YALE JOURNAL OF BIOLOGY AND MEDICINE 90 (2017), pp.625-634.

Review

Science and Bioethics of CRISPR-Cas9 Gene
Editing: An Analysis Towards Separating Facts
and Fiction
Adam P. Cribbsa,c,* and Sumeth M. W. Pererab,caComputational Genomics and Training Centre (CGAT), MRC Weatherall Institute of Molecular Medicine, University of Oxford,
John Radcliffe Hospital, Headington, Oxford, UK; bDepartment of Physiology, Anatomy and Genetics, University of Oxford,
Oxford, UK; cCampion Hall, Oxford, UK

Since its emergence in 2012, the genome editing technique known as CRISPR-Cas9 and its scientificuse have rapidly expanded globally within a very short period of time. The technique consists of using
an RNA guide molecule to bind to complementary DNA sequences, which simultaneously recruits
the endonuclease Cas9 to introduce double-stranded breaks in the target DNA. The resulting doublestranded break is then repaired, allowing modification or removal of specific DNA bases. The technique
has gained momentum in the laboratory because it is cheap, quick, and easy to use. Moreover, it is also
being applied in vivo to generate more complex animal model systems. Such use of genome editing
has proven to be highly effective and warrants a potential therapy for both genetic and non-genetic
diseases. Although genome editing has the potential to be a transformative therapy for patients it isstill in its infancy. Consequently, the legal and ethical frameworks are yet to be fully discussed andwill be an increasingly important topic as the technology moves towards more contentious issues suchas modification of the germline. Here, we review a number of scientific and ethical issues which may
potentially influence the development of both the technology and its use in the clinical setting.
INTRODUCTION
In the era of “gene editing,” CRISPR-Cas9 has become hugely attractive for both the scientific community
and the general public. The metaphorical use of the term
“gene editing” gives the impression that genes as texts
are static in nature and therefore can be corrected easily.
However, a simplistic view of genes or editing may not

be useful to appreciate the analogy of gene editing for it
may easily dismiss collateral damage or adverse consequences.
This review considers science and ethics of CRISPR-Cas9 as two co-dependent factors required for better
applications and effective ways of treating diseases. The
first part of the review uncovers the science behind CRISPR-Cas9 and its applications. The second part elaborates*To whom all correspondence should be addressed: Dr. Adam P Cribbs, Botnar Research Centre Windmill Road, Oxford, OX3 7LD,
UK, Phone: +441865222443, adam.cribbs@imm.ox.ac.uk.
†Abbreviations: CRISPR, Clustered Regularly Interspaced Short Palindromic Repeat; Cas9, CRISPR-associated protein 9; sgRNA,single guide RNA; ZFNs, Zinc Finger Nucleases; TALENs, Transcription Activator-Like Effector Nucleases; NHEJ, Non-Homologous
End-Joining; HDR, Homology-directed repair; RAC, Recombinant DNA Advisory Committee; PAM, Protospacer Adjacent Motif;
Indels, Insertions or deletions of DNA.
Keywords: CRISPR, Cas9, genome editing, bioethics
Author Contributions: APC wrote the manuscript and both authors were involved in the composition, reviewing, and editing the final
manuscript. APC and SMWP contributed equally to the manuscript. No author received funding for their involvement.
Copyright © 2017

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Cribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

Figure 1. CRISPR-Cas9 mediated gene-editing mechanisms. A single guide RNA (sgRNA) recognizes a genomic
region followed by 5’-NGG-3’ PAM sequence, which recruits the Cas9 DNA endonuclease. This introduces a double-stranded break that is repaired by (i) non-homologous end joining (NHEJ), an error prone pathway that can resultin the creation of Indels that can disrupt the gene, or by (ii) homology directed repair (HDR) in the presence of adonor construct.

