A2 Bioengineering Topics 2
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CRISPR-CAS9: A REVOLUTIONARY CANCER TREATMENT
Elliott Hammersley, [email protected], Sanchez 5:00, Claire Kraft, [email protected], Mena Lora 1:00
Abstract- This paper primarily addresses the next step in
cancer treatment: the use of clustered regularly interspaced
short palindromic repeats (CRISPR) and a Cas9 protein
complex in cancer treatment. Other topics covered in this
paper include background history of the CRISPR-Cas9
system, a detailed explanation of recent developments in
CRISPR-Cas9 technology, discussion of clinical trials,
proposed experiments, financial sustainability, life-saving
potential, and related ethical issues. Originally a bacterial
defense mechanism, CRISPR has been converted into a
technology that can edit the genome of any organism by
removing and replacing DNA strands. CRISPR-Cas9 is
highly programmable, allowing scientists to selectively create
double-stranded breaks in DNA and remove mutations or
otherwise detrimental sequences. Scientists are then able to
repair those breaks with manufactured DNA. The primary
application discussed in this paper is the use of CRISPR-Cas9
to replace three specific genes in human T cells. These three
edits work in conjunction to improve the immune cell’s ability
to locate cancerous cells, as well aim to boost its resiliency.
Overall, CRISPR-Cas9 engineered T cells are providing the
means for a monumental step forward in the war against
cancer.
Key words—cancer, cancer treatments, clinical trials,
CRISPR-Cas9, gene editing, sustainability, T cells
ENGINEERING WITH CRISPR-CAS9
Until recently, researchers could modify the genes of
only plants and animals, resulting in what are commonly
referred to as genetically modified organisms (GMOs). Now,
the clustered regularly interspaced short palindromic repeats
(CRISPR) and CRISPR-associated protein (Cas9)—
commonly referred to as the genome-editing tool CRISPRCas9—promise to simplify genetic engineering, healthcare,
and the human genome. Their potential to halt the
proliferation of viruses and cancer is opening new frontiers
for exploration in medicine, therapy, and engineering. One of
the newest relevant uses of this technology is in identifying
potential avenues of eradication for the Zika and Dengue
viruses. CRISPR-Cas9 enabled scientists to identify human
proteins that the viruses need to reproduce, which likely will
University of Pittsburgh, Swanson School of Engineering 1
Submission date: 03.31.2017
lead to development of vaccinations and treatments for these
two dangerous and costly diseases.
In addition, CRISPR-Cas9 is on the verge of clinical
trials for use in the fight against cancer. As mentioned in an
article about CRISPR pioneers in Time Magazine, CRISPR is
being used to edit the DNA of T cells, a type of immune cell
that locates and destroys infected cells directly within an
organism. The edited sections of DNA in the T cell are
responsible for the efficacy in targeting tumors and allow the
T cells to effectively attack cancerous cells [1]. If the trials
succeed, use of CRISPR-Cas9 on a larger scale is imminent,
particularly as a replacement for outdated and often
insufficient cancer treatments.
THE INSUFFICIENCY OF CURRENT
CANCER TREATMENTS
Understanding the deficiencies of current cancer
treatments requires examining their numerous side effects and
economic impacts. The treatments available, although they
provide a relatively high average success rate of 62%, as
calculated by the American Cancer Society, come with a
plethora of taxing side effects and exorbitant expenses for
patients and their families [2].
Treatments and Side Effects
Cancer is one of the most prolific diseases of this age.
The American Cancer Society estimates that in 2017 alone
nearly 1.7 million Americans will be diagnosed with cancer,
and roughly 600,000 Americans will die from a previously
diagnosed case [2]. The most common treatments—surgery,
chemotherapy, and radiation therapy, according to the
National Cancer Institute at the National Institutes of
Health—provide an opportunity for cancer patients to be
cured or at least relieved of symptoms [3]. The goal of using
surgery is to remove the tumor entirely, remove part of the
tumor so other treatments can work more effectively against
the cancer, or reduce the symptoms of the cancer. However,
as with many treatments, surgery involves side effects and
risks. For example, most people treated surgically experience
pain and a higher risk of infection afterward. Other
complications can include internal bleeding, harm to tissue
Elliott Hammersley
Claire Kraft
surrounding the incision site and the site of the cancer, and
adverse reactions to general anesthetics [3].
