Cell Sources for iPSCs

The series Advances in Stem Cell Biology is a timely and expansive collection of comprehensive information and new discoveries in the field of stem cell biology. Somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) by the expression of specific transcription factors. These cells are transforming biomedical research in the last 15 years. Cell Sources for iPSCs, Volume 7 teaches readers about current advances in the field. It shares up-to-date comprehensive overviews of current advances in the field. This book describes the derivation of iPSCs from different sources in vitro, enabling us to study the cellular and molecular mechanisms involved in different pathologies. Further insights into these mechanisms will have important implications for our understanding of disease appearance, development, and progression. The authors focus on the modern state-of-art methodologies and the leading-edge concepts in the field of stem cell biology. In recent years, remarkable progress has been made in the obtention of iPSCs and their differentiation into several cell types, tissues, and organs using state-of-art techniques. These advantages facilitated identification of key targets and definition of the molecular basis of several disorders. Thus, this book is an attempt to describe the most recent developments in iPSCs biology, which is one of the rising hot topics in the field of molecular and cellular biology today. Here, we present a selected collection of detailed chapters on how we derive iPSCs from distinct sources. Ten chapters written by experts in the field summarize the present knowledge about different cell sources for iPSCs. This volume is written for researchers and scientists in stem cell therapy, cell biology, regenerative medicine, and organ transplantation and is contributed by world-renowned authors in the field.

• Provides overview of the fast-moving field of stem cell biology and function, regenerative medicine, and therapeutics
• Covers the following: myoblast-derived iPSCs, lymphoblastoid-derived iPSCs, amniotic fluid stem cell–derived iPSCs, spermatogonial stem cell–derived iPSCs, iPSCs derived from postmortem tissue, and more
• Contributed by world-renowned experts in the field

• Language: English
• Publisher: Academic Press
• Release date: May 9, 2021
• ISBN: 9780128223277

Book preview

Cell Sources for iPSCs, Volume 7

Editor

Alexander Birbrair

Federal University of Minas Gerais, Department of Pathology, Belo Horizonte, Minas Gerais, Brazil

Columbia University Medical Center, Department of Radiology, New York, NY, United States

Table of Contents

Cover image

Title page

Advances in Stem Cell Biology

Copyright

Dedication

Contributors

About the editor

Preface

Chapter 1. Induced pluripotent stem cells derived from amniotic fluid stem cells

Introduction

Induced pluripotent stem cells derived from amniotic fluid stem cells

Summary

Chapter 2. Induced pluripotent stem cells from spermatogonial stem cells: potential applications

Introduction

Spermatogonial stem cell as source of pluripotent stem cells (Germline cell-derived pluripotent stem cells)

Molecular characteristics of germline cell-derived pluripotent stem cells

Differentiative potential of germline cell-derived pluripotent stem cells

Multipotency of spermatogonial stem cell

Future trends and perspectives

Chapter 3. Induced pluripotent stem cell derivation from myoblasts

Introduction

Induced pluripotent stem cells

Chapter 4. Lymphoblastoid-derived human-induced pluripotent stem cells: a new tool to model human diseases

hiPSC technology

Limitations to the use of human-induced pluripotent stem cells

Lymphoblastoids

Establishing human-induced pluripotent stem cells from lymphoblastoid cell lines

Differentiation of lymphoblastoid cell line–derived human-induced pluripotent stem cells into functional cardiac, neuronal, and muscle cells

Conclusion

Chapter 5. Oral tissues as sources for induced pluripotent stem cell derivation and their applications for neural, craniofacial, and dental tissue regeneration

Introduction

Oral tissues as a cell source to generate induced pluripotent stem cells

Limitation of dental tissues–derived mesenchymal stem cells and the advantage of induced pluripotent stem cells as a cell source for craniofacial regeneration

Application of induced pluripotent stem cells in dental and craniofacial regeneration

Application of induced pluripotent stem cells in studying inherited/genetic dental diseases