the moral reasoning for the use of this rather attractive
and useful technique for the betterment of humanity.
DEVELOPMENT OF THE CRISPR-Cas9
SYSTEM: A HISTORICAL PERSPECTIVE
Since the emergence of CRISPR-Cas9 technology in2012, techniques for making precise and targeted manipulations of DNA sequences—so called gene editing—inliving cells have dominated the field of biology. However,genome editing is not a new concept as transgenic mice
were successfully employed in research in the 1970s [1].
Transgenesis thereby became a powerful research tool todecipher the underlying biological mechanisms that exist
in disease. Although this technique was largely employed
to introduce a genetic component (transgene) into a cellit was unable to execute a targeted insertion into the genome. Further advances in the 1980s revealed directionality could be achieved using alterations in the genome ofembryonic stem (ES†) cells which retained their pluripotency to give rise to many other distinct cell types [2].
However, it was technically challenging and remained aninefficient method (success rate of less than 10 percent).
These limitations led to a concerted effort in developing alternative gene targeting technologies. In 2005,
zinc finger nucleases (ZFNs) [3] and in 2010, Transcription activator-like effector nucleases (TALENs) [4,5], revealed the first systems that can be engineered to recognize specific sequences of DNA. These specific enzymes
were able to recognize their target sequences on the genome to introduce double-stranded DNA breaks permitting a repair process by the cell to prevent lethality. This
repair may occur in two ways (Figure 1). First, the endsof the DNA breaks are re-joined by the cell repair machinery, a process known as non-homologous end-joining (NHEJ) [6]. However, the imprecise nature of thisrepair process has the propensity to introduce insertions
or deletions of DNA (Indels) that in turn may disrupt thetranslation of the targeted gene. Second, with the use of
a complementary matching sequence of the DNA, a homology-directed repair (HDR) may occur to repair the
double-stranded break in a targeted manner [7]. Although
this technique can be used to add or remove specific DNA
sequences at the site of the double-stranded break, it isCribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

found to be more inefficient when compared with NHEJ.
The role of ZFNs and TALENs in introducing double-stranded breaks is highly specific because of the requirement for two engineered proteins. However, to design this process, which involves the synthesis of proteins
and optimization of the protocol to generate these breaks,
requires considerable time and effort. These constraints
led to limited adoption of this technology in the wider
field of biology but sought for a simpler method for targeting double-stranded breaks in DNA. In 2012, it was
discovered that the bacterium Streptococcus pyogenes
contained a remarkable system of viral defense that could
be adapted as a programmable system for genome editing [8]. This system is consisted of two parts, first, the“Clustered Regularly Interspaced Short Palindromic Repeat” (CRISPR) of RNA that acts as a guide for genome
targeting and the second is the “CRISPR-associated protein 9” (Cas9) that acts as an endonuclease to enable double-stranded breaks. It was subsequently found that scientists could manipulate the CRISPR RNA molecule intoa single guide RNA (sgRNA) that could be engineered
to specifically target a genomic area of interest. The only
requirement was that the sgRNA recognize a 17 to 22 bp
genomic region that is followed by a 5’-NGG-3’ protospacer adjacent motif (PAM) site. Similar to ZFNs and
TALENs, the endonuclease Cas9 can direct DNA cleavage to create double-stranded breaks that can be repaired
through the NHEJ or HDR processes. Subsequently, thistechnology was adapted and shown to be capable of editing the mammalian genome with high efficiency andselectivity [9-11].
TECHNICAL LIMITATIONS OF THE CRISPRCas9 SYSTEM
Given the rapid advancement of this technology, froma technical perspective, there are a number of questions
that arise surrounding the potential limitations of thistechnology. One major concern is the potential off-target
effects in areas of the genome that are sensitive to double-stranded breaks [12]. Moreover, the short length ofan sgRNA (typically around 17 to 22 bp in length) combined with the CRISPR-Cas9 system is able to tolerate up
to 1 to 3 mismatches between the sgRNA and the target
site, which may further increase the chances of off-target effects. This problem can be reduced somewhat byevaluating the potential off-target effects computationallyand only using sgRNAs that do not target other functional proteins or regions. However, given that the sgRNA
may also have off-target effects in unknown long-range
enhancer regions, such effects cannot be entirely eliminated. Despite this, scientists have engineered the Cas9
protein and sgRNA to increase specificity thereby lowering the off-target effects [13].

