Lung Bioengineering Research Articles

Enhancing Lung Recellularization with Mesenchymal Stem Cells via Photobiomodulation Therapy: Insights into Cytokine Modulation and Sterilization.

Several lung diseases can cause structural damage, making lung transplantation the only therapeutic option for advanced disease stages. However, the transplantation success rate remains limited. Lung bioengineering using the natural extracellular matrix (ECM) of decellularized lungs is a potential alternative. The use of undifferentiated cells to seed the ECM is practical; however, sterilizing the organ for recellularization is challenging. Photobiomodulation therapy (PBMT) may offer a solution, in which the wavelength is crucial for tissue penetration. This study aimed to explore the potential of optimizing lung recellularization with mesenchymal stem cells using PBMT (660 nm) after sterilization with PBMT (880 nm). The lungs from C57BL/6 mice were decellularized using 1% SDS and sterilized using PBMT (880 nm, 100 mW, 30 s). Recellularization was performed in two groups: (1) recellularized lung and (2) recellularized lung + 660 nm PBMT (660 nm, 100 mW, 30 s). Both were seeded with mesenchymal stem cells from human tooth pulp (DPSc) and incubated for 24 h at 37 °C and 5% CO2 in bioreactor-like conditions with continuous positive airway pressure (CPAP) at 20 cmH2O and 90% O2. The culture medium was analyzed after 24 h. H&E, immunostaining, SEM, and ELISA assays were performed. Viable biological scaffolds were produced, which were free of cell DNA and preserved the glycosaminoglycans; collagens I, III, and IV; fibronectin; laminin; elastin; and the lung structure (SEM). The IL-6 and IL-8 levels were stable during the 24 h culture, but the IFN-γ levels showed significant differences in the recellularized lung and recellularized lung + 660 nm PBMT groups. Greater immunological modulation was observed in the recellularized groups regarding pro-inflammatory cytokines (IL-6, IFN-γ, and IL-8). These findings suggest that PBMT plays a role in cytokine regulation and antimicrobial activity, thus offering promise for enhanced therapeutic strategies in lung bioengineering.

Orthotopic transplantation of the bioengineered lung using a mouse-scale perfusion-based bioreactor and human primary endothelial cells

Whole lung engineering and the transplantation of its products is an ambitious goal and ultimately a viable solution for alleviating the donor-shortage crisis for lung transplants. There are several limitations currently impeding progress in the field with a major obstacle being efficient revascularization of decellularized scaffolds, which requires an extremely large number of cells when using larger pre-clinical animal models. Here, we developed a simple but effective experimental pulmonary bioengineering platform by utilizing the lung as a scaffold. Revascularization of pulmonary vasculature using human umbilical cord vein endothelial cells was feasible using a novel in-house developed perfusion-based bioreactor. The endothelial lumens formed in the peripheral alveolar area were confirmed using a transmission electron microscope. The quality of engineered lung vasculature was evaluated using box-counting analysis of histological images. The engineered mouse lungs were successfully transplanted into the orthotopic thoracic cavity. The engineered vasculature in the lung scaffold showed blood perfusion after transplantation without significant hemorrhage. The mouse-based lung bioengineering system can be utilized as an efficient ex-vivo screening platform for lung tissue engineering.

Regional and disease-specific glycosaminoglycan composition and function in decellularized human lung extracellular matrix.

Decellularized lung scaffolds and hydrogels are increasingly being utilized in ex vivo lung bioengineering. However, the lung is a regionally heterogenous organ with proximal and distal airway and vascular compartments of different structures and functions that may be altered as part of disease pathogenesis. We previously described decellularized normal whole human lung extracellular matrix (ECM) glycosaminoglycan (GAG) composition and functional ability to bind matrix-associated growth factors. We now determine differential GAG composition and function in airway, vascular, and alveolar-enriched regions of decellularized lungs obtained from normal, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF) patients. Significant differences were observed in heparan sulfate (HS), chondroitin sulfate (CS), and hyaluronic acid (HA) content and CS/HS compositions between both different lung regions and between normal and diseased lungs. Surface plasmon resonance demonstrated that HS and CS from decellularized normal and COPD lungs similarly bound fibroblast growth factor 2, but that binding was decreased in decellularized IPF lungs. Binding of transforming growth factor β to CS was similar in all three groups but binding to HS was decreased in IPF compared to normal and COPD lungs. In addition, cytokines dissociate faster from the IPF GAGs than their counterparts. The differences in cytokine binding features of IPF GAGs may result from different disaccharide compositions. The purified HS from IPF lung is less sulfated than that from other lungs, and the CS from IPF contains more 6-O-sulfated disaccharide. These observations provide further information for understanding functional roles of ECM GAGs in lung function and disease. STATEMENT OF SIGNIFICANCE: Lung transplantation remains limited due to donor organ availability and need for life-long immunosuppressive medication. One solution, the ex vivo bioengineering of lungs via de- and recellularization has not yet led to a fully functional organ. Notably, the role of glycosaminoglycans (GAGs) remaining in decellularized lung scaffolds is poorly understood despite their important effects on cell behaviors. We have previously investigated residual GAG content of native and decellularized lungs and their respective functionality, and role during scaffold recellularization. We now present a detailed characterization of GAG and GAG chain content and function in different anatomical regions of normal diseased human lungs. These are novel and important observations that further expand knowledge about functional GAG roles in lung biology and disease.

