The general concept of cloning is widely known, even to small children. The word “cloning” refers to “making an identical copy” of a biological entity. We can thank various sci-fi movies for presenting the basic concept of this technique. However, such movies have led to some major misconceptions. The general public usually thinks of whole organism cloning because of the evil clone cliché. Nevertheless, in science, whole human cloning is considered unsafe and unethical. The general public is not familiar with the fact that this technique has a much broader sense and is much more complex. Furthermore, it can be applied to various fields and holds many possibilities. In medicine, some of the major health problems can be solved by cloning and many researchers believe that this technique can revolutionize regenerative medicine.
Basic principles of cloning
Before we delve deeper into the application and perspectives of cloning in medicine, let’s clear out some basic principles. Cloning doesn’t only happen in the laboratory, it also happens naturally. Asexual reproduction creates clones because, in this way, an organism produces identical copies of itself. Microorganisms and plants are widely known to reproduce in this manner, but some invertebrates and vertebrates are also able to asexually reproduce. However, this type of reproduction has never been reported in mammals in wild. The only form of natural clones that can be spotted in mammals and, therefore, humans are identical twins. However, some of the latest research has shown that due to mutations in early development, even identical twins don’t share a 100% identical genome.
The concept of cloning in vitro is somewhat different. Artificial cloning can be performed on different biological levels.
Because of this, there are three types of cloning:
1. Gene cloning (of a particular gene or DNA segment)
2. Reproductive cloning (whole organism cloning)
3. Therapeutic cloning (embryonic cloning)
Gene cloning in medicine
Reproductive cloning is fiction because of both technical and ethical reasons when it comes to humans. On the other hand, gene cloning and therapeutic cloning have found their application in medicine. Gene cloning is used in medicine indirectly. It’s a process where a DNA segment of interest is located and copied from one organism and transferred to a different organism to create numerous identical copies of this segment. DNA found in the host cell is called recombinant DNA because it contains both the gene of interest and the genetic material of the host. Hosts are usually bacteria since they replicate fast and are easy to maintain in culture. The first successful attempt of this method happened as early as the 1970s. Since then, recombinant DNA has been used primarily for the production of proteins such as insulin for diabetics, growth hormone, factor VIII, etc. This has had a gigantic impact on medicine when it comes to therapies, but when it comes to future perspectives, therapeutic cloning is much more promising.
In gene cloning, only one part of the genome is being cloned. When it comes to reproductive and therapeutic cloning, the entire nuclear material is transferred. This technique is called somatic cell nuclear transfer (SCNT) which means that the nuclear material of a somatic cell is taken from the donor and it’s transported in the enucleated oocyte. The goal of this procedure in reproductive cloning is to create an identical organism, but in therapeutic cloning, the goal is to derive embryonic cell lines with an identical genetic material to their donor. These cells called nuclear-transfer embryonic stem cells (ntESC) offer great promises in regenerative medicine. From these cells, differentiated cell lines can be generated with a specific genetic make-up.
Scientists can create these stem cells, but first, these stem cells must be researched. One of the areas that must be studied is molecular pathways of differentiation. The goal of this research is to understand these processes and then create methods, techniques and protocols for directed differentiation. Directed differentiation can be used for the creation of model systems, drug discovery and regenerative medicine.
Model systems enabled by directed differentiation can be used to study the early development of mammals. In this way, the role of specific genes can be studied in vitro in a relevant organism and not only in model organisms, such as zebrafish or Xenopus. The goal of these models is to find underlying mutations and causes of particular diseases, as well as develop new approaches for treating such states.
Drug discovery using stem cells enables us to directly test the effects of drugs on the heart and liver through developed cardiomyocytes and hepatocytes. Another benefit of such research is that it enables scientists to investigate the effects of a particular drug on different genotypes to identify specific drug responses and toxicity. So far, medical and pharmaceutical research in treatments has been conducted on animals. This kind of research can be very cruel and it’s condemned by animal rights organizations, such as PETA. Luckily, stem cells might replace animals completely in future. So, drug discovery can be cruelty-free thanks to advances in cloning and stem cell biology.
The best known potential application of therapeutic cloning is in regenerative medicine. It offers great promise as a novel source of cells for cell replacement therapies for various illnesses, such as cardiovascular diseases, blood cell diseases, some neurodegenerative diseases, etc. Also, through directed differentiation, one of the major goals is to be able to create organs for transplantation that have the identical genetic make-up as the recipient. Because of the matching genetic profile, both cell replacement therapy and organ transplantation would more successful because there would be no graft rejection. Also, burnt skin tissue, damaged muscles or nerves could be replaced through therapeutic cloning. Unfortunately, this type of therapy is still being heavily researched and it isn’t successful yet or ready for application.
To conclude, therapeutic cloning carries many promises, but a lot more research is required to make it applicable. The current reality is that such stem cells can only be used in research for now and we are still far from using all of its potentials. Since this type of research is very significant, a lot of funds are being invested and an enormous number of scientists are working on this. However, change doesn’t happen overnight and it will surely take a lot of time to enjoy all the benefits of cloning in medicine.
Ayala F. J. (2015). Cloning humans? Biological, ethical, and social considerations. Proceedings of the National Academy of Sciences of the United States of America, 112(29), 8879–8886. https://doi.org/10.1073/pnas.1501798112
Gupta, V., Sengupta, M., Prakash, J., & Tripathy, B. C. (2016). Production of Recombinant Pharmaceutical Proteins. Basic and Applied Aspects of Biotechnology, 77–101. https://doi.org/10.1007/978-981-10-0875-7_4
Kfoury C. (2007). Therapeutic cloning: promises and issues. McGill journal of medicine: MJM : an international forum for the advancement of medical sciences by students, 10(2), 112–120.
Keller G. (2005). Embryonic stem cell differentiation: emergence of a new era in biology and medicine. Genes & development, 19(10), 1129–1155. https://doi.org/10.1101/gad.1303605
https://www.genome.gov/25520302/online-education-kit-1972-first-recombinant-dna (Accessed: 1.6.2021.)
https://www.genome.gov/about-genomics/fact-sheets/Cloning-Fact-Sheet (Accessed: 1.6.2021)
https://www.nationalgeographic.org/encyclopedia/cloning (Accessed: 1.6.2021.)
https://archive.bio.org/articles/value-therapeutic-cloning-patients (Accessed 1.6.2021.)
https://www.healthline.com/health/stem-cell-research (Accessed 1.6.2021.)