627

CRISPR-Cas9 technology is rapidly providing researchers with a viable method for dissecting the molecular mechanisms that underpin cellular function. However, if the technology is to progress towards the clinic,
improvements in the delivery of the CRISPR-Cas9 must
be considered. The use of transfection reagents that simultaneously deliver the sgRNA and Cas9 protein into
target cells in the laboratory has proven its efficiency ina number of cell lines [14]. However, all or parts of theplasmids are often randomly integrated into the host genome [15,16]. It has been shown that plasmid DNA canalso be inserted into both the on-target and off-target sites[17]. Furthermore, host immune responses can also be induced by these bacterial sequences, thereby dampening
the efficiency of genome editing [18].
To overcome the challenges of transfection delivery systems, the use of viral delivery systems have been
evaluated. Viral vectors can enter a cell in large numbers
efficiently under both in vitro and in vivo conditions.
Presently, integrase-defective lentivirus vectors (IDLVs)[19], adenoviral vectors (AdVs) [20] and recombinantadeno-associated-viral vectors (rAAVs) [21] have beenused to transfer CRISPR technology to mammalian cells.
However, historically the use of viral vectors has beenmarred with controversy because of adverse events following clinical trials, leading to patient death [22,23].
Despite these early setbacks for gene therapy, a numberof improvements in viral delivery systems are beginningto translate some encouraging preliminary results into theclinic [24-26]. As with CRISPR-Cas9 technology, delivery systems need further development to increase safety
before they can be successfully used routinely.
APPLICATIONS OF THE CRISPR-Cas9
SYSTEM IN HUMAN HEALTH
The CRISPR-Cas9 system has many potential biological research uses because of its ability to cleave thegenome at a specifically desired location. Pertaining to
genome editing it has been used to generate stable celllines with specific functions to develop experimental
models to understand the underlying disease pathology.
CRISPR-Cas9 has been demonstrated to be effective in
multiple organisms, including bacteria, fish, birds, fruit
flies, and mammals [27,28]. In 2012, the application ofthis technology was successfully used in human cellsby engineering a novel version of CRISPR-Cas9 [9,14].
Subsequently, the use of CRISPR as a novel system forinvestigating biological processes and pathologies began
to expand to numerous fields. For example, it has been
modified to program specific transcription factors to target and activate or silence specific genes [29,30]. Further
adaptation of the Cas9, which enabled manipulation of
methyl groups at specific positions on the DNA, has al-628

Cribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

lowed researchers to evaluate how such changes affectgene expression [31]. More recently, CRISPR-Cas9 has
been used to turn cells into programmable computers,
where researchers have engineered molecular switches tocontrol cell fate to enable them to program conditional
behaviors [32]. Such examples demonstrate the versatility of the CRISPR-Cas9 system in generating basic research tools in vitro.
In addition to its in vitro application, CRISPR-Cas9
can also be used to generate in vivo animal models to
study diseases more effectively. For example, mousemodels have been developed to evaluate deleterious effects of mutations in cancer by using the system to introduce loss of function mutations in tumor suppressors
or gain of function mutations in oncogenes [33]. Gene
manipulation of mice at the germline level has enabledresearchers to generate whole organism or conditionalmodels that model human disease.
Germline editing is also a promising technique used
for understanding early onset of human diseases bymeans of human embryos. However, research committees have been reluctant until recently to grant permission
for such investigations. Recently, a group of researchers
from China have carried out a systematic analysis of genefunctions in modified human embryos in order to investigate the effectiveness of CRISPR-Cas9 for further research [34].
A major potential goal of developing CRISPR-Cas9
genome editing technology is its use in preventing or
treating disease or disability. There is evidence that using CRISPR-Cas9 to target the genome of viruses suchas Hepatitis B and HIV could control and ultimately curepatients of the disease [35]. For example, CRISPR-Cas9
has shown that introduction of Indels into HIV is lethal
to the virus, however, it has also been shown that other modifications to the virus lead to increased virulence[36]. Recently, modifying the immune system to attack
HIV has been gaining attraction as a promising therapeutic use of genome editing [37]. Similar strategies havebeen deployed for the treatment of leukemia and several
other blood cancers [38]. Interestingly, cell-based therapies have shown significant advantages as cells can beremoved, manipulated, expanded, and then reintroduced
into the patient to enhance the desired therapeutic effect.
However, for several other diseases such as solid tumor
cancers or those that effect tissues or organs, CRISPR-Cas9 is unlikely to be effective given the present stateof the technology. Despite the setbacks, there are currently active areas of research that are pursuing the application of CRISPR-Cas9 into editing CFTR gene in Cystic
Fibrosis and dystrophin in Duchenne muscular dystrophy[39,40]. Despite these advancements, such research iscurrently in its infancy and the technology is faced withchallenges related to delivery methods that were previ-

