Should Human Genome Editing Be Allowed?

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23/09/19 Sciences Reference this

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Discussion Topic: Should human genome editing be allowed?

 

 

INTRODUCTION:

Genome-editing permits versatile genetic modification of somatic, germline and embryonic cells (refer to Figure 1) by using enzymes called nucleases to snip DNA at specific locations and then delete/rewrite the genetic information at those locations; and has become a particularly salient topic due to the advent of a relatively novel tool called CRISPR-Cas9 that distinguishes itself from previous techniques (zinc-finger nucleases, TAL effector nucleases) due to its increased efficiency, specificity, ease of use/accessibility for researchers and its relatively affordable price (Howard et al., 2018). Current applications of the technology are in non-reproductive/somatic cells, but concerns focus on the use of gene editing to modify the genomes of embryonic cells.

Figure 1: Figure outlining the procedures of human germ line genome editing at the embryonic, oocyte and spermatogonial levels (Ishii, 2017).

Somatic modifications are non-inheritable, target genes in specific cells and have been tested and implemented for much longer; whereas germline modifications applied to embryos/sperm/eggs, alter the genes in all the resultant person’s cells, are inheritable and thus raise profound clinical and socio-ethical concerns over the safety and the potential misuse of gene-editing for human enhancement (Ishii, 2017).

This report reviews a number of clinical and ethical issues that have the potential to impact the implementation of genome-editing technologies, explores their objectives while analysing the risks and benefits of the technique and suggest paths for resolving the issue such that new therapies can be safely and rapidly translated to the clinic.

REVIEW: 

The naive state of pluripotency has favourable characteristics for efficient genome-editing (Jacobs et al., 2017), and the ability to optimise a workflow for gene-editing in naïve embryonic, neural and hematopoietic stem cells, has helped enhance therapeutic development for such disorders (Kohn et al., 2016). Genome-editing is also a powerful platform for treating diseases like HIV (Callaway, 2016), haemophilia, sickle-cell anaemia and several forms of cancer (Lanphier et al., 2015). Furthermore, gene-editing technologies have also made it possible to study transcriptional network of metastable pluripotent states in the embryo, epigenetic landscape of pluripotency transcriptional and epigenetic regulation of the mammalian germline (Alberio, 2017) and gain other valuable fundamental knowledge about cell regeneration and development (Pei et al., 2017).

Though most techniques currently in various stages of clinical development focus on modifying the genetic material of somatic cells (Cyranoski, 2015); a plethora of debate surrounds the possible implementation of gene-editing in human embryos, which might have unpredictable effects on future generations, making it dangerous, ethically unacceptable and vulnerable to exploitation for non-therapeutic modifications (Lanphier et al., 2015). Thus, the infusion of genetically modified WBCs that save the life of a baby with leukaemia is acceptable, but it would be unacceptable if the intervention affected her egg cells, and thus future children.

Some countries use federal money to fund human embryo research, while research in others relies solely on funding from private donors (Ledford, 2017). Additionally, while heritable-editing is ethically defensible in some countries under stringent conditions, in absence of reasonable alternatives for the prevention of a serious condition; others lack strong regulatory powers that oversee protocol design and ensure long-term follow-up (Pei et al., 2017). Thus, the current lack of a standardised legal framework and international co-operation allows for the possibility of irreversible, heritable damage due to gene-editing.

DISCUSSION:

Gene-editing research relies on the use of potentially wasted embryos (Pei et al., 2017) and provides platform to target about 10,000 diseases (Ledford, 2015), and is particularly beneficial to treat rare diseases. Though current alternatives that negate the need for permanent germline repair include implementing existing technologies to genetically screen/select healthy embryos before uterine transplantation; for cases involving multi-gene diseases, most embryos need to be discarded (Cyranoski, 2015). Gene-editing combined with recently improved culture conditions for human blastocysts (Pei et al., 2017), would not only help explore the genetic basis of early pregnancy loss and implantation defects, but also greatly increase the odds of obtaining a healthy embryo (Cyranoski, 2015).

There are however several unintended consequences (refer to figure 2) and scientific/clinical risks associated with the technique (summarised in table 1). Despite efforts to minimise some of the risks by injecting the Cas9 protein (bound to its guide RNA) directly into the cells or simultaneously injecting the sperm and CRISPR– Cas9 components into the egg (Ledford, 2017) to minimise off-target mutations and mosaics, it has been shown that these would only work for correction of heterozygous mutations and that such methods would require creating embryos for research, which is currently only permitted in a few countries (Pei et al., 2017). Different countries have diverse opportunities to access human, non-human primate embryos, depending on local regulatory and cost issues and though in some countries experimenting with human embryos at all would be a criminal offence, almost anything is permissible in others (Ledford, 2015).

Figure 2: Intended and Un-intended consequences of gene editing in human zygotes (Kohn et al., 2016).

Table 1: Scientific Risks associated with gene editing (Kohn et al., 2016).

