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investigated as elegant scaffolds for seeding cells (Uygun et al. 2010 ; Bhatia et al.
2014 ; Sudo 2014 ). In addition, cell sheet engineering using temperature-responsive
culture dishes enables detachment of cell sheets without enzymatic treatments. Cell
sheet engineering can hence be used to create three-dimensional structures by layer-
ing individual cell sheets, and cell positioning and prepositioning may be achieved
using 3D printing. In recent years, these technologies have advanced significantly
and have achieved compelling outcomes (Toyoshima et al. 2012 ; Hirayama et al.
2013 ; Assawachananont et al. 2014 ; Oshima et al. 2014 ; Nagamoto et al. 2016 ;
Takagi et al. 2016 ).
Current approaches to developing artificial organs are based on the formation of
final organ shapes of adult tissues from immature tissues. In contrast, we and others
are attempting to develop three-dimensional architectures using intrinsic self-
organizing capabilities of cells, as observed during embryonic development. Several
studies report organoid technologies that can be used to generate structures such as
the optic cup (Eiraku et al. 2011 ; Nakano et al. 2012 ), pituitary epithelium (Suga
et al. 2011 ; Ozone et al. 2016 ), the intestine (Sato et al. 2009 , 2011 ; Spence et al.
2010 , 2011 ; Yui et al. 2012 ; Watson et al. 2014 ), the cerebrum (Lancaster et al.
2013 ; Lancaster and Knoblich 2014 ; Camp et al. 2015 ), and the kidney (Chi et al.
2009 ; Osafune 2010 ; Takasato et al. 2014 , 2015 ; Toyohara et al. 2015 ). These
reports indicate the critical involvement of intrinsic self-organizing mechanisms in
the generation of patterned epithelial architectures. Moreover, these studies suggest
that extrinsic signals and forces from external structures, including surrounding
mesenchyme, cooperate with the intrinsic self-organizing capabilities of cells dur-
ing tissue morphogenesis.
Liver bud technology was developed to recapitulate the multicellular interactions
that are present at the start of organ morphogenesis and to allow the development of
multicell-driven, self-organizing, three-dimensional structures without scaffolds.
Using these methods, we developed unprecedented technology for establishing
multicellular organ primordia using progenitor cells from human pluripotent stem
cells. Multicellular interactions are ubiquitously present in multicellular organisms
and are essential for proper homeostasis and are likely descriptive of cancer tissue
processes. Hence, formation of MSC-driven self-organized cellular masses may
lead to the development of multicellular condensates from other cell sources.
Accordingly, we demonstrated the use of “organ bud technology” as a universal
culture platform for growing self-organized three-dimensional tissues from a pan-
creatic beta cell line and from developing kidney, liver, intestine, lung, heart, brain,
and even cancer tissues (Takebe et al. 2015 ).
Previous reports show that endothelial and mesenchymal cells are highly tissue
specific. In the liver, stellate cells act as mesenchymal stromal cells, and fibroblastic
mesenchymal cells may also be present, although it remains unclear whether these
differ from stellate cells. Tissue-specific stromal development must also require
immature progenitor-progenitor interactions, warranting studies of the effects of
blood cells and/or nerve cells that participate in organ development. Furthermore, in
addition to intra-tissue interactions, inter-tissue communication is likely required
for proper tissue maturation or organization.
K. Sekine et al.