Current challenges and future prospective of induced pluripotent stem cells

Conclusion

Chapter 6. Induced pluripotent stem cell derived from ovarian tissue

Introduction

Stem cells

Adult stem cells

Embryonic stem cells

Induced pluripotent stem cells

Homotypic differentiation

Ovarian anatomy and function

Disruption of ovarian function and treatment options

The reproductive system

Ovarian development

Oogenesis and stem cells

Anatomy of the ovarian follicle

Functions of the ovary and the hypothalamic-pituitary-ovarian axis

Induced pluripotent stem cell-mediated regeneration of ovarian tissue

Granulosa cells as a source for generating induced pluripotent stem cells

Induced pluripotent stem cell reprogramming methods

Virus-free technique

Sendai viral generation of induced pluripotent stem cells

Retroviral generation of induced pluripotent stem cells

Verification of induced pluripotent stem cell pluripotency

Induced pluripotent stem cell differentiation

Steroidogenic tissue

Homotypic differentiation of ovarian cells

Clinical translation

Future directions

An autologous model for cell-based stem cell therapies

Chapter 7. Muse cells as a robust source of induced pluripotent stem cells

Introduction

The characteristics of Muse cells

Fibroblasts are a heterogenous cell population

Pluripotent-like Muse cells are more prone to become induce pluripotent stem cells than general fibroblasts

Can the generation of induce pluripotent stem cells from pluripotent-like Muse cells be considered reprogramming?

Muse cells are realistic source of induce pluripotent stem cells

Different reporting systems may cause uncertainty in reprogramming efficiency

Chapter 8. Prostate cancer reprogramming and dedifferentiation into induced pluripotent stem cells

Introduction

Luminal-like versus stem-like prostate cancer cell types

Adenocarcinoma versus nonadenocarcinoma and small cell carcinoma

Stem cell transcription factor expression in LuCaP lines

Low B2M expression in stem cells and stem-like LuCaP

In vitro maintenance of LuCaP lines and reprogramming of LuCaP adenocarcinoma

Stromal induction of stem cells in organ development

Organ-specific stromal genes and identification of prostate-specific stromal cell factors

Absent expression of organ-specific stromal genes in cancer-associated stromal cells

Use of co-culture with stem cells to study stromal cell function

Stromal proenkephalin induction of LuCaP 145.1

The effect of proenkephalin on adenocarcinoma LuCaP 70CR

Summary

Future research

Comparison between inactivation of stem cell transcription factor by proenkephalin and other means

Prevention of reprogramming by proenkephalin

Incubation of LuCaP 145.1 in proenkephalin-containing media

Incubation of LuCaP 145.1 with media from cultured NPstrom

Proenkephalin influence on lung small cell carcinoma

Mechanism of proenkephalin on stem cell transcription factor transcription suppression

Other questions

Chapter 9. Melanoma-derived induced pluripotent stem cells: a model for understanding melanoma cell of origin and drug resistance

Introduction

Melanoma—a malignancy of melanocytes

Embryonic origin and distribution of melanocytes

Subtypes of melanoma

Diversity of melanoma driver mutations: indicators of distinct cell of origin?

Melanoma cell of origin: human studies

Zebrafish as a model for cell of origin of melanoma

Melanoma cell of origin: lessons from mouse models

Cancer cell–derived induced pluripotent stem cell: a strategy to dissect cancer cell of origin?

Melanoma-derived induced pluripotent stem cells: relevance to cell of origin and melanoma drug resistance

Conclusions/perspectives

Chapter 10. Induced pluripotent stem cell derived from postmortem tissue in neurodegenerative disease research

Introduction

Induced pluripotent stem cells

Validation of induced pluripotent stem cell

Disease modeling using induced pluripotent stem cell

Neurodegenerative disease

Alzheimer disease

Frontotemporal dementia

Amyotrophic lateral sclerosis

Vascular dementia

Lewy body dementia

Parkinson disease

Conclusions

Index

Advances in Stem Cell Biology

Series Editor

Alexander Birbrair

Copyright

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

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ISBN: 978-0-12-822135-8

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Dedication

This book is dedicated to my mother, Marina Sobolevsky, of blessed memory, who passed away during the creation of this volume. Professor of Mathematics at the State University of Ceará (UECE), she was loved by her colleagues and students, whom she inspired by her unique manner of teaching. All success in my career and personal life I owe to her.

