Prevention of small airway obliteration in a swine heterotopic lung allograft model

Background: In our swine model of obliterative bronchiolitis preventing obliteration by the standard immunosuppression with cyclosporine, methylprednisolone, and azathioprine was not successful. The purpose of this study was to test the ability of a new immunosuppressive regimen to prevent alloimmune reaction and obliteration of the allografts. This regimen includes the novel macrolide SDZ RAD, i.e., 40-O-(2hydroxyethyl)-rapamycin. Methods: Donor lung allografts of 1 cm(3) were implanted sub-cutaneously into 11 random-bred non-related domestic pigs receiving daily oral cyclosporine (10 mg/kg) and methylprednisolone (20 mg). In addition, the animals received either oral azathioprine (2 mg/kg) (Group 1) or oral SDZ RAD (1.5 mg/kg) (Group 2). Histologic alterations were graded from 0 to 3 based on repeatedly removed implants during a follow-up period of 3 months. Results: Total epithelial destruction and permanent luminal obliteration occurred within 37 days in Group 1. After an initial grade of 2.3 +/- 0.3 destruction, epithelial recovery was evident in Group 2 (P < 0.01), and the bronchi stayed patent. Cartilaginous destruction was milder in Group 2 (P < 0.05) than in Group 1, but chondrocytic proliferation was more intense (P < 0.05). Alveolar tissue and native structures of the bronchial wall were destroyed in Group 1, but preserved in Group 2 with total recovery after a mild-grade initial necrosis. Conclusions: Unlike the standard triple therapy, SDZ RAD combined with cyclosporine and methylprednisolone preserves the pulmonary allografts and prevents epithelial destruction and subsequent luminal obliteration. This suggests that this regimen might efficiently suppress obliterative bronchiolitis and improve long-term results in lung transplant recipients.