Immunobiology of embryonic stem cells: Foreign mtDNA as an immunological barrier in SCNT derived embryonic stem cells transplantation

• Published in: The Thoracic and Cardiovascular Surgeon
• Main Authors: Ricklefs, F, Hua, X, Velden, J, Kirak, O, Jaenisch, R, Weissman, I, Reichenspurner, H
• Format: Conference Proceeding
• Language: English
• Published: 23.01.2013
• ISSN: 0171-6425; 1439-1902
• DOI: 10.1055/s-0032-1332452

Objectives: Using somatic cell nucleus transfer (SCNT) for embryonic stem cell (ESC) extraction, the nucleus of a somatic cell is transferred to the cytoplasm of an enucleated egg. ESCs created from the inner cell mass of the blastocyst are not genetically identical with the nucleus donor. The mitochondrial DNA (mtDNA) resides inside the cytoplasm of the egg. This study aimed to investigate the immunological response against mtDNA in ESC transplantation. Methods: Balb/C (mitochondria-incompatible) or BDF1 (nucleus-incompatible) mice (n = 10) received injections of 1 × 10 6 SCNT-ESCs or SCNT-ESC-derived cardiomyocytes (CMs). Cellular and humoral response was investigated by ELISPOT, donorspecific antibodies, histopathology, and confocal immunofluorescence. Longitudinal in-vivo cell survival was observed using Bioluminescence Imaging (BLI) (n = 7). Immunodeficient SCIDbeige mice were used as controls (n = 6). Amounts of mitochondria were visualized using the TMRM assay in undifferentiated ESCs and differentiated CMs. Results: Mitochondria-incompatible mice caused a similar immune response compared to nuclear-incompatible in ELISPOT for Th1, Th2 and Th17-Cells, both being significant higher than in SCIDbeige (p < 0.001). The humoral response behaved similar. Re-injection of ESCs resulted in an increased immune response, highlighting the adaptive immunological character in this rejection process. Potent antigenicity of mtDNA was also observed in BLI measurements. With differentiation into CMs, MHCI-expression and amount of mitochondria increased. We observed a higher antigenicity of transplanted CMs. Interestingly, IgM-secretion was only significantly increased towards foreign mtDNA (p = 0.028) compared to ESCs with foreign nuclear DNA in CMs compared to pluripotent ESCs. Conclusion: Coding for only 13 proteins, foreign mtDNA is sufficient to result in an adaptive immune response and donorspecific antibody production after transplantation. With differentiation into CMs mitochondria amounts increased per cell, which lead to a higher immune response. To summarize, SCNT-derivates carrying foreign mtDNA are not capable to circumvent the hosts immune system as they are recognized and rejected after transplantation.