Recent advances in lung organoid development and applications in disease modeling

Abstract

Over the last decade, several organoid models have evolved to acquire increasing cellular, structural, and functional complexity. Advanced lung organoid platforms derived from various sources, including adult, fetal, and induced pluripotent stem cells, have now been generated, which more closely mimic the cellular architecture found within the airways and alveoli. In this regard, the establishment of novel protocols with optimized stem cell isolation and culture conditions has given rise to an array of models able to study key cellular and molecular players involved in lung injury and repair. In addition, introduction of other nonepithelial cellular components, such as immune, mesenchymal, and endothelial cells, and employment of novel precision gene editing tools have further broadened the range of applications for these systems by providing a microenvironment and/or phenotype closer to the desired in vivo scenario. Thus, these developments in organoid technology have enhanced our ability to model various aspects of lung biology, including pathogenesis of diseases such as chronic obstructive pulmonary disease, pulmonary fibrosis, cystic fibrosis, and infectious disease and host-microbe interactions, in ways that are often difficult to undertake using only in vivo models. In this Review, we summarize the latest developments in lung organoid technology and their applicability for disease modeling and outline their strengths, drawbacks, and potential avenues for future development.

Figure 1. Lung organoid models derived from adult mouse and human stem cells.

Several epithelial progenitor/stem cells located along the bronchoalveolar compartment of murine and human lungs are capable of generating organoids. (A) Murine models include organoids derived from basal cells that form tracheospheres containing basal, ciliated, and secretory cells (10, 30). Club cells can be used to develop bronchiolospheres containing club and ciliated cells (38, 39). Coculture of BASCs with lung mesenchymal cells can give rise to bronchoalveolar lung organoids (BALOs) containing tubular-like structures with basal, club, goblet, and ciliated cells and saccular-like structures composed of differentiated AEC1s and AEC2s (26). When cocultured with lung endothelial cells, BASCs can form alveolar organoids, bronchiolar organoids, and bronchiolar organoids (41). Lastly, cocultures of AEC2s with PDGFRα⁺ mesenchymal cells lead to the formation of alveolospheres, containing AEC1s and AEC2s (13, 45, 47, 111). (B) Lung organoids derived from human adult stem cells can be generated from basal cells and AEC2s. Basal cells can form either tracheospheres or bronchospheres, depending on their location in the airways (, –33). AEC2s form alveolar-like organoids when cocultured with feeder cells and display a similar composition to their mouse counterparts (13, 14, 50).

Figure 2. Lung organoid models derived from fetal and induced pluripotent stem cells.

Schematic representation of fetal stem cells and iPSC-derived lung organoids. (A) Bud tip progenitor cells obtained from fetal lung tissue can be differentiated into alveolar and airway organoids. Activation of WNT pathway signaling leads to the formation of alveolar organoids containing SFTPC⁺HOPX⁺ AECs, while dual SMAD activation and inhibition lead to the development of airway organoids composed of basal, club, goblet, and multiciliated cells (24, 51). Stimulation of bud tip progenitors with ATRA and FGF-7 gives rise to alveolar-like or airway-like organoids depending on the coculture with either LIFR⁺ or LIFR^– lung mesenchymal cells (52). (B) Lung organoids derived from iPSCs are generally generated from NKX2-1 lung progenitor cells. For this purpose, iPSCs are differentiated into definitive endoderm and polarized into anterior foregut endoderm before being differentiated into lung progenitors. Dual SMAD activation and inhibition of NKX2-1 or organoid-derived NKX2-1⁺TP63⁺ progenitor cells result in the formation of airway organoids containing basal, club, goblet, and multiciliated cells and, in some conditions, SYN⁺ neuroendocrine cells (27, 28). In contrast, stimulation of lung progenitor cells with DCI, FGF, and CHIR leads to the formation of alveolar organoids comprising AEC1s and AEC2s (27, 61). In contrast, lung organoids comprising both alveolar-like cell types and airway-like cell types can be generated by addition of FGF-10 (25). Stimulation of lung progenitor cells with ATRA, FGF-7, and CHIR results in the generation of bud tip organoids containing NKX2-1⁺ lung progenitor cells, AEC2s, and club and goblet cells (25).