Advances in lung bioengineering: Where we are, where we need to go, and how to get there.

Lung transplantation is the only potentially curative treatment for end-stage lung failure and successfully improves both long-term survival and quality of life. However, lung transplantation is limited by the shortage of suitable donor lungs. This discrepancy in organ supply and demand has prompted researchers to seek alternative therapies for end-stage lung failure. Tissue engineering (bioengineering) organs has become an attractive and promising avenue of research, allowing for the customized production of organs on demand, with potentially perfect biocompatibility. While breakthroughs in tissue engineering have shown feasibility in practice, they have also uncovered challenges in solid organ applications due to the need not only for structural support, but also vascular membrane integrity and gas exchange. This requires a complex engineered interaction of multiple cell types in precise anatomical locations. In this article, we discuss the process of creating bioengineered lungs and the challenges inherent therein. We summarize the relevant literature for selecting appropriate lung scaffolds, creating decellularization protocols, and using bioreactors. The development of completely artificial lung substitutes will also be reviewed. Lastly, we describe the state of current research, as well as future studies required for bioengineered lungs to become a realistic therapeutic modality for end-stage lung disease. Applications of bioengineering may allow for earlier intervention in end-stage lung disease and have the potential to not only halt organ failure, but also significantly reverse disease progression.

Assessment of Collagen in Translational Models of Lung Research.

The extracellular matrix (ECM) plays an important role in lung health and disease. Collagen is the main component of the lung ECM, widely used for the establishment of in vitro and organotypic models of lung disease, and as scaffold material of general interest for the field of lung bioengineering. Collagen also is the main readout for fibrotic lung disease, where collagen composition and molecular properties are drastically changed and ultimately result in dysfunctional "scarred" tissue. Because of the central role of collagen in lung disease, quantification, determination of molecular properties, and three-dimensional visualization of collagen is important for both development and characterization of translational models of lung research. In this chapter, we provide a comprehensive overview on the various methodologies currently available for quantification and characterization of collagen including their detection principles, advantages, and disadvantages.

Bioengineering lungs: An overview of current methods, requirements, and challenges for constructing scaffolds.

Chronic respiratory diseases remain a significant health burden worldwide. The only option for individuals with end-stage lung failure remains Lung Transplantation. However, suitable organ donor shortages and immune rejection following transplantation remain a challenge. Since alternative options are urgently required to increase tissue availability for lung transplantation, researchers have been exploring lung bioengineering extensively, to generate functional, transplantable organs and tissue. Additionally, the development of physiologically-relevant artificial tissue models for testing novel therapies also represents an important step toward finding a definite clinical solution for different chronic respiratory diseases. This mini-review aims to highlight some of the most common methodologies used in bioengineering lung scaffolds, as well as the benefits and disadvantages associated with each method in conjunction with the current areas of research devoted to solving some of these challenges in the area of lung bioengineering.