My beloved mom Marina Sobolevsky of blessed memory (July 28, 1959–June 3, 2020)

Contributors

Mohamed Al-Sayegh,     Division of Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates

Fiorella Altruda,     Deptartment of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Turin, Turin, Italy

Christopher J. Anchan,     Johns Hopkins University, Krieger School of Arts & Sciences, Baltimore, MD, United States

Raymond M. Anchan,     Division of Reproductive Endocrinology and Infertility, Center for Infertility and Reproductive Surgery, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Asma Bashir,     Department of Endodontics, Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates

Gisely T. Borges,     Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Edgardo Castro-Pérez

Center for Cellular and Molecular Biology of Diseases, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología (INDICASAT-AIP), City of Knowledge, Panama City, Panama

Department of Genetics and Molecular Biology, University of Panama, Panama City, Panama

Gian Paolo Caviglia,     Deptartment of Medical Sciences, University of Turin, Turin, Italy

Mohamed Chahine

CERVO Research Centre, Institut Universitaire en Santé Mentale de Québec, Quebec City, QC, Canada

Department of Medicine, Université Laval, Quebec City, QC, Canada

Mari Dezawa,     Department of Stem Cell Biology and Histology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Emily R. Disler,     Division of Reproductive Endocrinology and Infertility, Center for Infertility and Reproductive Surgery, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Derek M. Dykxhoorn

John P. Hussman Institute for Human Genomics, Miami, FL, United States

John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, FL, United States

Sharmila Fagoonee,     Institute of Biostructure and Bioimaging (CNR), Molecular Biotechnology Center, Turin, Italy

Pascale V. Guillot,     University College London, Institute for Women’s Health, Maternal and Fetal Medicine Department, London, United Kingdom

George T.-J. Huang,     University of Tennessee Health Science Center, College of Dentistry, Department of Bioscience Research, Memphis, TN, United States

Mohamed Jamal,     Department of Endodontics, Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates

Adelle D. Kanan,     Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Yasumasa Kuroda,     Department of Stem Cell Biology and Histology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Yoshihiro Kushida,     Department of Stem Cell Biology and Histology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Gen Li,     Department of Stem Cell Biology and Histology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Alvin Y. Liu,     Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Amanda J. Myers,     Department of Psychiatry and Behavioral Sciences, Miami, FL, United States

Nicholas W. Ng,     Division of Reproductive Endocrinology and Infertility, Center for Infertility and Reproductive Surgery, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Thuy G. Nguyen,     Division of Reproductive Endocrinology and Infertility, Center for Infertility and Reproductive Surgery, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Laura E. Pascal

Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Department of Urology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States

Rinaldo Pellicano,     Gastroenterology and Hepatology Unit, San Giovanni Antica Sede (Molinette) Hospital, Turin, Italy

Ellen Petzendorfer,     University College London, Institute for Women’s Health, Maternal and Fetal Medicine Department, London, United Kingdom

Davide G. Ribaldone,     Deptartment of Medical Sciences, University of Turin, Turin, Italy

Joseph Rogers,     John P. Hussman Institute for Human Genomics, Miami, FL, United States

Shreyans Sadangi,     Department of Dermatology, University of Wisconsin–Madison School of Medicine and Public Health, Madison, WI, United States

Vijayasaradhi Setaluri

Department of Dermatology, University of Wisconsin–Madison School of Medicine and Public Health, Madison, WI, United States

William S. Middleton VA Hospital, Madison, WI, United States

Mithalesh Singh,     Department of Dermatology, University of Wisconsin–Madison School of Medicine and Public Health, Madison, WI, United States

Ras Trokovic,     Research Programs Unit, Stem cells and Metabolism and Biomedicum Stem Cell Centre, Faculty of Medicine, University of Helsinki, Helsinki, Finland

Eneida F. Vêncio

Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Federal University of Goiás, School of Dentistry, Goiânia, Goiás, Brazil

Ricardo Z.N. Vêncio

Department of Urology, Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA, United States

Department of Mathematics, University of São Paulo, Ribeirão Preto, São Paulo, Brazil

Shohei Wakao,     Department of Stem Cell Biology and Histology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

Ian N. Waldman,     Division of Reproductive Endocrinology and Infertility, Center for Infertility and Reproductive Surgery, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, United States

Matthew L. Winder,     Research Programs Unit, Stem cells and Metabolism and Biomedicum Stem Cell Centre, Faculty of Medicine, University of Helsinki, Helsinki, Finland