Both chemotherapy and radiation therapy are used to
cure cancer, curtail its growth, prevent its relapse, and reduce
its symptoms. They share some side effects, such as damage
to nearby cells, fatigue, nausea, and hair loss [3]. Patients
subjected to chemotherapy or radiation therapy run the risk of
long-term side effects, as well. As reported by Susan Scutti, a
correspondent for Medical Daily and Newsweek, in an article
on childhood cancer survivors, the primary cause of the longterm side effects is damage to DNA in healthy cells
surrounding the tumor site. The major long-term
consequences include cardiovascular complications,
cognitive and physical growth impairments, and secondary
cancer caused by the early DNA damage rather than
metastasis (spreading) from the original tumor. Malignant
conditions arise years later because, in most cases, the DNA
damage goes undetected [4]. While these side effects often
emerge in adults, most result from treating childhood cancers.
Dr. Gregory Armstrong, a member of the Department of
Epidemiology and Cancer Control at St. Jude Children’s
Research Hospital, noted that, thirty years after recovery from
childhood cancer, nearly 20% of survivors face a second bout
with cancer. He added that “childhood cancer survivors are
15 times more likely to die from a second cancer than the
general population dying from any cancer” [4] because of the
damage suffered by surrounding tissues during chemotherapy
and radiation therapy. New cancer treatments in the works
aim to reduce the costs, both biologically and financially,
affiliated with current treatments.
HISTORY OF CRISPR-CAS9
CRISPR-Cas9, a protein-based system that operates
using a section of repeating DNA, originated in the genome
of ancient bacteria, but it was not internationally recognized
as a revolutionary genome-editing technology until recently,
as explained in an interview for National Public Radio by
Michael Specter, a science and technology staff writer for The
New Yorker. In 1987, Japanese scientists noticed a strange
group of nucleotides in segments of DNA and, although they
did not know what it was or how it functioned, they published
their findings in the Journal of Bacteriology to inform the
scientific community of their discovery. Then, about ten years
later, at a Dannon yogurt factory, researchers noticed some of
their bacterial colonies died faster than others. Dannon
scientists analyzed several samples and observed the
difference between the living and the dying: bacteria that
lived had short palindromic segments of DNA—repeating
sequences of nucleotides—at a locus (specific location) in
their genome. However, it was not until several years later,
when Spanish biostatistician Dr. Francisco Mojica ran a
computer analysis of all known proteins, that a definitive
hypothesis emerged [8].
Mojica realized the DNA segments were pieces of
viruses, and the bacteria were using them as a sort of adaptive
immune system to identify and effectively fight viral
infections. The bacterial cells took in the DNA, spliced it
using proteins, and inserted it into their own DNA to be stored
as an encyclopedia of previous virulent attackers. The bacteria
then passed the viral DNA encyclopedia to its progeny as part
of its inherited genetic material. Because of this monumental
finding, CRISPR science began to evolve quite rapidly.
After understanding that CRISPR was used by bacteria
as a locater for specific DNA sequences, scientists homed in
on the possibility of manually programming the system.
Detailed in a profile by New York Times biotechnology
reporter Andrew Pollack, it was not until this application
came to light that Dr. Jennifer Doudna’s work at the
University of California, Berkeley, came to prominence [9].
A professor in molecular biology, cell biology, and chemistry,
Doudna and her colleague, Dr. Emmanuelle Charpentier,
manipulated various pieces of CRISPR-Cas9 in an attempt to
effectively program it. The idea was to be able to insert any
RNA sequence into the CRISPR system, have it seek out the
matching DNA sequence, and then replace it with a new piece
of DNA. Finally, after decades of research and development
by numerous renowned scientists, Doudna and her associates
had a breakthrough: they adapted the CRISPR-Cas9 system
as a research tool by using laboratory-engineered RNA and
proposed it as a method to edit the human genome. In June of
2012, the publication Science detailed the technique used by
Doudna and how it was destined to revolutionize the geneediting world [9].
Economic Impact
While a variety of side effects can accompany surgery,
chemotherapy, and radiation therapy, there is another harsh
reality associated with cancer treatment. According to John
Seffrin, CEO of the American Cancer Society, in an interview
with CNN, 20% of people with health insurance cannot afford
the cancer therapy necessary to save their lives [5]. For those
who can afford it, according to the U.S. News and World
Report, the average cost of cancer treatment is $10,000 per
month, with some new therapies topping $30,000 monthly.