De Novo Donor Specific Antibody Expression in Lung Transplant Recipients with EVLP-Conditioned Allografts

<h3>Purpose</h3> Recipients of marginal donor lungs conditioned by ex-vivo lung perfusion (EVLP) have non-inferior short and long-term outcomes compared to recipients of non-EVLP lungs. Whether EVLP increases the risk of de novo donor specific anti-HLA antibodies (dnDSA) early post-transplant has not been reported. <h3>Methods</h3> We performed a single-center, retrospective analysis between 10/2019- 7/2021. EVLP was performed at a specialized center (Lung Bioengineering). Post-lung transplant (LTx) management was similar in both groups. DSA was measured at 1-month post-LTx using a Luminex single-antigen assay. Differences in baseline variables between groups were analyzed using Fisher's exact, Wilcoxon rank-sum or Kruskal-Wallis tests. Multiple logistic regression analysis was then performed to assess the relationship between EVLP and dnDSA, including covariates that were significant on univariate assessment at p<0.2. <h3>Results</h3> DSA were measured in 76 consecutive LTx recipients (LTRs) in the study period; 12 received EVLP-conditioned lungs and 64 did not. Baseline demographics were similar between cohorts except for total ischemic times (Fig 1). At 1-month post-LTx 3 patients (25%) in the EVLP cohort developed class II DSA (all DQ). In the non-EVLP cohort 6 patients (9%) developed class I DSA antibodies (all B) and 11 patients (17%) developed class II DSA (8 with DQ and 3 with DR). When adjusting for gram negative infection and transfused red blood cells, there was no difference in dnDNA incidence between cohorts (Fig 2). <h3>Conclusion</h3> The use of EVLP-conditioned donor lungs is not associated with increased incidence of dnDSA early post-LTx.

A Two-Step Bioreactor for Decellularized Lung Epithelialization

Bioreactors for the reseeding of decellularized lung scaffolds have evolved with various advancements, including biomimetic mechanical stimulation, constant nutrient flow, multi-output monitoring, and large mammal scaling. Although dynamic bioreactors are not new to the field of lung bioengineering, ideal conditions during cell seeding have not been extensively studied or controlled. To address the lack of cell dispersal in traditional seeding methods, we have designed a two-step bioreactor. The first step is a novel system that rotates a seeded lung every 20 min at different angles in a sequence designed to anchor 20% of cells to a particular location based on the known rate of attachment. The second step involves perfusion-ventilation culture to ensure nutrient dispersion and cellular growth. Compared to statically seeded lungs, rotationally seeded lungs had significantly increased dsDNA content and more uniform cellular distribution after perfusion and ventilation had been administered. The addition of this novel seeding system before traditional culture methods will aid in recellularizing the lung and other geometrically complex organs for tissue engineering.

Decellularized human-sized pulmonary scaffolds for lung tissue engineering: a comprehensive review.

The ultimate goal of lung bioengineering is to produce transplantable lungs for human beings. Therefore, large-scale studies are of high importance. In this paper, we review the investigations on decellularization and recellularization of human-sized lung scaffolds. First, studies that introduce new ways to enhance the decellularization of large-scale lungs are reviewed, followed by the investigations on the xenogeneic sources of lung scaffolds. Then, decellularization and recellularization of diseased lung scaffolds are discussed to assess their usefulness for tissue engineering applications. Next, the use of stem cells in recellularizing acellular lung scaffolds is reviewed, followed by the case studies on the transplantation of bioengineered lungs. Finally, the remaining challenges are discussed, and future directions are highlighted.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing.

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Leveraging Machine Perfusion to Ameliorate Geographic Disparities in Organ Allocation

Leveraging Machine Perfusion to Ameliorate Geographic Disparities in Organ Allocation

Advanced single-cell technologies to guide the development of bioengineered lungs.

Lung transplantation remains the only viable option for individuals suffering from end-stage lung failure. However, a number of current limitations exist including a continuing shortage of suitable donor lungs and immune rejection following transplantation. To address these concerns, engineering a decellularized biocompatible lung scaffold from cadavers reseeded with autologous lung cells to promote tissue regeneration is being explored. Proof-of-concept transplantation of these bioengineered lungs into animal models has been accomplished. However, these lungs were incompletely recellularized with resulting epithelial and endothelial leakage and insufficient basement membrane integrity. Failure to repopulate lung scaffolds with all of the distinct cell populations necessary for proper function remains a significant hurdle for the progression of current engineering approaches and precludes clinical translation. Advancements in 3D bioprinting, lung organoid models, and microfluidic device and bioreactor development have enhanced our knowledge of pulmonary lung development, as well as important cell-cell and cell-matrix interactions, all of which will help in the path to a bioengineered transplantable lung. However, a significant gap in knowledge of the spatiotemporal interactions between cell populations as well as relative quantities and localization within each compartment of the lung necessary for its proper growth and function remains. This review will provide an update on cells currently used for reseeding decellularized scaffolds with outcomes of recent lung engineering attempts. Focus will then be on how data obtained from advanced single-cell analyses, coupled with multiomics approaches and high-resolution 3D imaging, can guide current lung bioengineering efforts for the development of fully functional, transplantable lungs.

