses and therapeutic efficacy. Elucidating the molecular mediators of inflammatory and immune responses to adenoviruses injected into the brain should allow us to inhibit their inflammatory actions, thereby reducing vector clearance and enhance adenoviral-mediated gene transfer into the CNS. Cytokines are primary mediators of the immune response and are released during inflammation. Here we report for the first time that injection of replication-deficient adenovirus vectors into the cerebral ventricles of rats causes a rapid increase in body temperature. This fever response precedes any vector-encoded transgene expression and occurs with vectors encoding no transgene, as well as with vectors encoding a therapeutic transgene i.e., HSV1-thymidine kinase. No fever is detected after infection of the striatum, an important brain target in studies on neurodegeneration. After infection of the brain ventricles, CSF levels of immunoreactive tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta increase significantly (up to 300-fold). In the hypothalamus, the locus of thermoregulation in the brain, only IL-1beta and IL-6 are significantly elevated. A neutralizing TNF-alpha antibody has no effect on adenovirus-induced fever. However, pretreatment with either the IL-1 receptor antagonist or the cyclooxygenase inhibitor flurbiprofen completely abolishes adenovirus-induced fever, suggesting that IL-1 and prostaglandins are direct mediators of this response. These results are the first to demonstrate that IL-1, but not TNF-alpha, is the main mediator of a very early inflammatory response to adenovirus in the brain.

Adenoviral vectors are excellent vehicles to transfer genes into the nervous system due to their ability to transduce dividing and nondividing cells, their ability to be grown to very high titers, and their relatively large insert capacity. Also, adenoviral vectors can sustain very long-term transgene expression in the CNS of rodents and in neurons and glial cells in culture. Successful gene transfer into the nervous system is dependent on the development, production, and quality control of vector preparations, which need to be of the highest quality. This unit provides protocols to clone, rescue, amplify, and purify first-generation adenoviral vectors. Detailed quality control assays are provided to ensure that vector preparations are devoid of contamination from replication-competent adenovirus and lipopolysaccharides. Also included are methodologies related to adenoviral-mediated gene transfer into neurons and glial cells in culture, and the analysis of transgene expression using immunocytochemistry, enzymatic assays, and fluorescence-activated cell sorting (FACS) analysis.

The use of pituitary cell type-specific promoters is a powerful molecular tool to achieve pituitary cell type-specific transcriptional targeting of transgenes encoded by viral vectors. It has recently been proposed that transcriptional targeting of therapeutic genes could be harnessed as a gene therapy strategy for the treatment of pituitary disease. We describe the successful use of the human PRL promoter (hPrl) encoded within recombinant adenovirus vectors to target transgene expression of Herpes Simplex Virus Type 1-Thymidine Kinase (HSV1-TK) or beta-galactosidase to lactotrophic cells in vitro and in vivo. Functionally, the restriction of expression of HSV1-TK to lactotrophic tumor cells, using the hPrl promoter, resulted in the cell type-specific induction of apoptosis in the lactotrophic GH3 tumor cell line, in the presence of ganciclovir (GCV). In the corticotrophic AtT20 cell line, we detected neither HSV1-TK expression, nor apoptosis in the presence of GCV. The hPrl promoter encoded within a recombinant adenoviral vector also restricted transgene expression to lactotrophic cells in primary anterior pituitary (AP) cultures, and importantly, within the anterior pituitary gland in vivo. When the HSV1-TK driven by hPrl promoter was used in an in vivo model ofestrogen/sulpiride lactotroph induced hyperplasia within the AP in situ, the treatment was not effective in either reducing the weight of the gland, the number of lactotrophic cells within the transduced area in vivo, or the circulating PRL levels. This is in contrast to the human cytomegalovirus promoter (hCMV) driving expression of HSV1-TK in the same experimental paradigm, which was effective in reducing pituitary weight and circulating PRL levels. Our results have important implications in the design of gene therapy strategies for pituitary tumors. We demonstrate that both the choice of the in vivo animal model, i.e. adenoma in the AP gland in situ, and the particular gene therapy strategy chosen, i.e. use of strong ubiquitous promoters vs. weaker but cell type-specific promoters, determine the experimental therapeutic outcome.