Induced Pluripotent Stem Cells: Forging a New Biomedical Frontier or Unleashing Ethical Dilemmas?

Different transcription factors are used to transform somatic cells into IPSCs, or induced pluripotent stem cells. iPSCs have special abilities to self-renew and differentiate into a variety of cell lineages. As a result, they might take the place of embryonic stem cells (ESC) and help resolve the different moral dilemmas associated with the use and exploitation of  embryos in laboratories and medical facilities. A huge number of people were inspired to develop more genuine techniques for iPSC creation as a result of the overwhelming responses sparked by the use of iPSCs that were spurred by numerous studies across the globe.

Numerous molecules, including miRNAs, DNA modifying substances, NANOG, etc., are involved in the molecular processes that enable the production of iPSCs from various somatic cell sources.

Uses of IPSCs

 While promising a number of important roles in various clinical/research studies, iPSCs could also be of great use in studying molecular mechanisms of many diseases. There are various diseases that have been modeled using iPSCs for a better understanding of their etiology, which may be further utilized for developing potential treatments for these diseases. In addition, iPSCs are used for the production of patient-specific cells that can be transplanted to the site of injury or the site of tissue degeneration due to various disease conditions. Using iPSCs could  eliminate the chances of immune rejection,  as specific cells for each patient can  be used for transplantation in a variety of engraftment processes. Moreover, iPSC technology has been employed in various diseases for disease modeling and gene therapy. This  technique offers more convenience over other similar techniques such as animal models. Many toxic compounds and newly designed drugs may be evaluated for toxicity and effects by using iPSCs. In summary ,  the applications of iPSCs  in regenerative medicine, disease modeling, and drug discovery are enormous and should be explored and understood more comprehensively.

A Small History Lesson

The discovery of self-renewal by any living cell was one of the breakthroughs reported by Till and McCulloch in 1961. They found that while subjecting mice to lethal doses of radiation followed by injection of bone marrow cells, these cells formed clumps due to cells cloned from them, which was the main reason for the survival of the mice. Later studies defined their potential for differentiation into different cell types and self-renewal without senescence i.e the lack of deterioration with age , and termed them Stem Cells. Stem cells can be defined  based on their origin and potency into Adult Stem Cells and Embryonic Stem Cells (ESC). Similarly, considering their potency as the base of classification, stem cells can be classified into unipotent, multipotent, oligopotent, pluripotent, and totipotent. Totipotent cells can differentiate into embryonic as well as extra-embryonic tissues such as the placenta. Pluripotent stem cells can differentiate into other cells of the adult body. This property exists for only a specific period of pre-implantation development in the cells forming Inner Cell Mass (ICM). As the cells differentiate into other cell lineages, their self-renewing potential decreases due to various epigenetic changes, leading to the loss of pluripotency.

Further research conducted on human stem cells (HSCs) made burgeoning use of human ESCs for which embryos needed to be isolated regularly, evoking several ethical issues among socio-research communities.Various research groups have attempted to get beyond these moral and technical  issues. Subsequent studies demonstrated many advancements in related techniques such as cloning in frogs, generation of mouse Stem Cells (SCs), cloning in sheep, generation of HSCs, and development of Embryonic stem cell fusion techniques . These findings contributed greatly to the development of cells that could eliminate ethical issues. However, the major breakthrough came in 2006 when Takahashi and Yamanaka introduced the concept of induced pluripotent stem cells (iPSCs) by generating stem cells that had properties relating to ESCs. iPSCs were generated by using a combination of 4 reprogramming factors, including Oct4, Sox2, Klf4, and c-Myc, and were demonstrated as both self-renewing and differentiating like ESCs and thus could be used as an alternative for hESCs in various clinics/research. Since then, a number of different reprogramming factors/methods have been established. iPSCs generation may employ a combination of different reprogramming factors, a cocktail of various reprogramming factors, direct use of proteins, miRNA, peptide, etc.

Generation of iPSCs

Theoretically, iPSCs can be generated by using any somatic cell by employing appropriate reprogramming factors and the most convenient method for their introduction to somatic cells. iPSC generation is reported by using cells from different sources, such as fibroblasts, cord blood, peripheral blood. There are a large number of reports showing the whole process in a detailed manner that can be summarized in three major steps

(i) establishment of the initial cell culture, 

(ii) induction of iPSCs, 

 (iii) characterization and expansion of iPSCs.

The source cells are first separated and grown. Then, those cultivated cells are exposed to the reprogramming factors. The introduction of reprogramming elements may be done in two different ways: by integrating systems or through non-integrating procedures. Following the expression of these reprogramming factors, these transfected cells are cultured on feeder layers in the proper medium, leading to the production of iPSCs. Several morphological and physiochemical techniques can be used to describe the cultivated iPSC colonies. Similar to ESCs, iPSCs may be morphologically examined based on their round form, big nucleolus, and sparse cytoplasm. Because reprogrammed colonies have the ability to self-renew, they are flat, sharply edged, closely packed, and highly active during mitosis. While it is challenging to identify iPSCs based only on the basis of their morphology, these characteristics give a quick idea about their states. Further, iPSCs may be defined on the basis of the expression of different cell surface proteins and transcription factors Oct4, Sox2, Nanog, which can also be used for the characterization.

Application of iPSCs

The treatment of many diseases is difficult because of the lack of information about the mechanisms that play a role in the disease progression. For this reason, diseases need to be modeled so that treatment could be developed aiming the main cause of the disease. There are a large number of disease testing models which have developed during previous eras. Some of them are capable of mimicking human cellular microenvironment and metabolism to some extent.

 Many animal models such as rat, mice, dogs, monkeys, dogs, and primates have been used for disease modeling. However, the use of animals as disease models is limited due to existing variability in the genetic make-up of them that is highly responsible for the biological functions and hence differences are exhibited when compared with human individuals. Secondly, the problem further gets complicated when the individuals are of two different species. Different species have different genetic makeup and hence different proteins. And thus, none of the animal models is able to fully mimic the human cell microenvironment. So, a different approach which can provide the same environment as in human cells is required, and iPSCs pose to be a good alternative with some advantages as well. In the case of iPSCs, there is no need for proliferation again and again, and, their derivatives are functional in-vitro as well as in-vivo after transplantation. 

Ethical and practical considerations 

This technique could be helpful for treating infertility, however, the use of iPSC-derived gametes raises another  set of ethical concerns related to the potential exploitation of created embryos, human NT, and risk of change to natural reproduction including the possibility to derive gametes for same-sex reproduction, as well as in the asexual reproduction. As for hESCs the main safety issue regarding iPSC-based therapy is the risk of teratoma formation which can happen if patient receives  iPSC-derived cells that contain undifferentiated iPSCs. Uncontrolled proliferation and differentiation of transplanted undifferentiated iPSCs may result in generation of tumors and/or undesired differentiation of iPSCs in broad range of somatic cells Thus, development of more effective methods for generation of purified populations of autologous iPSC-derived differentiated cells remains a challenge for personalized and regenerative medicine 

Conclusion : 

In essence , induced pluripotent stem cells are an enormous discovery which could not only reshape the field of stem cell research but also alter the course of medicine as a whole  , assisting in treating countless diseases as well as minimizing the long standing moral and ethical concerns associated with regular embryonic stem cells .. However , a problem still stands .  some ethical  concerns still persist  regarding the possible exploitation of created embryos and the risks associated with the conversion of adult stem cells into induced pluripotent stem cells as well as their addition to the human body .