Circulating Extracellular Vesicle RNA : Potential Biomarkers in Acute Lung Allograft Rejection

Although lung transplantation has become a routine procedure and is optimal therapy for patients with end-stage pulmonary diseases, the lifespan of lung allografts is still shorter than that of other organ transplants. As acute allograft rejection is one of the main risk factors for the development of chronic lung allograft dysfunction (CLAD) which threatens the long-term survival rate of the recipients, it is crucial to predict and diagnose acute lung allograft rejection. However, there are no specific methods established so far to predict acute rejection (AR). Even though the histopathological evaluation of transbronchial biopsies (TBBs) is used as the gold standard to ensure the diagnosis of AR, it is essential to discover novel biomarkers for AR to overcome the limitations of the TBB-based invasive diagnostics. Recently extracellular vesicles (EVs) got noticed as potential biomarkers in various fields of medicine based on the findings that they exist in high concentration in body fluids and deliver functional genetic molecules which can modulate gene expression in target cells. In that regard, this preliminary study was designed with two different approaches; a time-point analysis and a case analysis of rejection and non-rejection episodes to validate their potentials as diagnostic and predictive biomarkers for acute lung allograft rejection. To discover biomarkers, EV RNA was isolated from the plasma of four patients that was collected at different time points, and whole EV mRNA transcriptome sequencing was performed on the Illumina platform to obtain at least 15 million reads. The time-point analysis showed that the mRNA contents of EVs changed according to the time points and clinical presentations of the patients. At the same time, gene expression profiles showed that mRNA molecules inside the EVs change from innate immunity to adaptive immunity related signatures with the time after transplantation. Furthermore, the case analysis identified that EVs contain RNA molecules that are closely related to the migration of leukocytes and adaptive immune system during acute rejection episodes. In conclusion, the profiles of EV RNA may reflect the immune responses that are taking place in the recipient’s body. Therefore, it is speculated that EVs may play an essential role in the development of AR by transferring functional mRNA molecules to the allograft, immune cells, and endothelial cells. On that account, EV transcriptome profiling could be used as a diagnostic tool for AR in the future, as well as a therapeutic tool by engineering EVs to target specific genes that may be involved in the development of AR. Keywords: extracellular vesicles, lung transplantation, transplantation immunology, RNA sequencing, acute lung allograft rejection, biomarker