Revascularization of the Graft in Obliterative Bronchiolitis After Heterotopic Tracheal Transplantation

Obliterative bronchiolitis is the principal long-term problem for lung transplant patients. One of the simplest and most reproducible animal models of obliterative bronchiolitis is heterotopic tracheal transplantation in subcutaneous tissue, where the graft is not primarily vascularized. We demonstrate here the rapid graft revascularization and the kinetics of expression of its angiogenic and lymphatic factors. We performed iso- and allotracheal transplantations harvested on day 0-21. The number of functional blood vessels, quantified after intravenous biotinylated dextran administration, increased from D0 (0 for both iso- and allografts) to D21 (44 ± 8 vessels/mm(2) in isografts and 22 ± 3 in allografts, P < 0.001 for both vs. D0). VEGF mRNA expression assessed by qPCR peaked on D1 (4.3-fold increase in isografts and 4.0-fold in allografts, P < 0.0001 for both vs. D0), but receded thereafter. Angiopoietin-1, involved in the maturation of the neoformed vessels, increased later on, by 6.2-fold (P < 0.05) in isografts and 11.5-fold in allografts (P < 0.001) by D21, and angiopoietin-2 by 7.8-fold in isografts (P < 0.05) and 13.8-fold in allografts (P < 0.01). Although always present in the iso- and allografts, there were significantly more and larger LYVE1(+) lymphatic vessels at D21 in allografts than in isografts. Thus, we demonstrate that tracheal grafts are rapidly revascularized by functional blood and lymphatic vessels, due to early VEGF and subsequent angiopoietins expression, which is a new advantage of this model, in addition to its ease of use, reproducibility, and viability in the absence of immunosuppressive treatment.