Three-Dimensional Cell Cultures as a Research Platform in Lung Diseases and COVID-19

A Brief History of Cell Culture: From Harrison to Organs-on-a-Chip

This comprehensive overview of the historical milestones in cell culture underscores key breakthroughs that have shaped the field over time. It begins with Wilhelm Roux's seminal experiments in the 1880s, followed by the pioneering efforts of Ross Granville Harrison, who initiated groundbreaking experiments that fundamentally shaped the landscape of cell culture in the early 20th century. Carrel's influential contributions, notably the immortalization of chicken heart cells, have marked a significant advancement in cell culture techniques. Subsequently, Johannes Holtfreter, Aron Moscona, and Joseph Leighton introduced methodological innovations in three-dimensional (3D) cell culture, initiated by Alexis Carrel, laying the groundwork for future consolidation and expansion of the use of 3D cell culture in different areas of biomedical sciences. The advent of induced pluripotent stem cells by Takahashi and Yamanaka in 2006 was revolutionary, enabling the reprogramming of differentiated cells into a pluripotent state. Since then, recent innovations have included spheroids, organoids, and organ-on-a-chip technologies, aiming to mimic the structure and function of tissues and organs in vitro, pushing the boundaries of biological modeling and disease understanding. In this review, we overview the history of cell culture shedding light on the main discoveries, pitfalls and hurdles that were overcome during the transition from 2D to 3D cell culture techniques. Finally, we discussed the future directions for cell culture research that may accelerate the development of more effective and personalized treatments.

Structured multicellular intestinal spheroids (SMIS) as a standardized model for infection biology

BACKGROUND

3D cell culture models have recently garnered increasing attention for replicating organ microarchitecture and eliciting in vivo-like responses, holding significant promise across various biological disciplines. Broadly, 3D cell culture encompasses organoids as well as single- and multicellular spheroids. While the latter have found successful applications in tumor research, there is a notable scarcity of standardized intestinal models for infection biology that mimic the microarchitecture of the intestine. Hence, this study aimed to develop structured multicellular intestinal spheroids (SMIS) specifically tailored for studying molecular basis of infection by intestinal pathogens.

RESULTS

We have successfully engineered human SMIS comprising four relevant cell types, featuring a fibroblast core enveloped by an outer monolayer of enterocytes and goblet cells along with monocytic cells. These SMIS effectively emulate the in vivo architecture of the intestinal mucosal surface and manifest differentiated morphological characteristics, including the presence of microvilli, within a mere two days of culture. Through analysis of various differentiation factors, we have illustrated that these spheroids attain heightened levels of differentiation compared to 2D monolayers. Moreover, SMIS serve as an optimized intestinal infection model, surpassing the capabilities of traditional 2D cultures, and exhibit a regulatory pattern of immunological markers similar to in vivo infections after Campylobacter jejuni infection. Notably, our protocol extends beyond human spheroids, demonstrating adaptability to other species such as mice and pigs.

CONCLUSION

Based on the rapid attainment of enhanced differentiation states, coupled with the emergence of functional brush border features, increased cellular complexity, and replication of the intestinal mucosal microarchitecture, which allows for exposure studies via the medium, we are confident that our innovative SMIS model surpasses conventional cell culture methods as a superior model. Moreover, it offers advantages over stem cell-derived organoids due to scalability and standardization capabilities of the protocol. By showcasing differentiated morphological attributes, our model provides an optimal platform for diverse applications. Furthermore, the investigated differences of several immunological factors compared to monotypic monolayers after Campylobacter jejuni infection underline the refinement of our spheroid model, which closely mimics important features of in vivo infections.

A comprehensive review on organ-on-chips as powerful preclinical models to study tissue barriers

In the preclinical stage of drug development, 2D and 3D cell cultures under static conditions followed by animal models are utilized. However, these models are insufficient to recapitulate the complexity of human physiology. With the developing organ-on-chip (OoC) technology in recent years, human physiology and pathophysiology can be modeled better than traditional models. In this review, the need for OoC platforms is discussed and evaluated from both biological and engineering perspectives. The cellular and extracellular matrix components are discussed from a biological perspective, whereas the technical aspects such as the intricate working principles of these systems, the pivotal role played by flow dynamics and sensor integration within OoCs are elucidated from an engineering perspective. Combining these two perspectives, bioengineering applications are critically discussed with a focus on tissue barriers such as blood-brain barrier, ocular barrier, nasal barrier, pulmonary barrier and gastrointestinal barrier, featuring recent examples from the literature. Furthermore, this review offers insights into the practical utility of OoC platforms for modeling tissue barriers, showcasing their potential and drawbacks while providing future projections for innovative technologies.

