Stem cell research
Celina Capistrano
In 2004, a Nathaniel Report article outlined ethical issues surrounding the use of human stems cells in research and medicine. The following is an update on that article, providing a description of the different types of stem cells and the ethical issues associated with these. It also reports on the recent discovery of a new gene-editing technique, CRISPR/Cas9, and some of the ethical issues that are involved with its use.
Human Stem Cells
Human stem cells, characterised by their ability to develop into a range of different cell types, were first discovered in the mid-20th century and isolated in embryos in 1998. They may be found in embryos or derived from non-embryonic sources.
Human embryonic stem cells (hESC) can be derived in two ways: (i) using early stage embryos (blastocysts) created from eggs fertilised with sperm in vitro, embryonic stem cells (ESCs) can be isolated from the inner cell mass of the blastocyst and exposed to factors that allow these ESCs to continue growing; (ii) by a process called Stem Cell Nuclear Transfer (SCNT) where genetic material from an adult cell (e.g. skin or connective tissue) is injected into an egg that has had its genetic material removed (enucleated egg). The egg is then stimulated to develop until it reaches the blastocyst stage, thus becoming a ‘cloned’ embryo, at which point the inner cell mass is removed and grown in a petri dish (in vitro). One of the key scientific advantages of producing pluripotent cells (cells that can give rise to all cell types)by SCNT is that it enables a patient’s own cells to be used, thus avoiding the problems of immunological rejection that occur when using stem cells originating from another person. Both of these procedures, however, involve the destruction of the embryo and consequently give rise to significant moral and ethical issues concerning the value of, and respect for human life. Additionally, with SCNT there is the extremely controversial issue of creating human clones. There have been research developments resulting in isolation of ESCs without destruction of the embryo thus bypassing concerns regarding embryo destruction. However, the further healthy development of such embryos remains uncertain.
Induced Pluripotent Stem Cells
Largely as a result of the ethical issues related to human cloning and embryo destruction, but also because of various research controversies, progress on human stem cell research from about 2001was somewhat stalled. However, in 2006, Japanese Scientists Dr Takahashi and Dr Yamanaka1 (Nobel prize winners in 2012) discovered how to re-programme ‘somatic’ cells (‘non-embryonic’ or ‘adult’ cells) to reverse their state back into pluripotent form through the re-expression of key embryonic genes (suppressed in the somatic state), thereby enabling these already differentiated adult cells to behave as embryonic stem cells2. These new cell forms, Induced Pluripotent Stem Cells (iPSCs), appeared to the have same essential characteristics as embryonic stem cells. With the ethical barriers to the development of stem cells now removed, these new methods have sped up the discoveries regarding stem cell research to a “near-exponential rate”3.
Since the Takahashi and Yamanaka discovery, developments in iPSC methods have provided the best opportunity to avoid the ethical objections associated with destroying human embryos as well as the problems of immunological rejection.
iPSC in therapy
With this new ability to differentiate pluripotent cells into any cell through iPSC technology, researchers are now developing new model systems to investigate the biology of early mammalian and human development as well as new approaches for regenerative medicine. These systems offer improvements in the ability to study disease at a patient specific level and to increase the potential for more efficient methods for drug discovery and screening for genetic disorders. Specific strategies to tackle a range of diseases and disorders including Parkinson’s disease, spinal cord injuries, heart disease, inflammatory diseases, joint injuries, and Age Related Macular degeneration are also being developed, and there is the potential to use iPSC in transplantation medicine.
There are still some significant safety issues that need to be overcome. For example, one of the early ways of creating iPSCs was by transfecting or inserting the desired genetic material into the adult cells through use of a virus to shuttle the transcription genes. The procedure, however, could have the potential for the virus to be integrated into the cell’s DNA and cause undesired mutations.
Though iPSC’s are the most ethical way to experiment with pluripotent stem cells, other ethical issues are likely to arise depending on where the research is heading. For example, scientists have now succeeded in creating human primordial germ cells (sperm and egg precursor cells). Some scientists will continue to advocate for the use of embryonic stem cells in research that aims to better understand embryonic development, and to find ways to treat infertility and improve in vitro fertilisation (IVF). The shift away from embryonic research due to the new technology may even lessen the rigidity of regulations in terms of these studies, which may be a problem in the future.
