Background: An important limitation to the success of lung transplantation is the development of bronchiolitis obliterans syndrome (BOS). It has been hypothesized that regulatory T lymphocytes (Tregs) are related to the risk of BOS. We aim to evaluate whether the number of forkhead box P3 (FoxP3+) cells/mm² in lung allograft biopsies is a predictor of long-term outcome.

Materials and Methods: A total of 58 consecutive lung transplant patients were included in the study. For 233 routine surveillance biopsy samples, the numbers of FoxP3+ cells/mm² were assessed by immunohistochemical staining with antibodies against FoxP3. BOS scores were calculated for the first five yr after transplantation.

Results: We determined that acute rejection was related to the time elapsed from transplantation to BOS with hazard ratios of 3.18 (p = 0.02) and 3.73 (p = 0.04) when comparing the levels of acute rejection grade 1 and grade 2/3, respectively, to no rejection. According to a Cox regression analysis, the number of FoxP3+ cells/mm² was not predictive of time to BOS.

Discussion and Conclusions: Our data indicate that the number of FoxP3+ cells in the lung allograft did not correlate with BOS-free survival time. Previous studies have been contradictory and included different time points. Our findings emphasize the importance of including a time factor.