Abstract 2110: Generation of Low-antigenicity MHC I Knock-down Human Embryonic Stem Cells Using Molecular Therapy
Introduction: The pluripotency of human embryonic stem cells (hESC) makes them a promising candidate for cell-based myocardial repair strategies. However, we show that hESC, in contrary to former beliefs, are not sufficiently immune privileged and undergo immune rejection after transplantation. To overcome this fundamental hurdle of hESC transplantation, we sought to generate a hESC line with reduced antigenicity that would be spared from a host immune response.
Methods and Results: The antigenicity of undifferentiated hESC, pre-differentiated embryoid bodies (hEB) and mature adult human cardiomyocytes (hCM) was assessed. MHC I surface expression increased with differentiation state in the order hESC< hEB< hCM. All cells were negative for MHC II. The hESC line was stably transduced to express firefly luciferase for in vivo bioluminescence imaging (BLI). 1×106 hESC were transplanted into the thigh muscle of WT Balb/C or immunodeficient Balb/C nude mice. Despite their relatively low MHC I expression, hESC were completely rejected within 7±1 days in WT mice, but not in nude mice, confirming the immunologic nature of their cell death. Immunocompetent Balb/C mice mounted a combined cellular and humoral immune response against hESC, as demonstrated by ELISPOT assays and the determination of hESC-specific antibodies, respectively. hESC MHC I expression was targeted on the transcriptional and translational level. Cells were first transfected with MHC class I siRNA and secondly underwent adenoviral gene transfer of anti-MHC class I intrabodies. MHC I surface expression on these genetically engineered hESC (ge-hESC) was successfully reduced after 36 h and remained suppressed in vitro throughout the observation period of 28 days. Transplantation of ge-hESC did not result in cell rejection in Balb/C mice and BLI confirmed steady cell signals for an observation period of 42 days. Only minor host cellular and no humoral immune activation was found.
Conclusion: We successfully generated low-antigenicity MHC I knock-down ge-hESC that did not undergo immune rejection after transplantation. Such barely immunogenic stem cell lines will be crucial for the success of future tissue regenerative approaches.