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Embryonic stem cells (ESC) are suggested to be immune-privileged, but they carry the risk of uncontrolled expansion and malignancy. Upon differentiation they lose their tumor-forming capacity, but they become immunogenic by the expression of a normal set of MHC molecules. This immunogenicity might trigger rejection after application in regenerative therapies. In this study MHC expression of and immune responses to endothelial derivatives of rat embryonic stem cell-like cells (RESC) under inflammatory conditions were determined in comparison to primary rat aortic endothelial cells (ECs). Cellular as well as humoral allo-recognition was analyzed in vitro. In addition, immune reactions in vivo were assessed by allo-antibody production and determination of interferon-gamma (IFNgamma)-secreting allo-reactive T cells. RESC derivatives expressed low but significant levels of MHC class I, and no MHC class II. In response to IFNgamma MHC class I expression was enhanced, while class II transactivator induction failed completely in these cells; MHC class II expression remained consistently absent. Functionally, the RESC derivatives showed a reduced allo-stimulatory capacity, protection against humoral allo-recognition in vitro and a slightly diminished susceptibility to cytotoxic T cell lysis. Furthermore, in vivo experiments demonstrated that these cells do not trigger host immune reactions, characterized by no allo-antibody production and no induction of allo-reactive memory T cells. Our results show that endothelial derivatives of RESC have a distinctive reduced immunogenic potency even under inflammatory conditions.

Background: Venous autografts used in cardiovascular surgery tend to deteriorate over time due to arteriosclerotic complications. Cadaveric vascular allografts represent a possible alternative for this application, but donor endothelial cells (ECs) and antigen presenting cells of the graft trigger alloresponses mediated by MHC class I (MHC I) antigen, leading to graft failure. Vascular allograft rejection might be prevented by reducing cell surface expression of MHC I and thereby lowering the immunogenicity of the grafts., Material and Methods: An Intrabody approach was used to reduce MHC I expression in vascular allografts. The efficacy of an adenovirus (Ad) carrying an anti-MHC I Intrabody gene (Ad-Intrabody) was first tested in vitro using rat aortic ECs. The effect of the Ad-Intrabody was then studied in vivo by a model of rat carotid artery transplantation. Grafts were analyzed 7 and 28 days after transplantation by immunohistochemistry and real time reverse transcriptase-polymerase chain reaction., Results: Ad-Intrabody gene transfer reduced MHC I surface expression of rat ECs and inhibited in vivo alloimmune responses to carotid allografts. Decreased T cell and macrophage infiltration was observed within Ad-Intrabody transduced arterial allografts at day 28. This was associated with an inhibition of intimal thickening formation. Analysis of mRNA showed diminished levels of T cell markers and Interferon-gamma expression in the Ad-Intrabody-treated group compared with control groups., Conclusions: Ex vivo adenoviral gene transfer of an Intrabody against MHC I into rat carotid arteries prior to transplantation reduced both graft arteriosclerosis and inflammation in the absence of any systemic immunosuppression.