About the editor

Alexander Birbrair

Dr. Alexander Birbrair received his bachelor's biomedical degree from Santa Cruz State University in Brazil. He completed his PhD in Neuroscience, in the field of stem cell biology, at the Wake Forest School of Medicine under the mentorship of Osvaldo Delbono. Then, he joined as a postdoc in Stem Cell Biology at Paul Frenette's laboratory at Albert Einstein School of Medicine in New York. In 2016, he was appointed as faculty at Federal University of Minas Gerais in Brazil, where he started his own lab. His laboratory is interested in understanding how the cellular components of different tissues function and control disease progression. His group explores the roles of specific cell populations in the tissue microenvironment by using state-of-the-art techniques. His research is funded by the Serrapilheira Institute, CNPq, CAPES, and FAPEMIG. In 2018, Alexander was elected affiliate member of the Brazilian Academy of Sciences, and, in 2019, he was elected member of the Global Young Academy. He is the Founding Editor and Editor-in-Chief of Current Tissue Microenvironment Reports, and Associate Editor of Molecular Biotechnology. Alexander also serves in the editorial board of several other international journals: Stem Cell Reviews and Reports, Stem Cell Research, Stem Cells and Development, and Histology and Histopathology.

Preface

This book's initial title was iPSCs: Recent Advances. Nevertheless, because of the ongoing strong interest in this theme, we were able to collect more chapters than would fit in one single volume, covering induced pluripotent stem cells (iPSCs) biology from different perspectives. Therefore, the book was subdivided into several volumes.

This volume Cell Sources for iPSCs offers contributions by known scientists and clinicians in the multidisciplinary areas of biological and medical research. The chapters bring up-to-date comprehensive overviews of current advances in the field. This book describes the derivation of iPSCs from different sources in vitro, enabling us to study the cellular and molecular mechanisms involved in different pathologies. Further insights into these mechanisms will have important implications for our understanding of disease appearance, development, and progression. The authors focus on the modern state-of-the-art methodologies and the leading-edge concepts in the field of stem cell biology. In recent years, remarkable progress has been made in the obtention of iPSCs and their differentiation into several cell types, tissues, and organs using state-of-the-art techniques. These advantages facilitated identification of key targets and definition of the molecular basis of several disorders. Thus, this book is an attempt to describe the most recent developments in the area of iPSCs biology, which is one of the rising hot topics in the field of molecular and cellular biology today. Here, we present a selected collection of detailed chapters on how we derive iPSCs from distinct sources. Ten chapters written by experts in the field summarize the present knowledge about different cell sources for iPSCs.

Ellen Petzendorfer and Pascale V Guillot from University College London introduce the derivation of iPSCs from amniotic fluid stem cells. Sharmila Fagoonee and colleagues from Molecular Biotechnology Center discuss iPSCs from spermatogonial stem cells. Matthew Winder and Ras Trokovic from University of Helsinki describe iPSCs derivation from myoblasts. Mohamed Chahine from Université Laval compiles our understanding of lymphoblastoid-derived iPSCs. George T.-J. Huang from University of Tennessee Health Science Center updates us with what we know about oral tissue-derived iPSCs. Raymond Manohar Anchan from Harvard Medical School summarizes current knowledge on iPSCs derived from ovarian tissue. Mari Dezawa and colleagues from Tohoku University Graduate School of Medicine address the importance of muse cells as a robust source of iPSCs. Alvin Y. Liu and colleagues from University of Washington focus on the dedifferentiation and reprogramming of prostate cancer cells to iPSCs. Vijayasaradhi Setaluri and colleagues from University of Wisconsin-Madison give an overview of melanoma-derived iPSCs. Derek M. Dykxhoorn and colleagues from University of Miami Miller School of Medicine update us on the derivation of iPSCs from postmortem tissue.

It is hoped that the chapters published in this book will become a source of reference and inspiration for future research ideas. I would like to express my deep gratitude to my wife, Veranika Ushakova, and Ms. Billie Jean Fernandez and Ms. Elisabeth Brown from Elsevier, who helped at every step of the execution of this project.

Alexander Birbrair

Editor

Chapter 1: Induced pluripotent stem cells derived from amniotic fluid stem cells

Ellen Petzendorfer, and Pascale V. Guillot University College London, Institute for Women’s Health, Maternal and Fetal Medicine Department, London, United Kingdom

Abstract

Pluripotent stem cells have the ability to differentiate down cell lineages of all three germ layers and self-renew indefinitely. Cellular reprogramming or pluripotent stem cell induction is reverting fully differentiated cells back to pluripotency [induced pluripotent stem cells (iPSCs)], through the reactivation of the endogenous pluripotency pathway. The discovery of cellular reprogramming to pluripotency provides significant promise as the derivatives of iPSCs have potential applications in regenerative medicine, drug screening, and disease modeling. Since the establishment of iPSCs, multiple reprogramming methods have been developed. However, a number of technical hurdles, such as reprogramming efficiency, remain to be overcome before translation of iPSC-derivates to the clinic. The amniotic fluid contains fetal cells, such as amniotic fluid stem (AFS) cells, which have great potential in regenerative medicine because of their low immunogenicity. It has been reported that human AFS cells are more rapidly and efficiently reprogrammed into iPSCs when compared to adult cells, making them ideal candidates for developing further methods. This chapter will review the methods used to reprogram AFS cells.