Furthermore, there is an additional financial burden linked to
these expensive treatments: patients must pay for still more
drugs to mitigate the harsh side effects of surgery,
chemotherapy, and radiation therapy [6].
The cost-effectiveness of current cancer treatments was
evaluated in a study completed by Harvard University, the
National Cancer Institute, and the National Bureau of
Economic Research. The study estimated that, split between
healthcare providers and the afflicted, the average cost of an
additional year of life for localized and metastatic (spreading)
cancer patients is $403,142 and $1,190,332 respectively [7].
When considering the overall cost, it becomes apparent that a
more inexpensive treatment than current methods must be
developed.
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STRUCTURE AND FUNCTION
A CRISPR-Cas9 complex is composed of two
components: CRISPR and Cas9. Their functionality depends
on the organism in which they are placed. In bacteria, they
function together as a defense system to identify viral DNA,
cut it into segments, and insert it into the genes of the bacterial
host, so the viral DNA can be stored for reference. In human
DNA, CRISPR and Cas9 work as a genome-editing system.
In the human genome, engineered DNA is identified by Cas9
and inserted into the existing strand of DNA at the CRISPR
locus, effectively editing the human genes. To properly
understand the functionality of a CRISPR-Cas9 complex, it is
important to differentiate between the intricate structure and
function of each of its constituent parts [8].
FIGURE 1 [11]
Difference between CRISPR in bacteria and CRISPR
genome editing in humans with highlighted PAM
sequence.
CRISPR Component
In bacteria, CRISPR is a gene location that serves as a
storage site for viral DNA. As explained in a case study of
CRISPR gene editing in Cryptococcus neoformans, the gene
locus contains a long string of repeated DNA sequences that
act as spacers between inserted foreign DNA. Viral DNA is
recognized in the cell because of Protospacer Adjacent Motif
(PAM) sequences, which are small sections of DNA—usually
three base pairs in length—found in all viral DNA. The
typical composition of PAM is any base (adenine, cytosine,
thymine, or guanine) followed by two guanine nucleotides.
Once the CRISPR-associated (Cas) proteins identify DNA as
foreign, they copy the DNA between twenty-four and fortyeight base pairs downstream of the PAM sequence and place
it into the CRISPR site between two palindromic repeats of
approximately thirty base pairs each [10].
In human DNA, the CRISPR component of CRISPRCas9 is a gene locus, but it does not contain the palindromic
repeats, which are specific to bacteria. Rather, CRISPR serves
as a target site for implanting engineered genes. Cas9 creates
a double-stranded break at the CRISPR locus before
introducing the selected and engineered DNA, which contains
an embedded PAM sequence. Figure 1, taken from the
Howard Hughes Medical Institute, shows the difference
between the CRISPR defense system in bacteria and targeted
CRISPR edits in humans.
Cas9 Component
The Cas9 protein is responsible for locating and
cleaving target DNA, both in natural and artificial CRISPRCas9 systems. According to a CRISPR-Cas9 website by Tufts
University, Cas9 consists of six specific regions that each play
a different functional role: REC1, REC2, Bridge Helix, PAM
Interacting, RuvC, and HNH. The REC1 domain is the largest
and is responsible for binding guide RNA, a single-stranded
copy of a DNA sequence. This segment of genetic code is
used to locate the piece of host DNA that is targeted for
replacement. While the REC2 domain’s function is still not
well understood, it appears to have a distinct function from
the other regions in Cas9. The PAM Interacting region
specifically examines DNA until it reaches the PAM
sequence, which, in humans, corresponds to where
replacement will begin. RuvC nuclease is a domain that
initiates the cutting of the DNA strand that is not
complementary to the guide RNA. HNH nuclease is
responsible for cutting the other strand of DNA, which is
complementary to the guide RNA [12]. While all domains
have a separate structure and function, they all work in
concert to locate and cut targeted DNA strands. Figure 2, from
Tufts University, depicts the location and approximate shape
of each part of Cas9.
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from human to mosquito and from mosquito to human,
allowing wider spread of Dengue with travel and shipping.
Now, nearly half of the global population lives in areas where
there is a risk of contracting Dengue, and there are over
20,000 deaths from Dengue every year, most of them
children. No treatments or vaccines for Dengue are available
[14].
With only a few proteins of their own, the Zika and
Dengue viruses can commandeer a host cell’s proteins and
resources to grow and replicate, as discussed in an article
published by the University of Massachusetts Medical School
in ScienceDaily. The human proteins used by Zika and
Dengue remained a mystery prior to a breakthrough made
possible with the use of CRISPR-Cas9 and pioneered by a
team led by Abraham Brass, MD, PhD, at the University of
Massachusetts Medical School. With the help of his team, Dr.
