antibodies [27] or T-cells [28] are innate. Fourth, the baculovirus
production is established on an industrial scale reaching high viral
titers (>10
9 pfu/mL) [29]. Fifth, the production conditions are
economically favorable as the virus is cultivated at 27
C in serumfree medium without CO 2, and subsequently stored at 4
C [30].
The aforementioned advantages make the BV very suitable for
gene therapy, although further adaptations are possible to increase
the efficiency of the gene transfer into human/mammalian cells.
Genetic modifications of the BV may positively influence the transduction efficiency in mammalian cells. Modifications include
(I) pseudotyping, (II) the integration of a corresponding promoter,
and (III) the utilization of regulatory elements.
Pseudotyping (I) means, producing baculoviruses in combination with foreign viral envelope proteins. The glycoprotein G of the
vesicular stomatitis virus (VSV), short VSV-G, is suitable to pseudotype the BV, and to enable the transduction of almost every
mammalian cell type [31–34]. Apart from an efficient transduction,
clearly the gene expression in the targeted cells or tissue is equally
important. This requires the selection of a strong mammalian promoter (II) and/or tissue-specific promoters [35, 36]. Numerous
studies have demonstrated the efficient transduction of different
cell lines and their gene expression under the control of mammalian
promoters, such as the cytomegalovirus (CMV) immediate early
promoter/enhancer, or the Rous sarcoma virus promoter [17, 37,
38]. Moreover, regulatory elements (III) (e.g., the Woodchuck
hepatitis virus posttranscriptional regulatory element) can be used
to enhance gene expression [39].
Different preclinical studies have shown the potential of the BV
as a viral vector targeting mammalian cells, for example for cancer
therapy [40–43] or bone regeneration purposes [44–47]. Apart
from these studies, future prospects of utilizing the baculovirus as
a vaccine vector are evaluated [16, 48–50].
As the pseudotyped and further optimized BV is an efficient
vector to deliver genetic information into human/mammalian
cells, they can be used to transduce human stem cells. The generated genetically modified stem cells are then applied as cell therapy
products. This combines the therapeutic effects of stem cells and
transferred nucleic acids, which may encode for proteins (e.g.,
growth factors) or downregulate certain genes [51]. The choice
of the target cell line strongly depends on the desired properties of
the product. Mesenchymal stem cells (MSC) have been shown to
be a favored cell type due to their immunomodulatory properties.
Accordingly, native MSCs are logical candidates for the treatment
of immune disorders, including the graft-versus-host disease, the
inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and diabetes [52]. Additionally, MSCs promote the regeneration of damaged tissue by stimulating cell proliferation and
migration, promoting angiogenesis, and suppressing apoptosis
Baculovirus-Mediated Gene Transfer to Stem Cells
369
production is established on an industrial scale reaching high viral
titers (>10
9 pfu/mL) [29]. Fifth, the production conditions are
economically favorable as the virus is cultivated at 27
C in serumfree medium without CO 2, and subsequently stored at 4
C [30].
The aforementioned advantages make the BV very suitable for
gene therapy, although further adaptations are possible to increase
the efficiency of the gene transfer into human/mammalian cells.
Genetic modifications of the BV may positively influence the transduction efficiency in mammalian cells. Modifications include
(I) pseudotyping, (II) the integration of a corresponding promoter,
and (III) the utilization of regulatory elements.
Pseudotyping (I) means, producing baculoviruses in combination with foreign viral envelope proteins. The glycoprotein G of the
vesicular stomatitis virus (VSV), short VSV-G, is suitable to pseudotype the BV, and to enable the transduction of almost every
mammalian cell type [31–34]. Apart from an efficient transduction,
clearly the gene expression in the targeted cells or tissue is equally
important. This requires the selection of a strong mammalian promoter (II) and/or tissue-specific promoters [35, 36]. Numerous
studies have demonstrated the efficient transduction of different
cell lines and their gene expression under the control of mammalian
promoters, such as the cytomegalovirus (CMV) immediate early
promoter/enhancer, or the Rous sarcoma virus promoter [17, 37,
38]. Moreover, regulatory elements (III) (e.g., the Woodchuck
hepatitis virus posttranscriptional regulatory element) can be used
to enhance gene expression [39].
Different preclinical studies have shown the potential of the BV
as a viral vector targeting mammalian cells, for example for cancer
therapy [40–43] or bone regeneration purposes [44–47]. Apart
from these studies, future prospects of utilizing the baculovirus as
a vaccine vector are evaluated [16, 48–50].
As the pseudotyped and further optimized BV is an efficient
vector to deliver genetic information into human/mammalian
cells, they can be used to transduce human stem cells. The generated genetically modified stem cells are then applied as cell therapy
products. This combines the therapeutic effects of stem cells and
transferred nucleic acids, which may encode for proteins (e.g.,
growth factors) or downregulate certain genes [51]. The choice
of the target cell line strongly depends on the desired properties of
the product. Mesenchymal stem cells (MSC) have been shown to
be a favored cell type due to their immunomodulatory properties.
Accordingly, native MSCs are logical candidates for the treatment
of immune disorders, including the graft-versus-host disease, the
inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and diabetes [52]. Additionally, MSCs promote the regeneration of damaged tissue by stimulating cell proliferation and
migration, promoting angiogenesis, and suppressing apoptosis
Baculovirus-Mediated Gene Transfer to Stem Cells
369