Keywords

Amniotic fluid stem cells; Cell lineage; Cellular reprogramming; Chemical reprogramming; Differentiation; Episomal reprogramming; Fetal; Human stem cells; Induced pluripotent stem cells; Nonviral integrating vectors; Pluripotency; Regenerative medicine; Viral integrating vectors

Introduction

Pluripotency

Assessment of pluripotency

Cellular reprogramming of somatic cells to pluripotency

Induced pluripotent stem cells derived from amniotic fluid stem cells

Amniotic fluid stem cells

Overview of reprogramming methods

Viral integrating vectors

Viral nonintegrating vectors

Episomal reprogramming

Chemical reprogramming

Summary

References

Introduction

Pluripotency

Pluripotency describes the ability of a cell to differentiate down cell lineages from all three germ layers of the developing embryo (endoderm, mesoderm, and ectoderm) without contributing to the formation extraembryonic tissues such as the placenta. Pluripotent cells also have the ability to self-renew indefinitely (De Los Angeles et al., 2015). Pluripotent cells have been derived from embryonic sources such as the inner cells mass of the blastocyst, the epiblast, and primordial germ layers (Jaenisch and Young, 2008). Pluripotency is sustained by various molecular mechanisms which inhibit differentiation and maintain self-renewal. The expression of OCT4, NANOG, and SOX2 is also key in defining pluripotency, with OCT4 being the most preeminent pluripotency factor (De Los Angeles et al., 2015). There are six transcript variants of OCT4: OCT4A, OCT4B, OCT4B1, OCT4B2, OCT4B3, and OCT4B4. OCT4A is a transcription factor found in the nucleus of pluripotent cells. It controls early stages of mammalian embryogenesis; it acts as a repressor of differentiation specific genes and regulates the pluripotent downstream network in human embryonic stem (ES) cells. Unlike OCT4A, OCT4B cannot regulate nuclear gene transcription to sustain pluripotency (Vlahova et al., 2019). The derivatives of pluripotent cells have potential applications in medicine, for example, for the treatment of patients with cancers, heart diseases, and diabetes and in tissue replacement in injuries, degenerative diseases, and autoimmune disorders (Baranek et al., 2017) (Fig. 1.1).

Assessment of pluripotency

A variety of cellular, molecular, and functional assays can be used to assess the developmental potential of pluripotent cells. Confirming cellular pluripotency involves assessing the function by looking at the self-renewal and developmental abilities of the cell and confirming pluripotency as a state by assessing pluripotency transcription factor activation and DNA methylation (De Los Angeles et al., 2015). The first assay is the morphology of the cells and if they form pluripotent colonies, however, this is not specific to pluripotent cells. Alkaline phosphatase staining is a commonly used assay but is also not specific to pluripotent cells (Stadtfeld and Hochedlinger, 2010). The expression of pluripotency markers associated with pluripotency is also commonly used, despite some genes also being activated in partially reprogrammed cells. The markers of TRA-1-60, DNMT3B, and REX1 can be used to identify fully pluripotent cells. Whereas alkaline phosphatase, SSEA4, GDF3, hTERT, and NANOG are insufficient in identifying pluripotency (Chan et al., 2009). DNA methylation is used and can show promoter demethylation of pluripotency genes; however, some somatic cells show demethylation of pluripotency genes (Stadtfeld and Hochedlinger, 2010). One of the least stringent assays of pluripotency is the in vitro differentiation into cell lineages of the three germ layers; this shows expression of markers at RNA and protein level but does not test for functionality. This assay relies on robust differentiation protocols which are not available for all cell types (Jaenisch and Young, 2008; De Los Angeles et al., 2015). The cells can also be differentiated into embryoid bodies (aggregates of loosely organized tissues which resemble the gastrulating embryo) in vitro and then also assessed for derivatives of the three germ layers (Robinton and Daley, 2012). Teratoma formation asses the production of tissues from the three germ layers after injection of cells into immunocompromized mice. There are serval limitations to this assay including; it is not quantitative, partially reprogrammed cells can produce masses which resemble teratomas, and it does not show the ability of the cell to promote normal development. Chimera formation assess if the cells can contribute to normal development when injected into host embryos/blastocysts. Pluripotent cells can contribute to development and produce chimaeras with tissues from the three germ layers. Germline transmission involves breeding chimaeras, subsequently producing offspring derived from donor pluripotent cells. This shows the ability of the cells to produce functional gametes. Tetraploid complementation assesses the ability of the cells to direct development of an entire organism (Jaenisch and Young, 2008; De Los Angeles et al., 2015).

