Source: Front Line Genomics
Experiments in DNA editing using the CRISPR/Cas method are pushing the scientific and ethical boundaries
Author: Agata Młodzińska
CRISPR system is a defense method of prokaryotic organisms (archaea and bacteria) from "foreign" genetic material such as plasmids and bacteriophages. It can be described as the immune system of microorganisms that recognizes "foreign" genetic material in cells and destroys it by cutting a strand of DNA using enzymes called nucleases (e.g. Cas).
For the first time the method of DNA editing with the use of CRISPR/Cas complex was published by the MIT and Harvard scientists in February 2013 (source: Science. 2013 February 15; 339(6121): 819–823. doi:10.1126/science.1231143). The research had been conducted on human and mice cell lines. The scientists had used the CRISPR system of the Streptococcus pyogenes bacteria, which relies on the Cas9 enzyme responsible for cutting the strand of DNA. Simply put, the experiment had aimed at directing the Cas9 enzyme to cut the strand of DNA in a specific place in the genome. Consequently, it would trigger the automatic DNA repair process that may take place in two ways: by removing/adding nucleotides or by incorporating a fragment of genetic information delivered from the outside, which would fill the “hole” in a sequence and modify its biological relevance. Modifications to the CRISPR system allowed for the effective removal of genetic mutations in eukaryotic cells and the use of this method by other scientists on other organisms.
The development of CRISPR/Cas technique has opened up incredible possibilities of editing genetic information. Shortly after that its other uses have been discovered, including animal and cell disease models, visualization of specific areas in a living cell genome, or activation/deactivation of gene expression in selected genes. Despite the multitude of its uses in medicine and their potential, there is one thing that requires consideration. In the early stages of embryonic development, there is a possibility of editing DNA of the entire organism (since it is comprised of a relatively low number of cells). In theory, this technique enables the “enhancement” of a human being. Are we perhaps taking a step too far here?
In April 2015 a group of researchers from China announced the results of their research concerning the modification of a gene associated with blood disorders in human embryos (source:Nature:10.1038/nature.2016.19718). At the same time, another group of Chinese researchers published the results of a similar study – an attempt to make human embryos resistant to HIV infection. Genetic analysis showed that 4 of 26 human embryos were successfully modified. In order to dismiss the suspicion of conducting experiments on unborn children, the authors of the publication took two precautions. Firstly, they created a human embryo by fertilizing an egg cell with two sperm cells, thus, according to the authors, preventing the “creation of a new life”. It is, however, supposed to be a satisfactory research model in human DNA editing. Secondly, the embryos were to be utilized after 3 days. The presented publications have led to the first global discussion about the ethics of modifying embryos and human reproductive cells.
Researchers have been considering the bioethical side of the conducted research for a very long time. Until recently, internal regulations of specific countries stated whether a controversial experiment could be conducted or not. For example, research on human embryo modification is not illegal in the US if it is privately funded. As a general rule, the state does not fund such research. Europe is free from such dilemmas – basically no research centers plan to undertake experiments of this type. One exception may include a group of researchers from the Great Britain, who in 2016 were granted a “licence” from a government agency (regulating matters such as the in vitro fertilization) to use living human embryos in their research on DNA editing, in order to discover the causes of miscarriages. To obtain the permission, they had to meet the condition of concluding the tests on an embryo within 14 days. Granting the permission may serve as a precedent and give a green light to future plans for similar experiments.
In February 2017, a prestigious United States institute – US National Academics of Science, Engineering, and Medicine – published a report concluding that scientists should have the right to conduct research pertaining to editing human embryos (source: Nature:10.1038/nature.2017.21474). The document also stated that ultimately it may be acceptable to use this method in order to modify embryos for implantation (in the uterus), if it aimed at treating a disease. The report adds that at this point editing a genome should not be used to “enhance” human beings by, for example, boosting their intelligence or granting them other, naturally unattainable capabilities. The 261-page report was prepared on the basis of the findings of discussions during a summit in 2015, attended by scientists, ethicists and legal experts from all over the world. Publication of the document and establishing the formal position enabled the genetic research using the DNA editing method across the world. A few months later, the first scientific publications appeared.
In early August 2017, researchers from USA used the CRISPR/Cas DNA editing method on human embryos to modify the mutation of the MYBPC3 gene (source: Nature 548,13–14():10.1038/nature.2017.22382). The mutation causes the heart muscle to “thicken” – a condition known as hypertrophic cardiomyopathy – possibly resulting in sudden death, even at a young age. The mutation is dominant, meaning that a child inheriting only one copy of the mutated gene will experience its effects. The experiment resulted in successful repair of the MYBPC3 gene mutation in 42 of 58 human embryos. Test results confirmed the effectiveness of the CRISPR/Cas method. To everyone’s surprise, in late August 2017 questions have been raised about the published research (source: Nature:10.1038/nature.2017.22547). Another group of US researchers claim that their predecessors have not obtained correct results of DNA editing, and their doubts are included in a publication that will soon appear in Nature magazine.
The evolution of the CRISPR/Cas method is an ongoing process and we can surely expect groundbreaking new test results in the area. The accomplishments so far are at an early stage and lay foundations for future research. However, they are already raising doubts and hesitation not only among the scientists, but the whole society.
Until recently, tampering with our DNA seemed like a dream. Today we know that it is possible and the research in this area has just begun. Is giving a green light to this type of experiments a good decision?