Chapter 6: Gene Therapy and Viral Vectors: An Overview on Current Trends
50
as viral vectors expressing a therapeutic gene of
interest, into the patient directly.6
Typical considerations for the vector of
choice include the targeted indication and its
pathogenesis, identity, and characteristics of the
target cells, size of the genetic cargo, and desired
duration of gene expression required (sustained
or long term). However, insights gleaned from
the rapid advancements in the field bear addi-
tional concerns, including immunogenicity,
cytotoxicity, and genotoxicity, as well as the high
cost of manufacturing these gene therapy prod-
ucts at a sufficient scale to meet demand.
Non-Viral Vectors
In gene therapy, non-viral vectors include naked
plasmid DNA and chemical-based systems,
such as lipids, polymers, and inorganic particles
used to introduce the genetic materials inside
the cells.7 These vectors are typically less costly
to manufacture, are unencumbered by the size
of the nucleic acid to be delivered and may have
a better genotoxicity safety profile compared to
their viral vector counterparts due to lack of inte-
gration into the host genomic DNA. However, a
primary issue with the use of non-viral vectors is
their low transfection efficiency, which conse-
quently leads to low gene expression. Efforts
to circumvent this inefficiency include more
efficient delivery methods, such as electropo-
ration, wherein an electrical pulse temporarily
destabilizes the cell membrane to increase uptake
of the non-viral vector, or through the use of
lipid nanoparticle-based technologies.8 In 2018,
FDA approved an infusion treatment based on a
lipid nanoparticle delivery system.9
Bacterial vectors also are non-viral deliv-
ery systems largely used in cancer gene therapy.
Attenuated bacterial species, such as Listeria,
Escherichia coli, Clostridium, or Salmonella have
been used. Bactofection, which is an approach
that uses bacteria to deliver therapeutic genes of
interest to target cells, has been used successfully
in preclinical mouse models of disease. However,
despite the promising efficacy of bacterial vectors
in the killing of cancer cells in in vitro and in
in vivo animal models, this approach has fallen
short in human studies.10,11
Viral Vectors
The use of viruses in the delivery of therapeutic
genes of interest into target cells, arguably, have
been the most commonly used gene therapy
approach. Viral vectors regulated by OTAT
include12 but are not limited to:
• Adenovirus
• Adeno-associated virus (AAV)
• Herpes simplex virus
• Lentivirus
• Retrovirus
• Pox virus
Table 6-1. NIH Funding of Research Areas and Disease Conditions
Research Area/Disease Condition 2008 Fundinga 2020 Fundinga 2022 Fundinga,b
Biotechnology $5,179 $7,767 $7,912
Cancer Genomics -$1,098 $1,152
Gene Therapy $249 $403 $423
Immunotherapy -$1,769 $1,789
Precision Medicine -$2,078 $2,167
Regenerative Medicine $723 $1,126 $1,191
Stem Cellc $1,176 $2,555 $2,707
a Funding data for the fiscal year 2008, 2020, and 2022 as dollars in millions.
b Estimated funding value for 2022.
c Funding for pluripotent stem cell research including embryonic human and non-human sources.
Note: “-” indicates a new category. Funding information is not available.
Source: National Institutes of Health
50
as viral vectors expressing a therapeutic gene of
interest, into the patient directly.6
Typical considerations for the vector of
choice include the targeted indication and its
pathogenesis, identity, and characteristics of the
target cells, size of the genetic cargo, and desired
duration of gene expression required (sustained
or long term). However, insights gleaned from
the rapid advancements in the field bear addi-
tional concerns, including immunogenicity,
cytotoxicity, and genotoxicity, as well as the high
cost of manufacturing these gene therapy prod-
ucts at a sufficient scale to meet demand.
Non-Viral Vectors
In gene therapy, non-viral vectors include naked
plasmid DNA and chemical-based systems,
such as lipids, polymers, and inorganic particles
used to introduce the genetic materials inside
the cells.7 These vectors are typically less costly
to manufacture, are unencumbered by the size
of the nucleic acid to be delivered and may have
a better genotoxicity safety profile compared to
their viral vector counterparts due to lack of inte-
gration into the host genomic DNA. However, a
primary issue with the use of non-viral vectors is
their low transfection efficiency, which conse-
quently leads to low gene expression. Efforts
to circumvent this inefficiency include more
efficient delivery methods, such as electropo-
ration, wherein an electrical pulse temporarily
destabilizes the cell membrane to increase uptake
of the non-viral vector, or through the use of
lipid nanoparticle-based technologies.8 In 2018,
FDA approved an infusion treatment based on a
lipid nanoparticle delivery system.9
Bacterial vectors also are non-viral deliv-
ery systems largely used in cancer gene therapy.
Attenuated bacterial species, such as Listeria,
Escherichia coli, Clostridium, or Salmonella have
been used. Bactofection, which is an approach
that uses bacteria to deliver therapeutic genes of
interest to target cells, has been used successfully
in preclinical mouse models of disease. However,
despite the promising efficacy of bacterial vectors
in the killing of cancer cells in in vitro and in
in vivo animal models, this approach has fallen
short in human studies.10,11
Viral Vectors
The use of viruses in the delivery of therapeutic
genes of interest into target cells, arguably, have
been the most commonly used gene therapy
approach. Viral vectors regulated by OTAT
include12 but are not limited to:
• Adenovirus
• Adeno-associated virus (AAV)
• Herpes simplex virus
• Lentivirus
• Retrovirus
• Pox virus
Table 6-1. NIH Funding of Research Areas and Disease Conditions
Research Area/Disease Condition 2008 Fundinga 2020 Fundinga 2022 Fundinga,b
Biotechnology $5,179 $7,767 $7,912
Cancer Genomics -$1,098 $1,152
Gene Therapy $249 $403 $423
Immunotherapy -$1,769 $1,789
Precision Medicine -$2,078 $2,167
Regenerative Medicine $723 $1,126 $1,191
Stem Cellc $1,176 $2,555 $2,707
a Funding data for the fiscal year 2008, 2020, and 2022 as dollars in millions.
b Estimated funding value for 2022.
c Funding for pluripotent stem cell research including embryonic human and non-human sources.
Note: “-” indicates a new category. Funding information is not available.
Source: National Institutes of Health