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It can be concluded from these studies that the use of organoids in lung stem cell
biology has been a valuable tool for the discovery and mapping of stem/progenitor
cells in the adult lung. The knowledge gained can be easily applied to the develop-
ment of organoid systems for PSC-derived lung progenitors.
Since the field of lung-directed differentiation is still in its infancy, it is not sur-
prising that the number of published studies on organoid use remains small. Bishop
and coworkers (van Vranken et al. 2005 ) first reported coculture of murine ESCs
with dissected E11.5 lung mesenchyme. The presence of NKX2–1+ and SFTPC+
cells in the derived organoids was interpreted as ESC lung differentiation.
Nevertheless, no DE derivation took place before organoid formation, and alterna-
tive explanations, such as neuroectodermal NKX2–1 differentiation and stochastic
SFTPC expression, may explain the observed results. More recently, organoids
were employed for the culture of lung lineages derived from human PSCs (Dye
et al. 2015 ; Gotoh et al. 2014 ). As mentioned above, CPM was identified as a puta-
tive marker of human NKX2–1+ distal lung progenitors during directed differentia-
tion of hPSCs by microarray analysis (Gotoh et al. 2014 ). The authors engineered
SFPTC-GFP hPSC reporter lines and then used 3D Matrigel coculture of sorted
CPM+ AFE progenitors with fetal human lung fibroblasts in DCI + KGF media to
investigate the differentiation potential of CPM+ cells. The derived luminal struc-
tures contained mainly AQP5+ (type I AEC-like cells) and SFPTC-GFP+ cells with
the latter being ultrastructurally similar to fetal human type II AECs. In a more
recent paper, Spence and coworkers first derived lung-fated AFE spheroids by
TGF-β/BMP signaling inhibition and addition of Hh (SAG), Wnt (CHIR99021),
and FGF (FGF4) agonists (Dye et al. 2015 ). Embedding the spheroids in Matrigel
and culturing for a prolonged period of time in FGF10 resulted in the formation of
so-called human lung organoids (HLOs). The latter comprised alveolar- and airway-
like structures as demonstrated by detailed immunohistochemical and transcrip-
tomic analysis of markers for type II AECs (SFPTC, SFTPB), type I AECs (PDPN,
HOPX), ciliated cells (FOXJ1), and basal cells (P63). Although the global HLO and
human fetal lung transcriptomes were similar, the absence of any sorting steps in the
protocol does not exclude the possibility that some of these lineages are not derived
from lung progenitors.
As with decellularized lung scaffolds, organoid culture is bound to become a
widely used platform for multiple applications such as refinement and validation of
lung-directed differentiation protocols, in vitro modeling of human lung develop-
ment and disease, and drug screening (Fig. 13.3b).
13.9 Toward a Human-Scale Bioartificial,
Transplantable Lung
The last years have witnessed significant progress in the fields of lung stem cell and
developmental biology and lung tissue engineering. Yet, significant hurdles must be
overcome before these advances are translated into safe and efficacious cell/organ
A. Wilson and L. Ikonomou