Toxicity

Potential risks

Genotoxicity

(On-target) Local mutations at target locus: insertions/deletions, base substitutions; 1 sided or non-homologous recombination, and unintended gross chromosomal rearrangements; (off-target) mutations at sites other than target locus, including gross chromosomal rearrangements

Potential consequences: local gene inactivation, dysregulation, trans-activation; deletions, inversions, translocations; transformation, cell cycle disruptions, apoptosis

Nuclease related

Off-target endonuclease activity

Persistent endonuclease activity (off-target mutations and/or activation of the DNA damage response)

Immunogenicity

Vector related (nucleic acids, nucleoproteins, nanoparticles, viral vectors)

Random integration of donor vector leading to local gene inactivation, dysregulation, trans-activation

Random integration of nuclease expression vector leading to persistent nuclease expression

Delivery related (transfection, microinjection, electroporation, viral vector)

Acute cytotoxicity

Induction of inflammatory responses to vector components

Ex vivo cell processing related

Cell survival

Microbial contamination

Loss of stem cell activity and/or engraftment activity; impaired differentiation/function; inherent genome instability during culture

The Ethical, Legal and Social Issues(ELSI) associated with germline gene-editing are more challenging than those associated with somatic gene-editing and include: the rise of a new form of eugenics, genetic classism (Ledford, 2015), issues regarding respect for human dignity, the moral status of the human embryo, respect for cultural and biological diversity and pluralism, disability rights, equitable access to new technologies/health care, potential reduction of human genetic variation, stakeholder roles/responsibilities in decision making etc. (Howard et al., 2018). Some of the ELSI questions to be addressed while drafting regulatory policies/frameworks for gene-editing are summarised in Table 2.

Table 2: Questions that address some of the ethical, legal, and social issues (ELSI) surrounding somatic and heritable/germline gene editing (Howard et al., 2018)

Area

Example of questions

ELSI of somatic cell gene editing

Does the current legal framework need amendments/additions to address somatic gene editing? If so, who will further shape the legal framework for somatic gene editing?

How will trials in somatic gene editing be conducted and evaluated?

To what extent will commercial companies be able to, or be allowed to offer, potentially upon consumer request, treatments based on techniques where so much uncertainty regarding harms remains?

Which health-care professionals will be involved in the provision of somatic gene therapy and the care of patients who undergo such treatments?

How will we ensure that the use is driven by need and not the technological imperative?

Based on what criteria will the eligible diseases/populations to be treated be chosen?

How can we ensure that research funds are allocated to ELSI research proportional (in some way) to the amount of research on gene editing?

ELSI of heritable gene editing

Should gene editing of human germ line cells, gametes and embryos be allowed in basic research—for the further understanding of human biology (e.g., human development) and without the intention of being used for creating modified human life?

Why should we consider using heritable gene editing in the clinic if there are alternative ways for couples to have healthy (biologically related) children? Who will decide? Based on what criteria?

Should we first understand the risks and benefits of somatic gene editing before even seriously considering heritable gene editing?

How do commercial incentives and the technological imperative play a role in these decisions?

If we do entertain its use, what, if any criteria, will be safe enough according to different stakeholders (scientists, ethicists, clinicians, policy makers, patients, general public) for it to be legitimate to consider using gene editing for reproductive use? Who will set this safety threshold and based on what risk/benefit calculations?

If heritable gene editing was allowed, how would the fact that for the first time, a human (scientist or clinician) would be directly editing the nuclear DNA of another human in a heritable way cause some form of segregation of types of humans? Creators and the created?

 

CONCLUSION:

Gene-editing through CRISPR-Cas9 is a newly developed and rapidly progressing avenue. Though the use of this science can be very beneficial, enhancing both therapeutic development for disorders and the basic understanding of biology, the potential damage that can be done requires stringent regulation before it affects the entire human genome. It is thus crucial to have effective transnational co-operation with a well-designed agreement providing appropriate assessment of risk versus benefit and allowing gene-editing to proceed wherever legally permitted, financially feasible and logistically manageable; enabling pooling of the resulting knowledge to assess safety and efficacy and focus our limited scientific and human resources, time and finances on important areas that enable and support the responsible use of gene editing; thus achieving the greatest benefits of genome editing both in medicine and biology with transparency, economy, and efficiency.

REFERENCES:

  • Alberio, R. (2017). Transcriptional and epigenetic control of cell fate decisions in early embryos. Reproduction Fertility and Development 30(1) 73-84.
  • Callaway E. (2016) Gene-editing research in human embryos gains momentum.
  • Nature 532:289-90
  • Cyranoski (2015). Ethics of embryo editing divides scientists. Nature 519(7543) 272.
  • Howard, H. C., et al. (2018). One small edit for humans, one giant edit for humankind? Points and questions to consider for a responsible way forward for gene editing in humans. European Journal of Human Genetics 26(1) 1-11.
  • Ishii, T. (2017a). Germ line genome editing in clinics: the approaches, objectives and global society. Briefings in Functional Genomics 16(1) 46-56.
  • Ishii, T. (2017b). The ethics of creating genetically modified children using genome editing. Current Opinion in Endocrinology Diabetes and Obesity 24(6) 418-423.
  • Jacobs, E. Z., et al. (2017). CRISPR/Cas9-mediated genome editing in naive human embryonic stem cells. Scientific Reports 7 12.
  • Kohn, D. B., M. H. Porteus and A. M. Scharenberg (2016). Ethical and regulatory aspects of genome editing. Blood 127(21) 2553-2560.
  • Lanphier, E., et al. (2015). Don’t edit the human germ line. Nature 519(7544) 410-411.
  • Ledford H. (2017) CRISPR fixes disease gene in viable human embryos.
  • Nature. 548:13-14
  • Ledford H. (2015) Where in the world could the first CRISPR baby be born?
  • Nature. 526:310-1
  • Pei, D. Q., et al. (2017). Human Embryo Editing: Opportunities and Importance of Transnational Cooperation. Cell Stem Cell 21(4) 423-426.
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