ously encountered by gene transfer technologies in the
1990s.
OUTLINING THE ETHICAL QUESTIONS ON
CRISPR-Cas9 FOR GENE EDITING
With the most recent advances in biological and medical research, CRISPR-Cas9 has become controversial
because of its capacity to modify the plan of each cell in
the human body. By altering the germline genome, many
presume that it can even transfer not only the intended
modifications but also other “unforeseeable alterations”
to the offspring. Hence the question of “irreversible effects” on future generations is pronounced with trepidation. Recent discoveries from a Chinese group led by
Junjiu Huang has created some real concerns and opened
discussions regarding whether this technology shouldeven be applied to pre-implantation embryos [34]. The
research was published in Protein & Cell (following two
rejections on ethical grounds by Nature and Science) witha significant backlash from the general public [34]. The
story of CRISPR-Cas9, therefore, has awakened the potential power behind gene editing and the “nervousness”
it generates among the public.
From a historical perspective, genetics and social
engineering have had a profound toxic relationship, withthe most notable example being such misuse in Nazi Germany [40]. Many well-respected scientists at the time,
fearing the degeneration of the human race, attempted
to promote policies that legally blocked the “breedingof inferior humans.” The rhetorical misuse of natural
selection to promote eugenic policies led to widespreadabominations, which included the mass-sterilizationof thousands of individuals and the ethnic cleansing of
millions of individuals. However, even though the viewsof eugenics held by the Nazis were later discredited, thesterilization of women with intellectual disabilities, onsocial and therapeutic grounds, was still legal practice ina number of European countries and in North America
until the mid-twentieth century [41]. As a result of thesemisuses, there are significant ethical questions that arise
for CRISPR-Cas9 use, the most pressing being whether
its use may be harmful to society.
WHAT IS ETHICALLY “UNACCEPTABLE”
ABOUT CRISPR-Cas9?
As seen in the first part of this review CRISPR-Cas9
is still in its infancy of development. However, it is a rapidly evolving technology and with ever expanding applications it is also attracting private companies for investments despite certain ethical restrictions [42,43].
What is ethically repulsive about CRISPR-Cas9?
Although bioethicists hold a wide range of opinions,Cribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

the most compelling argument is about its ethical use in
human germline manipulations [44]. The authors argue
that the dearth of knowledge in the area of germ cell mutagenesis may cause uncertain future consequences. It
appears that this argument from “potentiality” seems toincorporate not just the concerns for the safety of future
generations susceptible of non-Mendelian (single gene)diseases, but how this technology can transform society
in terms of societal values, its economy status, individuality, injustices, and accessibility [45]. It seems to appeal
to the “transformative potential” of the technique which
may have wider concerns for the overall moral and ethical texture of the society in which humans live.
GENE EDITING WITH CRISPR-Cas9 AND
MAINTAINING ETHICAL INTEGRITY
Given the complexity of the debate, a brief note
about the current ethical stand may be necessary. There
are several regulatory bodies including the WHO, UNESCO, and the Decleration on the Human Genome andHuman Rights that are involved in the current debate on
gene editing in view of formulating helpful guidelines.
Although policies vary depending on the legal system,
there are legally binding conventions such as “Oviedo
Convention” (the Council of Europe Convention for theprotection of Human Rights and Dignity of the Human
Being with regard to the Application of Biology andMedicine: Convention on Human Rights and Biomedicine) and professional regulatory bodies (such as that of
the HFEA in the U.K. and FDA in the U.S.) which areheavily involved in the deliberations. More recently, theU.S. National Academy of Sciences (NAS) and National
Academy of Medicine (NAM) formulated a consensus
report highlighting the importance of public engagementin this debate considering the benefits and risks of genome editing in humans [46].
There is a ban on human germline modification by
many European countries [45] and in the United States,
any edited embryos for pregnancy requires permission
from the U.S. Food and Drug Administration. Similarly,
in China, any clinical use of gene editing must be permitted by the Chinese Ministry of Health. The recent
report by NAS/NAM classifies gene editing using CRISPR-Cas9 on the basis of purpose and heritability: purpose
being therapeutic interventions (treat or prevent disease)or enhancement and heritability involving somatic or
germline cells. From a public point of view, the reportobserves that the majority agrees with the use of genome
editing in both somatic (64 percent) and germline cells(65 percent) for therapeutic purposes but not for enhancement applications [47]. However, it is important to notethat basic research objectives in gene editing techniques
are also closely tied up with therapeutic/enhancement in-629

