Organoids represent a significant advance in biomedical research, offering a three-dimensional (3D) model that closely mimics the complexity of human organs compared to traditional flat cell cultures. An organoid is a miniature, self-assembling version of an organ grown in a laboratory dish from stem cells, allowing researchers to study human biology outside of the body. This technology is particularly valuable for the lung, whose intricate branching airway structure and specialized gas-exchange units are poorly represented in two-dimensional systems. Lung organoids provide a more accurate platform for understanding organ development, modeling diseases, and testing new therapies, accelerating the transition toward regenerative medicine.
Engineering Miniature Lung Structures
Generating a lung organoid relies on guiding stem cells through developmental stages that mirror the organ’s natural formation. This process begins by exposing stem cells to a cocktail of growth factors and signaling molecules, directing them to differentiate into definitive endoderm and then into early foregut cells. These cellular aggregates are then transferred into a three-dimensional scaffold, typically an extracellular matrix like Matrigel, which provides physical support and biochemical cues.
Once embedded, the cells begin self-assembly, organizing into complex structures without external physical guidance. This self-organization forms hollow spheres with internal cavities, mimicking the lung’s conducting airways and distal air sacs. Depending on the protocol, structures are classified as bronchospheres (modeling proximal airways) or alveolospheres (replicating distal gas-exchange units). These miniature structures exhibit a multi-lineage epithelium, containing cells like ciliated cells, mucus-secreting cells, and alveolar type II cells, reflecting the diversity of the native human lung.
Diverse Stem Cell Sources for Lung Organoids
The utility of a lung organoid is influenced by the type of stem cell used, with researchers primarily relying on two distinct sources. Induced Pluripotent Stem Cells (iPSCs) are adult cells, often skin or blood cells, that are genetically reprogrammed into an embryonic-like state, allowing them to become almost any cell type. iPSCs offer the advantage of creating patient-specific organoids, allowing for the study of diseases using the patient’s own genetic background and providing an unlimited supply of starting material.
Alternatively, Adult Lung Progenitor Cells are specialized stem cells isolated directly from mature lung tissue, such as basal cells or alveolar type II cells. Since these cells are already committed to a lung lineage, their differentiation process is highly efficient for generating specific lung cell types. Organoids derived from these adult progenitors often retain the in vivo regenerative activity of the tissue. However, they are limited by the difficulty of obtaining sufficient tissue samples and their finite capacity for expansion compared to iPSCs.
Current Applications in Disease Modeling and Drug Screening
Lung organoids offer a powerful tool for investigating the mechanisms of human lung diseases by replicating complex pathologies in a controlled laboratory environment. Researchers utilize these models to study infectious diseases, such as viral infections like SARS-CoV-2, observing how the virus enters and damages airway and alveolar cells. They are also employed to model chronic conditions like Idiopathic Pulmonary Fibrosis and Cystic Fibrosis, allowing for the observation of inflammation, tissue scarring, and compromised epithelial function.
The physiological relevance of organoids makes them superior platforms for drug screening and toxicology testing compared to traditional animal models. Patient-derived organoids (PDOs) sourced from non-small cell lung cancer tumors retain the genomic alterations and characteristics of the original tumor, making them excellent surrogates for testing cancer therapies. These cancer organoids have been successfully used to screen the efficacy of targeted therapies, demonstrating high consistency in predicting patient clinical responses.
Organoids are also used to evaluate the off-target toxicity of new compounds, a process often missed in preclinical testing. For example, bronchioalveolar organoids have been used to test antibody-drug conjugates (ADCs), revealing that the therapeutic deruxtecan can induce inflammatory activation in healthy lung cells. In non-cancer toxicology, organoids have helped determine the cytotoxic concentration of drugs like Ibrutinib, an anti-cancer agent. This ability to test compounds against human tissue before clinical trials reduces the risk of adverse drug effects.
Next Generation Organoid Technology
Current lung organoid models still lack the full complexity of a native organ, prompting researchers to develop next-generation technologies to enhance functionality. One significant advance is the successful incorporation of a vascular network, addressing the challenge where lung tissue (endoderm) and blood vessels (mesoderm) required conflicting signaling pathways. Researchers achieved this by co-differentiating both cell lineages within the same spheroid, allowing for spontaneous self-assembly of organ-specific blood vessel networks. This breakthrough in creating vascularized lung tissue provides new insights into congenital pulmonary vascular disorders and is a major step toward generating functional tissue for transplantation.
Another advancement focuses on recreating the mechanical and fluidic environment of the lung using microengineering platforms, often called “lung-on-a-chip” systems. These devices allow the organoid to be cultured under dynamic conditions, such as mechanical stretching that mimics breathing or continuous flow that simulates circulation. The Air-Liquid Interface (ALI) is a component of these chips where the apical surface of the airway organoid is exposed to air, which is necessary for the maturation of ciliated and mucus-producing cells.
These microfluidic systems are also used to create multi-organ-on-a-chip models, connecting the lung organoid with other miniature organs, such as the liver, via a shared circulatory medium. A lung-liver-on-a-chip model demonstrated the systemic effect of toxins, showing how the liver’s detoxification function can protect the lung tissue. These integrated systems move beyond single-organ biology to model systemic disease and drug metabolism, enhancing the relevance of the models.