Authors:
R. Dressel (Göttingen, DE)
D. Hübscher (Göttingen, DE)
S. Monecke (Göttingen, DE)
L. Elsner (Göttingen, DE)
T. Borchert (Göttingen, DE)
L. Cyganek (Göttingen, DE)
M. Stauske (Göttingen, DE)
M. Hejazi (Düsseldorf, DE)
M. Uhrberg (Düsseldorf, DE)
K. Guan (Göttingen, DE)
K. Streckfuß-Bömeke (Göttingen, DE)
We have shown previously that human natural killer (NK) cells can kill allogeneic and autologous induced pluripotent stem cells (iPSCs). Differentiated cells, in contrast, are expected to be protected at least from autologous NK cells by an up-regulation of HLA class I molecules, which serve as ligands for inhibitory NK receptors. However, this assumption needs to be verified for different types of iPSC-derived cells that are of therapeutic interest. Therefore, we have determined the susceptibility of cardiomyocytes derived from iPSCs to autologous and allogeneic NK cells. The cardiomyocytes were obtained by directed differentiation over three months and had a purity of more than 95 %. Killing by NK cells was determined by chromium release assays and the expression of NK receptor ligands on target cells was measured by flow cytometry. We observed that cardiomyocytes derived from five different iPSC lines were largely resistant to resting NK cells similarly to the respective iPSC lines. However, both, cardiomyocytes and iPSCs, were readily killed by allogeneic NK cells that had been activated by cytokines, e.g., by 100 U/ml IL-2 over four days. For three lines, autologous NK cells were available and the activated NK cells also killed the autologous cardiomyocytes. Human iPSCs express low amounts of HLA class I molecules and the differentiation into cardiomyocytes further reduced this low expression. Similarly to iPSCs, cardiomyocytes expressed ligands for activating NK receptors including the DNAM-1 ligands CD112 and CD155. This expression pattern could explain the susceptibility of the cardiomyocytes to NK cells. However, on cardiomyocytes, in contrast to iPSCs, HLA class I molecules were inducible by interferon-gamma (IFN-g) and treatment of cardiomyocytes with IFN-g reduced the killing by NK cells. Thus, iPSC-derived cardiomyocytes could be more resistant to NK cells in a pro-inflammatory milieu after transplantation than undifferentiated iPSCs that might contaminate grafts in trace amounts. Thereby, NK cells could reduce the risk of teratoma formation after transplantation of iPSC-derived cardiac grafts. However, in a non-inflammatory milieu, iPSC-derived cardiomyocytes could be at risk to be rejected by NK cells.