Advances in bioreactors for lung bioengineering: From scalable cell culture to tissue growth monitoring.

Lung bioengineering has emerged to resolve the current lung transplantation limitations and risks, including the shortage of donor organs and the high rejection rate of transplanted lungs. One of the most critical elements of lung bioengineering is bioreactors. Bioreactors with different applications have been developed in the last decade for lung bioengineering approaches, aiming to produce functional reproducible tissue constructs. Here, the current status and advances made in the development and application of bioreactors for bioengineering lungs are comprehensively reviewed. First, bioreactor design criteria are explained, followed by a discussion on using bioreactors as a culture system for scalable expansion and proliferation of lung cells, such as producing epithelial cells from induced pluripotent stem cells (iPSCs). Next, bioreactor systems facilitating and improving decellularization and recellularization of lung tissues are discussed, highlighting the studies that developed bioreactors for producing engineered human-sized lungs. Then, monitoring bioreactors are reviewed, showing their ability to evaluate and optimize the culture conditions for maturing engineered lung tissues, followed by an explanation on the ability of ex vivo lung perfusion systems for reconditioning the lungs before transplantation. After that, lung cancer studies simplified by bioreactors are discussed, showing the potentials of bioreactors in lung disease modeling. Finally, other platforms with the potential of facilitating lung bioengineering are described, including the in vivo bioreactors and lung-on-a-chip models. In the end, concluding remarks and future directions are put forward to accelerate lung bioengineering using bioreactors.

A Novel Pre-Clinical Strategy to Deliver Antimicrobial Doses of Inhaled Nitric Oxide

Background: Effective treatment of respiratory infections continues to be a major challenge. In high doses (³160 ppm), inhaled Nitric Oxide (iNO) has been shown to act as a broad-spectrum antimicrobial agent in preliminary studies. However, the safety of prolonged in vivo implementation of high-dose iNO therapy has not been studied. Herein we aim to explore the feasibility and safety of delivering continuous high-dose iNO over an extended period of time using an in vivo animal model. Methods: Yorkshire pigs were randomized to one of the following two groups: group 1, standard ventilation; and group 2, standard ventilation + continuous iNO 160 ppm + methylene blue (MB) as intravenous bolus, whenever required, to maintain metHb <6%. Both groups were ventilated continuously for 6 hours, then the animals were weaned from sedation, mechanical ventilation and followed for 3 days. During treatment, and on the third post-operative day, physiologic assessments were performed to monitor lung function and other significative markers were assessed for potential pulmonary or systemic injury. Findings: No significant change in lung function, or inflammatory markers were observed during the study period. Both gas exchange function, lung tissue cytokine analysis and histology was similar between treated and control animals. During treatment, levels of metHb were maintained <6% by administration of MB, and NO2 remained <5 ppm. Additionally, considering extrapulmonary effects, no significant changes were observed in biochemistry markers. Interpretation: Our findings showed that high-dose iNO delivered continuously over 6 hours with adjuvant MB is clinically feasible and safe. These findings support the development of investigations of continuous high-dose iNO treatment of respiratory tract infections, including SARS-CoV-2. Funding: The Toronto General Hospital Foundation supported this work. Declaration of Interest MC and SK are founders of Traferox Inc. MC and SK are consultants for Lung Bioengineering. All the other authors have no conflict of interest to report. Ethical Approval: Animal care and experimental protocol were approved by the Toronto General Hospital Research Institute Animal Care Committee. All animals received humane care in compliance with the Principles of Laboratory Animal Care formulated by the National Society for Medical Research and the Guidelines for the Care and Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources. This project was performed and reported according to the ARRIVE guidelines 2.0.

Bioengineering of Pulmonary Epithelium With Preservation of the Vascular Niche.

The shortage of transplantable donor organs directly affects patients with end-stage lung disease, for which transplantation remains the only definitive treatment. With the current acceptance rate of donor lungs of only 20%, rescuing even one half of the rejected donor lungs would increase the number of transplantable lungs threefold, to 60%. We review recent advances in lung bioengineering that have potential to repair the epithelial and vascular compartments of the lung. Our focus is on the long-term support and recovery of the lung ex vivo, and the replacement of defective epithelium with healthy therapeutic cells. To this end, we first review the roles of the lung epithelium and vasculature, with focus on the alveolar-capillary membrane, and then discuss the available and emerging technologies for ex vivo bioengineering of the lung by decellularization and recellularization. While there have been many meritorious advances in these technologies for recovering marginal quality lungs to the levels needed to meet the standards for transplantation – many challenges remain, motivating further studies of the extended ex vivo support and interventions in the lung. We propose that the repair of injured epithelium with preservation of quiescent vasculature will be critical for the immediate blood supply to the lung and the lung survival and function following transplantation.