terventions thereby adding a layer of complexity for the
principle purpose of the technique.
Therefore, a sound bioethical reasoning may be required to clarify the purpose of CRISPR-Cas9, like techniques with current advancement in biotechnology. It
also nurtures a healthy relationship between science andsociety and encourages public engagement in science forthe betterment of living.
ARGUMENTS TOWARDS RELEVANTAPPLICATIONS OF CRISPR-Cas9:
SEPARATING FACTS FROM FICTION
The consequentialist arguments, commonly usedin medical situations, weigh both potential benefits andrisks in ethical considerations. At the heart of such arguments would be to create some space for the moral
obligation to promote medical intervention for preservation and promotion of life threatened by diseases. It does
not necessarily mean that a significant risk for a serious
genetic condition would invariably allow gene editing a
reproductive option [45].
It is required to state that Pre-implantation Genetic Diagnosis (PGD) stands as the legal ethical stand incountries where secular bioethics discourse is permitted.
However, there are few cases in which selection of unaffected embryos using PGD would not be possible andeffective. In autosomal recessive diseases (e.g. cystic fibrosis, phenylketonuria) where both parents are homozygous and autosomal dominant diseases (e.g. Huntington’sdisease, familial adenomatous polyposis) where at least
one parent is homozygous, germline editing would be theonly option for parents desiring a healthy child [45]. This
makes CRISPR-Cas9 technology a potentially lucrative
option in reproductive applications. It must be mentionedthat PGD would be required to verify the success of theedits at least initially.
In general, the use of genome editing in somatic cells is ethically accepted because of its low risk tobenefit ratio and the presence of informed consent [43].
Given safety concerns, germline applications for humanembryos for implantation may have a high risk-to-benefit
ratio as it may have an “unforeseeable” harming effects
on future generations. This is justified given the nature of
the technique and the level of currently available scientific evidence. Nevertheless, as a proof of concept, Ma etal., may argue that correcting MYBPC3 gene that causes
hypertrophic cardiomyopathy may help better selectionof corrected embryos for implantation as a remedy formonogenic inherited disorders [48]. However, PGD as areproductive option is an effective and ethically acceptable mode of treatment for most of such diseases. Perhaps one may be able to justify the use of gene editing
research for these genetic conditions as a way of devel-

