A Serum-free Culture Medium for Long-term Expansion of Human Airway Basal Stem Cells

Background: Human basal stem cells, with their self-renewal and multilineage differentiation capacity, are essential tools for modeling airway diseases and advancing regenerative medicine. However, existing culture systems often rely on undefined components like serum, bovine pituitary extract, or feeder cells, limiting reproducibility and clinical translation. To address this limitation, we developed a well-defined culture medium that enables the long-term expansion of human airway basal stem cells while preserving their proliferative and differentiation potential. Methods: We formulated a novel medium (sfBSC) comprising 14 defined components, including basal media, supplements, growth factors (EGF, FGF10), and signaling inhibitors (Y-27632, A-83-01, DAPT, DMH1). Human bronchial and small airway epithelial cells were cultured over multiple passages in sfBSC and assessed for morphology, population doublings, marker expression, and differentiation capacity via air-liquid interface and organoid cultures. RNA-seq was performed to explore molecular changes across passages. Results: Bronchial and small airway epithelial cells were expanded up to 17 and 24 passages, respectively, with stable morphology and consistent cell size (10-15 μm). Cells maintained expression of canonical BSC markers (TP63, KRT5, NGFR) throughout long-term culture. Differentiation assays confirmed the ability to generate ciliated, goblet, and club cells. Optimized concentrations of EGF (1 ng/mL) and FGF10 (0.4 ng/mL) were critical for sustained proliferation. RNA-seq revealed stable marker expression and metabolic changes over time.Conclusions: sfBSC medium offers a defined, reproducible, and scalable platform for basal stem cell culture, enabling applications in disease modeling, regenerative medicine, and clinical-grade cell production.