Figure 1.1 The transduction of four transcription factors (OCT3/4, SOX2, c-myc, and KLF4) initiates cellular reprogramming of fibroblasts to pluripotency. Using the Fbx15 reporter system, the cells are partially reprogrammed, whereas using an OCT4 or NANOG reporter system, the cells are fully reprogrammed.

Cellular reprogramming of somatic cells to pluripotency

Pluripotent stem cell induction or reprogramming is reverting a fully differentiated cell back to pluripotency (Baranek et al., 2017). Since 1952, methods to reprogram somatic cells to pluripotency have been developed. Somatic cell nuclear transfer was developed by Briggs and Kings, which led to successfully cloned animals by transferring the nucleus from late stage embryos to enucleated oocytes. Although this method was successful, the cloned organisms presented phenotypic abnormalities. The results supported the hypothesis that the genome preserves the ability to revert to earlier states of plasticity and that the epigenetic modifications which lead to differentiation are reversable (Moschidou and Guillot, 2012).

Attempts to reprogram somatic cells using defined factors began after achieving an understanding of the mechanisms of pluripotency in ES cells (Okita and Yamanka, 2011). Subsequently, 24 candidate factors/reprogramming genes were transduced into mouse embryonic fibroblasts via a retrovirus carrying a FBx15 reporter system. After two weeks, G418 resistant mouse ES-like colonies had appeared. Out of the 24 candidate factors, four factors were identified which were able to revert fibroblasts to a pluripotent state: OCT3/4, SOX2, KLF4, and c-Myc. The somatic cells reprogrammed to pluripotency using these four factors were termed Induced pluripotent stem cells (iPSCs). The gene expression and proliferation of iPSCs are similar to ES cells, and iPSCs are capable differentiating into cells from all three germ layers in vitro and in vivo. However, using the FBx15 reported system, the cells were only partially reprogrammed. They could contribute to mouse embryos, but the chimeric embryo’s died before birth. Because of this, the reported system was changed to enable complete reprogramming of somatic cells. In ES cells, NANOG and OCT3/4A are more closely associated with pluripotency than Fbx15, so a NANOG or OCT3/4A reporter system was established. Using this system, the cells were fully reprogrammed, and the iPSCs contributed to chimeric mouse embryos which survived after birth. A year after the establishment of mouse iPSCs, human iPSCs (hiPSC) were established. A combination of knowledge on human ES cells and mouse iPSCs led to the derivation of hiPSCs. Two different combinations of reprogramming factors were used to produce hiPSC by different groups: (1) OCT3/4, SOX2, and KLF4 with or without c-Myc (Yamanka factors) (2) OCT3/4, SOX2, and NANOG with or without Lin28. hiPSCs have the ability to differentiate into cells from all three germs layers in vivo and in vitro (Tanabe and Takahasi, 2011).

Alternative methods for somatic cell reprogramming have been established to reduce safety issues, such as immunogenicity and tumorigenesis, to be translated into clinical settings, increase the efficiency of reprogramming, stabilize the pluripotent phenotype, and accelerate the kinetics (Baranek et al., 2017). Methods have also been developed to use less or no exogenous genetic manipulations. The end goal is to reprogram somatic cells with a small molecule cocktail which can replace the exogenous transcription factors and/or increase the efficacy or kinetics (Zhu et al., 2010). The molecular mechanisms controlling reprogramming are still not fully understood because of several different variables, the number of exogenous factors, and the heterogenicity of the somatic cells. Reactivation of the Myc oncogene can cause tumors in mice chimeras and the offspring-derived iPSCs. Alternative methods avoiding the use of oncogenes and reducing the number of factors are required (Qin et al., 2016).

All the methods of reprogramming can be split into viral and nonviral (Fig. 1.2). Viruses can be used as a vector to deliver sequences of reprogramming genes, including integrating vectors (lentiviruses and retroviruses) which