Clinical and Preclinical Lung Transplantation in the aspects of improving outcome

Abstract: Lung transplantation (LTx) is an established therapeutic option for end-stage pulmonary disease. However, it remains restricted by donor lung scarcity. Donor's lungs are rejected frequently due to severe lung damage caused by aspiration or neurogenic pulmonary oedema that can all lead to acute lung injury (ALI), and more severe acute respiratory distress syndrome (ARDS). Lung transplant patients face poor survival rates in comparison with other solid organ transplantations. This is primarily due to a high incidence of postoperative complications, such as primary graft dysfunction (PGD) and chronic lung allograft dysfunction (CLAD), especially bronchiolitis obliterans syndrome (BOS). The aim of this thesis was to expand the availability of a donor's lungs for transplantation. We sought to increase the chances of a lifesaving opportunity for recipients who may otherwise have remained on the transplant waiting list for years. We did this preclinically by utilising a variety of techniques to regain lung function in discarded lungs, thus increasing the donor pool. We investigated the role of cytokine adsorption during ex vivo lung perfusion (EVLP), and extracorporeal haemofiltration post-transplant as a means of treating and restoring the ARDS-damaged lungs and reducing the incidence of PGD post-transplantation. The lungs were evaluated regarding the development of primary graft dysfunction (PGD) in which cytokines seem to be an essential target given the outcome of significantly less PGD in the group receiving cytokine adsorption. We suggest this treatment method will increase the availability of the donor's lungs and increase the tolerability of the donor's lungs in the recipient. The results of this study formed the basis for our idea to investigate the effect of mesenchymal stromal cell (MSC) therapy to restore gastric content aspirations damaged lungs and reduce the incidence of PGD at 72 hours’ post-transplantation. Furthermore, we explored pulmonary function, survival, and the incidence of CLAD between patients receiving marginal lungs after ex vivo lung perfusion (EVLP) reconditioning and patients receiving clinically standard lungs (conventional lungs) at our centre. These patients were followed for over 10 years. We did not find any difference in pulmonary function, survival, or incidence of CLAD, indicating that EVLP is safe to use and does not increase mortality. We also explored the impact of allograft ischaemic time (IT) in lung transplantation survival rate which showed superior outcomes for IT between 120 and 240 minutes. Every 2-hour increase in IT was equivalent to an increased mortality of up to 24% within 5 years. This indicates that IT has a key role in improving LTx outcomes. We explored the role of plasma biomarkers in the largest subgroup of CLAD, patients with BOS. Plasma from lung- transplanted patients with different BOS grades was analysed for protein biomarkers using Olink proteomics. A selective number of biomarkers were then validated using an enzyme-linked immunosorbent assay (ELISA) at baseline and after 1 year. Corticotropin-releasing hormone (CRH) levels were found to be related to different stages of BOS which identified CRH as a potential marker in a novel diagnostic tool to detect BOS. In conclusion, using EVLP is a safe effective platform for cytokine adsorption therapy and MSC therapy which can restore pulmonary function in damaged donor lungs, thus increasing the donor pool. CRH is a novel potential biomarker in the progression of post-transplantation BOS grades.