My PhD project “Precision medicine in monitoring patients with heart or lung transplantation: towards the liquid biopsy based on the HLA-mismatch?” is part of the solid organ transplantation area of research. The aim of this project is to collect an observational cohort of heart and lung transplant patients to develop a quantification test based on donor circulating DNA, considered an informative index of the presence of organ damage associated with acute rejection. The data obtained will be correlated with clinical and laboratory data in order to carry out transversal and longitudinal analyses with the final aim of developing and validating a new non-invasive, highly sensitive and economically advantageous method for isolating, identifying and quantifying fragments of circulating DNA that can be used as biological markers for prognosis of acute rejection of the transplanted organ and prediction of clinical outcome.