Brass developed and tested the first CRISPR-Cas9 screen to
identify human proteins that the Zika and Dengue viruses
need for replication [15]. Because of this discovery, a vaccine
for these two prolific viruses may be available soon.
FIGURE 2 [12]
The six domains of the Cas9 protein shown in schematic,
crystal, and map form.
Lyme Disease
PREVIOUSLY DEVELOPED
APPLICATIONS
In Nantucket, Dr. Kevin Esvelt, a biochemist from
Harvard University, proposed a solution for dealing with
Lyme disease, which is a major problem on the island and is
swiftly making its way through the continental United States.
Approximately 40% of the island’s residents have been
infected, a number that is rapidly increasing. While many
people believe ticks are the source of Lyme disease, they are
merely an intermediary. Since the virus originates in whitefooted mice, Esvelt plans to focus on using CRISPR-Cas9 to
edit the genome of the mice and halt transmission.
Nantucket’s geographic isolation provides a controlled
environment and negligible chance of external interference. If
Esvelt’s team receives the green light from Nantucket
residents, it will breed a large number of mice that are immune
to Lyme disease and release them into the wild to create a
gene drive. Because ethical concerns could arise from his
proposal, Esvelt has agreed to proceed with his experiment
only as long as the community continues to show support [8].
As discussed by Michael Specter in an article on
CRISPR gene editing for The New Yorker, a gene drive
nullifies the rules of traditional Mendelian inheritance.
Normal inheritance dictates that the offspring of any sexuallyreproduced organism receives half its genome from each
parent. However, since the 1940s, scientists have known that
some genes are more dominant than others; they have better
than a 50% chance of being inherited [16]. Taking advantage
of this gene trait, scientists will use CRISPR-Cas9 to edit the
DNA of parent organisms and ensure the edited gene will
spread through the white-footed mouse population. This
application of CRISPR-Cas9 technology has the potential to
end a disease that currently has no vaccine or precautionary
treatment. According to an article in Oxford Academic, a
peer-reviewed journal, CRISPR-Cas9 has also proven
In the last fifteen years, CRISPR-Cas9 funding and
application have increased dramatically, and, consequently,
new possibilities and ideas have emerged. Some of the most
recent proposals and uses include eradication of viruses and
revolutionary cancer treatments. Furthermore, progress has
been made with genomic maladies such as Huntington’s
disease and sickle-cell anemia. Most recently, a proposal
arose to use CRISPR-Cas9 in treating Lyme disease. These
applications, in addition to aiding in the eradication and
treatment of diseases, will alter both the economic and
ecological footprints of these maladies.
Zika and Dengue
According to the Centers for Disease Control and
Prevention (CDC), Zika, first isolated from a macaque in
Africa, suddenly emerged in Micronesia in 2007, rapidly
expanded into Southeast Asia, and then into Brazil by May
2015. Several severe risks are associated with Zika, including
serious birth defects and pregnancy complications. Zika is
transferrable through bodily fluids and mosquitoes.
Mosquito-borne Zika is preventable but is immune to all
treatments attempted. As a result, the World Health
Organization declared it a public health emergency in
February of 2016[13].
Dengue originally was found only in Africa and
Southeast Asia, as stated in another article by the CDC.
However, with the increased shipping of cargo during World
War II in the mid-1900s, the virus spread, carried by
mosquitoes in the cargo. The virus is transferred repeatedly
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effective with many other ailments, such as Huntington’s
disease and sickle-cell anemia, and has immense promise for
cancer treatments [17].
APPLICATIONS IN CANCER
A key objective in the fight against cancer is enabling
the human body to defend itself without using powerful drugs
or invasive procedures. CRISPR-Cas9 provides a way to
better equip the body for this fight using the patient’s own
immune cells, specifically T cells, to attack malignant tumors.
According to Nature International Weekly Journal of Science
and Genetic Engineering & Biotechnology News, there are
currently two major players in this type of CRISPR-Cas9
implementation: Dr. Carl June, director of translational
research and a professor of pathology and laboratory
medicine in the University of Pennsylvania’s Abramson
Cancer Center and Perelman School of Medicine, and Dr.