CRISP/Cas9
CRISPR-Cas9 is a molecular tool that is being used in laboratories to edit genes. It was noticed that in some bacteria the DNA sequence in cells was repeated many times, interspersed with unique sequences between the repeats, and this configuration was called ‘clustered regularly interspaced short palindromic repeats’ or CRISPR. It was later found that these unique sequences matched the DNA sequences of invading viruses, and that the bacteria made RNA copies of these unique sequences. This RNA would link up with an enzyme named Cas (CRISPR Associated Protein, a nuclease that can cut DNA) and guide the CRISPR/Cas complex to a matching DNA sequence, enabling the Cas enzyme to cut and disable the invading gene.
This discovery became a genome engineering tool when it was found that this technique could be used to cut not only viral DNA but any DNA sequence by altering the guide RNA to match a targeted gene sequence. Scientists can synthesise RNA sequences to match the DNA sequence they wish to target and use CRISPR/Cas9 to repair or inhibit the gene. There are a number of Cas enzymes but Cas9 is the best known.
In 2015, researchers in China used CRISPR technology to edit the genes of human embryos in their research into a cure for the blood disease, beta-thalassaemia4, and again in 2016 in an attempt to introduce a mutation that would make people immune to HIV. UK researchers were recently successful in obtaining permission from the Human Fertilization and Embryology Authority to edit human embryos using CRISPR/Cas9 genome editing technology5. Their research was aimed at developing a better understanding of successful human embryo development and the causes of miscarriage and infertility.
With CRISPR/Cas9 genome editing technology it is possible to cut out and replace defective genes, which also means that primordial germline cells can be altered. The removal of ‘defective’ traits and the possibility of creating enhanced human beings would usher in a new era of eugenics thinking and practice. A number of scientists, including Jennifer Doudna, one of the scientists who discovered the CRISPR/Cas9 technique, have noted that there are significant ethical issues associated with the development of germline editing, and that CRISPR should not be used on reproductive DNA, or germline cells, while allowing laboratory research to continue6. They are concerned that, unless there is education and discussion amongst both scientists and the public about the risks and benefits of scientific developments such as CRISPR, then (i) there a greater likelihood of unethical use of such technologies and (ii) research into the therapeutic use of genetic changes that cannot be inherited, will be put at risk.
The potential for a ‘new eugenics’ is a concern with CRISPR/Cas9 technology, and as described above, the destruction of embryos is a key ethical issue associated with stem cell research. However, there are other ethical issues associated with stem cell research and germline modification. These include the commodification of human reproductive materials; the potential for exploitation of donors (e.g. women donating eggs for the derivation of hESC lines); the possibility for human reproductive cloning; and, finally, uncertainties relating to the creation and use of human–animal hybrids and chimeras for research7.
Endnotes
1.Takahashi, K., and Yamanaka, S. (2006). “Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.” Cell 126, 663–676. DOI:http://dx.doi.org/10.1016/j.cell.2006.07.024
2. Brunt K.R, Weisel R.D, Ren-Ke L. (2012) "Stem Cells and regenerative medicine- future perspectives" Can. J. Physiol. Pharmacol., 90(3), pp.327-335. doi: 10.1139/y2012-007
3. Ibid.
4. Cyranoski, D., and Reardon, S. (2015). “Chinese scientists genetically modify human embryos.” Nature News, 22 April 2015. doi:10.1038/nature.2015.17378 (Original Article of the Research from China, Liang, P., Xu, Y., Zhang, X. et al. (2015) Protein Cell, 6: 363. doi:10.1007/s13238-015-0153-5)
5. Callaway, E. (2016) UK scientists gain licence to edit genes in human embryos. Nature News, 530(1),18.doi:10.1038/nature.2016.19270
6. Doudna, J. (2015). “Genome-editing revolution: My whirlwind year with CRISPR.” Nature, 528(1), 469–471. doi:10.1038/528469a and Doudna, J. (2015). “Perspective: Embryo editing needs scrutiny.” Nature, 528 (S6). doi:10.1038/528S6a
7. Caulfield T, Kamenova K, Ogbogu U., Zarzeczny A, Baltz J, Benjaminy S, Cassar PA, Clark M., Isasi R., Knoppers B., Knowles L., Korbutt G., Lavery JV, Lomax GP, Master Z, McDonald M, Preto N, Toews M (2015) "Research ethics and stem cells" EMBO reports, 2015, Vol.16(1), pp.2-6 doi:10.15252/embr.201439819
Celina Capistrano graduated with a Bachelor in Biomedical Sciences (BBmedSc) specialising in Molecular Pathology and Genetics in 2015. She is currently undertaking a practicum with the Malaghan Institute of Medical Research as part of her Masters in Clinical Immunology course with Victoria University, Wellington.