Functional role of glycosaminoglycans in decellularized lung extracellular matrix

Despite progress in use of decellularized lung scaffolds in ex vivo lung bioengineering schemes, including use of gels and other materials derived from the scaffolds, the detailed composition and functional role of extracellular matrix (ECM) proteoglycans (PGs) and their glycosaminoglycan (GAG) chains remaining in decellularized lungs, is poorly understood. Using a commonly utilized detergent-based decellularization approach in human autopsy lungs resulted in disproportionate losses of GAGs with depletion of chondroitin sulfate/dermatan sulfate (CS/DS) > heparan sulfate (HS) > hyaluronic acid (HA). Specific changes in disaccharide composition of remaining GAGs were observed with disproportionate loss of NS and NS2S for HS groups and of 4S for CS/DS groups. No significant influence of smoking history, sex, time to autopsy, or age was observed in native vs. decellularized lungs. Notably, surface plasmon resonance demonstrated that GAGs remaining in decellularized lungs were unable to bind key matrix-associated growth factors FGF2, HGF, and TGFβ1. Growth of lung epithelial, pulmonary vascular, and stromal cells cultured on the surface of or embedded within gels derived from decellularized human lungs was differentially and combinatorially enhanced by replenishing specific GAGs and FGF2, HGF, and TGFβ1. In summary, lung decellularization results in loss and/or dysfunction of specific GAGs or side chains significantly affecting matrix-associated growth factor binding and lung cell metabolism. GAG and matrix-associated growth factor replenishment thus needs to be incorporated into schemes for investigations utilizing gels and other materials produced from decellularized human lungs. Statement of significanceDespite progress in use of decellularized lung scaffolds in ex vivo lung bioengineering schemes, including use of gels and other materials derived from the scaffolds, the detailed composition and functional role of extracellular matrix (ECM) proteoglycans (PGs) and their glycosaminoglycan (GAG) chains remaining in decellularized lungs, is poorly understood. In the current studies, we demonstrate that glycosaminoglycans (GAGs) are significantly depleted during decellularization and those that remain are dysfunctional and unable to bind matrix-associated growth factors critical for cell growth and differentiation. Systematically repleting GAGs and matrix-associated growth factors to gels derived from decellularized human lung significantly and differentially affects cell growth. These studies highlight the importance of considering GAGs in decellularized lungs and their derivatives.

Utilization of Natural Detergent Potassium Laurate for Decellularization in Lung Bioengineering.

Recent advances in tissue engineering using decellularized organ scaffolds have expanded the possibilities for organ replacement therapy. However, detergent-based decellularization itself damages the extracellular matrix (ECM), which results in failure associated with the transplanted bioengineered organ. This study determined that potassium laurate (PL), a natural detergent, significantly reduces lung ECM damage during the decellularization process compared with protocols using sodium dodecyl sulfate. PL-decellularized lungs showed better microarchitecture preservation and low biological reactions after subcutaneous implantation. PL-decellularized scaffolds supported rat lung endothelial cell attachment/proliferation and the bioengineered lungs significantly reduced lung congestion after transplantation.

Lung Transplantation Using Hepatitis C Viremic Donors: An Open-Label Single Center Pilot Trial of Prevention of Viral Transmission

