Human Induced Pluripotent Stem Cells for Tissue Engineered Cardiac Repair

Objectives: Myocardial infarction causes unrecoverable loss of cardiomyocytes. Engineered heart tissue (EHT) is an in vitro model of three-dimensional cardiomyocyte network with morphological and functional similarity to native heart tissue. We transplanted EHTs from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CM) on cryo-injured guinea pig hearts and investigated whether hiPSC-CM-EHTs support left ventricular function.

Methods: Human iPSC were generated by retroviral reprogramming of dermal fibroblasts. Cardiac differentiation of hiPSC was performed by an embryoid body-based three-stage differentiation protocol. EHTs were created from hiPS-CM (5*10^6 cardiomyocytes and 2*10^6 GFP+-HUVECs per EHT) and cultivated for 3 weeks. Development of contractile force was monitored prior to transplantation. Left ventricular myocardial cryo-injury was induced in adult guinea pigs (n = 21). 7 days after injury EHTs (2 per animal, n = 12) or cell-free constructs (n = 9) were implanted. Animals received ciclosporin and methylprednisolon for immunosuppression. Functional parameters were examined by echocardiography and histology at baseline, before and 28 days after transplantation.

Results: The cardiac differentiation protocol resulted in a cell population with ∼50% cardiomyocytes, which was further enriched by lactate-based selection to > 90% purity and directly used for EHT generation. HiPSC-CM-EHTs developed contractile force and displayed morphological properties of native heart tissue. Cryo-injury of the guineea pigs resulted in large transmural scars (∼30% of ventricular wall), which were verified histologically. Immunohistochemical staining for dystrophin and MLC2v showed the formation of large islets of cross-striated muscle tissue in the scar. The human origin was demonstrated by fluorescent-in-situ-hybridization. The new myocardium was vascularized with endothelium partly being of human origin. Animals receiving cell-free constructs showed left ventricular dilatation 28 days after transplantation. The EHT-group showed less dilatation (LV end-diastolic diameter 8.9 ± 0.4 mm versus 9.7 ± 0.7 mm in 28d control [basal 8.1 ± 0.2 mm, 7d post cryo-injury 8.2 ± 0.2 mm]) and significantly better fractional area shortening (42.0 ± 4.5% versus 23.0 ± 3.2% in 28d control [basal 42.2 ± 1.9%, 7d post cryo-injury 26.1 ± 2.1%]).

Conclusion: Transplantation of hiPSC-derived EHTs in a guinea pig cryo-injury model under generates new myocardium and improves cardiac function.