Properties of Adult Lung Stem and Progenitor Cells

Lung Multipotent Stem Cells of Mesenchymal Nature: Cellular Basis, Clinical Relevance, and Implications for Stem Cell Therapy

Significance: Tissue-resident stem cells are essential for normal organ homeostasis as well as for functional tissue regeneration after severe injury. Herein, mesenchymal stem cells, also designated as mesenchymal stromal cells (MSCs), contribute to the maintenance of organ integrity by their ability to replace dysfunctional cells or secrete cytokines locally and thus support the repair and healing processes of affected tissues. Recent Advances: Besides epithelial stem and progenitor cells, substantial evidence exists that tissue-resident multipotent stem cells of mesenchymal nature also exist in adult human lungs. These lung MSCs may function to regulate pulmonary tissue repair and/or regeneration, inflammation, fibrosis, and tumor formation. Critical Issues: Although therapeutically applied MSCs turned out to be a valuable therapeutic option for the prevention of lung diseases and/or the regeneration of diseased lung tissue, the true function of tissue-resident MSCs within the lung, and identification of their niche, which presumably dictates function, remain elusive. Future Directions: A detailed understanding of lung MSC localization (in the potential vascular stem cell niche) as well as of the signaling pathways controlling stem cell fate is prerequisite to unravel how (i) endogenous MSCs contribute to lung diseases, (ii) exogenous MSCs affect the proliferation of endogenous stem cells to repair damaged tissue, and (iii) a potential on-site manipulation of these cells directly within their endogenous niche could be used for therapeutic benefits. This review focuses on the central role of lung-resident MSCs, which are closely associated with the pulmonary vasculature, in a variety of chronic and acute lung diseases. Antioxid. Redox Signal. 35, 204-216.

Treatment of Cystic Fibrosis: From Gene- to Cell-Based Therapies

Prognosis of patients with cystic fibrosis (CF) varies extensively despite recent advances in targeted therapies that improve CF transmembrane conductance regulator (CFTR) function. Despite being a multi-organ disease, extensive lung tissue destruction remains the major cause of morbidity and mortality. Progress towards a curative treatment strategy that implements a CFTR gene addition-technology to the patients’ lungs has been slow and not yet developed beyond clinical trials. Improved delivery vectors are needed to overcome the body’s defense system and ensure an efficient and consistent clinical response before gene therapy is suitable for clinical care. Cell-based therapy–which relies on functional modification of allogenic or autologous cells ex vivo, prior to transplantation into the patient–is now a therapeutic reality for various diseases. For CF, pioneering research has demonstrated proof-of-principle for allogenic transplantation of cultured human airway stem cells into mouse airways. However, applying a cell-based therapy to the human airways has distinct challenges. We review CF gene therapies using viral and non-viral delivery strategies and discuss current advances towards autologous cell-based therapies. Progress towards identification, correction, and expansion of a suitable regenerative cell, as well as refinement of pre-cell transplant lung conditioning protocols is discussed.

Application of autologous SOX9+ airway basal cells in patients with bronchiectasis

INTRODUCTION

Bronchiectasis is a common condition and a leading cause of respiratory morbidity and mortality. The treatment method for bronchiectasis is mainly symptomatic treatment or surgery; however, this condition is extremely prone to recurrence.

OBJECTIVES

To preliminarily evaluate the safety and efficacy of applying SOX9⁺ autologous airway basal cells (BCs) in patients with bronchiectasis.

METHODS

SOX9⁺ BCs were isolated from microscale tissue of a grade 3-5 bronchus by bronchoscopic brushing and expanded in vitro for approximately 4 weeks. Subsequently, the autologous SOX9⁺ BCs were transplanted into the diseased bronchus to treat patients with bronchiectasis.

RESULTS

The forced expiratory volume in1 second (FEV1)%, forced vital capacity (FVC)%, total lung capacity (TLC)%, residual volume (RV)% and RV/TLC ratio of predicted value in patients with bronchiectasis were improved at 4, 12, 24 and 48 weeks after cell transplantation, although the differences were not statistically significant (P > .05). Chest CT scans showed that the lesions in the pulmonary segment had not progressed at 4, 12 and 24 weeks after transplantation. No patients died during the follow-up. At 4, 12 and 24 weeks after transplantation, routine blood tests, liver function tests, renal function tests and myocardial enzymatic indexes were normal (P > .05).