Michel Sadelain, director of the Center for Cell Engineering
at the Memorial Sloan Kettering Cancer Center. These two
researchers are using distinctly separate CRISPR-edited T cell
engineering methods to combat cancer. However, both types
of edited T cells will be able to evade detection by cancer
cells, allowing them to effectively attack and destroy the
disease and help patients avoid the majority of side effects that
result from current cancer treatments [21][22].
Economic and Environmental Impact
CRISPR-Cas9 applications in Zika, Dengue, and Lyme
disease have the potential to reduce the total cost of these
diseases, which includes more than just treatment. As
reported by Ed Leefeldt, an investigative and business
journalist for CBS News, women who contract Zika while
pregnant run the risk of birth defects in their children,
specifically microcephaly, a condition in which the child’s
head and brain are severely underdeveloped. The financial
estimate for lifelong care of each of these children falls in the
$1 million to $10 million range, an amount that few can
afford. Even with fewer than 15,000 children born with
microcephaly each year, the cost of their aggregate care will
rise quickly into the billions of dollars [18].
Another prolific disease with massive economic
consequences is Dengue. According to Break Dengue, a nonprofit organization focused on connecting different Dengue
initiatives around the globe, the annual cost of Dengue is
about $8 billion for all types of Dengue cases, from nonmedical to fatal. Dengue is one of the most rapidly spreading
mosquito-transmitted diseases worldwide, and, as such, the
costs will only increase [19]. Similarly, Lyme disease
treatment costs over $1 billion annually, according to the
Bloomberg School of Public Health at Johns Hopkins
University. Patients often develop longer-lasting symptoms,
known as post-treatment Lyme disease syndrome, that can
cost upwards of $3,000 per patient in return visits and
treatments [20]. At present, there is only one treatment option
with the potential to not only lower the initial cost of
treatment, but also eliminate the cost associated with return
visits.
CRISPR-Cas9 can reduce the overall cost of these
diseases by creating cost-effective vaccines and therapies.
With vaccinations, fewer cases of Zika and Dengue will
occur, nearly eliminating the financial burden of the
treatments and care for patients. In particular, the chances of
children born with microcephaly will decrease, eliminating
the expensive lifelong care that those children would require.
For those who contract Zika and Dengue despite the
availability of vaccinations, treatments will be more
accessible and affordable. Additionally, when mice are
genetically engineered to no longer carry Lyme disease, it will
cease to spread, thus diminishing the total cost of the disease.
However, as discussed by Michael Specter on National Public
Radio, with the elimination of Lyme disease and the potential
elimination of mosquitoes that transmit Zika and Dengue,
there could be environmental repercussions. Since nothing
like this has been attempted previously, what will happen if
these genetically engineered organisms are released into the
wild is unknown [8].
T Cells
Cancer-T cell interactions are limited by the T cell’s
ability to attack cancerous cells. As stated in an article
published by the Fred Hutchinson Cancer Research Center in
ScienceDaily, T cells are naturally programmed not to attack
the body, because to do so would result in an autoimmune
disease. All cancerous cells, regardless of type, have in
common unique proteins on their surface, known as antigens,
which characterize them as foreign and malignant. When T
cells recognize these proteins, they mobilize for attack against
the cancer cells. However, the cancerous cells can detect T
cells because of a specific antigen analogous to immune cells,
and deactivate the T cells permanently, inhibiting attacks by
those cells [23]. To prevent tumors from protecting
themselves from immune response, researchers have altered
the DNA of T cells to be unrecognizable to cancer cells. While
current procedures to edit T cells are effective, they often
result in unwanted gene placement that can cause additional
problems, such as mutated T cells. CRISPR-Cas9 technology
has emerged as a new approach to editing the DNA of T cells
that makes gene edits more precise, allowing both improved
structure and function of the T cells without harmful
insertions of genes. Both June and Sadelain have proposed
clinical trials that will use CRISPR to edit T cells and make
them undetectable by cancer [21][22].
Pioneers of Genetically Modified T Cells
June intends to insert three separate DNA fragments into
the genome of his patients’ T cells. The first edit will program
T cells to produce a protein that enables them to better
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recognize cancer cells. The second edit is a sequence that
removes a natural T cell protein, which, if present on the T
cell after the first edit, would interfere with the canceridentification process. The third edit will remove the gene for
the antigen on T cells that enables cancer cells to recognize
them, thereby preventing cancer cells from incapacitating the
T cells [21]. The result of the third edit is exemplified in
Figure 3, found on the American Association for Cancer
Research’s website.
already use CAR T cells, but Sadelain aspires to demonstrate
the efficacy and security of CRISPR-edited CAR T cells [22].
