Part II, The CRISPR/Cas controversy

Feb ,16 2017

Since the discovery of CRISPR/Cas in 2012 results involving the technique are published daily inside and outside of the scientific community, demonstrating the impact of this method on life sciences. CRISPR/Cas facilitates the manipulation of genetic material, which was possible before as detailed below, however the ease and precision of this method is unprecedented. This technology re-ignited already intense debates on Genetically Modified Organisms and fears of “designer babies”, whilst inspiring others to cure diseases. Modification of human cells, which would not be passed onto the next generation (somatic cells) was already being developed, however, it is the possibility of manipulating the germ-line (i.e. eggs, sperm, embryos), which poses great controversy.




Gene therapy aims to replace or counteract any malfunctioning gene by its correct version in either somatic or germline cells. Technologies such as Transcription Activator-Like Effector Nucleases (TALENs) and Zinc Finger Nucleases (ZFNs) use one enzyme, which acts as a molecular scissor that recognises the DNA fragment to be cut. Therefore, TALENs and ZFNs are custom made for each DNA target, a process which is labour-intense and very expensive. In contrast, CRISPR/Cas uses one enzyme acting as the scissors (Cas), and bound to it an RNA molecule, which guides the enzyme to the targeted DNA segment. The guide RNA will determine the target in the DNA genome, as the guide RNA sequence is complementary to the desired target DNA sequence. The CRISPR/Cas technology is easier to handle, because the cleaving enzyme remains the same for every manipulation, whilst the only variable component is the guide RNA.

Due to the ease of the CRISPR/Cas technology there are now numerous laboratories using this method for their research, and the field is ever-expanding. However, this rapid development does re-kindle former debates on GMOs, the value of life, and the environment.

One of the scientists who discovered the CRISPR/Cas system in 2012, Jennifer Doudna, decided to address the issues surrounding this novel technology and its impact on society at a meeting organised in Napa, California in January 2015. There are numerous advantages, which will improve biomedical and agricultural research:

- Correction of malfunctioning genes in somatic tissue
- Deletion of latent virus infections such as herpesviruses or Human immunodeficiency virus
- Precise disease modelling, in particular of diseases caused by single mutations
- Eradication of disease vectors, for example, of malaria and Zika virus
- Improve food production

However, genome editing and the CRISPR/Cas technology are still in their early phases, and many aspects require further study, such as:
- Type and frequency of potential off-targets (off-targets are DNA sequences, which will by cleaved because they are too similar to the intended target sequence)
- Un-intended on-target effects (deletion of a particular gene might yield undesired effects if the gene and/or its sequence has more functions than are currently known)
- Modification of cells and tissue resulting from the process of gene editing itself
- Impact of GMOs on environment

The conference attendees, which included leading scientists in the field of genome editing, some of which participated in the 1975 Asilomar conference, and representatives from industry, government bodies and the public, discussed these issues and concluded that scientists should voluntarily impose a moratorium on the use of CRISPR/Cas to therapeutically manipulate the human germline until the full scope of its consequences are known. In many countries such as Canada, the EU, Australia, Mexico and Brazil, research on the human genome is limited through legislation or guidelines provided by governments and/or funding agencies. Others have no regulations set in place and the joint letter by Doudna and other scientists published in Science in 2015 urges research groups in these countries to halt and postpone these types of experiments until it is safe to proceed.

The development of gene editing has revolutionised the field of biomedical research and led to great discoveries and treatments, however the examples of recombinant DNA and the CRISPR/Cas technology demonstrate that researchers are aware of the fact that risks will be associated with them – a continuous discussion with the public and governments is required to ensure the safe development of new technologies, whilst allowing researchers to unravel the natural world.