Non-replicating viral vector-based AIDS vaccines: interplay between viral vectors and the immune system.

During the past 20 years, the development of HIV vaccines has come a long way. The focus has progressively changed from the traditional protein-based HIV vaccines that induce humoral immunity to the live recombinant viral vector-based HIV vaccines capable of eliciting both cellular and humoral immune responses. These new viral vector-based vaccines encoding multiple HIV antigens, delivered either alone or in heterologous prime-boost modalities elicited antigen-specific CTL responses in immunized hosts and protected animals from disease. The viral vector-based vaccines have proven to be potent vaccines in pre-clinical studies and foster the hope to put an end to the ever-increasing threat of the AIDS epidemic. Several unique features of viral vector-based HIV vaccines have contributed to their success, including their intrinsic immune-modulating properties, high transduction efficiency, and in vivo production of immunogens within the cell mimicking a natural infection without the associated health risks. In this review, we will discuss the characteristics of non-replicating viral vectors most commonly used for HIV vaccines with a particular focus on immune responses elicited by the vector particles alone and their effect on the potency of viral vector-based HIV vaccines.

Feline immunodeficiency virus vectors. Gene transfer to mouse retina following intravitreal injection.

BACKGROUND: Transduction of the murine retinal pigmented epithelium (RPE) with adenovirus vectors requires technically difficult and invasive subretinal injections. This study tested the hypothesis that recombinant vectors based on feline immunodeficiency virus (FIV) could access the retina following intravitreal injection. METHODS: FIV vectors expressing E. coli beta-galactosidase (FIVbetagal) were injected alone, or in combination with adenovirus vectors expressing eGFP, into the vitreous of normal mice and eyes evaluated for transgene expression. In further studies, the utility of FIV-mediated gene transfer to correct lysosomal storage defects in the anterior and posterior chambers of eyes was tested using recombinant FIV vectors expressing beta-glucuronidase. FIVbetagluc vectors were injected into beta-glucuronidase-deficient mice, an animal model of mucopolysacharridoses type VII. RESULTS: The results of this study show that similar to adenovirus, both corneal endothelium and cells of the iris could be transduced following intravitreal injection of FIVbetagal. However, in contrast to adenovirus, intravitreal injection of FIVbetagal also resulted in transduction of the RPE. Immunohistochemistry following an intravitreal injection of an AdeGFP (adenovirus expressing green fluorescent protein) and FIVbetagal mixture confirmed that both viruses mediated transduction of corneal endothelium and cells of the iris, while only FIVbetagal transduced cells in the retina. Using the beta-glucuronidase-deficient mouse, the therapeutic efficacy of intravitreal injection of FIVbetagluc (FIV expressing beta-glucuronidase) was tested. Intravitreal injection of FIVbetagluc to the eyes of beta-glucuronidase-deficient mice resulted in rapid reduction (within 2 weeks) of the lysosomal storage defect within the RPE, corneal endothelium, and the non-pigmented epithelium of the ciliary process. Transgene expression and correction of the lysosomal storage defect remained for at least 12 weeks, the latest time point tested. CONCLUSION: These studies demonstrate that intravitreal injection of FIV-based vectors can mediate efficient and lasting transduction of cells in the cornea, iris, and retina.

Functional correction of established central nervous system deficits in an animal model of lysosomal storage disease with feline immunodeficiency virus-based vectors.

Gene transfer vectors based on lentiviruses can transduce terminally differentiated cells in the brain; however, their ability to reverse established behavioral deficits in animal models of neurodegeneration has not previously been tested. When recombinant feline immunodeficiency virus (FIV)-based vectors expressing beta-glucuronidase were unilaterally injected into the striatum of adult beta-glucuronidase deficient [mucopolysaccharidosis type VII (MPS VII)] mice, an animal model of lysosomal storage disease, there was bihemispheric correction of the characteristic cellular pathology. Moreover, after the injection of FIV-based vectors expressing beta-glucuronidase into brains of beta-glucuronidase-deficient mice with established impairments in spatial learning and memory, there was dramatic recovery of behavioral function. Cognitive improvement resulting from expression of beta-glucuronidase was associated with alteration in expression of genes associated with neuronal plasticity. These data suggest that enzyme replacement to the MPS VII central nervous system goes beyond restoration of beta-glucuronidase activity in the lysosome, and imparts improvements in plasticity and spatial learning.

Viral-mediated gene transfer to mouse primary neural progenitor cells.

Neural progenitor cells may provide for cell replacement or gene delivery vehicles in neurodegen-erative disease therapies. The expression of therapeutic proteins by neural progenitors would be enhanced by viral-mediated gene transfer, but the effects of several common recombinant viruses on primary progenitor cell populations have not been tested. To address this issue, we cultured cells from embryonic day 16-18 mouse brain in serum-free medium containing epidermal growth factor or basic fibroblast growth factor, and investigated how transduction with recombinant viral vectors affected maintenance and differentiation properties of progenitor cells. Neurosphere cultures were incubated with feline immunodeficiency virus (FIV), adeno-associated virus (AAV) or ade-noviral (Ad) constructs expressing either beta-galactosidase or enhanced green fluorescent protein at low multiplicity of infection. Nestin-positive neurospheres were regenerated after incubation of single progenitor cells with FIV, indicating that FIV-mediated gene transfer did not inhibit progenitor cell self-renewal. In contrast, adenovirus induced differentiation into glial fibrillary acidic protein (GFAP)-positive astrocytes. The AAV serotypes tested did not effectively transduce progenitor cells. FIV-transduced progenitors retained the potential for differentiation into neurons and glia in vitro, and when transplanted into the striatum of normal adult C57BL/6 mice differentiated into glia, or remained undifferentiated. In the presence of tumor cells, FIV-transduced progenitors migrated significantly from the injection site. Our results suggest that FIV-based vectors can transduce progenitor cell populations in vitro, with maintenance of their ability to differentiate into multiple cell types or to respond to injury within the central nervous system. These results hold promise for the use of genetically manipulated stem cells for CNS therapies.