Background: A significant proportion of organ donors currently test positive for hepatitis C virus (HCV) infection. To date, only a few studies have evaluated the safety of using lungs from these donors for transplantation, and no direct interventions to donor organs have been performed with the aim of preventing HCV transmission via organ transplantation. Methods: We performed a single center prospective non-randomized trial where donor lungs from HCV viremic donors were transplanted into HCV negative (HCV-ve) recipients. Outcomes of study recipients were compared to patients receiving HCV-ve donors. Primary endpoints were survival and HCV status at 6 months after transplantation. Prior to implantation, all donor lungs were treated with ex vivo lung perfusion (EVLP) with (n=11) or without (n=11) ultraviolet C (UVC) perfusate irradiation to reduce HCV RNA levels and infectivity. All patients becoming viremic received 12 weeks of sofosbuvir/velpatasvir (S/V) starting at least 2 weeks after transplantation. Findings: During the 13-month study period, 22 patients were transplanted using viremic HCV donors and 187 with HCV-ve donors. Recipient age, lung disease, urgency status and positive donor-recipient HLA crossmatch were similar between the 2 groups. Post-transplant outcomes such as primary graft dysfunction grades, ICU and hospital length of stay, and survival were similar between the 2 groups. Twenty patients (91%) developed HCV viremia within the first week after transplantation and underwent S/V treatment starting at a median of 21 days after transplantation (range 14-71 days). Donor organ treatment with EVLP+UVC was associated with significantly lower recipient viral loads in blood within the first week after transplantation, and prevention of transmission in 2/11 patients. All infected patients achieved negative HCV PCR within 6 weeks of treatment initiation. Two patients presented with HCV relapse within 3 months after S/V completion requiring retreatment. Interpretation: Early and intermediate-term clinical outcomes using viremic HCV donors were similar to patients receiving HCV-ve donor lungs. Donor organ treatment using UVC perfusate irradiation during EVLP showed a significant impact in decreasing HCV viral loads within the first 7 days after transplantation. Trial Registration Number: The trial was registered at clinicaltrials.gov (NCT03112044). Funding Statement: This study was an investigator-initiated study funded by an operating grant from the Canadian Institutes of Health Research (CIHR). Gilead Sciences provided S/V (Epclusa) for all patients in the study. XVIVO perfusion (Gothenburg, Sweden) provided Steen solution for EVLP Declaration of Interests: Dr. Cypel, Waddell and Keshavjee are co-founders of Perfusix Canada, XOR Labs Toronto, and consultants for Lung Bioengineering (United Therapeutics). Ethics Approval Statement: This study was approved by the Research Ethics Board of University Health Network and subjects provided written informed consent while on the transplant waiting list prior to the offer of HCV+ve donor lungs.

Lung bioengineering: advances and challenges in lung decellularization and recellularization.

Bioengineering the lung based on its natural extracellular matrix (ECM) offers novel opportunities to overcome the shortage of donors, to reduce chronic allograft rejections, and to improve the median survival rate of transplanted patients. During the last decade, lung tissue engineering has advanced rapidly to combine scaffolds, cells, and biologically active molecules into functional tissues to restore or improve the lung's main function, gas exchange. This review will inspect the current progress in lung bioengineering using decellularized and recellularized lung scaffolds and highlight future challenges in the field. Lung decellularization and recellularization protocols have provided researchers with tools to progress toward functional lung tissue engineering. However, there is continuous evolution and refinement particularly for optimization of lung recellularization. These further the possibility of developing a transplantable bioartificial lung. Bioengineering the lung using recellularized scaffolds could offer a curative option for patients with end-stage organ failure but its accomplishment remains unclear in the short-term. However, the state-of-the-art of techniques described in this review will increase our knowledge of the lung ECM and of chemical and mechanical cues which drive cell repopulation to improve the advances in lung regeneration and lung tissue engineering.

Cell replacement in human lung bioengineering.

As the number of patients with end-stage lung disease continues to rise, there is a growing need to increase the limited number of lungs available for transplantation. Unfortunately, attempts at engineering functional lung de novo have been unsuccessful, and artificial mechanical devices have limited utility as a bridge to transplant. This difficulty is largely due to the size and inherent complexity of the lung; however, recent advances in cell-based therapeutics offer a unique opportunity to enhance traditional tissue-engineering approaches with targeted site- and cell-specific strategies. Human lungs considered unsuitable for transplantation were procured and supported using novel cannulation techniques and modified ex-vivo lung perfusion. Targeted lung regions were treated using intratracheal delivery of decellularization solution. Labeled mesenchymal stem cells or airway epithelial cells were then delivered into the lung and incubated for up to 6 hours. Tissue samples were collected at regular time intervals and detailed histologic and immunohistochemical analyses were performed to evaluate the effectiveness of native cell removal and exogenous cell replacement. Regional decellularization resulted in the removal of airway epithelium with preservation of vascular endothelium and extracellular matrix proteins. After incubation, delivered cells were retained in the lung and showed homogeneous topographic distribution and flattened cellular morphology. Our findings suggest that targeted cell replacement in extracorporeal organs is feasible and may ultimately lead to chimeric organs suitable for transplantation or the development of in-situ interventions to treat or reverse disease, ultimately negating the need for transplantation.