Can you imagine a world where human beings can design new crops, edit mosquitoes to prevent malaria, cure diseases by playing with genes, or even design babies? Believe it or not, in 2020 this is all possible. Theoretically. CRISPR/Cas9 is an innovative genetic engineering tool, whose unprecedented ease to edit diverse genomes, has turned it into a modern scientific revolution. Editing human genomes to cure diseases might have seemed provocative and delusional decades ago, however, it is a rising star for curing challenging conditions today. How is a simple complex of DNA/RNA and one protein changing our way of perceiving therapeutics?
CRISPR/Cas9 or the Clustered Regularly Interspaced Short Palindromic Repeats – CRISPR-associated protein 9 system, is, in principle, less complicated than its name. It was first discovered as an acquired prokaryotic immune system, but it has slowly and firmly evolved into a powerful DNA-targeting tool. In a nutshell, the basic CRISPR/Cas9 consists of short invading DNA fragments that integrate into the host chromosome. Transcription and enzymatic processing of these new genes results in RNA transcripts, commonly known as guide RNAs, which can recognize complementary DNA regions. Their close collaboration with the Cas9 enzymes, which cut DNA, like molecular scissors, introduces site-specific mutations which can precisely target genes. (1)
By changing the guide RNA sequence, this two-component system can be programmed to target virtually any DNA sequence of interest in the genome, potentially empowering it with boundless possibilities. CRISPR/Cas9 is easy to design, simple to use, and highly efficient. This has boosted its applicability in elucidating functions of target genes, genetically modifying crop strains, and functionally inactivating genes in human cell lines and cells. As such, it holds immense promise to treat or even cure genetic disorders, including many forms of cancer, neurodegeneration, and genodermatoses. (1) The vastest, to date, medical application of CRISPR/Cas9 is in fighting cutaneous diseases. Starting from melanoma, viral and bacterial infections, to debilitating genetic disorders, dermatology has long been in the centre of translational studies for CRISPR-Cas9 therapeutics. The skin is an easily accessible organ, its visibility allows simpler monitoring of clinical amelioration and most importantly, can be targeted topically, giving rise to multiple attempts in in vivo gene editing research. (2)
One of the first human trials involving CRISPR-Cas9 was centred in refractory melanoma, among other neoplasms, targeting T-cell programmed death genes. As we speak, multiple clinical trials testing CRISPR are ongoing, mainly on viral cutaneous infections, like the in vivo targeting of E6/E7 in HPV-infected patients, after convincing proof of cervical tumour burden decrease, in animal models. Of the genodermatoses, the inherited Epidermolysis Bullosa disorders have been the most extensively studied and several in vivo studies have been successful in correcting defective genes for the production of new, much-needed proteins. Besides, other diseases lie in CRISPR/Cas9 horizon. The method is viewed as a promising tool to target Xeroderma Pigmentosum or Merkel-cell polyomavirus, in the near future. (2)
Despite recent exciting advances, there are still many challenges to overcome for the final applications of CRISPR-Cas9 to clinical gene therapy, such as the specificity and efficacy of CRISPR-Cas9 in therapeutic genome editing, efficacy and translatability of in vivo delivery methods, and potential immunogenicity of CRISPR-Cas9 and the delivery vehicles. (3) The risk of improper use, especially in germline cells, is a hot topic, in terms of ethical concerns among the scientific society. Even though its future in genetic and biomedical research seems bright, there is room for many amendments to increase its specificity, safety, and efficacy in the levels of its potential. When and if CRISPR will overcome its challenges, is not certain. However, no one can deny the power that it possesses in radically transforming clinical therapies.
References:
1. Jiang, F. & Doudna, J. A. CRISPR – Cas9 Structures and Mechanisms. 505–531 (2017).
2. Baker, C. & Hayden, M. S. Gene editing in dermatology: Harnessing CRISPR for the treatment of cutaneous disease. F1000Research 9, 281 (2020).
3. Dai, W. J. et al. CRISPR-Cas9 for in vivo Gene Therapy: Promise and Hurdles. Mol. Ther. - Nucleic Acids 5, e349 (2016).