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oping research tools and conditions for more complex
applications in the future. In this case it may be equallyimportant to justify the use of human embryos in gene
editing as monkey germline editing is not subjected toany particular restrictions [49].
Informed consent is another area of dispute concerning gene editing as a reproductive option [50]. It isa decision that may impact on the genetic traits of future
generations whose informed consent cannot be obtained[51]. One might ask whether it is a logical oversimplification to expect an informed consent knowing the natureof the situation. In most countries, in vitro fertilization(IVF) is the standard way by which germline transmission of inherited diseases in human embryos can bescreened. Obviously, the informed consent is given by acouple desiring the IVF who are properly informed of andconscious of their choice for the offspring. In contrast, it
is not unfounded to reason that with CRISPR-Cas9 “theunforeseeable effects” may be greater than the actual level of genetic interference, thereby effectively making it
impossible to derive an informed consent on behalf ofthe offspring. Moreover, because of the off-target effectsof this technology on the germline, some of the potential
side effects transmitted to future offspring may not be observed until several subsequent generations. In support ofthis some scientists are expressing a preference for a moratorium on the use of genome editing in human embryos,
at least until the technology has developed to a stage that
it is deemed mature [52,53]. Perhaps “deemed mature”
may beg several questions including an assessment about
the probability of successes/harmful effects of the application. Interestingly, in principle, this encourages ana priori condition for research to eliminate those factors
hindering the success of gene editing.
Having a powerful tool in hand such as CRISPR-Cas9 to modify the human germline is constantly
faced with criticisms about its potential future applications. It appears that the ethical dilemma of the technology is closely interwoven with potential but unforeseen
harm or “abuses,” a secondary effect of the technology.
At another layer those secondary effects may have lasting
impact on human life because of their inherent capacity
to be incorporated into the gene pool of human species.
More recently, an international team of scientists showed
improved efficiency and accuracy for CRISPR-Cas9 taking a significant step towards using the technology to correct debilitating birth defects [48]. We have learned fromthe past that advances in therapeutic treatment can beutilized for previously unintended cosmetic applications.
For example, plastic and reconstructive surgery that was
initially intended for the management of patients sufferingfrom disfiguring conditions has been utilized for cosmetic
purposes. However, it is understood that any discovery
may have various unforeseen applications which may

bring about beneficial or harmful effects. The discoveryof radium sparked numerous benefits and several harmful
consequences too. Should a benevolent technique suchas CRISPR-Cas9 be penalized for the “unforeseen abuses?” In spite of sound moral reasoning, some argue that
CRISPR-Cas9 may warrant “designer baby” technology
and thereby may actively take part in societal change
towards greater global inequality than that already seen
today [54].
Considering the consequentialist arguments on modification of somatic cells by CRISPR-Cas9 does not havethe same level of ethical impact as those raised by germline modification (Table 1). The ethical considerations
for using CRISPR-Cas9 as a treatment for patients arefocused on defining an appropriate risk-to-benefit ratiothat favors beneficial outcome to the patient [55]. For
CRISPR-Cas9 treatments, this balance will likely follow the same approach as other well-established medical
treatments. It may depend on several factors such as disease type, disease progression, the type of cells/tissues
treated, and the mode of therapeutic applications (e.g.
enhancement vs. therapeutic applications). Importantly,
risk-to-benefit ratio is likely to be affected significantly
by the delivery methods used in the treatment. For example, a favored delivery method is a lentivirus approach
because of its efficiency and stability. However, there had
been adverse effects following gene therapy using lentiviral vectors in clinical trials [56]. With the developmentof safer delivery methods, some of these risks may beovercome.
As indicated above, CRISPR-Cas9 may be used insomatic cells for modifying physical traits and capacities.
These cosmetic applications may lead to “enhancement”
of certain traits such as muscle development or intelligence. Some argue that enhancing applications should
not be equated with treatments using CRISPR-Cas9 formuscular dystrophy or mental disability [45]. It may become clear in those cases the potential benefits may beunlikely to outweigh the risks involved. However, as noted by others, any proposed intervention by CRISPR-Cas9
for cosmetic applications will have to pass the well-established threshold that the potential risk-to-benefit ratio is
acceptable, informed consent is given, and all regulatory
approvals are obtained from the relevant medical regulatory bodies [55].
DO THE RISKS OUTWEIGH THE
BENEFITS?
Any discussion about the use of CRISPR-Cas9 inthe clinic needs prior assessment about the level of risks,since the technology has demonstrated to have potentially damaging off-target effects. It has been observed that
CRISPR-Cas9 has a high propensity for off-target effects

Cribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

631

Table 1. The potential risks associated with CRISPR-Cas9 gene editing technology.
Specific CRISPR-Cas9-based applications in humans: Potential risks
Technical

Social

Off-target Insertions
and deletions(Indels)

Random integrationof vector

Toxicity

Exacerbating social
inequalities

Germline editing

High - A potentiallysignificant issue
but screening ofembryos prior to
implantation could
overcome this risk.

