Vaccinia virus serves as an efficient vector for expressing heterologous proteins in human NTera 2 neurons

Vaccinia virus infection and gene transduction in cultured neurons

The study of neurons in culture would benefit from the development of a gene transduction system capable of delivering foreign genes at high efficiency, as transduction of primary neurons with existing systems is inefficient. The efficacy of lytic vaccinia virus (VV) infection of primary retinal cultures and PC12 cells (a model of neuronal differentiation) was examined in order to determine the efficiency of gene transduction using VV in neuronal primary culture. VV was able to infect retinal cells and PC12 cells and express transgenes of Escherichia coli beta-galactosidase (lacZ) and epithelial fatty acid binding protein (E-FABP) in a virus dose-dependent manner. Most (50-100%) of the retinal cells were positive for transgene protein at multiplicities of infection (MOI) between 10 and 100 plaque-forming units (PFU), while over 50% of VV-infected PC12 cells expressed the virus encoded gene at an MOI = 10. The production of foreign mRNA and protein by VV following infection was verified by PCR and Western blot. Because VV is a lytic virus, cytopathic effects were examined. Retinal cultures maintained for 0.5 days in vitro showed greater than 90% survival at 24 h post-infection, while 14-day cultures were equally viable for 48 h. Retinal ganglion cells and differentiated PC12 cells appear to be more protected against lytic VV infection than proliferating glial and undifferentiated PC12 cells. These data suggest that VV may be a useful vector for delivering foreign genes to neuronal cells with an efficient transient transgene expression.

Genetically modified NT2N human neuronal cells mediate long-term gene expression as CNS grafts in vivo and improve functional cognitive outcome following experimental traumatic brain injury

Human Ntera-2 (NT2) cells can be differentiated in vitro into well-characterized populations of NT2N neurons that engraft and mature when transplanted into the adult CNS of rodents and humans. They have shown promise as treatments for neurologic disease, trauma, and ischemic stroke. Although these features suggest that NT2N neurons would be an excellent platform for ex vivo gene therapy in the CNS, stable gene expression has been surprisingly difficult to achieve in these cells. In this report we demonstrate stable, efficient, and nontoxic gene transfer into undifferentiated NT2 cells using a pseudotyped lentiviral vector encoding the human elongation factor 1-alpha promoter and the reporter gene eGFP. Expression of eGFP was maintained when the NT2 cells were differentiated into NT2N neurons after treatment with retinoic acid. When transplanted into the striatum of adult nude mice, transduced NT2N neurons survived, engrafted, and continued to express the reporter gene for long-term time points in vivo. Furthermore, transplantation of NT2N neurons genetically modified to express nerve growth factor significantly attenuated cognitive dysfunction following traumatic brain injury in mice. These results demonstrate that defined populations of genetically modified human NT2N neurons are a practical and effective platform for stable ex vivo gene delivery into the CNS.

Functional expression of L-, N-, P/Q-, and R-type calcium channels in the human NT2-N cell line

The biophysical and pharmacological properties of voltage-gated calcium channel currents in the human teratocarcinoma cell line NT2-N were studied using the whole cell patch-clamp technique. When held at -80 mV, barium currents (I(Ba)s) were evoked by voltage commands to above -35 mV that peaked at +5 mV. When holding potentials were reduced to -20 mV or 5 mM barium was substituted for 5 mM calcium, there was a reduction in peak currents and a right shift in the current-voltage curve. A steady-state inactivation curve for I(Ba) was fit with a Boltzmann curve (V(1/2) = -43.3 mV; slope = -17.7 mV). Maximal current amplitude increased from 1-wk (232 pA) to 9-wk (1025 pA) postdifferentiation. Whole cell I(Ba)s were partially blocked by specific channel blockers to a similar extent in 1- to 3-wk and 7- to 9-wk postdifferentiation NT2-N cells: 10 microM nifedipine (19 vs. 25%), 10 microM conotoxin GVIA (27 vs. 25%), 10 microM conotoxin MVIIC (15 vs. 16%), and 1.75 microM SNX-482 (31 vs. 33%). Currents were completely blocked by 300 microM cadmium. In the presence of nifedipine, GVIA, and MVIIC, approximately 35% of current remained, which was reduced further by SNX-482 (7-14% of current remained), consistent with functional expression of L-, N-, and P/Q-calcium channel types and one or more R-type channel. The presence of multiple calcium currents in this human neuronal-type cell line provides a potentially useful model for study of the regulation, expression and cellular function of human derived calcium channel currents; in particular the R-type current(s).

