Current strategies and opportunities to manufacture cells for modeling human lungs

The Development of Lung Tissue Engineering: From Biomaterials to Multicellular Systems

The challenge of the treatment of end-stage lung disease poses an urgent clinical demand for lung tissue engineering. Over the past few years, various lung tissue-engineered constructs are developed for lung tissue regeneration and respiratory pathology study. In this review, an overview of recent achievements in the field of lung tissue engineering is proposed. The introduction of lung structure and lung injury are stated briefly at first. After that, the lung tissue-engineered constructs are categorized into three types: acellular, monocellular, and multicellular systems. The different bioengineered constructs included in each system that can be applied to the reconstruction of the trachea, airway epithelium, alveoli, and even whole lung are described in detail, followed by the highlight of relevant representative research. Finally, the challenges and future directions of biomaterials, manufacturing technologies, and cells involved in lung tissue engineering are discussed. Overall, this review can provide referable ideas for the realization of functional lung regeneration and permanent lung substitution.

In silico model development and optimization of in vitro lung cell population growth

Tissue engineering predominantly relies on trial and error in vitro and ex vivo experiments to develop protocols and bioreactors to generate functional tissues. As an alternative, in silico methods have the potential to significantly reduce the timelines and costs of experimental programs for tissue engineering. In this paper, we propose a methodology to formulate, select, calibrate, and test mathematical models to predict cell population growth as a function of the biochemical environment and to design optimal experimental protocols for model inference of in silico model parameters. We systematically combine methods from the experimental design, mathematical statistics, and optimization literature to develop unique and explainable mathematical models for cell population dynamics. The proposed methodology is applied to the development of this first published model for a population of the airway-relevant bronchio-alveolar epithelial (BEAS-2B) cell line as a function of the concentration of metabolic-related biochemical substrates. The resulting model is a system of ordinary differential equations that predict the temporal dynamics of BEAS-2B cell populations as a function of the initial seeded cell population and the glucose, oxygen, and lactate concentrations in the growth media, using seven parameters rigorously inferred from optimally designed in vitro experiments.

De-Epithelialization Protocol with Tapered Sodium Dodecyl Sulfate Concentrations Enhances Short-Term Chondrocyte Survival in Porcine Chimeric Tracheal Allografts

Background: Tracheal transplantation is indicated in cases where injury exceeds 50% of the organ in adults and 30% in children. However, transplantation is not yet considered a viable treatment option partly due to high morbidity and mortality associated with graft rejection. Recently, decellularization (decell) has been explored as a technique for creating bioengineered tracheal grafts. However, risk of post-operative stenosis increases due to the death of chondrocytes, which are critical to maintain the biochemical and mechanical integrity of tracheal cartilage. In this project, we propose a new de-epithelialization protocol that adequately removes epithelial, mucosal, and submucosal cells while maintaining a greater proportion of viable chondrocytes. Methods: The trachea of adult male outbred Yorkshire pigs were extracted, decontaminated, and decellularized according to the original and new protocols before incubation at 37 °C in DMEM for 10 days. Chondrocyte viability was quantified immediately following post-decellularization and on days 1, 4, 7, and 10. Histology was performed pre-decellularization, post-decellularization, and post-incubation. Results: The new protocol showed a significant (p < 0.05) increase in chondrocyte viability up to four days after de-ep when compared to the original protocol. We also found that the new protocol preserves ECM composition to a similar degree as the original protocol. When scaffolds created using the new protocol were re-epithelialized, cell growth curves were near identical to published data from the original protocol. Conclusion: While not without limitations, our new protocol may be used to engineer chimeric tracheal allografts without the need for cartilage regeneration.

In Vitro Systems for Toxicity Evaluation of Microbial Volatile Organic Compounds on Humans: Current Status and Trends

Microbial volatile organic compounds (mVOC) are metabolic products and by-products of bacteria and fungi. They play an important role in the biosphere: They are responsible for inter- and intra-species communication and can positively or negatively affect growth in plants. But they can also cause discomfort and disease symptoms in humans. Although a link between mVOCs and respiratory health symptoms in humans has been demonstrated by numerous studies, standardized test systems for evaluating the toxicity of mVOCs are currently not available. Also, mVOCs are not considered systematically at regulatory level. We therefore performed a literature survey of existing in vitro exposure systems and lung models in order to summarize the state-of-the-art and discuss their suitability for understanding the potential toxic effects of mVOCs on human health. We present a review of submerged cultivation, air-liquid-interface (ALI), spheroids and organoids as well as multi-organ approaches and compare their advantages and disadvantages. Furthermore, we discuss the limitations of mVOC fingerprinting. However, given the most recent developments in the field, we expect that there will soon be adequate models of the human respiratory tract and its response to mVOCs.

Short-Term Preclinical Application of Functional Human Induced Pluripotent Stem Cell-Derived Airway Epithelial Patches

Airway pathologies including cancer, trauma, and stenosis lack effective treatments, meanwhile airway transplantation and available tissue engineering approaches fail due to epithelial dysfunction. Autologous progenitors do not meet the clinical need for regeneration due to their insufficient expansion and differentiation, for which human induced pluripotent stem cells (hiPSCs) are promising alternatives. Airway epithelial patches are engineered by differentiating hiPSC-derived airway progenitors into physiological proportions of ciliated (73.9 ± 5.5%) and goblet (2.1 ± 1.4%) cells on a silk fibroin-collagen vitrigel membrane (SF-CVM) composite biomaterial for transplantation in porcine tracheal defects ex vivo and in vivo. Evaluation of ex vivo tracheal repair using hiPSC-derived SF-CVM patches demonstrate native-like tracheal epithelial metabolism and maintenance of mucociliary epithelium to day 3. In vivo studies demonstrate SF-CVM integration and maintenance of airway patency, showing 80.8 ± 3.6% graft coverage with an hiPSC-derived pseudostratified epithelium and 70.7 ± 2.3% coverage with viable cells, 3 days postoperatively. The utility of bioengineered, hiPSC-derived epithelial patches for airway repair is demonstrated in a short-term preclinical survival model, providing a significant leap for airway reconstruction approaches.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.