Novel organoid model of distal lung based on primary human cells to study mechanisms of lung diseases and responses to treatment

Introduction
Despite impressive progress in development of human pulmonary organoid models,majority of these models are comprised predominantly of epithelial cells, with just a few reporting presence of supporting mesenchymal cells. These organoids do not yet recapitulate the complex structure and cellular interactions of the highly vascularized alveolar region. Therefore, more complex models utilizing the entirety of the lung architecture are required.

Methods
We have devised a novel organoid model system that better recapitulates normal distal lung complexity. This model is based on the self-aggregation of primary human small airway epithelial cells (SAECs), pulmonary microvascular endothelia cells (HPMECs) and lung mesenchymal stromal cells (MSCs) in Matrigel.

Results
These organoids develop alveoli-like budding structures with a lumen, which are positive for alveolar epithelial markers (Surfactant Protein C (SPC) and Aquaporin5, markers of Alveolar Type II (ATII) and Type I (ATI), respectively, and reach 200µm in diameter (this size is comparable to the size of human alveolus), remarkably, these organoids support the presence of endothelial cells up to21 day. To test the ability of these model to recapitulate features of human disease, MSCs from healthy lungs were replaced by MSCs isolated from lungs of patients with COPD. Organoids seeded with MSCs derived from COPD lungs are characterised by non-symmetrical morphology and smaller size compared to organoids seeded with MSCs isolated from lungs of healthy donors and were unable to support endothelial cells, recapitulating loss of vasculature in emphysema. Both COPD lung MSCs and COPD organoids had lower levels of HGF10 secretion compared to their healthy lung counterparts which also is a characteristic feature of emphysema. Furthermore, organoids composed of COPD MSCs also demonstrate increased deposition of collagen compared to organoids composed of healthy MSCs. We also show that this model is amenable to model lung fibrosis and lung responses to treatment. Exposure of organoids to bleomycin (15 µg/ml for 72 hrs) resulted in increased accumulation of 1A1 collagen, which was reduced by the treatment with mesenchymal stromal cell derived extracellular vesicles.

Discussion & Conclusions
Condensation of primary pulmonary cells provides a physiologically relevant distal lung organoid model that features endothelial cell presence. Lung MSCs are critical to support growth of endothelial cells and regular spatial organisation of the alveolar epithelial cells.