Implantation of VEGF-functionalized cell-free vascular grafts: regenerative and immunological response

Recently, our group demonstrated that immobilized VEGF can capture flowing endothelial cells (ECs) fromthebloodin vitroandpromoteendothelializationandpatencyof acellular tissue–engineeredvessels (A-TEVs) into the arterial systemof an ovine animal model. Here,we demonstrate implantability of submillimeter diameter heparinandVEGF-decoratedA-TEVs inamousemodelanddiscussthecellularandimmunologic response.At1mo postimplantation, the graft lumenwas fully endothelialized, as shown by expression of ECmarkers suchasCD144, eNOS, CD31, and VEGFR2. Interestingly, the same cells coexpressed leukocyte/macrophage (Mf)markers CD14, CD16, VEGFR1, CD38, and EGR2. Notably, there was a stark difference in the cellular makeup between grafts containing VEGF and those containing heparin alone. In VEGF-containing grafts, infiltrating monocytes (MCs) converted into anti-inflammatoryM2-Mf, and the grafts developed well-demarcated luminal and medial layers resemblingthose ofnative arteries. Incontrast, ingrafts containingonlyheparin,MCs convertedprimarilyintoM1- Mf, and the endothelial and smoothmuscle layerswere notwelldefined.Our results indicate thatVEGFmayplay animportant role inregulatingA-TEVpatencyandregeneration, possiblybyregulatingthe inflammatory response to the implants.