Inhaled immunosuppression using tacrolimus

Backround: To investigate the feasibility of tacrolimus delivery via aerosol, assess its immunosuppressive efficacy, reveal mechanisms of action, and evaluate its air-way toxicity. Methods: Orthotopic BN-Lew tracheal transplantations were performed and tacrolimus (4mg/kg) was administered orally (TO) or via aerosol (TA). Drug pharmacokinetics, graft pathology, host immune responsiveness and side effects were closely monitored over time. Human airway cells were grown in vitro at an air-liquid interface to study cell biology during tacrolimus treatment. Results: Tracheal tissue-level-AUCs were similar for TO and TA, but blood-AUCs were 5.5-fold lower with TA. Histology revealed that both TO and TA showed significantly reduced graft infiltration on day 6 (p<0.05), while preserving epithelial cell viability and gene expression profile. Although TO and TA treatments both markedly suppressed the cellular (IFNg/IL4-Elispots) and humoral response (donorspecific antibodies), TO was far more effective. After 60 days, BUN, cholesterol, and triglycerides were significantly higher in TO animals (p≤0.041). After 60 days, obliterative airway disease (OAD) was similarly inhibited with TO (15±3%) and TA (13±4%) vs. untreated animals (44±7%, p<0.001). In vitro, tacrolimus (10-1000ng/ml) did neither impair airway cell morphology, viability, or proliferation, nor epithelial integrity. It did, however, interfere with cell activation and suppressed cytokine production on the level of gene transcription. Conclusions: TA(1) provides adequate local airway immunosuppression, (2) alleviates cellular rejection and (3) OAD, (4) eliminates systemic side effects, (5) shows no obvious airway toxicity, and (6) counteracts airway cell activation. Thus, TA has the potential to markedly reduce morbidity after lung transplantation.