CONCLUSION

Transplantation of autologous SOX9⁺ BCs has positive effects and is safe for patients with bronchiectasis.

Recapitulating idiopathic pulmonary fibrosis related alveolar epithelial dysfunction in a human iPSC-derived air-liquid interface model

Idiopathic pulmonary fibrosis (IPF) is a fatal disease of unknown cause that is characterized by progressive fibrotic lung remodeling. An abnormal emergence of airway epithelial-like cells within the alveolar compartments of the lung, herein termed bronchiolization, is often observed in IPF. However, the origin of this dysfunctional distal lung epithelium remains unknown due to a lack of suitable human model systems. In this study, we established a human induced pluripotent stem cell (iPSC)-derived air-liquid interface (ALI) model of alveolar epithelial type II (ATII)-like cell differentiation that allows us to investigate alveolar epithelial progenitor cell differentiation in vitro. We treated this system with an IPF-relevant cocktail (IPF-RC) to mimic the pro-fibrotic cytokine milieu present in IPF lungs. Stimulation with IPF-RC during differentiation increases secretion of IPF biomarkers and RNA sequencing (RNA-seq) of these cultures reveals significant overlap with human IPF patient data. IPF-RC treatment further impairs ATII differentiation by driving a shift toward an airway epithelial-like expression signature, providing evidence that a pro-fibrotic cytokine environment can influence the proximo-distal differentiation pattern of human lung epithelial cells. In conclusion, we show for the first time, the establishment of a human model system that recapitulates aspects of IPF-associated bronchiolization of the lung epithelium in vitro.

Chronic lung disease, lung regeneration and future therapeutic strategies

Chronic lung diseases have been recognized as one of the world's leading causes of death in recent decades. Lacking effective treatments brings the patients not only bad quality of life but also higher risk for lung cancer development. By increasing the understanding of deeper mechanism of how lung develops and regenerates, researchers now focus on studying lung regenerative medicine, aiming to apply different and more efficient therapies to treat chronic lung diseases. This review will provide a wide picture of both basic lung developmental, regeneration mechanism and different designed strategies for treating chronic lung diseases in the future decades.

Epithelial disruption: a new paradigm enabling human airway stem cell transplantation

BACKGROUND

Airway disease is a primary cause of morbidity and early mortality for patients with cystic fibrosis (CF). Cell transplantation therapy has proven successful for treating immune disorders and may have the potential to correct the airway disease phenotype associated with CF. Since in vivo cell delivery into unconditioned mouse airways leads to inefficient engraftment, we hypothesised that disrupting the epithelial cell layer using the agent polidocanol (PDOC) would facilitate effective transplantation of cultured stem cells in mouse nasal airways.

METHODS

In this study, 4 μL of 2% PDOC in phosphate-buffered saline was administered to the nasal airway of mice to disrupt the epithelium. At 2 or 24 h after PDOC treatment, two types of reporter gene-expressing cells were transplanted into the animals: luciferase-transduced human airway basal cells (hABC-Luc) or luciferase-transduced human amnion epithelial cells (hAEC-Luc). Bioluminescence imaging was used to assess the presence of transplanted luciferase-expressing cells over time. Data were evaluated by using two-way analysis of variance with Sidak's multiple comparison.

RESULTS

Successful transplantation was observed when hABCs were delivered 2 h after PDOC but was absent when transplantation was performed 24 h after PDOC, suggesting that a greater competitive advantage for the donor cells is present at the earlier time point. The lack of transplantation of hAECs 24 h after PDOC supports the importance of choosing the correct timing and cell type to facilitate transplantation.

CONCLUSIONS

These studies into factors that may enable successful airway transplantation of human stem cells showed that extended functioning cell presence is feasible and further supports the development of methods that alter normal epithelial layer integrity. With improvements in efficacy, manipulating the airway epithelium to make it permissive towards cell transplantation may provide another option for safe and effective correction of CF transmembrane conductance regulator function in CF airways.