Infectivity and Potential Zoonotic Characteristics of Porcine Pseudorabies Virus in Human Cells

Pseudorabies virus (PRV) is widely spread, characterized by high contagiousness, high viral load, and strong infectivity, and poses severe threats to the global pig farming industry. Apart from pigs, PRV can also infect several other mammals, including mice, cattle, cats, dogs, and wolves, with diverse clinical symptoms. Notably, approximately more than 20 cases of human PRV infection have been reported in recent years, with fever, seizures, human encephalitis, intraocular inflammation, and severe central nervous system symptoms. However, whether PRV can infect humans or belongs to a zoonotic virus is still controversial. In this study, human neuronal cells were infected with PRV and blindly passaged to obtain human cell-adapted PRV, followed by comparing the characteristics of human cell-adapted PRV and pig-derived PRV in vitro and in vivo, to determine whether PRV has the potential to infect humans. The results showed that PRV could be stably passaged in human cells and produced progeny viruses similar to the parental virus, including morphology, infectivity, and pathogenicity. The human cell-adapted PRV can also cross-transmit to cells from other origins, including humans, mice, pigs, and monkeys, causing different cytopathic effects. Moreover, multiple tissue damage can be detected in mice infected with human cell-adapted PRV. These results demonstrate that PRV is a potential zoonotic virus, and it is necessary to pay close attention to the spread and variation of the virus in animals and humans.

3D bioprinting of the airways and lungs for applications in tissue engineering and in vitro models

Tissue engineering and in vitro modeling of the airways and lungs in the respiratory system are of substantial research and clinical importance. In vitro airway and lung models aim to improve treatment options for airway and lung repair and advance respiratory pathophysiological research. The construction of biomimetic native airways and lungs with tissue-specific biological, mechanical, and configurable features remains challenging. Bioprinting, an emerging 3D printing technology, is promising for the development of airway, lung, and disease models, allowing the incorporation of cells and biologically active molecules into printed constructs in a precise and reproducible manner to recreate the airways, lung architecture, and in vitro microenvironment. Herein, we present a review of airway and lung bioprinting for applications in tissue engineering and in vitro modeling. The key pathophysiological characteristics of the airway, lung interstitium, and alveoli are described. The bioinks recently used in 3D bioprinting of the airways and lungs are summarized. Furthermore, we propose a bioink categorization based on the structural characteristics of the lungs and airways. Finally, the challenges and opportunities in the research on biofabrication of airways and lungs are discussed.

Design and Realization of Lung Organoid Cultures for COVID-19 Applications

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been spreading globally and threatening public health. Advanced in vitro models that recapitulate the architecture and functioning of specific tissues and organs are in high demand for COVID-19-related pathology studies and drug screening. Three-dimensional (3D) in vitro cultures such as self-assembled and engineered organoid cultures surpass conventional two-dimensional (2D) cultures and animal models with respect to the increased cellular complexity, better human-relevant environment, and reduced cost, thus presenting as promising platforms for understanding viral pathogenesis and developing new therapeutics. This review highlights the recent advances in self-assembled and engineered organoid technologies that are used for COVID-19 studies. The challenges and future perspectives are also discussed.

Current Trends on Bioengineering Approaches for Ovarian Microenvironment Reconstruction

Ovarian tissue has a unique microarchitecture and a complex cellular and molecular dynamics that are essential for follicular survival and development. Due to this great complexity, several factors may lead to ovarian insufficiency, and therefore to systemic metabolic disorders and female infertility. Techniques currently used in the reproductive clinic such as oocyte cryopreservation or even ovarian tissue transplant, although effective, have several limitations, which impair their wide application. In this scenario, mimetic ovarian tissue reconstruction comes as an innovative alternative to develop new methodologies for germ cells preservation and ovarian functions restoration. The ovarian extracellular matrix (ECM) is crucial for oocyte viability maintenance, once it acts actively in folliculogenesis. One of the key components of ovarian bioengineering is biomaterials application that mimics ECM and provides conditions for cell anchorage, proliferation, and differentiation. Therefore, this review aims at describing ovarian tissue engineering approaches and listing the main limitations of current methods for preservation and reestablishment of ovarian fertility. In addition, we describe the main elements that structure this study field, highlighting the main advances and the challenges to overcome to develop innovative methodologies to be applied in reproductive medicine. Impact Statement This review presents the main advances in the application of tissue bioengineering in the ovarian tissue reconstruction to develop innovative solutions for ovarian fertility reestablishment.

Advances of microfluidic lung chips for assessing atmospheric pollutants exposure

Atmospheric pollutants, including particulate matters, nanoparticles, bioaerosols, and some chemicals, have posed serious threats to the environment and the human's health. The lungs are the responsible organs for providing the interface betweenthecirculatory system and the external environment, where pollutant particles can deposit or penetrate into bloodstream circulation. Conventional studies to decipher the mechanismunderlying air pollution and human health are quite limited, due to the lack of reliable models that can reproduce in vivo features of lung tissues after pollutants exposure. In the past decade, advanced near-to-native lung chips, combining cell biology with bioengineered technology, present a new strategy for atmospheric pollutants assessment and narrow the gap between 2D cell culture and in vivo animal models. In this review, the key features of artificial lung chips and the cutting-edge technologies of the lung chip manufacture are introduced. The recent progresses of lung chip technologies for atmospheric pollutants exposure assessment are summarized and highlighted. We further discuss the current challenges and the future opportunities of the development of advanced lung chips and their potential utilities in atmospheric pollutants associated toxicity testing and drug screening.

