The goal of this clinical trial is to evaluate the therapeutic effect of extracorporeal photopheresis in subclinical antibody-mediated rejection after lung transplantation.The main questions it aims to answer are: 1. Does ECP therapy result in a significant reduction in MFI (Mean Fluorescence Intensity) from the baseline MFI in clinically stable patients with persistent (\>6 months) dnDSAs (MFI\>1000)? 2. What is the impact of ECP therapy on the following outcomes in these patients: ACR, clinical AMR, CLAD, infections, drop-out rate, survival, adverse events? Participants will be randomized into two groups. Each group will include 40 patients. The control group will be observed and no active treatment will be administered. The treatment group will receive extracorporeal photopheresis. First, a two-day treatment cycle will be performed once every second week for the first two months. Then, a two-day treatment cycle will be performed once a month for 6 months. Researchers will compare the two groups regarding: MFI value, development of ACR, clinical AMR, CLAD, infections, survival, adverse events, immunophenotyping, miRNA expression profiling, cytokine expression, gene expression signature of PBMCs and proteomic characterization.