biomolecules Review Potential of Induced Pluripotent Stem Cells for Use in Gene Therapy: History, Molecular Bases, and Medical Perspectives Agnieszka Fus-Kujawa 1, Barbara Mendrek 2 , Anna Trybus 1,† , Karolina Bajdak-Rusinek 3 , Karolina L. Stepien 1 and Aleksander L. Sieron 1,* 1 Department of Molecular Biology, Faculty of Medical Sciences in Katowice, Medical University of Silesia, Katowice, Medykow 18 Street, 40-752 Katowice, Poland; [email protected] (A.F.-K.); [email protected] (A.T.); [email protected] (K.L.S.) 2 Centre of Polymer and Carbon Materials, Polish Academy of Sciences, M. Curie-Sklodowskiej 34, 41-819 Zabrze, Poland; [email protected] 3 Department of Medical Genetics, Faculty of Medical Sciences in Katowice, Medical University of Silesia, Katowice, Medykow 18 Street, 40-752 Katowice, Poland; [email protected] * Correspondence: [email protected] † M.D. student participating in activities of Student’s Scientific Society. Abstract: Induced pluripotent stem cells (iPSCs) are defined as reprogrammed somatic cells exhibit- ing embryonic stem cell characteristics. Since their discovery in 2006, efforts have been made to utilize iPSCs in clinical settings. One of the promising fields of medicine, in which genetically patient- specific stem cells may prove themselves useful, is gene therapy. iPSCs technology holds potential in both creating models of genetic diseases and delivering therapeutic agents into the organism via auto-transplants, which reduces the risk of rejection compared to allotransplants. However, in order Citation: Fus-Kujawa, A.; Mendrek, to safely administer genetically corrected stem cells into patients’ tissues, efforts must be made to B.; Trybus, A.; Bajdak-Rusinek, K.; establish stably pluripotent stem cells and reduce the risk of insertional tumorigenesis. In order Stepien, K.L.; Sieron, A.L. Potential of to achieve this, optimal reprogramming factors and vectors must be considered. Therefore, in this Induced Pluripotent Stem Cells for review, the molecular bases of reprogramming safe iPSCs for clinical applications and recent attempts Use in Gene Therapy: History, to translate iPSCs technology into the clinical setting are discussed. Molecular Bases, and Medical Perspectives. Biomolecules 2021, 11, Keywords: iPSCs; stem cells; gene therapy; differentiation; auto-transplantation; regenerative medicine 699. https://doi.org/10.3390/ biom11050699 Academic Editor: Antonella Motta 1. Introduction Received: 9 April 2021 Since the advent of the term ‘stem cells’ in the 19th century [1], the idea of single- Accepted: 4 May 2021 cell capacity to differentiate into any type of tissue has been appealing to both biologists Published: 7 May 2021 and clinicians. Currently, stem cells are defined as undifferentiated cells capable of self- renewal (extensive proliferation) and with potential to give rise to different cell types [2], Publisher’s Note: MDPI stays neutral and they are found in multicellular organisms in all stages of life. However, adult stem with regard to jurisdictional claims in cell renewal is limited because they can only differentiate into cells specific to one tissue, published maps and institutional affil- although attempts have been made to prove otherwise [3]. Hematopoietic stem cells iations. in the bone marrow, for instance, are able to give rise only to blood cells. Despite this and other drawbacks, human bone marrow stem cells were the first ones to be used in clinical practice back in 1957 [4] as bone marrow transplantation—now used frequently in the treatment of blood disorders [5]. The more recent focus of stem cell research has Copyright: © 2021 by the authors. broadened their potential in regenerative and personalized medicine and modelling of Licensee MDPI, Basel, Switzerland. human diseases; however, finding stem cells capable of differentiating into all types of This article is an open access article tissue is challenging. Embryonic stem cells meet these conditions, but their obtaining distributed under the terms and process is met with opposition of ethical nature [6]. A possible way of overcoming this conditions of the Creative Commons obstacle has been found in 2006 when Takahashi and Yamanaka published the results of Attribution (CC BY) license (https:// their elegant work on reprogramming mouse embryonic fibroblasts into a new type of cell, creativecommons.org/licenses/by/ called induced pluripotent stem (iPSCs) cells. The iPSCs exhibited morphology, growth 4.0/). Biomolecules 2021, 11, 699. https://doi.org/10.3390/biom11050699 https://www.mdpi.com/journal/biomolecules Biomolecules 2021, 11, x FOR PEER REVIEW 2 of 16 Biomolecules 2021, 11, 699 2 of 15 work on reprogramming mouse embryonic fibroblasts into a new type of cell, called in- duced pluripotent