Ultracellular Imaging of Bronchoalveolar Lavage from Young COVID-19 Patients with Comorbidities Showed Greater SARS-COV-2 Infection but Lesser Ultrastructural Damage Than the Older Patients

In this study, we examined the cellular infectivity and ultrastructural changes due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the various cells of bronchoalveolar fluid (BALF) from intubated patients of different age groups (≥60 years and <60 years) and with common comorbidities such as diabetes, liver and kidney diseases, and malignancies. BALF of 79 patients (38 cases >60 and 41 cases <60 years) were studied by light microscopy, immunofluorescence, scanning, and transmission electron microscopy to evaluate the ultrastructural changes in the ciliated epithelium, type II pneumocytes, macrophages, neutrophils, eosinophils, lymphocytes, and anucleated granulocytes. This study demonstrated relatively a greater infection and better preservation of subcellular structures in these cells from BALF of younger patients (<60 years compared with the older patients (≥60 years). The different cells of BALF from the patients without comorbidities showed higher viral load compared with the patients with comorbidities. Diabetic patients showed maximum ultrastructural damage in BALF cells in the comorbid group. This study highlights the comparative effect of SARS-CoV-2 infection on the different airway and inflammatory cells of BALF at the subcellular levels among older and younger patients and in patients with comorbid conditions.

Mesenchymal Stem Cell-Derived Extracellular Vesicles in the Management of COVID19-Associated Lung Injury: A Review on Publications, Clinical Trials and Patent Landscape

The unprecedented COVID-19 pandemic situation forced the scientific community to explore all the possibilities from various fields, and so far we have seen a lot of surprises, eureka moments and disappointments. One of the approaches from the cellular therapists was exploiting the immunomodulatory and regenerative potential of mesenchymal stromal cells (MSCs), more so of MSC-derived extracellular vesicles (EVs)-particularly exosomes, in order to alleviate the cytokine storm and regenerate the damaged lung tissues. Unlike MSCs, the EVs are easier to store, deliver, and are previously shown to be as effective as MSCs, yet less immunogenic. These features attracted the attention of many and thus led to a tremendous increase in publications, clinical trials and patent applications. This review presents the current landscape of the field and highlights some interesting findings on MSC-derived EVs in the context of COVID-19, including in silico, in vitro, in vivo and case reports. The data strongly suggests the potential of MSC-derived EVs as a therapeutic regime for the management of acute lung injury and associated complications in COVID-19 and beyond.

Better In Vitro Tools for Exploring Chlamydia trachomatis Pathogenesis

Currently, Chlamydia trachomatis still possesses a significant impact on public health, with more than 130 million new cases each year, alongside a high prevalence of asymptomatic infections (approximately 80% in women and 50% in men). C. trachomatis infection involves a wide range of different cell types, from cervical epithelial cells, testicular Sertoli cells to Synovial cells, leading to a broad spectrum of pathologies of varying severity both in women and in men. Several two-dimensional in vitro cellular models have been employed for investigating C. trachomatis host–cell interaction, although they present several limitations, such as the inability to mimic the complex and dynamically changing structure of in vivo human host-tissues. Here, we present a brief overview of the most cutting-edge three-dimensional cell-culture models that mimic the pathophysiology of in vivo human tissues and organs for better translating experimental findings into a clinical setting. Future perspectives in the field of C. trachomatis research are also provided.

A drug-responsive multicellular human spheroid model to recapitulate drug-induced pulmonary fibrosis

Associated with a high mortality rate, pulmonary fibrosis (PF) is the end stage of several interstitial lung diseases. Although many factors are linked to PF progression, initiation of the fibrotic process remains to be studied. Current research focused on generating new strategies to gain a better understanding of the underlying disease mechanism as the animal models remain insufficient to reflect human physiology. Herein, to account complex cellular interactions within the fibrotic tissue, a multicellular spheroid (MCS) model where human bronchial epithelial cells incorporated with human lung fibroblasts was generated and treated with bleomycin (BLM) to emulate drug-induced PF. Recapitulating the epithelial-interstitial microenvironment, the findings successfully reflected the PF disease, where excessive alpha smooth muscle actin (α-SMA) and collagen type I secretion were noted along with the morphological changes in response to BLM. Moreover, increased levels of fibrotic linked COL13A1, MMP2, WNT3 and decreased expression level of CDH1 provide evidence for the model reliability on fibrosis modelling. Subsequent administration of the FDA approved nintedanib and pirfenidone anti-fibrotic drugs proved the drug-responsiveness of the model.