Crispr-Mediated Gene Editing Will
CRISPR-mediated gene editing will eradicate genetic disease within my lifetime
In 1987 the unusual repeats of DNA that form CRISPR were discovered in the DNA of Escherichia Coli by Ishino et al. (1). However, it was not until 2002 that Mojica et al first characterized this locus, which is a type II prokaryotic immune system (2), as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) (3). Since then CRISPR, alongside Cas9 (CRISPR associated protein 9), has rapidly grown into one of the most valuable and easy to use genome editing tools in both molecular and cell research, this rapid growth most likely due to the system being straightforward, and both highly adaptable and efficient (4). These fundamentals of CRISPR have made it easy for CRISPR to be used in a wide range of research in gene therapy for infectious diseases such as HIV and hepatitis B and for genetic disorders such as Duchenne muscular dystrophy (5) and Huntington’s disease. In 2017, CRISPR is now being used in around 20 clinical trials around the world including one genetic disease based trial attempting to use this tool to edit cells inside the body, with an aim to destroy HPV genes responsible for tumours, therefore, preventing cervical cancers. The CRISPR-Cas9 system was only first introduced to mammalian organism research in 2013, with this considered, the major question now for CRISPR is will it ever eradicate genetic disease and if so will this be within our lifetime.
CRISPR-mediated gene editing has been applied to many genetic diseases to date and this research is ever continuous with new methods applied to different disorders all the time. At first, CRISPR demonstrated its affectivity in its ability to correct monogenic diseases, such as that of Duchenne muscular dystrophy (DMD). In 2015, Long et al. demonstrated that CRISPR was effective in correcting the gene mutation responsible for DMD in a germ-line mouse model of DMD. After treatment, the genome editing gave rise to a range of genetically altered mice with a range of 2-100% gene correction (6). CRISPR has also had notable advances in the correction of genes responsible for Cystic Fibrosis in Intestinal stem cells, Schwank et al (2013) was successfully able to correct the mutant allele using CRISPR and demonstrated that these corrected alleles were functional in the mouse intestinal organoid system (2). Another genetic disease in which CRISPR has made strides in correcting is Huntington’s disease, again Huntington’s monogenic structure lends it easily to CRISPR-Cas9 mediated editing and in 2017 a method used to inactivate mutant HTT alleles was practiced in rodent models, this was overall successful yielding selective reducing of mutant genes and general improved function, although it did not extend mutants survival (7). Although this research is promising, critics have become aware of ethical and safety issues when applying discoveries made in-vitro to human cells in-vivo for medical practices. This has previously prevented CRISPR technology from moving forward and eradicating genetic disease within humans (1).
One issue for the safety of using CRISPR to edit the genome of germ-line cells or embryos is that of making unwanted mutations to the gene and the creation of embryos containing cells with different DNA sequences – mosaics. Mitalipov et al. (2017) overcame this issue by using a new technique of CRISPR insertion to the embryo, inserting both the CRISPR and sperm into the egg cell that the same time. This technique yielded only one mosaic embryo out of 54 compared to post fertilisation insertion of CRISPR, which yielded 13 out 54 mosaic embryos. This is promising and may lead to more encouragement of human germline cell gene editing moving CRISPR ever closer to eradicating genetic diseases (8). However this doesn’t come without ethical concern, research into CRISPR and embryos gives the possibility of scientists permanently changing the human genome, an idea that has come under high levels of scrutiny. This has the potential to prevent CRISPR-mediated gene editing from truly progressing, for example in the US research cannot be carried out on human embryos using taxpayer money, the research can only be funded by private donors, National Geographic, August 2017. This could prevent one of the major scientific research bases in the western world from aiding with the development of CRISPR technologies.
CRISPR is repeatedly praised for how easy it is to use and how versatile it is in comparison to other gene editing techniques such as ZFN (Zinc finger nucleases) and TALENs (transcription activator-like effector nucleases). Its major benefit is that it requires a simpler guiding protein than ZFN and TALEN, which require synthesis of a larger, heavier guiding protein. CRISPRs other advantage is its ability to “multiplex” the process of editing loci simultaneously (9). However, studies have shown that TALEN has fewer restrictions than CRISPR in where it can target on the genome and has been credited for producing fewer effects away from the targeted area than CRISPR. This leads us to question is there another biological product, yet to be discovered, which may have the benefits of both CRISPR and TALEN.
In conclusion, although CRISPR is making major strides in genome editing tools and techniques it still requires a large amount of development before it can start to treat genetic diseases in-vivo in humans and not just have effects in-vitro. For CRISPR to truly be able to eradicate genetic disease, laws regarding the use of human embryos need to change, allowing for embryos to be edited using CRISPR before being inserted into the womb and allowing it to develop. Until this point CRISPR will only be able to be used in humans via somatic cell and stem cell insertion into the body, which may cure the disease but does not mean it will be eradicated as the disease will still be present until treatment. CRISPR is revolutionary and will be useful in the treatment of genetic disease in years to come, but will it eradicate genetic disease? From examining the evidence, I believe that it quite probably does have the ability to, just not within my lifetime.