Targeted Cancers
As highlighted in an article on SingularityHub, a site
specializing in publishing technological breakthroughs, three
classes of cancers caught the attention of both June and
Sadelain: melanoma, myeloma, and sarcoma [26]. Each type
is often difficult to treat with current methods. According to
the American Cancer Society, melanoma (skin cancer) is
identified in roughly 95,000 people every year and kills more
than 13,000 known victims. Myeloma, or cancer of the bone
marrow, is discovered in approximately 30,000 individuals
each year and kills upwards of 12,000 people in previously
identified cases [2]. As explained on OncoLink, a site
sponsored by The Abramson Cancer Center of the University
of Pennsylvania, sarcoma is cancer in the connective tissues
of the body, such as blood vessels, tendons, bones, and
cartilage. Sarcoma is among the most untreatable types of
cancers, constituting roughly 15% of childhood cancers and
appearing in 12,000 people each year, making it an ideal
candidate for demonstrating the value of a successful
CRISPR-Cas9 treatment [27]. The prevalence of these
cancers and the difficulty associated with treating them
explain why June and Sadelain have elected to treat patients
suffering from them.
FIGURE 3 [24]
Normal and engineered T cells and their interactions
with cancer
CRISPR-CAS9 SUSTAINABILITY
June plans to extract his patients’ T cells, edit them, and
reintroduce them into the subjects. He is awaiting approval
from The University of Pennsylvania, as well as endorsement
by the Food and Drug Administration (FDA), before his
clinical trial can begin. Once authorized, his study will
proceed with eighteen patients for whom other treatments
have failed. These volunteers likely will be the first people in
the world to be injected with CRISPR-edited cells [21].
While June’s application may be farther along in the
approval process, another utilization of this technology is
under way in New York City. Sadelain at Memorial Sloan
Kettering Cancer Center is focused on inserting one sequence
of DNA into T cells, rather than three separate edits. The
fragment of DNA he aims to insert will program T cells to
produce a chimeric antigen receptor (CAR) on their surface.
CAR is a protein that helps T cells identify pre-cancerous
cells. Additionally, by shielding T cells from attack by cancer
cells, CAR aids in reducing T cell exhaustion, defined in a
Nature Immunology article as a condition common in cancer
patients characterized by long periods of inactivity associated
with protein-silenced expression [22][25]. By extending the
period of activity for CAR, Sadelain believes T cells will
deploy more effective attacks against cancer, allowing
malignant cells to be eradicated expediently. Clinical
treatments of blood cancers, such as lymphoma and leukemia,
When compared to other gene-editing techniques, such
as transcription activator-like effector nucleases (TALEN)
and zinc-finger nucleases (ZFN), the cost of CRISPR-Cas9 is
very low. A single TALEN for human use starts at $1,125,
according to the pricing on the University of Utah’s website,
and a single ZFN for human use has a $5,000 price tag, based
on pricing by Sigma-Aldrich, a chemical and biochemical
supply company [28][29]. In contrast, the cost of enough Cas9
to change an entire organism, though not yet approved for use
in humans, averages $500, as stated on the pricing page for
the biotechnology company Takara [30]. The pricing
difference among these three technologies makes the cost of
CRISPR-Cas9 the most sustainable and cost-effective product
on the market, not to mention it boasts the highest success rate
and simplest utilization.
With this new and inexpensive technology, the ability to
edit genes is not limited to just research institutions and
biotechnology companies. CRISPR-Cas9 provides everyone
who has access to a lab the opportunity to experiment with
and develop new uses for this technology. Now that geneediting is accessible to anyone, people from impoverished
nations and low-income backgrounds can gain access to
affordable treatments for diseases such as cancer, Zika,
Dengue, and many others for which no treatment exists or for
which prices are high. This is especially important for use in
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cancer treatments. With high costs and undesirable side
effects, current treatment methods are less than optimal both
financially and medically, but CRISPR enables favorable
progress. CRISPR-Cas9 is not only financially feasible but
also provides the unique opportunity to improve human life
on a global scale. Nevertheless, the countless possibilities are
all contingent upon the success of clinical trials and resolving
potential difficulties with implementation.
enhancement is finite today and ethically governed. Even so,
new discoveries of gene locations will open the door to greater
experimentation that could lead, for example, to designer
babies, with potential parents choosing the most desirable
traits, regardless of what natural inheritance would dictate
[32].
