Constitutive expression of the anti-apoptotic Bcl-2 family member A1 in murine endothelial cells leads to transplant tolerance.

Anti-apoptotic genes, including those of the Bcl-2 family, have been shown to have dual functionality inasmuch as they inhibit cell death but also regulate inflammation. Several anti-apoptotic molecules have been associated with endothelial cell (EC) survival following transplantation; however, their exact role has yet to be elucidated in respect to controlling inflammation. In this study we created mice expressing murine A1 (Bfl-1), a Bcl-2 family member, under the control of the human intercellular adhesion molecule 2 (ICAM-2) promoter. Constitutive expression of A1 in murine vascular ECs conferred protection from cell death induced by the proinflammatory cytokine tumour necrosis factor (TNF)-α. Importantly, in a mouse model of heart allograft transplantation, expression of A1 in vascular endothelium increased survival in the absence of CD8⁺ T cells. Better graft outcome in mice receiving an A1 transgenic heart correlated with a reduced immune infiltration, which may be related to increased EC survival and reduced expression of adhesion molecules on ECs. In conclusion, constitutive expression of the anti-apoptotic molecule Bfl1 (A1) in murine vascular ECs leads to prolonged allograft survival due to modifying inflammation.