Combination of Everolimus or Tacrolimus with Clopidogrel substantially reduces obliterative bronchiolitis (OB) in an experimental mouse model

Objectives: Obliterative Bronchiolitis (OB) is the primary limiting factor for long-term survival after lung transplantation. The aim of this study was to investigate if platelet inhibition with Clopidogrel in combination with Everolimus or Tacrolimus has an additional effect on the development of OB.

Methods: Fully major histocompatibility complex-mismatched C57BL/6 (H2(b)) donor tracheas were orthotopically transplanted into CBA (H2(k)) recipients. Mice received 1mg/kg/d or 20mg/kg/d Clopidogrel combined with 0.05mg/kg/d Everolimus or 12mg/kg/d Tacrolimus. Grafts were analysed by histology, morphometry and immunflourescence for CD4+ and CD8+ T-cells on day 30 and alloantibody-production was analysed by FACS.

Results: Untreated controls showed substantial luminal obliteration on postoperative day 30. Animals treated with 1mg/kg/d Clopidogrel and 0.05mg/kg/d Everolimus showed less luminal obliteration in comparison to mice treated with 1mg/kg/d Clopidogrel (31.14 7.34% (1mg/kg/d Clopidogrel + 0.05mg/kg/d Everolimus) vs. 42.25 12.82% (1mg/kg/d Clopidogrel) vs. 49,924.71% (untreated control), n=5). Increased dose of 20mg/kg/d Clopidogrel in combination with 0.05mg/kg/d Everolimus resulted in an even lower amount of airway obliteration (24,723.63% (20mg/kg/d Clopidogrel+ 0.05mg/kg/d Everolimus) vs. 34,048.41% (20mg/kg/d Clopidogrel) vs. 49,924.71% (untreated control), n=5). Treatment with 1mg/kg/d Clopidogrel and 12mg/kg/d Tacrolimus also resulted in a reduction of luminal obliteration (30,950.71% (1mg/kg/d Clopidogrel+ 12mg/kg/d Tacrolimus) vs. 42.25 12.82% (1mg/kg/d Clopidogrel) vs. 49,924.71% (untreated control), n=5). Infiltration with CD4+ cells was reduced after treatment with Everolimus and Clopidogrel. Clopidogrel and Everolimus or Tacrolimus also decreased the amount of alloantibodies production.

Conclusions: Clopidogrel in combination with Everolimus or Tacrolimus substantially reduces Obliterative Bronchiolitis (OB).