Despite recent advances in diagnostic and therapeutic method, many diseases which affect the organs and tissue structures in the thorax are either difficult to treat, or in fact not treatable at all. Millions of patients suffer from chronic and acute respiratory dysfunction, cardiac related disorders, esophageal problems and other diseases in the thorax. And, for many decades, doctors and researchers have been unable to develop new therapeutic options that may be able to benefit these millions. Depending on the extent of the disease, therapeutic possibilities currently range from palliative approaches to only modest improvements in quality of life. Only a minority of disorders are currently completely curable.
Regenerative Medicine (RM) appears to be the most promising option for many of these terminally-ill patients. RM is an emerging interdisciplinary field of research and clinical applications. It focuses on the repair, replacement, or regeneration of cells, tissues or organs. Dysfunction of organs can be a result of many causes, including congenital defects, disease, trauma and aging.
RM has the potential to transform traditional transplantation approaches. It enables the combination of several biological techniques, such as cell-based therapy (cell therapy), with engineering methods, such as the use of natural or synthetic scaffolds to replace organs and tissues (tissue engineering). In addition, mathematical modeling of tissue engineering methodscan be used to produce better clinical and experimental outcomes.Our research group investigates different organs and tissues in the thorax and the potential to recover and/or reconstitute normal physiological function, via the use of RM and tissue engineering.
Our aim is to evaluate and improve different methodologies in the field of tissue engineering and cell-based therapy. Cell types, such as adult progenitor/stem cell, embryonic, and induced pluripotent stem cells are currently under investigation for their potential use in a clinical context. The culture and differentiation abilities of these cells are analyzed through in vitro and in vivo models. We also investigate strategies to mobilize and activate endogenous stem cells, and increase their integration into damaged tissues, in order to stimulate tissue regeneration and in situ angiogenesis via specific growth and boosting factors. Bioengineering methods play a part in tissue engineering, and we also focus on the development of both natural and synthetic scaffolds to engineer organs and different tissues of the thorax (such as trachea, lung, esophagus, heart, chest wall and diaphragm).
The early and prompt clinical transfer of these novel approaches form the principles of our clinical research group, and constitute the major aims of our efforts. In the field of cell therapy, we investigate different cell types (adult stem/progenitor cells, embryonic, and induced pluripotent stem cells) for their potential use in various acute and chronic respiratory and cardiac disease models.
Embryonic stem cells (ESCs) are one of the most versatile types of stem cell. They can proliferate indefinitely to generate daughter cells of identical characteristics without senescence (self-renewal), and can maintain their ability to differentiate into all tissue specific cell lineages upon receiving appropriate signals (pluripotency). We utilize different differentiation protocols e.g. growth factors and media composition, to explore methods of controlling differentiation into specific progenitor cells. These include endothelial progenitor cells, neural crest cells, or differentiated cell types eg. type II pneumocytes, cardiomyocytes and neuronal cells. The ultimate aim of this work is to be able to use these cells in different clinical conditions.
Induced pluripotent stem cells (iPSCs) form another promising basis for the generation of patient-specific stem cells of any lineage, but without the need for embryonic materials (as is the case with ESCs). iPSCs have been demonstrated to exhibit the essential characteristics of ESCs, i.e. normal karyotype, ESC-like morphology, and expression of cell surface markers and genes that characterize ESCs. iPSC also have a significantly lower level of immunological and ethical concern, as compared to ESCs. Our aim is to optimize and evaluate the differentiation and culturing conditions of ESCs and iPSCs on scaffolds that can be implanted/delivered to the host.
Our established animal model of pulmonary hypertension has also revealed improvements in the underlying disease after intratracheal treatment with mesenchymal stem cells1. Burn injuries that affected the respiratory tract and esophagus also demonstrated a significant beneficial effect on the clinical outcome. A multicenter study using stem cells in patients with cardiac infarction is planned for the near future. A study with patients on ECMO (extracorporeal membrane oxygenator) support with respiratory distress is also currently under design.
DEVELOPMENTS OF SCAFFOLDS:
Tissue engineering with natural or synthetic scaffolds aims to improve the recovery and/or reconstitution of different organs and tissues. We investigate the development and use of three-dimensional (3D) scaffolds that can mimic the structural morphology of the target organ, as well as providing the structural base (matrix) for attachment, proliferation and differentiation of cells.
It is important to mimic the target tissue structurally and mechanically when engineering biomedical scaffolds for different applications in RM. Electrospinning is one method that allows the fabrication of 3D porous scaffolds with different architectures and morphologies. This technique includes the structural development from simple electrospun fibrous mats having random or aligned orientation to fiber bundles, membranes and highly porous 3D complex scaffolds mimicking specific organs. The structural size of electrospun nanofibrous webs can be engineered to mimic the natural extracellular matrix (ECM) fibrous components.
The development of the 3D scaffold is followed by a bioprinting procedure capable of creating functional living tissues. This procedure involves depositing “bioink” (cell aggregates or spheroids) and “bio-paper” (scaffold materials) as a novel vehicle for delivery, retention, growth, and differentiation of stem cells. Bioprinting of naturally derived materials such as proteins and polysaccharides is useful for increasing the hydrophilicity of the scaffolds which have been electrospun from synthetic polymers. This ultimately results in better cell-scaffold interactions2. This technique has increased our understanding of cell attachment, proliferation, and differentiation on bioengineered scaffolds.
A key strategy in our research is to use mathematical modeling techniques to assist the development of tissue engineering therapies. We utilize our extensive expertise in mathematical modeling for the interactions between cells and biomaterials3, angiogenesis4, and tissue growth into porous scaffolds5. Based on the surgical operation reported by Macchiarini and colleagues (2008), we developed a mathematical model to predict the regeneration in situ of a donor trachea seeded with mesenchymal stem cells (MSCs) and epithelial cells (EPCs). The model predicts the extent of inflammation and stenosis of the implanted trachea in relation to the seeding densities of EPCs and MSCs. This is a useful theoretical tool for exploring the mechanisms of tracheal regeneration and understanding why regeneration may fail.
Our aim is to extend such a model to make it more realistic. For example, we wish to include cell interactions with the electospun nanofibres in artificial tracheae, and the mechanisms contributing to neovascularization. Incorporating these processes in the model will help us simulate novel cell-based therapies and to explore in detail the mechanisms that can give rise to pathological conditions e.g. biomaterial-induced thrombosis.
Recently, we have also demonstrated successful clinical transplantations of tissue engineered trachea using both decellularized6 and synthetic7 scaffolds to show the feasibility of this promising methodology. These clinical studies clearly demonstrate the enormous potential of RM: altering the current practice of treating patients affected by failing respiratory tissues and organs. Unfortunately, this emerging field of RM is extremely cost intensive. Health systems and insurance companies are hesitant to support RM sufficiently, and thus patients have to cover these costs without assistance. We therefore aim to establish a funding system that can support our preclinical research as well as assist patients with any financial background to undergo these novel therapeutic procedures.