Gene therapy is described as the capacity for gene improvement by means of the correction of altered (mutated) genes or site-specific modifications with purpose of therapeutic treatment. Food and Drug Administration (FDA) , for instance, defined that gene therapy was a technique that modified a person’s genes to treat or cure disease and that gene therapy could work by several mechanisms. Firstly, by replacing a disease-causing gene with a healthy copy of the gene. Secondly, by inactivating a disease-causing gene that was not functioning properly or for example by introducing a new or modified gene into the body to help treat a disease.
The early days
History of gene therapy starts in 70s and 80s with two, eventually halted, clinical trials of which one was related to specific enzyme and other to hemoglobin deficiency. Early attempts to treat patients with novel approach did not grant success in terms of assuring effective therapy. But, the significance of these trials reflects in providing new insights for development and improvement of technique. Furthermore, development of new techniques led to development of significant number of registered gene therapy medicinal products worldwide.
Currently, not only we are able to replace defective gene, but also, we are developing methods for correcting specific sequence within a genomic DNA region – known as gene editing. In fact, CRISPR-Cas9 gene editing might be the most known method considering that in 2020 Emmanuelle Charpentier and Jennifer Doudna have been awarded by Nobel Prize in Chemistry for development of a method for gene edition.
By regulating the malfunctioning genes, gene therapy could radically improve the treatment of monogenic disorders and other genetically defined diseases. In other words, it represents the most recent advances of the biotechnology revolution in medicine.
During the past half century, the aim was to develop promising gene therapy drugs for human use. Since 1998, twenty-two gene therapy drugs have been approved for treatment of human diseases (Picture 1) as a result of advanced biotechnologies applied in the pharmaceutical field. Also, several types of therapies were developed through years including naked nucleic acids, a non-viral vector, viral vectors and cell-mediated gene therapy products. For example, treatment of diseases such as head and neck cancer (Gendicine), nasopharyngeal carcinoma (Oncorine), soft tissue sarcoma and osteosarcoma (Rexin-G), LPL deficiency (Glybera), spinal muscular atrophy (Spinraza and Zolgesma), etc. involve the approved gene therapies.
In 2015, Chinese scientists reignite the ethical debate after reporting editing the genomes of human embryos. By this time, there have been studies regarding editing mouse embryos and human adult cells. But, gene editing of human germline was not studied yet. The team used non-viable embryos, which cannot result in a live birth, and attempted to modify gene responsible for β-thalassemia using CRISPR/Cas9 technique. The results revealed that technique should be improved considering large amount of ,,off-target” mutations. That was one of the main safety concerns when it comes to editing germline, considering harmful effect of these mutations.
When it comes to developing new technics for treatment of human diseases, bioethics is always present to assess risk and benefit ratio, and moral implications involved. Nowadays, large part of scientific community approves genetic therapy of somatic cells, especially in cases of severe disorders. However, the possibility of genetically modifying germlines has been the object of debates for a long time.
- FDA website
- Capone, F., Nappi, F., & Galli, M. C. (2020). Gene Therapy Clinical Trials: Past, Present and Future. In Second Generation Cell and Gene-based Therapies (pp. 285-301). Academic Press.
- Cyranoski, D., Reardon, S. (2015). Chinese scientists genetically modify human embryos. Nature
- Gonçalves, G. A. R., & Paiva, R. D. M. A. (2017). Gene therapy: advances, challenges and perspectives. Einstein (Sao Paulo), 15(3), 369-375.
- Ma, C. C., Wang, Z. L., Xu, T., He, Z. Y., & Wei, Y. Q. (2020). The approved gene therapy drugs worldwide: from 1998 to 2019. Biotechnology advances, 40, 107502.