Transplants of stem cells with nuclear DNA identical to that of a patient could still trigger immune responses because of the presence of mismatched mitochondria.

Sonja Schrepfer at Stanford University in California and her colleagues transferred nuclei from a donor mouse's adult cells into mouse embryonic stem cells with genetically matched nuclear DNA but different mitochondrial DNA. When the cells were transplanted back into the donor, they were attacked by the immune system. Isolated mismatched mitochondria also triggered an immune response.

Cell Stem Cell 16, 1–6 (2015)