Next generation bioengineering of lung tissue for transplantation

Sammanfattning: Lung transplantation is the only option for end-stage lung diseases, but organ shortage remains problematic. Generating lungs ex vivo could overcome shortages with current approaches being explored for lung tissue engineering utilizing a biologically derived, synthetic or hybrid scaffold which is seeded with cells and cultured ex vivo. Ideally, cells could be sourced from the transplant recipient and thus are conceptualized to reduce the long-term requirements for immunosuppressive drugs and the risk for rejection. Progenitor cell populations can be controlled more easily than induced pluripotent stem cells (IPSCs), with lower risk of tumour formation. However, as presented in this thesis, progenitor cells can be deranged in diseased lungs such as for example idiopathic pulmonary fibrosis (IPF) and are therefore unlikely candidates to generate healthy tissue. In addition to healthy cells, scaffolds with attributes known to be pro-regenerative are required to generate healthy tissues. In the thesis it is shown that both scaffold and cell age plays a role in the regenerative capacity of a tissue. From this it is clear that to generate a healthy tissue or organ, it is critical to find the appropriate scaffold and cell type. Additionally, bioengineering manufacturing methods that generate reproducible, custom-made, high resolution constructs using cytocompatible materials are ideal for tissue engineering approaches. One such method which is compatible with the criteria above and that has emerged in recent years is 3D printing. 3D printing or bioprinting (when cells are printed) can generate custom structures relevant for human lungs. In this thesis, potential bioinks for bioprinting lung tissue are investigated. A tissue-specific hybrid bioink consisting of alginate, reinforced with extracellular matrix from decellularized lung tissue (rECM) was used to 3D bioprint human airways comprised of regionally specified primary cells which remained patent over time. The biocompatibility and vascularisation of rECM hydrogels was investigated in both T-cell immunodeficient mice mimicking the clinical scenario and immunocompetent mice. Bioprinted rECM hydrogels support the formation of an intact vascular network throughout the full thickness of the graft, comprised of both large and small size blood vessels and integrate well in the surrounding tissue.