stem (iPSCs) cells. The iPSCs exhibited morphology, growth proper- ties, and cell marker gene expression of embryonic stem cells [7]. This procedure makes it properties,possible to and gather cell genetically marker gene patient-specific expression of stem embryonic cells from stem many cells types [7]. This of easily procedure obtain- makesable somatic it possible cells to [8]. gather Methods genetically of creating patient-specific safe iPSCs stem for clinical cells from use manyare still types under of easilydevel- obtainableopment [9]; somatic however, cells the [8 ].technology Methods ofholds creating enormous safe iPSCs potential, for clinical especially use arein creating still under pre- developmentcise medical [techniques.9]; however, In the this technology review, th holdse molecular enormous bases potential, of cell especially reprogramming in creating and precisepossible medical applications techniques. of iPSCs In this in review,this develo theping molecular branch bases of medicine, of cell reprogramming namely gene andther- possibleapy, are applications discussed. of iPSCs in this developing branch of medicine, namely gene therapy, are discussed. 2. What Are Stem Cells? 2. What Are Stem Cells? A stem cell is an undifferentiated cell that can divide to produce daughter cells that continueA stem as cellstem is cells an undifferentiated (self-renew), and cell some that of can them divide are todestined produce to daughterdifferentiate cells to that spe- continuecialized cells. as stem Stem cells cells (self-renew), are an ongoing and somesource of of them differentiated are destined cells to that differentiate make up tothe specialized cells. Stem cells are an ongoing source of differentiated cells that make up the tissues and organs of animals and plants. Therefore, the medical definition of a stem cell tissues and organs of animals and plants. Therefore, the medical definition of a stem cell is is an unspecialized cell capable of perpetuating itself through cell division and having the an unspecialized cell capable of perpetuating itself through cell division and having the potential to give rise to differentiated cells with specialized functions. potential to give rise to differentiated cells with specialized functions. 2.1.2.1. Where Where Do Do the the Stem Stem Cells Cells Originate Originate From? From? InIn nature, nature, stem stem cells cells can can be be isolated isolated from from a a variety variety of of sources; sources; however, however, they they express express aa different different range range of of stemness, stemness, depending depending on on their their origin. origin. Therefore, Therefore, their their classifications classifications alsoalso vary. vary. The first first criterion criterion for for discussion discussion of ofstem stem cell cell classification classification is based is based on their on origin their origin(Figure (Figure 1). Pluripotent1). Pluripotent stem stem cells cells obtained obtained under under specific specific conditions conditions from from the the inner inner cell cellmass mass (ICM) (ICM) of an of embryo, an embryo, called called embryonic embryonic stem stem cells cells (ESCs), (ESCs), were were first first isolated isolated in 1981 in 1981[10] [and10] andare being are being currently currently used usedonly onlyfor rese forarch. research. Isolation Isolation of the ofICM, the however, ICM, however, results resultsin the inblastocyst’s the blastocyst’s destruction, destruction, which which raises raisesserious serious resistance resistance of the ofethical the ethical nature. nature. FigureFigure 1. 1.The The potential potential of of stem stem cell cell differentiation differentiation depends depends on on the the source source of of their their origin. origin. AnotherAnother potentially potentially applicable applicable type type of of stem stem cells cells are are adult adult stem stem cells cells (ASCs), (ASCs), many many ofof which which have have roles roles in in postnatal postnatal tissue tissue remodeling remodeling and and repair. repair. Acquiring Acquiring ASCs ASCs does does not not raiseraise ethical ethical concerns, concerns, but but as theyas they do not do exhibit not exhibit pluripotency, pluripotency, their applications their applications are limited. are However, some studies suggest the expression of pluripotency markers in ASCs, but most Biomolecules 2021, 11, 699 3 of 15 of these experiments involved long in vitro cultures or did not demonstrate pluripotency at the single-cell level [3,11]. In 2006, a new type of stem cell was reported by Yamanaka and colleagues [7], who generated iPSCs directly from murine somatic cells. This procedure requires transducing cells with transcription factors, shown previously to be upregulated