A 'tool box' for deciphering neuronal circuits in the developing chick spinal cord.

The genetic dissection of spinal circuits is an essential new means for understanding the neural basis of mammalian behavior. Molecular targeting of specific neuronal populations, a key instrument in the genetic dissection of neuronal circuits in the mouse model, is a complex and time-demanding process. Here we present a circuit-deciphering 'tool box' for fast, reliable and cheap genetic targeting of neuronal circuits in the developing spinal cord of the chick. We demonstrate targeting of motoneurons and spinal interneurons, mapping of axonal trajectories and synaptic targeting in both single and populations of spinal interneurons, and viral vector-mediated labeling of pre-motoneurons. We also demonstrate fluorescent imaging of the activity pattern of defined spinal neurons during rhythmic motor behavior, and assess the role of channel rhodopsin-targeted population of interneurons in rhythmic behavior using specific photoactivation.

Modeling of human cytomegalovirus maternal-fetal transmission in a novel decidual organ culture.

Human cytomegalovirus (HCMV) is the leading cause of congenital infection, associated with severe birth defects and intrauterine growth retardation. The mechanism of HCMV transmission via the maternal-fetal interface is largely unknown, and there are no animal models for HCMV. The initial stages of infection are believed to occur in the maternal decidua. Here we employed a novel decidual organ culture, using both clinically derived and laboratory-derived viral strains, for the ex vivo modeling of HCMV transmission in the maternal-fetal interface. Viral spread in the tissue was demonstrated by the progression of infected-cell foci, with a 1.3- to 2-log increase in HCMV DNA and RNA levels between days 2 and 9 postinfection, the expression of immediate-early and late proteins, the appearance of typical histopathological features of natural infection, and dose-dependent inhibition of infection by ganciclovir and acyclovir. HCMV infected a wide range of cells in the decidua, including invasive cytotrophoblasts, macrophages, and endothelial, decidual, and dendritic cells. Cell-to-cell viral spread was revealed by focal extension of infected-cell clusters, inability to recover infectious extracellular virus, and high relative proportions (88 to 93%) of cell-associated viral DNA. Intriguingly, neutralizing HCMV hyperimmune globulins exhibited inhibitory activity against viral spread in the decidua even when added at 24 h postinfection-providing a mechanistic basis for their clinical use in prenatal prevention. The ex vivo-infected decidual cultures offer unique insight into patterns of viral tropism and spread, defining initial stages of congenital HCMV transmission, and can facilitate evaluation of the effects of new antiviral interventions within the maternal-fetal interface milieu.

Infant lungs are preferentially infected by adenovirus and herpes simplex virus type 1 vectors: role of the tissue mesenchymal cells.

BACKGROUND: Adenovirus (AD) and herpes-simplex-virus-1 (HSV-1) have been extensively applied as vectors for gene and cancer therapy in clinical trials. AD5, from which the vector was constructed, is a common respiratory virus that infects mainly infants, yet the reasons for infant sensitivity to infection, other than immunity, are not clear. HSV-1, usually a neurotropic virus, may also cause severe pneumonia or disseminated diseases in infants and immunocompromised patients. METHODS: The tropism of these viruses to different human and mouse lung tissues of newborn and adult was studied in an ex vivo organ culture and it was also applied in vivo using a murine model. RESULTS: The data obtained indicated preferential viral infection of young lung tissues versus adult tissues in organ culture. Further studies indicated that the preferential infection of young tissues was not related to differences in receptor expression or exposure but rather to the different distribution of cell types in these tissues. Murine and human young lungs consist of a relative abundance of mesenchymal cells and these cells were much more susceptible to viral infection compared to adjacent epithelial-pneumocyte cells. These observations were further confirmed using an in vivo model of mouse infection. CONCLUSIONS: The similarity of the human and mouse tissues, with respect to viral vector tropism, validates the mouse model in studies of gene transfer to the lung. Furthermore, the results should facilitate the improved design of gene therapy trials for lung-related diseases in young and adults patients. Copyright © 2011 John Wiley & Sons, Ltd.

Tropism of lentiviral vectors in skin tissue.

The skin is an attractive tissue for gene therapy applications to treat genetic disorders and to express systemically delivered transgenes encoding therapeutic proteins. Understanding the tissue tropism of vectors is a prerequisite for the design of gene therapy trials. Using an ex vivo system of organ culture, we studied factors that determined viral tropism to the epidermal and dermal cells in human and mouse skin. We applied in these studies a lentiviral vector pseudotyped with two glycoproteins that use different cell receptors (vesicular stomatitis virus glycoprotein [VSV-G] and amphotropic murine leukemia virus envelope). The extent of infection with the amphotropic pseudotype was much higher than that of VSV-G, especially at low multiplicities of infection. In contrast, the tropism of these two pseudotypes in skin tissues was similar; at low multiplicities the infection was limited to areas near the basal layer of the epidermis, whereas at high multiplicities the infection extended to the dermal layer. To overcome physical barriers in the skin, the epidermal and dermal layers were separated and infected. Whereas the human epidermis was readily infected, we could not detect infection of stem and early progenitor cells in their niche. In contrast, mouse epidermis was completely resistant to infection. Dermal cells of both species were readily infected with the two pseudotypes. Molecular analysis indicated that infection of mouse epidermal cells was restricted after proviral DNA synthesis and before integration. In conclusion, we show that lentiviral tropism in a solid tissue is dependent on several factors, extra- and intracellular, distinct of the cellular receptors.

Gene delivery by viral vectors in primary cultures of lacrimal gland tissue.

