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(Takahashi and Yamanaka 2006 ). However, compared with ESCs, these iPSCs
expressed lower levels of several pluripotent genes and failed to produce viable
chimeras or to contribute to the germline. These mouse-derived iPSCs only achieved
reprogramming. The “gold standard” for PSCs, that the cells could generate viable
chimeric models and contribute to the germline, was able to be reproduced and
improved after this study. For example, the selection of Nanog instead of Fbxo15
could obtain ESCs closely functional to iPSCs (Maherali et al. 2007 ; Okita et al.
2007 ). Unfortunately, these cells still contain oncogenic c-Myc, and thus 20 % of
the chimeric models develop cancer (Nakagawa et al. 2008 ; Okita et al. 2007 ).
Yamanaka and others later succeeded in generating iPSCs without c-Myc (Nakagawa
et al. 2008 ; Wernig et al. 2008 ). Thomson and Yu used two other factors, Nanog and
LIN28, instead of Klf-4 and c-Myc (Yu et al. 2007 ), a milestone achieved in 2007,
successfully generating human iPSCs , as well as that of Yamanaka and colleagues
using four typical factors on the same day (Takahashi et al. 2007b ). Since these
earlier studies, iPSCs have been derived from a wide range of species, such as
human (Gianotti-Sommer et al. 2008 ; Takahashi et al. 2007b ; Warren et al. 2010 ; Yu
et al. 2007 ), buffalo (Deng et al. 2012 ), cattle (Han et al. 2011 ), dog (Shimada et al.
2010 ), horse (Nagy et al. 2011 ), mouse (Heng et al. 2010 ; Nakagawa et al. 2008 ;
Takahashi and Yamanaka 2006 ), pig (Esteban et al. 2009 ), goat (Sandmaier et al.
2015 ), rat (Chang et al. 2010 ), and rhesus monkey (Liu et al. 2008 ), using the four
factors selected by Yamanaka’s group.
In recent years, a number of methods have been established to generate iPSCs
(Fig. 4.1 ) (Kumar et al. 2015 ).

Factor delivery method Auxillary methods

Viral Non- viral

• Retrovirus


• Lentivirus


• Adenovirus


• Sendai virus
  
  
  • Episoma plasmid
  
  
  • Minicircle DNA
  
  
  • Modified RNAs
  
  
  • Recombinant protein
  
  
  
  

Transposon:

• PiggyBac


• Sleeping Beauty

Small

molecules

Somatic

stem cells

ERK inhibitor

MEK inhobitor

Epigenetic modifiers

Endogenous

expression of core

reprograming

factors

Rerpograming factors

OCT4, SOX2, KLF-4, C-MYC,

LIN28, NANOG, GLIS1

CELLs

iPSCs

Fig. 4.1 Several approaches to produce induced pluripotent stem cells (iPSCs). iPSCs are cur-
rently generated by various strategies using different inducing factors, different donor cells, and
different gene delivery methods

P.V. Pham et al.