Tissue Engineering of Endothelial Cells and the Immune Response

BackgroundWhile tissue engineering offers promise for organ and tissue transplantation, it can also be used to examine transplant and immune biology. Endothelial cells engrafted within 3-dimensional matrices create stable units that produce all of the factors of a functional quiescent endothelium. Perivascular implantation of tissue engineered endothelial cell constructs provides long-term control of vascular repair after injury. This control is established without restoration of the natural luminal:mural endothelium, and most intriguingly, without engendering host allo- and xenogeneic immune responses. We examined how endothelial immunogenicity is controlled by interaction with 3-dimensional matrices.Materials and MethodsHuman aortic endothelial cells (HAE) were either grown to confluence on polystyrene tissue culture plates or within 3-dimensional collagen-based matrices. Major histocompatibility complex (MHC) class II, integrin, interferon (IFN)-γ receptor expression, and signaling were analyzed via confocal microscopy, flow cytometry, reverse transcription polymerase chain reaction (RT-PCR), and microarray. Splenocyte proliferation was assayed by thymidine incorporation.ResultsDespite similar expression levels of IFN-γ receptors, matrix-embedded HAE elicited far less STAT-1 phosphorylation upon IFN-γ stimulation, and expressed 2-fold less MHC II than HAE grown to confluence on culture plates (P < .001). This effect correlated with reduced expression of integrin αv and β3 (P < .002), and muted proliferation of porcine splenocytes (P < .001).ConclusionsMatrix architecture is critical for modulation of endothelial immunogenicity. Embedding HAE within a physiologic 3-dimensional environment affects activity of intracellular signaling pathways, MHC II expression, and subsequent activation of immune cells. These findings might offer novel insights into our understanding of endothelial-mediated diseases and might enhance our ability to leverage the potential for cell-based therapies.