PURPOSE: To test the feasibility of gene transfer into lacrimal gland tissue in primary culture, using different viral vectors. METHODS: Lacrimal glands were dissected from adult Sabra rats and divided by pincers to 0.3-0.4 mm fragments. Tissue was maintained under primary organ culture conditions using the "raft" technique. The ability of three different viral vectors to conduct beta-galactosidase (beta-gal) gene delivery was examined: adenovirus (Ad5CMVLacZ), vaccinia (VSC9), and herpesvirus (tkLTRZ(1)). Tissue fragments were incubated for 60 minutes with one of the viral vectors and transferred to fresh medium. After 3 and 7 days, beta-gal expression was examined by X-gal staining in gross preparations and in histologic sections. RESULTS: At 3 days, beta-gal expression was observed in 33% of tissue fragments exposed to the vaccinia vector and in 18% and 14% of fragments exposed to the adenoviral and herpes vectors, respectively. After 7 days in culture, successful gene delivery occurred in 77% of vaccinia, 41% of adenovirus, and only 13% of herpesvirus applications. Vector-specific reporter gene expression patterns were observed: With the vaccinia vector, lacrimal duct cells were predominantly stained; in contrast, the adenoviral vector tended to transduce the interacinar areas, with beta-gal expression mainly occurring within the myoepithelial cells. CONCLUSIONS: Vaccinia and adenovirus are efficient vectors for gene transfer into lacrimal gland tissue in primary culture. The specific expression pattern obtained by the vaccinia vector probably reflects its characteristic tissue tropism to lacrimal duct cells. The results presented in this ex vivo system may be a first step toward expressing genes with products that could be continuously delivered to the eye through the tears. Such proteins could include anti-inflammatory, anti-angiogenic, anti-herpetic, anti-bacterial, or anti-glaucomatous agents, among others.

Viral mediated gene transfer to sprouting blood vessels during angiogenesis.

Several experimental systems have been applied to investigate the development of new blood vessels. Angiogenesis can be followed ex-vivo by culturing explants of rat aorta 'rings' in biomatrix gels. This angiogenesis system was modified for the study of viral vector mediated gene transfer, using adenovirus, vaccinia- and retroviral vectors. Two modifications were introduced to the model in order to facilitate efficient viral mediated gene transfer, (i) placing the aorta ring on top of a thin layer of collagen such that the angiogenic tissue will be accessible to the viral vector; and (ii) infection of the aorta rings prior to embedding them into the collagen matrix. While adenovirus and vaccinia vectors infected efficiently the aorta rings they induced cell death. Subsequent gene transfer experiments were, therefore, carried with retroviral vectors containing vascular endothelial growth factor (VEGF) and the beta-interferon (IFN) genes. Overexpression of VEGF enhanced significantly microvessel sprouting, while overexpression of IFN-beta induced an antiviral effect. The experimental system described in this study can facilitate the application of other viral vectors to the study of genes that may regulate the complex angiogenic process and thereby open new avenues for vascular gene therapy.

Integrated strategy for the production of therapeutic retroviral vectors.

The broad application of retroviral vectors for gene delivery is still hampered by the difficulty to reproducibly establish high vector producer cell lines generating sufficient amounts of highly concentrated virus vector preparations of high quality. To enhance the process for producing clinically relevant retroviral vector preparations for therapeutic applications, we have integrated novel and state-of-the-art technologies in a process that allows rapid access to high-efficiency vector-producing cells and consistent production, purification, and storage of retroviral vectors. The process has been designed for various types of retroviral vectors for clinical application and to support a high-throughput process. New modular helper cell lines that permit rapid insertion of DNA encoding the therapeutic vector of interest at predetermined, optimal chromosomal loci were developed to facilitate stable and high vector production levels. Packaging cell lines, cultivation methods, and improved medium composition were coupled with vector purification and storage process strategies that yield maximal vector infectivity and stability. To facilitate GMP-grade vector production, standard of operation protocols were established. These processes were validated by production of retroviral vector lots that drive the expression of type VII collagen (Col7) for the treatment of a skin genetic disease, dystrophic epidermolysis bullosa. The potential efficacy of the Col7-expressing vectors was finally proven with newly developed systems, in particular in target primary keratinocyte cultures and three-dimensional skin tissues in organ culture.

Gene transfer mediated by different viral vectors following direct cannulation of mouse submandibular salivary glands.

The salivary gland has been suggested as an accessible organ for gene transfer to express recombinant proteins locally in the saliva, as well as for secretion to the blood circulation. The aim of this study was to evaluate the efficiency of gene transfer to salivary glands using different viral vectors: adenovirus, vaccinia, herpes simplex type 1 (HSV), and two retroviral vectors (murine leukemia virus (MuLV) and lentivirus). We show, by in situ staining and beta-galactosidase reporter activity assay, that the adenoviral and vaccinia vectors were able to deliver the reporter gene efficiently to acinar and duct cells. The HSV vector was less efficient and infected only the acinar cells. The lentiviral vector infected acinar and duct cells, but at a relatively low efficiency. The MuLV vector did not infect the salivary gland unless cell proliferation was induced. Host immune responses to viral infection, inflammation, apoptosis and lymphocyte infiltration, in the transduced glands, were assessed. The DNA viral vectors induced local lymphocyte infiltration and apoptosis. In contrast, the retroviral vectors did not induce an immune response. Our results describe the outcome of salivary gland infection with each of the five different viral vectors and indicate their advantages and limitations for transferring genes to the salivary glands.