Viral Manipulation of Neural Stem/Precursor Cells - Viral Vector Approaches in Neurobiology and Brain Diseases - page 259

spherical aggregates termed neurospheres, in response to basic
fibroblast growth factor (bFGF) and epidermal growth factor
(EGF), while remaining karyotypically stable and under normal cell
cycle control [ 13 - 15 ]. Upon mitogen withdrawal, NPCs still retain
the ability to give rise to a differentiated progeny in vitro [ 16 ].
Most of the above-mentioned characteristics make NPCs an
attractive source for the generation of stable and CNS lineage-
matched cell lines with high therapeutic potential. Indeed, solid
evidences from our and many other laboratories exist that NPCs
survive transplantation procedures in the host CNS, specifically
migrate within the damaged tissue, and protect the nervous system
from inflammatory and other forms of damage [ 15 , 17 - 28 ].
Furthermore, viral vectors can be successfully used to improve
NPCs properties both for ex vivo (e.g., through NPC viral manip-
ulation before transplantation) and for in vivo manipulation (e.g.,
by injecting in the animal the viral particles) of the CNS, with sev-
eral different applications [ 29 , 30 ].
For example, NPCs can be tagged with a reporter gene (e.g.,
luciferase, green fluorescent protein, etc.) in order to study neuro-
genesis [ 31 ] or to monitor cells after transplantation; in the latter
case this allows an improvement of the treatment conditions, study-
ing the survival time, the extent of migration, and the degree of
NPC differentiation in situ [ 32 , 33 ]. Furthermore, the integrating
viral vectors are being used to make NPCs as gene delivery system,
thus forcing the NPCs to express exogenous proteins relevant in
the context of different neurodegenerative disorders to improve
novel brain repair strategies. A popular strategy is to use NPCs to
deliver growth and survival factors after a CNS damage, such as
brain-derived neurotrophic factor (BDNF) in degenerating neu-
rons or spinal cord injury [ 34 , 35 ]; fibroblast growth factor (FGF)-2
after brain damage [ 36 ]; insulin-like growth factor (IGF)-1 for
brain repair and Parkinson disease [ 37 , 38 ]; glial-derived growth
factor (GDNF) in amyotrophic lateral sclerosis, Parkinson and
Huntington diseases [ 24 , 39 - 41 ] and bone morphogenetic protein
(BMP) inhibitors in spinal cord injury [ 42 ]; and the β-glucuronidase
in the Mucopolysaccharidosis type VII [ 43 ].
NPCs are also intrinsically able to generate a differentiated
progeny, giving rise to astrocytes, neurons, and oligodendrocytes,
in different proportions depending on the developmental stage
and area of derivation and differentiation conditions. Viral vectors
have also been recently used in order to foster NPC differentiation
toward a specific lineage of interest by forcing the expression of
one or more transcription factors. For example, lentiviral vector
encoding for Nurr1 and/or Pitx3 have been used to direct NPCs
toward the generation of dopaminergic neurons in vitro [ 44 - 46 ].
Similarly, to promote the generation of oligodendrocytes in vitro,
NPCs have been transduced with vectors encoding for, among the
others, Olig1, Olig2, and Sox10 [ 47 , 48 ]. Interestingly, a retrovi-
ral vector encoding for Ascl1/Mash1 has been used to redirect the