Medium - Random
integration may
result in inactivation/
dysregulation ofgene expression.
Sequencing forthe presence ofintegration would
identify this.

LowHigh – Dependency
upon “enhancement”
applications

Ex vivo delivery(cell transplants)

High - For clonallyexpanded cells,
screening can be
performed to identify
off-target Indels.

Low

Low

Low

In vivo delivery(tissues & organs)High - Poses themost significant risk
because screening
would be difficult toperform.

High – It would
be very difficult todetermine integrationin vivo. If theintegration occurs ina tumour suppressor
or oncogene thedevelopment ofcancer could be anissue.

High – The inductionof inflammatory
responses to vector
components.

Low

and single nucleotide variants in humans, due to the large
number of repeats and highly homologous genome, andcan cleave unintended sequences causing mutations that
may have a likely effect on developing cancer like diseases. Therefore, further improvements are needed, especially for more precise modifications that will be required fortherapeutic interventions [57]. In the drive towards using
the technology in a clinical setting, it may not be practically possible to increase the biosafety in time for the firstclinical trial, nonetheless reviewing the critical balance
between risk and safety may help assess its impact prior
to a clinical trial. Such safety reviews, performed at the
Recombinant DNA Advisory Committee (RAC) at the
U.S. National Institute of Health, are already at the stageof being granted [37,58]. The proposed 2-year trial will
be conducted on 18 people with myeloma, sarcoma, or
melanoma. Recruiting those that have stopped responding
to conventional therapy has somewhat negated the risks
associated with the technology. Following this approval,
it is expected that other trials in different diseases will
apply for permission. However, careful attention should
be given by ethics committees to accurately evaluate therisks in different diseases, since the risk-to-benefit ratiochanges with each disease.
It is important to bear in mind the drive towards
commercialization of the technology and the conflicts
that this creates when evaluating the safety aspects of any
potential clinical trial. Filing a utility patent applicationin the United States or Europe generally gives the applicant protection for 20 years from the date the patent isfiled. Therefore, there is a drive towards commercializing
the technology quickly to recoup developmental investments. This sometimes conflicts with safety evaluations
when clinical trials are not conducted effectively. For
example, in 2004, the drug rofecobix (Vioxx) was withdrawn from the market over safety concerns after 88,000
to 140,000 people suffered heart attacks from taking it[59]. This was despite the pre-clinical finding that it hada protective effect. Therefore, if we are to avoid some ofthese failures when looking at the application of CRISPR-Cas9, we could reinvestigate the failure of gene therapy trials that were conducted in the 1990s to see if there
are lessons that could be relevant to CRISPR-Cas9 trials.
As the genome-editing technology is rapidly progressing but still a way off from being adopted as a reliable technique, to modify somatic/germline cells in a

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Cribbs and Perera: Ethical implications of CRISPR-Cas9 in genome editing

clinical setting, discussions are required to debate theoverall implications of the technique. If the technology
advances to a stage that safety concerns are acceptable,
then further discussions will be needed to consider the social, legal, and ethical implications of using this technology to avoid potential “abuses” of germline editing. As amatter of fact, although modification of human embryos
for implantation is illegal in many countries, ethically informed discussions at public level may be necessary toevaluate the effects of gene editing techniques against a
global picture, not just in the present but also into the
future [60].
CONCLUSIONSGenome editing techniques, particularly those related to CRISPR-Cas9, have lowered the cost and increased
the output of genomic research, thereby allowing the genetic manipulation of cells and organisms that have traditionally been difficult or impossible to perform. The major direction the technology is moving towards is making
it possible to alter gene function, rather than knocking out
the function of the gene altogether. This approach will gosome way towards making this technology applicable totreating a number of human diseases. However, there aresome serious concerns regarding the ethical and moral
aspects of the delivery of the technology, the creation of
new variants on the human population and the potential
negative impact on unintended consequences. Many researchers have urged a public discussion over the social,
ethical, and legal implications of genome editing in the
germline, however there are many other health concernsthat also need to be discussed and debated. Although thistechnology is some way from being utilized in a clinicallyeffective manner there is some urgency for these discussions to take place at a national, local, and governmental
level.
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