Stem cells, cell therapies, and bioengineering in lung biology and diseases. Comprehensive review of the recent literature 2010-2012

Abstract

A conference, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," was held July 25 to 28, 2011 at the University of Vermont to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy and ex vivo bioengineering approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, to discuss and debate current controversies, and to identify future research directions and opportunities for basic and translational research in cell-based therapies for lung diseases. The goal of this article, which accompanies the formal conference report, is to provide a comprehensive review of the published literature in lung regenerative medicine from the last conference report through December 2012.

Figure 1.

Sschematic of proposed lung epithelial candidate stem or progenitor cells and their niches in the proximal conducting airways and distal alveoli. Cells whose localization or existence is not clear or accepted are indicated with dashed boxes and/or question marks. AEC2 = type 2 alveolar epithelial cell; BADJ = bronchoalveolar duct junction; Gland = submucosal gland duct; NEB = neuroepithelial body. Marker abbreviations used for each cell subtype include the following: CCSP = Club cell secretory protein; CGFP = calcitonin gene–related peptide; Itg = integrin; K = cytokeratin; SPC = surfactant protein C. Adapted by permission from Reference .

Figure 2.

Alveolar differentiation repertoire of embryonic stem cell (ESC)-derived Nkx2–1+ lung progenitors. (A and B) Immunostaining for alveolar epithelial markers T1α, pro-surfactant protein C (SPC), and Nkx2–1 on cells at the completion of the 25-day directed differentiation protocol. ESCs sorted on Day 15 based on Nkx2–1^GFP+ expression gave rise to cells reminiscent of type 1 alveolar epithelial cells (AEC1) as they lost Nkx2–1 nuclear protein expression (green immunostain) while expressing T1α protein (A). (B) Other patches of cells appeared more reminiscent of distal SPC⁺ alveolar epithelial cells because they expressed punctate cytoplasmic pro-SPC protein and displayed SPC promoter activation while retaining Nkx2–1^GFP expression. Arrow = SPC-dsRed and Nkx2–1^GFP coexpressing cell (orange). Arrowhead = cell expressing only Nkx2–1^GFP. (C) Schematic summarizing the decellularization-recellularization assay. (D) Hematoxylin and eosin stains of lung sections showing lung scaffold appearance with no recellularization (left panel) versus hypercellular sheets after reseeding with undifferentiated ESCs (middle panel) versus cells of alveolar structural morphologies after seeding with Nkx2–1^GFP+ purified ESC-derived progenitors (right panel). Scale bars = 100 μm in three left panels. Zoom of the indicated boxed region is shown in far right panel with scale bar = 20 μm. (E and F) Nkx2–1⁺ nuclear protein (brown; arrowheads in E) immunostaining of engrafted cuboidal epithelial cells in the corners of alveoli derived 10 days after reseeding with Nkx2–1^GFP+ sorted cells. Arrow = flattened nucleus of an Nkx2–1 negative cell (purple) lining the alveolar septum. Many of these flattened cells were T1α⁺ (F; arrowhead). Scale bars = 20 μm. (G) Control mouse lung without decellularization showing T1α apical membrane staining pattern (brown) of mature AEC1 (see Figure S7 in the online supplement). (H) Ciliated airway epithelial cell (arrow) 10 days after reseeding with differentiated/unsorted ESC-derived cells. Scale bar = 20 μm. All nuclei were counterstained with hematoxylin (purple). Adapted by permission from Reference .

Figure 3.

Stepwise differentiation of Nkx2.1+ lung progenitors from human induced pluripotent stem cells (iPSCs). (A) Schematic strategy and time line to generate Nkx2.1+ lung multipotent progenitors from human iPSCs. (B) High yield of definitive endoderm from CF1 RNA-induced pluripotent stem cells (RiPSCs) was obtained after treatment for 4 days in RPMI-1640 medium in the presence of 2% B27 supplement, Activin A (100 ng/ml), and 5 μM PI3 kinase inhibitor LY294002 with more than 90% of cells coexpressing transcription factors SOX17 and FOXA2. Scale bar = 200 μm. (C) Anteriorization of endoderm into foregut endoderm cells with SOX2 expression in Foxa2+ cells derived from CF1 RiPSCs after 4 days of treatment with 500 nM A-83–01 (TGF-β antagonist) and 100 ng/ml Noggin (bone morphogenetic protein [BMP]4 antagonist). Scale bar = 100 μm. (D) Confocal image after immunofluorescence staining showing that some Nkx2.1+ spheres contain basal cells positive for p63. Scale bar = 40 μm. Adapted by permission from Reference .

Figure 4.

Schematic illustrating the range of in vitro immune-modulating effects described for mesenchymal stromal (stem) cells (MSCs). DC = dendritic cell; HGF = hepatocyte growth factor; IDO = indoleamine 2,3-dioxygenase; IFN-γ = interferon γ; Ig = immunoglobulin; IL = interleukin; IL-1RA = interleukin-1 receptor antagonist; Mac = macrophage; NK = natural killer; PGE2 = prostaglandin E-2; SDF-1 = stem-cell–derived factor 1; TNF-α = tumor necrosis factor-α; TGF-β1 = transforming growth factor-β1; TLR = Toll-like receptor; VEGF = vascular endothelial growth factor. Adapted by permission from Reference .

Figure 5.

Schematic of known mesenchymal stromal (stem) cell (MSC) actions in different preclinical lung injury models. Ang-1 = angiopoietin 1; EGF = epidermal growth factor; FGF2 = fibroblast growth factor 2; HGF = hepatocyte growth factor; IGF-1 = insulin-like growth factor 1; IL-10 = interleukin 10; KGF = keratinocyte growth factor; PGE2 = prostaglandin E2; sIL-1R = soluble interleukin 1 receptor antagonist; STC-1 = stanniocalcin 1; Treg = T regulatory cell; TSG-6 = tumor necrosis factor–inducible gene 6 protein; TNF-α = tumor necrosis factor-α; TGF-β1 = transforming growth factor-β1; VEGF = vascular endothelial growth factor. Adapted by permission from Reference .

Figure 6.

Changes in FEV₁% predicted, Borg dyspnea scale, and in circulating C-reactive protein (CRP) levels after systemic administration of mesenchymal stromal (stem) cell (MSCs) or vehicle control in patients with moderate-severe chronic obstructive pulmonary disease (COPD). Changes in circulating CRP levels are shown only for those who had elevated levels at screening (> 4.0 mg/L). *P < 0.05. Adapted by permission from Reference .