Cross-talk between human airway epithelial cells and 3T3-J2 feeder cells involves partial activation of human MET by murine HGF

There is considerable interest in the ex vivo propagation of primary human basal epithelial stem/progenitor cells with a view to their use in drug development, toxicity testing and regenerative medicine. These cells can be expanded in co-culture with mitotically inactivated 3T3-J2 murine embryonic feeder cells but, similar to other epithelial cell culture systems employing 3T3-J2 cells, the aspects of cross-talk between 3T3-J2 cells and human airway basal cells that are critical for their expansion remain largely unknown. In this study, we investigated secreted growth factors that are produced by 3T3-J2 cells and act upon primary human airway basal cells. We found robust production of hepatocyte growth factor (HGF) from fibroblast feeder cells following mitotic inactivation. Consistent with the limited cross-species reactivity of murine HGF on the human HGF receptor (MET; HGFR), MET inhibition did not affect proliferative responses in human airway basal cells and HGF could not replace feeder cells in this culture system. However, we found that murine HGF is not completely inactive on human airway epithelial cells or cancer cell lines but stimulates the phosphorylation of GRB2-associated-binding protein 2 (GAB2) and signal transducer and activator of transcription 6 (STAT6). Although HGF induces phosphorylation of STAT6 tyrosine 641 (Y641), there is no subsequent STAT6 nuclear translocation or STAT6-driven transcriptional response. Overall, these findings highlight the relevance of cross-species protein interactions between murine feeder cells and human epithelial cells in 3T3-J2 co-culture and demonstrate that STAT6 phosphorylation occurs in response to MET activation in epithelial cells. However, STAT6 nuclear translocation does not occur in response to HGF, precluding the transcriptional activity of STAT6.

Bronchopulmonary Dysplasia: Where Have All the Stem Cells Gone?: Origin and (Potential) Function of Resident Lung Stem Cells

Celebrating its 50th anniversary in 2017, bronchopulmonary dysplasia (BPD)-the chronic lung disease of prematurity that follows ventilator and oxygen therapy for acute respiratory failure-remains the most frequent complication of extreme prematurity. Survival of premature infants born at increasingly earlier stages of gestation has made the prevention of lung injury increasingly challenging. BPD is postulated to be a misdirection of many functions in the developing lung, including growth factor signalling and matrix as well as cellular composition, resulting in impaired alveolar and lung vascular growth. Despite improvements in understanding the mechanisms that regulate normal lung development, BPD remains without therapies. Insights into stem cell biology have identified the repair potential of stem cells. Promising preclinical studies demonstrated the lung protective effects of stem cell-based therapies in animal models mimicking BPD, leading to early-phase clinical trials. Although the time is ripe to conduct well-designed early-phase clinical trials, much more needs to be learned about the biology of these cells to develop safe, efficient, high-quality, clinical-grade cell products. Stem cells are essential for normal organ development, maintenance, and repair. It is therefore biologically plausible that exhaustion/dysfunction of resident lung stem cells contributes to the inability of the immature lung to repair itself. Understanding how normal lung stem cells function and how these cells are perturbed in BPD may prove useful in designing superior cell products with enhanced repair capabilities to ensure the successful translation of basic research into clinical practice.

Developmental pathways in lung regeneration

The key processes of lung development have been elucidated in the past several decades, helping to identify and characterize the resident progenitor cells that ultimately generate the mature organ. The adult lung is a complex organ consisting in scores of different cell lineages that are remarkably quiescent in the absence of injury. Despite low cellular turnover, the lung can respond quickly and dramatically to acute damage, with spatially restricted stem and progenitor cells re-entering the cell cycle and differentiating to promote repair. The findings from lung developmental biology are now being used to examine the mechanisms that underlie lung regeneration. The use of in vitro models such as pluripotent stem cells and new methods of gene editing have provided models for understanding lung disease and exploring the mechanisms of lung regeneration and have raised the prospect of correcting lung dysfunction. We outline the way that basic studies into lung developmental biology are now being applied to lung regeneration, opening up new avenues of research that may ultimately be harnessed for treatments of lung disease.