Characterization of promoter function and cell-type-specific expression from viral vectors in the nervous system

Viral vectors have become important tools to effectively transfer genes into terminally differentiated cells, including neurons. However, the rational for selection of the promoter for use in viral vectors remains poorly understood. Comparison of promoters has been complicated by the use of different viral backgrounds, transgenes, and target tissues. Adenoviral vectors were constructed in the same vector background to directly compare three viral promoters, the human cytomegalovirus (CMV) immediate-early promoter, the Rous sarcoma virus (RSV) long terminal repeat, and the adenoviral E1A promoter, driving expression of the Escherichia coli lacZ gene or the gene for the enhanced green fluorescent protein. The temporal patterns, levels of expression, and cytotoxicity from the vectors were analyzed. In sensory neuronal cultures, the CMV promoter produced the highest levels of expression, the RSV promoter produced lower levels, and the E1A promoter produced limited expression. There was no evidence of cytotoxicity produced by the viral vectors. In vivo analyses following stereotaxic injection of the vector into the rat hippocampus demonstrated differences in the cell-type-specific expression from the CMV promoter versus the RSV promoter. In acutely prepared hippocampal brain slices, marked differences in the cell type specificity of expression from the promoters were confirmed. The CMV promoter produced expression in hilar regions and pyramidal neurons, with minimal expression in the dentate gyrus. The RSV promoter produced expression in dentate gyrus neurons. These results demonstrate that the selection of the promoter is critical for the success of the viral vector to express a transgene in specific cell types.

Intrastriatal and intranigral grafting of hNT neurons in the 6-OHDA rat model of Parkinson's disease

The clinical findings on neural transplantation for Parkinson's disease (PD) reported thus far are promising but many issues must be addressed before neural transplantation can be considered a routine therapeutic option for PD. The future of neural transplantation for the treatment of neurological disorders may rest in the discovery of a suitable alternative cell type for fetal tissue. One such alternative may be neurons derived from a human teratocarcinoma (hNT). hNT neurons have been shown to survive and integrate within the host brain following transplantation and provide functional recovery in animal models of stroke and Huntington's disease. In this study, we describe the transplantation of hNT neurons in the substantia nigra (SN) and striatum of the rat model for PD. Twenty-seven rats were grafted with one of three hNT neuronal products; hNT neurons, hNT-DA neurons, or lithium chloride (LiCl) pretreated hNT-DA neurons. Robust hNT grafts could be seen with anti-neural cell adhesion molecule and anti-neuron-specific enolase immunostaining. Immunostaining for tyrosine hydroxylase (TH) expression revealed no TH-immunoreactive (THir) neurons in any animals with hNT neuronal grafts. THir cells were observed in 43% of animals with hNT-DA neuronal grafts and all animals with LiCl pretreated hNT-DA neuronal grafts (100%). The number of THir neurons in these animals was low and not sufficient to produce significant functional recovery. In summary, this study has demonstrated that hNT neurons survive transplantation and express TH in the striatum and SN. Although hNT neurons are promising as an alternative to fetal tissue and may have potential clinical applications in the future, further improvements in enhancing TH expression are needed.

Recombinant vaccinia viruses. Design, generation, and isolation

The technologies of recombinant gene expression have greatly enhanced the structural and functional analyses of genetic elements and proteins. Vaccinia virus, a large double-stranded DNA virus and the prototypic and best characterized member of the poxvirus family, has been an instrumental tool among these technologies and the recombinant vaccinia virus system has been widely employed to express genes from eukaryotic, prokaryotic, and viral origins. Vaccinia virus is also the prototype live viral vaccine and serves as the basis for well established viral vectors which have been successfully evaluated as human and animal vaccines for infectious diseases and as anticancer vaccines in a variety of animal model systems. Vaccinia virus technology has also been instrumental in a number of unique applications, from the discovery of new viral receptors to the synthesis and assembly of other viruses in culture. Here we provide a simple and detailed outline of the processes involved in the generation of a typical recombinant vaccinia virus, along with an up to date review of relevant literature.