Also, while editing the genetic code of embryos offers
the option to remove deleterious mutations that cause diseases
such as Huntington’s and sickle cell anemia, changing the
DNA of human embryos poses moral and religious
conundrums. Dr. David Baltimore, a renowned biomedical
engineer, president emeritus of the California Institute of
Technology, and recipient of the 1975 Nobel Prize in
Physiology or Medicine, believes that general consensus in
the United States regarding these concerns will be necessary
before allowing any sort of embryonic application for
CRISPR, let alone embryonic clinical trials [33]. However, in
areas with fewer regulations, clinical trials on embryos have
occurred already. In early 2015, Chinese scientists performed
the first clinical trials of CRISPR on embryos. Their
experiments aroused skepticism and trepidation, despite the
use of non-viable embryos in their trials. As described in a
journal article from the publication Nature, much of the
concern surrounding embryonic modification stems from the
fact that all edits made in viable embryos can be passed down
through generations, and as these trials have never occurred
before, the results of such inheritance are unknown [34]. All
of this points to the need for a stringent regulatory framework
for CRISPR-Cas9.
DIFFICULTIES WITH IMPLEMENTATION
Although CRISPR-Cas9 technology has many potential
applications in medicine, its implementation is shrouded with
potential complications. For example, researchers must
devise efficient ways of getting CRISPR-Cas9 into the
specific tissues they wish to edit. CRISPR-Cas9 also poses
some safety risks associated with the cleaving process—
namely, it could make cuts in unintended places, which might
cause the same deleterious mutations it means to eliminate
[26].
The most prominent prospective shortcoming of
CRISPR-Cas9 is, once it cuts DNA, the cell then must replace
the deleted segment using a process called Homology
Directed Repair (HDR). HDR, a cellular DNA repair
mechanism, is responsible for fixing double stranded breaks
and is an integral component in the CRISPR-Cas9 editing
process. It works by repairing the break with a spare piece of
DNA from the cell’s nucleus or the surrounding area, and can
even work using manufactured DNA. However, as discussed
in a report from Science, a peer-reviewed publication, HDR is
present only in dividing cells, which means just a tiny number
of body cells are HDR-capable; the majority, such as liver,
neural, muscle, eye, and blood cells, are HDR incapable.
While HDR is active in only a few cells, the genes responsible
for its expression are present in all cells and potentially can
be reactivated [31]. If HDR can be reactivated, implementing
CRISPR-Cas9 editing will not present any major technical
difficulties; its only hindrance will stem from ethical
concerns.
THE FUTURE OF CRISPR-CAS9
CRISPR-Cas9 technology is progressing at a rapid rate
and is outpacing society’s ability to regulate it; because of the
lack of regulation, CRISPR’s proliferation and diversification
is susceptible to challenge and termination based on ethical
concerns surrounding its applications. Stricter guidelines and
better methods for deciding when its use is appropriate should
be developed, and the pace of CRISPR-Cas9 evolution
demands that they be introduced sooner rather than later.
Having relevant and effective regulations can ease ethical
concerns and quell consumer qualms. Finally, finding a way
to reactivate HDR in nondividing body cells is paramount to
increasing the efficacy of CRISPR-Cas9. If the technology
cannot be applied in nondividing cells, CRISPR’s future in
curing genetic diseases and in the medical field will be limited
to helping only a fraction of those in need.
ETHICAL CONCERNS
With a technology as revolutionary as CRISPR-Cas9,
ethical considerations abound, and as its development
continues, so does the growth of new ethical concerns. A
primary concern as the field of genetic engineering expands
is the potential of CRISPR-Cas9 to change the genome of
humans based on personal preference, rather than on medical
necessity. Potential human enhancement has fostered anxiety
ever since the possibility arose of changing the human
genome. Now, technologies such as CRISPR have moved it
closer to becoming reality. According to Dr. Andrew Otieno,
a professor in technology at Northern Illinois University, in
an article published in the Journal of Clinical Research &
Bioethics, the number of known gene locations available for
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ACKNOWLEDGEMENTS
We would like to thank our parents, high school
teachers, Megan, Andja, and the editors at the writing center
for proofing several drafts and helping us write the best, most
concise paper possible. Finally, we would like to thank
Benedum and Hillman for hosting us through excessive binge
writing sessions.
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