Abstract 554: Human Embryonic Stem Cell-Derived Cardiomyocytes Survive and Mature after Intramyocardial Transplantation in the Mouse Heart
Background Loss of cardiomyocytes (CM), as occurs in myocardial infarction and other cardiovascular diseases, is irreversible due to limited regenerative capacity of the human heart. Pluripotent human embryonic stem cells (HESC) can proliferate indefinitely, as well as differentiate into CM, and thus serve as a possible source of CM for replacement therapy. Transplantation of HESC-CM into the mouse heart was used to investigate their behavior in myocardial tissue in vivo.
Methods HESC, genetically marked by GFP, were co-cultured with visceral endoderm-like cells, which induce differentiation into CM. After 12 days (optimal CM-differentiation time) spontaneously beating areas, originating from HESC, were dissociated into small clumps containing 15% CM. Per transplantation 2x105 cells in 15μl PBS were injected intramyocardially in a SCID (severe combined immunodeficient) mouse (n=22). Two days to 4 weeks post-transplantation HESC-CM were traced in cryosections by GFP-epifluorescence, which was confirmed by measuring emission wave length spectrum. Transplanted cells were characterized by immunofluorescent staining with human (nuclei and mitochondria)- and CM specific antibodies.
Results GFP-expressing cells were found both in scarred myocardium and, integrated and aligned with host CM, in non-injured parts of the heart. Immunofluoresence confirmed human origin and indicated the absence of fusion with mouse CM. The proportion of α-actinin positive HESC- derived grafted cells with a typical sarcomeric structure increased from 20% at 2 days to 95% at 4 weeks post-transplantation. Cell survival was 0.2–1.4% of the total number of injected cells and 2.0 –12% of CM. Phenotypic changes, including down-regulation of smooth muscle actin and up-regulation of Cx43 and MLC2V, suggested maturation of the HESC-CM in vivo. No teratomas, mortality, arrhythmias or other adverse effects were observed.
Conclusion HESC-CM survive and mature in vivo after intramyocardial transplantation in the mouse heart independently of fusion with host CM, whereas non-CM cells die or differentiate into CM. As one of the few bona fide sources of human CM, these findings emphasize the potential of HESC-derived cells in CM replacement therapies in terms of efficacy and safety.